Liquid film–induced critical heat flux enhancement on structured surfaces

Enhancing critical heat flux (CHF) during boiling with structured surfaces has received much attention because of its important implications for two-phase flow. The role of surface structures on bubble evolution and CHF enhancement remains unclear because of the lack of direct visualization of the liquid- and solid-vapor interfaces. Here, we use high-magnification in-liquid endoscopy to directly probe bubble behavior during boiling. We report the previously unidentified coexistence of two distinct three-phase contact lines underneath growing bubbles on structured surfaces, resulting in retention of a thin liquid film within the structures between the two contact lines due to their disparate advancing velocities. This finding sheds light on a previously unidentified mechanism governing bubble evolution on structured surfaces, which has notable implications for a variety of real systems using bubble formation, such as thermal management, microfluidics, and electrochemical reactors.

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Rupture of thin liquid film based premature critical heat flux prediction in microchannel

International Journal of Heat and Mass Transfer ◽

10.1016/j.ijheatmasstransfer.2018.04.154 ◽

2018 ◽

Vol 125 ◽

pp. 933-942 ◽

Cited By ~ 4

Author(s):

Hui He ◽

Liang-ming Pan ◽

Hao-jie Huang ◽

Run-gang Yan

Keyword(s):

Heat Flux ◽

Liquid Film ◽

Critical Heat Flux ◽

Thin Liquid Film

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H222 Critical Heat Flux of Counter-Current Two-Phase Flow : Effect of Subcooled Liquid Film

The Proceedings of the Thermal Engineering Conference ◽

10.1299/jsmeted.2011.371 ◽

2011 ◽

Vol 2011 (0) ◽

pp. 371-372

Author(s):

Ayaka Fujiwara ◽

Takuya Suzuki ◽

Takeyuki Ami ◽

Hisashi Umekawa ◽

Mamoru Ozawa

Keyword(s):

Heat Flux ◽

Liquid Film ◽

Critical Heat Flux ◽

Two Phase Flow ◽

Phase Flow ◽

Two Phase ◽

Subcooled Liquid ◽

Flow Effect ◽

Counter Current

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Spray Cooling Heat Transfer Enhancement and Degradation Using Fractal-Like Micro-Structured Surfaces

ASME/JSME 2011 8th Thermal Engineering Joint Conference ◽

10.1115/ajtec2011-44331 ◽

2011 ◽

Cited By ~ 2

Author(s):

Alex Tulchinsky ◽

Deborah V. Pence ◽

James A. Liburdy

Keyword(s):

Heat Transfer ◽

Heat Flux ◽

Critical Heat Flux ◽

Smooth Surface ◽

Single Phase ◽

High Volume ◽

Spray Cooling ◽

Volume Flux ◽

Two Phase ◽

Structured Surfaces

In the present study, spray cooling curves are presented for two micro-structured surfaces and are compared to smooth surface results. The micro-structured surfaces consisted of bio-inspired fractal-like geometries, denoted as grooves or fins, extending in a radial direction from the center to the periphery of a 37.8 mm circular disc. Depending on the location on the surface, dimensions of groove widths and heights varied from 100 to 500 μm, and 30 to 60 μm, respectively. Fin width and height dimensions remained constant over the surface at 127 and 60 μm, respectively. Results are presented as heat flux versus the surface-to-exit spray temperature difference at each of five volume flux conditions ranging from 0.54 to 2.04 × 10−3 m3/m2-s. Convection heat transfer coefficients are also presented for each case as a function of heat flux. Results indicate that at low and high volume fluxes, an improvement in heat transfer occurs in the single phase regime for the fin geometry. Enhancement in the single phase regime does not occur at the intermediate volume flux condition. In the two phase regime for the fin structure significant enhancements, up to 50%, are observed. Whereas the groove structure performs similarly to the smooth surface in the single phase regime and exhibits large degradation in the two phase and critical heat flux regimes, up to 50%. Critical heat flux for the fin surface compares well to that of the flat surface, with a slightly increase at high volume flux conditions.

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Experimental Study on Liquid Film Dryout Under Oscillatory Flow Conditions

Volume 4: Codes, Standards, Licensing and Regulatory Issues; Student Paper Competition ◽

10.1115/icone17-75400 ◽

2009 ◽

Cited By ~ 1

Author(s):

Yosuke Yamagoe ◽

Taisuke Goto ◽

Tomio Okawa

Keyword(s):

Heat Flux ◽

Liquid Film ◽

Power Density ◽

Critical Heat Flux ◽

Boiling Water ◽

Boiling Water Reactors ◽

Flow Oscillation ◽

Two Phase ◽

Water Reactors ◽

Liquid Film Dryout

The use of high power density core is one of the promising ways to improve economic efficiency of advanced boiling water reactors. It is however known that in boiling two-phase flows, an increase in power density commonly reduces the margin to the onset of unanticipated flow instability. Hence, in the development of a boiling water reactor of high power density core, ability to predict the occurrence of boiling transition is considered indispensable even when the coolant flow rate is not in the steady state. In the present work, sinusoidal oscillation was applied to the inlet mass flux and the experimental measurement of the critical heat flux was carried out under flow oscillation conditions. It was shown that the critical heat flux decreases monotonically with increased values of oscillation amplitude and oscillation period. These results are consistent with experimental data reported by previous investigators. A simple theory was then proposed to estimate the critical heat flux in oscillatory flow condition. Considering the application to the advanced boiling water reactors, the triggering mechanism of the critical heat flux condition is supposed to be the liquid film dryout in annular two-phase flow regime of high vapor quality. Under the flow oscillation condition, it is expected that long waves are formed on a liquid film due to the time variation of inlet mass flux. Assuming that the wave evolution within a boiling channel is influential in the occurrence of the local dryout of a liquid film, an available nonlinear wave theory was applied to the estimation of critical heat flux under the flow oscillation condition. It was demonstrated that the critical heat fluxes measured under the oscillatory conditions agree with the proposed theory fairly well.

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