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A review on methodology of artificial roughness used in duct

of solar air heaters

Brij Bhushan*, Ranjit Singh

Department of Mechanical Engineering, Beant College of Engineering and Technology, Gurdaspur 143521, Punjab, India

a r t i c l e i n f o

Article history:

Received 31 March 2009

Received in revised form

5 September 2009

Accepted 9 September 2009

Available online 9 October 2009

Keywords:

Solar air heater

Artificial roughness

Nusselt number

Friction factor

a b s t r a c t

In order to enhance rate of heat transfer to flowing air in the duct of a solar air heater, artificiallyroughened surface of absorber plate is considered to be an effective technique. Investigators reported

various roughness geometries in literature for studying heat transfer and friction characteristics of an

artificially roughened duct of solar air heaters. In the present paper an attempt has been made to

categorize and review the reported roughness geometries used for creating artificial roughness. Heat

transfer coefficient and friction factor correlations developed by various investigators for roughened

ducts of solar air heaters have also been reported in the present paper.

2009 Elsevier Ltd. All rights reserved.

1. Introduction

Energy in various forms has been playing an increasinglyimportant role in world wide economic progress and industriali-

zation. The growth of world population coupled with rising mate-

rial needs has escalated the rate of energy usage. Rapid increase in

energy usage characteristic of the past 50–100 years cannot

continue indefinitely as finite energy resources of earth are

exhaustible. On the other hand, environment degradation with the

use of fossil fuels is a threat to life on this planet earth. In view of

world’s depleting fossil fuel reserves and environmental threats,

development of renewable energy sources has received an impetus.

Of many alternatives, solar energy stands out as brightest long

range resource for meeting continuously increasing demand for

energy. It is considered to be a dominating renewable energy

source due to its large potential. The freely available solar radiation

provides an infinite and non-polluting reservoir of fuel.The simplest method to utilize solar energy for heating appli-

cations is to convert it into thermal energy by using solar collectors.

Solar water heaters and solar air heaters are flat plate collectors

which are generally used for heating water and air respectively.

Solar air heaters are considered to be compact and less complicated

as compared to solar water heaters. These are also free from

corrosion and freezing problems. Solar air heater can be fabricated

using cheaper as well as lesser amount of material and is simpler to

use than solar water heater. Solar air heaters are generally

considered to be useful for applications like space heating, cropdrying, seasoning of timber etc. A solar air heater occupies an

important place among solar thermal systems because of minimal

use of materials and cost. The thermal efficiency of a solar air heater

is generally considered to be less because of low rate of heat

transfer capability between absorber plate and air flowing in the

duct. In order to make a solar air heater more effective solar energy

utilization system, thermal efficiency needs to be improved by

enhancing heat transfer rate. It is reported in literature that heat

transfer rate can be enhanced by increasing the surface area by

using corrugated surfaces or extended surfaces called fins and by

increasing convective heat transfer coefficient by creating turbu-

lence at heat transfer surface by providing artificial roughness on

underside of the absorber plate. Under method of artificial rough-

ness, many experimental investigations have been reported inliterature by various authors. In the present paper an attempt has

been made to categorize and review the reported roughness

geometries used for creating artificial roughness. Heat transfer

coefficient and friction factor correlations developed by various

investigators for roughened duct of solar air heaters have also been

reported in the present paper.

2. Performance analysis of conventional solar air heater

It is required to analyse thermal and hydraulic performance of

a solar air heater for making an efficient design of such type of * Corresponding author. Tel.: þ91 9855566294; fax: þ91 1874 221463.

E-mail address: [email protected] (B. Bhushan).

Contents lists available at ScienceDirect

Energy

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / e n e r g y

0360-5442/$ – see front matter 2009 Elsevier Ltd. All rights reserved.

doi:10.1016/j.energy.2009.09.010

Energy 35 (2010) 202–212

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a system. Thermal performance concerns with heat transfer

process within the collector and hydraulic performance concerns

with pressure drop in the duct. A conventional solar air heater

shown in Fig. 1 is considered for brief analysis of thermal and

hydraulic performance in the following sub-sections. Design and

construction detail of such type of a conventional system are

described by Garg and Prakash [1].

2.1. Thermal performance

In order to evaluate thermal performance of a solar air heater,

following Hottel–Whillier–Bliss equation reported by Duffie and

Beckman [2] is commonly used.

Q u ¼ AcF R

I ðsaÞeU L ðT i T aÞ

(1)

or

qu ¼ Q u= Ac ¼ F R

I ðsaÞeU L ðT i T aÞ

(2)

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:

Q u ¼ _mC pðT o T iÞ ¼ hAc

T pm T am

(3)

As discussed above, heat transfer coefficient (h) can be increased by

applying artificial roughness on the surface of absorber plate. It can

be represented in non-dimensional form by using the following

relationship of Nusselt number (Nu) reported by Duffie and Beck-

man [2].

Nu ¼ hL=k (4)

Further, thermal efficiency of a solar air heater can be expressed

by the following equation;

Nomenclature

Ac surface area of absorber plate, m2

B half length of full V-rib element, m

C p specific heat of air, J/kg K

d, d0 print diameter of dimple/protrusion or geometric

parameter of broken rib, m

D, Dh equivalent or hydraulic diameter of duct, m

e rib height, m

g groove position, m

h heat transfer coefficient, W/m2 K

H depth of air duct, m

I intensity of solar radiation, W/m2

k thermal conductivity of air, W/m K

L length of test section of duct or long way length of

mesh, m_m mass flow rate, kg/s

P pitch, m

DP pressure drop, Pa

qu useful heat flux, W/m2

Q u useful heat gain, W

Q l heat loss from collector, WQ t heat loss from top of collector, W

S length of discrete rib or short way length of mesh, m

T o fluid outlet temperature, K

T i fluid inlet temperature, K

T a ambient temperature, K

T pm mean plate temperature, K

T am mean air temperature, K

U L overall heat loss coefficient, W/m2 K

v velocity of air in the duct, m/s

w width of rib, m

W width of duct, m

Dimensionless parameters

B/S relative roughness length

d/W relative gap position

eþ roughness Reynolds number

e/D, e/Dh relative roughness height

e/H rib to channel height ratio

f friction factor

f average friction factor

F R heat removal factor

g /e relative gap width

g /P relative groove position

G momentum heat transfer function

L/e relative long way length of mesh

l/s relative length of metal grit

Nu Nusselt number

Nus Nusselt number for smooth channel

Nur Nusselt number for rough channel

Nuav area-averaged Nusselt number

Nuo Nusselt number for fully developed flow smooth

channel

p/e relative roughness pitch

Pr Prandtl number

R roughness function

Re Reynolds number

St Stanton number

St average Stanton number

S /e relative short way length of mesh

W /H duct aspect ratio

Greek symbols

f rib chamfer/wedge angle, degree

hth thermal efficiency

heff effective thermal efficiency

m dynamic viscosity, Ns/m2

r density of air, kg/m3

a angle of attack, degree

(sa)e effective transmittance-absorptance product

Transparent cover

Reflection loss

Radiation loss

Convection loss

Conduction loss

Air out at To

Air in at Ti

Air passage

Bottom of

collector

InsulationI (τα)e

Solar radiation (I)

Absorber plate

Fig. 1. Conventional solar air heater.

