The interaction of thermocapillary perturbations with 3D waves in a heated falling liquid film

The evolution of three-dimensional (3D) waves into thermocapillary-wave structures in a locally heated water film flowing down a vertical plate has been experimentally studied. The interaction of hydrodynamic perturbations with thermocapillary instabilities was monitored using a high-speed high-resolution IR imager. The existence of thermocapillary structures has been observed for the first time at high Reynolds numbers (Re = 150) in regime A, which is characterized by high temperature gradients on the film surface and a definite value of the “most dangerous” wavelength of instability that arises when the heat flux density exceeds a certain threshold. It is established that structures periodically appear in which the distance between temperature maxima is much shorter than that observed before. As the heat flux density is increased, the thermal entry length exhibits a sharp drop when thermocapillary instabilities arise in the vicinity of the upper edge of the heater.