Generation of a Wave on a Liquid Film Flowing Down a Heated Inclined Plane. 2nd Report, Disturbance and Marangoni Waves.

Abstract

An investigation was conducted into the generation of a disturbance wave on a liquid film flowing down a heated inclined plane. Theoretical analysis shows that the Marangoni effect due to the surface tension gradient contributes to reduction of the critical flow rate of the liquid on the generation of a disturbance wave. Theoretical results also suggest the existence of two boundaries for generation of a disturbance wave, at a fixed inclined angle. The lower boundary, however, could not be observed for thin water film because liquid film breakdown occurred before the lower critical flow rate was achieved. In this paper, silicone oil with high viscosity was used as the working fluid instead of water. Small waves were observed under the lower critical flow rate. The surface temperature gradient along a wave is one order of magnitude larger than that of a disturbance wave under the higher critical flow condition. We defined a wave under lower critical condition as a Marangoni wave. The measured velocity of a Marangoni wave is almost the same as the liquid surface velocity.