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International Journal of Mechanical Engineering and Technology (IJMET)

Volume 8, Issue 12, December 2017, pp. 491–508, Article ID: IJMET_08_12_050

Available online at http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=8&IType=12

ISSN Print: 0976-6340 and ISSN Online: 0976-6359

© IAEME Publication Scopus Indexed

HEAT TRANSFER AUGMENTATION OF

VARIOUS ROUGHNESS GEOMETRY USED IN

SOLAR AIR HEATERS

Dhananjay Kumar

Research Scholar, National Institute of Technology Jamshedpur, India

Laljee Prasad

Assistant Professor, National Institute of Technology Jamshedpur, India,

ABSTRACT

Artificial roughness used on the absorber plate is most convenient method to

enhance the rate of heat transfer to flowing fluid in the roughened duct of solar air

heater. Artificial roughness is provided in the form of various geometries such as ribs,

dimple shape roughness, baffles, wire mesh, delta winglets, etc. The objective of this

paper is to studies over the various roughness geometries of small height elements

used on absorber plate in order to improve the heat transfer rate with little penalty of

friction. It also summarizes the various correlations developed for Nusselt number and

friction factor in roughened duct of solar air heater by previous investigators and

comparison of thermo-hydraulic performance have been investigated and presented.

Key words: Artificial roughness, Friction factor, Nusselt number, Reynolds number,

Roughness geometry, Solar air heater.

Cite this Article: Dhananjay Kumar and Laljee Prasad, Heat Transfer Augmentation

of Various Roughness Geometry Used in Solar Air Heaters, International Journal of

Mechanical Engineering and Technology 8(12), 2017, pp. 491–508.

http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=8&IType=12

1. INTRODUCTION

Energy is a basic need for human being; it is a prime agent in the generation for social and

economic growth of any country. Energy resources may be classified in two ways

conventional and non-conventional energy resources. The use of solar energy is freely

available on the earth in the form of radiation provides an infinite and non-polluting source

for various applications [1]. Schematic diagram of conventional solar air heater is shown in

Figure 1. The flat plate collectors are generally used for solar air heater for heating air.

Thermal efficiency of solar air heater is poor because low rate of heat transfer capability

between air and absorber plate also air cannot be used as storage fluid due to low thermal

capacity [2]. It can be used for various applications like space heating, crop drying, seasoning

of timber, cooking [3] as well as curing of industrial products [4] etc. In order to make a solar

air heater is economically viable and more effective in solar energy utilization system,

Dhananjay Kumar and Laljee Prasad


thermal efficiency needs to be improved by enhancing the rate of heat transfer capability

between air and absorber plate. The attempts adopted to enhance the rate of heat transfer

includes provision of artificial roughness underside the absorber plate in the form of ribs,

grooves, dimples, winglets, baffles, twisted tapes, mesh wire in various configurations on

heated surface. These roughness elements break-up the boundary layer and creates local wall

turbulence as a result thermal resistance reduces and heat transfer rate gets greatly enhance.

Several roughness geometry has been tested by various authors so far to enhance the heat

transfer with consumption of pumping power. This review is an attempt to summarize all the

efforts and to arrive at a conclusion regarding the previous experimental and analytical work

and developed the correlation for heat transfer coefficient and friction factor by various

investigators of solar air heater duct having artificial roughness of different geometries have

also been reported in the present paper.

Figure 1 Schematic diagram of conventional solar air heater.

2. THERMAL PERFORMANCE OF CONVENTIONAL FLAT PLATE

SOLAR AIR HEATER

For improvement in the efficiency of a system it is required to analyse thermal and hydraulic

performance of a solar air heater. The thermal performance of flat plate solar air heater could

be observed by considering energy balance between solar energy absorbed by absorber plate

and useful thermal energy output of the system accompanied by some losses. The thermal

network of conventional flat plate solar air heater is shown in Figure 1. Such types of solar air

heater are design and construction details described by Garg and Prakash [5].

2.1. Thermal Performance

Thermal performance of flat plate solar collector was first investigated by Hottel-Whillier-

Bliss equation reported by Duffie and Beckman [6].

(1)

or

(2)

Heat Transfer Augmentation of Various Roughness Geometry Used in Solar Air Heaters


Bliss [7] introducing ‘collector heat removal factor’, , defined as the ratio of actual

useful energy gain to the useful energy gain if the whole collector absorbing surface were at

the fluid inlet temperature .

(3)

The rate of useful energy gain by the flowing air through duct of a solar air heater may

also be calculated by using the following equation:

(4)

As discussed above, heat transfer coefficient (h) is represented in non-dimensional form

by using relationship of Nusselt number (Nu) reported by Duffie and Beckman [8].

