Effective moisture diffusivity and drying simulation of walnuts under hot air

Abstract

This study was conducted to determine the effective moisture diffusivity of walnuts for the understanding of drying mechanism and improved drying simulation. The drying characteristics of walnut shell and kernel were investigated during the single layer drying of in-shell walnuts at 43, 55, 65 and 75 °C with hot air. The values of average effective moisture diffusivity for walnut shell and kernel ranged from 1.51 × 10−9 to 9.28 × 10−9 m2/s and 1.13 × 10−9 to 2.85 × 10−9 m2/s, respectively. The 3rd order polynomial-exponential relationship well correlated the effective moisture diffusivity with sample moisture content (MC) and temperature (Radj2 > 0.983). A mathematical model with changing moisture diffusivity and heterogeneous components was developed. It simulated the in-shell walnut drying characteristics using finite element approach with good accuracy (Radj2 > 0.985). The outcomes provide important information for the understanding of moisture transfer mechanisms and have practical value for the optimization of operating conditions in the walnut drying industry.