Apparatus for the study of Rayleigh-Benard convection in gases under pressure

We review the history of experimental work on Rayleigh-Benard convection in gases, and then describe a modern apparatus that has been used in our experiments on gas convection. This system allows for the study of patterns in a cell with an aspect ratio (cell radius/fluid layer depth) as large as 100, with the cell thickness uniform to a fraction of a mu m, and with the pressure controlled at the level of one part in 10(5). This level of control can yield a stability of the critical temperature difference for the convective onset of better than one part in 10(4). The convection patterns are visualized and the temperature field can be inferred using the shadowgraph technique. We describe the flow visualization and image processing necessary for this. Some interesting results obtained with the system are briefly summarized. (C) 1996 American Institute of Physics.