Flow and heat transfer characteristics of thermocapillary convection of high prandtl number fluid in cylindrical bridge

The onset of oscillation of thermocapillary convection (or Marangoni convection) in cylindrical liquid bridge has been a target of extensive studies from view points not only of the material processing in microgravity but also of the fundamental instability mechanism in this unique convection. The uniqueness lies in the facts (1) that the convection is driven by the surface tension gradient present along the liquid-gas interface, (2) that there is a strong coupling between fluid motion and fluid temperature, and (3) that the liquid surface may be deformed statically and dynamically. The last feature, particularly the dynamic surface deformation (DSD, hereafter), has not been paid enough attention so far even though some recent studies (e.g., Masud et al. 1997 and Kamotani & Ostrach 1998) have pointed out possible roles of DSD in the mechanism of onset of oscillation. This report describes the results gained in experimental work done at Heat Transfer Laboratory of Yokohama National University in the period from April 2000 through March 2001. The work consists of (1) measurement of static surface deformation caused by the onset of convection, (2) simultaneous observation of flow patterns and DSDs of oscillatory convection, and (3) evaluation of heat loss from the free liquid surface. All of these are aiming at obtaining direct experimental clues that support the importance of DSD in the onset of oscillation of thermocapillary convection in cylindrical liquid bridge.