EFFECTS OF ROUGHNESS ELEMENTS ON V-CORRUGATED ABSORBER PLATE SOLAR AIR HEATERS

Abstract

Solar air heaters (SAHs) generally have low thermal efficiency, hence numerous research has been done to enhance their performance and to widen their applications. Although there has been extensive research on them, adding roughness elements on the corrugations of V-corrugated absorber plate SAHs to enhance their performance have not been investigated. Hence this work is an effort to address this gap by performing a numerical study to investigate the thermal performance enhancement caused by attaching transverse and longitudinal fins on 60o V-corrugated absorber plate SAH. It is also aimed to investigate the effect of same roughness elements on simple flat plate SAH. ANSYS Fluent program was utilized to simulate and analyze the three-dimensional airflow through the SAHs. The simulations were performed for three different Reynolds numbers; 4000, 8000 and 12000. The effects of adding fins on the outlet air temperature, Nusselt number and friction factor were analyzed and discussed. The results indicated that addition of roughness in the form of transverse and longitudinal fins offered enhancement in the thermal performance, leading the corrugated plate-longitudinal fins SAH to achieve the maximum outlet air temperature (315.3 K) and the flat plate-transverse fins SAH to attain the highest Nusselt number (58.4). For the V-corrugated SAH, transverse fins enhanced the Nusselt number by 17% compared to the smooth case, while the longitudinal fins offered 4 degrees increase in the outlet temperature. For the flat SAH on the other hand, transverse fins enhanced the Nusselt number by 26% as compared to the smooth case, while the longitudinal fins resulted in 2 degrees increase in the outlet temperature.