Temperature fluctuation measurement at oscillatory thermocapillary flow in a half-floating zone of low Prandtl number fluid

摘要

Oscillatory thermocapillary flow (or Marangoni convection) in a half-floating zone of low Prandtl number (Pr) fluid was investigated experimentally. The test section with a pair of rod that sustains liquid bridge is in a vacuum chamber to prevent oxidation of free surface of the liquid bridge and also to prevent heat loss caused by heat exchange between the free surface and an atmosphere. The temperature difference as driving force was imposed along the liquid bridge. The temperature fluctuation from the steady to the oscillatory flow was successfully observed by a radiation thermometer. The characteristic frequency of this temperature fluctuation and frequency shift as temperature difference increasing are extracted from FFT analysis. The results of several numerical simulations have predicted that the thermocapillary flow of low Pr fluid has two transition points (bifurcation points) changing thermohydraulic fields in a liquid bridge as imposed temperature difference (hence, Marangoni number) increasing. The onset is supposed to be near the second bifurcation point. Marangoni number (Ma) at this onset agrees with numerical results calculated under similar liquid bridge configuration.