Session: 10-07-01: Fluid Mechanics and Rheology of Nonlinear Materials and Complex Fluids

Paper Number: 117082

117082 - The Limits to Bubble Capture Through Porous Aerophilic Membranes 

Bubbles are present and form problems in many industrial applications. Hence, the ability to efficiently capture bubbles could have an impact on an array of industries, such as energy, biomanufacturing, electrochemical gas evolving systems, biomedicine development, desalination, methane capture, and others. Hydrophobic membranes are a common tool used to capture unwanted bubbles in these applications. Here, rapid bubble capture on the order of tens of milliseconds is required as longer bubble capture times will lead to bottlenecks. For example, in microfluidics a larger channel would be required to capture sufficient gas fluxes ; while in the anti foaming case, foaming will not be prevented if the sparging rate exceeds the bubble capture rate. Hence, in this work we seek out the mechanisms behind transport of a bubble through hydrophobic membranes of different permeabilities. For this, we designed and fabricated a silicon membrane platform. This membrane platform is created using a Deep Reactive Ion Etching (DRIE) process on 200 μm thin silicon. We have created membranes with different hole sizes (d) and open area fractions (𝜙) (defined as the ratio between the total area of the holes divided by the total area of the membrane). The membrane surface is made nano structured and super hydrophobic or aerophilic, with a contact angle of 150 degrees. 

Through bubble evacuation experiments on our membrane platform, we have uncovered three different distinct regimes limiting the bubble evacuation through an aerophilic membrane. These regimes include a viscous limiting regime, an inertially limiting regime, and a porosity limiting regime. Through the use of scaling laws and pre factors, and by experimental validation, we can predict the transition between these regimes. These results are then combined on a design map. This design map allows for prediction of the evacuation time of a bubble through a membrane, given a certain set of experimental conditions including radius, a set of viscosities, and a membrane permeability.

At the high end, bubble capture times under 1ms have been recorded for a 3.5mm diameter bubble. As far as the authors are aware, no faster time has been recorded in literature as of March 2023. This work elucidates the limiting factors behind bubble transport through a membrane. Our work can be directly used by anyone requiring bubble evacuation through a membrane driven by Laplace pressure, regardless of the properties of the medium, the bubble, the surface tension, or the membrane. Hence its results can be directly translated to applications where bubble capture is required.

Presenting Author: Bert Vandereydt Massachusetts Institute of Technology

Presenting Author Biography: Bert is a PhD student in the Varanasi group at MIT. He completed his master's in Nuclear Engineering from ETH-Zurich. He currently works on eliminating bottle-necks on the interface, for applications ranging from energy to medicine.

Authors:

Bert Vandereydt Massachusetts Institute of Technology
Saurabh Nath Massachusetts Institute of Technology
Tal Joseph Massachusetts Institute of Technology
Kripa Varanasi Massachusetts Institute of Technology