On Earth, convection or thermal diffusion dominates heat transfer. But these effects are extremely weak in zero gravity, and adiabatic compression can dominate. To observe local overheating and adiabatic compression, Régis Wunenburger from the University of Bordeaux and colleagues placed a small cylinder containing sulfur hexafluoride (SF6) in both its liquid and gas forms on Mir last year. The compound was heated to just below 318.5 Kelvin - its liquid-vapour transition point - to reduce the effect of heat diffuison on the liquid and to induce adiabatic compression.

When the SF6 was slowly heated above this point, Wunenburger and co-workers discovered that the expanding fluid outer layer squeezes the inner gas bubble within seconds. This process heats the inner core to temperatures some 23% higher than the cylinder walls. However, after 130 seconds or so, the system strives to reach equilibrium, and diffusion cools the gas to the same temperature as the liquid and walls.