Comparison Between Heat Pump and Electric Heater for Drying Onion Slices

Abstract

Food and agricultural products require drying to ensure that their nutritional value is unaffected during handling and storage. Numerous techniques of drying are in use. This work compares drying with a heat pump dryer (HPD) and an electric heater dryer (EHD) for Egyptian onion slices. Empirical equations were obtained to calculate the change of moisture over time. This comparison used the following criteria: moisture content, energy consumption, moisture extraction rate, specific moisture extraction rate, and drying time. The onions were cut into slices 3 mm thick and 15 to 20 mm long. The slices were dried at temperatures of 50, 60, and 70 °C and drying air velocities of 0.2, 0.3, and 0.4 m/s. The results indicated that a drying of 83% to 26% moisture content on a wet basis or from 4.88 gmwater/gmdm to 0.35 gmwater/gmdm on a dry basis was achieved in one stage in the multiple stages of drying. The experiments showed that the energy savings resulting from using HPD was 22.2%. The best value for the R 2 of moisture content change over time was obtained by drying Egyptian onion slices according to different drying models for EHD and HPD.