A review study on the active methods of heat transfer
enhancement in heat exchangers using impingement jet
technique
Mahir Faris Abdullah1*, Bassim Mohmmed Majel1 , Ali Ahmed Gitan2, Rozli Zulkifli1*, Zambri
Harun1
1Department of Refrigeration and Air Conditioning Engineering, Al-Rafidain University
college, Iraq
2Department of Mechanical Engineering, University of Tikrit, Iraq
*Corresponding author: maher.fares@ruc.edu.iq, rozlizulkifli@ukm.edu.my,
GRAPHICAL ABSTRACT
ABSTRACT
Impingement jets have a wide range of industrial
applications and its effectively is recently
improved significantly. Jet impingement caused
considerable augmentation in heat transfer
characteristics. This paper presents a review of
the literature on the heat transfer characteristics
of impingement jet system. Impinging air jets are
characterized by different control factors, and
their dependence on performance-defining
criteria must be investigated. Factors that must
be consider in order to arrive at the optimised
impinging jet geometry, which creates one or a
combination of the following conditions that are
favourable for heat transfer enhancement: (a)
increasing turbulent intensity, (b) using nanofluid
and improving surfaces by nanocoating, (c)
increasing heat transfer area and (d) generating
vortex or secondary flows. The potential for
enhancing these characteristics is a pivotal issue.
The present review examines thermodynamic
behaviour of impingement jet techniques and
reviews
experimental
and
numerical
investigations reported in the literature to study
the dependence of control factors on heat
transfer, flow characteristics and decision-making
methods towards the optimisation of control
factor combinations for an optimal impinging jet
design. This review provides a platform for
researchers who work in the same research field
to design a noble heat transfer enhancement
contrivance in the form of jet control factors for
improving thermo performance by maximising
heat transfer and flow characteristic of the
system. The main contribution of this paper is that
it thoroughly discusses the heat transfer issue of
steady jet impingement. The literature suggests
that heat transfer characteristics can be
enhanced when optimal levels of the influential
factors and nanofluid technology are used.
Surface coating with the nanosolution and the
selection of a suitable impingement system
affect the heat transfer rate positively.
𝜑
Keywords:
impingement jet, heat transfer
enhancement,
nanofluids,
nano
coating,
experimental and numerical method, multiple
jets.
RANS
Re
Nu
𝛼
RMS
SASJ
Thet
a
St
PIV
Inclination
angle
Reynolds
number
Nusselt
number
Impingement
angle
Root mean
square
Synthetic
jets,
which
act in single
acting
Hole
inclination
CFD
Strouhal
number
Particle
image
velocimetry
Reynolds
averaged
Navier–
Stokes
E
Hole–hole
spacing,
nozzle–target
distances
Eccentricities
OE
M
One-equation
model
LES
Large
eddy
simulations
Pr
3-D
1-D
S/D
H/D
e
H/D
n
Computational
fluid dynamics
Prantel
number
Threedimensional
Onedimensional
Nozzle–nozzle
spacing
Nozzle–plate
distance
Notations
1.0 INTRODUCTION
Enhancement of heat transfer is one of the most
promising ways to optimize heat transfer
equipment [1], and to increase heat recovery in
engineering and industrial application. Although
jet impingement systems effectively enhance
convective processes because of their high heat
and mass transfer rates, difficulties in increasing
heat transfer have gained the attention of
researchers, especially in the last four decades
[1]. Such enhancement mechanism considerably
improves the efficiency of heat transfer, reduces
energy consumption and minimises effort and
costs. It also has a wide range of applications in
cooling and heating that may help reduce
economic expenditure in terms of materials,
energy consumption, weight, and size, thereby
improving
heat
exchange
efficiency
or
performance [2], [3]. Therefore, the heat transfer
enhancement mechanism must be identified
because the technology is closely linked with
many industrial applications [4]- [7].
At present, the number of industrial
applications used in impinging jets is growing.
Impinging jet systems are used in cooling hot
metal, plastic or glass sheets and in drying paper
and fabric. Compact heat exchangers often use
several impinging jets in dense arrangements,
with applications in the aeronautical or
automobile sector. Impingement systems are
widely used for cooling electronic components in
micro
scale
applications,
particularly
in
electronic chips.
Jet impingement has long been routinely used
in gas turbine applications. Demands for
increased power output and efficiency, as well
as reduced emissions, are being imposed. High
thermal efficiency can be realised by increasing
turbine inlet temperatures and compressor ratios.
As a result, various gas turbine components, such
as rotor disks, turbine vanes and blades or
combustion chamber walls, are maintained at
temperatures far above the most permissible
material standards. Effective cooling concepts
for these highly loaded components are needed
to ensure durability and long operating intervals
because of the complex geometry and high
turbulence of the turbine system.
Furthermore, high thermal efficiency can be
realised
by
using
nanofluid
technology.
Nanocoating for the surfaces also has an
important role in heat transfer in terms of
increasing the surface area and enhancing the
plate feature that will improve heat transfer and
flow characteristic. However, understanding flow
and heat transfer characteristics remains a
challenging subject. [8]- [12].
1.1 Classification of heat transfer
enhancement techniques
Heat transfer enhancement techniques can
be divided into two categories, namely,
passive
and
active
[13].
Passive
techniques do not involve any external
power and employ either surface
amendment on heated plate surfaces or
swirl devices in the flow domain. These
techniques outperform complex active
techniques because they require an
external power supply. Nonetheless,
active techniques offer considerable
potency and thermal control. They
include
mechanical
aid,
surface
vibration, fluid vibration, electrostatic
fields,
injection,
suction
and
jet
impingement.
Fluid
additives,
flow
disruption, out-of-plane mixing, secondary
flow, re-entrant obstruction, channel
curvature and surface roughness are
considered passive techniques [13]. The
taxonomy of heat transfer enhancement
techniques is illustrated in Figure 1.
Figure 1 Taxonomy of enhancement Heat transfer techniques
1.2 Impingement jet
Jet impingement is an active technique that
can be used to capture the flow field and
predict jet efficiency. This literature review
reveals that the jet impingement
mechanism is an important technique
that has captured the interest of many
researchers, especially in the last two
decades. Impingement jets provide an
effective and elastic path to transfer
energy
or
mass
in
engineering
applications. Large amounts of mass or
thermal energy can be efficiently
transferred between the fluid and the
surface when directed gas or liquid flow
are released on a surface [14]. Heat
transfer enhancement and Assessment of
TiO2 Nano Concentration and Twin
Impingement Jet—A Statistical Approach
Using Response Surface Methodology to
improve the heat transfer and flow
characteristics into different zones [15]
(Figures 2-4). The flow of a submerged
impingement jet passes over various
distinct zones. The jet emerges from a
nozzle or opening with a certain velocity
and temperature profile, and the
turbulence characteristics depend on the
upstream flow.
Figure 2 Jet flow characteristics (a) Single flow, (b) Single impinging jet configuration
Figure 4 Stagnation and secondary
Figure 3 Twin jets configuration.
The thermal conductivity of fluids must be
enhanced to improve the efficiency of
heat transfer in numerous applications
[16]. The jet impingement heat transfer
technique has attracted considerable
research interest because of the high
heat transfer coefficients produced by
forced convection action [17]. Many
applications, especially those involved in
the food industry, drying of textiles,
cooling of turbine blades, electronic chip
cooling, annealing of metals and
tempering of glass, can be developed by
using the jet impingement technology
(JIT). Extensive research has been
conducted to study the effects of
stagnation points of twin impingement jets
applying single and multi-impinging
steady jets on flow and heat transfer
characteristics. The effect of changing
the Reynolds number (Re), which can be
𝒅
defined as 𝝆𝒗 , where ρ is the density of
𝝁
fluid (kg/m3), μ is the dynamic viscosity of
fluid (in N·s/m2), and v is the mean
velocity of fluid (in m/s), has been studied
actively.
The effects of distance between nozzles,
spacing between nozzle and plate, different
velocities and conduction and convection on jet
flow structure and impingement heat transfer
rates have been discussed in several papers,
such as [18]–[19]. The combined influence of twin
jets on flow and heat transfer behaviour remains
under consideration, and insufficient information
is provided in the literature. This review aims to
confirm the lack of knowledge on the flow and
heat transfer enhancement of twin jets,
determine critical parameters involved and
emphasise the lacking information on the heat
transfer of impingement jets. The literature on the
heat transfer characteristics of impingement jets
can be improved when optimal levels of the
influencing factors and a suitable impingement
system are selected. Previous studies explained
the flow and heat transfer characteristics of
steady impingement jets, although many areas
need further investigation to enhance thermal
performance.
1.3 Research Questions
Impingement jets employ a high convective heat
transfer coefficient, which is a crucial factor. The
challenges in this research are presented as
follows:
123-
4-
5-
Information regarding the mechanism of
twin impingement jets is lacking (still
unreported).
How can maximum heat transfer rate be
achieved within the radial distance from
the stagnation point?
How does cross-flow region affect the
two nozzles, and how does heat flux
cover all the holes present in the
transaction area?
How can the twin impingement jet
technique
be
enhanced
through
experimental and numerical methods
via computational fluid dynamic (CFD)?
What is the effect of using nano coating
as TiO2, CNT, AL2O3, ZNC and CU on heat
transfer rate and flow characteristics in
different applications?
6-
Information regarding the mechanism of
twin impingement jets is lacking (still
unreported).
7- How can maximum heat transfer rate be
achieved within the radial distance from
the stagnation point?
8- How does cross-flow region affect the
two nozzles, and how does heat flux
cover all the holes present in the
transaction area?
9- How can the twin impingement jet
technique
be
enhanced
through
experimental and numerical methods
via computational fluid dynamic (CFD)?
10- What is the effect of using nano coating
as TiO2, CNT, AL2O3, ZNC and CU on heat
transfer rate and flow characteristics in
different applications?
2.0 FLOW CHARACTERISTICS OF
MULTIPLE STEADY JETS
Examining the flow characteristics of multiple jets
is vital in the establishment of a background for
understanding the behaviour of impingement
heat transfer. One must distinguish between the
flow characteristics of multiple jets and single jet
by presenting a zone of interference amongst
jets. Amongst neighbouring jets, this interference
occurs before the jets’ impingement on the
target. Jets produce varying flow structures, as
observed on the impingement surface. The
effect of the interference zone on an individual
jet can be used for the characterisation of the
flow structure of multiple jets. Interfering jets may
influence turbulence intensity significantly.
Related works recognised other effects of
multiple jets on flow characteristics [20] (Figure 5).
Figure 5 Twin impinging jets with (a) interference before impingement and (b) jet fountain formed after impingement.[20]
Further examination was conducted by
presenting the flow structure of each system to
distinguish between single and double impinging
jets [21]. The effects of nozzle–plate distance
(H/De) and low Re on velocity and pressure
distribution were experimentally examined for
both jet systems. Hot-wire anemometry was used
to measure velocity. An increase in secondary
stagnation pressure as the Re increased was
observed in double jets. A sub-atmospheric
region was observed on the impingement plate
when nozzle–plate spacing reached 2 (H/D) or
when Re was over 2,700. Thus, interference effect
is the key difference between single and double
jets. Reference [22] discussed convective heat
transfer accretion and fluid flow structures for
multiple jet impingements. Examination of the
results for these complex flow phenomena aims
to offer an improved understanding of the effect
of near-wall flow structures on convective heat
transfer accretion.
The effect of jet interference for a hexagonal
array of circular jets that impinged a flat plate
was investigated by using particle image
velocimetry (PIV) [23]. The study also discussed
the effect of jet–jet interference on the jet core’s
length, as well as the influence of that plate
impingement on turbulence kinetic energy. The
results revealed that the central jet in the array
possessed a shorter core length compared with
lateral jets because of variations in interference
levels. The upwash generated by the collision of
wall jets increased the gradient of the axial
velocity in the jets’ shear layers, which in turn,
augmented the transformation of mean flow
momentum into turbulent stress.
The effects of Re, nozzle–nozzle centreline
spacing, nozzle–plate spacing and jet angle on
2D impinging circular twin jets were examined
numerically [24]. The finite volume method was
utilised to determine the governing mass,
turbulent kinetic energy, momentum and
turbulent kinetic energy dissipation rate. The
results show a reduction on pressure at the
secondary stagnation point when the Re
decreased and/or the jet angle increased. The
recirculation zone’s intensity between two jets
decreased when the jet angle and nozzle–plate
spacing increased. Furthermore, turbulent kinetic
energy increased within each vortex region.
Javad et al. [25] used CFD to conduct a
numerical study on the impingement of a
turbulent jet on a curved plate. Hydraulic
diameter (2B) and jet exit velocity (U) for various
jet–surface (h/B) distances at varying Re of 2,960
and 4,740 were determined. The results were
compared with the experimental data found in
literature to obtain the results from Reynolds
averaged Navier–Stokes (RANS) k-ϵ model. The
comparisons illustrated that the two models (e.g.
RANS and k-ϵ) could generate comparatively
good results. Accurate results were produced by
one-equation model (OEM), particularly at the
impingement zone within small jet-to-surface
distances. The OEM could predict heat transfer in
various small jet-to-surface widths efficiently. The
two models exhibited similar performance at high
h/B ratios. Fluid flow and heat transfer of nonNewtonian
multiple
impinging
jets
were
examined numerically by [26]. Re of 100 and 200,
dimensionless jet–plate spacing of 0.25e1.0 and
power law index of 0.4e1.6 were obtained on the
basis of the numerical results. The results showed
that an increase in the power law index resulted
in high wall Nusselt number (Nu) and
impingement
velocity.
Environmental
entrainment vortices were made to form around
the body of the jet for high jet plate spacing. A
reduction in the spacing made these vortices
disappear. The numerical results showed that a
reduction in the jet–plate spacing led to a
substantial increase in wall Nu.
The oblate jet shape was considered and
compared with the circular configuration in a jet
array system to increase turbulent kinetic energy
[27]. Instantaneous velocity fields gathered using
digital PIV along the cross-flow direction were
also analysed. The flow’s energetic content
demonstrated that the oblate jets showed
improved kinetic energy production, that is, an
increase in turbulent kinetic energy.
Turbulent intensity of twin jets was determined
using instantaneous velocity measured at the
centreline of the axial jet [18]. Hot-wire
anemometry was used to conduct the
measurements. The distribution of pressure on the
confinement surface and impingement plate
was also measured. In addition to different
nozzle–nozzle and H/De, high values for Re
(30,000 to 50,000) were adopted. The results
showed an increase in the centreline turbulence
levels during the development. The distributions
of pressure on confinement and impingement
surfaces did not depend on Re but on jet–jet and
nozzle–plate spacing. Taghinia et al. [28]
conducted a numerical investigation on the twinjet impingement along with the hybrid-type
turbulence modelling through a large-eddy
simulation (LES). A numerical study was
conducted for various Re and spacings. The
study considered a domain of values for Re, H/D
spacing and S/D spacing. The H/D spacing was
set up such that the re-circulation structures were
made up of two stagnation areas. The first and
second regions at the impinging region were
found in the zones between two impinging jets
that had an upwash fountain-like structure.
The fluid flow, entropy generation and heat
transfer in air jet impingements were based on a
model with rough surface [29]. The effects of jet
flow Re, surface roughness and jet impingement
dimensions were quantified. Furthermore, the
temperature difference, which occurs between
the impinging target on the jet impingement’s
heat transfer and the jet flow, was determined.
The effect of roughness was evident in the wall
jet region but was obscure in the impingement
area. Furthermore, the surface roughness played
a more significant role in the heat transfer rate’s
enhancement factor compared with the jet’s
geometrical dimension.
A previous study [30] investigated the
heat transfer performance of an internal
cooling
channel
with
a
singlerow impingement jet array by varying the
jet flow rates. The findings revealed that
total flow varied by approximately 65%
from that of the baseline. Heat transfer on
the
objective
plate
surface
was
enhanced
by
approximately
35%.
