Numerical analyses of bubble point tests used for membrane characterisation: model development and experimental validation

A numerical model for simulating the microhydrodynamics inside different pore sizes was developed in this work, using a continuous penalty finite element scheme. This scheme combines the flexibility in modelling two phase systems, as the one simulated in this work with accuracy. The volume of fluid (VOF) method was applied to track the motion of the gasliquid interfacial boundary as an approach to monitor the repulsion of the wetting liquid from the pores to detect their bubble pressures. To resolve the complexities arising from the inclusion of the surface tension at the liquid-gas interface as an unknown dynamic condition it is treated as a resistance force in the equations of motion. The effects of the surface tension and other forces such as the buoyancy are then determined by model calibration with respect to a set of experimental data. To obtain the experimental data, the bubble point test was used to characterise different Nuclepore track etched membrane samples, which provided insights into the mechanisms underlying the test and into the interpretation of the pore size distribution. The experimental data are used to calibrate the numerical model. The calibrated model was, in turn, used to predict the outcome of bubble point tests for a range of inlet boundary conditions. The results obtained from these simulations are shown to be in good agreement with of the experimental data, indicating the ability of the developed model to accurately predict the bubble point pressure.