VAPOR BUBBLE GROWTH IN SATURATED POOL BOILING BY MICROLAYER EVAPORATION OF LIQUID AT THE HEATED SURFACE

1970 ◽  
Author(s):  
G. S. Dzakowic ◽  
Walter Frost
Keyword(s):  
Vapor Bubble ◽  
Bubble Growth ◽  
Heated Surface ◽  
Pool Boiling ◽  
Microlayer Evaporation

Self-Propelled Sliding Bubble Motion Induced by Surface Microstructure in Pool Boiling of a Dielectric Fluid Under Microgravity

2015 ◽  
Vol 137 (2) ◽  
Author(s):  
Naveenan Thiagarajan ◽  
Sushil H. Bhavnani ◽  
Vinod Narayanan
Keyword(s):  
Vapor Bubble ◽  
Bubble Dynamics ◽  
Heated Surface ◽  
Pool Boiling ◽  
Bubble Nucleation ◽  
Radius Of Curvature ◽  
Dielectric Fluid ◽  
Bubble Motion ◽  
Reduced Gravity ◽  
Modification Technique

This paper reports bubble dynamics observed during pool boiling over microstructures with an asymmetric saw-tooth cross section, under reduced gravity. The periodic saw-toothed ratchets etched on a silicon surface include fabricated vapor bubble nucleation sites only on the shallow slope. Reduced gravity pool boiling experiments were conducted aboard a Boeing 727 aircraft carrying out parabolic maneuvers. The fluid used was FC-72, a highly wetting dielectric fluid used as a coolant for electronics. Under microgravity, it was observed that the bubble diameters were six times larger than in terrestrial gravity. Also, self-propelled sliding bubble motion along the surface of the saw teeth was observed in reduced gravity. The velocity of the sliding bubbles across the saw teeth, following lateral departure from the cavities, was measured to be as high as 27.4 mm/s. A model for the sliding bubble motion is proposed by attributing it to the force due to pressure differences that arise in the liquid film between the vapor bubble and the saw-toothed heated surface. The pressure difference is due to difference in the radius of curvature of the interface between the crest and trough of the saw teeth. The surface modification technique, which resulted in the sliding bubble motion, has the potential to alleviate dry-out caused due to stagnant vapor bubbles over heat sources under microgravity when the buoyancy forces are negligible compared to the surface tension forces.

0607 Vapor Bubble Lift-off from a Heated Surface in Subcooled Pool Boiling

2007 ◽  
Vol 2007.3 (0) ◽  
pp. 135-136
Author(s):  
Hiroshi NAGAKURA ◽  
Hayato KUBOTA ◽  
Tomio OKAWA ◽  
Isao KATAOKA
Keyword(s):  
Vapor Bubble ◽  
Heated Surface ◽  
Pool Boiling ◽  
Lift Off

scholarly journals Modelling Microlayer Formation in Boiling Sodium

Fluids ◽  
2020 ◽  
Vol 5 (4) ◽  
pp. 213
Author(s):  
Giovanni Giustini ◽  
Hyungdae Kim ◽  
Raad I. Issa ◽  
Michael J. Bluck
Keyword(s):  
Solid Surface ◽  
Vapor Bubble ◽  
Bubble Growth ◽  
Liquid Metals ◽  
Heated Surface ◽  
Algebraic Model ◽  
Optical Observations ◽  
Working Fluid ◽  
Sodium Vapor ◽  
Flow Solver

During boiling at a solid surface, it is often the case that a liquid layer of a few microns of thickness (’microlayer’) is formed beneath a bubble growing on the heated surface. Microlayers have been observed forming beneath bubbles in various transparent fluids, such as water and refrigerants, subsequently depleting due to evaporation, thus contributing significantly to bubble growth and possibly generating the majority of vapor in a bubble. On the other hand, boiling of opaque fluids, such as liquid metals, is not amenable to optical observations, and microlayers have not yet been observed in liquid metals. Among that class of fluids is sodium, suitable as a coolant for nuclear reactors and as the working fluid in phase-change solar power receivers. In order to support these applications, it is necessary to understand the boiling behavior of sodium and identify the parameters that might influence microlayer formation during boiling of this important fluid. This paper presents simulations of the hydrodynamics of sodium vapor bubble growth at a surface. An interface capturing flow solver has been implemented in the OpenFOAM code and used to predict the behavior of a sodium vapor bubble near a solid surface in typical boiling conditions. The methodology has been validated using recently reported direct experimental observations of microlayer formation in water and then applied to sodium boiling cases. Simulations indicate that microlayers are formed in sodium in a similar fashion to water. Comparison of simulation results with an extant algebraic model of microlayer formation showed good agreement, which increases confidence in the current predictions of microlayer formation. Typical values of microlayer thickness thus computed indicate that the microlayer is likely to play an important role during bubble growth in sodium.

