| Liquid motion around a bubble placed on a heated wall of a flowing liquid channel is investigated under both normal and micro-gravity conditions. The configuration is similar to forced convection boiling. The present study focuses on understanding the roles of the bulk liquid motion and wall heating in governing the flow and temperature fields.; A ground-based experiment is set up to visualize the flow around the bubble. In parallel, a spectral element method based two-dimensional computational model is developed. Good qualitative and quantitative agreement is observed between the two. The model, validated by the normal gravity experimental data, is extended to micro-gravity condition. A comparison of the transport fields in the two gravity levels is conducted.; It is shown that in both gravity levels, the two dominant mechanisms governing the flow and temperature fields are the thermocapillary convection arising at the bubble surface and forced convection due to the bulk liquid flow in the channel. They assist each other at the front side of the bubble facing the channel flow, while at the downstream side an opposing interaction between the two creates a recirculation cell. The bulk liquid flow stagnates on the bubble surface and separates thereafter. In addition to these convection modes, in normal gravity natural convection becomes an important mechanism, which opposes the thermocapillary convection. The channel flow velocity, length of the heated wall before the bubble, liquid viscosity, and the temperature difference between the heated wall and the bulk liquid are shown to be the most important parameters. Their effects on the flow around the bubble, the bubble surface temperature and velocity, the stagnation point on the bubble surface, the length of the recirculation cell along the heated wall, and the wall heat transfer near the bubble are investigated, under normal and micro-gravity conditions.; The thermocapillary effect due to wall heating is observed to significantly alter the flow around the bubble. It is proposed that a combination of flowing liquid and wall heating can be utilized to precisely control the bubble formation, detachment, size and formation frequency in micro-gravity environment. |
