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Based on the mechanism of moisture and heat transfer in wood during microwave-vacuum drying (MVD), a one-dimensional mathematical model to describe the process of wood MVD was established and verified by experiments in this research. The results showed that the process of MVD of wood experienced three distinct periods: (1) accelerating rate with rapid warming-up drying period, (2) a constant temperature and constant rate drying period, and (3) a heating-up with falling rate drying period. Compared with conventional hot air drying, the total drying process is almost governed by a constant rate period in vacuum-microwave drying of wood. The predicted temperature and moisture content in wood match well with the experimental data, the square of the relevant coefficient of the values of simulation and test is above 0.9, and the simulation precision of the change rule of the moisture is higher than that of the temperature. [ABSTRACT FROM AUTHOR]

The drying kinetics (maximum drying rate, drying constants) and center temperature of selected powder (aspirin, paracetamol, lactose, and maize starch)–solvent (water, ethanol, methanol, and acetone) systems were monitored during microwave-vacuum drying. An experimental microwave-vacuum system (650 W and 2.45 GHz) operated at 61–81 kPa was used. The drying rate profile did not vary with the powder–solvent system; an initial warming-up period was followed by a constant-rate stage and two falling-rate periods. However, the drying kinetics were found to be both powder and solvent dependent, with the drying times for acetone-, ethanol-, and methanol-wetted materials being considerably shorter (up to 89.8%) than those of samples containing water. Although the general form of the temperature profile (short warming-up period, constant-rate stage, and decreasing temperature phase) was similar for all systems, the maximum temperatures varied quite significantly with solvent type, ranging from highest to lowest in the order water-ethanol-methanol-acetone. For most powder–solvent systems, reduced operating pressure facilitated increased drying rates and thus shorter drying times. [ABSTRACT FROM AUTHOR]