The Influence of the Magnitude of Gravitational Acceleration on Marangoni Convection About an Isolated Bubble under a Heated Wall

Thermocapillary or Marangoni convection is the liquid motion caused by surface tension variation in the presence of a temperature gradient along a gas-liquid or vapor-liquid interface. This work numerically investigates the effect of the magnitude of gravitational acceleration on the flow and temperature fields resulting from the presence of a hemispherical air bubble of constant radius of 1.0 mm, situated on a heated wall immersed in a liquid silicone oil layer of constant depth of 5.0 mm. The model is oriented such that the Marangoni and gravitational forces act to oppose one another. To elucidate the effect of gravity on Marangoni flow and heat transfer, the simulations were carried out for a silicone oil of Prandtl number 83, at a Marangoni number of 915. The gravity levels tested were 0g, 0.01g, 0.1g, 0.25g, 0.5g, 0.75g, and 1g, where g represents the earth gravitational acceleration of 9.81 m/s2. The influence of the magnitude of gravitational acceleration on the velocity profile along the bubble interface and on the location of maximum velocity was analyzed. It was found that the gravity level affects the velocity profile by influencing the interfacial temperature gradient, but that the location of maximum velocity was almost independent of gravity level. The increase in heat flux on the wall to which the bubble is attached was calculated and it has been determined that local heat transfer enhancement of up to nearly 1.7 times that of the conduction only case can be achieved for the parameter range tested. Furthermore, local enhancement was observed to occur up to a distance of seven bubble radii for the zero-gravity case, but increased gravity levels cause a reduction in the effective radius of enhancement. The influence of the Marangoni flow on the heat transfer for the opposite cooled wall has also been analyzed.