Microwave Drying of Parsley: Modelling, Kinetics, and Energy Aspects

Parsley (Petroslinum crispum Mill.) leaves were dried in a 900 W 2450 MHz domestic microwave oven to assess the effects of material load on drying time, drying rate, drying efficiency, and specific energy consumption. Microwave drying experiments with different material loads ranging from 64·30 to 128·57 g were performed at microwave power cycle of 9 s on/9 s off at 900 W microwave output power. Drying took place mainly in constant rate and falling rate periods. A relatively long constant rate period was observed after a short heating period. Among the 11 mathematical models tested to fit the drying rates of parsley leaves, the Midilli et al. model with drying rate as a log–log and linear function of time gave the best fit for all the data points. The value of the drying coefficient k decreased with the increase in the dried material load. The multiple regression on the coefficients of the Midilli et al. model for the effects of material load being dried gave the successful results and showed to satisfactorily represent microwave drying kinetics of parsley leaves for the material loads between 64·30 g and 128·57 g. Increasing the material load resulted in a considerable increase in drying efficiency and a significant decrease in specific energy consumption. About 9·5% increase in drying efficiency and about 18% (0·92 MJ kg−1 [H2O]) decrease in specific energy consumption could be obtainable by increasing the material load from 64·30 to 128·57 g.