Optimization of flow-channel depth for conventional flat-plate solar air heaters

An analytical criterion for determining the optimum flow-channel depth of conventional flat-plate solar air heaters has been developed. The criterion gives the minimum channel-depth required to maximize the useful heat gain from the absorber plate to the flowing air for a particular pumping power. A parametric study was carried out to validate the engineering accuracy of the optimization criterion which was found to be considerably accurate over the entire range of variables covered. An expression for estimating the channel-depth-to-length ratio that yields an outlet air temperature equal to the absorber-plate mean temperature is also derived in terms of flow pumping power. This expression is of great importance for designers of this type of solar air heater.