B. Bhushan, R. Singh / Energy 35 (2010) 202–212 203



hth ¼ qu

I ¼ F R

ðsaÞeU L

T i T a

I

(5)

The above equation shows that the plot between hth and parameter

(T i T a)/I can be approximated by a straight line, of which intercept

and slope are given by the values of F R (sa)e and F R U L respectively.

2.2. Hydraulic performance

Hydraulic performance of a solar air heater concerns with

pressure drop (DP ) in the duct. Pressure drop accounts for energy

consumption by fan to propel air through the duct. Pressure drop

can be represented in non-dimensional form by using the following

relationship of friction factor ( f ), reported by Frank and Mark [3].

f ¼ ðDP ÞDh

2rLV 2 (6)

2.3. Thermohydraulic performance

It is desirable that design of collector should be made in such

a way that it should transfer maximum heat energy to the flowing

fluid with minimum consumption of fan energy. Therefore in order

to analyse overall performance of a solar air heater, thermohy-

draulic performance should be evaluated by considering thermal

and hydraulic characteristics of the collector simultaneously.

3. Methodology of artificial roughness

In the duct of a solar air heater, presence of laminar sub-layer

between the absorber plate and flowing air is generally considered

to be the main cause of thermal resistance for heat transfer. Arti-

ficially roughened absorber plate is considered to be a good

methodology to break laminar sub-layer in order to reduce thermal

resistance and to increase heat transfer coefficient. The ribs

provided by artificial roughness break laminar sub-layer and create

local wall turbulence due to flow separation and reattachment

between the consecutive ribs, which reduces thermal resistance

and greatly enhance rate of heat transfer. However simultaneous

increase in friction loss also takes place in an artificially roughened

air duct. It is therefore desirable to create turbulence in the region

very close to the heat transferring surface i.e. in the laminar sub-

layer only, in order to reduce the friction loss with application of

artificial roughness. This can be done by keeping roughnesselement of small height in comparison with the duct dimension.

Attempt to increase heat transfer coefficient by applying artifi-

cial roughness has been recorded over a century with one of the

formal studies being published by J.P. Joule in 1861 as reported by

Bergles et al. [4]. Significant improvement in heat transfer

coefficient for in-tube condensation of steam has been reported,

when a wire was inserted in the cooling water jacket and spiralled

around the condenser tube. Afterwards many experimental inves-

tigations on artificial roughness were carried out in an area of gas

turbine airfoil cooling system, gas cooled nuclear reactors and

design of compact heat exchangers. In these investigations many

types of roughness geometries were used and classified as regular

and irregular roughness geometries.

In regular roughness geometries different shapes, sizes and

arrangements of roughness elements are studied in heat exchangerequipments. Mittal et al. [5] reported that early studies beginning

with that of Nikuradse in 1950 attempted to develop velocity and

temperature distribution for roughened surfaces. Special functions

known as heat transfer function and momentum transfer function

have been proposedto correlate data on heat transfer and fluid flow

characteristics. Webb and Eckert [6] developed heat transfer and

friction factor correlations for turbulent air flow in tubes having

rectangular repeated rib roughness based on the law of wall simi-

larity and application of the heat-momentum transfer analogy to

flow over rough surface having relative roughness height of 0.01–

0.04 at a relative roughness pitch of 10–40 and range of Prandtl

number of 0.71–37.6. Lewis [7] defined new efficiency parameter

for optimising thermohydraulic performance of rough surfaces.

Ravigururajan and Bergles [8] developed general statistical corre-

lations for heat transfer and pressure drop for four types of

roughness elements i.e. semicircular, circular, rectangular and

triangular for single-phase turbulent flow in internally ribbed

tubes. Han [9–12] carried out an experimental study of the effect of

rib shape,angle of attack, pitch to height ratio and spacing in square

duct with two opposite rib roughened wall. Parallel full ribs having

an angle of attack, ‘a’ of 45 and 30 had the best thermal perfor-

mance. Han et al. [13] investigated the effect of parallel and

V-shaped broken rib orientation on the local heat transfer distri-

bution and pressure drop in a square channel with two opposite

ribbed walls and found that 60o staggered discrete V-shaped ribs

provide higher heat transfer than parallel discrete ribs. Liou and

Hwang [14] reported experimental study on turbulent heat transfer

and friction in a channel having ribs of semicircular, square and

triangular shapes and mounted on two opposite walls. For therange of Reynolds number studied, ribs of semicircular, triangular

and square shape yielded about 1.6–2.0, 1.7–2.2 and 1.9–2.7 fold

A

B

C

Air flow

Fig. 2. Three channel portable experimental set-up.

Absorber plateWiresP

e

Air

Fig. 3. Roughened absorber plate fixed with transverse continuous wires.

Air

P Wires Absorber Plate

Fig. 4. Roughened absorber plate with transverse broken ribs.

α

Air

Absorber PlateWires

P

Fig. 5. Roughened absorber plate with inclined ribs.

B. Bhushan, R. Singh / Energy 35 (2010) 202–212204



increase in average Nusselt number while friction factor increased

by 4–8, 5–10 and 7–15 fold respectively. Lau et al. [15], Taslim et al.

[16] and Olssom and Sunden [17] investigated the effect of V-sha-

ped ribs in square channel and found enhancement in heat transfer

as compared to inclined ribs and transverse ribs. Results showed

that an average Stanton number for the inclined 45 and 60

discrete ribs was 20–35% higher than in 90o full rib case. Gao and

Sunden [18] also reported that V-shaped ribs pointing downward

perform better than the ribs pointing upward in rectangular ducts.

