A Review of Energy and Exergy Analyses of a Roughened Solar Air Heater

Abstract

In this paper, energy and exergy analyses of eleven roughness elements in solar air heater ducts were reviewed. Various roughness geometries, such as ribs, twisted tap, baffles, and metal waste, were surveyed for their effects on heat transfer and friction when the air flow passed over the absorber plate. The evaluation criteria for roughness elements on the absorber plate, including the thermohydraulic performance parameters, thermal efficiency, effective efficiency, and exergy efficiency, were presented and compared. The results showed that protruding ribs in an arc shape resulted in the largest Nusselt number. The ribs exhibited the highest thermohydraulic performance parameters at a Reynolds number greater than 5000. Jet impingement with arc-shaped ribs and roughness elements in metal waste were found to result in the smallest exergy efficiencies. The largest effective and exergy efficiencies were 70% and 1.9%, respectively. The thermohydraulic performance parameter varied from 0.5 to 2.0. This review paper aims to provide information about roughness geometries by investigating both the first and second laws of thermodynamics and the figure of merits to describe artificial roughness in a solar air heater.