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

Abstract

Energy and mass transfer investigations in thermal processing of fruits serve as a breakthrough in the design and scale up of drying s ystems. Diffusivity characteristics and specific energy consumption for drying of fig fruit in a laboratory scale microwave dryer were assessed. Several intervals for microwave powe r intensity including 0.5, 1, 1.5, 2, and 2.5 W g -1 , and 6 levels of power on-off stated as pulsing ra tios of 1.5, 2, 2.5, 3, 3.5, and 4 were employed. The results showed that the drying r ate decreased with the pulsing ratio and increased with microwave power intensity. Effec tive moisture diffusivity as an indicator of mass transfer was obtained to be highe r at elevated microwave power intensities. Also, increased pulsing ratios had a r educing effect on moisture diffusivity. Using 2 nd law of Fick, moisture diffusivity was calculated t o be varying from 5.93E-10 to 1.42E-08 m 2 s -1 depending on the experimental conditions. Furtherm ore, 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 cor relation with pulsing ratio and drying time. However, due to the dependence of ener gy consumption on MW power intensity, a multiple regression analysis with R 2 of 0.968 was developed. Keywords : Activation energy, Diffusivity, Pulsed drying, Spec ific energy consumption.