Liquid–vapor structure near heating surface at high heat flux in subcooled pool boiling

Ono, Ayako; Sakashita, Hiroto

doi:10.1016/j.ijheatmasstransfer.2007.01.026

Cited by 35 publications

(10 citation statements)

References 9 publications

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“…I (Introduction), Ono and Sakashita 22) measured the liquid-vapor behaviors for horizontal upward surfaces and obtained results similar to the present measurements: in subcooled boiling, the liquid layer exists beneath the vapor masses in the nucleate boiling region even at heat fluxes much higher than the CHF for saturated boiling and the thickness of the liquid layer increases with the increase in the degree of subcooling. Furthermore, Ono and Sakashita 23) measured 2-dimensional dryout behaviors of the liquid layer and concluded that the CHF is triggered by the rapid expansion of the dryout area over the heating surface due to the consumption of the liquid layer during the vapor mass hovering period above the surface.…”

Section: (5) Liquid Layer Thickness Beneath Vapor Massessupporting

confidence: 85%

“…22). An AC voltage of 24 kHz, the resonance frequency of the measurement circuit, was applied between the conductance probe and the heating surface, and the inverse of the resonance frequency of the electrical circuit, 42 ms, was the time resolution of the measurements.…”

Section: Measurement System With Conductance Probementioning

confidence: 99%

“…This section indicates the thicknesses of this liquid layer. Ono and Sakashita 22) measured liquid-vapor behaviors near the horizontal upward heating surface using the conductance probe in saturated and subcooled pool boiling of water under atmospheric pressure. They assumed that the region from the heating surface to the height above which the oscillation of the interface at the bottom of the vapor mass does not occur corresponds to the liquid layer (macrolayer), and then specified the thickness of the liquid layer from the location where the vapor mass signals disappear: In the present paper, the liquid layer thickness determination is based on the same assumption.…”

Section: (5) Liquid Layer Thickness Beneath Vapor Massesmentioning

confidence: 99%

“…Full details of the method used to determine the liquid layer thickness are indicated in the previous paper, 22) and an outline of the method is shown next. The time-series data of the pulse signals were measured at various locations away from the heating surface by moving the probe in the direction normal to the heating surface (total number of pulses: 4,096 or 8,192).…”

Section: (5) Liquid Layer Thickness Beneath Vapor Massesmentioning

confidence: 99%

“…21) Through those measurements, the existence of the liquid layer beneath the vapor mass was confirmed and the thickness of the liquid layer was determined by several researchers. Ono and Sakashita 22) measured the liquid-vapor behaviors in saturated and subcooled pool boiling on upward surfaces, and established that the thickness of the liquid layer beneath the vapor masses increases with increasing degree of subcooling. Furthermore, Ono and Sakashita 23) measured the 2-dimensional dryout behaviors of the liquid layer and concluded that the macrolayer dryout model proposed by Katto and Yokoya 4) is the most appropriate model of the CHF for pool boiling on upward heating surfaces, and that the increase in CHF with the degree of subcooling is due to the formation of a thicker liquid layer.…”

Section: Introductionmentioning

confidence: 99%

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Critical Heat Flux and Near-Wall Boiling Behaviors in Saturated and Subcooled Pool Boiling on Vertical and Inclined Surfaces

Sakashita¹,

Ono²,

NYUI³

2009

J. Nucl. Sci. Technol.

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The mechanism of the critical heat flux (CHF) where the departure from nucleate boiling (DNB)-type boiling transition takes place has not been fully elucidated. In this paper, we examine the trigger mechanism of the CHF for saturated and subcooled pool boiling on vertical and inclined surfaces based on measurements of the liquid-vapor behaviors near heating surfaces by using a conductance probe. The angle of inclination was varied from 90 (vertical) to 170 (facing almost horizontally downwards). The probe signals and the void fraction distributions showed that a liquid layer remains beneath the vapor masses moving upward along the heating surface at high heat fluxes near the CHF. The thickness of the liquid layer was determined from the location where the probe signals corresponding to the vapor masses disappeared. The thickness of the liquid layer formed on the vertical surface increased with increasing degree of subcooling, which may be the cause of the increases in CHF with increasing degree of subcooling. The measurements of saturated boiling on the inclined surface confirmed that the orientation of the heating surface greatly affects the period it takes for vapor masses to pass, but it negligibly affects the liquid layer thickness. This suggests that the decrease in CHF with increasing angle of inclination is primarily caused by the lengthening of the duration of vapor mass passage.

