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A NUMERICAL ANALIYSIS ON INCREASING THE HEAT-EXCHANGE EFFICIENCY FOR UNGLAZED TRANSPIRED SOLAR COLLECTORS
Abstract
Unglazed transpired solar collectors (UTC) are simple and effective devices for applications such air heating, induced ventilation, crop drying etc. A numerical model for typical unglazed transpired collector is proposed with blackened plate exposed to the sun and circular holes on square pitch arrangement in no wind working conditions. The steady-state conservation of mass equation, momentum and energy equations were considered in order compute the air pressure and velocities, flow pattern and the total air heating effect on the front of the plate, the hole and the back of the plate. The numeric simulations show that the heat transfer on the back of the plate is dependent on the recirculated eddies resulting as an effect of braking the air jet after it is emerging from the hole. In order to minimise the recirculating air motion which returns the flow on the plate with cooling down effect, the suction velocity must be varied in a direct relation with front plate temperature. A comparison between experimental results reported in literature and numerical solution, reveal that increasing of heat exchange is possible if the relation between internal flow of the collector and holes diameter reduce the influence of the vortices from the back side of the plate. In practice this result can be achieved if the variable rotating speed of the collector's fan is adjusted as function of solar irradiation and plate temperature respectively.
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References15
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