The applying of the short — term cross correlation in optical diagnostics of melt convection in laser metal deposition

The time dependences of the surface temperature and the surface area of the melt bath during the formation of the single track in the laser metal deposition technology were obtained using a multi-wave optical diagnostics complex. The short - term cross-correlation method was used to analyse the measured parameters of the bath surface, and relationship of the measured parameters with the processes of thermocapillary convection in the melt was shown.

Stability Analysis of Thermocapillary Convection of B2O3/Sapphire Melt in an Annular Pool

Aiming at the thermocapillary convection stability of sapphire crystal grown by liquid-encapsulated Czochralski method, by non-linear numerical simulation, obtained the flow function and temperature distribution of R-Z cross section, as well as the velocity and temperature distribution at liquid-liquid interface and monitoring point of B2O3/sapphire melt in annular two liquid system, covered with solid upper wall and in microgravity. By means of linear stability analysis, obtained the neutral stability curve and critical stability parameters of the system, and revealed the temperature fluctuation of the liquid-liquid interface. The calculated results of B2O3/sapphire melt were compared with 5cSt silicone oil/HT-70. The results show that under the same geometrical conditions, the flow of B2O3/sapphire melt system is more unstable than 5cSt silicone oil/HT-70, there are two unstable flow patterns, radial three-dimensional steady flow cell and hydrothermal waves near the hot wall. The larger the ratio of Pr number of upper and lower fluid layers is, the better the effect of restraining the flow of lower fluid layers is.

Convective and Absolute Instabilities Induced by Viscous Dissipation in the Thermocapillary Convection with Through-Flow

The mixed convection in a thin liquid film flow over a horizontal plate is investigated under finite Prandtl numbers. The gas-liquid interface is considered free, non-deformable and subject to surface tension gradients and convection, while gravity is assumed negligible. Therefore, Marangoni instead of buoyancy effects appear due to the unstable temperature stratification induced by the internal heating generated by viscous dissipation. A linear and modal stability analysis of this model is then performed to identify its convective/absolute nature. This is achieved by solving the resulting differential eigenvalue problem with a shooting method. Longitudinal rolls are the most unstable at the onset of instability for most parametric conditions. Otherwise, transverse rolls are the first to become convectively unstable. Finally, longitudinal rolls are absolutely stable. A transition to absolute instability occurs through transverse rolls, but only within a limited region in parametric space.

The Payload Development and the Experiments for Studying Thermocapillary Convection in TG-2 Liquid Bridge

The development of space experiment payload for studying thermocapillary convection in the liquid bridge with large Pr number on TG-2 space laboratory as well as the experiments are presented in detail in this paper, and the objectives of the space experiments are confirmed. The functions of the payload are analyzed, and the technical and engineering specifications are determined. Detailed designs and experimental verifications are performed on the structure of liquid bridge columns, the method of bubble removing in the liquid, the bridge cleaning system, the accurate control of aspect ratio and volume ratio, and the high-sensitivity measurement of fluid temperature. Matching experiments on the ground according to space experiment properties are carried out, 5cSt silicone oil is selected as the fluid medium in space experiments. And the states of liquid bridge and temperature oscillation signals obtained from space experiments are presented at the end of this paper. Specific summarizations and discussions to the experiment project on fluid science in space are conducted in this paper, which will provide a useful reference for scientists participating space experimental research in the future.