Hu and Shen [19] investigated the effect of inclined discrete ribs

with and without groove and reported performance improvement

for discrete arrangement without groove. Cho et al. [20] examined

the effect of angle of attack and number of discrete ribs in rectan-gular duct and reported that gap region between discrete ribs

accelerates the flow and results an increase in local heat transfer

coefficient. Chyu et al. [21,22] reported local heat transfer

measurements on ribs of hemispherical and teardrop shapes by

using a transit liquid crystal technique and obtained 2.5 times

greater heat transfer enhancement and air pressure penalty is half

the valuesproduced by conventional rib turbulator. Moon et al. [23]

investigated effects of channel height on heat transfer in a rectan-

gular duct with a dimpled surface and observed enhancement in

heat transfer by about 2.1 times regardless of channel height and

friction factor of 1.6–2.0 times that of smooth channel. Mahmood

and Ligrani [24,25] measured local heat transfer on dimpled surface

of opposite walls with various temperature ratios having ratio of

channel height to dimple print diameter of 0.5 and observed thatvortex structures augment local Nusselt number near downstream

rim of each dimple. Burgess et al. [26] conducted an experimental

study to investigate effect of dimple depth on heat transfer with

aspect ratio of 8 and for Reynolds number range of 12,000–70,000

and reported that Nusselt number increases with increase in

dimple depth. Sang et al. [27] investigated heat transfer with

dimple/protrusion arrays in a rectangular duct with low Reynolds

number range and observed heat transfer enhancement of 14 and 7

times for double protrusion wall and double dimpled wall at Rey-

nolds number of 1000. However at high Reynolds number of

10,000, enhancement level observed was from 2 to 3. Chang et al.

[28] examined heat transfer characteristics for four sets of dimpled

channels with Reynolds number ranging from 1500 to 11,000 and

determined effect of dimpled arrangement, fin length to channelhydraulic diameter ratio and Reynolds number on heat transfer

over the dimpled fin channel. Varun et al. [29] also reported

different investigations on roughness geometries carried out in

heat exchangers as well as in air heaters. Application of artificial

roughness methodology in a solar air heater for improvement of

thermal performance owes its origin to these investigations.

4. Roughness geometries used in solar air heater ducts

In solar air heaters, artificial roughness in the form of fixingsmall diameter wires, machining ribs of different shapes, forming

dimples/protrusion have been investigated for enhancement of

heat transfer from the absorber plate. Although there are several

parameters that characterize the arrangement and shape of the

roughness elements; height (e) and pitch (P ) of roughness element

are the most important parameters. These are specified in non-

dimensional form as relative roughness height (e/D) and relative

roughness pitch (P /e) respectively. The other parameters include

Reynolds number, rib cross-section, angle of attack, chamfering and

combined turbulence promoters. Literature on application of arti-

ficial roughness in a solar air heater covers wide range of roughness

geometries for studying heat transfer and friction characteristics.

General arrangement of different types of roughness geometries

reported by various investigators can be divided into four cate-gories i.e. (i) wire fixation (ii) rib formation by machining process

(iii) wire mesh or expanded metal mesh fixation and (iv) dimple/

protrusion formation. These have been discussed in detail under

following sub-sections.

4.1. Wire fixation

Various investigators studied heat transfer enhancement and

friction loss by fixing protruding wires of different shape, size and

orientation as an artificial roughness element on absorber plate as

has been discussed below.

4.1.1. Transverse continuous ribs

Kays [30] suggested that by fixing small diameter protrusionwires perpendicular to flow direction on surface of absorber plate

may help to break laminar sub-layer. It was suggested that

protrusion wire diameter of yþ ¼ 50, spaced 10–20 times diameter

and placed within the laminar sub-layer are better than turbulence

promoters.

Prasad and Mullick [31] used three unglazed collector channels

placed side-by-side as shown in Fig. 2. Middle collector channel ‘B’

was plane GI sheet, channel ‘A’ was plane GI sheet having 24 gauge

GI wires soldered in transverse direction on its underside and

channel ‘C’ was corrugated with wires soldered on the underside of

absorber plate in the same way as in second channel. It is reported

that protruding wires improve plate efficiency factor from 0.63 to

0.72 resulting in 14% improvement in thermal performance.

Prasad and Saini [32,33] reported an experimental investigationof fully developed turbulent flow in a solar air heater duct having

small diameter protrusion wires fixed on absorber plate as shown

V - Down V - Up

AirAir

P

S

Fig. 6. Roughened absorber plate with staggered discrete V-apex up and down ribs.

Air

Wires P

Fig. 7. V-shape and transverse roughness elements on absorber plate.




in Fig. 3. Nusselt number and friction factor correlations were

developed by using experimental data. An enhancement in Nusselt

number and friction factor was observed over smooth duct of the

order of 2.38 and 4.25 times respectively corresponding to relative

roughness height of 0.033 and relative roughness pitch of 10.

Gupta et al. [34] reported effect of transverse wire roughness on

heat and fluid flow characteristics for solar air heater ducts with an

absorber plate having transverse wires fixed on its underside as

shown in Fig. 3 for Reynolds number range of 3000–18000, duct

aspect ratio of 6.8–11.5, relative roughness height of 0.018–0.052 at

a relative roughness pitch of 10 with a range of roughness Reynolds

number ðe=D ffiffiffiffiffiffiffiffiffiffiffiffiffi f =2Re

p Þ between 5 and 70. It is reported that Stanton

number increased initially with an increase in Reynolds number up

to 12,000 and registered a slight fall thereafter.

Verma and Prasad [35] reported effect of transverse wire

roughness on heat and fluid flow characteristics for three rectan-

gular solar air heaterducts; twowere roughened collectors and one

was a plane surface. Transverse wires were fixed on underside of

absorber plate as shown in Fig. 3. Investigations were carried out

for Reynolds number range of 5000–20,000 for high duct aspect

ratio, relative roughness height of 0.01–0.03 at a relative roughnesspitch of 10–40 and roughness Reynolds number range of 8–42. An

optimum value of thermohydraulic performance of about 71% has

been reported corresponding to roughness Reynolds number of 24.

4.1.2. Transverse broken ribs

Sahu and Bhagoria [36] reported effect of broken transverse ribs

on absorber plate of a solar air heater. Integral rib roughened

absorber plates were prepared by fixing wires of 1.5 mm diameter

over one side of absorber plate as shown in Fig. 4. Roughness

geometry was having pitch (P ) ranging from 10 to 30 mm, height of

rib (e) was 1.5 mm and duct aspect ratio was 8. Investigated range

of Reynolds number was 3000–12,000. Heat transfer coefficient

enhancement over smooth duct was reported to be 1.25–1.4 times

and maximum thermal efficiency of the order of 83.5% was

obtained.

4.1.3. Inclined and V-shaped or staggered ribs

Gupta et al. [37] established optimum design parameters under

actual climatic conditions for roughened solar air heaters for

varying relative roughness height (e/D) and for a relative roughness

pitch (P /e) of 10 at an angle of attack (a) of 60. Geometry of

roughened absorber plate is shown in Fig. 5. An enhancement of

heat transfer and friction factorwas obtained of the order of 1.8 and

2.7 times respectively. Maximum heat transfer coefficient and

friction factor values were obtained at an angle of attack of 60

respectively in the range of investigated parameters.

Muluwork et al. [38,39] compared thermal performance of

roughened absorber plate fixed with staggered discrete V-apex (up

and down) as shown in Fig. 6. It is reported that Stanton number

increased with an increase of relative roughness length ratio in the

range of 3–7. Reported Stanton number for V-down discrete ribs

was higher than the corresponding V-up and transverse discrete

roughened surfaces. Enhancement in Stanton number ratio was

found to be of the order of 1.32–2.47.

