The effect of wave formation and wetting angle on the thermocapillary breakdown of a falling liquid film

An experimental investigation is performed of the breakdown of a liquid film flowing down a vertical plate with a heater sized $150\times150$ mm. The main parameters which are varied in the experiment are the Reynolds number $\mathrm{Re}=0.47$ to $331$ and the heat flux $q=0$ to $1.92$ W/cm$^2$. It is found that the effect of the heat flux on the wave motion of the liquid film causes the formation of a jet flow. Dry spots are formed in the region of thin film between the jets. For the purpose of investigating the effect of wave formation on the film breakdown, the distance between the nozzle and heater is varied from $41.5$ to $200$ mm. It is found that the distance between the nozzle and heater defines the hydrodynamics of the liquid at relatively low heat fluxes, but has no appreciable effect on the heat flux at which the film breakdown occurs. Different working liquids and coatings of the working surface are used in the experiments to investigate the effect of the wetting angle on the film breakdown. The equilibrium wetting angle is measured by the "bubble" method. No effect of the equilibrium wetting angle on the nonisothermal breakdown of the film was revealed.