Modeling and Testing a New Once-through Air Solar Energy Collector

A new once-through air solar collector was modeled and tested. In this solar heater a transpired absorber was used. The cover of the collector was double glazed and consists of many slats and assembled in such a way that it formed a stair step fashion and made many slots through which inlet air was sucked into the collector. The sucked air is believed to recover part of the sort wavelength radiation absorbed by the glass sheets. furthermore,the long wavelength emission from the transpired absorber was trapped by the double glazing cover and could also be captured by the air thus reducing total heat loss. A mathematical model was developed to predict the effects of variations in the input parameters on the collector thermal efficiency. The theoretical results showed that the thermal performance of the collector was sensitive to air flow rate, ambient temperature, solar irradiance, absorber emissivity variations, Slat length and slot height. The collector was tested under a solar simulator over a wide range of air flow rates. The experimental results were in good agreement with the theoretical values. An absorbing efficiency as high as 82% could be obtained. Since the air heater was once-through, it is very suitable for grain drying purposes