DESIGN AND PERFORMANCE EVALUATION OF A MULTI FUNCTIONAL PASSIVE SOLAR DRYER FOR PADDYR. Venkatesh and W. Christraj
A multi functional passive solar dryer was designed and constructed by adding the solar water heater and the solar air heater. The dryer consists of solar collector, reflector, riser tube cum heat storage unit and drying chamber. The storage tank of the conventional solar water collector is modified as riser tubes and header, which is fitted in the bottom of the solar air heater as an absorber in the normal air heater. The drying chamber was located under the collector. The system is worked as a solar dryer only, by preventing the flow of water, during the sun-shine (without water heating) in a sunny day, the drying system efficiency was found 21.44% whereas, it found 35.83% when adding heat energy from the water heater with a low intensity of solar radiation during the sun-shine and the drying process by the multi functional solar dryer only. The solar dryer was tested for drying of paddy. The capacity of the dryer was to dry about 5-10 kg of paddy in 8 h in sunny day from an initial moisture content of 76.4% to the final moisture content of 9.4% (wb). For a drying time about 8 h, the moisture content of the paddy using the solar dryer was 0.16 kg/kg (db) and for the dried paddies by the sun drying was 0.44 kg/kg (db). Thermal efficiency of the solar drier was estimated to be about 35.83% with drying rate of about 6.12 kg/kg of dry matter h. In all cases the use of this drier led to better results in colour, aroma, texture and drying time of the solar dried products in comparison to traditional open-sun drying.
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