(5)

The thermal efficiency of a solar air heater can be expressed by the following equation:

(6)

The above equation shows that the graph plot between and parameter can

be approximated by a straight line, of which intercept and slope are given by the values of

(τα) and respectively.

2.2. Hydraulic Performance

Hydraulic performance of a conventional flat plate solar air heater concerns with pressure

drop ( in the duct. Pressure drop accounts for energy consumption by fan to propel air

through the duct and it can be represented in non-dimensional form by using the following

relationship of friction factor (f), reported by Frank and Mark [9].

(7)

2.3. Thermohydraulic Performance

It is desirable the design of solar collector in such a way it should transfer maximum heat

energy to the fluid flowing with minimum consumption of pumping power. Therefore in order

to analyse overall performance of solar air heater, thermohydraulic performance should be

evaluated by considering thermal and hydraulic characteristics of solar collector

simultaneously. Lewis [10] used the parameter (η) in terms of Stanton number and friction

factor ratios for roughened and smooth surfaces, all operated at the same channel Reynolds

number.

(8)



Figure 2 Flow pattern of rib as a function Figure 3 Flow Pattern of rib as a function

of relative roughness height. of relative roughness pitch.

3. CONCEPT OF ARTIFICIAL ROUGHNESS

The use of artificial roughness is basically a heat transfer enhancement technique by which

thermo hydraulic performance of solar air heater can be improved. The thermal efficiency of

solar air heater is generally poor due to formation of laminar sub layer on the absorber plate.

So there required to break the laminar sub-layer, for improvement of heat transfer capability

between the absorber plate and air flowing in the duct, broadly artificial rib roughness has

been used, which further requires flow at the heat transferring surface to be turbulent. The

wires provided by artificial roughness break laminar sub-layer and create local wall

turbulence due to flow separation between the reattachment of consecutive wires, which

reduces thermal resistance and greatly enhance the rate of heat transfer coefficient between

the absorber plate and air flowing in the duct. However energy for creating such turbulence

has to come from fan or blower and excessive power is required to flow air through the duct.

The concept of artificial roughness was first applied by Joule [11] in 1861 as reported by

Bergles et.al [12] to enhance the heat transfer coefficient for in-tube condensation of steam

and since then many experimental investigations were carried out on the application of

artificial roughness in an area of gas turbine air foil cooling system, gas cooled nuclear

reactors, electronic equipment and design of compact heat exchangers. For the arrangement

and shape of the roughness there are various parameters that can be characterize the

roughness element height (e) and pitch (P) are the most important parameters. The basic non-

dimensional geometric parameters that are used to characterize on heat transfer and friction

factor of artificially roughened solar air heater:

3.1. Relative Roughness Height (e/D)

An enhancement of heat transfer coefficient depends on the flow rate and relative roughness

height. As relative roughness height increases, both friction factor and Nusselt number are

generally increases. Figure 2 shows the flow pattern downstream of a rib and effect on the

laminar sub-layer as the rib height is changed respectively.



3.2. Relative Roughness Pitch (P/e)

Various investigators have shown the effect of relative roughness pitch on the flow pattern i.e.

heat transfer coefficient and friction factor. The flow separation occurs downstream of a rib

and reattachment does not occur, if relative roughness pitch is less than about 8-10. As shown

in Figure 3. The flow patterns downstream of a rib with variation in rib pitch.

3.3. Angle of Attack

The angled ribs gives higher heat transfer as compared to transverse ribs, because secondary

flow induced by angle rib in addition to breaking viscous sub-layer and producing local wall

turbulence as shown in Figure 4. Fluid vortices are generated upstream and downstream side

of the rib. The gap between two ribs allows release of secondary flow and mix with main flow

which helps increasing the heat transfer rate and friction factor. This results in strong span

wise variation of heat transfer [13].

Figure 4 Generation of secondary flow Figure 5 Rib geometry used by Firth and Meyer’s.

along differents ribs.

4. FLUID FLOW AND HEAT TRANSFER CHARACTERISTICS OF

ARTIFICIALLY ROUGHENED SOLAR AIR HEATER SURFACE

Efforts for improving the heat transfer rate have been directed towards artificially disturbing

the viscous sub-layer by providing artificial roughness on heated surface. Many experimental

investigations have been carried out to studies the flow of fluid, heat transfer and friction

factor characteristics of roughened tubes, annuli and ducts [14] and [15-17]. Firth and

Meyer’s [18] investigated the heat transfer and friction characteristics performance of four

different types of artificially roughened surfaces with square transverse rib, helical rib,

trapezoidal transverse rib, and three dimensional surfaces in gas cooled reactor as shown in

Figure 5. Webb et al. [19] developed the correlations for heat transfer and friction factor for

fully rough flow region in tubes. Nikuradse [20] developed the velocity distribution and

temperature profile for sand grain roughened pipe flow and contributed to the study of the

laws governing turbulent flow of fluids in roughened tubes, channels and along rough plane

surfaces.

