1
THERMAL AND CFD ANALYSIS FOR FINDING HEAT TRANSFER
THROUGH AN ANNULAR BEND TUBE FOR VARIOUS NANO FLUIDS
1
S.Raja Rajeswari, 2G. Satyanarayana
M.Tech [Thermal Engg], Koneru Lakshmiah Universty, AP-India
2
Professor, Mechanical Engg Dept, Koneru Lakshmiah Universty, AP-India
1

greater molecular kinetic energy to pass this energy to
Abstract-- Heat transfer by convection is very important for
regions with less kinetic energy. Several material properties
many industrial heating and cooling applications. The heat
serve to modulate the heat transferred between two regions
convection can passively be enhanced by changing flow
geometry,
boundary
conditions or by
enhancing
fluid
at differing temperatures. Examples include thermal
conductivities, specific heats, material densities, fluid
thermophysical properties. A colloidal mixture of nano-sized
particles in a base fluid, called nanofluids, tremendously
enhances the heat transfer characteristics of the original fluid,
velocities, fluid viscosities, surface emissivity, and more.
Taken together, these properties serve to make the solution
and is ideally suited for practical applications due to its
of many heat transfer problems an involved process. Heat
marvelous characteristics. In this papers, different nano fluids
transfer is categorized into three broad classes known as
will be analyzed for their thermal behavior passing through an
conduction, convection and radiation.
annular bend tube with turbulence flow. The nano fluids
considered in this thesis are nanofluids made from base fluids
II. CONTEMPORARY RESEARCH IN THE FIELD
ethylene and tri-cloroethylene gycols, copper nano fluid and
aluminum nano fluid. Thermal and CFD analysis is performed
to determine the thermal behavior using finite element analysis
software Ansys. 3D modeling is done in Solidworks. Thermal
analysis is also done on the tube in tube heat exchanger for
water and better fluid of above mentioned nano fluids.
In the thesis by WILLEM I. LOUW etal [1], helically
wound tube-in-tube heat exchangers are manufactured by
coiling two tubes, one placed inside the other. This method
often results in the tubes not sharing the same center line,
and therefore annular contact occurs in some cases. An
Index Terms--
Thermal; CFD; Ansys; Solidworks; 3D
experimental comparison was made of such tubes in a heat
exchanger with annular contact, as opposed to an aligned
modelling .
(concentric) device without annular contact, in order to
I. INTRODUCTION
quantify the effect of annular contact in terms of heat
In the simplest of terms, the discipline of heat transfer is
transfer coefficients and pressure drop. By comparing the
concerned with only two things: temperature, and the flow
heat transfer characteristics, it was concluded that the heat
of heat. Temperature represents the amount of thermal
transfer coefficient in the annulus was found to increase
energy available, whereas heat flow represents the
substantially. The result was an improved performance by
movement of thermal energy from place to place. On a
the heat exchanger where annular contact occurs, compared
microscopic scale, thermal energy is related to the kinetic
to the heat exchanger with the inner tube in a concentric
energy of molecules [1]. The greater a material's
position. In the paper by Mohamed H. Shedid[2], Spalart-
temperature, the greater the thermal agitation of its
Allmaras (S-A) turbulence modeling is used to study
constituent molecules (manifested both in linear motion and
numerically thermal behavior for annular flow of nanofluids.
vibrational modes). It is natural for regions containing
The flow is subjected to a constant wall temperature at the
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outer wall. The nanofluids considered are alumina (Al2O3)
low temperature for the case of a gradual U bend was
and oxide titanium (TiO2) nanoparticles and water as the
achieved with a stack of 18 flow-straightener screens. The
base fluid. To conduct the investigation, a grid is
no-load temperature for this case of a gradual ‘U’ bend, with
constructed that give y+ for all velocities below 1. The
and without flow straighteners, was 57.7 K and 88.8 K,
model is validated with Gnielinski correlation for the flow of
respectively, for a charging pressure of 16 bar. When the
pure water. Validated model was used for different
gradual 180 degree bend at the cold end was replaced by a
concentration ratios of Al2O3 and TiO2 for different Peclet
sharp U bend, the no load temperature increased from 88.8
numbers. The results were compared with many correlations
K to 137 K without flow straighteners. In the paper by
for convection of nanofluids flow and revealed better
Quamrul H. Mazumder [5], Solid particle erosion is a
agreement with Spalart-Allmaras [2] model rather than k-Ɛ
micromechanical process that is influenced by flow
model. Results of numerical simulations are compared and
geometry, material of the impacting surface, impact angle,
showed an enhancement of Nusslet number as Peclet
particle size and shape, particle velocity, flow condition and
number grows with increasing concentration ratio. In the
fluid properties. Among the various factors, particle size and
paper by Mrunal P.Kshirsagar etal [3], Conventional heat
velocity have been considered to be the most important
exchangers are large in size and heat transfer rate is also less
parameters that cause erosion. Particle size and velocity are
and in conventional heat exchanger dead zone is produce
influenced by surrounding flow velocities and carrying fluid
which reduces the heat transfer rate and to create turbulence
properties. Higher erosion rates have been observed in gas-
in conventional heat exchanger some external means is
solid flow in geometries where the flow direction changes
required and the fluid in conventional heat exchanger is not
rapidly, such as elbows, tees, valves, etc, due to local
in continuous motion with each other. Tube in tube helical
turbulence and unsteady flow behaviors. This paper presents
coil heat exchanger provides a compact shape with its
the results of a Computational fluid dynamic (CFD)
geometry offering more fluid contact and eliminating the
simulation of dilute gas-solid flow through a U-Bend and the
dead zone, increasing the turbulence and hence the heat
dynamics behavior of entrained solid particles in the flow.
