Development of a desiccant integrated solar dryer
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Date
2012
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Publisher
CCSHAU
Abstract
A desiccant integrated solar dryer was developed and its performance was studied under the
climatic conditions of Hisar, India. The system consisted of flat plate solar collector, drying chamber
and desiccant unit. Drying with solar heated air is satisfactory during sunshine hours and to continue
this process through the night-time desiccant was integrated within the drying system. The desiccant
was developed from 60% bentonite, 20% vermiculite, 10% CaCl2 and 10% cement. The regeneration
studies of developed desiccant were carried out for moisture adsorption at 30°C and 96% RH for 144 h
and moisture desorption at 40°C, 50°C, 60°C, 70°C and 80°C for 8 h. The maximum adsorption
capacity of desiccant was 35.12% (db) and it was efficiently regenerated by solar energy. The dryer
was operated in two modes sunshine hours and off-sunshine hours. During sunshine hours the hot air
from flat plate solar collector was forced into the drying chamber and simultaneously the desiccant unit
received solar radiations directly for regeneration. In off-sunshine hours, the dryer was operated by
circulating the air inside the drying chamber through the desiccant bed by blower fan in a closed loop.
Performance of desiccant integrated solar dryer was observed at three different air mass flow rates of
0.010 kg/s, 0.015 kg/s and 0.020 kg/s for day and night operations. In desiccant integrated solar dryer
10 kg of green peas were dried from initial moisture content of 75% (wb) to 5%(wb) in 18 h at air mass
flow rate of 0.020 kg/s whereas in solar dryer without desiccant unit it took 30 cumulative hours as the
drying continued for 2 sunshine days. The average collector thermal efficiency and dryer thermal
efficiency were 62.18% and 52.21%, respectively at air mass flow rate of 0.020 kg/s. The pickup
efficiency of dryer varied from 18.17% to 68.25% and specific moisture extraction rate of 1.4 kg/kWh
at air mass flow rate of 0.020 kg/s. In the drying experiments it was observed that 68% of moisture was
removed by hot air using solar energy and remaining by the desiccant material at air mass flow rate of
0.020 kg/s. The green peas dried in desiccant integrated solar dryer had higher overall acceptability and
rehydration ratio as compared to drying in solar dryer without desiccant unit.
Description
Keywords
Solar dryer, Desiccant material, Desiccant regeneration, Green peas, Dryer thermal efficiency, Rehydration ratio