Modeling steam penetration into hollow devices: Effects of phase change and non-condensable gases during steam sterilization

• Accurate numerical modeling of condensation and re-evaporation processes during steam sterilization in the presence of air, validated against experimental temperature data. • New wall adhesion model implemented within the Eulerian wall film framework enables efficient simulation of adhering condensate on solid surfaces. • Excellent agreement between simulated and measured water vapor mole fractions inside hollow devices using 2f/1f wavelength modulation spectroscopy at 1364 nm. • Practical recommendations for improving steam penetration: ensure early 100% steam atmosphere and enhance thermal coupling within medical devices. To ensure effective sterilization of medical devices during a steam sterilization cycle, all non-condensable gases must be removed from both the chamber and the interior of the devices. This removal is facilitated by defined phases of increasing and decreasing pressure, which cause steam to condense and re-evaporate, resulting in repeated heating and cooling of the devices. To better understand the influence of phase changes on steam penetration, a computationally efficient numerical model was developed, coupling the Eulerian wall film model with the Eulerian–Lagrangian approach. A new wall adhesion model was developed to account for condensate adherence during phase change. The numerical model was first validated by comparing measured and simulated temperature profiles of stainless steel and aluminum cylinders during typical steam sterilization cycles. The validation covered steam environments with mole fractions from 0 to 0.99 and showed excellent agreement during both condensation and re-evaporation phases. In a second step, steam penetration into a simplified medical device was measured using a setup based on 2f/1f wavelength modulation spectroscopy at 1364 nm. The numerical model accurately predicted the water mole fraction over the entire observed period. Based on the results, several recommendations for improving steam penetration were derived: (1) a 100 % steam environment should be established in the chamber as early as possible, as even small amounts of residual air reduce penetration depth; and (2) internal surfaces of medical devices should be well thermally connected to their exteriors to promote heating via conduction. In summary, the proposed model captures all relevant physical processes of steam sterilization and provides a valuable tool for improving sterilization effectiveness and the safe reuse of medical devices.