Effect of thermocapillary instability on liquid film breakdown

The film of water flowing down along a vertical surface with a heater was studied experimentally at Re = 10-50. The initial temperature of the water film varied from 15 to 70 degrees C and heat fluxes on the heater varied from 0 to 6.5 W/cm(2). Simultaneous measurements of the film thickness and surface temperature carried out. The effect of development of thermocapillary instability type A on wave amplitudes, deformation of the liquid film surface, and formation of the first stable dry spot on the heater was investigated. It is shown that when the longitudinal temperature gradients reach values larger then 7-10 K/mm formation of thermocapillary structures begins. At the leading edge of the heater, X/mm < 10-15, the thermocapillary structures in the form of a series of rivulets with a thin film between them are formed on the surface of residual liquid film after wave front propagation. The distance between the rivulets is lambda/mm = 10. It is shown that the formation of the first stainable dry spots occurs in areas where deformation liquid film reaches its maximum value, and the value of the wave's amplitudes decreases. The interaction of waves with thermocapillary structure type A leads to an increase in the critical heat flux corresponding to the liquid film breakdown on 75% in comparison with the data known in literature. A new mechanism of action on the film flow was first identified and studied in detail. (C) 2019 Elsevier Ltd. All rights reserved.