SIMULATION OF FLUIDIZED-BED DRYING OF CARROT WITH MICROWAVE HEATING

ABSTRACT

A mathematical model of coupled heat and mass transfer was applied to batch fluidized-bed drying with microwave heating of a heat sensitive material—carrot. Four kinds of microwave heating with intermittent variation were examined. The numerical results show that different microwave heating patterns can affect the fluidized bed drying significantly. Changing the microwave input pattern from uniform to intermittent mode can prevent material from overheating under the same power density. Supplying more microwave energy at the beginning of drying can increase the utilization of microwave energy while keeping temperature low within the particle. For a particle diameter of 4 mm, fluidization velocity of 2 m/s, inlet airflow temperature of 70°C and the bed area factor of 80, the drying time are 750 and 1000 s, respectively, for the two good operating conditions with on/off periods of 125/375 s and 375/375 s. The cumulative microwave energy absorbed by particles at the end of drying is 1415 and 2300 kJ/kg (dry basis), respectively.

Keywords:

• Intermittent heating
• Moisture
• Product quality
• Temperature

ACKNOWLEDGMENTS

Mr. Wei Wang is partly supported by RGC grant of HKUST 6044/009. Dr. B. N. Thorat was financially supported by the Post-Doc Fellow matching Fund of VPAA of HKUST.