A. Semenov

Viscosity Effect on Thermocapillary Rupture of Falling Liquid Films

Rupture of a subcooled liquid film flowing over an inclined plate with a 150×150 mm heater is studied for a wide range of liquid viscosity (dynamic viscosity μ = (0.91–17.2)x10−3 Pa·s) and plate inclination angle with respect to the horizon (Θ = 3–90 deg). The main governing parameters of the experiment and their respective values are: Reynolds number Re = 0.15–54, heat flux q = 0–224 W/cm2 . The effect of the heat flux on the film flow leads to the formation of periodically flowing rivulets and thin film between them. As the heat flux grows the film thickness between rivulets gradually decreases, and, upon reaching a certain threshold heat flux, qidp , the film ruptures in the area between the rivulets. The threshold heat flux increases with the flow rate of liquid and with the liquid viscosity, while the plate inclination angle has little effect on qidp . Criterion Kp, which is traditionally used in the literature to predict thermocapillary film rupture, was found to poorly generalize data for high viscous liquids (ethylene glycol, and aqueous solutions of glycerol) and also data for Θ≤45 deg. The criterion Kp was modified by taking into account characteristic critical film thickness for film rupture under isothermal conditions (no heating), deduced from existing theoretical models. The modified criterion has allowed to successfully generalize data for whole ranges of μ, Re, Θ and q, studied.Copyright

The Effect of Liquid Viscosity on the Formation of Thermocapillary Structures

An experimental study of the formation of thermocapillary structures at low Reynolds numbers and temperature gradients at the surface of the film in a wide range of the liquid viscosity is performed. The data on the distance between the jets are generalized. It is demonstrated that the transverse dimension of the structures is determined by the capillary constant and does not depend on either the liquid viscosity or the flow rate (Reynolds number of the film).