(i) For smooth surface

(9)



(10)

(11)

(ii) For roughened surface

The velocity distribution in the turbulent flow region is dependent upon the roughness height

along with the flow Reynolds number . A parameter is called roughness Reynolds number

is expressed as:

√

(12)

R( ) known as momentum transfer function and can be written as:

√

(13)

Dipprey and Sabersky [21] reported on the application of a heat transfer in terms of heat

transfer function G( ) over roughened circular pipes and is expressed as:

√

(14)

Table 1 Maximum enhancement in values of Nusselt number and friction factor.

Sr. no. Investigators Roughness geometry Nusselt number

(Nu)

Friction factor (f)

1 Prasad and Saini [24] Transverse continuous rib 2.38 4.25

2 Gupta et al. [27] Inclined continuous rib 1.8 2.7

3 Saini and Saini [29] Expanded metal mesh 5.00 5.00

4 Momin et al. [30] V-shaped rib 2.30 2.83

5 Hans et al. [31] Multi v-shaped rib 6.00 5.00

6 Singh et al. [32] Discrete v-rib 3.04 3.11

7 Kumar et al. [34] Multi V shape with gap

rib

6.74 6.37

8 Kumar et al. [35] Discrete W-shaped rib 2.16 2.75

9 Layek et al. [36] Chamfered compound rib 2.60 3.35

10 Jaurker et al. [39] Rib-groove 2.75 3.61

11 Saini and Verma [40] Dimpled shaped rib 7.58 4.68

12 Saini and Saini [41] Arc shaped rib 3.80 1.75

13 Bhusan et al. [42] Protrusion 3.80 2.20

14 Bopche and Tandale [43] U shaped rib 2.82 3.72

5. ROUGHNESS GEOMETRIES USED IN SOLAR AIR HEATERS

The investigation of various authors ribs of different roughness geometries and orientation are

extensively used for enhance the rate of heat transfer in solar air heater. The various rib

geometries used by investigators and its effect on flow of fluid, heat transfer and pressure

drop are discussed.

5.1. Transverse Continuous Ribs

Kays. [22] has been suggested by fixing of small diameter protrusion wires perpendicular to

flow direction on surface of absorber plate may help to trip and break laminar sub-layer. It



was also suggested that protrusion wire of diameter , spacing 10–20 times diameter

and placed within the laminar sub-layer for better than turbulence promoters.

Prasad and Mullick. [23] has used three unglazed collectors channels are placed in side-by

side of 300cm long and 14.1cm wide for drying purpose as shown in Figure 6. Middle

collector channel ‘B’ are plane GI sheet, Channel ‘A’ was also a plane GI sheet having 24

gauge GI wires soldered on its lower side perpendicular to the direction of flow at distance of

1.27cm. Channel ‘C’ was corrugated with wires soldered on the underside of absorber plate in

the same way as in ‘A’ channel. It is reported that small diameter protruding wires enhance

collector efficiency factor from 0.63 to 0.72, and 14% improvement in thermal performance

as plane one.

Prasad and Saini [24] experimentally investigated of fully developed turbulent flow using

small diameter transverse wire fixed on absorber plate as shown in Figure 7. They developed

the expression for heat transfer and friction factor of experimental data. An enhancement in

Nusselt number and friction factor was found to be 2.38 and 4.25 times respectively over

smooth one corresponding to relative roughness height of 0.030 and relative roughness pitch

of 10.

Figure 6. Three channel portable experimental Figure 7. Transverse continuous ribs.

set-up.

5.2. Transverse Broken Ribs

Sahu and Bhagoria [25] reported effect of broken transverse ribs on thermal performance of

solar air heater for fixed roughness height value of 1.5mm; aspect ratio value of 8; pitch in the

range of 10-30 mm and Reynolds number varying from 3000-12,000. The rib arrangement is

shown in Figure 8. They found that roughened absorber plates enhance the heat transfer rate

by 1.25–1.4 times as compared to smooth surface and maximum thermal efficiency of the

order of 83.5% was obtained.

Figure 8 Transverse broken ribs.

