Vibrations improve oil droplet drainage from fleece filters

Air compressors are widely used across many industries from electronics to pharmaceutical. These compressors require lubricating oils to function properly and use air filters to contain aerosolized oil droplets. Over time, the filters become saturated with oil, which leads to a pressure drop across the filtration system. As a result, the air compressor compensates by operating at a higher load, which can increase electrical bills by several thousand US dollars per year.

Fink-Metzmacher et al. developed a method to accelerate the drainage of oil droplets from compressor air filters to improve the pressure drop. Inspired by previous studies showing water and water-based droplet drainage increased when excited at their natural frequencies, the researchers sought to see if the findings could extend to oil droplets.

After determining the oil droplets’ natural frequencies, the researchers ran experiments collecting oil droplets on filter fleece. They vibrated the fleece at various frequencies, including the droplets’ natural frequencies, and recorded their detachment. The results showed clearly that the vibrated filters shed oil droplets at smaller volumes than the non-vibrated filters, allowing quicker drainage and less buildup. A slight improvement in drainage was found at around twice the natural frequency.

“This shows that the concept works even for highly viscous fluids like oil, which are typically much harder to mobilize than water-based droplets,” said author Andreas Fink-Metzmacher.

The findings are promising for industrial use, though conditions relevant to real-world systems, such as shear flow, still need to be investigated.

“From an industrial perspective, the findings could lead to substantial cost savings if successfully implemented,” Fink-Metzmacher said. “Scientifically, it opens up new possibilities to better understand droplet dynamics under external excitation, especially on porous or fibrous materials.”

Source: “Vibration-induced droplet drainage on filter fleeces for compressed air filtration,” by Andreas Fink-Metzmacher, Nick Schoeneich, Jan Schultz, Manuel Ettel, Sebastian Burgmann, and Uwe Janoske, Physics of Fluids (2025). The article can be accessed at https://doi.org/10.1063/5.0281639 .