Heat transfer and dynamic deformation in infusion bags during hot water shower sterilization: A numerically efficient two-step CFD multiphase model

Hot water shower sterilization is crucial for ensuring patient safety during the manufacturing of liquid pharmaceutical products. This process, when performed at lower temperature levels, can also be applied to the thermal processing of foods. The energy-intensive heating and cooling of pharmaceutical or food products by water showering lack numerically efficient multiphase models for optimization. This study introduces a numerically inexpensive two-step simulation model. In the first step, the multiphase flow and heat transfer to the product are analyzed, and a local, time-averaged surface heat transfer coefficient is calculated. This coefficient is then used as a convective boundary condition in the second step, which simulates only the internal flow of the product. A 500 ml polypropylene infusion bag was used as a test product. The model considers the influence of the water film, dynamic deformation of the bag wall, conduction between the bag and the underlying hole plate, and possible condensation. The numerical model was validated with product temperature, qualitative flow regime analysis, and film thickness measurements on a lab-scale test bench. The error between the simulated and experimental product temperature was mostly within $\pm$1.0 K. The critical slowest heating and cooling zones inside the bag were found to be at 15 % and 85 % of the bag height, respectively. Heat transfer from the bag underside and the hole plate significantly influenced the total heat transfer during the heating of the bag. The model’s high numerical efficiency enables practical application and upscaling, offering valuable insights into heat transfer mechanisms in infusion bags.