Experimental study on drying characteristics of amla and apple using a dual‐mode heat pump dryer

Abstract The present research investigation focuses on analyzing the energy and exergetic efficiencies of Heat Pump Dryers (HPD) while running in closed and open‐cycle modes. The main aim of this study is to perform the comparative performance analysis of the HPD in both closed and open‐cycle configurations for Amal and Apple with a 0.5 m/s constant air flow rate. The performance parameters like total energy consumption, drying temperature, relative humidity, Coefficient of Performance (COP), energy efficiency, drying efficiency, Specific Moisture Extraction Rate (SMER), Moisture Extraction Rate (MER), and exergy destruction rate have been analyzed with respect to drying time. To analyze the performance, a convective batch‐type drying chamber was designed with 8 trays with a spacing of 2.5 cm, and a 5 kg sample was used for experimentation. The research emphasizes that the closed‐cycle mode of the HPD demonstrates more energy efficiency, average drying temperature, MER, SMER, drying efficiency, and less drying time, total energy consumption, and COP in the drying process as compared to the open‐cycle mode. The performance of closed‐mode HPD is observed to be superior for Amla as compared to Apple drying products. The average drying air temperatures and SMER for amla and apple in the open system were 52–60°C, and 2.09 kg/kWh, and 58–60°C, and 1.53 kg/kWh, respectively, but temperatures and SMER in the closed system were 58–65°C, and 1.4 kWh, and 58–67°C, and 3.0 kWh, respectively. The exergy loss in apple drying was the highest at 0.243 kW, highlighting the need for future system optimization.