Multi-jet flows and bubble emission during subcooled nucleate boiling of aqueous n-butanol solution on thin wire

• Multi-jet flows for n-butanol solution were observed around a platinum micro heating wire.
• The multi-jet flows can sustain for a long period and cause microbubble emission near the heated surface.
• Sharp temperature gradient and vertical velocity were presented in the simulation for microbubble emission.
• Thermocapillary convection is crucial to the mechanisms of subcooled nucleate boiling of various fluids.

Jet flow phenomenon is important in enhancing the nucleate boiling heat transfer processes. When heater sizes scale down, jet flow can be observed due to the thermocapillary convection around bubbles attached on microscale heated surface. In this paper, a self-rewetting fluid, aqueous n-butanol solution, was employed for demonstrating the effect of thermocapillary convection on bubble behaviors during subcooled nucleate boiling on thin wire, comparing with deionized water. 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 thermocapillary convection that attracts the subcooled water to flow from the superheated microlayer at the base to the top of a stationary bubble. For n-butanol solution, however, the thermocapillary convection can induce it to flow oppositely, causing the subcooled solution to flow onto the heated surface. The simulation for the solution was in good agreement with the experiment where the subcooled liquid near the bubble top flow towards the bubble base, or the heated surface, and hence the multi-jet flows occur. The multi-jet flows can sustain for a long period and cause bubble emission at the superheated thin liquid layer near the heated surface. The temperature around the bubble presented sharp temperature gradient and the velocity in the near-wall region was almost vertical to the wall. The experimental and numerical studies on the effect of surface tension and thus thermocapillary convection are crucial to the mechanisms of subcooled nucleate boiling of fluids.