Boiling Investigation on a Surface With Artificial and Natural Nucleons Sites

2008 ◽  
Author(s):  
Yu. A. Kuzma-Kichta ◽  
A. Lavrikov ◽  
S. Afonin ◽  
M. Shustov
Keyword(s):  
Heat Flux ◽  
Video Processing ◽  
High Speed ◽  
Water Solution ◽  
Pool Boiling ◽  
Digital Camera ◽  
Vapor Bubbles ◽  
Artificial Cavity ◽  
Single Cavity ◽  
Engineering Institute

The water and Na2SO4 water solution boiling investigation had been carried in pool on the surfaces with artificial and natural nucleons sites under different pressures using high speed digital camera. The boiling of water was investigated at atmosphere pressure on a surface with a artificial nucleons site, which had a micro scale (cavity’s diameters – 100 and 200 μm and depth – 80 μm), in the Fridrich-Alexander University Erlangen-Nu¨rnberg, Germany in the Institute of Fluid Mechanics. The boiling of water and Na2SO4 water solution with concentration 20 g/l was investigated on a surface with natural nucleons sites in the pressure range 0.1 – 1 MPa in the Moscow Power-Engineering Institute (Technical University) on department of Thermal Physics. The “hand” video processing was used for the study’s results in case of the pool boiling on a surface with a artificial nucleon site. The data processing was realized for the study’s results using with a program “Bubble Detector”, which was specially developed for case of the pool boiling on a surface with the natural nucleon sites, and the “hand” processing was carried for video, which showed the reliability of the program “Bubble Detector”. First the distributions and dependences of basic boiling characteristics (frequency, departure diameter) were obtained at water pool boiling on a surface with a artificial cavity in the range of heat flux from 20 to 128 kW/m2 and the time dependence of vapor bubble’s grow. It was obtained, that departure diameters of vapor bubbles do not depend in case of boiling on a surface with a single cavity practically on heat flux. First the distributions and dependences of swimming velocities and equivalent diameters were obtained at water and Na2SO4 water solution with concentration 20 g/l pool boiling on a surface with natural nucleon sites in range of pressures from 0.1 to 1 MPa. The comparison of diameters’ and swimming velocities’ distributions of vapor bubbles was carried for under consideration conditions.

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.

Pool Boiling Using Thin Enhanced Structures Under Top-Confined Conditions

2006 ◽  
Vol 128 (12) ◽  
pp. 1302-1311 ◽  
Author(s):  
Camil-Daniel Ghiu ◽  
Yogendra K. Joshi
Keyword(s):  
Heat Flux ◽  
High Speed ◽  
Pool Boiling ◽  
Single Layer ◽  
Temperature Limit ◽  
Heat Fluxes ◽  
The Other ◽  
Vapor Flow ◽  
Maximum Heat ◽  
Maximum Heat Flux

An experimental study of pool boiling using enhanced structures under top-confined conditions was conducted with a dielectric fluorocarbon liquid (PF 5060). The single layer enhanced structures studied were fabricated in copper and quartz, had an overall size of 10×10mm2, and were 1mm thick. The parameters investigated in this study were the heat flux (0.8-34W∕cm2) and the top space S(0-13mm). High-speed visualizations were performed to elucidate the liquid/vapor flow in the space above the structure. The enhancement observed for plain surfaces in the low heat fluxes regime is not present for the present enhanced structure. On the other hand, the maximum heat flux for a prescribed 85°C surface temperature limit increased with the increase of the top spacing, similar to the plain surfaces case. Two characteristic regimes of pool boiling have been identified and described: isolated flattened bubbles regime and coalesced bubbles regime.

Study of Subcooled Film Boiling on a Horizontal Disc:1 Part 2—Experiments

2000 ◽  
Vol 123 (2) ◽  
pp. 285-293 ◽  
Author(s):  
D. Banerjee ◽  
V. K. Dhir
Keyword(s):  
Liquid Phase ◽  
Particle Tracking ◽  
Bubble Growth ◽  
High Speed ◽  
Particle Tracking Velocimetry ◽  
Digital Camera ◽  
Film Boiling ◽  
Convection Flow ◽  
Vapor Bubbles ◽  
Natural Convection Flow

Experiments were performed to study subcooled film boiling of performance liquid PF-5060 (made by 3-M Company) on a horizontal copper disc. The experiments were performed for two regimes of film boiling involving departing vapor bubbles (low subcooling) and nondeparting vapor bubbles (high subcooling). By employing high speed digital camera, data were obtained for temporal variation of bubble height, bubble shape and bubble growth rate over one cycle. Heat flux data were deduced from temperatures measured with thermocouples embedded in the solid. The results from the numerical model are compared with experimental data and are found to be in general agreement. Particle Tracking Velocimetry (PTV) experiments were performed for a configuration of non-departing vapor bubbles to study the flow field in the liquid phase. The PTV experiments point to the existence of natural convection flow in the liquid phase and is in qualitative agreement with the predictions available in the literature.

