Investigation of microwave dryer effect on energy efficiency during drying of apple slices

Characteristics of thin layer microwave drying of apple were evaluated in a laboratory scale microwave dryer at 2450 MHz. The drying experiments were carried out at 200, 400 and 600 W. The experimental data were fitted to nine drying models. The models were compared using the coefficient of determination (R^2), root mean square error (RMSE) and reduced chi-square (v^2). The Midilli et al. model best described the drying curve of apple slices. The effective moisture diffusivity was determined by using Fick’s second law and was observed to lie between 3.93 · 10^-7 and 2.27 · 10^-6 m^2/s for the apple samples. The microwave power dependence of the effective diffusivity coefficient followed an Arrhenius-type relationship. The activation energy for the moisture diffusion was determined to be 12.15 W/g. The highest energy efficiency was recorded for the samples dried at 600 W as 54.34% and lowest at 200 W as 17.42%.