Design and Development of a Heat Pump Based Moisture Control System for Industrial Drying of Medicinal Plants

Abstract

Moisture control is one of the most common preservation methods used for enhancing the shelf life of agricultural produce. When processing or storing of fresh produce, a special attention has to be given in maintaining low temperature of the drying air. A heat pump based dehumidifier, which comprised of an evaporator, condenser, compressor, expansion device, a control unit, main frame and a covering chamber, was designed and fabricated for moisture control of agricultural produce. The air with high relative humidity coming from the evaporator was passed through the condenser unit and reheated up to 30 °C. The control unit was designed using Arduino controller to maintain preferable relative humidity in the storage room with minimum working cycle. Duty cycle of the system was 20 minutes ‘switch on’ and 5 minutes ‘switch off’ time. The performance of the heat pump based dehumidifier system was evaluated by studying the temperature and relative humidity of empty store room and with stored Gotukola (Centella asiatica). The relative humidity of the empty store room was found to be reduced from 50% to 16% within 6 hours of operation of heat pump dehumidifier. It was also possible to reduce the moisture content of fresh Gotukola from 88% to 12% within 27 hours. During this period the air temperature of the storeroom varied from 25°C to 44 °C. The specific moisture extraction rate of the heat pump dehumidifier system was 0.49 kg/kWh. The designed and developed heat pump based moisture control system performed satisfactorily and could be effectively used in moisture control of medicinal plants.