Experimental Study and Energy Evaluation of Heat Pump–Solar Hybrid Drying of Bitter Melon

Abstract: This study experimentally investigates the performance of a hybrid drying system that integrates a heat pump with solar thermal energy, aiming to improve energy efficiency in the drying of bitter melon (Momordica charantia). The research focuses on the effects of slice thickness on drying time, Specific Energy Consumption (SEC), and the quality of the dried product. Drying trials were conducted using slices of bitter melon of three different thicknesses: 1 mm, 2 mm, and 3 mm. The hybrid system employed a flat-plate solar collector to preheat the inlet air before it entered the heat pump drying chamber. Results show that slice thickness had a significant effect on drying kinetics. Slices with 1 mm thickness reached the target moisture content in 4 hours, whereas 3 mm slices required up to 5.5 hours. The integration of solar preheating reduced total electrical energy consumption from 4.3 kWh to 2.7 kWh per batch, yielding an energy savings of approximately 37.2%. The SEC was also reduced, from 5.73 to 3.60 kWh/kg of evaporated water. In addition to energy improvements, the hybrid system helped retain favourable product characteristics, including a final moisture content of 10–12%, natural green colour, aroma, and essential bioactive compounds such as momordicin and flavonoids. These outcomes demonstrate the hybrid system’s potential as a sustainable solution for smallto medium-scale agricultural drying. A slice thickness of 1–2 mm is recommended for optimizing both drying efficiency and product quality. The findings support further research on the drying parameters that affect nutrient retention and the physical properties of dried agricultural products.