Design of a Modular Ultrasonic Defoaming System

Authors

• Jake E. Green, University of Nebraska - LincolnFollow

First Advisor

Carl Nelson

Committee Members

Eric Markvicka, Gregory Bashford, Yusong Li

Date of this Version

5-2026

Document Type

Thesis

Citation

A thesis presented to the faculty of the Graduate College at the University of Nebraska in partial fulfillment of requirements for the degree of Master of Science

Major: Mechanical Engineering and Applied Mechanics

Under the supervision of Professor Carl Nelson

Lincoln, Nebraska, May 2026

Comments

Copyright 2026, Jake E. Green. Used by permission

Abstract

Aqueous foams pose significant challenges across a wide range of industries, from bioreactors and wastewater treatment to pharmaceutical manufacturing, where excessive foaming leads to product loss, contamination, and process inefficiency. Conventional defoaming methods—chemical, thermal, and mechanical—each carry inherent limitations. Chemical and mechanical risk introducing foreign materials into the medium and thermal can denature heat-sensitive components. Ultrasonic defoaming offers a promising alternative: it is non-contact, introduces no foreign material into the solution, and does not impose thermal loads on the process.

This work presents the design, fabrication, and testing of a compact, modular ultrasonic defoaming system intended for straightforward integration into existing laboratory-scale processes. The system comprises three main components: an ultrasonic transducer and driving circuit, a foam generation apparatus, and a custom-built electrical conductivity probe for in situ measurement of foam liquid fraction.

A significant contribution to this work is the development and validation of the custom conductivity probe. Commercial laboratory probes have specified geometries that are not conducive to measuring the conductivity of foam. For this reason, a custom probe was designed with wider electrode gap and larger plate area to allow foam to pass through the measurement volume without structural disruption. The probe was calibrated against an Atlas Scientific commercial probe using potassium chloride solutions, and its performance was validated through nondimensionalized comparison, confirming that it reliably captures relative conductance—the quantity required for liquid fraction determination. A calibration curve was then established using sodium dodecyl sulfate solutions across a range of concentrations spanning the critical micelle concentration.

In its current configuration, the ultrasonic defoaming system produced no statistically significant reduction in foam height relative to natural drainage. However, the underlying method is well supported in the literature, and a diagnostic analysis identified several avenues for improving system performance, including acoustic impedance matching layers, ultrasonic horn and stepped-plate resonators, and driving circuit optimization. These findings establish a clear path toward an effective, non-contact foaming system in future iterations of this work.

Advisor: Carl Nelson