International Journal of Engineering Trends and Technology (IJETT) – Volume 4 Issue 10 – Oct 2013
Heat Transfer Enhancement Of Solar Air Heater
By Using Artificial Roughness –Review
Dharam Singh#1, V.N.Bartaria*2
#
*
M.E Scholar, Lakshmi Narain College of Technology, Bhopal, Madhya Pradesh- 462041(India)
Mechanical Engg. Department, Lakshmi Narain College of Technology, Bhopal, Madhya Pradesh- 462041(India)
Abstract—-Artificial roughness applied on the absorber plate is
the most acclaimed method to improve thermal performance of
solar air heaters at the cost of low to moderate friction penalty.
Providing an artificial roughness on a heat transferring surface
is an effective passive heat transfer technique to enhance the rate
of heat transfer to fluid flow.The objective of this paper is to
review various studies, in which different artificial roughness
elements are used to enhance the heat transfer rate with little
penalty of friction.
Keywords - Artificial roughness, Solar air heater, Heat transfer,
Active and passive technique.
I. INTRODUCTION
Energy is a basic need for human being; it is a prime agent
in the generation and economic development. Energy
resources may be classified in two ways conventional and
non-conventional energy resources. Solar energy is available
abundance on earth in the form of radiation. Solar energy is
used for heating application and converts it into thermal
energy. Solar air heater is the cheapest way of converting
solar energy into thermal energy. Thermal performance of
solar air heaters is comparably poor from solar water heaters.
Thermal performance may be increased by increasing
convective heat transfer coefficient. There are two way for
increasing heat transfer coefficient either increase the area of
absorbing surface by using fins or create the turbulence on the
heat transferring surfaces .
II. . HEAT TRANSFER ENHANCEMENT TECHNIQUE
Heat transfer inside flow passages can be enhanced by using
passive surface modifications such as rib tabulators,
protrusions, pin fins, and dimples.These heat transfer
enhancement techniques have practical. Application for
internal cooling of turbine airfoils, combustion chamber liners
and electronics cooling devices, biomedical devices and heat
exchangers.
The heat transfer can be increased by the following
differentAugmentation Techniques. They are broadly
classified into three different categories:
(i) Passive Techniques
(ii) Active Techniques
(iii) Compound Techniques.
III. MECHANISMS OF AUGMENTATION OF HEAT TRANSFER
To the best knowledge of the authors, the mechanisms of
ISSN: 2231-5381
heat transfer enhancement can be at least one of the
following.
1. Use of a secondary heat transfer surface.
2. Disruption of the unenhanced fluid velocity.
3. Disruption of the laminar sub layer in the turbulent
boundary layer.
4. Introducing secondary flows.
5. Promoting boundary-layer separation.
6. Promoting flow attachment/reattachment.
7. Enhancing effective thermal conductivity of the fluid
under static conditions
8. Enhancing effective thermal conductivity of the fluid
under dynamic Conditions
9. Delaying the boundary layer development.
10. Redistribution of the flow.
III. CONCEPT OF ARTIFICIAL ROUGHNESS
Thermohydraulic performance of a solar air heater can be
improved by providing artificial roughness on the absorber
plate. The artificial roughness has been used extensively for
the enhancement of forced convective heat transfer, which
further requires flow at the heat-transferring surface to be
turbulent. However, energy for creating such turbulence has to
come from the fan or blower and the excessive power is
required to flow air through the duct. Therefore, it is desirable
that the turbulence must be created only in the region very
close to the heat transferring surface, so that the power
requirement may be lessened. This can be done by keeping the
height of the roughness elements to be small in comparison
with the duct dimensions.
The key dimensionless geometrical parameters that are
used to characterize roughness are:
1. Relative roughness pitch (p/e): Relative roughness pitch
(p/e) is defined as the ratio of distance between two
consecutive ribs and height of the rib.
2. Relative roughness height (e/d): Relative roughness
height (e/d) is the ratio of rib height to equivalent
diameter of the air passage.
3. Angle of attack: Angle of attack is inclination of rib
with direction of air flow in duct.
4. Shape of roughness element: The roughness
elements can be two-dimensional ribs or threedimensional discrete elements, transverse or inclined
ribs or V-shaped continuous or broken ribs with or
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International Journal of Engineering Trends and Technology (IJETT) – Volume 4 Issue 10 – Oct 2013
5.

without gap. The roughness elements can also be arcshaped wire or dimple or cavity or compound ribgrooved. The common shape of ribs is square but
different shapes like circular, semi-circular and
chamfered have also been considered to investigate
thermo hydraulic performance.
Aspect ratio: It is ratio of duct width to duct height.
This factor also plays a very crucial role in
investigating thermo-hydraulic performance.
IV. LITERATURE REVIEW
Saini and Saini [1] experimentally investigate the heat transfer
coefficient and friction factor for arc shape parallel wire
having relative roughness height (e/d) and relative angle of
attack (α/90) .This arc-shape parallel wire geometry is Fig. 1.
The maximum enhancement in the Nusselt number was
obtained as 3.80 times corresponding to the relative arc angle
(α/90) of 0.3333 at relative roughness height of 0.0422.
