CNES, in association with Novespace, offered three student teams in master (4 years after high school) the opportunity to participate in a campaign of parabolic flight aboard the A300 Zero-G aircraft. Virginie Alleaume and Florian Carle, two fourth year students in Mécanique Energétique (ME 4A) (main subject: thermal, energy, mechanical...) at Polytech' Marseille responded to this offer by proposing the infrared visualization of pool boiling on a heated wire under microgravity. This project has two major objectives. The first is to study physical phenomena in microgravity by designing and creating a test bed that must withstand extrem physical conditions (microgravity, hypergravity, extremely intense vibrations...) to study the evaporation of a fluid on a platinum wire. The second is to allow these students to work on a phase change project related to their training. They will be supervised by David Brutin (Lecturer, HDR) and Pierre Lantoine (CNRS researching engineer).
The experimental set-up
Our goal is to conduct a study on phase change by boiling. Boiling can transfer a lot of heat through the latent heat of vaporization. Exchangers with phase change are much more efficient than monophasic exchangers. But heat transfer in zero gravity poses a problem because bubbles won't ascend to the surface as is the case on Earth. We want to measure the amount of heat we can transfer to a liquid in weightlessness/zero gravity and watch to the behavior of the vapor bubbles. When gravity disappears, the bubbles should remain stuck to the wire and its temperature should increase. We will use an infrared camera to measure the temperature of the wire and the camera to vusualise the behavior of the bubbles. This technique requires the use of special windows that let out the infrared radiation. The use of this technology is a direct application of the semi-transparent class we had.
The parabolic flight campaign V84 ran from November 29th to December 9th, 2011 in Bordeaux. The flight consists of 31 parabolas of 21 seconds each. The entire aircraft will be in weightlessness/zerogravity (0.05g). We will use these conditions to study the evolution of the fluid with the bubble formation and the saturation temperature of the fluid in microgravity by varying the electric current applied to the platinum wire at each parabola. We will be able to trace the Nukiyama curve in microgravity.
47th ESA Parabolic Flight Campaign Introduction Movie [Credits: ERASMUS CENTRE (HSF-UC) ESA-ESTEC]
The results of the flight campaign will be shown during presentations in Novespace facilities in Bordeaux and before a student audience at Polytech 'Marseille. We would like to thank Novespace and CNES for this amazing opportunity to participate in this campaign, David Brutin and Pierre Lantoine for their scientific and technical assistance and their availability and Polytech 'Marseille for its administrative and financial support.
After the flight
We went to Bordeaux on 1 December for 15 days of flight campaign. The first week was devoted to prepared and boarded the experience on the plane. We had some problems with leaks due to freezing temperatures and the blocking of experience under the snow on the tarmac but nothing insurmountable. Then, after a long safetybriefing on Monday, we boarded early on Tuesday, December 7 in the aircraft for theflight. We were about 40 people for this 3 and a half hours flight (3 drivers, 4 mechanics and the rest of researchers). After an injection of scopolamine (to prevent vomiting due to hyper gravity) we took off around 9:30 for a flight over the Atlantic to Britain.Constant change of gravity is very tiring for the human body: the head swells in microgravity phase and the feet in hypergravity. The inner ear is very stimulated with mixed signals which creates the risk of nausea and vomiting.
The results of the experiment were surprising. In microgravity, the buoyancy disappears and the bubbles created by Joule effect on the wire start to grow and coalesce to form larger bubbles leaving the wire in a sheath of steam. This phenomenon stops and all the effects with the convective fluid and causes a local temperature rise.