Energy-Efficient Low-Temperature Heat Pump Drying of Mint Leaves: Preserving Quality and Energy

High-temperature drying can damage heat-sensitive materials if dried directly by heaters, sun drying, or heat pumps operating at 40℃ to 90℃, causing loss of fragrance and colour. Vacuum and freeze-drying are common low-temperature methods, but they're expensive and slow that limits their uses. A more efficient alternative is low-temperature heat pump drying. This research concentrates on designing and developing energy-efficient low-temperature heat pump drying system for heat-sensitive materials. Present paper provides two-stage heat pump drying system that works below 35℃, producing high-quality dried products. The paper focuses on designing, dimensioning, and operating a low-temperature heat pump dryer. Drying properties of mint leaves are also analyzed at 2, 2.5, and 3 m/s air velocities and low temperatures from 30-40℃. The system performance includes heating load, power consumption, coefficient of performance, specific moisture extraction rate (SMER) etc. Average coefficient of performance (COP) achieved was 4.8, with average SMER being 0.84 kg/kW-hr. Experimental results demonstrate system's ability to preserve quality in addition to properties of heat-sensitive materials. These results hold important relevance for industries such as pharmaceuticals, food processing, and biotechnology, where maintaining integrity of products is essential. This study advances drying technology by introducing an innovative approach for drying heat-sensitive materials that reduces energy usage while maintaining quality. The proposed system presents a viable alternative to traditional drying techniques, especially in sectors where both product quality and energy savings are critical. By providing a consistent airflow at controlled sub-zero temperatures, the system eliminates reliance on external heating for defrosting, thereby improving overall energy efficiency.