Influence of inner vapor transfer property of a freeze dryer on the design space of drying process

A freeze dryer with a radiative heating device was constructed and the inner vapor transfer property was regulated by separating the drying chamber and the condenser with an orifice. A mathematical model was used to obtain the contour diagrams of the selected parameters (e.g., product temperature and total drying period) during drying as a function of the heating condition and chamber pressure. Furthermore, the inner vapor transfer coefficients of the freeze dryer were used to draw the operation lines on the diagrams. The combinations of contour diagrams and operation lines clearly depict the design spaces. It was confirmed that the inner vapor transfer property substantially affected the acceptable operation range, and it was revealed that this coefficient is key to quantify the performance of a freeze dryer. This coefficient could also be used to predict the occurrence of choked flow during a freeze-drying run.