MARANGONI CONVECTION AROUND A MICROBUBBLE ATTACHED TO A LOCALLY HEATED CHANNEL WALL

The flow and thermal characteristics of the Marangoni convection (thermocapillary flow) around a microbubble are described in this study for the case in which a bubble is attached to a locally heated microchannel wall (hot spot applied). By providing a heat source near the bubble and generating a temperature gradient on the surface of the bubble, Marangoni convection can be produced in the surrounding fluid. In the microscale, this effect is significant, and strong vortices and streaming flow can be formed in the channel. We investigate the effects of the location of the hot spot on the temperature field and vortex structure based on numerical simulations. A circulating flow is generated when the hot spot is located at the center of the bubble, while a pair of strong vortices appears when the hot spot is located away from the center of the bubble. Further, we evaluate the effect of heat conduction and temperature dependence of the fluid viscosity on the temperature field and the resulting Marangoni convection. To compare the present results with the experimentally measured ones and to visualize the flow using particles, we solve the equations governing the motion of the particles and evaluate the contribution of each force term. The results show that the trajectory of the particle follows the streamline, but can deviate to a certain degree at the location where the streamline curvature is large.