Mathematical Modeling of Moisture Diffusivity and Mass Transfer During Drying of Coffea arabica L. var. Catimor

Understanding mass transfer mechanisms during coffee drying is essential for optimizing postharvest processing conditions. This study aimed to estimate the effective moisture diffusivity coefficient ($D_{eff}$) and convective mass transfer coefficient ($h_m$) of Coffea arabica L. var. Catimor through mathematical modeling. Drying experiments were conducted in an automated convection dryer (CE 130) at four constant temperatures (40, 50, 60, and 70 °C) and an air velocity of 1.5 m/s. Drying time, equilibrium moisture content ($M_{eq}$), and critical moisture content ($M_c$) were determined. A MATLAB based algorithm was developed to solve Fick’s second law and estimate $D_{eff}$ and $h_m$ during coffee drying. An Arrhenius-type model was further applied to describe the temperature dependence of both coefficients. Although the model captured the general increasing trend with temperature, only moderate coefficients of determination were obtained (R² = 0.63 for $D_{eff}$ and R² = 0.74 for $h_m$). Drying times were 26.5, 17.5, 16.5, and 13.5 h at 40, 50, 60, and 70 °C, respectively. $M_{eq}$ ranged from 11.30% to 11.76% (wet basis), while $M_c$ remained close to 46% (wet basis) at all temperatures. $D_{eff}$ ranged from $0.232\times {10}^{-10} \mathrm{to} 1.397\times {10}^{{-}^{10}} {\mathrm{m}}^2/\mathrm{s}$, whereas $h_m$ ranged from 1$.668\times {10}^{-9} \mathrm{to} 3.998\times {10}^{-9} \mathrm{m}/\mathrm{s}$. Both coefficients increased with temperature, indicating enhanced internal diffusion and external mass transfer. These findings provide useful engineering parameters for modeling, design, and optimization of industrial coffee drying processes.