Numerical investigation of heat and mass transfer behavior of freeze drying of milk in vial

The transient heat and mass transfer characteristics of the freeze-drying process of milk in a vial is numerically investigated. The paper reports the influence of semi- stoppered vial on mass transfer resistance and the relative importance of the bottom curvature of the vial on the drying time. Moreover, the variation of product temperature and mass transfer resistance as a function of time is predicted. The study revealed that the vial heat transfer coefficient strongly depends on chamber pressure; however, the effect of shelf temperature is minimal. The analysis is conducted for two fill heights (8.25 and 16.5 mm.) It is observed that the presence of curvature at the bottom of the vial increases the primary drying time but decreases the product temperature. Based on the simulation, it is observed that 16.5 mm product fill height provided higher mass transfer resistance than 8.25 mm fill height.