Experimental Investigation of non‐periodic oscillations in a surface tension driven flow around a bubble

Abstract

AbstractThermocapillary convection around an air bubble under a heated wall is experimentally investigated under gravitational conditions. The flow is basically studied through temperature fluctuation plots near the bubble periphery, which is subjected to an upward flow driving temperature gradient. This study illuminates the thermocapillary‐buoyancy convective flow behaviour within the regime of non‐periodic oscillations. Moreover, the fluid flow is qualitatively categorized according to the transient behaviour of the thermocapillary vortex boundary line around the bubble using the shadowgraph technique. A low viscous silicone oil as test fluid restricts reaching higher temperature gradients to avoid the formation of undesired vapour bubbles. However, pursuing the experiments under high pressures allowed reaching higher temperature gradients in order to achieve the non‐periodic flow regime. Both periodic and chaotic oscillations of the liquid flow around the bubble were recorded. They were distinguished from each other through the periodicity of the visualized thermocapillary vortex boundary line movements. The recording of temperature fluctuations at positions near the bubble during a time period Δt demonstrated the thermocapillary fluid flow behaviour at different Marangoni‐numbers Mg.