Assessment of Moisture Distribution Through Rough Rice Kernel During a Combined Hot Air and Far Infrared Drying

Abstract

Accurate characterization of moisture migration within rough rice kernels during drying is essential for improving energy efficiency and mitigating fissure formation. This study presents a physics‐based investigation of moisture transport in rough rice subjected to combined hot‐air and far‐infrared (FIR) drying under different inlet air temperatures and FIR intensity levels. Spatiotemporal moisture distributions within the kernel were quantified by solving Fick's second law using the finite element method. For homogeneous kernels with uniform temperature and moisture, the effective moisture diffusivity ( D eff ) ranged from 0.89 to 7.39 × 10 −11  m 2  s −1 and followed a modified Arrhenius‐type relationship, incorporating both kernel temperature and FIR intensity. Introducing moisture‐dependent diffusivity, represented as a third‐degree function of moisture ratio, enhanced predictive accuracy and revealed strong temporal variability, with elevated diffusivities during early drying stages followed by asymptotic behavior at lower moisture levels. To account for kernel structural heterogeneity, an inhomogeneous three‐layer model representing the endosperm, bran, and husk was developed. Layer‐specific diffusivities exhibited distinct magnitudes and transport resistances ( D 1  = 0.31–2.73 × 10 −10 , D 2  = 1.21–9.23 × 10 −12 , and D 3  = 2.37–20.34 × 10 −11  m 2  s −1 ), each following modified Arrhenius‐type behavior. After decoupling thermal and FIR effects, remaining diffusivity variations were attributed solely to intrinsic layer properties, with diffusivity magnitudes decreasing sequentially from the endosperm to the husk and bran layers. These results provide a physically consistent framework for describing moisture transport in rough rice by coupling moisture‐dependent, temperature‐sensitive diffusivity with kernel structural heterogeneity under combined hot‐air and FIR drying.