This paper studies the effects of the absorber plate geometry on the thermal performance of an indirect solar dryer considering temperature dependent thermal conductivity and heat transfer coefficients. The main goal was to explore the effects of the absorbers confined air as well as the absorber plate thicknesses and to provide more realistic characterizations of the thermal dynamic of an indirect solar dryer. The heat transfer process is described using highly nonlinear partial differential equations. The mathematical model accounts the contribution of the upper soil surface temperature calculated using the boundary layer similarity theory. The established mathematical equations describing heat transfer in the solar drying system are solved numerically using a developed MATLAB program. The investigations of heat transfer of the proposed model reveal excellent agreement of prediction responses with the experimental results from the literature. Mathematical model of indirect solar drying prototype developed with double absorber plates separated with a confined air layer operates more effectively with a thermal efficiency greater than 6% compared to the model without confined air configuration. The numerical experiments also show the non-negligible effects of the absorber plate thickness on the thermal dynamic of an indirect solar dryer.

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