Session: 11-17-01: Micro/Nanofluidics 2025 - Fluid Engineering in Micro- and Nanosystems

Paper Number: 173582

Acoustic Mitigation of Cake Formation in Microfluidic Membrane Filtration 

It is estimated that 50% of the operational costs for membrane microfiltration is linked to particulate fouling.  This fouling is the result of particulates building up on the membrane surface, forming what is known as a cake layer.  The pressure required to drive fluid through a cake layer, known as the transmembrane pressure (TMP), increases with time, thus requiring a significant pumping power input.  The impact of cake layer growth on membrane microfiltration can have significant consequences. For example, membrane fouling can reduce access to clean water, which negatively impacts human health, creates economic disparity and contributes to food insecurity.  One approach to extending membrane microfilter operational lifetime is by using external fields.  External fields (e.g., magnetic, electric, acoustic) act on particulate matter entrained in flow and can be used to trap particulates before they reach the membrane microfilter or disrupt cake layer formation.

Specifically, our work focuses on the use of acoustic fields as filtration support mechanism. 
Acoustic fields generate localized flows, known as acoustic streaming, that the authors hypothesize can break up the cake layer due to increased fluid mobility. To test this hypothesis, a microfilter was constructed in polydimethylsiloxane (PDMS) that consists of a series of 10-micron wide microchannels.  The distance between 10-micron microchannels can be modified to examine the impact that membrane porosity has on experimental results.  Fifteen-micron diameter polystyrene particles are introduced to the microfilter to act as model solids, which permits the observation of cake layer formation.  A differential pressure sensor is employed to observe the TMP while the microfilter is in operation under passive and acoustic streaming conditions.  Two flow rates, 100 mL/hr and 300 mL/hr, are used to introduce solids to the microfilter.  Acoustic streaming is observed at a resonance frequency of 5.9 kHz with excitation voltages of 60 V and 90 V.  We find that acoustic streaming breaks up the cake layer and achieves a 50% pressure drop at 90 V when compared to passive conditions.  Particle image velocimetry with one-micron diameter polystyrene particles was also performed to map out the fluid flow field in the presence and absence of acoustic fields.  The measurements performed in this work will provide valuable insight into microfilter clogging dynamics and cake layer formation kinetics.  These findings demonstrate that acoustic streaming can serve as a non-invasive, energy-efficient method to improve microfilter performance.  Beyond microfilters, we expect that acoustic fields may also find use in liquid-liquid separation to reduce the environmental impact of industrial waste streams or remove contaminants to prevent adverse downstream impact.

Presenting Author: Jaime Juarez Iowa State University

Presenting Author Biography: Dr. Jaime Juarez is an associate professor of mechanical engineering at Iowa State University. His research primarily focuses on external field interactions in microfluidic devices and soft matter.

Authors:

Md. Mohaimeen Ul-Islam Iowa State University
Michael Olsen Iowa State University
Jaime Juarez Iowa State University