In a compound parabolic solar collector, a glass cover is normally used for decreasing the rate of heat loss from the absorber. In this paper, a solar collector with two glass covers and a concentration ratio of 1.6 is simulated and examined for the purpose of higher performance. The distance between covers is 45 mm and the cavity of solar collector is filled with air. Due to the temperature gradient, the turbulent free convection airflow takes place inside the cavity. As the main aim, the effect of the second glass sheet on performance improvement is examined. Towards this end, the equations govern to the turbulent buoyant airflow in the collector’s cavity was numerically solved by the finite element method using the COMSOL Multiphysics software. Also the conduction equation is employed for temperature computation in the solid elements. Numerical findings demonstrate the effective role of the second glass sheet in decreasing the rate of heat loss from solar collectors and a more than 6% increase in the thermal efficiency of the studied test cases is found because of the second glass sheet. Comparison between the numerical findings of free convection airflow with experimental data shows good consistency.
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