Optical Diagnostics of Nucleate Boiling From Transparent Heated Surfaces

2003 ◽  
Author(s):  
Anton Zimmermann ◽  
Adrian M. Holland ◽  
Colin P. Garner
Keyword(s):  
Void Fraction ◽  
Indium Tin Oxide ◽  
High Speed ◽  
Imaging System ◽  
Nucleate Boiling ◽  
Nucleation Site ◽  
Heat Fluxes ◽  
Diagnostic Methods ◽  
Frame Rate ◽  
Site Density

Indium Tin Oxide (ITO) coated glass was used to provide transparent heated surfaces with heat fluxes high enough to generate nucleate boiling in water. The technique enables extended horizontal surfaces exhibiting nucleate boiling to be analysed with novel optical diagnostic methods. A horizontal glass substrate coated with an ITO layer on its top surface was immersed in demineralised water of temperatures between 70 and 80°C. A direct electrical current was passed through the ITO to heat the water. A high-speed imaging system comprising an infrared laser and CCD camera was used to analyse the resulting nucleate pool boiling from the ITO surface. This system was operated at up to 1 kHz frame rate and the bubbles analysed in terms of size and shape. Statistical data regarding bubble size and nucleation site density were obtained for heat fluxes ranging from 63 to 105 kW.m−2. Nucleation site densities were found to be up to 35 000 sites.m−2. Furthermore, non-intrusive cross-sectional void fraction measurements were made, and ranged from zero to 14% of surface area. The increase in both site density and void fraction with increasing heat flux was found to be in good agreement with published literature.

Nucleate Boiling From Micro-Machined Surfaces

2003 ◽  
Author(s):  
Adrian M. Holland ◽  
Colin P. Garner
Keyword(s):  
Heat Transfer ◽  
High Speed ◽  
Imaging System ◽  
Laser System ◽  
Ccd Camera ◽  
Nucleate Boiling ◽  
Heat Fluxes ◽  
Frame Rate ◽  
High Speed Imaging ◽  
Machined Surfaces

This paper discusses the production and use of laser-machined surfaces that provide enhanced nucleate boiling and heat transfer characteristics. The surface features of heated plates are known to have a significant effect on nucleate boiling heat transfer and bubble growth dynamics. Nucleate boiling starts from discrete bubbles that form on surface imperfections, such as cavities or scratches. The gas or vapours trapped in these imperfections serve as nuclei for the bubbles. After inception, the bubbles grow to a certain size and depart from the surface. In this work, special heated surfaces were manufactured by laser machining cavities into polished aluminium plates. This was accomplished with a Nd:YAG laser system, which allowed drilling of cavities of a known diameter. The size range of cavities was 20 to 250 micrometers. The resulting nucleate pool boiling was analysed using a novel high-speed imaging system comprising an infrared laser and high resolution CCD camera. This system was operated up to a 2 kHz frame rate and digital image processing allowed bubbles to be analysed statistically in terms of departure diameter, departure frequency, growth rate, shape and velocity. Data was obtained for heat fluxes up to 60 kW.m−2. Bubble measurements were obtained working with water at atmospheric pressure. The surface cavity diameters were selected to control the temperature at which vapour bubbles started to grow on the surface. The selected size and spacing of the cavities was also explored to provide optimal heat transfer.

Boiling in Enhanced Surface Microchannels

2005 ◽  
Author(s):  
Chih-Jung Kuo ◽  
Ali Kosar ◽  
Michael K. Jensen ◽  
Yoav Peles
Keyword(s):  
Large Scale ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Nucleation Site ◽  
Heat Fluxes ◽  
Bubble Frequency ◽  
Large Scale Systems ◽  
Site Density ◽  
Enhanced Surface ◽  
Nucleation Site Density

An experimental investigation is presented on flow boiling of de-ionized water in 227-μm hydraulic diameter microchannels with reentrant type cavities. Key features of nucleate boiling are discussed. Active nucleation site density, bubble frequency and departure diameter, and flow patterns over mass velocities ranging from 41 kg/m2-s to 302 kg/m2-s and heat fluxes ranging from 28 to 445 W/cm2 are studied. Similarities and differences with results obtained on large-scale systems and unenhanced microchannels are discussed.

