Oscillate boiling from microheaters

Fenfang Li, S. Roberto Gonzalez-Avila, Dang Minh Nguyen, and Claus-Dieter Ohl

Phys. Rev. Fluids 2, 014007 – Published 27 January 2017

Abstract

We report about an intriguing boiling regime occurring for small heaters embedded on the boundary in subcooled water. The microheater is realized by focusing a continuous wave laser beam to about $10 μ m$ in diameter onto a 165-nm-thick layer of gold, which is submerged in water. After an initial vaporous explosion a single bubble oscillates continuously and repeatedly at several $100 kHz$ albeit with constant laser power input. The microbubble's oscillations are accompanied with bubble pinch-off, leading to a stream of gaseous bubbles in the subcooled water. The self-driven bubble oscillation is explained with a thermally kicked oscillator caused by surface attachment and by the nonspherical collapses. Additionally, Marangoni stresses induce a recirculating streaming flow which transports cold liquid towards the microheater, reducing diffusion of heat along the substrate and therefore stabilizing the phenomenon to many million cycles. We speculate that this oscillate boiling regime may overcome the heat transfer thresholds observed during the nucleate boiling crisis and offers a new pathway for heat transfer under microgravity conditions.

Received 10 April 2016
Revised 29 August 2016

DOI:https://doi.org/10.1103/PhysRevFluids.2.014007

Physics Subject Headings (PhySH)

Evaporation Marangoni convection

Gas-liquid interfaces

Condensed Matter, Materials & Applied PhysicsStatistical Physics & Thermodynamics

Authors & Affiliations

Fenfang Li, S. Roberto Gonzalez-Avila, Dang Minh Nguyen, and Claus-Dieter Ohl^*

Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore

^*cdohl@ntu.edu.sg

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Issue

Vol. 2, Iss. 1 — January 2017

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Images

Figure 1
Laser powered microheater: (a) The 532 nm CW laser (29.5 mW) is focused onto a thin layer of gold (around 165 nm thickness). (b) A bubble forms on the gold layer and sheds microbubbles into the bulk (see inset). (c) Details of the bubble oscillation leading to the microbubble pinch-off at the bubble's apex. The selected frames show one typical period of the bubble dynamics. The oscillation frequency is around 90 kHz as detected by the hydrophone and the images are taken from a recording at 100 000 frames/s.
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Figure 2
Measurement of the bubble oscillation through acoustic emission. (a) The signal picked up by a hydrophone at nucleation and during continuous illumination with the laser beam. The inset shows the sinusoidal signal oscillatg at $320 kHz$ . (b) The spectrogram depicts the fundamental frequency and higher harmonics at nearly constant frequency over the duration of the laser heating of $250 ms$ .
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Figure 3
Modeling results of bubble oscillation and comparison to experiments. (a) Solution of the kicked bubble oscillator model (see text) for two initial conditions $R (t = 0)$ : one starting at a bubble radius larger than the steady state maximum radius $R_{max}^{s s}$ and one at a smaller radius. The phase-space inset demonstrates that both trajectories approach the same attractor. The bubble's effective radius is calculated by assuming a hemispherical cap of the same volume. (b) Dependence of the resonance frequency (solid line) and laser power (dashed line) on the maximum bubble radius $R_{max}^{s s}$ . The experimental data points are plotted as filled circles and squares.
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Figure 4
Modeling results of the thermocapillary flow and comparison to experiments. (a) Simulation of the heat transfer (right) and the thermocapillary effect induced flow (left) of a steady bubble under laser irradiation of 40 mW for 10 miliseconds. (b) Flow field obtained from particle image velocimetry with $2 μ m$ diameter particles. Due to illumination constraints we could not identify particles in the bottom part of the image. Note the different image scales on the left and right panels.
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Figure 5
Oscillate boiling for potential heat transfer application. (a) Oscillate boiling on a $30^{\circ}$ tilted substrate with 89 mW laser power. (b) Temperature evolution of liquid region located $250 μ m$ above the bubble with two different boiling regimes. (c) Independent behavior of two closely placed oscillate boiling bubbles. In (a) and (c), the time interval between two consecutive frames is $3.33 μ s$ and the length scale represents $20 μ m$
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