Exergy based modeling and optimization of solar thermal collector provided with impinging air jets

The irreversible absorption of solar energy accompanied by emission for conversion into thermal energy takes place at the cost of exergy losses from the collector and the effectiveness of this conversion is evaluated in terms of exergy efficiency based upon second law of thermodynamics. Presented in this paper is the exergetic efficiency of impinging jet solar thermal collector and its comparison with that of conventional solar collector. The effect of flow Reynolds number, jet diameter, streamwise and spanwise pitch between the jets on exergetic efficiency of impinging jet solar air collector during conversion of solar energy into thermal energy has been studied based upon the correlations developed for heat transfer coefficient and friction factor in the range of investigated flow and geometric parameters. The results reveal that the impinging air jets extract the absorbed exergy from the absorber to the air flowing beneath with higher efficiency than that of the conventional solar air collector. Also, the design plots have been prepared for jet plate parameters with temperature rise parameter in order to obtain an optimum parameter values that would deliver maximum exergetic efficiency for desired value of temperature rise. Design procedure has also been discussed to evaluate the optimum parameters with respect to operating conditions.