Bubbles that form on a heated surface have been shown to create a tiny recoil which could be used to cool high power microelectronics in space and other applications, according to researchers at the University of Illinois at Chicago (UIC), under funding from NASA.
"In flights to Mars or the moon, equipment like computers generate a lot of heat," said UIC Professor Alexander Yarin.
Engineers have looked to ‘pool-boiling’, which is liquid-cooling at a temperature near the boiling point of the fluid. In boiling, all heat is absorbed in converting the liquid to vapour, with no further rise in temperature until the phase change is complete.
But the lack of gravity in space poses a problem for pool-boiling as the bubbles have no buoyancy.
"On Earth, the bubbles rise, and cold coolant comes in," Prof Yarin said. "But in space, the bubbles don't rise. They stay on the submerged surface, and can merge together to form an insulating vapour layer, and the heat-removal process is interrupted.
"You can try mechanical mixing, but a motor also creates heat. You can try a strong electric field, but that also produces heat and creates other problems," he said. Both methods take up space and require power.
Looking to solve the problem, the team sandwiched two heat-generating chips back to back. By alternating the voltage between the two chips, they caused the apparatus to swing back and forth through the coolant at 1cm/s.
"When one chip operates, it produces bubbles and a recoil force, and it pushes back enough to swing the chips in the cooling fluid and shed the bubbles," Prof Yarin explained. "It works with or without gravity – in space, exactly as on Earth."
Author
Peggy Lee
Source: www.newelectronics.co.uk