Stopper water vapor transport

Fig. 1.87. Influence of different forms of stoppers on the water vapor transport out of the vials into the chamber. At a pressure of 1 mbar in the vial the following relative amounts of water vapor are transported into the chamber in 3 h ...

Transport out of the container (2) into the drying chamber produces no measurable pressure drop if the product surface is equal to the opening of the container (e. g. with trays). Vials without stoppers in the vial neck do not produce a measurable pressure drop, if e. g. 1 g/h water at a Tice of -20 °C and a pressure difference of 0.6 mbar are transported. In this example the velocity of water vapor is a few m/s. 

If the product is filled in syringes (Figure 4) the heat transfer is reduced. If the product to be frozen is in contact with the stopper this will present an additional material to be cooled. Especially in that case one can expect a freeze concentration in the product that is in contact with the stopper. The sublimated water vapor has to be transported through the small bottle neck. Both circumstances, the freeze-concentrated product and the limited opening, require a low product temperature and a low shelf temperature (T h), a small AT during... 

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