Distribution of temperature gradient when the wave mooves over the heater.
Distilled water was pumped to film-former, which consisted of an accumulation chamber, distributing device and nozzle with calibrated flat slot. The working sections consisted of textolite base plate with a 150 × 150 mm heater located on it and temperature stabilizer. The heater was based on a 150x150 mm stainless steel plate 6 mm thick. The heat-releasing element was made of steel foil 55 µm thick in the form of interconnected parallel strips. The video shows the distribution of temperature gradient when the wave mooves over the heater. X is the longitudinal coordinate on the heater with the reference from the upper edge of the heater, Z is the transverse coordinate on the heater with the reference from the side edge of the heater. As a result of thermocapillary instability in the residual layer in front of the crest of a wave, transverse temperature inhomogeneities are formed. At the wave front, different temperature gradients appear. Higher tangential stresses (corresponding to high temperature gradients) lead to local braking (decreasing velocity) of the wave front at Z=64mm. Liquid flows around the braking zone, forming a new wave crest at Z=70mm. Further, the wave crests (at Z=53mm and Z=70mm) continue to increase despite at relatively high temperature gradients at the front. High temperature gradients are explained by a large temperature difference between a cold rowing liquid and a heated residual layer ahead of the wave front. At Z=64mm, the temperature gradients do not change significantly, which is caused by heating a relatively thin layer of liquid. The velocity of the wave front at at Z=64mm slightly decreases. As the liquid film warms up in the region of Z=64mm, the wave-front boundary disappears. As a result, the wave crests line up one after another forming rivulets.