Oil droplet behavior at a pore entrance in the presence of crossflow: Implications for microfiltration of oil-water dispersions

TL;DR

This study numerically investigates how shear flow affects oil droplet entry and breakup at a micropore, revealing critical pressure increases and breakup conditions relevant for microfiltration processes.

Contribution

It provides a validated numerical model for droplet behavior at pore entrances under shear flow, including breakup conditions and effects of physical parameters.

Findings

Critical permeation pressure aligns with Young-Laplace theory without shear.

Shear flow increases critical pressure and causes droplet breakup.

Droplet breakup is influenced by surface tension, viscosity ratio, and size, but not contact angle.

Abstract

The behavior of an oil droplet pinned at the entrance of a micropore and subject to clossflow-induced shear is investigated numerically by solving the Navier-Stokes equation. We found that in the absence of crossflow, the critical transmembrane pressure required to force the droplet into the pore is in excellent agreement with a theoretical prediction based on the Young-Laplace equation. With increasing shear rate, the critical pressure of permeation increases, and at sufficiently high shear rates the oil droplet breaks up into two segments. The results of numerical simulations indicate that droplet breakup at the pore entrance is facilitated at lower surface tension, higher oil-to-water viscosity ratio and larger droplet size but is insensitive to the value of the contact angle. Using simple force and torque balance arguments, an estimate for the increase in critical pressure due to crossflow and the breakup capillary number is obtained and validated for different viscosity ratios, surface tension coefficients, contact angles, and drop-to-pore size ratios.