5.3. Inclined Continuous Ribs

Han and Park [26] studied the effect of angled or inclined ribs on heat transfer and friction

factor with narrow aspect ratio and concluded that the angled ribs gives higher heat transfer as

compared to transverse ribs, because secondary flow induced by the angled rib.

Gupta et al. [27] established optimum design parameters under actual climatic conditions

for roughened solar air heater for e/D= 0.020-0.050; P/e= 10; . The arrangement of



roughness geometry is shown in Figure 9. The maximum enhancement of heat transfer and

friction factor was reported to be 1.8 and 2.7 times as compared to smooth surface

corresponding to angle of attack of , respectively.

Figure 9 Inclined ribs.

5.4. Combination of Inclined and Transverse Ribs

Varun et.al. [28] experimentally studied on heat transfer and friction characteristics by using a

combination of inclined and transverse ribs roughened solar air heater with parameters e/D=

0.030; P/e= 3-8 and Re= 2000-14000. The roughness geometry is shown in Figure 10. It was

found that roughened collector at relative roughness pitch value of 8 gives better performance.

Figure 10 Combination of inclined and transverse ribs.

Table 2 Values of thermo hydraulic performance parameter .

5.5. Expanded Metal Mesh

Saini and saini [29] reported effect of expanded metal mesh roughened solar air heater for

fully developed turbulent flow with parameters W/H= 11; L/e= 25-71.87; S/e= 15.62-46.87;

e/D= 0.012-0.039 and Re= 1900-13,000. The arrangement of roughness geometry is shown in

Figure 11. They found that an enhancement of heat transfer and friction factor to be 4 and 5

times over the smooth duct corresponding to an angle of attack of and respectively.

Sr. no. Authors Roughness geometry

]

1 Prasad and Saini [24] Transverse wire 1.78

2 Saini and Saini [29] Expanded metal mesh 2.34

3 N.S. Deo et al. [33] Multigap V-down ribs

combined with staggered ribs

2.45

4 Karmare and Tikekar [38] Metal grits ribs 2.39

5 Jaurker et al. [39] Rib groove 1.76

6 Bopche andTandale [43] Inverted U shape rib 1.82



Figure 11 Wires mesh roughness.

5.6. V-Shaped Rib Roughness

Momin et al. [30] experimentally performed the effect of v-shaped ribs roughened absorber

plate with geometrical parameters e/D= 0.02-0.034; Re= 2500-18000; and P/e=

10. The maximum enhancement of Nusselt number and friction factor has been found to be

2.30 and 2.83 times respectively over the smooth surface for an angle of attack of . It was

also reported that for e/D= 0.034 and v-shaped ribs increase the values of Nusselt

number by 1.14 and 2.30 times over inclined ribs and smooth absorber plate respectively. The

geometry investigated has been shown in Figure 12. Developed the expression for Nusselt

number and friction factor.

Hans et.al. [31] experimentally studied the effect of multi v-shaped ribs roughened solar

air heater with geometrical parameters e/D= 0.019-0.043; P/e= 6-12; ; W/w= 1-

10; Re= 2000-20,000. The rib geometry is shown in Figure 13. The maximum enhancement

of Nusselt number and friction factor has been observed to be 6 and 5 times respectively as

compared to smooth duct for angle of attack of . It was also observed that maximum

improvement in heat transfer and friction factors occur at relative roughness width of 6 and 10

respectively.

Figure 12. Roughness geometries used by Figure 13. Multi v-rib roughness.

Momin et al.

5.7. Discrete V-Shaped Rib Roughness

Singh et al. [32] experimentally investigated using discrete v-down ribs roughened solar air

heater with geometrical parameters e/D= 0.015-0.043; P/e= 4-12; g/e= 0.5-2.0; d/w= 0.20-

0.80; and Re= 3000-15,000. It was observed that maximum increase of Nusselt



number and friction factor to be 3.04 and 3.11 times respectively over the smooth surface.

The maximum value of Nusselt number and friction factor occur at P/e= 8; e/D= 0.043;

d/w= 0.65 and g/e= 1.0. The arrangement is shown in Figure 14.

Deo et.al. [33] investigation performed of solar air heater for multi-gap v-down ribs

combined with staggered ribs with geometrical parameters W/H= 12; P/e= 4-14; ; ; g/e= 1; w/e= 4.5; p/P= 0.65; Re= 4000-12,000 and two

numbers of gap on each side of v-legs roughness geometry is shown in Figure 15. They found

two peaks for Nusselt number corresponding to P/e= 6 and 12, then decrease in Nusselt

number was observed for increase in relative roughness height value beyond 0.044. The

maximum enhancement achieved in Nusselt number and thermohydraulic performance

parameters was 3.34 and 2.45 times respectively

over the smooth one.

