Heat Transfer and Friction Characteristics of V Rib with Symmetrical Gaps Roughened Solar Air Heater

Abstract

newline Solar air heaters systems are cheap and easy to maintain, but accompanies a disadvantage of low thermal efficiency because of low heat transfer coefficient between absorber plate and air in the duct. The application of sixty degree V ribs with symmetrical gaps wire roughness in a solar air heater appears to be worth for enhancing the performance of a solar air heater. It has been, therefore, taken up to investigate the effect of geometrical parameters of V ribs with symmetrical gap on the heat transfer and friction factor of the roughened duct. newline An experimental setup was designed and fabricated, and extensive experiments were conducted on a rectangular duct using an open loop with one broad wall of the duct heated with constant heat flux and roughened with V ribs with symmetrical gaps to investigate its heat transfer and friction characteristics. The range of roughness geometry and flow parameters considered in this experimental investigation are Reynolds number from 4000 to 18000, Number of gaps from 1 to 5, relative gap width from 1 to 5, Relative roughness pitch from 6 to 12 and Angle of attack from thirty to sixty degree. newline The V ribs with symmetrical gaps wire roughness duct with number of gaps of 3, relative gap width of 4, relative roughness height of 0.043, relative roughness pitch of 10 and angle of attack of sixty degree showed the maximum value of Nusselt number which was 3.67 times greater than that of the smooth duct. Similarly, the maximum value of the friction factor of V ribs with symmetrical gaps wire roughness duct was of the order of 3.67 times that of smooth duct. newlineThe correlations for Nu and f in terms of roughness and operating parameters are developed. It has been observed that on the basis of thermal efficiency criterion, a single set of roughness geometry parameters yielded optimum performance for the entire range of operating parameters and is given as Number of gaps 3, relative gap width 4, roughness pitch 10 and angle of attack sixty degree. newline