Thermohydraulic performance of air heating solar collectors with variable width, flat absorber plates

Abstract

The study investigates the more general and fundamental case when variable width absorbers are utilized instead of conventional rectangular plates in collecting incident solar radiation. The geometries considered include trapezoidal and concave parabolic absorbers having the same surface area. The effect of absorber shape on collector thermohydraulic performance has been examined for three common models with air flowing over the flat absorber, or under it, and on both sides of the absorber. The results are compared with those of rectangular absorber models over a wide range of mass flow rate and solar energy flux. Under the same operating conditions, the comparisons indicate that variable width collectors exhibit performance behavior similar to those of the constant width corresponding models, but it is accompanied by a marginal decrease in air temperature rise and collection efficiency along with a slight increase in fan power consumption. The comparisons do, thus, support the idea of employing variable width collectors in solar air heating applications, especially those which have design constraints on the investment costs and on the space available to install air collectors. For such applications, trapezoidal shape collectors are highly recommended.