View of CFD BASED PERFORMANCE OF ARTIFICIALLY ROUGHENED SOLAR AIR HEATER - A REVIEW

(1)

ACCENT JOURNAL OF ECONOMICS ECOLOGY & ENGINEERING Peer Reviewed and Refereed Journal IMPACT FACTOR: 2.104 (ISSN NO. 2456-1037) Vol.03, Issue 09, Conference (IC-RASEM) Special Issue 01, September 2018 Available Online: www.ajeee.co.in/index.php/AJEEE

1

CFD BASED PERFORMANCE OF ARTIFICIALLY ROUGHENED SOLAR AIR HEATER - A REVIEW

Arun Kumar Yadav¹& Dr. Anil Singh Yadav²

1Assistant Professor, Mechanical Engineering Department, Sagar Institute of Research and Technology, Indore, MP.

2Professor, Mechanical Engineering Department, LaxmiNarain College of Technology Excellence, Bhopal, MP.

Abstract: Solar air heaters, because of their simplicity are cheap and most widely used collection devices of solar energy, has great potential for low temperature applications, particularly for drying of agricultural products. The thermal efficiency of a solar air heater is significantly low because of the low value of the convective heat transfer coefficient between the absorber plate and the air, leading to high absorber plate temperature and high heat losses to the surroundings. The objective of this article is to present a detailed review of the literature that deals with the application of CFD in the design of solar air heater. Solar air heater is one of the basic equipment through which solar energy is converted into thermal energy.

Keywords: Solar Energy, Solar Air Heater, Heat transfer, Pressure Drop, CFD I. INTRODUCTION

The demand of energy is growing rapidly today, and it is not possible to meet the future demand with the present available exhaustible energy sources. So, the technology is focusing on harnes- sing new and renewable sources of energy.

Furthermore, the conventional energy sources are causing an alarming health hazard to the planet life. The use of solar energy is an intelligent option for the use of mankind which is available free of cost, in abundant and is aclean source for various applications [1].

A solar collector absorbs incident solar radiations and transforms them into useful heat for heating the collector fluid such as water and air. Solar air heaters, being inherently simple and cheap, are most widely used collection devices. Solar air heaters find several applications in space heating, seasoning of timber and crop drying. Efficiency of flat plate solar air heater is low because of low convective heat transfer coefficient between absorber plate and flowing air which in turn increases the absorber plate temperature, leading to higher heat losses to the environment. The low value of heat transfer coefficient is generally attributed to the presence of a viscous sublayer, which can be broken by providing artificial roughness on the heat- transferring surface. Due to this artificial roughness, turbulent flow is created which helps in better enhancement of heat transfer.

Different parameters used in artificial roughened rib analysis are:

a) Relative roughness pitch (p/e): It is proportion of distance between adjacent ribs and rib height.

b) Relative roughness height (e/D): It is proportion of rib height to air passage equivalent diameter.

c) Pitch: Distance between starting points of two adjacent ribs.

d) Angle of attack: It is inclination provided to rib with respect to direction of flow in solar air heater duct.

e) Aspect ratio: It is proportion of width of duct to height of duct.[2].

Fig. 1.Solar air heater [3].

II. CFD Modeling and Analysis

Computational Fluid Dynamics (CFD) is the science of determining numerical solution of governing equation for the fluid flow whilst advancing the solution through space or time to obtain a numerical description of the complete flow field of interest. The equation can represent steady or unsteady, Compressible or Incompressible, and in

(2)

2 viscid or viscous flows, including non- ideal and reacting fluid behaviour. The particular form chosen depends on intended application. The state of the art is characterized by the complexity of the geometry, the flow physics, and the computing time required obtaining a solution.

The 2-D computational domain used for CFD analysis having the height (H) of 20 mm and width (W) 100 mm and length of 461 mm as shown in Fig. 2. In the present analysis, a 2-dimensional computational domain of artificially roughened solar air heater has been adopted which is similar to computational domain of Yadav and Bhagoria [4].

Fig. 2 computational domain

Yadav and Bhagoria [5] conducted a numerical prediction to study only heat transfer behavior of a rectangular duct of a solar air heater having triangular rib roughness on the absorber plate. Yadav and Bhagoria [6] presented the numerical prediction of fluid flow and heat transfer in a conventional solar air heater by CFD.

A commercial finite volume package ANSYS FLUENT 12.1 was used to analyze the nature of the flow across the duct of a conventional solar air heater. Yadav and Bhagoria [7] presented a detailed literature survey about different CFD investigations on artificially roughened solar air heater. The aim of our study is to improve the prediction of the flow in the solar air heater. A near-wall function for TKE will be implemented in Computational Fluid Dynamics code Fluent. Second order upwind and SIMPLE algorithm were used to discretize the governing equations. The FLUENT software solves the following mathematical equations which governs fluid flow, heat transfer and related phenomena for a given physical problem.

III. ARTIFICIAL ROUGHNESS GEOMETRIES USED BY RESERARCHERS Table 1

Summary of major experimental works on artificially roughened solar air heater having different roughness geometries applied on the absorber plate.

S.

