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I’m presently in Japan for a last training session with the Japanese Space Agency (JAXA) before my mission to the ISS in March.
Today Dan Burbank and I received training on the Marangoni Convection Experiment that will be conducted on the International Space Station. The experiment is named for Italian physicist Carlo Marangoni, who studied surface phenomena in liquids and published the results of his experimentation in 1865. His work included the study of the flow of liquid caused by differences in surface tension. Today we call this flow the Marangoni Convection effect.
Did you ever wonder how some objects that are denser than water can rest on the surface of the water, or how some insects and reptiles can run on the surface of water? This is made possible through surface tension. Surface tension is a property of a liquid that allows it to resist an external force. Surface tension is possible because in a liquid, each molecule is pulled equally in every direction by neighboring molecules, resulting in a net force of zero. The molecules at the surface do not have other molecules on all sides of them, and therefore are pulled inwards. This creates internal pressure forcing liquid surfaces to contract. Surface tension is responsible for the shape of liquid droplets. Droplets of water tend to be pulled into a spherical shape by the cohesive forces of the surface layer. In the micro-g environment of the space station, drops of liquids form nearly perfect spheres.
Surface tension is also responsible for the phenomenon called tears of wine which appear as a ring of clear liquid, near the top of a glass of wine, from which droplets continuously form and drop back into the wine. It is most obvious in wine which has high alcohol content and is also referred to as wine legs, curtains, or church windows.
Tears of Wine
Tears of wine form because alcohol has a lower surface tension than water. In regions of the wine with a lower concentration of alcohol there is a stronger pull on the surrounding fluid than in the region with a higher alcohol concentration. The result: liquid tends to flow away from regions with higher alcohol concentration. This can also be demonstrated by spreading a thin film of water on a smooth surface and then allowing a drop of alcohol to fall on the film. The water will rush out of the region where the drop of alcohol fell.
In the 145 years since Carlo Marangoni first published his observations, we have yet to fully understand and model the phenomena we call Marangoni Convection.
In the micro-g environment of the space station, the Marangoni Convection effect can be isolated from other factors such as gravity induced sedimentation and buoyancy convection.
Even in the absence of significant gravity, the Marangoni effect still leads to a pull of a liquid from an area of high temperature (low surface tension) to an area of low temperature (high surface tension).
This unique orbital experiment will help unlock the underlying natural laws of the Marangoni Convection effect.
Improving Life On Earth
A better understanding of the Marangoni Convection effect can have numerous applications including:
- Improved silicon chip manufacturing which can lead to faster, more powerful and smaller computers
- Improved capability to handle small volumes of liquids which can lead to advancements in new drugs, DNA examinations and analytical chemistry
- Improved methods of removing heat from electronic devices
- Higher quality materials
- More efficient welding techniques which provide stronger welds using less material
- Advancements in micro and nano-technology