Bubbles and fluid flow in microgravity

The experimental setup
11 June 2013

A new study into the behaviour of bubbles has been published based on a student experiment conducted as part of ESA Education’s Drop Your Thesis! Programme. The results will be useful for understanding any system that uses fluids in space – including life support.

On Earth, the effects of gravity dominate the behaviour of fluids. Under microgravity conditions, such as in orbit, the effects of gravity are removed. The team behind the Bubjet  (Bubble Jet Impingement in Microgravity Conditions) experiment chose to investigate these effects.

‘No one had really done these experiments before,’ says Francesc Suñol, who was a student at Universitat Politècnica de Catalunya (UPC), Spain, when he performed the experiment in 2010.

Motivated primarily out of ‘pure curiosity’, according to Suñol, the team used two jets of water, positioned facing one another. The jets were laced with bubbles so that the team could see what happened as the jets collided.

Then, to create the microgravity conditions of space, they hoisted the experiment more than 140 metres above the ground and dropped it.

It took just 4.7 seconds to fall to Earth. During this time, high-speed video cameras recorded the jets and bubbles so that the team could later analyse the behaviour.

Of course, they didn’t just drop their experiment anywhere.

The Drop Your Thesis! programme is designed to allow students access to the ZARM drop tower in Bremen, Germany. This 147-metre-high tower allows experiments to be dropped safely to Earth, recreating the microgravity conditions of space for a few seconds.

The BubJet Team

The work will have practical applications. Many industrial processes rely on mixing different fluids together. The more efficiently this can be done, the easier it is to control the liquid.

In space, the basic understanding of the way fluids behaviour is imperative if we are to create more sophisticated systems. Applications such as propulsion, refrigeration and oxygenation systems all rely on the efficient mixing of different fluids. So too do life support systems.

Under normal gravity, bubbles in this experiment would rise due to their buoyancy; under microgravity, the bubbles more accurately trace the flow of the liquid. This means that the bubbly jets collide in the central zone of the tank and this gives rise to a high number of bubble collisions. These in turn lead to bubbles bouncing around and coalescing. The movement of the bubbles shows the behaviour of the liquids.

As well as these scientific results, which will be published in the journal Chemical Engineering Science on 28 June 2013, Suñol says that he benefited personally from the experience:

“I have learned ways of working of people from other countries; we have solved problems together. The experience convinced me that I want to work in this amazing area of science.’

Notes to editors:

Effects of momentum flux and separation distance on bubbly jet impingement in microgravity conditions by Francesc Suñol, Ricard González-Cinca will be published in Chemical Engineering Science Volume 97, 28 June 2013, Pages 272–281.

For more information, please contact:
Francesc Suñol
Universitat Politècnica de Catalunya (UPC), Spain

email: francesc.sunol @ upc.edu

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