Technical note: Optimizing the thermohydraulic performance of flat-plate solar air heaters operating with fixed⧸variable pumping power

Abstract

The validity of the analytical criterion derived for predicting optimum channel depth of conventional Solar Air Heaters (SAHs) has been explored for other flat-plate models of practical importance. Compared to the conventional design with air-channel under the absorber, the considered two models have airflow over the absorber and on both sides of it, respectively. Particularly examined is the effect of channel depth-to-length ratio ( D⧸ L) on the performance characteristics of these single-pass SAHs. Performance simulation results confirm the applicability of the criterion for these models over a wide range of influencing parameters including specific pumping power (P), emissivity of channel surfaces and wind heat transfer coefficient. It is found that the criterion successfully estimates the channel depth parameter ( δ p) that optimizes the performance for fixed or variable pumping-power operation. For the latter mode of operation, however, the ratio D⧸ L = 3 ∗ 10 −3 is recommended. Also, the performance diagram of a particular model design can easily be generalized if it is rated in terms of the analytical parameters δ p and P⧸ L which tightens up the intimate dependence of heater performance on both channel dimensions and flow pumping power.