A previous study [31] examined a
turbulent impingement jet on a vibrating,
heated
wall
through
large
eddy
simulation (LES). Mean radial velocity
increased and decreased when the
displacement of the wall was positive and
negative, respectively. Periodic shifts in
secondary Nu peak were observed. The
heat transfer in the stagnation region was
enhanced, but this beneficial effect of
vibration on heat transfer was limited to
the impingement area.
The flow field of multiple jets was
investigated for a cooling turbine blade
application. An enlarged model of a
trapezoidal duct near the leading edge
of the blade was constructed by Liu et al
[32]. Two lines that consisted of 40
staggered circular side impingement
holes that had two diameter sizes were
opened into the duct subsequently.
Effects of impingement jets, cross flow,
swirl flow and effusion flow were
considered. Detailed flow structures had
two impingement angles: 35° and 45°. The
results revealed that small jets affected
the target wall effectively, whereas large
jets primarily focused on driving and
inducing the vortex.
Reference [33] discussed the physics that involves
impinging jets for a low Re regime in a large array.
The result showed that the contraction effect at
the nozzle entrance and viscous losses caused a
major pressure to drop in the system. Simulations
were performed to determine the sensitivity of
pressure drop and to study the heat transfer
characteristics and expected manufacturing
tolerances in practical engineering applications of
these jet arrays. Reference [34] examined the
effects of volumetric quality on fluid flow
characteristics, as well as heat transfer in airassistant jet impingement. The results showed that
the stagnation Nu increased with volumetric
quality, thereby achieving a maximum value at
almost 0.8 of the volumetric quality. Then, Nu
began to decrease subsequently. The stagnation
pressure dominated the stagnation Nu of the air-
assistant water jet impingement. Reference [35]
numerically investigated and examined the boiling
heat transfer rate of thermal water for a turbulent
jet impingement placed on a heated surface. The
results showed an increase in convective heat
transfer coefficient at the stagnation point, as well
as the water velocity of a fluid. In addition, the
convective heat transfer coefficient would
increase with a decrease in the fluid jet
temperature. Reference [36] examined the flow
and heat transfer characteristics of the fluid jet to
solve the three-domain conjugation heat transfer
problem. The results were based on the
experiments on the wall temperature of the solid–
air interface.
Different configurations of multiple jets were
considered to investigate the flow field
behaviour caused by the interference of jets.
Steady jets generally exhibited almost similar
interference characteristics, such as secondary
stagnation point formation and fountain vortices,
at different Re. However, turbulence intensity
and velocity profiles might exhibit different
behaviours. In summary, studies indicated that
interference zone characterises the flow field of
multiple jets and alters the impingement heat
transfer response.
3.0 MULTIPLE STEADY JET
IMPINGEMENT HEAT TRANSFER
The involvement of multiple jets in impingement
heat transfer has introduced a wide area of
investigation in several aspects. The most
influential parameters associated with multiple
jets
were
investigated
analytically
and
experimentally. Different configurations and
effects related to impingement target were
discussed in several works. The effect of inclined
multiple-jet impingement on heat transfer was
considered in various cases. Impingement heat
transfer was investigated using different multiplejet arrangements. The effect of nozzle
configuration in multiple-jet impingement heat
transfer problems was studied. All these issues
might delimit the multiple-jet impingement heat
transfer
problem.
However,
single-jet
impingement heat transfer was still considered to
verify and compare experimental methods [37],
[38].
3.1 Influential Parameters of MultipleJet Impingement
This part of the literature review aims to delimit
the most influential parameters associated with
multiple-jet impingement heat transfer by
reviewing all research that discussed the effects
of flow and geometrical factors and any
parameters that are expected to influence heat
transfer
substantially.
Although
different
applications have been used in several works,
the focus on investigating the influential
parameters was the common theme in this
research.
Optimisation of various influential factors was
examined for multiple-jet impingement heat
transfer [39], Nozzle spacing demonstrated
optimum values because of the influence of the
interference amongst jets [40]. The influence of
parameter on local stagnation Nu was examined
experimentally by considering five jets that were
in equilaterally staggered arrays. It also
considered the Re of 10,000, 20,000 and 30,000
and various nozzle–target distances (H/Dn). The
results revealed that jet interference is a vital
factor that influences the heat transfer
characteristics. Several applications only require
a minimal quantity of coolant, such as
compressed air within a turbine internal cooling
system. For practical purposes, Can [40]
presented the nozzle array optimisation under
impinging air jets. This work presented an
optimum mixture of design parameters in
addition to the effects of velocity and air
temperature. From a practical standpoint,
examining the running and capital costs, fan
power consumption and nozzle design cost
would be helpful. Several examinations on heat
and flow transfer features of twin turbulent slot
jets impinging on rough and planar smooth
surfaces were conducted on the basis of CFD
[41]. The jet interaction decreased the
performance of heat transfer for each jet in the
area where the collision of the wall jets occurred.
A single jet had better performance compared
with its equivalent twin jet. Under twin jets,
alternate injection of average heat transfer
occurred such that each jet pair behaved
similarly to a single jet. This approach is
considered better than a simultaneous issuance
of the twin jets. Alternating jet flows within a twin
jet system is a new and simple way of improving
the jet pairs’ thermal performance. Reference
[33] discussed the physics behind impinging jets
given a large array within a low-Re scheme.
Numerical simulations were conducted using
results from LES and RANS to establish the heat
transfer features of several impingement jets. CFD
simulations and experimental works revealed an
increase of approximately 10% for heat transfer
coefficient. The upwash of the primary vortices
and wall jets resulted in a surface renewal
impact upstream of jets, which led to a rise in the
local heat transfer at X/D = 1. If it plugged a jet
that generated the highest rate for local heat
transfer, then average heat transfer rate would
decrease by about 6%, and pressure drop would
increase by 15%.
The flow and heat transfer characteristics were
examined at different nozzle–nozzle spacing
(S/D) and H/De for impinging laminar multiple
square jets [42]. A numerical simulation was used
to solve the 3D Navier–Stokes and energy
equations in steady state. The results showed that
the flow structure of multiple square jets
impinging on a heated plate is strongly affected
by the H/De. The local maximum Nu at the
stagnation point is not affected by S/D.
Furthermore, Wang et al. [43] employed different
parameters
to
enhance
the
cooling
performance in the impinging jet for efficient
machining and power transmissions. They also
introduced additional parameters for the cooling
system’s design. The nozzle diameter can be
reduced to achieve a higher convective heat
transfer coefficient that possesses the same flow
rate whilst increasing either the oil supply pressure
or the nozzle number. Reference [44] examined
the effect of geometric parameters on the
axisymmetric impingement heat transfer jet. The
study showed that each model possesses its own
dependency style. A secondary peak was
observed at the exact location upon validating
the turbulence model for H/D=2. The authors
briefly discussed the results related to the effect
of grooves based on averaged Nu and surface
Nu.
impinging jets and with Re ranging from 1,039 to
5,175. The 1D results were higher than the 3D
results, the local maximum and minimum heat
transfer
values
were
overvalued
by
approximately 15% to 20%, and the overall heat
transfer was overvalued by approximately 12%.
The effects of S/D and H/De on the shape and
the heat transfer characteristics of a single and
an array of three laminar pre-mixed butane/air
slot flame jets impinging on a flat plate were
examined on the basis of the Re of 1,000 [47]. A
heat flux transducer with an effective sensing
area of 6 mm2 was used to measure the local
heat flux from the flame to the plate. The
interference amongst jets decreased with the
increase in S/D and H/De. Strong interference
was obtained at S/D = 1 and H/de = 2. The
resultant heat flux distribution of the central jet of
a multiple-slot jet system was higher than that of
a single-slot jet when the S/D was small. This
advantage in thermal performance diminished
when the S/D was increased.
Reference [45] predicted the heat transfer of
two and three jets impinging on two and three
cylinders beneath one another using CFD. Re
and S/D were the influential factors considered in
this study. The results illustrated that an increase in
Re leads to higher Nu. The interaction between
two jets is advantageous. The average heat
transfer is higher for two jets than for a single jet.
The heat transfer on the cylinders under three jets
would also differ individually. The heat transfer
distribution on the central cylinder differs from
that on the outer cylinders.
Free-surface and confined submerged
impinging cooling water jet arrays were
investigated experimentally [48]. Rectangular jet
arrays with different hole–hole spacings, H/Dn
and volumetric flow rates were used in this work.
The heat flux and surface temperature were
measured by using three thermocouples fixed at
the impingement plate centreline. The results of
the submerged jet arrays showed strong
dependence on both nozzle–target spacing and
S/D. By contrast, the free-surface jets showed a
nonmonotonic change with the nozzle–target
spacing with a local minimum in the heat transfer
coefficient at approximately H/Dn = 10. In
general, the submerged jets obtained a high
heat transfer coefficient for a given pumping
power requirement. Liu et al. [49] experimentally
investigated the heat transfer distributions on
array impingement jets on a half-rough and halfsmooth target surface by using the transient
liquid crystal technique. The impact of cross flow
was explored in three exit flow orientations,
namely, a jet Re ranging from 2,500 to 7,000, jetto-jet spacing of 4 and jet-to-surface spacing of
3. than a fully rough target surface.
Reference [46] investigated the effect of an
experimental
method
on
heat
transfer
coefficient distribution on jet impingement target
surface in a confined cavity. A transient liquid
crystal method was employed and compared
with a 1D scheme using hue angle and a 3D
inverse transient conduction scheme. The study
was performed with an 8 × 11 array of confined
A numerical investigation on the effect of the
nozzle–plate spacing on the heat transfer rate for
the five impinging confined and inline laminar
square jets was performed [50]. A simulation was
also conducted by solving the energy and
Navier–Stokes equations for the nozzle–plate
spacing value between 2 B and 20 B and for the
S/D value of 4 B, where B refers to the jet width.
This study also considered the cross-flow effect
generated by confinement. The predicted results
revealed that a horseshoe vortex formed at
various locations between the orifice and the
impinging plates as a result of the interaction
between the two jets. The number of combined
jets had no effect on the magnitude of the local
Nu of the combined impinging jets. The peaks in
local Nu increased as H/De decreased.
An investigation on the effects of Mach and Re
numbers on an array of impinging jets was
conducted [51]. The data were provided in the
form of local and spatially averaged Nus,
discharge coefficients and spatially and locally
averaged recovery factors. The values of the Re
varied from 5200 to 8200. Furthermore, the Mach
number ranged from 0.16 to 0.74. The heat flux
was determined using the power generated by
the thermofoil heater and the result of energy
balance analysis. The experimental results
revealed independent and substantial Mach
number effects (when the Re is kept constant).
The data of local recovery factor were high as
high as 1.03 beneath and near the impact
locations of the impingement jets.
Chander and Ray [52] investigated three
interacting methane/air flame jets that were
impinged on a flat surface. The distributions of
surface heat flux were determined using different
burner–target separation and interjet spacing
distances given a Re of 800. The surface
temperature was measured using a row of K-type
thermocouples that were equally spaced in one
radial direction. Then, a heat flux micro sensor
was used to measure the local heat flux. The
results showed an outward deflection of flames
that occur from the centroid of the triangular
arrangement as a result of the strong interaction
amongst the jets given their small separation and
interjet spacing distances.
Comparative investigations were conducted
on confined submerged and unconfined freesurface water jets to examine the effects of
confinement on the impinging array and liquid
circular jets [53]. On the back side or dry side of
the heater, 48 K-type thermocouples were
welded along the centreline. This arrangement
was illustrated by the planar jet-like structure
produced by the inline array-circular jet in the
wall jet that resulted in the absence of a
transition region for every tested case instead of
offering a monotonic decrease in the convection
coefficient. Furthermore, the single-circular jet
went through a transition of V ≥ 6.1 m/s. Mixing
and turbulence were substantially enhanced by
the confining circular jets as a result of the radial
flows being forced to become two-way channel
flows. Therefore, the transition to turbulence took
place within 1 ≤ r/d ≤ 2. Furthermore, the
convection coefficients significantly enhanced
within the stagnation region.
The parameters of Re, C/D and H/Dn on a row
of circular jets impinging a concave surface
were investigated [54]. A computational study
was performed on the flow and heat transfer
characteristics using the FLUENT 6.2.16 software.
The results demonstrated that the flow field could
be characterised by the upwash fountain flow,
the existence of a pair of counterrotating vortices
and entrainment. Jet interaction only occurred
after the impingement of current geometries
(H/D = 1, 3, 4 and C/D = 3.33, 4.67).
Ozmen and Ipek [55] investigated the flow
structure and heat transfer characteristics in an
array of impinging slot jets. They considered the
H/D of 1 to 10, different Re in the range of 00 to
15,000, jet–jet centreline spacing (S/D) of 9 and
the Nusselt distributions on the impingement
plate for both unconfined and confined jet
configurations depending on the Re and nozzle–
plate spacing. A strong correlation between the
subatmospheric zone and secondary peaks in
the Nusselt division was observed. The numerical
results acquired using the realisable k–ε
turbulence model were consistent with the
experimental results of reasonable values of
nozzle–plate spacing. Zhu et al. [56] carried out
an in-depth analysis on the process of conjugate
heat transfer of the impingement jet, whereby
different parameters altered the thermal
condition and the Nu at the fluid–solid interface.
The boundary heat flux was redistributed by the
thermal conjugate effect, which was then
converted into thermal boundary. Decay in the
Nu due to the conjugation effect was observed.
Goodro and Park [57] demonstrated the
effect of hole spacing on the spatially resolved
heat transfer using an array of jets impinging a
flat plate. This study considered the hole spacings
of 8D and 12D for the spanwise (Y/D) and
streamwise (X/D) directions at varying Mach and
Re numbers, where D represents the hole
diameter. A total of 10 calibrated, copper–
constantan thermocouples were then installed at
various spanwise and streamwise locations within
the impingement plate to measure the surface
temperature. The results illustrated that every jet
generated through X/D = Y/D = 12 determined
the behaviour of a single jet.
The effects of H/Dn, Re and S/D on flow field
and heat transfer were investigated on double
jets impinging on the isothermal wall [58]. The
energy and Navier–Stokes equations were
discretised on a nonstaggered grid arrangement
with a finite volume procedure using a modified
simple algorithm. A multicellular flow in the
impingement
region
resulted
from
the
interference of jets. An almost linear increase in
the mean Nu occurred with the increase in Re on
the isothermal surface. A significant improvement
was observed in the heat transfer rate when the
Re of the first jet surpassed that of the second
one.
Katti and Prabhu [59] investigated the effect of
spanwise jet–jet spacing on the distribution of
local heat transfer in a confined array of circular
jets. The mean Re of the jet ranged from 3000 to
10000; the jet–plate spacing ranged from 1D to
3D; and the spanwise pitches were 2, 4 and 6 d,
where d is the nozzle diameter. The flat heat
transfer surface was made of thin stainless-steel
metal foil. The local temperature distribution on
the target plate was measured using a thermal
infrared camera. The results showed that the
stagnation Nu with a spanwise pitch of 6 d were
higher than those with spanwise pitches of 2 d
and 4 d. The spanwise variations in the
coefficient of local heat transfer at different
streamwise lines were large at high spanwise
pitches likely due to the increase in spanwise jet
interaction with low spanwise pitches. The
experimental analysis on the heat transfer of jet
impingement of the inlet condition [60] visualised
the
temperature
distribution
over
the
impingement surface by using liquid crystal
thermography,. The correlations progressed to
the Nu as a function of the Re and separation
distance.
The influential factors associated with the
impingement heat transfer of multiple jets are
presented through a review of related works.
Accordingly, the most important parameters
investigated are listed as follows:
1234-
Reynolds number (Re)
Nozzle–nozzle spacing (S/D)
Nozzle–target distance (H/Dn)
Surface roughness
These five common factors significantly alter
the interference amongst jets in multiple-jet
impingement problems. The heat transfer
characteristics of the interference zone may be
influenced or enhanced by the improvement in
flow characteristics. Thus, these parameters
should be considered when investigating the
impingement heat transfer of twin jets.