Momin et al. [40] investigated effect of geometrical parameters

on heat transfer and fluid flow characteristics of rectangular duct of

solar air heater having V-shaped ribbed roughness on the absorberplate as shown in Fig. 7. This experimental investigation covered

a Reynolds number range of 2500–18,000, relative roughness

height (e/D) of 0.02–0.034 and angle of attack (a) of 30–90 for

a fixed relative roughness pitch (P /e) of 10. It was reported that V-

shape ribs with an angle of attack (a) of 60 enhanced Nusselt

number by 1.14 and 2.30 times and friction factor by 2.30 and 2.83

times over inclined ribs and smooth plate respectively.

Karwa [41] investigated effect of inclined discrete and contin-

uous ribs on thermohydraulic performance of solar air heater for

Reynold number range of 2800–15,000, relative roughness height

Transverse

Inclined

V-up continuous

V- down continuous

V- down discrete

V-up discrete

Wire pieces

Air

P

Fig. 8. Roughened absorber plate with transverse, inclined discrete and continuous ribs.

d

d’

P

P

P

W

Air

L

Fig. 9. Roughness geometries in rectangular channel with transverse and V-shaped

broken ribs.

θ = 600

l

P Se = 2 mm

Air

Fig. 10. Roughness geometry in rectangular channel as grit shape ribs.

P

d d

d dd

W60

0

Continuous rib d/W = 0.16 d/W = 0.25

d/W = 0.33 d/W = 0.5 d/W = 0.67

Fig. 11. Roughness geometry as inclined non-continuous arrangement ribs.




of 0.0467–0.050, fixed relative roughness pitch of 10 and duct

aspect ratio of 7.19–7.75. Roughness geometries used in this

investigation are shown in Fig. 8. Stanton number and friction

factor correlations were developed. Enhancement in Stanton

number and friction factor over smooth duct was observed of the

order of 65–90% and 2.68–2.94 times respectively. It is reported

that 60 inclined rectangular ribs produce better results than

transverse ribs. It is also reported that enhancement in Stanton

number over smooth duct is 102–137%, 110–147%, 93–134% and

102–142% for rib arrangement of V-up continuous, V-down

continuous, V-up discrete and V-down discrete respectively.

Tanda [42] made investigations using Liquid Crystal Thermog-

raphy to obtain detailed distributions of heat transfer coefficient in

rib-roughened channels. The roughness geometries induced by

transverse continuous, transverse broken and V-shaped broken ribs

were deployed on a heated surface as shown in Fig. 9. The highest

value of enhanced Nusselt number was reported for the transverse

broken ribs having relative roughness pitch (P /e) value of 4. Large

increase in friction factor was induced by ribs as compared to the

smooth channel.

Karmare and Tikekar [43] developed heat transfer coefficient

and friction factor correlation for artificially roughened duct with

metal grit ribs as shown in Fig. 10. Effect of range of system

parameters of grit geometry on heat transfer coefficient and friction

factor was investigated for Reynolds number range of 4000–17,000.It is reported that plate having roughness parameters l/s ¼ 1.72,

e/D ¼ 0.044 and P /e ¼ 17.5 resulted optimum performance and as

compared to smooth duct yields up to two-fold enhancement in

Nusselt number and three-fold enhancement in friction factor.

Aharwal et al. [44] investigated effect of artificial roughness by

using an inclined non-continuous rib arrangement in a rectangular

duct shown in Fig. 11. Maximum enhancement in Nusselt number

and friction factor as compared to smooth duct was observed to be

2.59 and 2.87 times respectively.

Varun et al. [45] studied heat transfer and friction characteristics

by using a combination of inclined as well as transverse ribs as

shown in Fig. 12 for Reynolds number range of 2000–14,000. It is

reported that roughened absorber plate having relative roughness

pitch (P /e) of 8 resulted best performance.Saini and Saini [46] investigated effect of arc shaped ribs on heat

transfer and fluid flow characteristics of rectangular duct of solar air

heater as shown in Fig.13. This experimental investigation covered

a Reynolds number range of 2000–17,000, relative roughness

height (e/D) of 0.0213–0.0422 and relative angle of attack of flow

(a/90) of 0.3333–0.6666 for a fixed relative roughness pitch (P /e) of

10. Maximum enhancement in Nusselt number and friction factor

as compared to smooth duct was observed to be 3.6 and 1.75 times

respectively.

Lee et al. [47] investigated effect of aspect ratio on heat/mass

transfer in rectangular channels with two different V-shaped rib

configurations, which were continuous V-shaped rib configuration

with a 60

attack angle, and multiple (staggered) V-shaped ribconfiguration with a 45 attack angle. It is reported that the effectof

channel aspect ratio was more significant for the continuous 60 V-

shaped rib than for the multiple 45 V-shaped rib configuration.

4.2. Rib formation by machining process

Experimental investigations are reported in literature to study

heat transfer and friction characteristics by using integral ribs

generated on absorber plate by machining process. Different

shapes, sizes and orientation of ribs have been used to generate

artificial roughness on absorber plate by this method as discussed

in the following sub-sections.

4.2.1. Chamfered ribsKarwa et al. [48] proposed use of repeated integral chamfered

ribs to generate artificial roughness as shown in Fig. 14. Experi-

mental study was carried out by taking rib chamfer angles of 15,

0, 5, 10, 15 and 18 for a rectangular duct having aspect ratio of

4.8, 6.1, 7.8, 9.66 and 12 under a Reynolds numbers range of 3000–

20,000. Range of relative roughness heights (e/D) and relative

roughness pitch (P /e) was 0.0141–0.0328 and 4.5–8.5 respectively.

As compared to the smooth duct, artificial roughened duct yielded

up to about two and three times increase in the Stanton number

and friction factor respectively.

Karwa et al. [49] conducted experimental study under actual

climatic conditions by using repeated integral chamfered ribs as

P

W

L

600

Fig. 12. Roughness geometry as a combination of inclined and transverse ribs.

L

W

P

Air

Fig. 13. Roughness geometry in rectangular channel as arc shape ribs.

AirRib

Pw

e φ

Fig. 14. Integral chamfered rib roughness on absorber plate.

Glass Cover

Absorber Plate

Chamfered Rib

Back Insulation

Air

Qt

Qu

Ql

Ι (τα)

Fig.15. Integral chamfered rib roughness on absorber plate with fixed chamfer angle.




shown in Fig. 15. Investigated parameters were different from

Karwa et al. [48] i.e. relative roughness pitch (P /e) of 4.58 and 7.09,

rib chamfer angle fixed at 15, relative roughness height (e/D) for

three roughened plates was kept 0.0197, 0.0256 and 0.0441 for

a Reynolds number range of 3750–16,350. This study showed

enhancement in thermal efficiency (10–40%) over solar air heaters

with smooth absorber plates. Considerable enhancement in

pumping power requirement due to increase in pressure drop has

also been observed.

