Studies on Heat pump drying of ‘Sonaka’ seedless grapes (Vitis vinifera) for the production of raisins

  • Ramesh Kumar - Selvan TNAU
Keywords: grapes, drying, kishmish, chemicals


Studies were conducted with Sonaka seedless grapes with different pretreatments NaOH (0.5%), Olive oil (2.5%) plus K2CO3 (6.0%) and Ethyl oleate (2.0%) plus K2CO3 (2.5%). Drying was carried out under sun and also at 45, 55 and 65°C in heat pump dryer. The initial moisture content of 456.54 per (db) has been reduced to a final moisture content of 18 per cent (db). The time taken for drying varies with respect to different treatment and drying temperature. Drying at 45, 55 and 65°C took 32, 27 and 21 hours for Ethyl oleate plus K2CO3  pretreatment. The highest drying rate observed in heat pump dryer was 1.549 kg/kg min. at 65°C. The initial drying rate was found to be higher in case of heat pump dryer. The energy requirement for drying of grapes in heat pump dryer was found to be 35 per cent less than that of cabinet dryer. The efficiency of the evaporator and condenser coils was found to be 68 and 60 per cent respectively. Moisture extraction rate (MER) and Specific moisture extraction rate (SMER) values were higher and increased with temperature because of the decreased drying time. The coefficient of performance of the heat pump dryer at 45, 55 and 65oC were 1.89, 4.31 and 6.58 respectively. The COP increased with temperature as lower the evaporator temperature, higher the heat released at the condenser.

Author Biography

Ramesh Kumar - Selvan, TNAU


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