Exergetic performance estimation for roughened triangular duct used in solar air heaters

Abstract

A solar air heater (SAH) is a heat exchanger that is capable of converting radiations (solar) into thermal energy, which is further utilized for heating purposes. But due to poor thermal conductivity of air, SAH has poor thermal performance. Roughness is one of the effective techniques used to improve the performance of SAH. Two different roughness geometries, semicircular and square, were used in the present article, and the effect of different parameters on the exergy efficiency of a SAH is investigated. The flow passage used for the solar air heater has a triangular cross section with an equal side length of 160 mm. The positive impact of various roughness parameters (relative roughness height, e/D and relative roughness pitch, p/e) and operating parameters (Reynolds number) has been obtained on the exergetic efficiency of the SAH. Comparing both the roughness geometries, it is concluded that the exergetic efficiency found in semicircular ribbed SAH is 26% higher than that of square roughness at e/D and p/e value of 0.04 and 10, respectively. The exergetic efficiency of a SAH is suitable for design as it includes the quality of useful energy and its associated pumping power. The design plots are also developed and based upon that recommendations are made to develop an efficient solar air heater.