A multiphase porous medium transport model with distributed sublimation front to simulate vacuum freeze drying

•Validated and developed distributed sublimation front freeze drying model.•Model incorporates effects of Knudsen flow in porous media.•Presents sublimation velocity and magnitude, with and without microwave heating.

A porous medium transport model with a distributed sublimation front is developed for low pressure freeze drying of beef by radiant surface heating and volumetric microwave heating. The model incorporates the importance of Knudsen flow in porous materials during low pressure freeze drying. This effort is part of fundamental physics-based framework building for simulating food and biomaterial processes involving rapid evaporation/sublimation. Temperature, pressure and ice saturation histories were computed. Drying rates and spatial temperature profiles showed excellent agreement with literature experimental data. Sublimation front width, a novel result, is seen to increase as ice saturation decreases, justifying the importance of this distributed sublimation formulation in contrast with the sharp sublimation front commonly employed in literature. The insulation effect of the gas fraction in the pores is observed by the slow movement of the sublimation front in ‘thick’ samples. Effects of porosity, initial ice saturation and microwave heating are illustrated.