Numerical Study of Models for Estimating Edge Heat Loss in Solar Absorbers

Abstract

Absorbers are the prime heat transfer components of solar energy devices. The effects of variable edge loss coefficients on heat transfer performance of flat-plate solar absorbers are examined. From fundamental energy relations, an edge loss coefficient is obtained which embodies the geometric and ambient parameters for estimating the edge heat loss. This model is similar in form to that given by Kaligrou (2009, Solar Energy Engineering Processes and Systems, Elsevier, New York, pp. 156–163) but differs from that obtained by Duffie and Beckman (1991, Solar Engineering of Thermal Processes, Wiley & Sons, Inc., New York), which can be corrected by employing a correction factor given here. The results confirm that the edge loss can significantly affect the absorber performance depending on Ae/Ap ratios, and the prevailing ambient conditions. However, previous models neglect these effects. It is found that the model given by Duffie and Beckman erroneously exceeds the total energy input and overestimates the loss by as much as a factor of 6, which goes against the first law of thermodynamics. When the correction factor is applied, the model gives a better approximation.