Condensation/Collapse of Vapor Bubble Injected to Subcooled Pool

2011 ◽  
Author(s):  
Ichiro Ueno ◽  
Ryota Hosoya ◽  
Chungpyo Hong
Keyword(s):  
Heat Flux ◽  
Boundary Conditions ◽  
Critical Heat Flux ◽  
Vapor Bubble ◽  
Heated Surface ◽  
Vapor Bubbles ◽  
Different Boundary Conditions ◽  
Induced Flow ◽  
Vapor Generator ◽  
Micrometer Scale

We focus on condensation and collapse processes of vapor bubble(s) in a subcooled pool. We generate the vapor in the vapor generator and inject it/them to form vapor bubble(s) at a designated temperature into the liquid at a designated degree of subcooling. In order to evaluate the effect of induced flow around the condensing/collapsing vapor bubble, two different boundary conditions are employed; that is, the vapor is injected through the orifice and the tube. We also focus on interaction between/among the condensing/collapsing vapor bubbles laterally injected to the pool. Through this system we try to simulate an interaction between the vapor bubble and the subcooled bulk in a complex boiling phenomenon, especially that known as MEB (microbubble emission boiling) in which a higher heat flux than critical heat flux (CHF) accompanying with emission of micrometer-scale bubbles from the heated surface against the gravity is realized under a rather high subcooled condition.

Microbubble Formation in Collapsing Process of a Single Vapor Bubble Injected in Subcooled Pool

2009 ◽  
Author(s):  
Ichiro Ueno ◽  
Yasusuke Hattori
Keyword(s):  
Heat Flux ◽  
Vapor Bubble ◽  
High Speed ◽  
Narrow Range ◽  
Heated Surface ◽  
Lighting System ◽  
Vapor Bubbles ◽  
Bubble Behavior ◽  
Subcooled Liquid ◽  
Boiling Process

‘Microbubble emission boiling,’ known as MEB, is a phenomenon that emerges in a narrow range of subcooled condition with a higher heat flux than critical heat flux (CHF) accompanying with microbubble emission from the heated surface. The authors focus on the condensing process of vapor bubbles in order to comprehend the mechanism of the microbubble formation and emitting processes. In order to simplify a surely complex boiling process, the authors try to extract an interaction between the vapor bubble and the subcooled bulk in a boiling phenomenon, that is, growing and collapsing processes of a vapor bubble ejected to subcooled liquid bath. Vapor bubble is produced by vapor generate system, and ejected to a bulk of saturated distilled water at a designated degree of subcooling. The degree of subcooling is varied from 0 to 50 K. The growing/collapsing of vapor bubble behavior is detected by employing a high-speed camera at frame rates up to 50,000 fps with a back-lighting system. In the present study, the process of microbubble emission as well as the process of the irrupting vapor bubbles to the subcooled bulk is compared to that in a MEB on a thin wire.

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.

scholarly journals Predicting Critical Heat Flux With Multiphase CFD: 4 Years in the Making

2017 ◽  
Author(s):  
Emilio Baglietto ◽  
Etienne Demarly ◽  
Ravikishore Kommajosyula
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Bubble Dynamics ◽  
Flow Boiling ◽  
Heated Surface ◽  
Force Balance ◽  
Modeling Framework ◽  
Lift Off ◽  
Limiting Condition

Advancement in the experimental techniques have brought new insights into the microscale boiling phenomena, and provide the base for a new physical interpretation of flow boiling heat transfer. A new modeling framework in Computational Fluid Dynamics has been assembled at MIT, and aims at introducing all necessary mechanisms, and explicitly tracks: (1) the size and dynamics of the bubbles on the surface; (2) the amount of microlayer and dry area under each bubble; (3) the amount of surface area influenced by sliding bubbles; (4) the quenching of the boiling surface following a bubble departure and (5) the statistical bubble interaction on the surface. The preliminary assessment of the new framework is used to further extend the portability of the model through an improved formulation of the force balance models for bubble departure and lift-off. Starting from this improved representation at the wall, the work concentrates on the bubble dynamics and dry spot quantification on the heated surface, which governs the Critical Heat Flux (CHF) limit. A new proposition is brought forward, where Critical Heat Flux is a natural limiting condition for the heat flux partitioning on the boiling surface. The first principle based CHF is qualitatively demonstrated, and has the potential to deliver a radically new simulation technique to support the design of advanced heat transfer systems.

