Abstract
This study aims to investigate the thermocapillary migration of long bubbles in closed cylinder tubes. Different experimental conditions like bubble length, temperature gradient, tube radius and surface property were changed to find the influence on the migration velocity. Linear temperature field was established by using current experimental setup. The temperature gradient in current experiment can be adjusted ranging from 0 to 4℃/cm. The molecule based temperature sensor technique has also been applied to the experiments for fluid temperature measurements inside cylinder tubes. The temperature data acquired by molecule based temperature sensor show good agreement with the one measured by thermocouples and the deviation between them is within 5 %. The glass cylinder tubes with hydrophilic surface have also been prepared by evaporating silane inside the cylinder surface. Deionized water and Ethanol which can form wetted surface inside cylinder tubes regardless the surface properties were chosen as the working fluid. It is found that the migration velocity linearly increases with the temperature gradient and the tube radius which differ from previous studies. They are due to the effect of evaporation/condensation and the vertical thermocapillary force observed in current experiments. These effects make the film thicker at the top of cylinder which causes fluid passing similar to parallel plate flow. Previous studies reported that the migration velocity has a linear dependence on modified capillary number if parallel plate flow dominates the flow field around the bubble. The results also show that bubble moving speed in hydrophobic cylinder tubes at low temperature gradients has 46 percent faster compared to the hydrophilic cylinder tubes.