Thermal performance investigation of three sides concave dimple roughened solar air heaters

Abstract

A novel work conducted upon three sides concave dimple roughened SAHs is presented here. Exhaustive experimental investigations were carried out in Feb-May 2017 upon one and three sides roughened solar air heaters on test setup installed at terrace of Mechanical Engineering Dept., NIT Jamshedpur and results are presented as rise in heat transfer and thermal performance of three sides over one side roughened duct against corresponding frictional losses. The experimental setup was validated using Nusselt number and friction factor correlation derived by Saini and Verma (2008) using one side roughened similar duct model. The geometrical parameters were used as dimensionless ratio as relative dimple pitch (p/e), relative dimple height (e/Dh) and relative dimple depth (e/d) in the range of 8–15, 0.018–0.045 and 1–2 respectively. The range of Reynolds number covered during experimentation was 2000–13500. Heat transfer augmentation for three sides over one side roughened ducts was appreciable considering rise in frictional losses. The thermal efficiency was measured in terms of collector heat removal factor (FR) and collector efficiency factor (F') and the collector’s performance parameters were given as FRτα and (FRUL). The optimum roughness parameter was found to be p/e = 12, ‘e/Dh’ = 0.036 and ‘e/d’ = 1.5. For ṁ = 0.0293 kg/s and Cp = 1.005 kJ/kg K, FRτα and FRUL comes out equal to 0.7346 and 8.85 W/m2 K, respectively. Three sides roughened SAHs have high thermal efficiency of the order of 44–67% more than that of one side roughened SAH for the range of flow and roughness parameters investigated.