Numerical simulation of dripping and jetting in supercritical fluids/liquid micro coflows

In this work, a two dimensional simulation of segmented micro coflows of CO2 and water in micro-capillaries (20 < T (degrees C) < 50 and 8 < p (MPa) < 16.5) was carried out using a combination of the one-fluid model and the volume of fluid (VOF) method to describe the two-phase flow and a penalty method to account for the wetting property of the capillary walls. The computational work was validated by comparing numerical and experimental results in both the dripping and jetting regimes. The agreement of the calculated pressure difference across the droplet or jet interface with the Laplace-Young's law was assessed as supplementary criteria. The effects of CO2/water interfacial tension (5 < sigma (mN m(-1)) < 35) and wall wettability (contact angle CO2/wall varying from 0 to 180 degrees) on the segmented water-supercritical CO2 microflows were specially described. It was shown that switching the wall surface from hydrophilic to hydrophobic by tuning the contact angle allows for changing the droplet curvature so that the continuous water phase eventually undergoes a phase inversion resulting in water droplets/slugs formation in a continuous CO2 phase. (C) 2013 Elsevier B.V. All rights reserved.