Enhancement of Thermocapillary Effect in Heated Liquid Films for Large Waves at High Reynolds Numbers

Abstract

The characteristics of the heated water film flowing down a vertical plate at Re = 150, 300, and 500 were studied. The fluorescence method was used for measuring the film thickness. The temperature field on the film surface was measured by an infrared scanner. The analysis of the temperature pulsations on the heated film surface was made. The high-frequency component of temperature pulsations faded at the bottom area of the heater. Part of the temperature perturbations (small waves) was removed from interrivulets regions (valleys) to the rivulets by transverse thermocapillary forces. At high heat flux, only largest waves with maximum ripple of temperature reached the lower edge of the heater. There is a decrease in the mean integral energy fluctuations of temperature in the interrivulets regions near the heater lower edge. In the heated regions between rivulets, the relative amplitude of large waves increases with decreasing average thickness (or local Reynolds number). The analysis of results obtained for large Reynolds numbers showed that the relative amplitudes of large waves in the regions between rivulets at high heat fluxes are much greater than those for small Reynolds numbers and in isothermal falling films. In the interrivulet zone, Marangoni number increases with a rise of the heat flux. The growth of relative amplitude of low-frequency waves in interrivulets regions helps prevent film rupture and crisis of heat transfer.