transfer rate. An experimental setup is fabricated for the
The effect of liquid and gas velocities on location of erosion
estimation of the heat transfer characteristics. A wire is
were investigated for 50, 100, 150, 200, 250 and 300
wounded in the core to increase the turbulence in turn
microns sand particles. Three different fluid velocities of 15,
increases the heat transfer rate. The paper deals with the
30.48 and 45 m/s were used in the CFD analysis. The
pitch variation of the internal wounded wire and its result on
magnitude and location of erosion presented in the paper can
the heat transfer rate. The Reynolds number and Dean
be used to determine the areas susceptible to maximum
number in the annulus was compared to the numerical data.
erosive
The experimental result was compared with the analytical
corresponding rate of metal loss in these areas. In the paper
result which confirmed the validation. This heat exchanger
by Predrag S. Hrnjak [6], experimental results and analysis
finds its application mostly in food industries and waste heat
of heat transfer in a thermally developing region of round
recovery. In the paper by A.D. Badgujar etal [4], the work
pipes for three fluids typically used as low temperature
deals with experimentation and CFD modeling related to U-
coolants, in the range of 0–−40°C. The experiments were
type PTCs. Two cases of ‘U’ bends have been studied;
performed at low Re (200–1000) and high Pr (80–140)
gradual ‘U’ bends and sharp ‘U’ bends. Experimentation has
numbers that are typically found in secondary refrigeration
been carried out using copper screens of 100-mesh size as
loop conditions. The effect of horizontal U-bend is also
flow straighteners. The optimum performance in terms of
presented. It is shown that the positive effect of thermal
wear
in elbows and U-bends, along with
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development (high Nu number) lasts long because of the
dilute liquid suspensions of nanoparticles with at least one of
technically significant length of the thermally developing
their principal dimensions smaller than 100 nm. From
region. Secondary flows developed in and after the U-bend
previous investigations, nanofluids have been found to
are so significant that they have almost an identical effect as
possess enhanced thermophysical properties such as thermal
the thermal development at the pipe entrance. That is a
conductivity, thermal diffusivity, viscosity and convective
reason for the extremely good performance of the heat
heat transfer coefficients compared to those of base fluids
exchangers with secondary refrigerants in laminar flow
like oil or water.
regimes. Experimental data are presented with developed
empirical correlations, which show good relationships to
From the current review, it can be seen that nanofluids
several existing correlations.
clearly exhibit enhanced thermal conductivity, which goes
up with increasing volumetric fraction of nanoparticles. The
III. CONCEPT OF NANO FLUIDS
current review does concentrate on this relatively new class
ZigBee Nanofluids are fluids containing nanoparticles
of fluids and not on colloids which are nanofluids because
(nanometer-sized particles of metals, oxides, carbides,
the latter have been used for a long time. Review of
nitrides, or nanotubes). Nanofluids exhibit enhanced thermal
experimental studies clearly showed a lack of consistency in
properties, amongst them; higher thermal conductivity and
the reported results of different research groups regarding
heat transfer coefficients compared to the base fluid.
thermal properties. The effects of several important factors
Simulations of the cooling system of a large truck engine
such as particle size and shapes, clustering of particles,
indicate that replacement of the conventional engine coolant
temperature of the fluid, and dissociation of surfactant on
(ethylene glycol-water mixture) by a nanofluid would
the effective thermal conductivity of nanofluids have not
provide considerable benefits by removing more heat from
been studied adequately. It is important to do more research
the engine [7-10]. Additionally, a calculation has shown that
so as to ascertain the effects of these factors on the thermal
a graphite based nanofluid developed jointly by Argonne
conductivity of wide range of nanofluids. Classical models
and Valvoline could be used to eliminate one heat exchanger
cannot be used to explain adequately the observed enhanced
for cooling power electronics in a hybrid electric vehicle.
thermal
This would obviously reduce weight, and allow the power
developed models only include one or two postulated
electronics to operate more efficiently. The benefits for
mechanisms of nanofluids heat transfer. For instance, there
transportation would be Radiator size reduction, Pump size,
has not been much fundamental work reported on the
Possible of elimination of one heat exchanger for hybrid-
determination of the effective thermal diffusivity of
electric vehicles and Increased fuel efficiency. Using silicon
nanofluids nor heat transfer coefficients for nanofluids in
carbide nanoparticles from partner Saint Gobain, the team
natural convection.
conductivity
of
nanofluids.