Figure 14. Discrete v-down rib roughness. Figure 15. Multi-gap v-down combined

with staggered ribs.

5.8. Multi V-shaped with Gap Ribs

Kumar et al. [34] established results using multi v-shaped ribs with gap underside the

absorber plate with geometrical parameters e/D= 0.043; W/w= 6; ; g/e=

0.5-1.5; P/e= 10; ; Re= 2000-20,000. The geometry investigated as shown in Figure

16. They found that maximum improvement in Nusselt number and friction factor to be 6.32

and 6.12 times as compared to smooth surface respectively. It was also observed that at

and g/e= 1.0 gives best thermohydraulic performance.

Figure 16 Multi v-shaped with gap ribs.

5.9. Discrete W-Shaped Rib Roughness

Kumar et al. [35] studied on heat transfer and friction characteristics of discrete w-shaped

roughened solar air heater provided on one broad wall as shown in Figure 17. They found that



maximum enhancement of Nusselt number and friction factor to be 2.1 and 2.7 times

respectively compared to smooth duct at angle of attack of .

Figure 17 Discrete w-shape ribs.

5.10. Chamfered Rib Roughness

Layek et al. [36] studied the entropy generation of solar air heater duct having repeated

transverse chamferd rib-groove roughness on one broad wall as shown in Figure 18. The duct

has varying parameter P/e= 4.5-10; ; g/P= 0.3-0.6; . The

Reynolds number has combined effect of heat transfer as well as fluid friction. He was found

that entropy generation decreases with increase in relative roughness height and minimum for

P/e= 6; g/P= 0.4 for chamfer angle of .

Karwa et al. [37] investigated the performance of solar air heaters using integral

chamfered rib underside the absorber plate with investigation parameters P/e= 4.58 and 7.09;

; e/D= 0.0197, 0.0256 and 0.0441 for Re= 3750-16530. The geometry investigated

has been shown in Figure 19. They show that an enhancement in thermal efficiency (10–40%)

over smooth surface. They also observed considerable enhancement in pumping power due to

increase in pressure drop.

Figure 18. Transverse chamfered rib-groove Figure 19. Integral chamfered ribs.

roughness.

5.11. Metal Grit Ribs

Karmare and Tikekar [38] conducted experimental studied on thermohydraulic performance

of roughened solar air heater with metal rib grits with geometrical parameters e/D= 0.035-

0.044; P/e= 15-17.5; l/s= 1.72 and Re= 3600-17,000. The arrangement is shown in Figure 20.

They observed that maximum enhancement in thermal efficiency 10-35% over smooth

surface and developed the correlation for Nusselt number and friction factor.



Figure 20 Metal grit ribs.

5.12. Rib-Groove Roughness

Jaurker et al. [39] investigated the thermo-physical characteristics of combination of rib and

groove geometry roughened solar air heater duct as shown in Figure 21. They used

geometrical parameters e/D= 0.0181–0.0363; P/e= 4.5–10.0; and g/P= 0.3–0.7 and Re= 3000–

21,000. It has been observed that an enhancement in Nusselt number and friction factor to be

2.7 and 3.6 times over smooth one. The maximum heat transfer occurs at P/e= 6.0; g/P= 0.4

and its decreases either side of relative roughness pitch and similar trend is found for either

side of groove position to pitch ratio both Nusselt number and friction factor decreases.

Figure 21 Rib-grooved roughness.

5.13. Dimpled Surfaces

Saini et al. [40] carried out an investigation using dimple shaped underside the absorber plate

with geometrical parameters e/D= 0.018-0.037; P/e= 8-12; and Re= 2000-12,000. The

roughness geometry is shown in Figure 22. They found that maximum heat transfer occurs at

e/D= 0.0379 and minimum at e/D= 0.0289 for relative roughness pitch of 10.

Figure 22 Dimple shape.



5.14. Arc Shape Roughness

Saini and Saini [41] reported effect of an arc shaped ribs roughened solar air heater duct with

parameters Re= 2000–17,000; e/D= 0.0213–0.0422; – and fixed value

of relative roughness pitch of 10. The investigated geometry is shown in Figure 23. Maximum

enhancement in Nusselt number and friction factor was observed to be 3.6 and 1.75 times

respectively as compared to smooth surface.

Figure 23 Arc shape roughness.

