Combination of electric and acoustic actuation removes bubbles from liquid without buoyancy

Most forms of bubbles we interact with on a daily basis use gravity and buoyancy to separate a solution’s gas phase from its liquid component. In certain contexts, such as zero gravity or on microscopic scales, bubbles can instead coalesce and form a bubble film that can cavitate and disrupt heat transfer.

Hyun et al. describe a process that completely removes bubbles from a surface without the use of gravity. The group’s technique produces a microstreaming flow and oscillatory motion that use electrical actuation in a process called dielectrowetting to first remove bubbles and then clear them from the surface with acoustic actuation tuned to the bubbles’ frequency.

“There were studies to separate bubbles from the surface of a substrate by an electric force, more specifically dielectrophoresis force,” said author Sang Kug Chung. “However, the bubbles can be easily attached on the surface again without the continuous electric actuation.”

When testing with a high-speed camera, the group removed air bubbles micropipetted into various volumes nearly simultaneously from a liquid tank of 98 % propylene glycol. Acoustic excitation in a liquid medium proved challenging.

“The bubbles only respond to acoustic waves at their natural frequencies, which are highly dependent on their volume,” Chung said. “The investigation of the dynamic behavior of an acoustically excited bubble in a wide range of frequencies is essential in this work.”

The group looks to apply their approach to create a microrobot propelled by acoustic bubbles through the bloodstream to fight against bacteria. Additionally, Chung sees potential for an efficient way for removing bubbles from heat exchangers.

Source: “Bubble removal by electric and acoustic actuation for heat transfer enhancement,” by Youngbin Hyun, Kang Yong Lee, Deasung Jang, and Sang Kug Chung, AIP Advances (2021). The article can be accessed at https://doi.org/10.1063/5.0042503 .