AN EXPERIMENTAL STUDY ON THE DYNAMICS OF A LIQUID FILM UNDER SHEARING FORCE AND THERMAL INFLUENCE

摘要

A profound knowledge of dynamics and instability of a liquid film is crucial for the thorough study on the physical mechanisms of boiling crisis (i.e., departure from nucleation boiling -- DNB, and dryout), which is important to the performance and safety of light water reactors. To address this, a series of tests were carried out at various water and air flow rates under atmospheric pressure and different heat fluxes. A confocal optical sensor system was employed to investigate the dynamics of a liquid film in a horizontal aluminum channel. The liquid film was sheared by co-flowing air from above and heated from below. We obtained the experimental data about the variation of thickness of the liquid film under different flow conditions and tried to analyze how it is affected by liquid/gas flow rates, shearing force and heat flux. We found that the shear force, evaporation and the generation of the bubbles enhanced the instability of the liquid film. We also found that the occurrence of the rupture was random and the critical thickness at the rupture increased with increasing heat flux. The spectrum analysis indicated that the effect of the shear force on the liquid film instability became weak when the liquid film is very thin, but the heat flux always enhanced the instability of the liquid film.