Performance Evaluation of a Heat Pump System with Dual Condensers for Drying Herbs

Abstract

A dual condenser heat pump dryer (HPD) was utilised for herb drying, demonstrating its capability to provide a cost-effective drying solution via economical energy consumption, expedited drying processes, and improved system coefficient of performance (COP). The drying properties, exergy energy, and techno-economic feasibility were comprehensively evaluated. The HPD employed refrigerant R-32, operating within a temperature range of 6 °C for the evaporator and 47 °C for the condenser to dry kesum and pandan leaves. The experimental results demonstrate that the dryer required a modest amount of electricity, 0.012 and 0.143 kW/kg of fresh kesum and pandan, respectively. The dryer effectively removed moisture during its passage through the dual condensers and evaporator, yielding 16.85 kg and 3.39 kg of condensate water from the initial mass of 50 kg and 5.5 kg, respectively. The specific moisture extraction rate (SMER) for the HPD mode was calculated at 11.23 and 2.26 kg/ kWh, and the average COP was 5.7 and 5.34 for kesum and pandan, respectively. The dual condenser improved the COP by approximately 11%. A maximum dryer productivity of about 0.75 kg/m²h is obtained at the air with a temperature of 47°C, velocity of 2.32 m/s and dryer surface load of 3.39 kg/m². The exergy efficiency of the thorough drying period varied from 56.85% to 96.33%. Moreover, the economic analysis determined a payback period of 3.24 months and 6.09 months for drying 24,000 kg and 2,640 kg of kesum and pandan leaves annually, with calculated annual incomes of 147,822.48 and 27,046.80 USD, respectively.