Abstract
Fluid transport and handling in extraterrestrial conditions, i.e. microgravity, require significantly different system engineering than here on Earth. On Earth, a notable part of fluid processing units inherently relies on buoyancy to transport and handle fluids. In space, however, buoyancy effects are negligible due to the strong diminishment of gravity, resulting in the domination of surface tension forces. Surface tension forces are also dominating micro-scale processes in gravity, making microfluidics a promising technology for fluidic transport and handling in microgravity. Recently, three different microfluidics-suitable fluid behavior phenomena have been studied on the ISS that might further facilitate the manipulation of fluids in space: capillary-driven flow, thermocapillary Marangoni forces, and electrolytic gas evolution-driven flow. Furthermore, attention is drawn for strategies to eliminate unwanted bubbles from liquid bodies in space, as they can damage sensitive equipment: Mesh-screen capillarity and open wedge channels have been identified as promising approaches. Finally, the relevance of fluid handling in space is illustrated with everyday activities during space missions, such as drinking, plant watering, and gathering biometric data.
Highlights
On Earth, fluid handling often relies on gravity-induced effects such as buoyancy and natural convection
Capillary flow occurs both in Space and on Earth when a body of liquid comes into contact with a cavity of a sufficiently small diameter
The experimental setup consisted of a large-scale liquid bridge (LB) of high-Pr fluids and allowed the realization of pure Marangoni convection without buoyancy effects
Summary
On Earth, fluid handling often relies on gravity-induced effects such as buoyancy and natural convection. There is still limited data on these issues, which is why many of the current experiments onboard the ISS are designed to further investigate the effect of microgravity on physical and chemical processes In this context, crewed space stations in low Earth orbit, such as the ISS, are invaluable for investigating the effects of long-term exposure to microgravity, for testing new technologies and devices for monitoring astronauts’ health, and to translate current Earthly fluid handling applications to space. Gravity and density effects (e.g., buoyancy) are negligible in space, so other forces such as surface tension and capillary and viscous forces become important, which makes bubble management challenging. This section will touch on passive gas removal, drinking in microgravity, watering plants in space, biosensors, and electrowetting heat pipes
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