Recently
most
has created an ethylene glycol/water fluid with silicon
carbide nanoparticles that carries heat away 15 percent more
There is a growth is the use of colloids which are nanofluids
effectively than conventional fluids. And working with
in the biomedical industry for sensing and imaging purposes.
industrial partner Valvoline, they’ve developed a graphite-
This is directly related to the ability to design novel
based nanofluid that has an enhanced thermal conductivity
materials at the nanoscale level alongside recent innovations
of 50 percent greater than the base fluid, which would, under
in analytical and imaging technologies for measuring and
specific conditions, eliminate the need for a second heat
manipulating nanomaterials. This has led to the fast
exchanger for cooling power electronics. Nanofluids are
development of commercial applications which use a wide
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variety of manufactured nanoparticles. The production, use
and disposal of manufactured nanoparticles will lead to
discharges to air, soils and water systems. Negative effects
are likely and quantification and minimization of these
effects on environmental health is necessary. True
knowledge of concentration and physicochemical properties
of manufactured nanoparticles under realistic conditions is
important to predicting their fate, behavior and toxicity in
the natural aquatic environment. The aquatic colloid and
atmospheric ultrafine particle literature both offer evidence
Fig.2: Meshed model
as to the likely behavior and impacts of manufactured
nanoparticles, and there is no pretense that a review
duplicating similar literature about the use of colloids which
are also nanofluids is attempted in the current review.
Owing to their enhanced properties as thermal transfer fluids
for instance, nanofluids can be used in a plethora of
engineering applications ranging from use in the automotive
industry to the medical arena to use in power plant cooling
systems as well as computers.
IV. RESULTS
Fig.3: Outlet
The results pertaining to the proposed model are presented
in this section. The proposed model is divided into two
sections A and B. In section A the CFD analysis of the 3D
The proposed model is as shown in the fig.1. The mesh
model and outlet are given in the fig.2 and fig.3.
model of the annular tube without contact and in section B
with contact are presented here.
B. WITH CONTACT
A. WITHOUT CONTACT
Fig.1: 3D model of the proposed geometry
Fig.4: 3D model of the proposed geoemtry with contact
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Fig.8: Thermal Flux
Fig.5: Mesh model
V. CONCLUSION
NODAL
THERMAL
TEMPERATURE
GRADIENT
(K)
(K/mm)
353
92.0705
16.5727
353
6.036135
1.08658
THERMAL FLUX
It can conclude by comparing the results for without contact
(W/mm2)
and with contact, the heat transfer rate is more for tubes
without contact. CFD analysis is done to verify the outlet
ALUMINUM
NANOFLUID
COPPER
NANOFLUID
pressure, velocity etc in Fluid Flow Fluent. By observing the
results for without contact, the pressure developed is less
when ethylene glycol nanofluids are used, velocity is more
ETHYLENE
353
GLYCOL
7.03144
1.265666
when aluminum nano fluid is used and mass flow rate is
more when copper nano fluid is used. By observing the
TRICHLORO
ETHYLENE
353
8.01495
GLYCOL
1.422269
results for with contact, the pressure developed is less when
ethylene glycol nanofluids are used, velocity is more when
NODAL
TEMPERATURE(K)
aluminum nano fluid is used and mass flow rate is more
when tri-cloroethylene gycol nano fluid is used. By
400
300
200
100
0
comparing the results for with and without contact, the
pressures developed are less in without contact, velocities
are less in without contact.
VI. REFERENCES
THERMAL
GRADIENT(K/MM
)
Fig.6: NODAL TEMPERATURE
100
50
0
Fig.7: Thermal Gradient
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Tube Mohamed H. Shedid, Proceedings of the International
Conference on Heat Transfer and Fluid Flow Prague, Czech
Republic, August 11-12, 2014.
3. Fabrication and Analysis of Tube-In-Tube Helical Coil Heat
Exchanger by Mrunal P.Kshirsagar, Trupti J. Kansara, Swapnil M.
Aher, International Journal of Engineering Research and General
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U-Type Pulse Tube Cryocoolers by A.D. Badgujar, M.D. Atrey,
Department of Mechanical Engineering Indian Institute of
Technology Bombay, Mumbai, Maharashtra.
6
5. Effect of liquid and gas velocities on magnitude and location of
maximum erosion in U-bend by Quamrul H. Mazumder, Open
Journal of Fluid Dynamics 01/2012; 2(02):29-34. DOI:
10.4236/ojfd.2012.22003
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Developing Laminar Flow in Round Pipes of Some Heat Transfer
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