Gravity Scaling Parameter for Pool Boiling Heat Transfer

Although the effects of microgravity, earth gravity, and hypergravity (>1.5 g) on pool boiling heat flux have been studied previously, pool boiling heat flux data over a continuous range of gravity levels (0–1.7 g) was unavailable until recently. The current work uses the results of a variable gravity, subcooled pool boiling experiment to develop a gravity scaling parameter for n-perfluorohexane/FC-72 in the buoyancy-dominated boiling regime (Lh/Lc>2.1). The heat flux prediction was then validated using heat flux data at different subcoolings and dissolved gas concentrations. The scaling parameter can be used as a tool to predict boiling heat flux at any gravity level in the buoyancy dominated regime if the data under similar experimental conditions are available at any other gravity level.

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Gravity Scaling Parameter for Pool Boiling Heat Transfer

Volume 9: Heat Transfer, Fluid Flows, and Thermal Systems, Parts A, B and C ◽

10.1115/imece2009-12624 ◽

2009 ◽

Author(s):

Rishi Raj ◽

Jungho Kim ◽

John McQuillen

Keyword(s):

Heat Flux ◽

Pool Boiling ◽

Gravity Level ◽

Low Gravity ◽

Experimental Conditions ◽

Scaling Parameter ◽

Flux Data ◽

Variable Gravity ◽

Continuous Range ◽

Good Agreement

The effect of low gravity on pool boiling heat flux has been studied by researchers, but pool boiling heat flux data over a continuous range of gravity levels (0g–1.8g) was unavailable until recently. The current work uses the results of a variable gravity subcooled pool boiling experiment to develop a gravity scaling parameter for prediction purposes. The heat flux prediction at various gravity levels was found to be in good agreement with the measured heat flux data. The scaling parameter can be used as a tool to predict boiling heat flux at any gravity level if the data under similar experimental conditions are available at any other gravity level. The scaling parameter has been demonstrated to be valid for pool boiling of n-perfluorohexane in heater size independent boiling regime (Lh/Lc>2.8).

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On the Scaling of Pool Boiling Heat Flux With Gravity and Heater Size

ASME/JSME 2011 8th Thermal Engineering Joint Conference ◽

10.1115/ajtec2011-44449 ◽

2011 ◽

Author(s):

Rishi Raj ◽

Jungho Kim ◽

John McQuillen

Keyword(s):

Surface Tension ◽

Heat Flux ◽

Pool Boiling ◽

Threshold Value ◽

Prediction Errors ◽

Gravity Level ◽

Experimental Conditions ◽

Scaling Parameter ◽

Boiling Regime ◽

Using Data

A framework for scaling pool boiling heat flux is developed using data from various heater sizes over a range of gravity levels. Boiling is buoyancy dominated for large heaters and/or high gravity conditions and the heat flux is heater size independent. The power law coefficient for gravity is a function of wall temperature. As the heater size or gravity level is reduced, a sharp transition in the heat flux is observed at a threshold value of Lh/Lc = 2.1. Below this threshold value, boiling is surface tension dominated and the dependence on gravity is smaller. The gravity scaling parameter for the heat flux in the buoyancy dominated boiling regime developed in the previous work is updated to account for subcooling effect. Based on this scaling parameter and the transition criteria, a methodology for predicting heat flux in the surface tension dominated boiling regime, typically observed under low-gravity conditions, is developed. Given the heat flux at a reference gravity level and heater size, the current framework allows the prediction of heat flux at any other gravity level and/or heater size under similar experimental conditions. The prediction is validated using data at over a range of subcoolings (7°C ≤ ΔTsub ≤ 32.6°C), heater sizes (2.1 mm ≤ Lh ≤ 7 mm), and dissolved gas concentrations (3 ppm ≤ cg ≤ 3500 ppm). The prediction errors are significantly smaller than those from correlations currently available in the literature.

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On the Scaling of Pool Boiling Heat Flux With Gravity and Heater Size

Journal of Heat Transfer ◽

10.1115/1.4004370 ◽

2011 ◽

Vol 134 (1) ◽

Cited By ~ 16

Author(s):

Rishi Raj ◽

Jungho Kim ◽

John McQuillen

Keyword(s):

Surface Tension ◽

Heat Flux ◽

Pool Boiling ◽

Threshold Value ◽

Prediction Errors ◽

Gravity Level ◽

Experimental Conditions ◽

Scaling Parameter ◽

Boiling Regime ◽

Using Data

A framework for scaling pool boiling heat flux is developed using data from various heater sizes over a range of gravity levels. Boiling is buoyancy dominated for large heaters and/or high gravity conditions and the heat flux is heater size independent. The power law coefficient for gravity is a function of wall temperature. As the heater size or gravity level is reduced, a sharp transition in the heat flux is observed at a threshold value of Lh/Lc = 2.1. Below this threshold value, boiling is surface tension dominated and the dependence on gravity is smaller. The gravity scaling parameter for the heat flux in the buoyancy dominated boiling regime developed in the previous work is updated to account for subcooling effect. Based on this scaling parameter and the transition criteria, a methodology for predicting heat flux in the surface tension dominated boiling regime, typically observed under low-gravity conditions, is developed. Given the heat flux at a reference gravity level and heater size, the current framework allows the prediction of heat flux at any other gravity level and/or heater size under similar experimental conditions. The prediction is validated using data at over a range of subcoolings (11 °C ≤ ΔTsub ≤ 32.6 °C), heater sizes (2.1 mm ≤ Lh ≤ 7 mm), and dissolved gas concentrations (3 ppm ≤ cg ≤ 3500 ppm). The prediction errors are significantly smaller than those from correlations currently available in the literature.