4.2.2. Wedge shaped ribs

Bhagoria et al. [50] investigated air heater rectangular duct

roughened by wedge shaped transverse integral ribs as shown in

Fig. 16 for Reynolds number range of 3000–18,000. Range of rela-

tive roughness height (e/D), relative roughness pitch (P /e) and rib

wedge angle (f) was 0.015–0.033, 60.17f1.0264< p/e < 12.12 and

8–15 respectively. Authors reported an enhancement in Nusselt

number and friction factor of the order of 2.4 and 5.3 times

respectively as compared to smooth duct.

4.2.3. Combination of different integral rib roughness elements

Jaurker et al. [51] reported an experimental investigation on

heat and fluid flow characteristics for fully developed turbulentflow in a rectangular duct having repeated integral transverse rib-

groove roughness as shown in Fig. 17 for Reynolds number range of

3000–21,000. Range of relative roughness height (e/D), relative

roughness pitch (P /e) and groove position to pitch ratio ( g /P ) was

0.0181–0.0363, 4.5–10.0 and 0.3–0.7 respectively.

Enhancement of Nusselt numberof the orderof 2.75 times of the

smooth duct and 1.57 times of ribbed duct with similar rib height

and rib spacing was observed. Whereas ribbed duct with similar rib

height and rib spacing provides Nusselt number values of the order

of 1.7 times that of smooth duct for range of parameters. On the

other hand friction factor increases in the order of 3.61 times that of

smooth duct and 1.17 times that of ribbed duct. Whereas a ribbed

duct with similar rib height and rib spacing results in friction factor

value of the order of 3 times that of the smooth duct.Layek et al. [52] investigated heat transfer and friction charac-

teristics of repeated integral transverse chamfered rib-groove

roughness as shown in Fig. 18 for a Reynolds number range of

3000–21,000, relative roughness pitch of 4.5–10, chamfer angle of

5–30, relative groove position of 0.3–0.6 and relative roughness

height of 0.022–0.04. Authors reported that Nusselt number and

friction factor increased by 3.24 times and 3.78 times respectively

as compare to smooth duct. Maximum enhancement of Nusselt

number and friction factor was obtained corresponding to relative

groove position of 0.4.

4.3. Wire mesh or expanded metal mesh ribs

Generation of artificial roughness on the absorber plate is

considered to be a cumbersome task and may not be economically

feasible for large scale production of solar air heaters for various

applications. In order to solve this problem up to some extent, few

experimental investigations based on wire mesh or expanded

metal mesh as roughness element are reported in literature.

Saini and Saini [53] used expanded metal mesh as roughness

geometry and obtained an enhancement of heat transfer coefficient

and friction factor of the order 4 and 5 times over the smooth duct

corresponding to an angle of attack of 61.9 and 72 respectively.

Roughness geometry investigated by Saini and Saini is shown in

Fig. 19.

Gupta et al. [54] conducted performance evaluation of artificial

roughness geometry of expanded metal mesh in terms of energy

augmentation ratio (EAR), effective energy augmentation ratio

(EEAR) and exergy augmentation ratio (EXAR) for a range of

parameters reported by Saini and Saini [53]. It was evident that l/e

of 40 resulted highest EXAR followed by l/e of 55.

4.4. Dimple/protrusion shaped geometry

Formation of dimples/protrusions on surface of absorber plate is

also considered to be a simple and economical methodology to

create artificial roughness. It is a subject of many recent experi-

mental investigations. Use of dimple shape roughness produced

augmented surface heat transfer levels as compare to channels

with smooth surfaces and at par with other artificial roughness

geometries. On the other hand pressure drop or friction loss usually

does not increase appreciably as compare to other rough channels.

Saini and Verma [55] investigated heat transfer and friction

characteristics of dimple shaped artificial roughness geometry

shown in Fig. 20 for Reynolds number 2000–12,000. Range of relative roughness height (e/D) and relative pitch ( p/e) was 0.018–

0.037 and 8–12 respectively. Authors reported that Nusselt number

and friction factor increased by 1.8 and 1.4 times respectively as

compared to smooth duct.

P

P

P

e φ

Fig. 16. Absorber plate having transverse wedge shaped rib roughness.

L

P

e

gRibs Groove

Fig. 17. Absorber plate having rib-grooved artificial roughness.

L

g

P

eAir

Fig. 18. Absorber plate having chamfered rib-grooved artificial roughness.

L

S

Expanded Metal Mesh

Air

Fig. 19. Expanded metal mesh fixed on absorber plate.




5. Discussion

It has been observed that regular roughness geometries being

used in solar air heaters are of many types depending upon shape,

size, arrangement and orientation of roughness elements on the

absorber plate. General arrangement of different types of rough-

ness geometries reported by the various investigators can be

divided into four categories i.e. (i) wire fixation (ii) rib formation by

machining process (iii) wire mesh or expandedmetal mesh ribs and

(iv) dimple/protrusion shaped geometry. In transverse fixed wire

ribs, penalty of friction is almost twice the enhancement of heat

transfer, whereas in inclined and V-shaped or staggered ribs,

increase in friction factor is at par or slightly more than enhance-

ment of Nusselt number except for arc shaped ribs. For machined

ribs, it is observed that friction penalty is approximately three-fold

and Nusselt number enhancement is two fold except chamfered

rib-groove combination where friction penalty and heat transfer

enhancement are almost at par. As for as wire mesh ribs are

P

d

e

Air

Fig. 20. Absorber plate with dimple-shaped geometry.

Table 1

Heat transfer coefficient and friction factor correlations for different roughness geometries used in solar air heater duct.

Roughnessgeometry

Author/s Rangeof parameters

Correlations

Heat transfer coefficient Friction factor

A. WIRES

1. Transverse

Small diameter

protrusion wire

Prasad and

Saini[32]

e/D: 0.020–0.033

p/e: 10–20

Re 103: 5–50

S t ¼ f =2=1 þ ffiffiffiffiffiffiffiffi f =2

p f4:5ðeþ Þ0:28Pr 0:57

0:95ð p=eÞ0:53o f r ¼ 2=½0:95ð p=eÞ0:53 þ 2:5 lnðD=2eÞ 3:752

Small dia. Transverse

protrusion wire

Gupta

et al. [34]

e/D: 0.018–0.052

Re: 3000–18,000

Nu ¼ 0:000824ðe=DÞ0:178ðW =H Þ0:284

ðReÞ1:062e 35

f ¼ 0:06412ðe=DÞ0:019ðW =H Þ0:0237ðReÞ0:185

Nu ¼ 0:00307ðe=DÞ0:469ðW =H Þ0:245

ðReÞ0:812e 35

Small dia. Transverseprotrusion wire

Verma andPrasad [35]

