Study on flow structure transition in thermocapillary convection under parallel gas flow

Abstract

In this paper, the influence of direction, velocity and temperature of parallel gas flow on the flow structure of non-isothermal liquid bridge is studied using PIV technique with 10 cSt silicone oil as the working fluid. Experimental results show that thermocapillary convection can be weakened by entering the parallel gas flow at a lower velocity (Vg = 0–2 m/s) from the upper disc of liquid bridge, which makes the shape of the vortices in the liquid bridge to transit from a semilune to a sickle-shaped form. Vortices approach toward the free surface gradually because the farthest radial position that the vortex can reach becomes from 2.99 mm to 2.24 mm. The velocity of particle near the free surface is also inhibited from 1.89 mm/s to 1.36 mm/s. When the velocity of parallel gas flow is increased to Vg = 3 m/s, the thermocapillary convection is enhanced. The farthest radial position that the vortex can reach is increased to 2.66 mm, and the velocity of particle is also increased from 1.36 mm/s to 2.30 mm/s. Then experiments are conducted with the velocity of parallel gas flow keeping at Vg = 2 m/s, and the temperature of parallel gas flow is set at the upper disc temperature, the lower disc temperature and the average temperature of upper and lower discs, respectively. It is found that the thermocapillary convection becomes weak obviously when the temperature of parallel gas flow is set at the average temperature of upper and lower discs. Under this condition, the farthest radial position that vortex can reach is decreased to 2.04 mm, and the velocity of particle is also the smallest (vE0 = 1.18 mm/s). When the parallel gas flow enters from the lower disc, the thermocapillary convection weakens gradually. The farthest radial position that vortex can reach decreases from 2.99 mm to 1.98 mm, and the velocity of particle near the free surface is inhibited from 1.89 mm/s to 0.32 mm/s with the increasing parallel gas velocity. Keeping the velocity of parallel gas flow at Vg = 2 m/s and changing the temperature of parallel gas flow, it is found that reducing the temperature difference between the parallel gas flow and the free surface of the liquid bridge can inhibit the thermocapillary convection.