Experimental Investigation of Wall Nucleate Boiling Models in Narrow Channel

2013 ◽  
Author(s):  
Weihong Chen ◽  
Ang Guo ◽  
Lixin Yang
Keyword(s):  
High Speed ◽  
Rectangular Channel ◽  
Digital Camera ◽  
Narrow Channel ◽  
Nucleate Boiling ◽  
Nucleation Site ◽  
Bubble Nucleation ◽  
Site Density ◽  
Visual Graphic ◽  
Nucleation Site Density

Using deionized water as working medium, studies on visualization of the behavior of subcooled boiling bubbles in narrow rectangular channels have been conducted at atmospheric pressure, with the help of a high-speed digital camera. The effects of wall superheat, fluid subcooling and mass flux on the bubble dynamic model of nucleation site density, bubble departure frequency and bubble departure diameter were investigated. This paper analyzed the visual graphic results and obtained quantitative values about bubble nucleation site density, bubble departure frequency and bubble departure diameter under different conditions. Based on the results, wall nucleate boiling models in the conventional channel put forward by Nilanjana Basu have been corrected. The new correlation agrees reasonably well with existing experimental data in 2mm narrow rectangular channel.

Evaporation and Nucleate Boiling of an Individual Droplet on Surfaces

2005 ◽  
Author(s):  
X. D. Wang ◽  
G. Lu ◽  
X. F. Peng ◽  
B. X. Wang
Keyword(s):  
Heat Flux ◽  
High Speed ◽  
Bubble Dynamics ◽  
Imaging System ◽  
Dynamical Behavior ◽  
Saturation Temperature ◽  
Nucleate Boiling ◽  
Dynamical Process ◽  
Boiling Regime ◽  
Film Evaporation

A visual study was conducted to investigate the evaporation and nucleate boiling of a water droplet on heated copper, aluminum, or stainless surfaces with temperature ranging from 50°C to 112°C. Using a high-speed video imaging system, the dynamical process of the evaporation of a droplet was recoded to measure the transient variation of its diameter, height, and contact angle. When the contact temperature was lower than the saturation temperature, the evaporation was in film evaporation regime, and the evaporation could be divided into two stages. When the surface temperature was higher than the saturation temperature, the nucleate boiling was observed. The dynamical behavior of nucleation, bubble dynamics droplet were detail observed and discussed. The linear relationships of the average heat flux vs. temperature of the heated surfaces were found to hold for both the film evaporation regime and nucleate boiling regime. The different slopes indicated their heat transfer mechanism was distinct, the heat flux decreased in the nucleate boiling regime more rapidly than in the film evaporation due to the strong interaction between the bubbles.

scholarly journals CNN-based visual analysis to study local boiling characteristics

2021 ◽  
Vol 2119 (1) ◽  
pp. 012068
Author(s):  
A N Chernyavskiy ◽  
I P Malakhov
Keyword(s):  
Network Architecture ◽  
High Speed ◽  
Visual Analysis ◽  
Nucleation Site ◽  
High Speed Video ◽  
Site Density ◽  
Segmentation Approach ◽  
Nucleation Site Density ◽  
Instance Segmentation

Abstract Visual analysis allows an estimate of different local boiling characteristics including bubble growth rate, departure diameters and frequencies of nucleation, nucleation site density and evolution of bubbles and dry spots in time. At the same time, visual determination of the presented characteristics in case of big amounts of data requires the development of the appropriate software which will allow not only determination of bubble location, but also an estimate of their sizes based on high-speed video. The presented problem can be solved by using the instance segmentation approach based on a convolutional neural network. In the presented work Mask R-CNN network architecture was used for estimation of the local boiling characteristics.

scholarly journals The Simultaneous Analysis of Droplets’ Impacts and Heat Transfer during Water Spray Cooling Using a Transparent Heater

Water ◽  
2021 ◽  
Vol 13 (19) ◽  
pp. 2730
Author(s):  
Vladimir Serdyukov ◽  
Nikolay Miskiv ◽  
Anton Surtaev
Keyword(s):  
Heat Transfer ◽  
High Speed ◽  
Heating Surface ◽  
Nucleate Boiling ◽  
Spray Cooling ◽  
Capillary Waves ◽  
Heat Fluxes ◽  
Small Scale ◽  
Unsteady Temperature ◽  
The Impact

This paper demonstrates the advantages and prospects of transparent design of the heating surface for the simultaneous study of the hydrodynamic and thermal characteristics of spray cooling. It was shown that the high-speed recording from the reverse side of such heater allows to identify individual droplets before their impact on the forming liquid film, which makes it possible to measure their sizes with high spatial resolution. In addition, such format enables one to estimate the number of droplets falling onto the impact surface and to study the features of the interface evolution during the droplets’ impacts. In particular, the experiments showed various possible scenarios for this interaction, such as the formation of small-scale capillary waves during impacts of small droplets, as well as the appearance of “craters” and splashing crowns in the case of large ones. Moreover, the unsteady temperature field during spray cooling in regimes without boiling was investigated using high-speed infrared thermography. Based on the obtained data, the intensity of heat transfer during spray cooling for various liquid flow rates and heat fluxes was analyzed. It was shown that, for the studied regimes, the heat transfer coefficient weakly depends on the heat flux density and is primarily determined by the flow rate. In addition, the comparison of the processes of spray cooling and nucleate boiling was made, and an analogy was shown in the mechanisms that determine their intensity of heat transfer.