3.2 Multiple jets with different
impingement target
configurations
The impingement target is an important part
of the jet impingement heat transfer
system. In most applications, obtaining a
uniform temperature distribution on an
impingement-cooled or -heated target is
desirable. Heat transfer characteristics are
expected to be enhanced when the
effect of several impingement target
features, such as moving, rough and
nonflat surfaces, are considered. The
same influential parameters that were
determined
previously
have
been
discussed in several studies under the
effect of impingement target attributes.
Nadda et al. [61] investigated the effect
of the heat and fluid flow characteristics
of the solar air passage of a circular
impingement jet. The results showed
optimal enhancement in heat transfer
and friction by 6.29 and 9.25 times that of
a smooth absorbent plate. The optimal
value of thermal hydraulic efficiency was
3.64 for a Re value of 13,000. Draksler et
al. [62] performed tests to examine the
heat transfer conditions and fluid flow
dynamics of a multiple-impingement jet
by using LES, under different Re of up to
20,000. Numerical models were used to
analyse the dynamics and complexity of
the immediate flow field and thoroughly
test the local flow technique associated
with the improvement of heat transfer at
the heated flat plate with a Re of 20,000
for 13 air jets. Numerous parameters
govern
the
performance
of
jet
impingement in rapid food freezing and
cooling
systems
[16].
JIT
refersto
a heat transfer enhancement technique.
The literature proves the extensive
application of JIT in combustion chamber
cooling, critical parts of turbines, glass
technology,
electronic
components,
drying of paper, textile materials,
biomaterials and food preservation. JIT
has
interesting
fluid
dynamics
and heat transfer properties. Its relative
simplicity and low cost, abundance of air,
generation
of
high heat transfer and
rapid freezing rates have made it an
important
research
topic.
Several
approaches,
such
as
visualisation,
experimentation,
computational
simulation,
numerical
analysis
and
factorial and mathematical modelling
on jet impingement in rapid food freezing
and
cooling
systems
have
been
conducted. This paper reviews the
literature on the governing parameters of
jet impingement in rapid food freezing
and cooling systems.
Yang and Hao [63] and Aldabbagh and
Mohamad [64] investigated the configuration of
moving impingement plate and its effect on flow
and heat transfer as a result of multiple impinging
jets (Figure 6). In the designing systems of
multiple-jet impingement, one has to select the
geometrical and flow parameters in such a way
that it achieves an adequately high average
heat transfer coefficient and a sufficient extent of
uniformity in the surface distribution to avoid
local hot (or cold) spots [63]. Three turbulent slot
jets impinging on a moving flat plate were
investigated numerically to examine the design
of
multiple-impingement
jets.
Parameters,
including the dimensionless nozzle–surface
space, entrance Re, dimensionless velocity ratio
(plate-to-jet) and dimensionless pitch, were
considered. According to the results, the
interference effects in closely spaced jets were
enhanced. In cases of a moving surface, the skin
friction coefficient of impinging surface had a
strong effect on the surface motion. In another
work, parameters similar to those above were
considered numerically for an array of square jets
impinging on a moving heated flat plate. This
study aimed to examine the effect of flow
structure on the characteristics of heat transfer
[64]. A 3D simulation was performed on the
comparison of a current moving plate case and
a fixed-plate case. The results revealed that the
velocity ratio of moving plate increased the cross
flow. Thus, unlike the case of fixed surfaces, a
ground vortex cannot form in front of the second
and third column jets. Spatially strong periodic
oscillations
were
demonstrated
by
the
streamwise profile of the Nu. The oscillatory
behaviour of Nu profiles remained unaffected
regardless of whether the plate was fixed or
moving.
Figure 6 Moving impingement plate. [63]
Although
[65]
already
explored
the
characteristics of transient heat transfer of flat
plate for circular air–jet impingement, the local
Nu rapidly increased upon the initiation of air jet
impingement. As the jet impingement continued
to cool down, the increasing speed of Nu also
slowed down (at the 50–80 s region). Reference
[66] investigated the heat transfer and fluid flow
during the heat transfer of slot jet impingement
numerically. A secondary peak was observed in
the Nu at a small value of the nozzle–plate
spacing. The results showed a change in the
mean velocity profile from the standard law of
the wall in the stagnation region. The Nu was
higher than that without perturbations. Largescale vortical structures were observed near the
location of the secondary Nu peak.
Microgrooved surfaces of boiling jet array
impingement and the heat transfer performance
were examined in [67]. The heat transfer
efficiency of impinging jet is insensitive to the Re
under fully developed boiling condition. The
radial microgroove surface achieved the
maximum heat transfer coefficient of h = 230
kW/m2 K, whilst a substantial heat flux of 380
W/cm2
was
transported.
Moreover,
[68]
evaluated the impingement heat transfer with
different jet geometries in a cylindrical surface.
The technique of transient liquid crystal was used
to investigate the state of Nu distributions in a
cylindrical surface. They evaluated the impact of
the hole shape and the difference in the hole
inlet. Exit conditions were examined on the basis
of racetrack-shaped and cylindrical holes. Nu is
associated with Re for the racetrack-shaped and
cylindrical holes. The racetrack-shaped holes
obtained higher heat transfer rate than the
cylindrical holes. Reference [69] presented a
strategy for building a model of mechanistic heat
transfer that allows the cooling of steel. This study
was
based
on
systematic
experimental
investigations. The cooling behaviour of
stationary steel plates was explored, and the
heat fluxes that occur in stationary plates during
jet impingement boiling were calculated.
Farahani et al. [70] examined the heat transfer
coefficient of the slot jet impingement by using a
conjugate gradient technique along with the
adjoint equation. The increasing separation
space reduced the heat transfer coefficients,
and the increase in Re increased the
coefficients. With this method, the variation in the
local Nu with time could be determined.
Furthermore, the effect of utilising different plate
materials was assessed in [71] whilst exploring the
rectangular step case. The results showed that
the local Nu increased with the Re.
In the context of further increase in the levels of
heat transfer enhancement, rough surfaces with
different configurations, such as ribbed and
dimpled surfaces, were investigated to solve the
issue of jet impingement. Given this problem, an
array of circular jets impinging on a dimpled
surface was compared with those impinging on
a plain surface [72]. The technique of transient
liquid crystal was used for measuring heat
transfer. This study considered the two-dimple
configurations
of
inline
and
staggered
arrangements with respect to the position of the
jet impingement hole. The results revealed that
lower heat transfer coefficients were produced in
the presence of dimples on the target surface
compared with those of a nondimpled target
surface. Yan and Mei [73] tested the effect of
surface ribbing on the impingement heat transfer
as a result of an elliptic jet array. This study
discussed the broken and continuous V-shaped
rib configurations with three angles. In Figure 7,
the liquid crystal thermograph technique was
used to measure heat transfer. The results also
revealed that the enhancement or retardation of
heat transfer might occur as a result of the ribbed
surface. The best heat transfer was obtained
when the rib angle was 45° and the ribs are
continuous. The effect of dimple shape on heat
transfer that resulted from multiple impinging jets
was examined further by introducing convex[74] and concave-dimpled [75] surfaces and the
fusion of both shapes [76]. These works
considered a separation distance (S/Dj) of 0.5 ≤
S/Dj ≤ 10 or 11 and a jet Re of 5000 ≤ Re ≤ 15,000.
Furthermore, three eccentricities (E) between the
dimple and jet centres were considered. In terms
of the convex-dimpled surface, heat was
augmented by using a sufficient selection of Re
and S/Dj, the shrinkage of the interjet region,
moderated jet–jet interference and elevated
heat transfers over the stagnation areas.
Uniformity also improved over the convexdimpled surface. In terms of the concavedimpled surface, given a sufficient selection of
Re, E/H and S/Dj ratios, the augmentation of heat
transfer in the average Nu from the smoothwalled level could be achievable over the
dimpled surface. A study was conducted on the
dimpled-concave and -convex surfaces in the
presence and absence of effusion. The results
showed that in the absence of effusion, a lower
average Nu was obtained for a surface with
concave dimples compared with those of
surfaces with convex dimples. Akhilesh P.
Rallabandi [77] investigated two impingement
surface configurations. This study presented an
array of circular jets impinging on ribbed and
porous surfaces. The methodology of transient
liquid crystal was used to obtain heat transfer
coefficients for values of Re range from 5000 to
20000. A significant increase in the heat transfer
coefficient was exhibited by the porous foam.
Therefore, the smooth surface is convenient for
enhancing the impingement heat transfer.
Figure 7 Dimpled impingement surface. [76]
The characteristics of flow and heat transfer for
multiple jets impinging on nonflat impingement
surfaces, particularly concave surfaces [78]
(Figure [8]) were investigated. Iacovides and
Launder [79] experimentally investigated the
cooling of a rotating semi cylindrical passage as
a result of the effect of a row of impinging jets.
Laser Doppler anemometry and PIV techniques
were used to visualise the flow, whereas the
liquid crystal method was used to measure the
local Nu. The results of the stationary case
revealed that high rates of Nu were obtained
within the vicinity of impingement points and
halfway between them. However, the Nu
reduced in those areas due to the rotation
effect, which increased the spreading rates of
jets. T.J. Craft [78] simulated the nonrotating case
of this study for applications of turbine blade
cooling. The models of nonlinear and linear eddy
viscosity with wall function were considered. The
results of the simulation revealed that the
standard log law-based form of wall function was
insufficient for the prediction of heat transfer.
Furthermore, the exact approximation of
convective terms was crucial. Given the same
surface configuration, the effect of high relative
curvature (d/D) was examined by altering the jet
tube diameter (d) whilst the impinging surface
diameter (D) remained unchanged [80]. The
heat transfer characteristics were measured
using the heat foil technique and infrared
thermal imagers. The local heat transfer
coefficient
was
determined
using
linear
regression. The results revealed that the Nu
distribution was similar to the distribution of a
concave surface over a flat plate. The heat
transfer near the impinging zone enhanced with
the increase in relative curvature.
Figure 8 Concave impingement surface. [78]
This study presented three varying cases of
impingement target being impinged by various
arrangements of jets. The nonstationary, nonflat
and rough surfaces affected the impingement
heat transfer and flow pattern differently. The
fixed, flat and smooth plates were often utilised
when the focus of the research objective was on
the effect of interference amongst the
characteristics of impingement heat transfer and
jets on flow.
3.3 Inclined multiple jet impingement
The inclination angle in a jet impingement system
is expected to alter the flow and heat transfer
characteristics when it interacts with other
multiple-jet
factors.
This
parameter
was
investigated by considering the angle between
the jets and impingement surface on the one
hand and by investigating the orientation of the
entire system (jets and impingement target) on
the other. The importance of reviewing such
relevant works lies in the selection of an efficient
system configuration that focuses on the
common factors related to impinging twin jets.
The inclination angle (φφ) of the impingement
surface from the normal to the axial directions of
the jets [81] (Figure 9) was first investigated by
impinging a row of circular jets on an inclined
surface in a triangular duct and again by
impinging a pair of rectangular jets on an
inclined wall [82]. Three inclination angles (e.g.
30°, 45° and 60°) of jets impinged within a duct
were considered during the experimental study
to ensure that the static wall pressure reduces
and the coefficients of local heat transfer in
leading-edge triangular ducts could be
measured. The technique of transient liquid
crystal was used to perform heat transfer
measurements at different jet Re (3000 ≤ Re ≤
12600) and jet spacing values (s/d = 3.0, 6.0). The
results showed that Duct C obtained the largest
rate of wall-averaged heat transfer because it
had the smallest jet inclined angle and highest
jet centre velocity. The normal impingement had
better performance than heat transfer. A
numerical study on the effect of jet impingement
angle ( ) on average and local Nu was
conducted in a pair of jets impinged on an
inclined surface. The 3D Navier–Stokes equations
were solved using the finite volume method and
FLUENT 5.2 software. The Re ranged from 500 to
20000. Furthermore, the impingement angle
ranged from 30° to 90° in increments of 15°. Two
cases were considered, that is, Case A with wall
boundary conditions and Case B with conditions
for the atmospheric pressure boundary. The
computational results revealed that Case A
obtained a higher peak Nu than Case B. An
increase in the jet impingement angle could
improve Nuavg by almost four times the value of
Re at 20000. To summarise, the inclination angle
for the two works had a similar effect on heat
transfer. In local heat transfer, self-similar
behaviour was examined on the basis of
submerged jets and jet impingement of laminar
slot [83]. By using the analytic Prandtl number
dependencies for stagnation point flows, the
corresponding correlations associated with
impinging slot jets were valid in a broad range
(0.0005 ≤ Pr ≤ 4500).
nozzle size, cross-section shape, type (e.g. orifice,
pipe, convergent or divergent) and edge (e.g.
sharp, straight and round).
Figure 9 Inclination and impingement angles. [81]
Different
orientations
of
multiple-jet
impingement systems were presented in an array
of slot jets impinged on a hot flat plate [84]. This
study discussed the interactions of the effects of
cross
flow,
buoyancy-induced
flow,
the
orientation of hot surface with respect to gravity
and the Re and Rayleigh numbers on heat
transfer characteristics. The impingement plate
was heated with a panel heater powered by
controlled DC power supply, and type T
thermocouples were used to measure the
surface temperatures. In Re ≥ 400 and Ra ≥
10000, the Nu was independent of the hotsurface orientation. The Nu of vertical and
horizontal orientations with a hot surface facing
up were approximately equal.
Reference [85] presented the data of local and
averaged heat transfer coefficients to prove that
the
stream-wise
development
of
low
impingement distance surface would increase
the Nu but decreased with large impingement
distance. Any variations (decrease or increase in
span-wise and stream-wise spacing) would
affect the Re. The results of previous works
relevant to the effect of inclination angle
revealed the important conclusion that the
vertical impingement plate is the efficient
configuration that produces the characteristics
of high heat transfer in multiple impinging jets.
3.4 Effect of the individual nozzle
geometry in multiple impinging jets
The nozzle configuration in a multiple-jet system
was manipulated to enhance the impingement
characteristics of heat transfer. Multiple nozzles
were configured in the arrangement of
associated nozzles in addition to the factors
related to the individual nozzle. A single nozzle is
configured by using different factors, such as
The effect of nozzle size on the heat transfer
and flow of jet impingement was investigated
along with various geometrical considerations
related to multiple jets. In Figure 10, Su and
Chang [86] adopted a grooved orifice array
plate with various nozzle diameters to augment
the impingement heat transfer. A small S/D (S/D <
1) was measured with Re ranging from 1000 to
4000. For the three cases (e.g. A, B and C), the
combined effect of the nozzle and groove size
was considered. Infrared thermography was
used to measure heat transfer. The results
showed that at S/D = 0.5, jet-array C was
consistent in generating high average Nu.
Koncar et al. [87] numerically examined the
effect of nozzle sizes on the flow characteristics
and heat transfer of divertor cooling situated at
the power plant of conceptual fusion. The nozzles
were distributed in four circles located around
the central nozzle. Then, a cartridge issued
helium jets impinging on a thimble-shaped
target. The code ANSYS CFX 11.03D was used to
solve the governing equations. The results
revealed that it achieved the highest divertor
efficiency as a result of the reduction in
temperature for formulating equal nozzle
diameters. In another study, Terri B. Hoberg [88]
analysed the effect of nozzle size on the heat
transfer of a staggered array of jets with fusion
holes. Three scaled models with varying nozzle
diameters and Re ranging from 500 to 10000
were utilised. The impingement plate was heated
with an electrical resistance heater, and the
surface temperature was measured via a k-type
thermocouple. The results revealed that the use
of small-scale arrays could help achieve high
transfer coefficients of dimensional heat.