Critical Heat Flux Enhancement in Water-Based Nanofluid With Honeycomb Porous Plate on Large Heated Surface

2016 ◽  
Author(s):  
Suazlan Mt Aznam ◽  
Shoji Mori ◽  
Kunito Okuyama
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Heated Surface ◽  
Porous Plate ◽  
High Heat ◽  
High Heat Flux ◽  
Heater Surface ◽  
Solid Structure ◽  
Water Based ◽  
Plain Surface

Heat removal through pool boiling is limited by the phenomena of critical heat flux (CHF). CHF enhancement is vitally important in order to satisfy demand for the cooling technology with high heat flux in In Vessel Retention (IVR). Various surface modifications of the boiling surface, e.g., integrated surface structures and coating of a micro-porous have been proven to effectively enhance the CHF in saturated pool boiling. We have been proposed a novel method of attaching a honeycomb structured porous plate on a considerably large heater surface. Previous results, by the authors in [1] reported that CHF has been enhanced experimentally up to more than approximately twice that of a plain surface (approximately 2.0 to 2.5 MW/m2) with a diameter of 30 mm heated surface. However, it is necessary to demonstrate the method together with infinite heater surface within laboratory scale. It is important that cooling techniques for IVR could be applicable to a large heated surface as well as remove high heat flux. Objective of this study is to investigate the CHF of honeycomb porous plate and metal solid structure in nanofluid boiling or water boiling on a large heated surface. Water-based nanofluid offers good wettability and capillarity. While metal solid structure is installed on honeycomb porous plate to increase the number of vapor jet. Experimental results of honeycomb porous plate and combination of honeycomb porous plate and metal solid structure in water-based nanofluid boiling shows that CHF is increased up to twice [2] and thrice, respectively compared to plain surface in water boiling. To the best of the author’s knowledge, the highest value (3.1 MW/m2) was obtained for a large heated surface having a diameter of 50 mm which is regarded as infinite heated surface. This demonstrates potential for general applicability to have more safety margin in IVR method.

A critical heat flux model for saturated flow boiling on the downward curved heated surface

2018 ◽  
Vol 114 ◽  
pp. 458-463 ◽  
Author(s):  
Qiang Hu ◽  
Xiao Yan ◽  
Shanfang Huang ◽  
Junchong Yu
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Flow Boiling ◽  
Heated Surface ◽  
Saturated Flow ◽  
Flux Model ◽  
Heat Flux Model

On the Mechanism of Pool Boiling Critical Heat Flux Enhancement in Nanofluids

2010 ◽  
Vol 132 (6) ◽  
Author(s):  
Hyungdae Kim ◽  
Ho Seon Ahn ◽  
Moo Hwan Kim
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Heated Surface ◽  
Pure Water ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Titania Nanoparticles ◽  
Nanoparticle Layer ◽  
Wall Superheat ◽  
Dry Spot

The pool boiling characteristics of water-based nanofluids with alumina and titania nanoparticles of 0.01 vol % were investigated on a thermally heated disk heater at saturated temperature and atmospheric pressure. The results confirmed the findings of previous studies that nanofluids can significantly enhance the critical heat flux (CHF), resulting in a large increase in the wall superheat. It was found that some nanoparticles deposit on the heater surface during nucleate boiling, and the surface modification due to the deposition results in the same magnitude of CHF enhancement in pure water as for nanofluids. Subsequent to the boiling experiments, the interfacial properties of the heater surfaces were examined using dynamic wetting of an evaporating water droplet. As the surface temperature increased, the evaporating meniscus on the clean surface suddenly receded toward the liquid due to the evaporation recoil force on the liquid-vapor interface, but the nanoparticle-fouled surface exhibited stable wetting of the liquid meniscus even at a remarkably higher wall superheat. The heat flux gain attainable due to the improved wetting of the evaporating meniscus on the fouled surface showed good agreement with the CHF enhancement during nanofluid boiling. It is supposed that the nanoparticle layer increases the stability of the evaporating microlayer underneath a bubble growing on a heated surface and thus the irreversible growth of a hot/dry spot is inhibited even at a high wall superheat, resulting in the CHF enhancement observed when boiling nanofluids.

