Study of thermocapillary film rupture using a fiber optical thickness probe

Abstract

Rupture of a subcooled water film flowing down an inclined plate with a 150×150 mm heater is studied using a fiber optical thickness probe. The main governing parameters of the experiment and their respective values are: Reynolds number (3.2–30.2), plate inclination angle from the horizon (3–90 deg), heat flux (0–1.53 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, but, upon reaching a certain critical thickness, the film spontaneously ruptures. The critical film thickness is practically independent on the film Reynolds number as well as on the plate inclination angle and lies in the neighborhood of 60 µm (initial film thickness varies from 93 to 368 µm). The heater surface temperature prior to rupture is also independent of Re and Θ, and is about 45°C (initial film temperature is 24°C). The process of rupture involves two stages: 1) abrupt film thinning down to a very thin residual film remaining on the heater; 2) rupture and dryout of the residual film. The threshold heat flux required for film rupture is scarcely affected by the plate inclination angle but grows with the Reynolds number.