Solar drying is one of the promising methods of reducing post-harvest losses in rural areas. Studies have shown that, heat transfer mechanisms in a solar collector influences the performance of solar dryers. This study aims at improving heat transfer in flat plate solar collectors by designing different air flow patterns inside the collector. Three flat plate solar collectors were constructed by using Pterocarpus timber (Mninga) and tested for their effect in heat transfer at various flow patterns. Three different flow patterns namely: single duct front pass, double duct parallel flow and double duct counter flow were designed and tested. Experimental results show that collector efficiency of single duct front pass, double duct front pass and double duct counter flow were 30.6, 36.1 and 38.2% respectively. It was found that, double duct flow gives improved performance compared to single duct flow due to the increased heat transfer area. In additional, double duct counter flow showed superior performance compared to double duct parallel flow due to extended heat transfer area and the advantage of air preheating at the inlet which reduces heat losses through glazing. Through this study, it was concluded that, solar collector designs with double duct counter flow can improve collector performance for up to 8.3% compared to single duct front pass.
Key words: Single duct front pass, double duct parallel flow, double duct counter flow, energy, solar intensity
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