Experimental evidence of mass transfer mechanisms during freeze-drying in a capillary porous medium

The morphology of the drying front at pore-scale was studied to gain a better understanding of the mass transport mechanisms that occur at pore-level. Therefore, a glass micromodel was built using a photolithographic technique. Micromodels can be defined as transparent networks of pores (pore bodies) and constrictions (pore throat) that capture the complexities of natural porous media. The micromodel was saturated with distilled water and frozen at −85 °C and then put into a laboratory lyophilizer maintained at −42 °C. Pore-level distribution of ice and vapor as the mass transport process advances were reported. Ice distribution in the bidimensional porous medium was slightly influenced by pore structure disorder. Two different sublimation regimes were also observed (fast front advance and slow front advance). Preliminary results show that the drying front for the slow front regimes scaling over time with an exponent of 0.577.

► We have shown experiments of freeze-drying in a glass micromodel. ► We have obtained images of sublimation front during freeze-drying. ► Sublimation front was slightly influenced by the pore structure. ► There were no ice clusters during the sublimation process. ► We have observed two different regimes during sublimation.