Analytical models for the computation and optimization of single and double glazing flat plate solar collectors with normal and small air gap spacing

Analytical models for the prediction of the heat loss from the top cover of single and double glazing flat plate solar collectors have been proposed. The models require no iteration to solve and therefore, are easy to use. The models allow the analysis of collectors with very small air gap spacing which was not previously possible. They are, therefore, applicable for cases with Rayleigh numbers ranges from 0 to 106. The comparison between the predictions from the proposed model and the results obtained from a more comprehensive 2-D CFD studies employing ANSYS FLUENT 13 software package shows that the proposed model is able to accurately predict the heat loss coefficients and glass temperatures with discrepancies of less than 9%. It was also found that if the air gap spacings for both the single and the double glazing solar collectors are such that the corresponding Rayleigh number is at the vicinity of the critical value of 1708 (which corresponds to an air gap of about 10mm in this study), there exists a minimum heat loss coefficient. With the optimized design, the water temperature increase is higher by about 14% as compared to that of the base design. These findings pave the way for future optimization of the solar collector designs.

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