CFD investigations of steam penetration, air-removal and condensation inside hollow loads and cavities

Highlights: • Multiphase flow (steam, water, non-condensable gases) was simulated using CFD. • CFD models were developed to simulate the air-removal inside hollow loads. • The contents of non-condensable gases were compared after different cycle times. • A numerically efficient heat transfer model was added to the CFD code. • The steam penetration near the closed ends of hollow loads was investigated. -- Abstract: Steam sterilization is the most commonly used method to sterilize re-usable medical devices. All non-condensable gases (NCGs) must be removed from every hollow space within the medical device in order to guarantee the high heat transfer rates that result from wall condensation. In this work, a computational fluid dynamics (CFD) model was developed to simulate the fluid flow, temperature, heat transfer, and steam penetration inside the steam sterilizer with a particular emphasis on hollow loads (cavities). The flow inside the steam sterilizer was modeled with a three-phase Eulerian-Eulerian model, which includes evaporation and condensation effects. A very numerically inexpensive model was developed and implemented into the CFD code in order to calculate the heat transfer that occurs due to wall condensation in the presence of NCGs. The CFD model was validated by the measurements of temperature, pressure, and NCGs content after different cycle times. The average error between the measured pressures and temperatures and the results of the simulations were 0.16% and 0.54%, respectively. Furthermore, the steam penetration at the ends of the hollow loads was measured using chemical indicators. The simulation results show that a steam concentration of approximately 5% is sufficient to change the color of the chemical indicators. The CFD model developed is able to predict the volume fraction of NCGs, as well as steam penetration inside the steam sterilizer, including the hollow loads (cavities). Thus, it should be easier for future developers of steam sterilizers to investigate steam penetration within hollow loads and cavities.