A review of the mathematical models for predicting solar air heaters systems

A mathematical model of the closed solar air heaters is used in particular, to assist in interpreting the observed phenomena in the solar air heaters, to design the system, to predict the trends, and to assist in optimization. In this paper, various mathematical models, mainly analyzing the heat transfer process of solar air heaters, are reviewed and classified based on the model, the number of the cover, the shape of the absorber and the presence or not of the packing bed. Although the models have evolved to a point where several features of the process can be predicted, more effort is required before the models can be applied to define actual operating conditions as well as to further investigate new closed solar air heaters. It is shown that the major governing equations in the models are based on the first law of thermodynamics.