Wave – Thermocapillary effects in heated liquid films at high Reynolds numbers

Abstract

The temperature distributions and wave characteristics of the water film flowing down a vertical plate with a heater of 100×150mm at Re=150, 300, 500 are studied. The field of film thicknesses at different heat flux values was measured using the fluorescence method. The temperature field on the film surface was measured by an infrared scanner. The experimental data were obtained for variations in temperature over the liquid film surface with time during the propagation of waves. Thermocapillary forces that arise on heating lead to the formation of rivulets separated by thin layer troughs, with three-dimensional (3D) waves propagating over the crests of rivulets. Averaging of measurements allowed the values of the transverse film deformation and distance between the rivulets to be determined. In the interrivulet zone Marangoni number increases with a rise of the heat flux. The amplitudes of 3D waves in a water film flowing down a vertical heated plate have been measured. The film thickness and 3D wave amplitudes on the heater grow with increasing heat flux and distance downstream the flow, but the relative wave amplitude remains unchanged. In the heated regions between rivulets, the relative amplitude of waves increases with decreasing average thickness (or local Reynolds number). Analysis of results obtained for large Reynolds numbers showed that the relative amplitudes of waves in the regions between rivulets at high heat fluxes are much greater than those for small Reynolds numbers and in isothermal falling films. Two mechanisms of thermocapillary forces influence on the motion of the wavy liquid film are marked. For the first time, the exhibition of such a strong thermocapillary effects is revealed in the heated liquid film at high Reynolds numbers.