The drying energy is proportional to the temperature difference between the shelf (Tf) and the phase change temperature of pure ice at the pressure (vacuum) controlled by the freeze dryer. The highest temperature gradient implies increased heat flow (faster process), but we need to be careful not to surpass the maximum temperature allowed at the product (Tc), also to do not exceed the freeze dryer capacity.
But at what temperature will my product be established for a specific freeze dryer pressure and temperature of the shelf?
The answer to this question is not trivial as it depends on multiple parameters such as: the heat transfer between the shelf and the vial, the filling height, the resistance of the dried product to the sublimation vapors (also the resistance of the stopper).
Also, it shall be noted that the temperature at the product will increase during the primary drying, being maximum at the end of this step, because while the drying process is progressing the larger the dryer layer of product to be crossed by the sublimation vapors.
Do you want to understand better the freeze-drying process, contact Lyoptimus team to expand you knowledge. (contact@lyoptimus.com)
At the example below: Tf=+15ºC, Pc=0.5mbar(-27ºC), Tpmax=-17ºC.
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