Simulation of walnut drying under hot air heating using a nonequilibrium multiphase transfer model

A nonequilibrium multiphase moisture and heat transfer model was developed to simulate the drying of a single walnut under hot air heating. The walnut was modeled as a 3-layer sphere by differentiating the shell, kernel, and an air gap between them. Drying characteristics of walnuts at 43, 55, 65, and 75 degrees C under 1.4 m/s air velocity were simulated using finite element method. The simulation results agreed well with experimental data, and the model showed good predictability for drying of walnuts with different initial moisture contents and dimension characteristics (R ( adj ) (3) > 0.996 for moisture and R ( adj ) (3) > 0.983 for temperature). The spatial distributions of liquid moisture, water vapor, and temperature in the walnut were determined through model simulation, which provided important information for understanding the mechanisms of heat and moisture transfer during walnut drying process. Findings from this study established theoretical basis for improving the walnut drying process and determining the suitable drying conditions.