A parametric study on the thermal performance of cross-corrugated solar air collectors

A comprehensive parametric study has been carried out in this paper on the thermal performance of cross-corrugated solar air collectors. These collectors consists of a wavelike absorbing plate and a wavelike bottom plate which are crosswise positioned to form the air flow channel. Two types of these collectors are considered. For the Type 1 collector, the wavelike shape of the absorbing plate is along the flow direction and that of the bottom plate is perpendicular to the flow direction, while for the Type 2 collector it is the wavelike shape of the bottom plate that is along the flow direction and that of the absorbing plate is perpendicular to the flow direction. The aim of the use of the cross-corrugated absorbing plate and bottom plate is to enhance the turbulence and the heat transfer rate inside the air flow channel which are crucial to the improvement of efficiencies of solar air collectors. To quantify the achievable improvements with the cross-corrugated absorbing and bottom plates, a flat-plate solar air collector which has both a flat absorbing plate and a flat bottom plate, is also considered. The thermal performance of these three types of solar air collector are analyzed and compared under various configurations and operating conditions. The results show that although the thermal performance of the Type 2 collector is just slightly superior to that of the Type 1 collector both of these cross-corrugated solar air collectors have a significantly superior thermal performance to that of the flat-plate one. It is also found that to achieve a higher collector efficiency, it is essential to construct the collectors having slender configurations along the air flow direction, to maintain a small mean gap between the absorbing plate and bottom plate, to use selected coatings on the absorbing plate and glass cover, to maintain a higher air mass flow rate, and to operate the collectors with the inlet fluid temperature close to that of the ambient fluid