Dual-mode comparative modeling of coupled electromagnetic–thermal–moisture transport with and without moving boundaries during pulsed microwave drying

Using moving boundaries to investigate shrinkage in simulating the drying of food materials is of great significance. Intermittent microwave (MW)-assisted drying has recently achieved notable popularity owing to its energy efficacy. The effect of applying moving boundaries (MB) on field waves, thermal state, and moisture profiles was compared against the assumption for fixed volume (NO-MB) in simulating a two-stage drying for potato pieces using periodic MW and hot air (HA). The absence of moving boundaries led to a higher electric field in the internal parts and a lower electric field at the edges. This was due to the shorter distance between the core and the exterior under the MB condition, owing to a smaller volume. Accordingly, the dispersal of the electric field with the application of moving boundaries was more uniform. Furthermore, in the NO-MB state, the average temperature exhibited a more significant rise, ascribed to a more extensive product volume and, consequently, a more substantial absorption of electromagnetic waves and increased heat production. Using moving boundaries brought the simulated data closer to the experimental ones. The established model may assist as a suitable basis for application in other products under various drying circumstances.