Experimental Assessment of Energy and Mass Transfer in Microwave Drying of Fig Fruit

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Energy and mass transfer investigations in thermal processing of fruits serve as a breakthrough in the design and scale up of drying systems. Diffusivity characteristics and specific energy consumption for drying of fig fruit in a laboratory scale microwave dryer were assessed. Several intervals for microwave power intensity including 0.5, 1, 1.5, 2, and 2.5 W g-1, and 6 levels of power on-off stated as pulsing ratios of 1.5, 2, 2.5, 3, 3.5, and 4 were employed. The results showed that the drying rate decreased with the pulsing ratio and increased with microwave power intensity. Effective moisture diffusivity as an indicator of mass transfer was obtained to be higher at elevated microwave power intensities. Also, increased pulsing ratios had a reducing effect on moisture diffusivity. Using 2nd law of Fick, moisture diffusivity was calculated to be varying from 5.93E-10 to 1.42E-08 m2 s-1 depending on the experimental conditions. Furthermore, the activation energy of fig fruit was obtained to be in the range of 60.094 to 92.189 kJ mol-1. Specific energy consumption variations showed a positive correlation with pulsing ratio and drying time. However, due to the dependence of energy consumption on MW power intensity, a multiple regression analysis with R2 of 0.968 was developed.