Figure 10 The orifice plate models adopted. [86]
The nozzle shape is expected to have a
remarkable effect on heat transfer because of
the impingement of multiple jets. Circular and slot
nozzle shapes were considered for an array of
jets [90] and as three lines of circular jets against
a single-slot jet at the same Re [91]. For circular
jet arrays, the peaks of the maximum heat
transfer coefficients are more pronounced than
those for slot jet arrays. Furthermore, the heat
transfer enhancement associated with three-row
jets is higher than that of slot jets. Other works
investigated the aspect ratio (AR) effect of the
elliptic nozzle shape experimentally through liquid
crystal thermography [92], [93]. Experiments were
conducted at different Res. The results reveal
that the mean heat transfer rates due to the
impingement on a flat surface by the elliptic jets
of AR = 0.5 are the highest at Re = 3000 and 4500;
in the low-Re case of 1500, jet arrays with AR = 2
and 1 perform better than those with AR = 0.5.
For an array of elliptic jets that impinges on a foil
hole target, the optimal heat transfer
performance is obtained with a circular jet of
AR = 1. In [94], Ai et al. experimentally
investigated the heat transfer characteristics of
a water impingement jet with a moving nozzle by
using a stepping motor governed by a nozzle
and the effect of the nozzle speed on the heat
transfer enhancement at various flow rates and
heat fluxes. Their experimental results reveal that
a moving nozzle is more efficient than a settled
nozzle at reducing the maximum temperature
difference of a heated surface and the mean
liquid film thickness, thereby resulting in steady
heat transfer rates and temperature. A high
nozzle speed can help enhance heat transfer
and achieve temperature uniformity.
The authors in [95] evaluated the two-phase
flow patterns, heat transfer, and jet impingement
during the boiling process in a Hele–Shaw cell.
For the liquid jet, high-volume flow rates resulted
in the heat transfer of the impingement jet, while
low-volume flow rates resulted in a Hele–Shaw
flow boiling system. Excellent heat transfer results
and a pressure drop with a diameter of 10 mm,
vva spacing of 0.1 mm and a jet diameter of 1
mm were obtained. The corresponding flow
boiling pattern for a heat flux is 327 W/cm2.
Likewise, the cooling process with an impinging
oil jet located in a cylindrically confined space
on both high-speed reciprocating and stationary
smooth discs without phase change and with
uniform heat flux was examined in a previous
study [96]. For jet impingement on a stationary
disc, a high stagnation zone Nu was observed
with a small overall surface average Nu for a
short impingement distance. For jet impingement
on a high-speed reciprocating disc, a high
rotational speed of the driven machine has a
great heat transfer coefficient. The turbulent
round jet impingement heat transfer on the high
temperature
difference
was
numerically
analysed by [97]. The numerical results indicate
that the heat transfer coefficient decreased with
the density, while the coefficient increased with
the augmentation of each thermal property.
Royne and Dey [98], as shown in Figure 11,
tested four-nozzle arrays with four edge shapes at
the same nozzle size, pitch and plate distance.
Liquid crystal thermography and a digital
camera were used to measure the surface
temperatures at Re = 1000 − 7700. Their results
show that countersunk nozzles produce higher
average heat transfer coefficients than the other
geometries.
Figure 11 Different nozzle edge shapes.[98]
The effect of the nozzle-to-plate spacing on the
fluid flow and heat transfer of submerged jet
impingement was examined by Choo et al. [99].
Their results indicate that the pressure and the Nu
were segmented into three zones:
1. Zone (I): jet deflection zone (H/d ≤ 0.6)
2. Zone (II): potential core region (0.6 < H/d
≤ 7)
3. Zone (III): free jet zone (7 < H/d ≤ 40)
In Zone I, a significant increase in pressure
and the Nu was observed with the decreasing
nozzle-to-plate spacing. In Zone II, the impact of
the nozzle-to-plate spacing on the pressure and
Nu was negligible. In Zone III, a monotonic
decrease in pressure and the Nu was observed
with the increase in nozzle-to-plate spacing. The
heat transfer characteristics were evaluated by
Wang et al. [100] by employing jet impingement
at a high-temperature plate surface. They
studied the effects of water temperature, initial
surface temperature and jet velocity on the heat
transfer characteristics, considering several
industrial applications. Jet velocity, water
temperature and surface temperature appeared
to influence heat flux the most.
arrangement case. Furthermore, the Nu has a
higher peak upstream than downstream in the
inline case. Staggered jets exhibited a
contrasting behaviour.
Two other dense and nine/spare nozzles with
straight edges were considered in addition to the
above four configurations [101]. The results
illustrate that nine-nozzle arrays perform poorly
than four-nozzle arrays. The sharp-edged orifices
and the contoured nozzle shapes were
investigated by Geers and Tummers [102]. At the
same Re, the sharp-edged orifice jets effectively
produced a higher initial core velocity than the
contoured nozzle shapes, thereby resulting in a
higher impingement-point heat transfer. The
geometrical configuration of multiple jets shows
a remarkable influence on impingement heat
transfer. The circular jet shape exhibits a more
efficient performance than the other jet shapes.
4.0 MULTIPLE JET ARRANGEMENT EFFECT
The geometrical arrangement of multiple jets,
especially the array of jets, is expected to
influence the behaviour of interference between
jets and thus affect the heat transfer
performance at the impingement target. This
issue has been studied by several researchers
with different multiple jet impingement system
configurations and scales. Although the
geometrical arrangement pertains to the array of
jets, the characteristics of interference between
jets are basically the same in all configurations.
However, the efficient arrangement may guide
important design considerations.
The interference between two inclined inline
and staggered arrangements with a cross flow,
as shown in Figure (12), demonstrates the test
section of a rectangular duct with two inclined
impinging jets issuing into a fully developed
turbulent crossflow. The height and width of the
duct were 21 and 432 mm, respectively, and
were studied experimentally by Nakabe et al.
[103]. They examined the Flow visualisation using
fluorescence dyes and PIV techniques and took
heat
transfer
measurements
using
the
thermochromic liquid crystal method and the
neutral network algorithm. Their results illustrate
that the interference between jets was affected
by the geometrical arrangement of jets, and thus
the enhanced zones of heat transfer were
influenced as well. In the staggered jets case,
four longitudinal vortices were formed, while only
three vortices were generated in the inline
Figure 12 Twin jets in (a) in-line and (b) staggered
arrangements with cross flow (the dimensions ducts
were 21 and 432 mm respectively). [103]
In [104], the heat transfer enhancement of a
slot jet impingement with multiple nozzles and
different
duty
cycles
was
investigated
numerically. The numerical results indicate that
the heat transfer performance of steady
impingement jets is better than that of unsteady
impinging jets in the case of double-slot
impingement jets under the same Re and a
phase difference (θ) of 0°. The heat transfer
enhancement of stead impingement jets has an
optimal effect. The heat transfer performance
under a duty cycle of 0.5 and above a threshold
frequency of 50 Hz is the worst. Aboghrara et al.
[105] experimentally studied the different
applications of a solar air heater on a corrugated
absorber plate. They investigated the outlet
temperature and efficiency of a solar air heater
to determine the effect of jet impingement on
the corrugated absorber flat plate. Their findings
indicate
the
strong
function
of heat transfer performance and the influence
of the mass flow rate of air on heat transfer in
solar air heaters. Furthermore, the thermal
efficiency of the proposed duct design was
nearly 14% more than that of a smooth duct.
Other arrangements of the square and
circular arrays of nine impinging jets, shown in
Figure 13, were considered in predicting the flow
and heat transfer characteristics [106]. The finite
volume method with the SIMPLE scheme was
used to solve the governing differential
equations. The numerical results reveal that the
square arrangements exhibited an asymmetric
flow pattern, while symmetrical behaviour was
observed in the circular array of jets. This flow
trend led to similar heat transfer characteristics of
individual jets, except for the central one in a
circular arrangement at high heat transfer, given
that one jet was produced at the expense of the
other in the square array case. At different crossflow Res, the authors of [107] examined the
impacts of vortex generators on jet impingement
heat transfer. Between the crossflow channel
and the upstream of the jet exit, a vortex
generator pair (VGP) was placed to improve the
impingement heat transfer rate. Rectangular
winglet (RW) and delta winglet (DW) were
applied at different heights. The heat transfer
mechanisms and flow structures were then
examined.
Figure 13 Top view of two arrays of jets in (a) square
and (b) circular arrangements. [106]
The heat transfer characteristics and the
impact of the jet Reynolds of impinging jet
arrays
[108]
were
numerically
and
experimentally
investigated
for
different
geometrical arrangements and parameters,
such as the non-corresponding slot widths for the
local Nu division, the non-corresponding nozzleto-plate and jet-to-jet spacings, the Re ranging
from 144 to 505 with the jet hydraulic diameter
(Dh) as the basis, the local Nu that corresponds
to the impingement region, the stagnation point
and relative minimum for any configuration
when the Re increases and the low ratios of the
plate spacing-to-jet hydraulic diameter. The
stagnated Nus decreased when the Re was
constant and the jet-to-jet spacing increased.
Michna et al. [109] studied the impact of
multiple micro-jet arrangements and the total jet
area-to-surface area ratio on impingement heat
transfer. The heat flux was determined based on
the difference between the heat dissipation of
the heater and the heat losses. Furthermore, the
highest Nus were observed with an inline array at
an area ratio of 0.159. In addition, the optimum
value of area ratio showed a staggered
arrangement. Likewise, the slot jet impingement
heat transfer for the moving nozzle and plate was
examined by [110]. On the basis of the analysis,
the Nu decreased with the increase in the nozzle
or plate velocity. A significant impact was
caused by the moving nozzle. The impact of
using twin impingement jet mechanism (TJIM) on
the enhancement of heat transfer and fluid flow
characteristics
have
been
investigated
experimentally in many studies, e.g. [5], [19], to
improve the heat transfer rate in the passive heat
transfer technique. Previous studies involved IR
infrared thermal imaging (Fluke Ti25) and heat
flux-temperature micro foil sensor measurements.
The results indicate a noticeable and substantial
improvement in the localised heat transfer
coefficient regarding the steady flow at radial
distance positions on the measured aluminium
surface at different Res and with the gradual
decrease when moving away subsequently from
the interference area’s centre, while the nine
models on the impinged flat of the target were
employed for the collection of heat fluxtemperature data. For the optimum condition to
establish higher heat transfer rates for the current
problem, we can consider the distance between
nozzles and the spacing between the nozzles
and the jet.
Previous studies [4], [17] explored the
experimental and numerical simulations of the
heat transfer enhancement in the twin
impingement jet system. This article presents
numerical and experimental analyses to improve
the heat transfer and investigate the effect on
the (Nu) and the heat transfer coefficient of the
distance from the nozzles and plates. The RNG kμ turbulence model was used to investigate the
computational study of the heated plate by
simulating electronic components. The position of
the jet-plate was changed at different distances.
The results contribute to a new way of improving
the flow and heat transfer functionality of the
TJIM. The results studies at various positions of the
TJIM indicate that the best model for the heat
transfer coefficient and the highest Nu is at the
nearest spacing between the nozzles and the
nozzle and the plate. For this case, the
investigators conducted a numerical simulation
based on the RNG k-μ turbulence model using
the TJIM of 9 models. In the calculation of the
heat transfer coefficient, the Nu and thermal
enhancement factor for the effects of the nozzlenut distance (S / D), H/De and the Re number
were further investigated. Model 1 has been
shown to be ideal for calculating the Nu number
of S / D = H / D = 0.5 in all jets. The worst results
were reported for Model 9, where S / D= 1.5 and
H / D = 5.5. The results show that a decrease or
increase in flow turbulence results in the irregular
distribution of the local Nu number (Nu) onto the
impacted surface. Kadiyala and Chattopadhyay
[9] conducted numerical investigations of the
transfer heat from a moving surface with a
uniform
wall
temperature
due
to
the
impingement of a series of slot jets, and the
transition–SST model was used for numerical
simulations. A good agreement with the existing
data for laminar and turbulent slot jets was
observed. The heat transfer was further studied to
understand the effect of surface velocity on the
flow regime. The Re ranges from 100 to 5,000. The
heat transfer from the moving wall at high
surface velocity is more than that at a stationary
case. Hatami et al. [8] studied the geometry and
dimensional effects of impingement synthetic jets
on the flow field and heat transfer. The effect of
confined and unconfined geometric designs on
the flow field and heat transfer rate was
examined. The effect of the confined synthetic
jet of impingement distances on the flow field
and heat transfer were examined. The flow field
and heat transfer effect of the Re was examined.
The differences in stroke length were tested for
flow and heat transfer behaviour. Increasing the
spacing from the jet to the surface affects the
vortex and therefore the heat transfer structure.
Experimental and numerical works were
carried out by [111] to investigate the effect of
the impingement dimples on the surface on the
heat transfer characteristics in a circular test
plate. The impingement jet technique and the
dimple shape can enhance the heat transfer
rate caused by the high turbulence intensity. The
cylindrical shape of the dimple was used in this
work. The simulation results were validated with
the experimental data obtained from four types
of test plates. The experimental results show that
the case of the dimple diameter (d) equal to the
jet diameter (Dj), and the distance between jet
and the test plate (B) is 2 times of Dj, yielded the
maximum heat transfer rate. The heat transfer
rate was enhanced up to 200% compared to a
flat plate at Rej = 14,500. Narrow channels were
fabricated to measure the heat transfer because
of the impinging row of jets in different
arrangements [112]. Figure 14 shows that the
temperature distribution on the impingement
target was measured using the transient liquid
crystal technique. The results indicate that the jet
arrangement affects the distribution of the
convection
coefficients
significantly.
Furthermore, the inline pattern allows the cooling
jets to cover the impingement surface efficiently.
Thus, the heat transfer coefficients exhibit higher
rates than those in staggered arrangement.
Figure 14 Impingement jets arrangements. [112]
The geometric shape of impinging jets is
a significant factor. A preferable heat transfer
was achieved when an elliptical shape was
used. Elliptic jets supply higher heat transfer
coefficients than rectangular jets. The heat
transfer efficiency was highest for the Re of
10,000 and the H/d of 2. The jet geometries
increase the heat transfer coefficient on the
target plate by approximately 6.01%–16.8% at the
principal surface and build on the AR, Re, and
jet–plate spacing. Subsequently, the distribution
of turbulent kinetic energy at (x/d, y/d) = (0.0,
0.0) is presented, indicating comparable
distributions for all nozzle geometries [113]- [115].
Impingement heat transfer shows different
behaviours because of the various arrangements
of multiple impinging jets. The different
arrangements lead to dissimilar numbers of
nearest neighbours of each nozzle and impinged
areas per nozzle. Therefore, the multiple-jet
pattern determines the way the jets interfere with
each other. Generally, multiple jets perform
efficiently when they are arranged in an inline
pattern. However, twin-jet arrangements can be
selected as a typical configuration to study the
interference between two neighbouring jets.
5. EFFECT OF NANOTECHNOLOGY IN
IMPINGING JETS TECHNIQUES
The
involvement
of
nanotechnology
in
impingement heat transfer has introduced a
wide area of investigation in several aspects.
Although many types of nanofluids and
nanocoating materials are available, twin-jet
impingement heat transfer is still considered in
verifying experimental methods [10]. These issues
might delimit the problem of multiple-jet
impingement heat transfer. In our previous work
[116], the effect of the TiO2 nanosolution
concentration
on
the
heat
transfer
enhancement of the twin impingement jet of
a heated aluminium plate was investigated using
three different processes for heat transfer
enhancement. The TiO2 nanosolution coat, the
heat sink and a twin jet impingement system
were considered. Several other parameters, such
as the distance between the nozzles, the
concentration of the nanosolutions and the
distance from the nozzle to the plate, were also
analysed. the results showed that the major
problem with the increase in heat transfer rate
was the flow structure of the twin impingement
jets at the interference zone. The nanoparticle
size ratio to the surface ruggedness affected the
Nu. Selecting an appropriate impingement
system and the optimum levels of other factors
could improve the heat transfer characteristics.
The surface coating with the TiO2 nanosolution
also had a positive effect on the heat transfer
rate.
