Dynamics of liquid film rupture under local heating

Abstract

Rupture dynamics of a horizontal liquid film non-uniformly heated from below was experimentally studied in a wide range of liquid viscosity. To visualize the liquid surface deformations and disruption of the film, an optical schlieren system was used. The instantaneous local film thickness was measured using a chromatic confocal sensor. In order to measure the thickness of thin liquid films, the substrate was covered with a black coating eliminating reflection of the incident light. Angular and frequency characteristics of the confocal sensor were studied in detail. The process of film rupture can be divided into three stages: 1) film thinning down to a residual film on the heater; 2) existence of a stable residual film for some time; 3) rupture and dry out of the residual film. The thickness of the residual film was found to strongly depend on the liquid viscosity: for water it is about 10 µm, whereas for silicone oil PMS-200 it is about 275 µm. The data obtained for various working liquids were generalized by a dimensionless correlation.