International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395 -0056 Volume: 02 Issue: 09 | Dec-2015 www.irjet.net p-ISSN: 2395-0072 © 2015, IRJET ISO 9001:2008 Certified Journal Page 2181 W-Discrete Rib for Enhancing the Thermal Performance of Solar Air Heater Alok Kumar Rohit 1 , A.M. Lanjewar 2 1 PhD Scholar, Mechanical Engineering Department, AISECT University Bhopal, M.P. - 462024 India 2 Assistant Professor Maulana Azad National Institute of Technology, Bhopal, M.P. – 462003, India Abstract - For the maximum efficiency of solar air heater it is necessary to enhance convective heat transfer coefficient with the help of artificial roughness in the form of repeated ribs. Experimental investigation on W-shaped ribs deals with the enhancement of Nusselt number which can be further enhanced beyond that of W-shaped ribs geometry while keeping minimum penalty of friction factor. W-discrete ribs with high-aspect-ratio rectangular duct give high performance heat transfer rate as compare to previous investigations. By using W-discrete ribs enhancement of heat transfer rate with respect to relative roughness height (e/Dh) is shown in this paper. The investigation is based on the following flow parameters that is Reynolds number (Re) from 4000 – 14500, relative roughness length (B/S) as 6, relative roughness pitch (p/e) as 10, relative roughness height (e/D) as 0.033753- 0.02250, angle of attack ȋαȌ range of 60 o . The duct has aspect ratio (AR) of 8. Key Words: Relative roughness height, Solar air duct, Thermal efficiency 1. INTRODUCTION A lot of active and passive techniques have been applied to enhance the thermal efficiency of solar air heater with minimum power consumption of fan and blower. For the enhancement of convective heat transfer coefficient and for minimum friction factor flow structure variation are achieved with the help of roughened wire orientation and geometry, pitch and relative roughness height. Angle of attack ȋαȌ, relative roughness pitch ȋp/eȌ and relative roughness height (e/D) these are the important parameter necessary for finding the heat transfer rate. An experimental investigation is performed to know about heat transfer, thermo hydraulic performance and friction factor of W-discrete ribs in the form of artificial roughness of solar air heater. A strict procedure is followed while testing with one roughened wall heated and keeping another three insulated. Under similar flow and thermal boundary condition the heat transfer coefficient and friction factor is found and thermo hydraulic performance of duct is presented. Han et. al. [1] studied rib pattern in V- down and V-up pattern on two opposite wall. Heating condition maintained at all four wall heated and he concluded that with parameter of W/H =1 , Re= 1.5 10 4 – 9 x 10 4 , e/ Dh = Ͳ.Ͳ͸ʹͷ , P/e = ͳͲ , α = 45 o & 60 o V-up pattern give better performance than V-down pattern. Karwa [2] worked on transverse, incline, V-continuous, V-discrete rib in both V-up and V-down pattern on one broad wall. Roughened wall heated by taking the parameter of