Use of Time Temperature Integrators for determining process uniformity in agitated vessels

Time Temperature Integrators (TTIs) were used to investigate the process uniformity of an industrial scale 250 1 agitated vessel. Factors such as fluid viscosity, fill level and direct and indirect heating have been examined. Different numbers of TTIs were added throughout each experiment and temperature was recorded using 2 thermocouples: one fixed in the centre and one on the wall of the vessel. TTIs were added at the start of the experiment and also at the end of the heat up time. Novel designs of TTI fitted inside either porous plastic balls or a series of plastic tie clips to prevent over-processing due to contact with the hot vessel wall were also used. P values recorded by the TTIs illustrated significant heterogeneity of heating for viscous fluids which could be partly overcome by steam injection. Overfilling also affected the heating efficiency, possibly due to changes in the flow field. The use of the novel TTIs enabled more accurate determination of the thermal processing of the fluid away from the vessel wall. This paper demonstrates that TTIs can be used for thermal monitoring and validation of processes in the food industry (centre and wall) which is more representative. (C) 2007 Elsevier Ltd. All rights reserved.