The Thermal Analysis of a Semi-Open Heat Pump Drying System: An Experimental Investigation

Abstract

One of the key advantages of heat pump (HP) systems is their ability to recover waste heat energy for useful input. In this study, the thermal performance of a heat pump drying system that recovers heat energy from the hot and moist exhaust air from the dryer was designed, constructed, and examined. The performance of this semiopen air source heat pump system was investigated and analysed by varying the refrigerant charge, the condenser fan speed, and the thermal expansion valve orifice size at ambient temperatures ranging from 23 – 26 C. The results indicated that by increasing the charge in the system, the refrigerant mass flow rate, heating capacity and coefficient of performance (COP) of the system increased to a certain maximum point before maximum charging. By increasing the refrigerant charge, both evaporation and condensation pressures of the system increased with condensation pressure indicating more sensitivity on the charge amount before optimum charging than evaporating pressure. The increase in refrigerant charge was observed to decrease the degree of superheat but increase the sub-cooling degree. At an optimum charge, the heating capacity for thermal expansion valve (TEV) of 0.3 mm diameter orifice is 15% greater than that of 0.2 mm diameter orifice. A system power consumption for O0.3 mm orifice was 3% greater than that of O0.2 mm orifice at the optimum charge amount. However, the COP of O0.3 mm orifice was 18% greater than that of O0.2 mm orifice.