Coupled radiative-electromagnetic-thermal modeling and multi-parameter optimization for enhancing heat transfer uniformity in radio frequency pulsed vacuum drying

In this study, the effects of tray shape, loading thickness, electrode gap, vacuum level, and vacuum pulsation ratio on the heating performance during radio frequency pulsed vacuum drying (RFPVD) were systematically investigated. First, based on the established RF heating model, the radiative heat transfer equation was coupled to improve the accuracy of heat transfer simulation under vacuum conditions. Simulation results showed that the temperature uniformity index (TUI) in RF heating stage was reduced to 0.13 by suppressing the edge aggregation effect of the electric field with circular tray. Additionally, single-layer stacking and increased loading thickness effectively improved the heating rate; however, the resulting enhancement of edge aggregation resulted in the TUI increased to 0.31. When a loading thickness of 45 mm was applied, adjusting the electrode gap to 95 mm increased the heating rate and avoided the localized overheating during the heating stage. At a defined drying temperature, an appropriate vacuum level modulated the moisture evaporation rate to optimize the temperature distribution. The RFPVD experiments verified that ideal temperature distribution uniformity (TUI < 0.112) and post-drying moisture content consistency (coefficient of variation<5 %) could be obtained using multi-parameter optimization guided by simulation results. This study provides a theoretical basis and process optimization strategy for improving heating uniformity in RFPVD drying of granular materials.