A variety of two‐phase flow experiments, currently available in the literature, are compared to study the effect of fluid relaxation on interfacial area generation. Interfacial area is an important parameter that controls mass transfer in many engineered multiphase systems, so it is important to develop accurate predictive tools describing multiphase flow to engineer efficient processes. An empirical predictive relationship was developed describing a specific interfacial area‐wetting saturation relationship that depends on the number of quasi‐equilibrium relaxation points obtained during a drainage or imbibition experiment. The empirical expression was tested and verified using a number of existing datasets. We found that different relationships were needed depending on the fluid properties as well as the porous medium. However, clear trends were observed that can, once a predictive relationship is established for the system, allow us to design multiphase flow systems to produce a desired amount of interfacial area tailored to a particular application.

Meisenheimer, D. E., & Wildenschild, D. (2021). Predicting the effect of relaxation on interfacial area development in multiphase flow. Water Resources Research, 57, e2020WR028770. abstract

Example relaxation pathways for (a) a main imbibition capillary pressure‐saturation and (b) a main drainage specific interfacial area‐saturation curve for non‐equilibrium and quasi‐equilibrium data. Arrows indicate the direction in which data points were collected. QuasiEq points were measured after 15 min of relaxation. The capillary pressure in quasi‐equilibrium systems recover to a comparable state as the non‐equilibrium system after relaxation, whereas specific interfacial area does not, illustrated by the divergence in curves in Figure 1b, and the convergence of curves in Figure 1a.