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UMN-Industry Collaboration Explores Filtration of Fluids

A collection of filters

Donaldson Company already knows its device to filter tiny water droplets out of diesel fuel works well. What the Minnesota-based global developer of filtration technologies wants to know now, however, is why.

Having a clearer understanding of what’s happening at the microscopic scale could help the company further improve its filter design and improve the lifespan of its filters.

“They came to me and said, ‘we want to understand what’s happening at the microscale inside this filter. Can you investigate and help us figure out what is going on?” said Sungyon Lee, PhD, assistant professor of mechanical engineering in the University of Minnesota’s College of Science and Engineering.

The project Lee is now leading—to figure out exactly what’s happening within the filter—is the latest in a series of research collaborations between Donaldson Company and the U. Since 2015, the company has sponsored eight projects through Minnesota Innovation Partnerships (MN-IP), a program led by UMN Technology Commercialization and Sponsored Projects Administration to lower the cost and risk for companies looking to sponsor University research and license the new technologies that result.

For example, Cari Dutcher, PhD, associate professor of mechanical engineering, is leading a project to better characterize the properties that affect how well filters can separate fuel and water. Using tiny laboratory “chips” that allow her to test fluid behaviors at the sub-millimeter scale, Dutcher’s team in the Complex Fluids and Multiphase Flows Lab aims to develop a method for quickly and reliably measuring properties like viscosity and the tension between the surfaces of the two fluids.

Another recent project, which wrapped up earlier this year, sought to develop new models for describing how filters change as they become clogged over time. The project, led by Chris Hogan, PhD, professor of mechanical engineering, focused on how efficiently the filter separates particles out from a fluid and how the fluid pressure level drops between two points in the system. Ultimately, the project resulted in a computer program that Donaldson can use to predict how long a filter will last before it becomes completely clogged, as well as to compare filter materials from different manufacturers to predict how each one performs.

Donaldson Company recently signed a master research agreement with the U, which expedites future collaborations by defining the terms up front. The agreement eliminates the extensive legal review and negotiation processes normally required with new projects and allows the research to get started sooner.

“As industry leaders in filtration technology, we’re continuously working to meet ever more difficult customer needs for clean processes and fluids,” said Paul Way, Donaldson’s director of advanced R&D. “Partnering with the University of Minnesota has enhanced our ability to build on our already deep understanding of the fundamental science of filtration. While most of the filtration industry continues to look at bulk phenomena, we are probing structures in-situ at a real-world microscopic scale, providing insight into the next generation of filtration technology.”

Tracking the Droplets 

When it comes to filtration, separating out one fluid that’s dispersed in another is more challenging than filtering a solid out from a fluid, said Lee, whose expertise includes fluid mechanics.

“Fluid, by definition, can dynamically change,” she said. “It can merge, it can grow bigger, or it can break up into even smaller droplets, which really makes filtration even more difficult.”

To understand how oil and water behave inside of Donaldson’s filter, Lee and her team must see inside the filter’s opaque, foamy material. They plan to immerse the filter material in a specialized liquid that corresponds with that material, allowing them to see through the filter and watch as the mixture of oil and water droplets moves through it. The water droplets in the oil will be tiny—between 10 and 100 microns in diameter, smaller than the thickness of printer paper—to match those that Donaldson’s filters encounter in fuel.

After successfully visualizing what’s going on inside the filter, Lee hopes to develop a model for explaining the water droplets’ behavior. The model would allow her team to predict what might happen in slightly different circumstances, such as if the filter material contained larger fibers or was more hydrophilic (water-attracting).

“Right now, it’s mainly an experimental project, but we are hoping to come up with the theoretical model to understand this process better,” she said. “The whole point of doing theory is to have a more generalized understanding, so you’re not forced to empirically test one filter after another.”

Predicting the Surprises

While it’s common for basic research, which aims to expand the overall scientific understanding in a field, to lead to applied research with real-world applications, Lee’s collaboration with Donaldson illustrates how this inspiration can also happen in reverse.

As she explores what’s happening inside this specific filter, Lee hopes to discover something more universal about how the droplets get through the pores in the filter material and advance knowledge in the field. Her research group is based in the fundamental, typically using a mixture of simple experiments and mathematical modeling to discover more about the physical phenomena at play with fluids.

Any insights they discover could inform many areas of fluid dynamics, in part because water droplets interact with many types of porous materials in our everyday lives, including soil, leaves, and even human skin. New discoveries, Lee said, could shine a light on why tiny differences—like a slight change in the size of a droplet—can lead to big and sometimes unexpected changes in how the fluid behaves.

“We’re really hoping to find some interesting fluid mechanics phenomena that we haven’t seen before,” she said. “That’s really the beauty of fundamental research: it gives you enough deeper understanding that you can predict the surprises.”

Kevin Coss

Kevin Coss

Kevin is a writer with the Office of the Vice President for Research.

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