Three-Dimensional Numerical Analysis of Temperature Uniformity in Far-Infrared Assisted Hot Air Drying: Effects of Airflow Configuration and Drying Strategy

Achieving uniform moisture removal remains challenging because heat and mass transfer within drying systems are strongly affected by spatial variations in temperature and airflow. In this study, a three-dimensional model coupling airflow, heat transfer, infrared radiation, and moisture transport was developed in COMSOL Multiphysics and compared with experimental measurements for far-infrared assisted hot air (FIR-HA), hot air (HA), and far-infrared (FIR) drying. Coefficients of determination (R2) exceeded 0.985 for moisture content and 0.913 for temperature. Temperature distributions corresponded closely to moisture migration. Maximum differences in regional average temperature were 28.27, 20.63, and 29.63 °C under FIR-HA, HA, and FIR, respectively, with corresponding moisture differences of 5.2%, 4.8%, and 6.5% wet basis (w.b.), respectively. FIR-HA shortened drying time by at least 44% relative to HA and at least 36% relative to FIR. Nine airflow configurations were evaluated under FIR-HA drying by combining three inlet configurations (vertical, right horizontal, and back horizontal) with three outlet configurations (left, center, and bilateral symmetry). The back horizontal inlet with left outlet yielded the lowest predicted COVd (surrounding-air temperature) of 0.0060, a peak \({COV̄}ₛ \)} (mean within-sample temperature) of 0.0184 across the three samples, and a peak COVs1 (within-sample temperature) of 0.0115. The proposed three-dimensional coupled model provides a quantitative framework for elucidating the relationship between airflow configuration, thermal distribution, and temperature uniformity, thereby supporting the design and optimization of drying systems for more homogeneous dehydration of rice grains.