5.15. Protruded Roughness Geometry

Bhushan and Singh [42] investigated the effect of protrusions roughness geometry underside

the absorber plate with geometrical parameters W/H= 10; S/e= 18.75-37.50; L/e= 25.0-37.50;

d/D= 0.0147-0.367; e/D= 0.03 and Re= 4000-22,000. They found that the maximum increase

in Nusselt number (Nu) and friction factor (f) to be 3.8 and 2.2 times respectively as

compared to smooth duct for S/e= 31.25; L/e=31.25 and d/D= 0.294. The arrangement is

shown in Figure 24.

Figure 24 Protruded roughness geometry.

5.16. U-Shaped Ribs

Bopche and Tandale [43] carried out an investigation using inverted U-shaped turbulators

underside the absorber plate with parameters Re= 3800-18000; e/D= 0.0186-0.03986; P/e=

6.67-57.14; . It was found that an enhancement of heat transfer and friction factor of

turbulator roughened duct to be 2.82 and 3.72 times respectively compared to smooth one.

The roughness geometry is shown in Figure 25.



Figure 25 Turbulator geometry.

6. DISCUSSION

Based on the literatures review of experiments with artificial roughness rib elements in duct

and solar air heater reveals that small height elements is used to increase the heat transfer

substantially with adverse effect of increase in friction losses. Thus, an external pumping

power is required to overcome the frictional forces. These elements can be of various shapes

and geometry like circular, triangular, square, inclined, v-shaped or staggered ribs, w-shape,

thin wires, wire mesh, grooves, dimples, protrusions arc shape etc. which are attached

underside the absorber plate. The different geometrical and flow parameters of these elements

like roughness height, relative roughness pitch, relative roughness height, angle of attack, duct

aspect ratio and flow Reynolds number play an important role in determining the heat transfer

and friction characteristics of the fluid flow process. These small height element break the

laminar sub-layer and create local wall turbulence due to reattachment between the

consecutive wires. The various statistical correlations have been developed by various

investigators can be used to understand the effect of geometrical parameters on

thermohydraulic performance. It has been also found that the generation of artificial rib

roughness underside the absorber plate is a tedious task and may not be economically feasible

for large scale production of solar air heaters for various applications. A suitable roughness

geometry are need to be selected which besides easily available should be easy to fixed or

fabricate on the absorber surface and also gives substantial enhancement in the heat transfer

coefficient at low friction penalty.

Table 4 Heat transfer coefficient and friction factor correlations for different roughness geometries

used in solar air heater duct.

Author/s Roughness

Geometry

Heat transfer coefficient friction factor

Prasad and

Saini [24]

Transverse rib √

–

Gupta et al.

[27]

Transverse rib

Saini and Saini

[29]

Expanded metal

mesh

Momin et al

[30]

V-shape

continuous ribs

V.S. Hans et al.

[31]

Multi V-shape

N.S. Deo et al. [33]

Multigap V-down ribs combined

with staggered ribs

Kumar et al. [34]

Multi V-shape with gap rib



Layek et al.

[36]

Chamfered rib-

groove combination

Karwa et al. [37]

Chamfered ribs

Karmare and

Tikekar [38]

Wire ribs-grid

shap

Jaurkar et al.

[39]

Rib-Groove Rib-

Groove

Saini and Saini

[41]

Arc shaped wire

ribs

Bhusan and

singh [42]

Protrusion

Bopche and

Tandale [43]

Turbulator shape

7. CONCLUSIONS

It can be concluded from the present review lot of work has been carried out to investigate the

effect of small height element artificial roughness geometries of different shapes and sizes in

order to enhance the heat transfer rate with little penalty of friction. The use of artificial

roughness is most effective technique to improve the thermal performance of solar air heaters.

From the review following conclusion are drawn:

1. Roughness in the form of ribs, wire matrix, dimples and protrusions were mainly suggested

by different investigators to achieve better thermal performance, because it offers minimum

friction factor.

2. The maximum enhancement on heat transfer in terms of Nusselt number and friction factor

of 7.58 and 4.68 was observed in the investigations of Saini and Verma [40] followed with

multi v-shaped with gap as the roughness element by Kumar et al. [34] of 6.74 and 6.37 and

multiple v-shaped ribs by Hans et al. [31] of 6 and 5. It has concluded that the increase in heat

transfer is achieved, but the friction factor is also increasing simultaneously. The maximum

enhancement in heat transfer and friction factor is enlisted in Table-1.

3. The value of thermo hydraulic performance of solar air heaters by various investigators

with artificial roughness so far ranges from 1.38 to 2.45. This parameter is also used to

compare the performance of various roughness elements arrangement combination to obtain

the best one. Various authors conducted experiments and measured the thermo hydraulic

performance parameters in their work are enlisted in Table-2.

