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Fluidized bed, microwave assisted fluidized bed drying of macaroni beads

Göksu, Emel Iraz
This study is aimed to compare the fluidized bed and microwave drying with microwave assisted fluidized bed drying. For this purpose, macaroni beads (2.4±0.08 mm diameter) were dried from about 20% to 12% moisture content in a fluidized bed of 7.6 cm diameter, in a domestic microwave oven with a power of 609 W and in the fluidized bed placed in the microwave oven conditions. In the experiments with the fluidized bed three air temperatures; 50, 60 and 70°C at an air velocity of 2.3 m/s and in those with the microwave oven two power levels; 50% and 100% were used. The drying curves indicated that the drying rate increased with the air temperature and microwave power in each drying method. Microwave assisted fluidized bed drying reduced the drying time by about 50% and 11% on the average compared with the fluidized bed and microwave drying, respectively. Therefore, it was concluded that the drying time was reduced more by the effect of microwave energy than the fluidization. The effective diffusivities in the fluidized bed and microwave assisted fluidized bed drying were found to be in the order of 4.125x10-11 and 8.772x10-11 m2/s on the average, respectively. The effective diffusivities for the fluidized bed drying were fitted to an Arrhenius type of equation and the magnitude of the activation energy was found to be in the order of 12595 kJ/kg mol.