Moisture desorption isotherm, diffusivity and finite element simulation of drying of macadamia nut (Macadamia integrifolia)

• Diffusivities of components of macadamia nut were determined.
• Finite element simulation of drying macadamia nut using component diffusivities was carried out.
• Predicted and measured moisture contents of macadamia nut were in reasonable agreement.
• Distribution of the moisture content inside the macadamia nut can be determined by the simulation model.

This paper presents moisture diffusivity, equilibrium desorption isotherm and finite element simulated drying of macadamia nut. In order to create the desorption isotherm, the equilibrium moisture content was determined by using the gravimetric method. The Modified Oswin model fitted the best experimental data and is satisfactory for the prediction of the moisture desorption isotherm of macadamia nuts. The thin layer drying experiments of the kernel and shell of the macadamia nuts were conducted at a temperature of 40 °C, 50 °C and 60 °C and relative humidity of 10%, 20% and 30%. The moisture diffusivity of the kernel and shell of the macadamia nut was determined by minimizing the sum of square of the deviation between the predicted and the experimental moisture contents values during the thin layer experiments. The diffusivity of the kernel and shell was expressed as functions of temperature using the Arrhenius type equation and the moisture diffusivity of the kernel was higher than that of the shell of the macadamia nuts. A two-dimensional finite element drying model of macadamia nut was developed and this model predicted reasonably the moisture contents during drying. The model can be used to reveal spatial and temporal changes in moisture content inside the macadamia nut.