Analytical predictions of exergoeconomic performance of a solar air heater with surface roughness of metal waste

Abstract

The current study is the authors’ next work from the perspectives of the second law and economics of an air collector having artificial roughness of metal waste. In a previous study, heat and fluid flow characteristics and thermo-hydraulic performance were experimentally investigated. In the present paper, thermal efficiency, effective efficiency, exergetic efficiency and economic-based optimization are analytically appraised. The influences of the relative roughness pitch, relative roughness height, collector area and Reynolds number on the above parameters are examined. The optimal roughness parameters to achieve the best exergetic performance are formulated as design plots for the design and operation of a solar air heater. The weighted sum method is used to optimize the objectives of exergetic performance and total annual cost. The results reveal that too high Reynolds numbers result in low effective performance and unexpected exergetic performance. In that case, a lower roughness should be used, i.e. a smaller relative roughness height and larger relative roughness pitch. This is because the pressure loss penalty and irreversibility are quite large at high Reynolds numbers. An absorber plate area of 1.3 m2 was found to achieve the maximum exergetic performance and minimum total annual cost.