Freeze Dryer Partition Temperature Control Uniformity Measurement

In terms of freeze-drying technology in pharmaceuticals, it is concerned about how to produce products with good consistency in accordance with key quality requirements, which requires ensuring the consistency of the production process. For the freeze dryer, in addition to the independent and controllable variables that have passed the test, the partition inlet temperature, chamber pressure, time, etc. must also be tested.
 
A common practice is to perform process qualification (PQ) on the freeze-drying process. Before performing specific PQ on a product, the performance of the freeze dryer must be confirmed in the factory. Once installed in place, the operation qualification (OQ) must be performed again as part of the commissioning. The verification shall ensure that the key process parameters are operating within the allowable error range as specified. For the freeze dryer, in addition to the independent and controllable variables that have passed the test, the partition inlet temperature, chamber pressure, time, etc. must also be tested, which is conducive to evaluating certain variables that directly affect product consistency. One of the important measurements is the temperature uniformity of the partition, sometimes referred to as the temperature distribution of the partition.
 
The temperature of the partition is generally controlled and monitored by a resistance temperature detector (RTD). The resistance temperature detector (RTD) is inserted into a heat source from the inlet to the slab of the hot well. The partition temperature is generally referred to as the partition inlet temperature (partition inlet). The heat transfer from the freeze dryer to the product that occurs from the surface of the partition to the vial interface. Measuring the actual temperature of the partition surface is the key to evaluating the performance of the freeze dryer. The measured partition temperature distribution should be compared with the relevant control points, and the partition entrance should be ensured within an acceptable range and uniformity.
 
The challenge in this type of verification is the ability to measure the actual surface temperature of the partition without being affected by the environment. Temperature measurement equipment can be divided into two categories, direct measurement and indirect measurement. Direct measurement is to use a fixed temperature sensor, usually a thermocouple, to directly measure the surface of the partition. However, the disadvantage of the direct measurement method is that the temperature sensor is difficult to fix and maintain it in a low or high temperature range, and it usually requires a lot of cleaning of the remaining adhesive or glue. The main advantage of this method is that it can measure the actual surface temperature at a specific location with correct operation. Indirect measurement is to embed a temperature sensor into a thermally conductive material placed on the surface of the board.
 
Some freeze dryers use the indirect measurement principle. The main disadvantage of this type of equipment is that the measured temperature is more susceptible to the environment of the chamber. However, these effects can be resolved by the test method. The main advantage of indirect measurement is that the device can be placed firmly and any potential residues can be eliminated.