Boiling over in zero-g

HERE ON EARTH, boiling is used for tasks ranging from cooking and heating to power generation. In space, boiling may be used for power generation and other applications.

But because boiling works differently in a zero-gravity environment, it is difficult to design hardware that will not overheat or cause other problems.

University of Maryland Professor Jungho Kim of the A. James Clark School’s Department of Mechanical Engineering, is working with John McQuillen, project scientist at NASA’s Glenn Research Centre in Ohio, to study how boiling is altered in zero-gravity.

Their experiment, the Microheater Array Boiling Experiment (MABE), launched on the space shuttle Discovery on February 24, 2011, bound for a long-term operation aboard the International Space Station (ISS).

The experiment has already been tested on NASA’s ‘Vomit Comet’ (‘weightlessness aircraft’) and the European Space Agency’s Parabolic Flight Campaign in France.

The results could help engineers design space hardware that uses boiling for multiple applications.

“In space, boiling may be required to generate vapour to power turbines in some advanced concepts for power generation, for temperature control aboard spacecraft, and for water purification,” says Kim.

The video at the top of the page shows the experimenters testing the equipment aboard the NASA’s ‘Vomit Comet’…an aircraft that flies parabolic trajectories to simulate short periods of weightlessness. The video below is a close-up of one of the experiments:

How it works

When a liquid is boiled on Earth, vapour, which is less dense than liquid, is removed from heated surfaces through the action of buoyancy. In zero-gravity, the buoyancy force becomes negligible and vapour can blanket the heated surfaces rather than moving away, potentially leading the surfaces to a state known as critical heat flux.

Critical heat flux occurs when a heater or plate becomes too hot, restricting the flow of liquid to the surface and causing the plate to overheat and potentially burn out.

Since liquids boil differently in space, an understanding of how these fluids behave can improve the reliability and expand the applications of space exploration hardware.

The experiment that will take place on the ISS will use two arrays of platinum microheaters bonded to a quartz plate. The arrays measure 7mm and 2.7mm across. The heaters are warmed when electricity is applied, and spaces between the heater lines will allow the boiling process to be seen through the transparent quartz. Boiling of a refrigerant-like fluid (FC-72) will be filmed at high speed and the video sent back to Earth along with the heater data in real-time for analysis.

More Information: Video about zero-G flight experiments

Adapted from information issued by the University of Maryland.

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