Testing of a Condensation-type Heat Pump System for Low-temperature Drying Applications

Abstract

Abstract A closed-type water source heat pump dryer integrated with a drying programme (DP) was designed and tested. The DP was developed using psychometric conditions of desired drying air and thermodynamic balance of heat pump. A drying algorithm was developed according to the technical specification of the dryer. Drying air temperature, relative humidity and drying air volumetric flow rate were entered from a programmable logic controller (PLC) screen. In this study, the drying of mint leaves was examined. Mint leaves were dried at different temperatures (35°C, 40°C and 45°C) and at different volumetric flow rates 300 m3/h for a velocity of 0.75 m/s and 600 m3/h for a velocity of 1.5 m/s in the PLC-controlled heat pump dryer. The relative humidity of the drying air entering the dryer chamber was kept between 13.88% and 6.81% and the two air dampers were controlled according to predetermined value. The coefficient of performance ($$\rm CO{\rm P_{{\rm{hp}}}}$$) values obtained were between 3.81 and 2.29. The specific moisture extraction rate for the whole system ($$\rm SME{\rm R_{{\rm{ws}}}}$$) was between the 0.034 and 0.044 kg/kWh. The drying air temperatures were controlled with an accuracy of ±0.41°C to ±0.76°C depending on the mode of operation.