Drying kinetics and energy-exergy analysis of an experimental heat pump dryer utilized horseshoe heat recovery heat pipes for drying different grapes

Abstract

In this study, nine different seeded and seedless grape cultivars (Vitis spp) were dried in a closed circuit heat pump-drying (HPD) system. The system’s drying performance was determined for each grape cultivar, and exergy analysis was performed. The evaporator efficiency increases when the external condenser is in the “on” position. This revealed that when the system reached the desired drying temperature, the longer the external condenser stayed in the “on” position, the more moisture can be drawn from the product. The heat pump highest coefficient of performance total (COPtotal,hp) and system coefficient of performance total (COPtotal,sys) were found to be 3.714 and 3.035, respectively, in the external condenser “on” position. The highest exergy efficiency values of compressor, condenser, TXV, evaporator and drying cabined were found to be 68 %, 75.41 %, 92.43 %, 77.35 % and 78.28 % respectively, when the external condenser “on” position. The highest exergy efficiencies were determined 75.75 %, 69.81 %, 87.5 %, 86.65 % and 80.46 % respectively, when the external condenser “off” position. The experiments of were evaluated in order to study the drying characteristics in HPD system. The changes in moisture ratio during the drying process were compared by six thin-layer drying models and then assessed in terms of various statistical criteria like root-mean-square-error (RMSE), diminished chi-square (χ2), and determination constant(R2). Fick’s second law of diffusion was used to obtained diffusivity of effective-moisture values, and they were found to range between 4.715 × 10–11 and 1.280 × 10-10 m2/s.