Investigation of Bubble Departure Radius in Subcooled Pool Boiling Under Microgravity Condition

2018 ◽  
Author(s):  
Xueli Wang ◽  
Zan Wu ◽  
Jinjia Wei ◽  
Bengt Sunden
Keyword(s):  
Heat Flux ◽  
Contact Angle ◽  
High Speed ◽  
Bubble Dynamics ◽  
Pool Boiling ◽  
Microgravity Condition ◽  
Force Balance ◽  
Balance Model ◽  
Silicon Chips ◽  
Static Contact

The bubble departure radius is a very important parameter for bubble dynamics during boiling heat transfer. In this study, experiments of highly subcooled nucleate pool boiling of FC-72 were conducted on two different sized silicon chips (chip S 2 × 2 and chip S 1 × 1) in short-term microgravity and normal gravity conditions by utilizing the drop tower in Beijing. During the experimental study, bubble dynamics were captured by a high-speed digital camera. From the images at the bubble departure moment, the bubble departure radius was obtained. Although the traditional force balance model is modified through the addition of a Marangoni force, it still cannot precisely predict the bubble departure radius in the microgravity condition, especially in the low heat flux regime. By using the advancing contact angle measured from the bubble departure moment instead of the static contact angle, and considering the bubble asymmetry due to the small bubble coalescence and the surrounding liquid motion, a revised force balance model is proposed. It can predict the experimental bubble departure radius within a deviation of ±3.8% for both silicon chips in the whole heat flux range.

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

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.

High Speed Imaging of Bubble Interface Motion in a Tapered Microgap

2020 ◽  
Author(s):  
Aranya Chauhan ◽  
Satish G. Kandlikar
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Critical Heat Flux ◽  
High Speed ◽  
Pool Boiling ◽  
Phase Flow ◽  
Two Phase ◽  
Interface Motion

Abstract The current industrial trend requires development of efficient heat dissipation systems. A tapered microgap on the heater surface provides an efficient pool boiling heat transfer technique in dissipating large heat fluxes. This study is focused on capturing the high-speed images of bubble nucleation, growth and expansion processes. The interface velocities are estimated by tracking the interface of the growing bubble. The insight into interface motion will help in estimating the magnitude of the expanding force and predicting the pressure recovery effect during two-phase flow in the gap. The expansion force helps in establishing high flow rates resulting in high heat transfer coefficient (HTC) and critical heat flux (CHF) values. The effect of design parameters such as taper angle and height of the microgap on the bubble growth patterns are evaluated. The results show that the bubbles are nucleated and are then confined in the narrow gap. The tapered configuration propels the leading bubble interface in the flow direction and eventually the entire bubble in that direction. The bubble motion causes liquid to enter from the narrow region of the microgap. This effect, combined with the pressure recovery resulting from the two-phase flow in the expanding section of the microgap provides a bubble pumping mechanism. This configuration results in improving both the critical heat flux and heat transfer coefficient during pool boiling.

Effect of Channel Width on Pool Boiling Enhancement of Open Microchannels With Selective Sintered Porous Coatings

2015 ◽  
Author(s):  
Arvind Jaikumar ◽  
Satish G. Kandlikar
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
High Speed ◽  
Pool Boiling ◽  
Underlying Mechanism ◽  
High Heat ◽  
Channel Width ◽  
High Heat Flux ◽  
Porous Coatings ◽  
Open Microchannel

Thermal management in microelectronic devices involves development of high heat flux removal systems to meet the cooling requirements. Pool boiling addresses these demands by using latent heat transfer. In this study, heat transfer surfaces are fabricated by depositing porous coatings on an open microchannel surface. Screen printing and sintering are identified as techniques to deposit porous coatings and ensure substrate bonding respectively. Firstly, the effect of selective enhancement was studied by depositing porous coatings on (i) fin tops only (sintered-fin-tops), (ii) channels only (sintered-channels), and (iii) completely covering the boiling surface (sintered-throughout). The pool boiling performance with saturated distilled water at atmospheric pressure was obtained and a maximum critical heat flux (CHF) of 313 W/cm2 at a wall superheat of 7.5 °C was reported here for a sintered-throughout surface. Furthermore, the effect of channel width on sintered-throughout surfaces was studied. The results indicated that channel width plays an important in improving the performance. High speed videos are taken to understand the underlying mechanism. Additional nucleation sites and separate liquid-vapor pathways are identified as contributing mechanisms for the enhancement in CHF and heat transfer coefficient (HTC).

Research on Bubble Growth and Frequency at Higher System Pressure in Narrow Rectangular Channel

2013 ◽  
Author(s):  
Jian Hu ◽  
Puzhen Gao ◽  
Qiang Zheng
Keyword(s):  
Heat Flux ◽  
Mass Flux ◽  
Bubble Growth ◽  
High Speed ◽  
Rectangular Channel ◽  
Bubble Diameter ◽  
Digital Camera ◽  
Bubble Frequency ◽  
Heating Wall ◽  
System Pressure

In present work, the characteristics of bubble growth and frequency were visually observed in a narrow rectangular channel using high-speed digital camera. The experiment was done over the following range of conditions: pressure, 0.55MPa; mass flux, 300–500kg/(m2·s); heat flux, 86.4–225.7 kW/m2; and inlet subcooling, 25.5–45.5K. The system pressure has a significant effect on the bubble growth. Experimental results show that the bubble diameters are just about 0.15mm under higher system pressure and the period during which bubbles attaching to the nucleate site is very short, or even unnoticeable. The bubbles keep growing when slide along the heating wall rather than lifting off the surface, and the bubbles rarely collapse under the working conditions. When the mass flux is high, the bubble diameter increases with increasing the heat flux, but when the mass flux is low, the variation trend of bubble diameters expresses no obvious law. The effect of thermal parameters on bubble frequency is also significant. When the mass flux is low, the bubble frequency decreases with increasing the heat flux or inlet subcooling, however when the mass flux is high, the bubble frequency increases first and then decreases. Generally, the bubble frequency increases with increasing the mass flux.

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