Vibration can do the work of gravity

during gas—liquid phase transitions. Fluids in space behave very differently from their Earthbound counterparts. For example, the phase separation of gas and liquid is dramatically slowed in micro-gravity conditions, in which capillary flows dominate and the buoyancy of gas bubbles plays no role. Scientists in France, led by Daniel Beysens, a researcher at the French Atomic Energy Commission, studied a 20-mm³ sample of molecular hydrogen near its critical point of 33 K. To simulate weightlessness, they levitated the sample in a strong magnetic field gradient. (See Physics Today, )September 1998, page 36, to learn about this technique.) The researchers found that subjecting the sample to high-speed, low-amplitude vibrations could restore the effects of gravity. The vibrations introduced velocity differences between gas and liquid domains—which have different densities—and thereby allowed shear flow and pressure differences across domains to greatly accelerate the phase transitions. (D. Beysens et al....