e/D: 0.01–0.03 p/e: 10–40

eþ: 8–42

Re: 5000–20,000

Nur ¼ 0:08596ð p=eÞ0:054

ðe=DÞ0:072Re0:723e 24

f r ¼ 0:0245ð p=eÞ0:0206ðe=DÞ0:021Re1:25

Nur ¼ 0:0245ð p=eÞ0:016

ðe=DÞ0:021Re0:802e 24

2. V-Shaped/Inclined

Wire Ribs

Inclined wire ribs Gupta et al. [56] e/D: 0.02–0.053

Re: 5000–30,000

a: 30–90

p/e: 7.5–10

Nu ¼ 0:000824ðe=DÞ0:178ðW =H Þ0:284ðReÞ1:062

exph

0:04ð1 a=60Þ2i

ðk=DÞe 35

f ¼ 0:06412ðe=DÞ0:019ðW =H Þ0:0237

ðReÞ0:185exph

0:0993ð1 a=70Þ2i

Nu ¼ 0:00307ðe=DÞ0:469ðW =H Þ0:245ðReÞ0:812

exph 0:475ð1 a=60Þ2

iðk=DÞe 35

V-Shaped staggered

discrete wire ribs

Muluwork

et al. [38,39]

e/D: 0.02

a: 60

B/S: 3–9

Re: 2000–15,500

Nur ¼ 0:00534 Re1:2991ð p=sÞ1:3496 f r ¼ 0:7117Re2:991ð p=sÞ0:0636

V-shaped continuous

Wire ribs

Momin

et al. [40]

e/D: 0.02–0.034

p/e: 10

a: 30–90

Re: 2500–18,000

Nur ¼ 0:067Re0:888ðe=DÞ0:424ða=60Þ0:077

exph

0:0782flnða=60Þg2i f r ¼ 6:266 Re0:425ðe=DÞ0:565ða=60Þ0:093

exph

0:719flnða=60Þg2i

G ¼ 103:77e 0:006ðW =H Þ0:5ð p=eÞ2:56

exph

0:7343flnð p=eÞg2i

ðeþÞ0:31

(continued on next page)




Table 1 (continued ).

Roughness

geometry

Author/s Range

of parameters

Correlations


Inclined discrete

and continuous

wire ribs

Karwa [41] e/Dh: 0.0467–0.05

p/e: 10

a: 60–90

B/S: 3

W /H : 7.19–7.75

G ¼ 32:26e0:006ðW =H Þ0:5 ð p=eÞ2:56

exph


eþ0:08

For 7 eþ < 20 R ¼ 1:66e00078ðW =H Þ0:4

ð p=eÞ2:695exph

0:762 flnð p=eÞg2

ðeþÞ0:075

i

Transverse continuous,

Transverse broken

and V-shaped

broken wire ribs

Tanda [42] p/e: 4813.3

e/H : 0.15, 0.25

a: 45, 60 & 90

e: 3 mm, 5 mm

Nuo ¼ 0:023Re0:8o Pr 0:4 For 20 eþ 60 R ¼ 1:325e0:0078 ðW =H Þ0:4

ð p=eÞ2:695exp½ 0:762flnð p=eÞg2

Reo ¼ ð21:74 f Re3Þ0:357 f o ¼ 0:046Re0:2o

Grid shaped wire ribs Karmare and

Tikekar [43]

e/Dh: 0.035–0.044

p/e: 12.5–36

l/s: 1.72–1

Re: 4000–17,000

Nu ¼ 2:4 ðReÞ1:3 ðe=DhÞ0:42

ðl=sÞ0:146ð p=eÞ0:27

f ¼ 15:55 ðReÞ0:26

ðe=DhÞ0:94ðl=sÞ0:27 ð p=eÞ0:51

Gap in an inclined

continuous

wire ribs

Aharwal

et al. [44]

p/e: 10

e & b: 2 mm

e/Dh: 0.0377

W /H : 5.87

Re: 3000–18,000

d/W : 0.167–0.5

(4 steps)a: 60

g /e: 0.5–2 (4 steps)

Nu=Nus ¼ 2:59 f = f s ¼ 2:87

Arc shaped

wire ribs

Saini and

Saini [46]

Re: 2000–17000

p/e: 10

W /H : 12

e/D: 0.0213–0.0422

a/90: 0.333–0.666

Nu ¼ 0:001047Re1:3186

ðe=DÞ0:3772ða=90Þ0:1198

f ¼ 0:14408Re0:17103ðe=DÞ0:1765 ða=90Þ0:1185

B. WIRE MESH

Expanded

metal mesh

Saini and

Saini [53]

Re: 1900–13000

e/D: 0.012–0.0390

L/e: 25–71.87

S /e: 15.62–46.87

Nur ¼ 4:0 104 Re1:22ðe=DÞ0:625ðs=10eÞ2:22

exph

1:25flnðs=10eÞg2i

ðl=10eÞ2:66

exph

0:824flnðl=10eÞg2i

f r ¼ 0:815Re0:361ðl=eÞ0:266ðs=10eÞ0:19ð10e=DÞ0:591

C. MACHINED RIBS

Chamfer ed r ibs Karwa et al.

[48,49]

Re: 3000–20000

e/D: 0.014–0.0320

p/e: 4.5–8.5

f: 15,0, 5, 10,

15 & 18

W /H : 4.8, 6.1, 7.8,

9.66, 12.0

G ¼ 103:77e0:006ðW =H Þ0:5ð p=eÞ2:56

exph


eþ0:31

For 7 eþ < 20 R ¼ 1:66e00078ðW =H Þ0:4

ð p=eÞ2:695exph

0:762flnð p=eÞg2

eþ0:075i

For 7 eþ < 20

G ¼ 32:26 e0:006ðW =H Þ0:5ð p=eÞ2:56

exph


eþ0:08

For 20 eþ 60 R ¼ 1:325e0:0078

ðW =H Þ0:4 ð p=eÞ2:695exph

0:762flnð p=eÞg2i

For 20 eþ 60

Wedge

shaped ribs

Bhagoria

et al. [50]

e/D: 0.015–0.033

p/e:

60.17f1.0264<

p/e< 12.12

f: 8, 10, 12, 15

Re: 3000–18,000

Nur ¼ 1:89 104 Re1:21ðe=DÞ0:426ð p=eÞ2:94

exp½0:71flnð p=eÞg2 ðf=10Þ0:018i

exph

1:5flnð==10Þg2i

f r ¼ 12:44 Re0:18ðe=DÞ0:99ð p=eÞ0:52ðf=10Þ0:49

Rib-Groove

combination

Jaurkar

et al. [51]

e/D: 0.0181–0.0363

p/e: 4.5–10 exp[1.513

{ln( g / p)2}

þ 0.8662{ln( g / p)3}]

Re: 3000–21,000

g / p: 0.3–0.7

Nur ¼ 0:002062Re0:936ðe=DÞ0:349ð p=eÞ3:318

exp½ 0:868flnð p=eÞg2 ð g = pÞ1:108

exph

2:486n

lnð g = pÞ2o

þ1:406n

lnð g = pÞ3oi

f r ¼ 0:001227Re0:199ðe=DÞ0:585

ð p=eÞ7:19exph

1:854flnð p=eÞg2i

ð g = pÞ0:645exph

1:513n

lnð g = pÞ2o

þ 0:8662n

lnð g = pÞ3oi




concerned, heat transfer enhancement is more than first two arti-

ficial roughness categories, but increase in friction loss is found

more than heat transfer enhancement. In dimpled/protrusion rib

geometry it is observed that friction penalty is less as compare to

heat transfer enhancement. Very little work is reportedin literature

to use this roughness geometry for solar air heaters.