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Effect of Fouling on Nucleate Pool Boiling in Microgravity and Earth Gravity

10.1115/imece1999-0997 ◽

1999 ◽

Author(s):

Daiju Motoya ◽

Ikuya Haze ◽

Masahiro Osakabe

Keyword(s):

Heat Flux ◽

High Speed ◽

Pool Boiling ◽

Film Boiling ◽

Gravity Level ◽

Nucleate Pool Boiling ◽

Bubble Volume ◽

High Speed Video ◽

Earth Gravity ◽

Bare Surface

Abstract Nucleate pool boiling of water on clean and fouling surfaces was conducted in microgravity and earth gravity. The microgravity experiments were conducted in 8 s JAMIC drop shaft in Hokkaido of Japan. Platinum wires of 0.2 mm in diameter with or without fouling scale were used to provide uniform heat flux and measurement of the mean temperature of wires. The generated bubble volume was measured with high-speed video or CCD images. The more vigorous bubbling was observed on the fouling wire compared to that on the clean wire at a same heat flux both in earth gravity and microgravity. The enhancement of the bubbling was associated with the fact that the hydrophilic porous structure in the fouling scale provided the sufficient number of active sites for bubbling nucleation. The wettability of the surface with the fouling scale was much higher than that of the clean bare surface. The bubble departure diameter on the fouling wire was smaller due to the high wettability than that on the clean wire. The latent heat transportation ratio to the total heat flux was calculated with the generated bubble volume measured with high-speed video or CCD images. The ratio was approximately the same at the clean and fouling wires in spite of the apparent difference in bubbling behavior, but it was significantly affected with the gravity level. The ratio increased with an increase of the heat flux in the earth gravity but it remained at the smaller value in the microgravity. The nucleate heat transfer coefficient on the bare surface did not depend on the gravity levels although the bubbling behavior strongly affected with the gravity level. As the wire radius is small compared to the capillary length scale in microgravity, a growing and coalescing bubble sometimes completely covered the clean wire, evaporating all liquid in contact with the surface and inducing a transition to film boiling. However, on the fouling wire, many small bubbles were generated and sprang from the surface in various directions in microgravity. The spring out action of bubbles suppressed the transition to the film boiling on the fouling wire in the present experimental range.

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An Induced-Convection Effect Upon the Peak-Boiling Heat Flux

Journal of Heat Transfer ◽

10.1115/1.3449633 ◽

1970 ◽

Vol 92 (1) ◽

pp. 1-5 ◽

Cited By ~ 11

Author(s):

J. H. Lienhard ◽

K. B. Keeling

Keyword(s):

Heat Flux ◽

Pool Boiling ◽

Reduced Pressure ◽

Flux Data ◽

Peak Heat Flux ◽

Variable Gravity

An induced-convection effect upon the peak pool-boiling heat flux is identified and described. A method is developed for correlating this effect under conditions of variable gravity, pressure and size, as well as for various boiled liquids. The effect is illustrated, and the correlation verified, with a large number of peak heat-flux data obtained on a horizontal ribbon heater. The data, obtained in a centrifuge, embrace an 87-fold range of gravity, a 22-fold range of width, a 15-fold variation of reduced pressure, and five liquids.

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Subcooled Pool Boiling in Variable Gravity Environments

Journal of Heat Transfer ◽

10.1115/1.3122782 ◽

2009 ◽

Vol 131 (9) ◽

Cited By ~ 33

Author(s):

Rishi Raj ◽

Jungho Kim ◽

John McQuillen

Keyword(s):

Heat Transfer ◽

Pool Boiling ◽

Gravity Level ◽

Dissolved Gas ◽

Subcooled Liquid ◽

Size Dependent ◽

Gravity Effects ◽

Parametric Effects ◽

Bubble Growth And Departure ◽

Continuous Range

Virtually all data to date regarding parametric effects of gravity on pool boiling have been inferred from experiments performed in low-g, 1g, or 1.8g conditions. The current work is based on observations of boiling heat transfer obtained over a continuous range of gravity levels (0g–1.8g) under subcooled liquid conditions (n-perfluorohexane, ΔTsub=26°C, and 1 atm), two gas concentrations (220 ppm and 1216 ppm), and three heater sizes (full heater-7×7 mm2, half heater-7×3.5 mm2, and quarter heater-3.5×3.5 mm2). As the gravity level changed, a sharp transition in the heat transfer mechanism was observed at a threshold gravity level. Below this threshold (low-g regime), a nondeparting primary bubble governed the heat transfer and the effect of residual gravity was small. Above this threshold (high-g regime), bubble growth and departure dominated the heat transfer and gravity effects became more important. An increase in noncondensable dissolved gas concentration shifted the threshold gravity level to lower accelerations. Heat flux was found to be heater size dependent only in the low-g regime.

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