4. Correlations developed for heat transfer and friction factor for solar air heater ducts having

artificial roughness of different geometries for different investigators are also shown in

tabular form these correlations can be used to predict thermal efficiency, effective efficiency

and then hydraulic performance of artificial roughened solar air heaters is enlisted in Table-3.

5. Experimental investigations employing compound enhancement techniques could be more

useful in order to achieve greater improvement in thermal performance of solar sir heaters.

REFERENCES

[1] J.S. Hsiesh, Solar energy engineering. New Jersey, Prentice Hall, 1986.

[2] G.N.Tiwari, Solar energy. Fundamentals, Design, Modelling and Application, Narosa

Publication, 2008.



[3] C.L. Gupta, H.P. Garg, Performance studies on solar air heaters, Solar Energy (11) (1967)

25-31.

[4] Varun, R.P. Saini, S.K. Singal, Areview of roughness geometry used in solar air heaters,

Solar Energy (81) (2007) 1340-1350.

[5] H.P. Garg, j. Prakash, Solar energy fundamentals and applications, New Delhi, Tata

McGraw-Hill, 1997.

[6] J.A. Duffie, W.A. Beckman, Solar engineering of thermal processes, Wiley, New York,

1980.

[7] W. Bliss, The derivations of several plate efficiency factors useful in the design of flat

plate solar heat collectors, Solar Energy (3) (1959) 55-64.

[8] J.A. Duffie, W.A. Beckman, Solar engineering thermal processes, John Wiley, New York,

1991.

[9] K. Frank, S.B. Mark, Principles of heat transfer Thomson Learning Inc, Colorado 2001.

[10] M.J. Lewis, Optimizing the thermohydraulic performance of rough surfaces, International

Journal of Heat Mass Transfer (18) (1975) 1243-1248.

[11] J.P. Joule, On the surface condensation of steam Philos Trans R Soc Lond, (151) (1861)

133-160.

[12] A.E. Bergles, R.L. Webb, G.H. Junkan, Energy conservation via heat transfer

enhancement, Energy (4) (1979)193-200.

[13] M.E.Taslim, T. Li, D.M. Kerche, Experimental heat transfer and friction in channels

roughened with angled, V-shaped and discrete ribs on two opposite walls, ASME J

Turbomach (118) (1996) 20-28.

[14] P.R. Chandra, C.R. Alexander, J.C. Han, Heat transfer and friction behaviours in

rectangular channels with varying number of ribbed walls, International Journal of Heat

Mass Transfer (46) (2002) 481-495.

[15] S.C. Lau, R.D. McMillian, J.C. Han, Turbulent heat transfer and friction in a square

channel with discrete rib tabulators, Trans ASME J Turbo Machi (113) (1991) 360-366.

[16] J.C. Han, Y.M. Zhang, C.P. Lee, Augmented heat transfer in square channels with

parallel, crossed and v-shaped angled ribs, Trans ASME J Heat Transfer (113) (1991)

590–596.

[17] J.C. Han, Y.M. Zhang, High performance heat transfer ducts with parallel, broken and v-

shaped broken ribs, Int J Heat Mass Transfer (35) (1992) 513–523.

[18] R.J. Firth, L. Meyer, A comparison of the heat transfer and friction factor performance of

four different types of artificially roughened surface, International Journal Heat &

MassTransfer 26(2) (1983) 175-183.

[19] R.L. Webb, E.R.G. Eckort, K.J. Goldstein, Heat transfer and friction in tubes with

repeated ribRoughness, International Journal Heat Mass Transfer (14) (1971) 601-617.

[20] J. Nikuradse, Laws of flow in rough pipes, NACA Technical Memorandom (1958) 1292.

[21] D.F. Dippery, R.H. Sabersky, Heat and momentum transfer in smooth and rough tubes at

various Prandtl numbers, International Journal Heat Mass Transfer (36) (1963) 1459-

1469.

[22] W.B. Kays, Convective heat and mass transfer, New York, McGraw Hill Book Co (1966)

197– 198.

[23] K. Prasad, S.C. Mullick, Heat transfer characteristics of a solar air heater used for drying

Purposes, Applied Energy 13(2) (1983) 83–93.



[24] B.N. Prasad, J.S. Saini, Effect of artificial roughness on heat transfer and friction factor in

a solar air heater, Solar Energy 41(6) (1988) 555-560.

[25] M.M. Sahu, J.L. Bhagoria, Augmentation of heat transfer coefficient by using broken

transverse ribs on absorber plate of solar air heater .Renew Energy (30) (2005) 2057-2063.

