Estimation of the effect of product shrinkage on the drying times, heat input and condenser load of the primary and secondary drying stages of the lyophilization process in vials

Abstract

The effects of cake shrinkage on the drying times and energy requirements of the primary and secondary drying stages of the freeze drying process involving the drying of a material in a vial, are estimated through the construction and solution of an extended unsteady state and spatially multidimensional model that accounts for the changes introduced by cake shrinkage on the internal and external mass and heat transfer mechanisms of the freeze drying process. The results of this study suggest that, apart from possible product stability problems that could occur because of cake shrinkage, economically effective drying with respect to drying time, heat input, and condenser load capacity is attained when there is no gap between the vial wall and the dried layer of the product in the vial.