A flat plate solar collector with dual channels for air flows

An analysis was made on the thermal performance of a flat-plate solar collector in which the air flows both in upper and under channels of the absorber plate. The results were compared with experimental results. The analytical results agreed well with the experimental results in the case that the ratio of the flow rate of the upper channel to the total flow rate, β₂, was in the range between 0 and 0.5. It was found that generally the flow in the upper channel increased the thermal efficiency. For example, the increase in thermal efficiency for turbulent flow was 14% at β₂=0.2 when the inlet air temperature was the same as the ambient air temperature. For laminar flow, larger increase of the efficiency, as much as 30%, was obtained. The effect of the total now rate and β₂ on the collector efficiency and temperature rise of the flow in each channel was also discussed