On the use of infrared thermography for monitoring a vial freeze-drying process

Monitoring a vial freeze-drying process without interfering with product dynamics is a challenging issue. This paper presents a novel device constituted by an IR camera designed to be placed inside the drying chamber, able to monitor the temperature of the vials, very close to that of the product inside. By this way it is possible to estimate the ending point of the primary drying, the heat transfer coefficient to the product (Kv) and the resistance of the dried product to vapour flux (Rp). Experiments were carried out in a pilot-scale freeze-dryer, processing 5% and 10% sucrose solutions at different values of shelf temperature and chamber pressure, using both thermocouples and the IR camera to track product dynamics. Results evidence that the measurements (of temperature) and the estimates (of the ending point of the main drying and of Kv and Rp) obtained using the two systems are very close, thus validating the IR camera as an effective PAT for the freeze-drying process. Besides, it was shown that the presence of the IR camera in the chamber is not responsible for any additional heating to the product, and that monitored vials are representative of the majority of the vials of the batch.