Ground Experiments Of Bouyant-Thermocapillary Convection Of Large Scale Liquid Bridge With Large Prandtl Number

Bouyant-thermocapillary driven convection in a large scale liquid bridge was investigated by ground experiments in this paper. A precise prototype system designed for space experiments of liquid bridge in Tiangong-2is used for this experiment:including liquid storage, establishing liquid bridge, heating and refrigeration system, thermocouples for temperature measurement. External instruments are used for temperature control and temperature signal acquisition in ground experiments. Temperature data is directly imported into a computer. We used2cst silicone oil (Pr=28.571) and5cst silicone oil (Pr=68.625).The column diameter of liquid bridge was20mm.Due to the limit by gravity, we constructed liquid bridge in the height range3mm-4.25mm with different volume.We strictly control the volume and height of the liquid bridge by motors which are used to pull bridge and to connect with liquid cylinder, observe the onset of liquid bridge with different aspect ratio (A=l/d) and volume, get the relation curves between the onset temperature difference and aspect ratio, and between the onset temperature difference and volume.At the same time, in the process of continuing to increase the temperature difference after onset of liquid bridge, through the analysis of the single point’s temperature oscillation curve, we discover the main frequency approximately increases linearly with the increase of temperature difference with a rate6.1228mHz/K. The frequencies appearing in the process to chaos of liquid bridge with different aspect ratio are different, but the way to chaos is the same, namely Feigenbaumb times cycle to chaos.With the help of5azimuthal thermocouples inserted in the liquid bridge interior, we discover that temperature oscillation in flow field occurs at the same time, bridges with different aspect ratio and volume have different flow modes, which are very sensitive to temperature difference, and which may change with the vary of temperature difference. The problem of hydrothermal waves is discussed preliminary.Finally, we simulate the temperature oscillations of liquid bridge with height4mm and volume ratio1.0in the condition of fixed temperature difference with FLUENT, and compare the calculation results with experiment results.