Nakharintr et al. [6] investigated the impact of
jet–plate spacing to jet diameter ratios on the jet
impingement heat transfer and pressure drop of
TiO2 nanofluids. The heat sink was fabricated from
the aluminium using a wire electrical discharge
machine with a length, width, and
base
thickness of 50, 50 and 3 mm, respectively. The
parameters and the ranges under consideration
include the jet–plate spacing to jet diameter
ratios (H/D = 0.8–4.0), mass flow rates (8–12 g/s)
and nanofluid concentrations (0.005%–0.015% by
volume). The jet–plate spacing to nozzle
diameter ratios have a significant impact on the
temperature and flow behaviours of jet
impingement that increased turbulent intensity
and heat transfer rate. Meanwhile, Naphon et al.
[117] investigated the continuous TiO2 nanofluids
jet impingement heat transfer and flow in
a micro-channel heat sink using three heat
transfer enhancement techniques, namely, jet
impingement, micro-channel heat sink and
nanofluids. The obtained results show that the
suspension of nanoparticles in the base fluid
remarkably increased the convective heat
transfer by 18.56% at the 0.015% nanofluid
concentration. In addition, the obtained heat
transfer coefficient tended to increase with the
nozzle diameter and the decreasing nozzle level
height.
The numerical investigation of heat
enhancement and fluid flow from a heated
surface using nanofluids with three impinging jets
was discussed by [11]. The effects of different
volume ratios, heat fluxes and types of nanofluids
(i.e. CuO-water, Al2O3-water, Cu-water, TiOwater and pure water) on heat transfer and fluid
flow were analysed numerically. The change in
volume from μ = 2% to 8% increases the average
Nu by 10.4%. The average Nu was not affected
by the six increase in heat flux. The use of Cuwater nanofluid results increased CuO-water, TiOwater, Al2O3-Water and pure water of 2.2%, 5.1%,
4.6% and 9.6%, respectively. An experimental
study [118] on heat transfer characteristics was
conducted on nano-scale modification surfaces
for high-velocity small slot jet impingement
boiling. The impact mechanism of the surface
distinguishing parameters was studied to
investigate the quantitative effects and increase
the critical heat flux. The heat transfer
characteristics were not affected greatly by the
changing
nanoscale.
The
Heat
transfer
coefficient could be enhanced via the
detraction of solid-liquid, whilst the Critical heat
transfer clearly deteriorated.
The impact of nanofluids on heat transfer
augmentation was investigated by [119] and
[120]. Nakharintr et al. [119] illustrated the
magnetic field effect of a confined impingement
jet in
a
mini-channel
heat
sink
on
the enhancement of nanofluid heat transfer.
Their results show that the Nu increases with the
magnetic field effect, unlike that without a
magnetic field effect on thin nanofluid
concentration. However, the test results reveal
that nanofluid concentration has no significant
effect on pressure drop. Tiara [120] investigated
the impact of an alumina nanofluid jet on
heat transfer enhancement on a steel plate. The
results reveal an enhancement of approximately
7.74% following the nanofluid jet impingement on
the plate surface roughness that increases the
number of nucleation sites.
In their second study [121], the researchers
investigated a single impingement jet by using
nanofluid (SiO2-water) freely. Their experimental
results demonstrate that the use of nanofluid
considerably
enhances
heat
transfer
countenance. The convective heat transfer
coefficient of the SiO2-water nanofluid that
contains a 3.0% nanoparticle volume fraction
with Re from 8,000 to 13,000 was 0.04 better than
that of pure water. The authors proposed the
investigation of the impact of suspended
nanoparticles and the state of the impingement
jet in future research. In their third study [122], the
heat transfer characteristics of a heated surface
were experimentally investigated on the basis of
the CuO-water nanofluid in circular impingent jet
cooling; the enhancements of the Nu were 14%
for φ = 0.15% and 90% for φ = 0.60%. The
characteristics of the test plate surface after
nanofluid jet impingement were investigated
through scanning electron microscopy. In a
previous work [123], a novel array cone heat sink
was studied quantitatively to enhance the heat
transfer and cooling effects of fluid impingement;
the findings show that the effect of fluid
impingement on a cone heat sink is preferable to
that on a conventional flat plate heat sink. In
a study of the enhancement of cooling in central
processing using jet impingement with and
without nanofluid [124], the heat transfer
coefficient h increased with the Nu. However,
between Re = 23000 and 50000 and a jet
impingement angle of 30 and 75, the Nu
remained constant at 831, thereby lying on a
turbulent region.
The enhancement of heat transfer and flow
characteristics improved through many ways
[125], [126] The use of nanotechnology that
involves nanofluid and nanocoating is a
common method because of the high
convective heat transfer that show a remarkable
influence on impingement heat transfer. In
addition, the effect of twin jet impingement on
different configurations of jet flow and heat
transfer was determined. Parameters, such as the
Re, S/D, H/De, the inclinations of a plate or nozzle
and heat flux, are significant factors that are
related to the heat transfer of twin impingement
jets.
6. DISCUSSION
A literature review refers to a methodical,
reproducible and outright design to
correct, interpret and distinguish the
existing documents. The methodological
path for building review articles has now
become communal across
various
disciplines
(e.g.
social
science,
engineering and medicine).
Online journal databases, such as Science
Direct, Scopus, Google Scholar and Emerald,
mostly enable the successful search and
procurement
of
research
papers. These
databases contain works from various publishers,
including Taylor, Elsevier, ASME, Springer, Emerald
and IEEE, and clarify the percentage of the
exercised database. Only English papers are
considered, and no selection was based on
journal ranking if they are all indexed in Scopus
and ISI. Nominated keywords, such as heat
transfer
enhancement,
impingement
jets,
multiple jets, nano fluid and nano coating were
used to establish clear boundaries that may
delimit the project or study. We downloaded
numerous suitable published articles based on
research
methodology,
study
objectives,
simulation, findings, data collection instruments
and data analysis tools to set the study standard
for the analysis. The research methodology was
considered for each study by emphasising the
philosophical background of the research
methodology to classify the papers. Authors
performed constructive evaluation of the
methodologies by considering their advantages
and disadvantages.
This paper presents a detailed review of the
numerical,
theoretical
and
experimental
investigations that identify the factors that
influence twin jet impingement and the
associated flow and heat transfer performance.
Numerous studies have focused on steady
impingement jets, but only the most relevant
cases of twin impinging jets have been included.
Nonetheless, the literature on twin impingement
jets remains limited. To the best of the authors’
knowledge, studies that involve numerical and
experimental analyses on twin jets are limited.
Despite the existence of many relevant
publications, the information on heat transfer
enhancement through twin jet impingement is
lacking. A special mechanism must be designed
and tested to generate twin impingement jets
(Figure 15) by controlling all the aforementioned
parameters.
Figure15 Twin-Jet Effect.
Furthermore, the interference zone between
two neighbouring jets and the effect of twin
impingement jets in this region on flow structure
and heat transfer have not been investigated
adequately. No correlation has been found
between the Nu and the significant parameters
found in the literature. In addition, the
interactions between the correlated factors have
not been investigated in detail. All these
shortcomings must be addressed to improve
knowledge on heat transfer characteristics in
cooling and heating applications.
Furthermore, we reviewed several studies
about the effect of different jet configurations on
the flow behaviour and the enhancement of
heat transfer. An extensive study was conducted
to determine the effect of twin jet impingement
on different configurations of jet flow and heat
transfer to focus on an area of study that has not
been covered previously. Parameters, such as
the Re, the S/D, the H/De, the inclinations of a
plate or nozzle and heat flux, are significant
factors related to the heat transfer of twin
impingement jets. The interference zone
between two neighbouring jets has not been
considered
adequately.
The
effects
of
impingement on the flow structure and heat
transfer at this region have not been investigated
sufficiently. In addition, the interactions between
the correlated factors have not been
investigated in detail. An extensive study on the
effect of twin jet impingement in multi-jet flow
and heat transfer was conducted to address an
area of study that has not been covered
previously.
Likewise, researchers should highlight the
significance of developing nanotechnologybased research for several heat transfer-related
applications. Furthermore, the effects of the
nanoparticle concentration on the Nu and the
jet configurations on the heat flux factor must be
discussed. A velocity increment was noted at
the centreline of the interference zone wherein
an increasing velocity enhanced heat transfer
and increased Nu. The literature generally
suggests that the heat transfer characteristics
can be enhanced when the optimal levels of the
influencing factors and a suitable impingement
system are selected. Several studies have
investigated cases of steady impingement jets,
but only the most relevant cases of twin
impingement jets are included in this paper. The
literature on twin jets is limited. Tables 1 to 4
present the list of the most relevant studies on
steady impingement jets. The conclusions of this
article are based on the currently available
information and other possibilities.
Table 1 steady impinging jet cases for Single jet.
No
Author
Type of
study
Type of
Jet
1
Factors
Single
jet
1.Re ranging from 500 to 1000
2. Indentation depths from 0.000125
to 0.0005 m for two different surface
configurations.
Single
jet
1. Nozzle diameter of 2 cm is fixed as
constant.
2. nozzle-To-plate spacing (H) of 4cm
is used for validation and 8cm for all
the other simulations.
3.Reynolds number of 23,000
Experiment
Single
jet
1. The diameter of the heated copper
rod was 10 mm, 2. The jet diameters
were 0.5 and 1 mm, 3. Spacing was
varied between 50, 100, and 200
<mu>m. 4. The heat was applied
through 4 cartridge heaters with a
maximum heat flux of 327 W/cm2
Experiment
and
Numerical
Single
jet
1. The circular nozzle has an inner
diameter of 6 mm. 2. Re=14,000 to
53,000.3. The nondimensional
distance is from 4 to 8.
Single
jet
1.The study carried out by CFD model
2.Different parameters (plate
thickness, plate material , jet
Reynolds number and nozzle
diameter)
Numerical
Single
jet
1. Two different scaling behaviors,
one for the stagnation region and
one for the fully developed wall-jet
region are shown.
2. nozzle-to-plate distance H/W.
3. 0.07⩽Pr≤1307,100⩽ReW⩽1000
and 4⩽h/W⩽20.
Ansu et al
Experiment
1.single
jet
2.row of
jets
(Array)
1. Re 5000, 10,000 and 15,000
2.distance between jet and the target
plate (L/D)) of 2, 4 and 6 for four
different jet configurations
Jordan et al
Experiment
Single
jet
1. Re of 13,600, 27,200, and 40,700
are investigated for the cylindrical
Dobbertean
et al
Numerical
2
Kannan et al
Numerical
3
Kapitz et al
4
Guo et al
5
Zhu et al
Numerical
6
Bieber et al
7
8
Problem statement-"Methods-Results"
1. The impact of using different plate materials was
explored for the rectangular step case.
2. Increasing the (Re) increases the local Nu for all
cases.
3. The average Nusselt number increased by 18.8%.
1. The impact of geometric parameters on the
axisymmetric impingement heat transfer jet.
2. Results about effect of grooves are discussed in
detail based on the surface Nusselt number and
averaged Nusselt number.
3. Maximum Nusselt number was approximately
140.
1. Study heat transfer, impingement jet and twophase flow patterns.
2. high-volume flow rates for the liquid jet led to jet
impingement heat transfer while low flow rates led
to a Hele-Shaw flow boiling system.
3. Good results concerning heat transfer and
pressure drop were discovered with a diameter of 10
mm, a spacing of 0.1 mm, a jet diameter of 1 mm
and. The corresponding flow boiling patterns for a
heat flux of 327 W/cm2.
1. The local Nusselt number rapidly increases when
the air jet began its impingement. 2. The increasing
speed of Nuloc slows down as the jet impingement
continues to cool down.
3. Maximum Nusselt number is around 145.
1. An in-depth analysis of conjugate heat transfer
process of impingement jet.
2. Parameters vary the Nusselt number and the
thermal condition at the fluid-solid interface.
3. Conjugate impact leads to the decay of Nusselt
number.
4. Maximum Nusselt number was approximately
160.
1. Laminar slot jet impingement and submerged
jets is investigated regarding self-similar behaviour
in local heat transfer.
2. Analytic Prandtl dependencies for stagnation
point flows range (0.0005⩽Pr⩽4500).
3. Maximum Nusselt number was approximately
40.
1. Jet impingement heat transfer of the inlet
condition to visualize the temperature distribution
over the impingement surface using liquid crystal
thermography.
2. Correlations are sophisticated to Nusselt number
as a function of separation distance and Reynolds
number.
3. Maximum Nusselt number was approximately
70.
1. Impingement heat transfer on a cylindrical
surface with varying jet geometries.
holes, and Reynolds numbers of
11,500, 23,000, and 34,600 are
investigated for the racetrack holes.
9
Nasif, et al
Numerical
Single
jet
The three-dimensional Navier-Stokes
and energy equations are numerically
solved using a finite-volume
discretization
Single
jet
Large eddy simulation has been
performed with a finite-volumebased computational fluid dynamics
code and using a dynamic
Smagorinsky
and
on
LES
computations
and
Reynoldsaveraged
Navier-Stokes-based
computations
Single
jet
1. Air and water were used as the test
fluids.
2. Volumetric quality <beta> = 0-0.9.
Single
jet
1.hot surface 800 °C
2. Volume fraction (VOF) has been
used to simulate boiling heat transfer,
Simulation has been done in a fixed
Tsub=55 °C, Re=5000 to Re=50,000
and also in different Tsub=Tsat−Tf
between 10 °C and 95 °C.
10
Dutta et al
Numerical
11
Friedrich et al
Experiment
12
Toghraie, D.
Numerical
13
Tiara, et al
Single
jet
1. Steel plate (100 mm × 100 mm × 6
mm).
2.initial temperature of around 900
°C at the surface.
Experiment
Single
jet
The cooling pattern employed on the
run-out table during steel processing
highly affects the final microstructure
of hot-rolled steel products and thus
their final mechanical properties.
Experiment
Single
jet
Distributions of the local heat transfer
coefficient on the impingement
surface were determined for various
Re and H/Dh
Experiment
14
Nobari, et al
15
Farahani et al
16
Liu et al
Experiment
Single
jet
Choo et al
Experiment
Single
jet
17
1. A simplified enlarged model of the
trapezoidal internal cooling passage
near the leading edge is built up.
2. The temperature on the side exit
wall
was
measured
by the
thermocouples.
The working fluids are air and water.
The effects of a wide range of nozzleto-plate spacing (H/d = 0.1 - 40)
5. Nu is related to the Re for both cylindrical and
racetrack-shaped holes.
6. The racetrack holes are present to provide
enhanced heat transfer compared to the cylindrical
holes
1. To evaluate the cooling process due to an
impinging oil jet with uniform heat flux and without
phase change.
2. The maximum stagnation zone Nusselt number is
carried out with jet impingement around 7% higher
than with a long jet for the cases.
1. Fluid flow and heat transfer of a slot jet
impingement heat transfer of the nozzle-to-plate
spacing at a small value which a secondary peak in
the Nusselt number is observed.
2.the Nusselt number better as compared to the case
with no perturbations
4. Large-scale vertical structures were observed near
the location of the secondary Nusselt number peak.
1. The stagnation Nusselt number increased with
volumetric quality, attained a maximum value at
around 0.8 of the volumetric quality, and then
decreased. 3. Maximum Nusselt number was
approximately 140.
1. Numerical thermal analysis of water's boiling heat
transfer based on a turbulent jet impingement on the
heated surface.
2. The results of this study show that by increasing
the velocity of a fluid jet of water, convective heat
transfer coefficient at stagnation point increases.
1. Heat transfer in jet impingement surface using
surfactant based Cu-Al layered double hydroxide
nanofluid on a hot steel.
2. Nanofluid is improved the thermal properties
which impact of the rate of heat transfer.
3. Maximum heat transfer coefficient is around
13500.
1. Describes a strategy to develop a mechanistic heat
transfer model for cooling of steel.
2. To investigate the cooling behavior of stationary
steel plates.
3. Calculate heat fluxes on stationary plates during
jet impingement boiling.
1. Heat transfer coefficients generally tended to
decrease with increasing separation distance and to
increase with an increase in Reynolds number.
