24 June 2014


A multi-commodity heat pump drying (MCHPD) system was designed, fabricated, assembled and evaluated following basic refrigeration and air-conditioning. The drying
chamber sized 1.22 m x 2.43 m x 1.22 m, and, dehumidifier with 2hp rotary, heavy-duty compressor; air-cooled type condenser; 2.0°C TD evaporator; thermostatic expansion valve
and attached- filter dryer. The system has a maximum 50°C operating temperature and minimum 10% drying air to favorably dry heat sensitive commodities. Onion as a sample
commodity is presented to evaluate the drying, thermal and dehumidifying efficiencies of the system. Moisture content was reduced from 83.0 % to 15.0% and satisfactorily dried for 33.0
hours with 0.029 kg/hr moisture reduction. Drying time and moisture loss was highly significant at R2 =0.97. Drying efficiency was 37.83 %, higher than the reported 33.0% efficiency by Canmet, 1988. The specific moisture extraction rate (SMER) described the total energy used during the process was the accumulated heat from the drying air and latent heat released from onion converted to sensible heat. Refrigerant 134a’s coefficient of
performance (COP) calculated 97.34 % thermal efficiency meeting the claim of Ragupathy (2004) that, the drying process of the system is circulatory, hence, approaches 100%. The
relative humidity of the ambient and drying air described 67.03% dehumidifying efficiency. The high efficiencies of the system meant that its configuration was very efficient in
producing a dehydrated onion safe for storage with reduced color degradation.