Heat and mass transport in microwave drying of porous materials in a spouted bed



A heat- and mass-transfer model was developed to simulate microwave and spouted-bed combined (MWSB) drying of diced apples, a hygroscopic porous material. A total gas-pressure equation was introduced to take into account internal vapor generation during microwave drying. The governing equations for heat and mass transfer were simplified using a scaling technique and numerically solved with the finite difference method. The physical, thermodynamic, thermal, transport and dielectric properties used in the simulation were either from our measurements or from the literature. Model predictions agreed well with experimental results. The pressure-driven moisture migration during MWSB drying resulted in a high drying rate. The numerical analysis predicted a temperature-leveling effect that was confirmed by experimental results. The unique temperature leveling in MWSB drying helps to control product temperature and improves product quality as compared to microwave-assisted fixed-bed hot-air drying methods.