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Section: (5) Liquid Layer Thickness Beneath Vapor Massessupporting

confidence: 85%

Section: Measurement System With Conductance Probementioning

confidence: 99%

Section: (5) Liquid Layer Thickness Beneath Vapor Massesmentioning

confidence: 99%

Section: (5) Liquid Layer Thickness Beneath Vapor Massesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Critical Heat Flux and Near-Wall Boiling Behaviors in Saturated and Subcooled Pool Boiling on Vertical and Inclined Surfaces

Sakashita¹,

Ono²,

NYUI³

2009

J. Nucl. Sci. Technol.

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Temperature measurements near a heating surface at high heat fluxes in subcooled pool boiling

Ono

Sakashita

2009

Heat Trans. Asian Res.

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In previous papers (Int J Heat Mass Transfer, 2008;50:3481-3489, 2009;52: 814-821), the authors conducted measurements of liquid-vapor structures in the vicinity of a heating surface for subcooled pool boiling on an upward-facing copper surface by using a conducting probe method. We reported that the macrolayer dryout model is the most appropriate model of the CHF and that the reason why the CHF increases with increasing subcooling is most likely that a thick macrolayer is able to form beneath large vapor masses and the lowest heat flux of the vapor mass region shifts towards the higher heat flux. To develop a mechanistic model of the CHF for subcooled boiling, therefore, it is necessary to elucidate the effects of local subcooling on boiling behaviors in the vicinity of a heating surface. This paper measured local temperatures close to a heating surface using a micro-thermocouple at high heat fluxes for water boiling on an upward-facing surface in the 0 to 40 K range of subcooling. A value for the effective subcooling, defined as the local subcooling during the period while vapor masses are being formed was estimated from the detected bottom peaks of the temperature fluctuations. It was established that the effective subcooling adjacent to the surface remains at considerably lower values than the bulk liquid subcooling. This suggests that, from nucleation to coalescence, the subcooling of a bulk liquid has a smaller effect on the behavior of primary bubbles than the extent of the subcooling would appear to suggest. An empirical correlation of the effective subcooling is proposed to provide a step towards quantitative modeling of the CHF for subcooled boiling.

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Diagnostic techniques for the dynamics of a thin liquid film under forced flow and evaporating conditions

Gong

Dinh

2010

Microfluid Nanofluid

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Motivated by quantification of micro-hydrodynamics of a thin liquid film which is present in industrial processes, such as spray cooling, heating (e.g., boiling with the macrolayer and the microlayer), coating, cleaning, and lubrication, we use micro-conductive probes and confocal optical sensors to measure the thickness and dynamic characteristics of a liquid film on a silicon wafer surface with or without heating. The simultaneous measurement on the same liquid film shows that the two techniques are in a good agreement with respect to accuracy, but the optical sensors have a much higher acquisition rate up to 30 kHz which is more suitable for rapid process. The optical sensors are therefore used to measure the instantaneous film thickness in an isothermal flow over a silicon wafer, obtaining the film thickness profile and the interfacial wave. The dynamic thickness of an evaporating film on a horizontal silicon wafer surface is also recorded by the optical sensor for the first time. The results indicate that the critical thickness initiating film instability on the silicon wafer is around 84 lm at heat flux of *56 kW/m 2 . In general, the tests performed show that the confocal optical sensor is capable of measuring liquid film dynamics at various conditions, while the micro-conductive probe can be used to calibrate the optical sensor by simultaneous measurement of a film under quasi-steady state. The microexperimental methods provide the solid platform for further investigation of the liquid film dynamics affected by physicochemical properties of the liquid and surfaces as well as thermal-hydraulic conditions.

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Liquid–vapor structure near heating surface at high heat flux in subcooled pool boiling

Cited by 35 publications

References 9 publications

Critical Heat Flux and Near-Wall Boiling Behaviors in Saturated and Subcooled Pool Boiling on Vertical and Inclined Surfaces

Critical Heat Flux and Near-Wall Boiling Behaviors in Saturated and Subcooled Pool Boiling on Vertical and Inclined Surfaces

Temperature measurements near a heating surface at high heat fluxes in subcooled pool boiling

Diagnostic techniques for the dynamics of a thin liquid film under forced flow and evaporating conditions

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