Wave-absorbing material-assisted microwave freeze-drying of initially unsaturated coffee frozen material: Numerical simulation and experimental verification

A multi-physics model of multiphase transport was formulated in describing freeze-drying. Traditional and microwave freeze-drying experiments were conducted using initially saturated and unsaturated coffee materials. The results demonstrated that microwave freeze-drying time of initially unsaturated material assisted by a waveabsorbing material was decreased by 40.4 % compared with traditional freeze-drying time of saturated material. The simulated drying curves achieved excellent agreements with the measured ones. The enhancement mechanisms were analyzed in terms of saturation level, temperature, Darcy's velocity and energy utilization. Waveabsorbing material-assisted microwave freeze-drying of unsaturated material realized a simultaneous enhancement of mass and heat transfer for the freeze-drying process.