Rensselaer Research Review Summer 2009
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* Constrained Vapor Bubble
Constrained Vapor Bubble
Image and diagram of the Constrained Vapor Bubble (CVB). Credit: Rensselaer/NASA
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Insights into Phase Change

Schadler and Blanchet’s nanocomposites experiments are the second Rensselaer project to launch into space this year. In August, an experimental heat transfer system designed by Rensselaer professors Joel Plawsky and Peter Wayner was carried to the ISS aboard Space Shuttle Discovery. The project, called the Constrained Vapor Bubble (CVB), will remain installed in the ISS for up to three years. The experiment could yield important fundamental insights into the nature of heat and mass transfer operations that involve a phase change, such as evaporation, condensation, and boiling, as well as engineering data that could lead to the development of new cooling systems for spacecraft and electronics devices.

 “After years of hard work to advance this project to its current state, I am very excited to see our Constrained Vapor Bubble make its way into space and onto the International Space Station,” said Wayner, a 1956 Rensselaer graduate and professor emeritus in Rensselaer’s Department of Chemical and Biological Engineering.

The CVB is concerned with the three-phase contact line where vapor, liquid, and solid meet, generally during the process of evaporation or condensation. This phenomenon is responsible for a number of everyday occurrences, such as a coffee ring stain on the inside of a mug, or the tears that form on the inner surface of a glass of wine. Even though the material interactions at the three-phase contact line occur in a region where film thicknesses are tens of nanometers, they are still connected to a bulk fluid region and are affected by gravity.

Removing Gravity from the Equation

To truly understand what occurs at the contact line, Plawsky said, gravity must be removed from the equation. Operating the CVB in the International Space Station, therefore, will allow them to test and observe how the three-phase contact line behaves in the near-weightlessness of microgravity. 

The CVB is a small glass vial with squared corners, about 30 millimeters long, filled with vapor and liquid. This tiny, wickless heat pipe is then exposed to a heat source on one end and a cold sink on the other. A camera attached to the NASA Light Microscropy Module (LMM) will capture the action as the liquid evaporates at the hot end, the vapor travels to the opposite end of the pipe where it is cooled, and the newly condensed liquid flows back toward the heat source, via capillary forces, to repeat the cycle.

The phase changes result in interesting films forming all along the inside of the glass heat pipe. This will be the first time that scientists will have the opportunity to observe evaporating and condensing menisci — the curved liquid regions at the corners of the CVB — in a microgravity environment.

From a fundamental science perspective, the experiment should allow researchers to develop a better understanding of how to control phase change processes. This potential ten-fold improvement that comes from moving to a microgravity environment could lead to the development of new cooling and heat-transfer systems for spacecraft or satellites. The new pool of knowledge about heat transfer could also lead to improvement in terrestrial heat transfer devices, such as heat pipes for the cooling of computer chips, LEDs, and photovoltaic devices, implantable heat pipes used to help mitigate the effects of epilepsy, and larger-scale machines that boil liquids. Molecular self-assembly processes that rely on exploiting evaporation would also benefit from the data.

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