No. Researcher’s Roughness geometry Range of parameters Principal findings 01 Singh et al. [8] Discrete V-down rib

roughness d/w: 0.2–0.8

e/D: 0.015–0.0.043 g/e: 0.5–2.0 P/e: 4–12 Re: 3000–15,000

3.04 and 3.11 times enhancement in Nusselt number and friction factor respectively were reported over smooth duct.

02 Karwa et al. [9] Chamfered repeated

rib-roughness e/D: 0.014–0.032 L/D: 32 & 66 P/e: 4.5–8.5 Re: 3000–20,000

2 and 3 times enhancement in Stanton number and friction factor respectively were reported over smooth duct.

03 Saini and Saini [10] Arc shaped rib

roughness e/d: 0.0213–0.0422 P/e: 10

Re: 2000–17,000 W/H: 12

a/90: 0.3333–0.6666

04 Sethi et al. [11] Dimple shaped elements arranged in angular fashion

e/D: 0.021–0.036 e/d: 0.5

P/e: 10–20 Re: 3600–18,000 W/H: 11 a: 45˚–75˚

The maximum value of Nusselt number was reported over smooth duct for P/e = 10 and e/D = 0.036.

05 Tanda [12] Angled continuous rib, transverse continuous and broken rib, and discrete V-shaped rib roughness

e/D: 0.09 e: 3mm P/e: 6.66–20 Re: 5000–40,000 W/H: 5

a: 45˚ & 60˚

Roughening the heat transfer surface by transverse broken ribs was found to be the most promising enhancement technique of the investigated rib geometries.

06 Lanjewar et al. [13] W-shaped rib

roughness e/D: 0.018–0.03375 e: 0.8–1.5 mm P/e: 10

Re: 2300–14,000 W/H: 8

(3)

3

a: 30˚–75˚

07 Hans et al. [14] Multi V-shaped rib roughness

e/D: 0.019–0.043 a: 30˚–75˚

Re: 2000–20,000 W/w: 1–10 P/e: 6–12

6 and 5 times enhancement in Nusselt number and friction factor respectively were reported over smooth duct.

IV. CONCLUSION

Increase in thermal efficiency of solar air heater is noticed by using Artificial Roughness Rib. Heat transfer coefficient in solar air heater with roughned rib depend upon performance parameters likes, Relative roughness pitch,relative roughness height, angle of attack and shape of roughned rib. An improvement in Nusselt number and friction factor is noticed by several researchers with the use of artificial roughness element. The effect of relative roughness pitch and Reynolds number on the heat transfer coefficient and friction factor have been studied. CFD Investigation has been carried out in medium Reynolds number flow (Re = 3800–18,000). Based on the CFD investigations of heat and fluid flow in a rectangular duct with protrusions as roughness element on one broad wall subjected to a uniform heat flux the following conclusions were drawn.

REFERENCES

1. Hsieh JS. Solar energy engineering. New Jersey: Prentice Hall; 1986..

2. B. Bhushan, R. Singh, Nusselt number and friction factor correlations for solar air heater duct having artificial roughened absorber plate, Solar Energy 85 (2011) 1109–1118.

3. A.K. Patil, J.S. Saini, K. Kumar, “A Comprehensive Review on Roughness Geometries and Investigation TechniquesUsed in Artificially Roughened Solar Air Heaters.” International Journal of Renewable Energy Research, pp 1-15, 2012.

4. A.S. Yadav, J.L. Bhagoria. A CFD based heat transfer and fluid flow analysis of a solar air heater provided with circular transverse wire rib roughness on the absorber plate, Energy, Elsevier, 55 (2013) 1127-1142.

5. A.S. Yadav, J.L. Bhagoria, A CFD analysis of a solar air heater having triangular rib roughness on the absorber plate, International Journal of ChemTech Research 5(2) (2013) 964-71.

6. A.S. Yadav, J.L. Bhagoria, A CFD based heat transfer and fluid flow analysis of a conventional solar air heater, Journal of Engineering Science and Management Education (2013), (Article in press).

7. A.S. Yadav, J.L. Bhagoria, Heat transfer and fluid flow analysis of solar air heater: a review of CFD approach, Renewable and Sustainable Energy Reviews 23 (2013) 60- 79.

8. 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.

9. R. Karwa, S.C. Solanki, J.S. Saini, Heat transfer coefficient and friction factor correlations for the transitional flow regime in rib roughened rectangular ducts, Int. J.

Heat Mass Transfer 42 (1999) 1597–1615.

10. 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, Solar Energy 82 (2008) 1118–1130.

11. M. Sethi, N.S. Varun, Thakur, Correlations for solar air heater duct with dimpled shape roughness elements on absorber plate, Sol. Energy 86 (2012) 2852–2861.

12. G. Tanda, Performance of solar air heater ducts with different types of ribs on the absorber plate, Energy 36 (2011) 6651–

6660.

13. A. Lanjewar, J.L. Bhagoria, R.M. Sarviya, Heat transfer and friction in solar air heater duct with W-shaped rib roughness on absorber plate, Energy 36 (2011) 4531–

4541.

14. V.S. Hans, R.P. Saini, J.S. Saini, Heat transfer and friction factor correlations for a solar air heater duct roughened artificially with multiple V-ribs, Sol. Energy 84 (2010) 898–911.