2. This presented method is able to estimate the
variation of the local Nusselt number with time.
1. Investigation on effects of impingement jets on
heat transfer characteristics of internal cooling
passage side wall.
2.The increase of the impingement angle makes the
peak of Nu become sensitive to the variation of the
impingement angle
3. The increase of the impingement Reynolds
number improves the heat transfer.
1. The influence of nozzle-to-plate spacing on heat
transfer and fluid flow of submerged jet
impingement.
18
Zhou et al
Numerical
Single
jet
19
Wang et al
Experiment
Single
jet
20
Heat transfer of round jet
impingement at high temperature
difference was numerically
investigated with V2F turbulent
model.
The heat transfer ability and cooling
uniformity in ultra-fast cooling
technology played a critical role in
improving the microstructure and
mechanical properties of hot rolling
steel.
1. Jet Reynolds number is fixed at
15,000.
2. The cross-flow Reynolds number
varies from 40,000 to 64,000.
3. The nozzle-to-surface distance to
jet diameter ratio is 4.0.
Experiment
Single
jet
Wang et al
Numerical
Single
jet
The computational fluid dynamics
method is used to simulate the jet
flow.
Xu et al
Numerical
Single
jet
Computational fluid dynamics
method with a model rough surface
Experiment
Single
air jet
multiple
air jet
1. Reynolds number from 300 to
10000.
2. Nozzle-to-plate spacing 0.5- 4.
Single
jet
Different jet-to-surface (h/B)
distances at two Reynolds numbers
namely, 2960 and 4740 based on the
jet exit velocity (Ue) and the
hydraulic diameter (2B)
investigated with (CFD) (LES) and
SST-SAS hybrid RANS-LES
Wang et al
21
22
23
Ertan Baydar
24
Taghinia, et al
Numerical
25
Seo et al
Experiment
1.single
jet
2.Array
jet
1. Re=1000-13650
2. Thermal performances of 10, 20,
and 40 PPI (pores per inch)
2. Nusselt number and pressure are divided into
three regions; region (I) jet deflection region (H/d ≤
0.6), region (II) potential core region (0.6 < H/d ≤
7), and region (III) free jet region (7 < H/d ≤ 40).
3. Maximum Nusselt number was approximately
70.
Numerical analysis of turbulent round jet
impingement heat transfer at high temperature
difference.
2. Numerical results show that the decrease of
density leads to decrease of the heat transfer
coefficient while the increase of each thermal
property leads to increase of the heat transfer
coefficient.
3. Maximum Nusselt number was approximately
200.
1. To investigate the effect of the initial surface
temperature, water temperature, and jet velocity at
the heat transfer characteristics for the many
industrial applications.
3. Heat flux maximum was influenced by the water
temperature, surface temperature, and jet velocity.
1. To investigate the effects of vortex generators on
the jet impingement heat transfer at different crossflow Reynolds numbers.
2. A vortex generator pair (VGP), placed in the
cross-flow channel and upstream of the jet exit, is to
enhance the impingement heat transfer. 3.
Maximum Nusselt number was approximately 130
1. To improve the cooling performance of the
impinging
jet
to
the
machining.
2. higher convective heat transfer coefficient are
obtained with the same flow rate by decreasing
nozzle diameter while increasing either the number
of nozzles or the oil supply pressure
1. To quantify the effect of jet flow Reynolds
number, jet impingement dimension, and surface
roughness as well as temperature difference between
jet flow and impinging target on the heat transfer of
jet impingement.
3. It is observed that the roughness effect is minimal
in the impingement zone while.
4. Maximum Nusselt number was approximately
100.
1. Determining the flow field of confined single and
double-jet impingement flows.
Determining the pressure distribution of the
domain.
1. CFD study of turbulent jet impingement on
curved surface.
2. Both models show similar performance at
higher h/B ratios.
3. Comparisons show that both models can produce
relatively good results.
4. Maximum Nusselt number was approximately
45.
1. Heat removal by aluminium-foam heat sinks in a
multi-air jet impingement.
2. Higher heat transfer enhancement than the single
jet impingement for high jet Reynolds number and
26
Can, M.,
Experiment
27
Wu et al.
Experiment
Ozmen, Y. and
G. Ipek,
Experiment
1.Single
jet
2.Array
jet
1.Single
jet
2. Array
jet
To provide data for designers of
industrial equipment
V ⩾ 6.1 m/s
28
1.Single
jet
2.Array
jet
1. nozzle-to-plate spacing (H/W) of
1–10 and for the Reynolds numbers in
the range of 5000–15,000 at the jetto-jet centreline spacing (S/W) of 9.
Single
jet
1.Re= 4800 to 14 800
2. The heat transfer measurements are
obtained using the transient liquid
crystal technique
29
Ekkad, S.V.
and D.
Kontrovitz,
Experiment
30
Terzis et al
Experiment
Single
jet
31
Modak, et al
32
33
Experiment
Single
jet
experiment
a
Single
jet
1. Solar radiation 500-1000 (W/M2).
2. 308 K ambient temperature.
3. Mass flow rate ranging 0.01-0.03.
Single
jet
1. The test section dimensions
(heat sink) is 50 ∗ 50 mm and 2 mm.
2. The nanofluids mixture of deionized water and nanoscale
TiO2 particles 0.005%, 0.010%,
0.015%.
3.Two various magnetic fields
strength of 0.084, 0.28 µT.
Single
jet
1. Steel surface of dimension
100 mm × 100 mm × 6 mm.
2. An initial surface temperature of
900 °C.
3. Nanoparticles size of 14 nm.
Aboghrara
et.all
Nakharintr,
and
Naphon,
Experiment
34
Tiara et al
1. Using the Transient Liquid Crystal
Technique.
2. range of Reynolds numbers
(11,100–86,000)
1.Initial temperature = 500 c0
2.5000 ≤ Re ≤ 12,000
3. Concentration of CuO-water
nanofluids (φ = 0.15%, 0.6%).
4. Nozzle to plate distance (l/d = 6,
12).
Experiment
smaller jet-to-jet spacing.
3. Maximum Nusselt number was approximately
120.
1. Experimental Optimization of Air Jets Impinging
on a Continuously Moving Flat Plate.
2. A programme of research has been implemented
to study the heat and mass transfer processes. 3.
Maximum
heat
transfer
coefficient
was
approximately 350.
1. The average single-phase convection coefficients
indicates that the confined jet provided the most
uniform convection.
2. The transition to turbulence was scouted to start
about x/d = 5.5 and end about x/d = 9.
1. Investigation of flow structure and heat transfer
characteristics in an array of impinging slot jets.
2. Nusselt distributions on the impingement plate
depend on the Reynolds number and nozzle-to-plate
spacing.
3. Maximum Nusselt number was approximately
100.
1. Jet impingement heat transfer on dimpled target
surfaces.
2. The presence of dimples on the target surface
produce lower heat transfer coefficients than the
non-dimpled target surface.
1.Hole Staggering Effect on the Cooling
Performance of Narrow Impingement Channels
2. The results indicated an effect of the jet pattern on
the distribution of convection coefficients.
1. Characteristic of heat transfer of heating surface
based on CuO-water Nanofluid in circular impingent
jet cooling was investigated.
2. Nu enhancement was found to be 14% at φ =
0.15% and 90%, for φ = 0.60%,
3. Test surface Characteristic using SEM
1. Outlet temperature and efficiency of Solar Air
heater to discuss effecting of the impingement jet on
the corrugated absorber flat plate. 2. Finding
illustrates
the
strong
function
of heat transfer performance likewise the mass flow
rate of air influences the heat transfer on solar air
heaters furthermore, the thermal efficiency of
proposed design duct is spotted almost 14% more as
compare to the smooth duct.
1. Impact of Magnetic field on the enhancement of
nanofluids heat transfer of
a
confined jet impingement in mini channel heat sink.
2. The result present that the Nusselt number is
going to increase with magnetic field impact
compared to that without magnetic field impact
Due to the thin nanofluids concentration in this
article.3. Concentration Of Nanofluids Has No
Significant Impact On The Pressure Drop Through
The Tests.
1. Impact of alumina nanofluid jet on the
heat transfer enhancement on a steel plate. 2.
There is an enhancement around 7.74% after the
nanofluid impingement jet on the surface
roughness of the plate, that way enhancing the
4. The concentration of the nanofluids
was varied from 1 to 20 ppm.
6.critical heat flux (CHF) of
2.10 MW/m2
35
Natarajan
et al,
Simulation
Single
jet
1. Frequency = 100 Hz. 2.
The jet Reynolds number is Re=DVb/ν
= 23,000. 3. The nozzle-exit is at y/D
= 2. 4. The wall vibrates between 0
and 0.5D. 5. Amplitude of vibration,
A = 0.25D
36
Experiment
Ai et al
Single
jet
37
Ly et al
Experiment
Single
jet
1. Different volume fractions (1%,
2% and 3%).
2. SiO2-water nanofluid containing
3.0% nanoparticles volume fraction.
3. Reynolds numbers ranging from
8000 to 13,000.
4. Convective heat transfer coefficient
is 40% higher than pure water.
5. Nozzle to plate distance.
Single
jet
11. Heat transfer of a sweeping jet
impinging on a flat wall for several
Reynolds number and nozzle-to-plate
spacings
2. Using PIV
Single
jet
1. TiO2 nanofluids have been
used
2. H/D = 0.8–4.0
3. Nanofluids concentrations (0.005–
0.015% by volume),
4. Mass flow rates (8–12 g/s).
38
Park et al
Experiment
39
Nakharintr et
al
Experiment
1. Different heat fluxes.
2.Different flow rates
3. Water jet impingement with a
moving nozzle by using a stepping
motor govern the nozzle.
1. Turbulent impinging jet on a vibrating heated
wall based on Large-eddy simulations 2. The mean
radial velocity increases upon positive displacement
of the wall and decreases upon negative
displacement. 3. Periodic shifts in the secondary
Nusselt number peak are spotted. 4. Enhancing in
heat transfer is shown in the stagnation region.
1. This article describe experimentally on heat
transfer characteristic of water jet impingement
and the impact of nozzle speed on the heat transfer
enhancement. 2.The experiment finding display
that a moving nozzle efficiency better than a settled
nozzle for decreasing the heating surface of
maximum temperature difference and the mean
liquid film thickness, which effect in steadier heat
transfer rates and a more steady temperature, a
higher nozzle speed better heat transfer enhancing
and temperature uniformity.
1. An Investigation of single impingement jet
freely using nanofluid (SiO2-water), 2. The
experimental
finding
present
that
the
implementation of nanofluids considerable
enhances the heat transfer countenance. For the
SiO2-water nanofluid containing 3.0% nanoparticles
volume fraction with Re from8000 to 13,000, the
convective heat transfer coefficient is 0.04 better
than pure water.
1. Flow structure and heat transfer of a sweeping
jet impinging on a flat wall has investigated.
2. The distribution of Nusselt number is correlated
with flow structure near the wall.
Effect of jet-plate spacing to jet diameter ratios
on nanofluids heat transfer in a mini-channel
heat sink. the jet-plate spacing to nozzle diameter
ratios have significant effect on the temperature
and flow behaviors of jet impingement.
Numerical analysis of heat transfer from a
40
Chattopadhya
y and Kadiyala
Numerical
Single
1. Re= 100-5000.
2. Surface velocity varied up to six
times the jet velocity at the nozzle
exit.
moving surface due to impingement of slot jets.
High surface velocities the heat transfer from the
moving wall is more than stationary case
1. The impact of Reynolds number on the flow
41
Hatami et al
41
number of nucleation sites. 3.Maximum cooling
rate of 104 °C/s.
Numerical
Single
Two types of turbulence models,
namely the v2−f and SST/k−ω
Single
1. Nanofluids concentration
2. Nozzle diameter
3. Nozzle-to-heat sink distances
4. Mass flow rate of nanofluids
Naphonl
and
Wiriyasart
Experiment
field and heat transfer is investigated.
2. The stagnation heat transfer rate reaches to the
maximum value at an optimum impingement
distance.
Experimental investigation on the TiO2
nanofluids jet impingement heat transfer and
flow characteristics in the micro-channel heat
sink are carried out. Suspending of nanoparticles
in the base fluid remarkably increases the
convective heat transfer by 18.56% at 0.015%
nanofluids concentration
1. Experimental and numerical works have been
42
carried
Parkpoom
and Paranee
Experiment
and
Numerical
Single
The simulate data displayed the flow
structure and contour temperature
surface on the test plate which
provided the complex flow and heat
transfer characteristics.
out
to
investigate
the
effect
of
impingement dimples surface on heat transfer
characteristics in a circular test plate. 2. The
experimental results showed that the case of the
dimple diameter (d) equal to the jet diameter
(Dj).
Table 2 steady impinging jet cases for Array jets.
No
Author
Type of
study
Type of Jet
1
Penumadu
et al
Numerical
Array jets
2
Li et al
Experiment
Experiment
1. Numerical simulations are
carried out on an array of
impinging jets using various
approaches such as Reynolds
averaged Navier-Stokes (RANS)
and Large Eddy Simulations
(LES)
Array jets
1.Jet-to-jet spacing (X/D, Y/D)
are 4∼8 and jet-to-target plate
distance (Z/D) is 0.75∼3
2. Re between 5,000 and
25,000.
3. Hole inclination pointing to
the upstream direction
(<theta>: 0 deg∼40 deg)
Array jets
Convection of water at
atmospheric pressure and
subcooling of 7°C with flow
rates up to 660 mL/min. A jet
array consisting of nine 1 mm
jets with 5 mm inter-jet spacing
and a 2 mm jet to target
spacing was employed to cool a
15 mm by 15 mm heated
surface
3
Jenkins et al
Factors
4
Ansu et al
Experiment
1. Row of
jets (array
jets).
2. Single jet.
1. Re 5000, 10,000 and 15,000
2. distance between jet and the
target plate (L/D)) of 2, 4 and 6
for four different jet
configurations
Problem statement-"Methods-Results"
1. Discusses the physics of impinging jets in a large
array in low Reynolds number regime.
2.lak in information of the pressure drop incurred in
impinging jets 3. Get a better understanding of the
flow physics 4. Show that the major pressure loss in the
system is due to contraction effect at the nozzle
entrance and due to viscous losses. 4. Maximum
Nusselt number was approximately 135.
1. Surface Nusselt numbers increase with streamwise
development for low impingement distance, while
decrease for large impingement distance. The increase
or decrease variations are also influenced by Reynolds
number, streamwise and spanwise spacings.2. Nusselt
numbers of impingement jets with inclined angle are
like those of normal impingement jets. 3. Presents
better prediction of row averaged Nusselt number. 4.
Maximum Nusselt number was approximately 95.
1. Heat transfer performance and micro-grooved
surfaces of boiling jet array impingement.
2. A maximum heat transfer coefficient of h = 230
kW/m2 K was achieved with the radial micro-groove
surface, transporting a substantial heat flux of 380
W/cm2.
3. Maximum Nusselt number is around 100.
1. Jet impingement heat transfer of the inlet condition
to visualize the temperature distribution over the
impingement surface using liquid crystal thermography.
2. Correlations are sophisticated to Nusselt number as
a function of separation distance and Reynolds
number.
3. Maximum Nusselt number is around 80.
5
Wang et al
Experiment
Rahimi and
Soran
Numerical
Array jets
Solid-liquid contact angle (CA)
and efficient heat transfer area
ratio (r: the ratio of the actual
heat transfer area to its
projected area) on the heat
transfer coefficient (HTC) and
the critical heat flux (CHF)
Array jets
Air jet Reynolds number and
nozzle-to-plate separation were
Re = 500 and H/W = 5
6
7
Bu et al
Experiment
3 row of jets
(Array)
8
Qiu et al
Experiment
and
Numerical
Array jets
1. Re from 50,000 to 90,000.
2. (H/d) from 1.74 to 20.0.
