Experimental study on transition characteristics of thermo-solutocapillary convection under buoyancy

Abstract

An experimental study on the spatial and temporal evolution of thermo-solutocapillary convection in liquid bridges under buoyancy effect is conducted by Particle Image Velocimetry (PIV). In this experiment, 5cst silicone oil and the n-hexane are used as the solvent and solute, respectively. The velocity field for the steady thermocapillary-buoyancy convection is investigated firstly, and then the transitional characteristic of thermo-solutocapillary convection under buoyancy effect is analyzed as well. Experimental results show that, in the steady thermocapillary-buoyancy convection of liquid bridge with volume ratio Vr = 0.9 or Vr = 0.8, the vortex center of thermocapillary convection moves gradually toward the free surface with the increasing temperature difference, and the vortex evolves from a semilune “Ͻ” at a small temperature difference to a sickle-shaped “ر” at a large temperature difference. When the volume ratio is relatively large (Vr = 0.9), as the temperature difference increases, the connection line for velocity values at monitoring particles at the intermediate height of liquid bridge R(X, 1.5) shows a weak monotonicity. However, when the volume ratio is decreased (Vr = 0.8), the monotonicity is significantly better than that at large volume ratio. When Vr is 0.6, the temperature difference affects weakly the vortex position of thermocapillary convection, and the shape of the vortex is always the semilunar—“Ͻ”. The oscillatory mechanism and flow pattern of thermo-solutocapillary convection under gravity are different at different volume ratios. When the volume ratio is large (Vr = 0.9), vortices of buoyancy convection and thermo-solutocapillary convection appear an oscillatory pattern of mutual wane-wax—a “synchronous” oscillatory type. When Vr is 0.6, vortices of thermo-solutocapillary convection show an asynchronous feature of wane-wax—an “asynchronous” oscillatory type.