Multi-Jet Flows Underneath Small Bubble in Nucleate Boiling of Subcooled Self-Rewetting Fluid Available to Purchase

Jet flow phenomenon is important in enhanced nucleate boiling heat transfer processes and applications. When heater sizes scale down, jet flow can be observed due to the Marangoni convection around bubbles staying on microscale heated surface. In this paper, two fluids were employed for comparing and demonstrating the effect of Marangoni convection on bubble behaviors on micro heating wire. One was ultrapure water and the other was aqueous n-butanol solution, a self-rewetting fluid. Bubble-top jet flow for water and multi-jet flows for n-butanol solution were observed around a platinum micro heating wire by high speed CCD camera. Corresponding numerical simulation proved that it is the Marangoni convection that attracts the sub-cooled water to flow from the super-heated microlayer at the bottom to the top of a stationary bubble. For n-butanol solution, however, the Marangoni convection can induce it to flow oppositely, which causes the subcooled solution to flow onto the heated surface. The simulation for the solution is in good agreement with the experiment where the subcooled liquid nears the bubble-top flow towards the bottom of bubble or the heated surface and hence the multi-jet flows occur. The multi-jet flows can sustain for a long period and cause transient chaos at the super-heated thin liquid layer near the heated surface. The temperature around the bubble presented sharp temperature gradient and the velocity in the near-wall region is almost vertical to the wall. The experimental and numerical studies on the effect of surface tension and thus Marangoni convection are crucial to the mechanisms of subcooled nucleate boiling of fluids.