Video file: Simple demonstration of a rarefied gas flow induced over a plane wall with a temperature gradient

Abstract

A rarefied gas flow induced over a plane wall set vertically and heated on its lower part is detected by a small windmill in front of the plate. The experiment is done under the pressure from the atmospheric condition down to 0.5 Torr in a vacuum chamber prepared in a bell jar found in most of chemistry departments. With decrease of the pressure, the transition from an upward flow due to natural convection to a downward rarefied gas flow induced by a temperature gradient on the wall is observed by the reversal of the direction of rotation of the windmill.