Heat-moisture-mechanical bidirectional coupling multiphase porous media model for microwave vacuum drying of pitaya

• The modelling of microwave vacuum drying of pitaya with heat-moisture and mechanical bidirectional coupling is established. • The effect of shrinkage on the processes of heat and moisture transfer is simulated. • Shrinkage accelerates moisture loss while concurrently impeding heat transfer. • The mass transfer process exhibits greater sensitivity to variations in physical parameters. Microwave vacuum drying (MVD) is widely adopted in the food industry helping maintain high product quality but the impact of shrinkage on heat and mass transfer is often overlooked. In the present study, the popular fruit, pitaya, was selected for a case study; a heat-moisture-mechanical (HMM) coupling multiphase porous medium model is developed to comprehensively analyse the effect of shrinkage on heat and mass transfer during the MVD. The findings indicate that the HMM model shows a faster decrease in moisture content, with the maximum deviation of 144.85%, and a larger evaporation rate peak, with a deviation of 36.76%. The average temperature predicted by the HMM model was lower than that of the HM model during the early drying stage, with a maximum temperature difference of 5.76℃. Throughout the drying process, axial shrinkage was greater than radial shrinkage. The HMM model can effectively predict the influence of material property parameters on the shrinkage process, in which the hygroscopic expansion coefficient exhibits the most significant impact on volumetric strain (reaching up to 10.1%). The model can more accurately simulate the food MVD process and provides technical support for optimizing the drying process and enhancing product quality.