Time-scale modeling and optimal control of freeze-drying

Abstract

Freeze–drying is considered to be an attractive dehydration method of preserving the quality of high value foods products. Unfortunately, it is an expensive operation, which calls for efficient tools capable of minimizing time and/or energy while preserving product quality.

In this work, time-scale analysis has been applied to a detailed first-principle-based model. From such analysis a simplified model, capable of describing freeze–drying at the time scales relevant to quality, has been proposed. The model has been solved by the Finite Element method, showing good agreement with the results in literature. Likewise, the efforts associated with the computation of optimal operation policies have been reduced.

In this regard, different operational scenarios that take into account shelf temperature (TL) and chamber pressure (Pc) have been considered on a simulation basis. In all cases the resulting optimal control profiles obtained led to significant reductions of cycle time while ensuring product quality.