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.

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.

Numerical Simulation and Experimental Validation of the Dynamics of a Single Bubble During Pool Boiling Under Constant and Time-Varying Reduced Gravity Conditions

2003 ◽  
Author(s):  
H. S. Abarajith ◽  
D. M. Qiu ◽  
V. K. Dhir
Keyword(s):  
Numerical Simulation ◽  
Heated Surface ◽  
Bubble Diameter ◽  
Pool Boiling ◽  
Growth Period ◽  
Single Bubble ◽  
Time Varying ◽  
Reduced Gravity ◽  
System Pressure ◽  
Vapor Liquid

The numerical simulation and experimental validations of the growth and departure of a single bubble on a horizontal heated surface during pool boiling under reduced gravity conditions have been performed here. A finite difference scheme is used to solve the equations governing mass, momentum and energy in the vapor liquid phases. The vapor-liquid interface is captured by level set method, which is modified to include the influence of phase change at the liquid-vapor interface. The effects of reduced gravity conditions, wall superheat and liquid subcooling and system pressure on the bubble diameter and growth period have been studied. The simulations are also carried out under both constant and time-varying gravity conditions to benchmark the solution with the actual experimental conditions that existed during the parabolic flights of KC-135 aircraft. In the experiments, a single vapor bubble was produced on an artificial cavity, 10 μm in diameter microfabricated on the polished silicon wafer, the wafer was heated electrically from the back with miniature strain gage type heating elements in order to control the nucleation superheat. The bubble growth period and the bubble diameter predicted from the numerical simulations have been found to compare well with the data from experiments.

Dynamics and Breakup Regime of a Vapor Bubble Traveling Through a Heated T-Shaped Branching Microchannel

2020 ◽  
Author(s):  
Zhe Yan ◽  
Shanshan Li ◽  
Lichun Li ◽  
Bili Deng ◽  
Zhenhai Pan
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Vapor Bubble ◽  
Bubble Dynamics ◽  
Surface Force ◽  
Bubble Motion ◽  
Heat Transfer Characteristics ◽  
Bubble Breakup ◽  
Wall Superheat ◽  
Frame Method

Abstract Dynamics and breakup characteristics of a vapor bubble when traveling through the T-junction of a heated branching microchannel are numerically investigated with the Volume of Fluid-Continuum-Surface-Force (VOF-CSF) method. The moving reference frame method, which has been demonstrated to help suppressing the unphysical spurious velocity around the liquid-vapor interface (Numer. Heat Trans. 67, 1–12), is employed and coupled to the VOF-CSF model. In order to evaluate the influence of the wall heating on the growth and breakup of vapor bubble, the saturated-interface-volume phase change model is further coupled to account for the phase change on the bubble interface. The numerical model is first validated against experimental results in literature. Then the effect of wall superheat on bubble dynamics and heat transfer coefficient is investigated. Bubble motion, growth, breakup and heat transfer characteristics at different wall superheats are analyzed in detail. Four bubble breakup regimes are observed, namely non-breakup (NB), breakup with tunnel (TB), combined breakup (CB) and breakup with permanent obstruction (OB). The present study reveals the transport details around an evaporating vapor bubble and helps understanding the underlying physics of bubble behaviors when traveling through a T-shaped branching microchannel.

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

Boiling Visualization and Critical Heat Flux (CHF) Phenomena on PCB in a Saturated Pool at Various Surface Orientations

2018 ◽  
Author(s):  
Elvira F. Tanjung ◽  
Daeseong Jo
Keyword(s):  
Image Processing ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Vapor Bubble ◽  
Bubble Dynamics ◽  
Heated Surface ◽  
Surface Orientation ◽  
The Other ◽  
Saturated Water ◽  
Other Hand

The onset of nucleate boiling (ONB) and critical heat flux (CHF) of saturated water on printed circuit board (PCB) that is immersed in a stainless steel pool were investigated at various surface orientations. Additionally, photographic analyses and image processing were conducted to observe the pool boiling phenomena and determine the bubble dynamics from upward to downward surface orientations (0°, 45°, 90°, 135°, 150°, and 180°). Results revealed that boiling commenced from downward to upward surface orientations (180° to 0°). When the heater was placed facing upwards (0° and 45°), the generated vapor bubble grew and coalesced together to form an elongated bubble which eventually departed from the heated surface due to the buoyancy in the vertical direction of the heated surface. In contrast to those orientations, at 90°, 135°, and 150°, the generated vapor bubble exhibited similar behavior except that it drifted along the heated surface before it departed at the most upper part of the heater. On the other hand, when the heater placed horizontally facing downward (180°), the generated vapor bubble grew and coalesced together until it ultimately covered the entire heated surface. Early ONB occurred when the heater was placed facing downwards (135°, 150°, and 180°). Moreover, it was observed that the CHF began when the heater was placed horizontally facing downward (180°) as the boiling commenced at this surface orientation. Furthermore, based on the photographic and image processing, the results revealed that the approximate bubble departure diameter with the heater facing upwards (0° and 45°) including at 90° was bigger compared to that of the heater facing downwards (135° and 150°). On the other hand, bubble frequency decreased with increasing surface orientation (0° to 90°) and increased as the surface orientation went beyond 90°. Moreover, it was observed that the bubble with the biggest departure diameter had the smallest departure frequency, and needs longer time to generate another bubble. Based on these results, it is apparent that the surface orientation significantly affects the ONB, CHF, and bubble dynamics on PCB in a saturated water pool.

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