Performance analysis of solar and heat pump dryer of small cardamom (Elettaria Cardamomum Maton) using energy analysis, drying kinetics, and quality

Cardamom, also known as the “Queen of Spices,” is the world’s oldest recognized spice with a high market value for its dried final product. In this work, the drying kinetics of small cardamom (cv. Njallani) has been studied using a solar and a heat pump dryer. Before drying, the produce was pre-treated in sodium carbonate (Na₂CO₃) at 1%, 2%, and 3%. The treated small cardamom samples are dried as a single and double layer at 40, 45, and 50 °C. The maximum temperature observed inside the solar dryer is 80 °C, resulting in a faster drying rate than the heat pump dryer but poor quality and greenness ((a*) − 0.8 to − 3.25) even after being pre-treated with Na₂CO₃. The heat pump dryer showed a constant and falling rate drying period at all the temperatures, with the highest drying rate at 50 °C. It required at least 12 h to dry the cardamom samples from 455.5 to 10.2% moisture content as a single layer. The temperature and the bed thickness have the maximum influence on the water activity of dried cardamom (0.54–0.64). A higher greenness value and essential oil percentage are obtained from the small cardamom dried in the heat pump dryer at 45 °C.The COP and SMER are found best at 50 °C. Four different models are used to predict the moisture ratio curve of the dried cardamom, with the quadratic model having the highest R² value.