Enhancing Paddy Rice Drying Quality with Non-Destructive LPG Refrigeration System in a Fixed-Bed Dryer

High relative air humidity in humid climates slows the process of paddy drying and leads to rehydration. The use of a liquefied petroleum gas (LPG) refrigeration system for dehumidifying ambient air effectively reduces drying time and improves product quality in a non-destructive manner. This environmentally friendly method enhances both the quality of the rice samples and the efficiency of the drying process. This study examined the impact of dehumidification on Hashemi rice quality and moisture reduction, using the Response Surface Method to optimize drying conditions at three levels of temperature (40, 45, and 50 °C), air velocity (1.7, 2.2, and 2.7 m/s), and relative humidity (70, 80, and 90%). The results showed that dehumidification led to a moisture content of 6% and the lowest cracking rate of 2%. Temperature was the most influential factor, affecting responses by 73.09% under dehumidified conditions. Optimal conditions of 40 °C, 80% RH, and 1.7 m/s air velocity resulted in a cracking rate of 2% and a desirability index of 0.958. The Response Surface Method showed an excellent fit for the cracking index (R² = 0.98). These results highlight the LPG refrigeration system as an effective, non-destructive, and environmentally friendly method for drying paddy in humid regions, making it suitable for industrial applications.