However, the increment in the friction factor corresponding to
these parameters was found to be only 1.75 times.
condition for heat transfer was found at a groove position to
pitch ratio of 0.4 as compared to the smooth duct.The
presence of rib grooved artificial roughness increased the
Nusselt number up to 2.7 times, compared with without
artificial roughness caes.While the friction factor raised up
to 3.6 times in the range of parameters investigated.
Fig. 2 Type and orientation of roughness element investigated by jaurkar et al
V.
1.
2.
Fig.1 Type and orientation of roughness element investigated by
Saini and Saini



Gupta et al. [2] investigated the effect of relative roughness
height at a relative roughness pitch of 10 and a duct aspect
ratio with the Reynolds number range of 3000 to 18000, and
developed the correlations for heat transfer and friction factor
for transverse rib roughness on the absorber plate. It has been
found that the behaviour of the Stanton number in a
transitionally rough flow region was different from its
behaviour in a fully rough flow region. Correlations for
transitionally rough flow regions have been developed for the
range of inves-tigation. These correlations showed good
agreement between the predicted and experimental values of
the heat transfer coefficient and friction factor.
Dhiman et al. [3] studied the thermal performance of a novel
parallel flow packed bed solar air heater. They found that
parallel flow solar air heater with packed bed material have a
higher heat flux as compared to the conventional non-porous
bed double flow system.
Momin et al. [4] carried out an experimental investigation to
show the effect of geometrical parameters of V-shaped ribs on
heat transfer and fluid flow characteristics of rectangular duct
of a solar air heater. They observed that using V- shaped ribs
maximum heat transfer occurred at relative roughness height
of 0.034 and at an angle of attack of 60.
 Jaurker et al. [5] investigated the effect of relative
roughness height, relative roughness pitch and relative
groove position on a heat transfer coefficient and friction
factor of rib-grooved artificial roughness as depicted in Fig.
2. The maximum heat transfer was obtained for a relative
roughness pitch of about 6, and heat transfer is decreased
either side of the relative roughness pitch. The optimum
ISSN: 2231-5381
3.
4.
5.
6.
7.
8.
9.
ROUGHNESS GEOMETRIES USED IN SOLAR
AIR HEATERS
Transverse ribs in the form of small diameter wires
Transverse and inclined ribs in the form of small
diameter wires
Roughness in the form of expanded metal mesh
Broken transverse rib roughness
Rib-grooved roughness
Arc shape roughness
Dimple shape roughness (Fig. 3)
Metal grit ribs (Fig. 4)
Inclinedbroken rib roughness (Fig. 5)
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Fig. 3 Dimple shape roughness
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International Journal of Engineering Trends and Technology (IJETT) – Volume 4 Issue 10 – Oct 2013
[9] Uttara Shakya R. P. Saini , M. K. Singhal (2013) A review on artificial
roughness geometry for enhancement of heat transfer and friction
characteristic on roughened duct of solar air heater. International Journal of
Emerging Technology and Advanced Engineering
Fig. 4 Metal grit ribs
Fig. 5 Combined inclined and transverse ribs
VI. CONCLUSION
In this paper an effort has been made to review the effect
of artificial roughness which providing by different shape
geometry on solar absorber plate and this review show that
artificial rouhness enhance the heat transfer rate. Different
mechanisms are also presented in this paper which increseas
heat trnsfer with the help of different shapes of artificial
geometry.
REFERENCES
[1] Saini, S.K. and Saini, R.P., (2008).Development of correlations for
Nusselt number and friction factor for solar air heater with roughened duct
having arc shaped wire as artificial roughness, Solar Energy, 82, pp. 1118 –
1130.
[2] Gupta, D. Solanki, S.C. and Saini, J.S.(1993). Heat and fluid flow in
rectangular solar air heater ducts having transverse rib roughness on absorber
plate, Solar Energy, 51,
[3] Prashant Dhiman, N.S.Thakur, Anoopkumar, Satyendersingh, “An
analytical model to predict the thermal performance of a novel parallel flow
packed bed solar air heater,” Applied energy 88(2011) 2157- pp. 31-37.
[4] Abdul- Malik Ebrahim Momin, J.S.Soni, S.C.Solanki, “Heat transfer and
Friction factor in solar air heater duct with V-shaped rib roughness on
absorber plate,”Internantional journal of heat and mass transfer 45(2002)
3383-3396.
[5] Jaurker, A.R. Saini, J.S. and Gandhi, B.K., (2006).Heat transfer and
friction characteristics of rectangular solar air heater duct using rib-grooved
artificial roughness, Solar Energy, 80, pp. 895 – 907.
[6] Suman saurabh, Heat transfer and thermal efficiency of solar air heater
having artificial roughness: a review International Journal of Renewable and
Sustainable Energy 2013; 2 (3):99-109
[7] Pushkar Dwivedi, Shankar Singh, Review Paper on the Use of Artificial
roughness inside a solar air duct to increase the heat transfer rate inside It.
International Journal of Scientific Engineering and Technology Volume 2
Issue 4, pp: 307-310
[8] Thakur SK, Thakur NS, Thakur Anoop, Vijay Mittal Use of artificial
roughness to enhance heat transfer in solar airheaters- A review .Journal of
Energy in Southern Africa 2010
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