Watching Water Droplets Merge on the International Space Station

Watching Water Droplets Merge on the International Space Station

Watching Water Droplets Merge on the International Space Station

Droplets (at centimeter scale) coalesce during an experiment on the International Space Station. Credit: Josh McCraney

Understanding how water droplets propagate and coalesce is essential for everyday life scenarios, such as raindrops falling from cars, planes, and rooftops, and for applications in power generation, aerospace engineering and cell adhesion at the microscopic scale. However, these phenomena are difficult to model and difficult to observe experimentally.

In Fluid Physics, researchers from Cornell University and Clemson University designed and analyzed droplet experiments performed on the International Space Station.

Droplets usually appear as small spherical caps of water because their surface tension exceeds gravity.

“If the drops get much larger, they begin to lose their spherical shape and gravity crushes them into something more like puddles,” said author Josh McCraney of Cornell University. “If we want to analyze drops on Earth, we have to do it on a very small scale.”

But on a small scale, the dynamics of the droplets are too fast to be observed. Therefore, the ISS. The weaker gravity in space means the team could study larger droplets, ranging from a few millimeters in diameter to 10 times that length.






Droplets (at centimeter scale) coalesce during an experiment on the International Space Station. Credit: Josh McCraney

The researchers sent four different surfaces with varying roughness properties to the ISS, where they were mounted on a lab table. The cameras recorded the droplets as they spread and coalesced.

“NASA astronauts Kathleen Rubins and Michael Hopkins would deposit a single droplet of the desired size at a central location on the surface. This droplet is near, but does not touch, a small pre-drilled porthole in the surface,” McCraney said. “The astronaut then injected water through the porthole, which essentially collects and expands an adjacent drop. The injection continues until the two drops touch, at which point they merge.”

The experiments aimed to test the Davis-Hocking model, a simple way to simulate droplets. If a drop of water rests on a surface, part of it touches the air and creates an interface, while the section in contact with the surface forms an edge or line of contact. The Davis-Hocking model describes the contact line equation. The experimental results confirmed and extended the parameter space of the Davis-Hocking model.

As the project’s initial principal investigator, the late Professor Paul Steen of Cornell University had written grants, traveled with collaborators around the world, trained doctoral students, and meticulously analyzed related earth studies, all with a desire to to see his work carried out successfully on board the ISS. . Tragically, Steen passed away just months before the launch of his experiments.

“While it’s tragic that he’s not here to see the results, we hope this work makes him and his family proud,” McCraney said.

The article “Coalescence-Induced Droplet Propagation: Experiments Aboard the International Space Station” is written by Joshua McCraney, Jonathan Michael Ludwicki, Joshua Bostwick, Susan Daniel, and Paul Steen. The article was published in Fluid physics on December 13, 2022.

More information:
Joshua McCraney et al, Coalescence-Induced Droplet Propagation: Experiments Aboard the International Space Station, Fluid physics (2022). DOI: 10.1063/5.0125279

Provided by the American Institute of Physics

Quote: Watching water droplets merge on the International Space Station (2022, December 13) retrieved December 14, 2022 from https://phys.org/news/2022-12-droplets-merge-international-space-station.html

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