Effect of thermal and optical properties of transparent plates on the collection characteristics of Volume Heat Trap solar collectors

The effect of thermal and optical properties of the transparent plate on the collection characteristics of a 'Volume Heat Trap' solar collector was studied theoretically and experimentally. For collectors with transparent plates of different material and thickness, the time changes of the temperature distribution were measured in the indoor and outdoor experiments. The calculated results, taking natural convection within the working fluid layer into consideration, were compared with the experimental data. It was found that the collection characteristics of the 'Volume Heat Trap' collector greatly depended upon both the thermal resistance and the transmittance of the transparent plate. When the transmittance decreased and the thermal resistance increased with increasing plate thickness, the optimum thickness of the transparent plate for collection efficiency increased with increasing temperature level.