[26] J.C. Han, C.K. Park, Augmented heat transfer in rectangular channels of narrow aspect

ratios with rib turbulators, International Journal of Heat Mass Transfer (32) (1989) 1619-

1630.

[27] D. Gupta, S.C. Solanki, J.S. Saini, Thermo hydraulic performance of solar air heaters with

roughened absorber plates, Solar Energy 61(1) (1997) 33–42.

[28] Varun, R.P. Saini, S.K. Singal, Investigation of thermal performance of solar air heater

having roughness elements as a combination of inclined and transverse ribs on the

absorber plate, Renew Energy (33) (2008) 1398–1405.

[29] R.P. Saini, J.S. Saini, Heat transfer and friction factor correlations for artificially

roughened ducts with expanded metal mesh as roughened element, Int J Heat Mass

Transfer (40) (1997) 973-986.

[30] A.M.E. Momin, J.S. Saini, S.C. Solanki, Heat transfer and friction in solar air heater duct

with V-shaped rib roughness on absorber plate, Int Journal of Heat Mass Transfer (45)

(2002) 3383–3396.

[31] Hans V.S., Saini R.P., Saini J.S. Heat transfer and friction factor correlation for solar air

heater duct roughened artificially with multiple v-ribs, Solar Energy (84) (2010) 898-911.

[32] S. Singh, S. Chander, J.S. Saini, Heat transfer and friction factor correlations of solar air

heater ducts artificially roughened with discrete V-down ribs. Energy (36) (2011) 5053–

5064 Proceedings of National Solar Energy Convention, Roorkee; (1998) 75–84.

[33] N.S. Deo, S. Chander, J.S. Saini, Performance analysis of solar air heater duct roughened

with multigap V-down ribs combined with staggered ribs, Renewable Energy (91) (2016)

484-500.

[34] Kumar A., Saini R.P., Saini J.S. Experimental investigation on heat transfer and fluid flow

characteristics of air flow in rectangular duct with Multi v-shaped rib with gap roughness

on the heated plate, Solar Energy (86) (2012) 1733-1749.

[35] A. Kumar, J.L. Bhagoria, R.M. Sarviya, International 19th national & 8th ISHMTASME

heat and mass transfer conference heat transfer enhancement in channel of solar air

collector by using discrete W-shaped artificial roughened absorber 2008.

[36] A. Layek, J.S. Saini, S.C. Solanki, Second law optimization of a solar air heater having

chamfered rib-groove roughness on absorber plate, Renewable Energy(32) (2007) 1967-

1980.

[37] R. Karwa , S.C. Solanki, J.S. Saini, Thermo-hydraulic performance of solar air heaters

having integral chamfered rib roughness on absorber plates, Energy (26) (2001) 161-176.

[38] S.V. Karmare, A.N. Tikekar, Heat transfer and friction factor correlation for artificially

roughened duct with metal grit ribs, Int J Heat Mass Transf (50) (2007) 4342–4351.

[39] A.R. Jaurker, J.S. Saini, B.K. Gandhi, Heat transfer and friction characteristics of

rectangular solar air heater duct using rib-grooved artificial roughness, Sol Energy 80(8)

(2006) 895–907.

[40] Saini R.P., Verma J. Heat transfer and friction factor correlations for a duct having dimple

shape artificial roughness for solar air heaters, Energy (33) (2008)1277–1287.

[41] S.K. Saini, R.P. Saini, Development of correlations for Nusselt number and friction factor

for solar air heater with roughened duct having arc-shaped wire as artificial roughness, Sol

Energy (82) (2008) 1118–1130.



[42] B. Bhusan, R. Singh, Thermal and thermohydraulic performance roughened solar air

heater having protruded absorber plate, Solar Energy (86) (2012) 3388-3396.

[43] S.B. Bopche, M.S. Tandale, Experimental investigations on heat transfer and frictional

characteristics of a turbulator roughened solar air heater duct, International Journal of

Heat and Mass Transfer (52) (2009) 2834–2848.

[44] A. Nalini Deepthi. Analysing the Metallic Foam-Filled Triple Tube Concentric Heat

Transfer. International Journal of Civil Engineering and Technology, 8(7), 2017, pp. 496–

502

[45] S Girish, M Surya Prakash, P Geeta Krishna and K Lavanya . Analysis of a Condenser in

a Thermal Power Plant for Possible Augmentation in its Heat Transfer Performance.

International Journal of Civil Engineering and Technology , 8(7), 2017, pp. 410-420

heat transfer augmentation of various roughness …€¦ · turbulence as a result thermal...

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