It hasalso beenobservedthat generationof artificial roughness on

absorber plate is a tedious task andmay not be economically feasible

for large scale production of solar air heaters for various applications.

A suitable geometry of roughness element therefore needs to be

selected, whichbesides being easilyavailable should be easy to fixor

fabricate on the absorber plate and also gives substantial enhance-

ment in heat transfer coefficient at low friction penalty.

6. Conclusion

In the present paper an attempt has been made to report heat

transfer and friction characteristics of artificially roughened duct of

solar air heaters. Methodology of artificial roughness and experi-

mental studies carried out by various investigators have been dis-

cussed and reported in detail.It is observed that artificial roughness

is a good technique to improve thermal performance of solar air

heaters. Heat transfer coefficient and friction factor correlations

reported in literature are presented in tabular form. Information

provided in the present paper may be useful to the beginners in this

area of research (Table 1).

References

[1] Garg HP, Prakash J. Solar energy fundamentals and applications. New Delhi:Tata McGraw-Hill; 1997.

[2] Duffie JA, Beckman WA. Solar engineering of thermal processes. New York:Wiley; 1980.

[3] Frank K, Mark SB. Principles of heat transfer. Colorado: Thomson Learning Inc;2001.

[4] Bergles AE, Webb RL, Junkan GH. Energy conservation via heat transferenhancement. Energy 1979;4:193–200.

[5] Mittal MK, Varun, Saini RP, Singal SK. Effective efficiency of solar air heatershaving different types of roughness elements on the absorber plate. Energy2007;32:739–45.

[6] Webb RL, Eckert ERG. Heat transfer and friction in tubes with repeated-ribroughness. Int J Heat Mass Transf 1971;14:601–17.

[7] Lewis MJ. Optimizing the thermohydraulic performance of rough surfaces. Int

J Heat Mass Transf 1975;18:1243–8.

[8] Ravigururajan TS, Bergles AE. General correlations for pressure drop and heattransfer for single-phase turbulent flow in internally ribbed tubes augmen-tation of heat transfer in energy systems. HTD 52. New York: ASME; 1985.pp. 9–20.

[9] Han JC, Glicksman LR, Rohsenow WM. Heat transfer and friction for ribroughened surfaces. Int J Heat Mass Transf 1978;21:1143–56.

[10] Han JC. Heat transfer and friction in channels with opposite rib roughenedwalls. Trans ASME J Heat Transf 1984;106:774–81.

[11] Han JC, Park JS. Developing heat transfer in a rectangular channel with ribturbulators. ASME J Heat Transf 1988;31:183–95.

[12] Han JC, Ou S, Park JS, Lei CK. Augmented heat transfer in rectangular channelsof narrow aspect ratio with rib turbulators. Int J Heat Mass Transf 1989;32:1619–30.

[13] Han JC, Zhang YM, Lee CP. Influence of surface heat flux ratio on heat transferaugmentation in square channel with parallel, crossed and V-shaped angled

ribs. ASME J Turbomachinery 1994;114:872–80.[14] Liou TM, Hwang JJ. Effect of ridge shapes on turbulent heat transfer and

friction in a rectangular channel. Int J Heat Mass Transf 1993;36:931–40.[15] Lau SC, Kukreja RT, McMillin RD. Effects of V shaped rib arrays on turbulent

heat transfer and friction of fully developed flow in a square channel. Int J HeatMass Transf 1991;34:1605–16.

[16] Taslim ME, Li T, Kercher DM. Experimental heat transfer and friction inchannels roughened with angled, V-shaped and discrete ribs on two oppositewalls. ASME J Turbomachinery 1996;118:20–8.

[17] Olsson CO, Sunden B. Thermal and hydraulic performance of a rectangularduct with multiple V-shaped ribs. Trans ASME 1998;120:1072–7.

[18] Gao X, Sunden B. Heat transfer and pressure drop measurements in ribroughened rectangular ducts. Exp Therm Fluid Sci 2001;24:25–34.

[19] Hu Z, Shen J. Heat transfer enhancement in a converging passage with discreteribs. Int J Heat Mass Transf 1996;39(8):1719–27.

[20] Cho HH, Wu SJ, Kwon HJ. Local heat/mass transfer measurement in a rectan-gular duct with discrete ribs. J Turbomachinery 2000;122:579–86.

[21] Chyu MK, Yu Y, Ding H, Downs JP, Seochting F. Concavity enhanced heattransfer in an internal cooling passage. ASME 42nd international gas turbine

and aero congress; 1997 paper no. 97-GT-437.[22] Chyu MK, Yu Y, Ding H, Downs JP, Seochting F. Heat transfer enhancement in

rectangular channels with concavities. Enhanced Heat Transf 1999;6:429–39.[23] Moon HK, O’Connell T, Glezer B. Channel height effect on heat transfer and

friction in a dimpled passage. ASME J Eng Gas Turbines Power2000;122(2):307–13.

[24] Mahmood GI, Hill ML, Nelson DL, Ligrani PM, Moon HK, Glezer B. Local heattransfer and flow structure on and above a dimpled surface in a channel.ASME Trans Turbomachinery 2001;123:115.

[25] Mahmood GI, Ligrani PM. Heat transfer in a dimpled channel: combinedinfluences of aspect ratio, temperature ratio, Reynold number and flowstructure. Int J Heat Mass Transf 2002;45:2011–20.

[26] Burgess NK, Oliveira MM, Ligrani PM. Nusselt number behaviour on deepdimpled surfaces within a channel. J Heat Transf 2003;125:11–8.

[27] Sang DH, Hyun GK, Hyung HC. Heat transfer with dimple/protrusion arrays ina rectangular duct with low Reynold number range. Int J Heat Fluid Flow2008;29:916–26.

[28] Chang SW, Chiang KF, Yang TL, Huang CC. Heat transfer and pressure drop in

dimpled fin channels.Experimental thermal and fluidscience 2008;33(1):23–40.

