Recent microgravity experiments of Frohberg et al. indicate that diffusion coefficients in liquid metals
increase in proportion to the square of absoloute temperature. Such interesting results of the temperature dependence would appear to be in accord with the prediction due to the fluctuation model of diffusion proposed by Swalin about 30 years ago. However, in this theory an inadequate assumption was adopted; in fact, the characteristic time in Einstein's equation used there was given in terms of the absolute reaction rate theory. The time scale estimated in this way is too short to define a diffusion coefficient in view of later studies on the microscopic atomic transport in liquids. Some remarks are given on basic points indispensable for the discussion of the temperature dependence of transport coefficients in liquids.
In order to investigate the deflection mechanism of columnar dendrite due to fluid flow the model experiments using succinonitrile-camphor alloy have been carried out. Deflection angle was found to increase with increasing flow velocity. The dendrite tip, which is parabolic in the stagnant liquid, asymmetrically deforms in the flowing liquid. Secondary dendrite arm spacing in the upstream direction is smaller than that in the downstream direction. No change in the morphology of dendrite was observed when the macroscopic thermal field was altered. The thermal and solutal fields around the columnar dendrite tip may be changed due to fluid flow. Since the change in the thermal field has little effect on the dendrite tip morphology, the change in the solutal field has an effect in a great deal on the dendrite tip morphology.
Basic equations, boundary conditions, and numerical solution procedures for the Marangoni convection are outlined. Two Marangoni convections, a flow in a floating zone and a flow around a bubble, are chosen as examples, and results obtained so far are given. The floating zone solution agrees well with other experimental and numerical investigations, while the bubble solution needs further investigations .