A Numerical Study of the Effect of Contact Angle on the Dynamics of a Single Bubble During Pool Boiling

2002 ◽  
Author(s):  
H. S. Abarajith ◽  
V. K. Dhir
Keyword(s):  
Heat Flux ◽  
Contact Angle ◽  
Bubble Growth ◽  
Numerical Study ◽  
Heated Surface ◽  
Pool Boiling ◽  
Growth Period ◽  
Single Bubble ◽  
Liquid Phases ◽  
Bubble Growth And Departure

The effect of contact angle on the growth and departure of a single bubble on a horizontal heated surface during pool boiling under normal gravity conditions has been investigated using numerical simulations. The contact angle is varied by changing the Hamaker constant that defines the long-range forces. A finite difference scheme is used to solve the equations governing mass, momentum and energy in the vapor and liquid phases. The vapor-liquid interface is captured by the Level Set method, which is modified to include the influence of phase change at the liquid-vapor interface. The contact angle is varied from 1° to 90° and its effect on the bubble departure diameter and the bubble growth period are studied. Both water and PF5060 are used as test liquids. The contact angle is kept constant throughout the bubble growth and departure process. The effect of contact angle on the parameters like thermal boundary layer thickness, wall heat flux and heat flux from the microlayer under various conditions of superheats and subcoolings is also studied.

Sliding Bubble-Pumped Motion Induced by Surface Micro-Structure in Pool Boiling of a Dielectric Fluid Under Reduced Gravity

2014 ◽  
Author(s):  
Naveenan Thiagarajan ◽  
Sushil H. Bhavnani ◽  
Vinod Narayanan
Keyword(s):  
Vapor Bubble ◽  
Bubble Dynamics ◽  
Heated Surface ◽  
Pool Boiling ◽  
Bubble Nucleation ◽  
Radius Of Curvature ◽  
Dielectric Fluid ◽  
Bubble Motion ◽  
Reduced Gravity ◽  
Modification Technique

This paper reports bubble dynamics observed during pool boiling over micro-structures with an asymmetric saw-tooth cross-section, under reduced gravity. The periodic saw-toothed ratchets etched on a silicon surface include fabricated vapor bubble nucleation sites only on the shallow slope. Reduced gravity pool boiling experiments were conducted aboard a Boeing 727 aircraft (Zero-g Inc.) carrying out parabolic maneuvers to achieve reduced gravity. The fluid used was FC-72, a highly wetting dielectric fluid used as a coolant for electronics. Under microgravity, it was observed that the bubble diameters were six times larger than in terrestrial gravity. Also, self-propelled sliding bubble motion along the surface of the saw teeth was observed in reduced gravity. The velocity of the sliding bubbles across the saw teeth, following lateral departure from the cavities, was measured to be as high as 27.4 mm/s. A model for the sliding bubble motion is proposed by attributing it to the force due to pressure differences that arise in the liquid film between the vapor bubble and the saw-toothed heated surface. The pressure difference is due to difference in the radius of curvature of the interface between the crest and trough of the saw teeth. The surface modification technique has the potential to alleviate dry out caused due to vapor blanketing of heat sources in microgravity due to negligible buoyancy forces compared to the surface tension forces.

Contribution of Microlayer Evaporation to Bubble Growth in Pool Saturated Boiling of Water

2013 ◽  
Author(s):  
Tomohide Yabuki ◽  
Takuya Saitoh ◽  
Osamu Nakabeppu
Keyword(s):  
Heat Transfer ◽  
Bubble Growth ◽  
Heated Surface ◽  
High Heat ◽  
High Heat Flux ◽  
Wall Heat Transfer ◽  
Heat Transfer Phenomenon ◽  
Microlayer Evaporation ◽  
Dry Out ◽  
Saturated Boiling

Heat transfer and formation characteristics of the microlayer are investigated by the surface temperature measurement with a MEMS thermal sensor and the wall heat transfer evaluation using an experimental data. The temperature data clearly indicated transition of heat transfer phenomenon on the heated surface from microlayer formation via dry-out of the microlayer to rewetting of the dry-out region. Microlayer evaporation transferred extremely high heat flux over 1 MW/m2 and was found to be the dominant heat transfer mechanism in the wall heat transfer during isolated bubble boiling of water. The contribution of microlayer evaporation to bubble growth was found to be 50% and not vary with wall superheat. Finally the spatial distribution of initial thickness of microlayer was calculated from the wall heat transfer.

A Simplified Model for Predicting Vapor Bubble Growth Rates in Heterogeneous Boiling

1995 ◽  
Vol 117 (4) ◽  
pp. 976-980 ◽  
Author(s):  
W. C. Chen ◽  
J. F. Klausner ◽  
R. Mei
Keyword(s):  
Experimental Data ◽  
Growth Rate ◽  
Vapor Bubble ◽  
Bubble Growth ◽  
Heating Surface ◽  
Simplified Model ◽  
Order Ordinary Differential Equation ◽  
Empirical Parameter ◽  
Wetting Fluids ◽  
Microlayer Evaporation

A simplified model, based on heat transfer through a wedge-shaped liquid microlayer and a lumped thermal analysis for a solid heater, is developed for predicting the vapor bubble growth rate in heterogeneous pool boiling. A first-order ordinary differential equation is obtained for the bubble growth rate. An empirical parameter, C2, which characterizes the region of the heating surface influenced by microlayer evaporation, is determined by matching the existing experimental data with the predicted growth rate. The present bubble growth model compares well with the available experimental data for intermediate and moderately wetting fluids in which Jacob number ranges from 0.52 to 1974.

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