Pore-scale simulation of multiphase flows using equations of state that preserve the correct surface tension

Abstract

[Abstract:] Surface tension plays a crucial role in determining the interfacial behavior between partially miscible fluid systems, and affects the overall dynamics of phase transition processes. Accurate modeling of surface tension is crucial for understanding and predicting various phase transition phenomena, such as capillary-driven flows, droplet formation, and interfacial dynamics. Cubic equations of state (EoS), such as the van der Waals (vdW) model, incorporate two corrective terms to account for intermolecular interactions. These terms improve the predictions of the equation of state at high pressures and low temperatures, where intermolecular forces become significant; however they also affect to the effective surface tension when the EoS is used in combination with diffuse-interface models of multiphase systems. The ability to capture the correct surface tension is essential in pore-scale models flow through permeable media, particularly in capillary-dominated flow regimes. For typical geological or industrial pore sizes the effective surface tension obtained using standard equations of state may be several orders of magnitude larger than the physical value, which greatly affects the accuracy and physical fidelity of the simulations. In this work we present a methodology that allows diffuse-interface numerical methods to reproduce the physical surface tension in pore-scale simulations of multiphase flow. The proposed methodology is applied to the simulation of interfacial processes at arbitrary length scales while honoring the physical surface tension driving capillary phenomena.