Critical Heat Flux of Butanol Aqueous Solution

2008 ◽  
Author(s):  
Shotaro Nishiguchi ◽  
Naoki Ono ◽  
Masahiro Shoji
Keyword(s):  
Heat Transfer ◽  
Aqueous Solution ◽  
Surface Tension ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Heated Surface ◽  
Pure Water ◽  
Liquid Temperature ◽  
Heat Transfer Characteristics ◽  
Heated Wire

Aqueous solutions of some alcohols such as butanol show peculiar temperature dependence of surface tension. Contrary to ordinary liquids or solutions, the surface tension increases with temperature at the range of high liquid temperature. So at the triple-phase point on a heated surface, the thermo-capillary force acts for the liquid to wet the heated surface, so the solutions are sometimes called as “self-wetting liquids”. Self-wetting liquids may prohibit the dry-out of a heated surface so that the heat transfer performance would be enhanced. For this reason, applications of self-wetting liquids to heat transfer devices such as heat pipes are actively studied in recent years. However, the heat transfer characteristics of boiling of self-wetting liquids are not fully understood. In the present research, a boiling experiment of butanol aqueous solution was performed on a heated fine wire in order to make clear the fundamental heat transfer characteristics. A heated wire configuration is easy to observe the phenomena and easy to address the fundamental issues of boiling. In the present experiment, nucleate boiling heat transfer were investigated with special attention to critical heat flux (CHF), by changing solution concentration and temperature. Bubbling aspects were observed by high-speed video camera. It is found from the experiment that CHF is generally enhanced 20 to 50% when compared to the case of pure water. It is also found that at a certain concentration and at a certain liquid temperature, peculiar boiling takes place where very small bubbles are emitted from the heated wire and CHF enhancement becomes very large from 2 to 3 times higher than CHF of pure water. The temperature when the peculiar boiling takes place is close to boiling temperature of the solution. These results suggest the possibility of application of aqueous solution to high-performance cooling devices utilizing micro-scaled channels because generating bubbles are small enough so that the pressure loss of the flow passage is small and heat transfer rate is very large.

A Study of Critical Heat Flux of Butanol Aqueous Solution

2009 ◽  
Author(s):  
Shotaro Nishiguchi ◽  
Masahiro Shoji
Keyword(s):  
Heat Transfer ◽  
Aqueous Solution ◽  
Surface Tension ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Heated Surface ◽  
Phase Point ◽  
Liquid Temperature ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics

Some alcohol aqueous solution such as butanol shows nonlinear surface tension dependence. Namely, contrary to ordinary liquid or solution, surface tension increases with temperature at the range of high liquid temperature. At the triple-phase point on a heated surface, the thermo-capillary force acts for the liquid to wet the heated surface, so the solutions are sometimes called as “self-rewetting liquid”. Self-rewetting liquids may prohibit the dry-out of a heated surface so that the heat transfer performance would be enhanced. For this reason, applications of self-rewetting liquids to heat transfer devices such as heat pipes are actively studied in recent years. However, the heat transfer characteristics of boiling of self-rewetting liquids are not fully understood. In the present research, a boiling experiment of butanol aqueous solution was performed on a heated wire in order to make clear the fundamental heat transfer characteristics, especially Critical Heat Flux (CHF), by changing solution concentration density and liquid temperature in a wide range. Bubbling aspects were observed by high-speed video camera with the rate of 1000 frames per second. It is found from the experiment that CHF is generally enhanced when compared to the case of pure water. CHF increases with concentration density at any temperatures. CHF generally increases with subcooling but at low subcooling region, it once decreases and then increases after taking a minimum. It is also found that peculiar boiling takes place where many tiny bubbles generate and bubbles are unlikely to coalesce. At high subcoolings, the mode of boiling similar to the so-called MEB (Micro-bubble Emission Boiling) was observed. These results of the present experiment indicate a possible application of butanol aqueous solution to high-performance-cooling-devices utilizing micro-channels because generating bubbles are small enough so that the pressure loss of the coolant may be small and the heat transfer rate is sufficiently high even at the saturated condition.

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