3. The jet impingement angle
(<alpha>) from 66° to 90°, and
4.the relative chordwise arc
length in the jet impingement
zone (r/d) from 13.2 to 34.8.
In the current design, the
saturated water flows into a
cylindrical chamber with a tube
array, whereas the hot air
travels outside of chamber and
boils the water inside
9
Dobbertean
et al
Numerical
Array jets
(Rectangula
r)
10
Aldabbagh
and.
Mohamad
Numerical
Array of jets
(square jet)
11
Robinson et
al
Experiment
Arrays
(Rectangula
r)
Re= ranging from 500 to 1000
and indentation depths from
0.000125 to 0.0005 m for two
different surface configurations
1.Jet-to-jet spacing (2D–5D)
2.Velocity ratios of the moving
heated plate to the jet velocity
(Rm = up/uj) (0.25–1.0)
3.Reynolds numbers (100–400)
4. Nozzle exit-to-plate distance
of 0.25 D.
5. Study a 3D laminar flow
model.
1. Jet-to-jet spacing’s of 3, 5
and 7 jet diameters.
2. Volumetric flow rates in the
range of 2L/min≤ ≤ 9L/min
3. Jet-to-target spacings
1. Heat transfer characteristics of high-velocity small
slot jet impingement boiling on nanoscale modification
surfaces. 2. To increase the critical heat flux.
3. To investigate the quantitative effects then the impact
mechanism of the surface distinguishing parameters.
4. Changing Nano scale has little impact on the heat
transfer characteristics; detraction solid-liquid CA can
enhance the HTC while worsening the CHF obviously.
1. Slot jet impingement heat transfer for the moving
plate and moving nozzle.
2. The analysis showed that the Nusselt number
decrease as the velocity of the nozzle or plate was
increased, where the effect of the moving nozzle was
substantial. 3. Maximum Nusselt number is around 120.
1. Jet impingement heat transfer on a concave surface in
a wing leading edge.
2. Heat transfer achievement at the stagnation point was
increased with increasing Re and <alpha>, and an
optimal H/d occurred to achieve the preferable heat
transfer performance.
3. Maximum Nusselt number is around 70.
1. To investigate the characteristics of its flow and heat
transfer. 2. To solve a three-domain conjugation heat
transfer problem. 3. The experiments indicate that the
wall temperature on the solid-air interface.
1. The effect of using different plate materials was
explored for the rectangular step case.
2. It is seen that increasing the Reynolds number (Re)
increases the local Nusselt number for all cases. 3.
There is around 15.7% increase in the average Nusselt
number.
A section of an array that consists of 24 square jets (3
rows × 8 columns) impinging on a moving heated flat
surface is considered a representative pattern. The
structure of the flow field and its effect on the heat
transfer characteristics are investigated numerically.
2. The average Nusselt number increases with surface
velocity ratio.
1. Investigation of liquid water jet impingement cooling
experimentally for free-surface jet and confined
submerged jet arrays.
2. Increasing S/d at a fixed pumping power for the free
jets causes the increasing of heat transfer.
between 26≤H/dn≤30
12
1. Effect of high relative
Fenot et al
Experiment
Array jets
(Row of
jets)
2.
3.
4.
5.
1.
13
S. A. Nada
Experiment
Row of jets
Array jets
2.
curvature (d /D) by changing
the jet tube diameter
Reynolds number
Injection temperature
Spacing between adjacent
jets
Jet exit to surface spacing
Reynolds number are more
than 400.
Rayleigh number are more
than 1000
1. Measuring heat transfer characteristics using a heat
thin foil technique and infrared thermography.
2. Determining an adiabatic wall temperatures and
local heat transfer coefficients by means of linear
regression.
3. Maximum Nusselt number is around 140.
1. Heat transfer characteristics associated with multiple
laminar impinging air jet cooling a hot flat plate at
different orientations.
2. The work aims to study the interactions of the effects
3. cross flow strength
4. orientation of the hot
14
Kumar et al
Numerical
Row of jets
Array jets
15
Hwang et al
Experiment
Air jet array
surface
1. Jet Reynolds number (Red =
5000–67800)
2. Inter-jet distance to jet
diameter ratio (c/d = 3.33
and 4.67)
3. Target plate distance to jet
diameter ratio (H/D = 1, 3
and 4).
1. Reynolds No. 3000-12600.
2. Jet-jet spacing 3 and 6.
3. Duct geometry
16
of cross flow, buoyancy-induced flow, orientation of
the hot surface with respect to gravity and Reynolds
numbers. 3. Maximum Nusselt number is around 65.
1. Studying the computationally flow and heat transfer
from a row of circular jets impinging on a concave
surface.
2. Maximum Nusselt number is around 55.
1. Measuring local heat transfer coefficients and static
wall pressure drops in leading-edge triangular ducts
cooled by wall/impinged jets.
2. Maximum Nusselt number is around 120.
1. Mean velocity and turbulent stresses are
presented in various horizontal and vertical planes.
Geers et al
Experiment
Array jets
Hexagonal
2. Identified some main features of impinging arrays
Using PIV
jet and investigated their mutual interaction,
collision on the flat plate.
17
Dano et al
Experiment
Array jets
18
Liu et al
Experiment
Array jets
19
Young et al
Experiment
1. Array
jets.
2. Single jets
20
San et al
Experiment
Array jets
21
Digital Particle Image
Velocimetry (DPIV) is used to
determine the velocity field of
the impinging jets.
1.Re 10,000, 25,000 and 65,000
2. Zr (ratio of passage height
to diameter of impingement
hole) of 1, 3 and 5
1. Re=1000-13650
2. Thermal performances of 10,
20, and 40 PPI (pores per inch)
1. The surface heat flux on the
plate is 1500 w/m^2.
2.The jet diameter is 3 mm. 3.
Re= 10,000, 20,000 and 30,000
1.The influence of the
Brevet et al
Experiment
Array jets
impingement distance
injection
Z/d,
Re and spanwise
1. Structure detection and analysis of non-circular
impinging jets in a semi-confined array configuration.
2. Increased surface interactions which may lead to
enhanced rates of heat and mass transfer
1. Aerodynamic investigation of impingement cooling
in a confined channel with staggered jet array
arrangement.
2. The jets impinged the target wall effectively along the
entire passage of Zr= 1
1. Heat removal by aluminium-foam heat sinks in a
multi-air jet impingement.
2. Higher heat transfer enhancement than the single jet
impingement for high jet Reynolds number and smaller
jet-to-jet spacing. 3. The enhancement is 2–29%.
1. The effect of jet-to-jet spacing on the local Nusselt
number for confined circular air jets.
2. The stagnation Nusselt number is correlated as a
function of Re, s/d and H/d.
3. Maximum Nusselt number is around 70.
1. Heat transfer to a row of impinging jets in
consideration of optimization.
2. Maximum Nusselt number is around 120.
spacing p/d
22
Can, M
Experiment
1.Array jets
2.single jet
To provide data for designers of
industrial equipment
Array jets
Reynolds number ranging from
1039 to 5175
Array jets
data are given for jet
impingement Mach numbers up
23
Wang et al
24
Goodro et al
Experiment
Experiment
1. Experimental Optimization of Air Jets Impinging on a
Continuously Moving Flat Plate.
2. a programme of research has been implemented to
study the heat and mass transfer processes
1. Flow and heat transfer of confined impingement jets
cooling using a 3-D transient liquid crystal scheme.
2. The local maximum and minimum heat transfer
values being overvalued by about 15–20% and the
overall heat transfer by approximately 12%.
3.Maximum heat transfer coefficient is around 550
1. Effects of Mach number and Reynolds number on jet
array impingement heat transfer.
to 0.74, and for Reynolds
numbers up to 60,000
25
Chander et
al
Experiment
Array jets
Experiment
1.Array jets
2.single jet
1. Various dimensionless interjet spacing’s (S/d = 3, 4, 6 and
7.58) and 3. Re=800
2. Separation distances between
the exit plane of the burners and
the target plate (H/d = 2, 2.6, 5
and 7)
26
Wu et al
27
Ozmen et al
Experiment
1.Array jets
2.single jet
1. nozzle-to-plate spacing of
1–10.
2. Reynolds numbers =5000–
15,000 at the jet-to-jet
centreline spacing (S/W) of 9
Experiment
Array jets
1. Re= 8200 to 30,500.
2. Mach numbers from 0.1 to
0.6
28
Goodro et al
29
Vadiraj et al
1. V ⩾ 6.1 m/s.
2. x/d = 5.5 and 9.
Experiment
Array jets
1. Re=3000, 5000, 7500 and
10,000.
2. jet-to-plate spacing studied
are d, 2d and 3d.
3.Spanwise pitches considered
are 2d, 4d and 6d in steps of
2. Show substantial, independent Mach number effect
for an array of impinging jets.
3. Maximum Nusselt number is around 300.
1. Heat transfer characteristics of three interacting
methane/air flame jets impinging on a flat surface.
2. The surface heat flux distributions were intimately
related to flame shapes.
3. Maximum Nusselt heat flux is around 390.
1. The average single-phase convection coefficients
indicates that the confined jet provided the most uniform
convection.
2. The confining circular jets enhanced mixing and
turbulence in the topic.
1. Investigation of flow structure and heat transfer
characteristics in an array of impinging slot jets.
2. Nusselt distributions on the impingement plate
depend on the Reynolds number and nozzle-to-plate
spacing. 3. Maximum Nu is around 110.
1. Effects of hole spacing on spatially resolved jet array
impingement heat transfer.
2. Mach number has a significant impact on overall heat
transfer. Maximum Nu =190
1. Influence of span wise pitch on local heat transfer
distribution for in-line arrays of circular jets with spent
air flow in two opposite directions.
2. Maximum Nusselt number is around 110.
2d keeping the streamwise
30
Aldabbagh
and
Mohamad
Numerical
Array jets
31
Yan et al
Experiment
Array jets
pitch at 5d
1. Re= 100 and 400. 2.An array
consisting of 24 square jets 3
rows × 8 columns 3.jet-to-jet
spacing in the range 2D–5D and
for nozzle exit to plate distance
of 0.25D
1. Using a liquid crystal
thermograph technique.
2. jet-to-plate spacing Z = 3 for
different Reynolds numbers.
32
Chang et al
Experiment
Array jets
33
Chang et al
Experiment
Array jets
1.5000 ⩽ Re ⩽ 15,000
2.0.5 ⩽ S/Dj ⩽ 11
3. three eccentricities of E/H =
0, 1/4 and 1/2
1. 4 × 3 in-line jet array with
jet
2. 5000 ⩽ Re ⩽ 15,000 and
0.5 ⩽ S/Dj ⩽ 10.
34
Shyy et al
Experiment
Array jets
1.5000 ⩽ Re ⩽ 15,000.
2.0.5 ⩽ S/D ⩽ 10.
3. Three eccentricities (E)
1. The streamwise profile of the Nusselt number exhibit
strong periodic oscillations, spatially
2. The ratio Rm has no effect on the oscillations of
Nusselt number.
3. Maximum Nusselt number is around 180.
1. Measurement of detailed heat transfer along ribroughened surface under arrays of impinging elliptic
jets.
2. The local heat transfer rates over the ribbed-surface
are characterized by obvious periodic-type variation of
Nusselt number distributions.
1. Heat transfer of impinging jet-array over convexdimpled surface.
2. The data illustrates the isolated and interactive
influences of Re, S/Dj and E/H on local and spatially
averaged heat transfers.
3. Maximum Nusselt number is around 190.
1. Heat transfer of impinging jet array over concavedimpled surface with applications to cooling of
electronic chipsets.
2. Experimental data illustrates the isolated and
interactive influences of surface topology.
1. Heat transfer of impinging jet-array onto concaveand convex-dimpled surfaces with effusion.
2. Maximum Nusselt number is around 160.
between jet-center and dimple.
35
Akhilesh et
al
Experiment
Array jets
(rectangular)
36
Iacovides et
al
Experiment
Array jets
Craft et al
Numerical
Row of jet
(Array)
37
1.Re=10,000 to 40,000 for the
channel flow
2. Re=5,000 to 20,000 for the
impingement jet.
1.fixed Reynolds number of
15,000
2.Using the liquid-crystal
technique
Linear and non-linear eddyviscosity models are applied,
with wall-functions to cover the
near-wall layer.
38
Fenot et al
Experiment
Row of jets
(Array)
Roy and
Patel
Experiment.
Array jets
(rectangle)
Heat transfer characteristics are
measured using a heat thin foil
technique and infrared
thermography
Re= 500 to 20 000
39
40
1. Re= 144 to 505.
Shariatmadr
et al.
Experiment
and
Numerical
Array jets
41
Michna et al
Experiment
Array jets
42
Su et al
Experiment
Array jets
43
Koncar et al
Numerical
Array jets
44
Hoberg et al
Experiment
Array jets
2. jet-to-target plate distance
from 2.3Dh to 3.1Dh..
3.jet-to-jet spacing in the range
of 0.1Dh to 0.8Dh, and slot
width of 0.2Dh to 0.8Dh at a
4. constant wall temperature=
70 °C.
1. D= 54 and 112 μm.
2. Area ratio was varied
between 0.036 and 0.35. 3
3. Re= 180–5100 for air and
50–3500 for water.
4. Heat flux of 1100 W/cm2.
1. 1000⩽Re⩽4000
2. 0.1⩽S/D ⩽8
The latest and the most
advanced divertor concept is
based on modular design cooled
by helium impinging jets
1. Inter-jet spacing of 2.34 jet
diameters.
2.Re = 500–10,000
3. Jet-to-target height was
varied from 0.44 to 3.97 jet
diameters.
45
46
Can et al
Experiment
Array jets
provide data for designers of
industrial equipment, a large
multi-nozzle rig was used
Yan et al.,
Experiment
Array jets
1.The elliptic jet holes of five
1. Heat transfer enhancement in rectangular channels
with axial ribs or porous foam under through flow and
impinging jet conditions.
2. Show a 50–90% increase in heat transfer due to the
use of axial ribs in both, impingement and channel flow
cases.
1. Flow and Thermal Development of a Row of Cooling
Jets Impinging on a Rotating Concave Surface.
2. The LDA and PIV studies help explain the rather
surprising thermal behaviour under rotating conditions.
1. Modelling of three-dimensional jet array
impingement and heat transfer on a concave surface.
2. Maximum Nusselt number is around 300.
1. An experimental study on hot round jets impinging a
concave surface.
2. The effect of high relative curvature (d/D) is
investigated by changing the jet tube diameter, Reynolds
number, injection temperature, spacing between
adjacent jets and jet exit to surface spacing.3. Maximum
Nu is around 140.
1. Study of heat transfer for a pair of rectangular jets
impinging on an inclined surface.
2. Local and average Nusselt numbers are evaluated
with two different boundary conditions.
1. Study on heat transfer characteristics of the various
geometrical arrangement of impinging jet arrays.
2. Stagnation and averaged Nusselt correlations are
presented.
3. Maximum Nusselt number is around 110.
1. The effect of area ratio on micro jet array heat
transfer.
2. Reynolds number, Prandtl number, and area ratio
were found to significantly affect the heat transfer
performance.
3. Maximum Nusselt number is around 75.
1. Detailed heat transfer measurements of impinging jet
arrays issued from grooved surfaces. 2. Develop the
correlations of spatially averaged Nusselt numbers.
3. Maximum Nusselt number is around 70.
1. The influence of nozzle sizes on the heat transfer and
flow characteristics.
2. Maximum heat transfer coefficient is around 5500.
1. Heat transfer measurements for jet impingement
arrays with local extraction.
2. Produce very high average heat transfer coefficients if
the jets are closely spaced.
3. Maximum Nusselt number is around 100.
1. Develop the relationship between heat transfer
coefficients, air mass flow and fan power which is
required for the optimum design of nozzle systems.
2. Maximum average heat transfer coefficient is around
260.
