Study on drying characteristics of combined microwave-hot air drying of paddy

Combining microwave drying with traditional hot-air drying can significantly enhance drying efficiency and uniformity owing to its unique internal heating characteristics, making it suitable for drying fresh paddy susceptible to mold. In this study, a fresh paddy was dried using a microwave fluidized-bed dryer to investigate the drying characteristics and assess the influence of microwave power, microwave duration, hot-air temperature, air velocity, and tempering time ratio. Key parameters, including drying rate, moisture diffusion coefficient, moisture transfer coefficient, activation energy, thermal efficiency, and specific energy consumption, were calculated. The results indicated that increasing microwave power and hot-air temperature significantly reduced drying time, achieving a maximum thermal efficiency of 54.26 % and a moisture diffusion coefficient of 10.995 × 10−9 m2/s at a hot-air temperature of 55 °C. This confirmed the high efficiency of the combined drying method. A tempering time ratio of 1:4 optimized energy utilization and maintained paddy quality. Additionally, the Verma model accurately predicted moisture content in this new drying system. The results provide valuable insights for applying combined microwave-hot air drying in the paddy drying industry.