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In this study, plum slices were dried in three different driers (tray, fluid bed, and heat pump (HP) driers). Drying experiments were carried out at an air temperature range of 45-55 °C with an air velocity of 1.5 m/s. The performance of the driers along with their main components was evaluated and compared by using the exergy analysis method. The most important component for improving the system efficiency was determined to be the fan-heater combination for both the tray and fluid bed driers, and the motor-compressor assembly for the HP drier. The exergy loss and flow diagram (the so-called Grassmann diagram) of the driers was also presented to give quantitative information regarding the proportion of the exergy input dissipated in the various system components. Effects of the drying air temperature on the performance of the drying process were discussed. The highest exergetic efficiency values were obtained to range from 72.72 to 75.66 per cent for the HP drier, followed by the tray and fluid bed driers varying between 37.94 and 39.46 per cent, and between 22.83 and 24.07 per cent, respectively. [ABSTRACT FROM AUTHOR]

A heat pump drier is designed and fabricated to investigate its performance for copra drying. The experiments are carried out at 40 °C drying air temperature with a velocity of 1.5 m/s. The results showed that moisture content (wet basis) of the coconut is reduced from 52.6 to 8.5 per cent in 48 h. The average coefficient of performance of the heat pump is estimated to be about 3.5. The specific moisture extraction rate is calculated to be about 0.85 kg/kW-h. The copra obtained is graded as 92.7 per cent milling copra grade 1 (MCG1) and 7.3 per cent MCG2 according to Bureau of Indian standards (BIS: 6220–1971). [ABSTRACT FROM AUTHOR]