Table 1 (continued ).

Roughness

geometry

Author/s Range

of parameters

Correlations


Chamfered

rib-groove

combination

Layek

et al. [52]

Re: 3000–21,000

e/Dh: 0.022–0.04

P /e: 4.5–10

g /P : 0.3–0.6

f: 5–30

Nu ¼ 0:00225Re0:92ðe=DÞ0:52

ð p=eÞ1:72ð g = pÞ1:21f1:34

h

expn

0:22ðlnfÞ2oi

hexp

n 0:46ðln p=eÞ

2oi

h

expn

0:74ðln g = pÞ2oi

f ¼ 0:00245Re0:124ðe=DÞ0:365ð p=eÞ4:32

ð g = pÞ1:134½exp 0:005fh

expn

1:09ðln p=eÞ2oi

hexpn 0:68ðln g = pÞ2

oi

D. DIMPLED RIBS

Dimpled ribs Saini and

Verma [55]

Re: 2000–12000

e/D: 0.018–0.037

P/e: 8–12

Nu ¼ 5:2 104Re1:27ð p=eÞ3:15

h

expð2:21Þflogð p=eÞg2i

ðe=DÞ0:033

h

expð1:30Þflogðe=DÞg2i

f e ¼ 0:0642Re0:423ð p=eÞ0:465

h

expð0:054Þflogð p=eÞg2i

ðe=DÞ0:0214

h

expð0:840Þflogðe=DÞg2i




[29] Varun, Saini RP, Singal SK. A review on roughness geometry used in solar airheaters. Sol Energy 2007;81:1340–50.

[30] Kays WB. Convective heat and mass transfer. New York: McGraw Hill Book Co;1966. pp. 197–8.

[31] Prasad K, Mullick SC. Heat transfer characteristics of a solar air heater used fordrying purposes. Appl Energy 1983;13(2):83–93.

[32] Prasad BN, Saini JS. Effect of artificial roughness on heat transfer and frictionfactor in a solar air heater. Sol Energy 1988;41(6):555–60.

[33] Prasad BN, Saini JS. Optimal thermo hydraulic performance of artificiallyroughened solar air heaters. Sol Energy 1991;47(2):91–6.

[34] Gupta D, Solanki SC, Saini JS. Heat and fluid flow in rectangular solar air heaterducts having transverse rib roughness on absorber plates. Sol Energy1993;51(1):31–7.

[35] Verma SK, Prasad BN. Investigation for the optimal thermo hydraulic perfor-mance of artificially roughened solar air heaters. Renew Energy2000;20:19–36.

[36] Sahu MM, Bhagoria JL. Augmentation of heat transfer coefficient by using 90

broken transverse ribs on absorber plate of solar air heater. Renew Energy2005;30:2057–63.

[37] Gupta D, Solanki SC, Saini JS. Thermo hydraulic performance of solar airheaters with roughened absorber plates. Sol Energy 1997;61(1):33–42.

[38] Muluwork KB, Saini JS, Solanki SC. Studies on discrete rib roughened solar airheaters. In: Proceedings of National Solar Energy Convention, Roorkee; 1998.pp. 75–84.

[39] Muluwork KB. Investigations on fluid flow and heat transfer in roughenedabsorber solar heaters. Ph.D. Thesis, IIT, Roorkee; 2000.

[40] Momin AME, Saini JS, Solanki SC. Heat transfer and friction in solar air heaterduct with V-shaped rib roughness on absorber plate. Int J Heat Mass Transf 2002;45:3383–96.

[41] Karwa R. Experimental studies of augmented heat transfer and friction inasymmetrically heated rectangular ducts with ribs on the heated wall intransverse, inclined, v-continuous and v-discrete pattern. Int Comm HeatMass Transf 2003;30(2):241–50.

[42] Tanda G. Heat transfer in rectangular channels with transverse and V-shapedbroken ribs. Int J Heat Mass Transf 2004;4:229–43.

[43] Karmare SV, Tikekar AN. Heat transfer and friction factor correlation forartificially roughened duct with metal grit ribs. Int J Heat Mass Transf 2007;50:4342–51.

[44] Aharwal KR, Gandhi BK, Saini JS. Experimental investigation on heat-transferenhancement due to a gap in an inclined continuous rib arrangement ina rectangular duct of solar air heater. Renew Energy 2008;33:585–96.

[45] Varun, Saini RP, Singal SK. Investigation of thermal performance of solar airheater having roughness elements as a combination of inclined and transverseribs on the absorber plate. Renew Energy 2008;33:1398–405.

[46] Saini SK, Saini RP. Development of correlations for Nusselt number and frictionfactor for solar air heater with roughened duct having arc-shaped wire asartificial roughness. Sol Energy 2008;82:1118–30.

[47] Lee DH, Rhee D, Kim KM, Cho HH, Moon HK. Detailed measurement of heat/

mass transfer with continuous and multiple V-shaped ribs in rectangularchannel. Energy 2009;34(11):1770–8.

[48] Karwa R, Solanki SC, Saini JS. Heat transfer coefficient and friction factorcorrelations for the transitional flow regime in rib-roughened rectangularducts. Int J Heat Mass Transf 1999;42:1597–615.

[49] Karwa R, Solanki SC, Saini JS. Thermo-hydraulic performance of solar airheaters having integral chamfered rib roughness on absorber plates. Energy2001;26:161–76.

[50] Bhagoria JL, Saini JS, Solanki SC. Heat transfer coefficient and friction factorcorrelations for rectangular solar air heater duct having transverse wedgeshaped rib roughness on the absorber plate. Renew Energy 2002;25:341–69.

[51] Jaurker AR, Saini JS, Gandhi BK. Heat transfer and friction characteristics of rectangular solar air heater duct using rib-grooved artificial roughness. SolEnergy 2006;80(8):895–907.

[52] Layek A, Saini JS, Solanki SC. Second law optimization of a solar air heaterhaving chamfered rib-groove roughness on absorber plate. Renew Energy2007;32:1967–80.

[53] Saini RP, Saini JS. Heat transfer and friction factor correlations for artificiallyroughened ducts with expended metal mesh as roughness element. Int J HeatMass Transf 1997;40(4):973–86.

[54] Gupta MK, Kaushik SC. Performance evaluation of solar air heater havingexpanded metal mesh as artificial roughness on absorber plate. Int J Therm Sci2009;48:1007–16.

[55] Saini RP, Verma J. Heat transfer and friction factor correlations for a ducthaving dimple-shape artificial roughness for solar air heaters. Energy2008;33:1277–87.

[56] Gupta D. Investigations on fluid flowand heat transfer in solar air heaters withroughened absorbers. Ph.D. Thesis, University of Roorkee, India; 1994.


a review on methodology of artificial roughness used in duct- brij bhushan

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