1. Measurement of detailed heat transfer on a surface
and
Numerical
47
Chiu et al
Experiment
Array jets
48
Royne et al
Experiment
Array jets
49
Royne et al
Experiment
Array jets
50
Liu et al
Experiment
Array jets
51
Tang et al
Numerical
Array jets
52
Siw et al
Experiment
and
Numerical
Array jets
different aspect ratios, AR = 4,
2, 1, 0.25, and 0.5
2. Re = 1500, 3000, and 4500.
under arrays of impinging elliptic jets by a transient
liquid crystal technique.
2. Maximum Nusselt number is around 100.
1.The aspect ratios (AR) of
1. The heat transfer under impinging elliptic jet array
along a film hole surface using liquid crystal
thermograph.
2. Nu increases with the increase of jet Reynolds
number.
3. Maximum Nusselt number is around 50.
elliptical jet with five different
values, 4, 2, 1, 0.5, and 0.25,
2.Re= 2000 to 4000, and jet-totarget spacing ranging from 1.5
to 4.5
1. The effect of Reynolds
number, Prandtl number,
nozzle-to-plate spacing, nozzle
pitch and nozzle geometry. 2.
Re= 1000 to 7700.
A cooling device based on
cooling of densely packed
photovoltaic cells under high
concentration.
1. Reynolds No=2500-7700
2. Jet-to-jet spacing and jet-tosurface spacing (Z/d) were 4
and 3
1. The cone angle = 0–70°.
2. Cone bottom diameter to
nozzle diameter ratio = 1–3.
3. jet height to nozzle diameter
ratio H/d = 3–7),
4. Re = 16,000–32,000.
5.heat flux density q = 60–100
W/cm2
1. The diameter D=9.35.
2. Height-to-diameter H/D=2.
3. Jet spacing-to-diameter S/D =
4.
4. Mass flow rate entering the
channel ranges from 52,000 to
78,000.
5. Using transient liquid crystal
technique.
1. Effect of nozzle geometry on pressure drop and heat
transfer in submerged jet arrays.
2. Maximum Nusselt number is around 165
1. Design of a jet impingement cooling device for
densely packed PV cells under high concentration.
2. Maximum Nusselt number is around 95.
1. Heat transfer distributions on array jets impingement
on half rough and half smooth target surface.
2. Enhancement of more than 50% and the half
roughness comparing with the fully roughness is more
effective for heat transfer
1. The cooling impact of fluid impinging on a cone heat
sink is preferable to that of a conventional flat plate heat
sink. 2. The best cooling impact was spotted at the
following conditions: A = 50°, d1/d = 2, and H/d = 5. In
addition, Nu‾ increased considerably when the Re
increased within the range of 16,000–32,000, and a
large q was acquired at increased top temperature on the
source of heat surface at the same jet flow rate
1. The results revealed that varying the jet flow rates,
total flow varied by approximately 65% from that of the
baseline state, 2. The enhancement of heat transfer on
the objective surface is enhanced up to approximately
35%. Furthermore, when transitioning to the varying
diameter jet flat plate, this principle enhancement is
suppressed due to the nature of flow distribution from
the plenum, combined with the complicated crossflow
impacts.
Table 3 steady impinging jet cases for multiple jets.
No
Author
Type of
study
Type of Jet
1
2
Terzis, A.
Experiment
Multiple jet.
Ertan
Baydar
Experiment
1. Multiple
air jets.
2.Single jet
Gharraei et
al
Numerical
Multiple
jets
3
Factors
Problem statement-"Methods-Results".
1. Particle image velocimetry
(PIV). 2. liquid crystal
thermography (LCT) are used in
order to investigate the aerothermal
characteristics of the channel with
high spatial resolution
1. Reynolds number from 30010000
2. Nozzle-to-plate spacing (0.5-4)
1. Re=100, 200,
2. power-law indices 0.4–1.6 and
dimensionless jet-to-plate spacing’s
0.25–1.0
1. The results are analysed aiming to provide a
better understanding about the impact of near-wall
flow structures on the convective heat transfer
augmentation for these complex flow phenomena.
1. Determining the flow field of confined single and
double-jet impingement flows. 2. Determining the
pressure distribution of the domain
1. Numerical investigation of the fluid flow and heat
transfer of non-Newtonian multiple impinging jets.
2. Decreasing the jet-to-plate spacing decreases the
size of entrainment vortices. 3. Maximum nusselt
4
Aldabbagh
et al
Numerical
Olsson et al
Numerical
Multiple
jets
1. jet-to-jet spacing’s of 4D, 5D and
6D.
2.Nozzle exit to plate distances
between 0.25D and 9D
Multiple
jets
Re= 23,000–100,000
Using CFD
Multiple
jets
1.Navier–Stokes and energy
equations were discretized with a
finite volume procedure on a nonstaggered grid arrangement using
SIMPLE-Modified algorithm
2. Pr = 0.71
5
6
Dagtekin et
al
Numerical
7
Yang et al
Numerical
Multiple
jets
Thielen et al
Numerical
Multiple
jets
8
9
Geers et al
Experiment
Multiple
jets
Wang et al
Experiment
Multiple
jets
10
1. Using K-ε model and Momentum
equations are solved by the SemiImplicit Method. 2.The parameters
interesting include entrance (Re),
dimensionless nozzle to surface
space (H/W), dimensionless pitch
(H/W)
1. Square set-up (3 × 3 regularly
spaced jets). 2. circular set-up (eight
jets surrounding a central jet)
1. Ranging from 5 × 103 to 2 × 104.
2. Liquid crystal thermography
(LCT) was used to determine the
temperature distribution on the flat
impingement plate.
1. Re= 7500 and 15,000.
2.heat fluxes ranging from 3350 to
13,400 W/m2
11
Nadda et al
Experiment
Multiple
jets
Lyu et al
Simulation
Multiple
jets
(double)
1. Re arranging 5000-19000.
2. Relative width ratio (WP/WAP)
from 1.0 to 6.0.
3. Jet diameter ratio (Dj/dH) of
0.065.
12
1. Using k-ε model.
2. Simulations are carried out with
various duty cycles.
number was approximately 115.
1. The flow and heat transfer characteristics of
impinging have been investigated through the
solution of the three-dimensional Navier–Stokes and
energy equations. 2. The magnitude of the local
maximum Nusselt number at the stagnation point is
not affected by jet-to-jet spacing. 3. Maximum
Nusselt number is around 23.
1. Flow and heat transfer from multiple slot air jets
impinging on circular cylinders.
2. The heat transfer increases for higher Reynolds
number. 3. Maximum nusselt number is around 450
1. Heat transfer due to double laminar slot jets
impingement onto an isothermal wall within one
side closed long duct.
2. The mean Nusselt number increases almost
linearly with increasing of Reynolds number at
isothermal surface.
3. Maximum nusselt number is around 110
1. Numerical studies of three turbulent slot jets
with and without moving surface.
2. The dimensionless pitch has a strong influence on
the heat transfer characteristics.
3. Maximum nusselt number is around 140
1. Effect of the nozzle arrangement on the heat
transfer of multiple impinging jets.
1. Heat transfer correlation for hexagonal of
impinging jets.
2. The multiple-jet heat transfer is strongly
influenced by jet interactions.
3. Maximum nusselt number is around 135
1. The wall temperature significantly decreased 2.
The maximum local enhancement is up to 800% by
injecting 3.5% of mist at low heat flux condition and
150%
1. Experimental study of the heat and fluid flow
characteristics of circular impingement jet solar air
passage. 2. Best enhancement in heat transfer and
friction is 6.29 and 9.25 times to that of smooth
absorber plate.
3. The optimum value of thermal hydraulic
efficiency has been found to be 3.64 for Re of
13,000.
1. Numerical simulation for enhancing heat
transfer by multiple
nozzles
slot
jet
impingement with different duty cycle.2. The
numerical results indicate that unsteady
impingement jets heat transfer performance is
lower than the steady impinging jets in the case of
double slot impingement jets under the condition
of the same Reynolds number and the phase
difference θ of 0°, 3. Enhancement of heat transfer
leads to the best impact. Heat transfer
performance with duty cycle of 0.5 is worse above
the threshold frequency of 50Hz.
13
Draksler et
al
Simulation
Multiple
jets
14
Caliskan et
al
Experiment
and
Simulation
Abdullah
et.al
Numerical
and
Experiment
Multiple
jets
1. The aspect ratios (AR) of elliptic
and rectangular jets for 1.0, 2.0 and
0.5. 2. Jet Reynolds numbers
ranging from 2000 to 10,000, 3. Jetto-target spacing’s ranging from 2
to 10.
Multiple jet
1. Multiple jet impingement
mechanism. 2.Using RNG k-ε
turbulence model.3. Re numbers of
17,000.
Multiple jet
Using nanofluids with three
impinging jets. Different heat flux.
Effects of different volume ratio.
and different types of nanofluids
(CuO-water, Al2O3-water, Cu-water,
TiO-water, and pure water).
15
16
Mustafa
and
Muhammad
Numerical
1. The experimental test case with
13 air jets.
2. Reynolds number is 20,000.
1. Heat transfer conditions and fluid flow dynamic
of multiple jet impinging are discussed by LES, 2.
Numerical models are used to study the dynamics
and complexity of the immediate flow field and to
thoroughly clarify the local flow technique
associated with the improvement
of heat transfer at the heated flat plate.
1. This article discuss the geometry impacts on
multiple jets impinging air. 2. There is a significant
factor for the geometric form of the impinging jets
for the characteristic of the fluid flow of impinging
jets. 3. preferable of heat transfer achievement was
gained with the jet arrangements when was
elliptic.4. Maximum Nusselt number is around 135
1. Impact of Multiple jet impingement heat-transfer
technique for enhancing heat-transfer at
Aluminium plate. 2. the best model is model 1
when nozzle-nozzle=1 cm, and nozzle-pate
distance=1 cm.
Numerical investigation of combined effect of
nanofluids and multiple impinging jets on heat
transfer. Increasing heat flux six times has not a
significant effect on average Nusselt number.
increasing volume ratio from φ=2% to 8% causes an
increase of 10.4% on average Nusselt number.
Table 4 steady impinging jet cases for twin jets.
No
Author
Type of
study
Type of Jet
Factors
Experiment
Twin jet
1. Re numbers of 10,000. 2. Heat
flux–temperature micro foil sensor.
3. Using IR thermal imaging.
Experiment
Twin
inclined jets
1. Jet arrangement.
2. Using thermchromic liquid crystal,
Particle Image Velocimetry PIV,
fluorescence dyes.
Twin jets
Carried out based on finite volume
method to solve the governing mass,
momentum, turbulent kinetic energy
and turbulent kinetic energy
dissipation rate.
1
Abdullah
et.al
2
Nakabe et
al
3
AbdelFattah, A
Experiment
4
Ozmen, Y
Experiment
Twin jets
1. Re from 30,000 to 50,000.
2. Nozzle-to-plate spacing (H/D) in
the range of 0.5–4 and jet-to-jet
spacing (L/D) in the range of 0.5–2.
5
6
Taghinia
et al
Numerical
Twin jets
1. LES & SST–SAS hybrid model
were applied for the first time for
impinging twin-jets.
2. 3 × 104 < Re < 5 × 104.
Singh et al
Numerical
Twin
oblique jets
Using Ansys fluent program (ANSYS)
Problem statement-“Methods-Results".
1. Effect of twin jet impingement heat-transfer
technique for enhancing heat-transfer at
Aluminium plate. 2. Maximum heat transfer
coefficient is around 170.
1. Examining the interaction between two inclined
impinging jets in in-line and staggered
arrangements twitwinjets
2. The geometrical arrangement of inclined jets is
affecting on heat transfer for impingement jet.
1. Study of the two-dimensional impinging circular
twin-jet flow with no-cross flow.
2. When the jet angle rises the pressure decreases
too.
1. Confined impinging twin air jets at high Reynolds
numbers.
2. Smoke-wire technique was used to visualize the
flow behaviour.
3. The relation between the subatmospheric regions
and peaks in heat transfer coefficients for low
spacing’s in the impinging jets.
1. SST–SAS produced good results in terms of
pressure distribution & velocity.
2. Maximum Nusselt number is around 45.
1. to Enhancement of Cooling in Central Processing
CPU by using Jet Impingement with and without
7
Peng et al
Numerical
Twin jets
Using a computational fluid dynamic
(CFD)
Twin jets
1. Re numbers of 17,000 and 13,000.
2. Heat flux–temperature micro foil
sensor. 3. Using IR thermal imaging.
Twin jet
1. Employing a twin jet impingement
mechanism (TJIM). 2.Using RNG k-ε
turbulence model.3. Re numbers of
17,000. 2. Using IR thermal imaging
to get the distribution of heat
transfer.
Twin jet
1. Using TiO2 for nanocoating surface
2. Carried out XRD
3. Carried out FESEM
8
Abdullah
et.al
Experiment
9
Abdullah
et.al
Numerical
and
Experiment
10
Abdullah
et.al
Experiment
7. CONCLUSION
This article presents a detailed review of the
numerical and experimental investigations that
helped identify the influential factors in multiple
impingement jets and the associated flow and
heat transfer performance. A detailed review of
the studies on multiple, single, array and twin
impingement jets for flow behaviour and heat
transfer enhancement is provided, and the
important parameters involved were determined.
The review highlights the deficiency of
information on the heat transfer issue in jet
impingement. The relevant literature covers the
different configurations of impingement jets. The
factors that influence the behaviour of flow and
heat transfer and the potential of enhancing
these characteristics are considered pivotal
issues. The research on impingement jet
techniques is limited. The heat transfer
enhancement using twin impingement jets at a
radial distance for stagnation point has not been
studied experimentally and numerically. The
influence of jet impingement on heat transfer
enhancement was investigated. The heat
transfer characteristics can be enhanced by
[1]
P. D. Behnia, M., S. Parneix, “Accurate
modeling of impinging jet heat transfer,” ."
Cent. Turbul. Res. Annu. Res. Briefs, no. 1,
Nano Fluid.
2.To study the twin oblique impinging jet heat
transfer problem
3. The peak Nusselt number at the impingement
surface is gradually reduced.
1. A Computational Study of Heat Transfer under
Twin Turbulent Slot Jets Impinging on Planar
Smooth and Rough Surfaces.
2. Maximum Nusselt number is around 50.
1. The study discussed the impact of twin jet
impingement heat-transfer technique for
enhancing heat-transfer at different parameters. 2.
The finding shows a considerable enhancement in
the localized Nu number at positions of radial
distance on the flat plate from 1–5 cm. 3. Maximum
Nusselt number is around 160.
1. Effect of twin jet impingement heat-transfer
technique for enhancing heat-transfer at
Aluminium plate. 2. the best model is model 1
when nozzle-nozzle=1 cm, and nozzle-pate
distance=1 cm.
1. Employing effect of the TiO2 nanosolution
concentration on the heat transfer of the twin jet
impingement on an aluminum plate surface. 2. The
surface coating with the TiO2 nanosolution also
positively affected the heat transfer rate
considering the optimal levels of the influential
factors and by selecting a suitable impingement
system. Studies on steady impingement jets can
provide insights into jet flow behaviour and heat
transfer enhancement. Flow characteristics
should be studied to enhance the understanding
of the thermal behaviour of impingement jets.
Knowledge on the behaviour of formed vortices
is insufficient. Thus, we suggest the further
investigation of this topic through visualisation
techniques, such as PIV and the use of highspeed cameras. The effect of nozzle geometry
on heat transfer and fluid flow is worth studying
given the limited information on this matter. The
turbulence intensity measurement near the
impingement wall in case of heat transfer is an
important matter given the significant effects of
wall jet characteristics. The correlation between
the Nu and the significant parameters must be
investigated. In addition, the interactions
between the correlated factors have not been
investigated in detail. The information regarding
changes in heat transfer rates in various
nanofluids due to jet impingement, spray, high
pressure temperature is limited. Nanofluid
applications in impingement jet techniques have
a huge potential and need further investigation.
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Int. J. Mech. Mechatronics Eng. IJMMEIJENS, vol. 17, no. 4, pp. 60–75.