Coupling of melting-solidification phase-change convection with floating-zone convection under microgravity

A finite element algorithm is used to analyze the process of floating zone crystal growth under microgravity. The effect of phase change convection coupled with surface tension convection is considered. The results show that the rate of crystal growth is very important. The single-crystal-melt interface is steeper than the feed-melt interface during the process of crystal growth. When the rate exceeds a critical value, the Marangoni vortex near the feed-melt interface will become so large that a secondary vortex will exist.

Principles of flow field diagnostics by laser-induced biacetyl phosphorescence

A new method for measuring the density, temperature and velocity of N2 gas flow by laser induced biacetyl phosphorescence is proposed. The characteristics of the laser induced phosphorescence of biacetyl mixed with N2 are investigated both in static gas and in one-dimensional flow along a pipe with constant cross section. The theoretical and experimental investigations show that the temperature and density of N2 gas flow could be measured by observing the phosphorescence lifetime and initial intensity of biacetyl triplet (3Au) respectively. The velocity could be measured by observing the time-of-flight of the phosphorescent gas after pulsed laser excitation. The prospect of this method is also discussed.

Characteristics of a CW HF chemical-laser calculated from a simplified two-dimensional model

A two-dimensional simplified model of an HF chemical laser is introduced. Using an implicit finite difference scheme, the solution of two adjacent parallel streams with diffusion mixing and chemical reaction is generated. A contour of mixing and reaction boundary is obtained without presupposition. The distribution of the HF(v) concentrations, gas temperature and the optical small signal gain (alpha sub V, J) on the flowing plane (X, Y) are presented. Compared with the solution solved directly from a set of Navier-Stokes equations, the results of these two methods agree with each other qualitatively. The influences of the different velocity, temperature (T sub 0) and composition of the two streams on the small signal gain after the nozzle exit are investigated. It is interesting that for larger J with a fixed v, the peaks of alpha sub v-T sub 0 profiles move towards higher T sub 0. The computing method is simple and only a short computing time is needed.

One possible way to promote the bond-selective chemical-reactions by frequency-modulated lasers

It is proposed in this paper that we can use frequency-modulated (FM) lasers to realize bond-selective chemical reactions or to raise the efficiency of molecular isotope separation. Examples are given for HF molecule and the C–H bond in some hydrocarbons.

Steady axi-symmetrical thermocapillary motion of a short melting column

This paper deals with the steady axi-symmetric thermo-capillary motion in a short meltingcolumn.with the assumptions that the Marangoni number M<<1, the Reynolds number Re<<1 andthe capillary number C<<1, at the leading order, the solutions of the problem are obtained inthe form of series. For two kinds of typical cases, symmetric and anti-symmetric distributionof air temperature, the numerical calculations are made. The results describe the effect ofendwalls on thermo-capillary flow.