Numerical modelling of the evaporative cooling effect on solid walls in steam sterilisers

Abstract

Steam sterilisation is based on high heat transfer rates which occur during the condensation of steam on medical devices or the steriliser walls themselves. To ensure these high heat transfer rates, non-condensable gases (NCGs) such as air must be removed from the chamber. One method is to extract the NCGs by using vacuum pumps. Due to the reduction in pressure, the saturation temperature drops as well, causing water droplets to evaporate; thus, the walls and loads cool down. This mechanism was investigated using a three-phase CFD model. A highly time-efficient heat transfer model for the evaporation process was developed as a result of this investigation. Evaporative cooling effects on the steriliser walls could be achieved by using a mass source term which varied in terms of time and space. Our results indicate that the model can be used to predict the temperatures of the fluid as well as the solids in a numerically inexpensive manner. In addition, this model allows the user to predict whether surfaces can be completely dried, an aspect which is crucial for ensuring the quality of a sterilisation process. The model created allows researches to simulate the entire sterilisation cycle, addressing a previously existing knowledge gap. Furthermore, the presented methods are also suitable for use in other industrial applications where condensation and evaporation effects on solids need to be effectively and inexpensively determined.