Use of a porous membrane for gas bubble removal in microfluidic channels: physical mechanisms and design criteria

TL;DR

This paper presents a simple, efficient microfluidic device using a hydrophobic porous membrane to remove gas bubbles from liquids, with a detailed physical model and design criteria ensuring complete separation.

Contribution

It introduces a novel microfluidic gas removal system with a comprehensive physical model and four key design criteria for effective operation.

Findings

Achieved gas removal rates up to 7.4 μL/s per mm² of membrane

Identified four critical operating criteria for complete gas-liquid separation

Demonstrated complete removal of gas plugs in a prototype device

Abstract

We demonstrate and explain a simple and efficient way to remove gas bubbles from liquid-filled microchannels, by integrating a hydrophobic porous membrane on top of the microchannel. A prototype chip is manufactured in hard, transparent polymer with the ability to completely filter gas plugs out of a segmented flow at rates up to 7.4 microliter/s per mm2 of membrane area. The device involves a bubble generation section and a gas removal section. In the bubble generation section, a T-junction is used to generate a train of gas plugs into a water stream. These gas plugs are then transported towards the gas removal section, where they slide along a hydrophobic membrane until complete removal. The system has been successfully modeled and four necessary operating criteria have been determined to achieve a complete separation of the gas from the liquid. The first criterion is that the bubble length needs to be larger than the channel diameter. The second criterion is that the gas plug should stay on the membrane for a time sufficient to transport all the gas through the membrane. The third criterion is that the gas plug travel speed should be lower than a critical value: otherwise a stable liquid film between the bubble and the membrane prevents mass transfer. The fourth criterion is that the pressure difference across the membrane should not be larger than the Laplace pressure to prevent water from leaking through the membrane.