scholarly journals Optimization of the nucleation-site density for the electrodeposition of cadmium sulfide on indium-tin-oxide

2019 ◽  
Vol 316 ◽  
pp. 105-112
Author(s):  
Sheng Shen ◽  
Xiaoyue Zhang ◽  
Syed Mubeen ◽  
Manuel P. Soriaga ◽  
John L. Stickney
Keyword(s):  
Cadmium Sulfide ◽  
Tin Oxide ◽  
Indium Tin Oxide ◽  
Nucleation Site ◽  
Site Density ◽  
Nucleation Site Density

Effect of Gap Distance on Confined Boiling Heat Transfer Over a Saturated Porous Structure

2005 ◽  
Author(s):  
M. J. Schertzer ◽  
M. Khammar ◽  
D. Ewing ◽  
C. Y. Ching ◽  
J. S. Chang
Keyword(s):  
Heat Transfer ◽  
Porous Media ◽  
High Speed ◽  
Imaging System ◽  
Porous Plate ◽  
Heat Removal ◽  
Heat Fluxes ◽  
Maximum Heat ◽  
Porous Wick ◽  
Maximum Heat Transfer

An experimental investigation was performed to study the effect that the introduction of a gap between a heated fin and a porous media would have on the heat removal characteristics of a capillary evaporator. In these experiments, a thin stainless steel resistive foil stretched between two copper electrodes was used to heat a saturated porous plate with an effective pore size of 50 microns. The temperature distribution on a 10 mm wide simulated fin was measured by a high-speed infra-red thermal imaging system. The heat removal performance was investigated for gap distances of 0.00 to 1.00 mm and for heat fluxes of 17 to 180 kW/m2. These results showed that the maximum heat transfer rate that could be achieved before persistent hot spots were observed on the surface increased with gap distance. Local temperature measurements made using thermocouples embedded in the porous media indicate that vapour penetration into the porous wick is intermittent, and that there is no stable single phase blanket of vapour. For a gap distance of 0.00 mm, this penetration is more uniformly distributed across the width of the heated fin than at a gap distance of 0.50 mm. In the latter case, the vapour distribution is much higher near the edge of the heated fin.

Flow Boiling Dynamics of Water and Nanofluids in a Single Microchannel at Different Heat Fluxes

2015 ◽  
Vol 137 (1) ◽  
Author(s):  
Zachary Edel ◽  
Abhijit Mukherjee
Keyword(s):  
Flow Boiling ◽  
Nucleate Boiling ◽  
Nucleation Site ◽  
Bubble Nucleation ◽  
Heat Fluxes ◽  
Forced Flow ◽  
Electronic Systems ◽  
Rectangular Microchannel ◽  
Nanoparticle Deposition ◽  
Flow Regime Transition

The preferable cooling solution for micro-electronic systems could be forced flow boiling in micro heat exchangers. Nanoparticle deposition affects nucleate boiling via alteration of surface roughness, capillary wicking, wettability, and nucleation site density. In this study, flow boiling was investigated using water and nanofluids in a single rectangular microchannel at different heat fluxes. The observed change in flow regime transition revealed the effect of nanoparticles on the onset of nucleate boiling (ONB) and the onset of bubble elongation (OBE). The addition of nanoparticles was found to stabilize bubble nucleation and growth and increase heat transfer in the thin film regions.

Flow Boiling on Micropin Fins Entrenched Inside a Microchannel—Flow Patterns and Bubble Departure Diameter and Bubble Frequency

2010 ◽  
Vol 132 (4) ◽  
Author(s):  
Santosh Krishnamurthy ◽  
Yoav Peles
Keyword(s):  
High Speed ◽  
Flow Boiling ◽  
Bubbly Flow ◽  
Nucleate Boiling ◽  
Flow Patterns ◽  
Heat Fluxes ◽  
High Speed Photography ◽  
Bubble Frequency ◽  
Pin Fins ◽  
Parallel Microchannels

Flow boiling of HFE 7000 in five parallel microchannels of 222 μm hydraulic diameter, each containing a single row of 24 in-line 100 μm pin fins, was investigated. High speed photography revealed the dominant flow patterns, namely, the bubbly flow, the multiple flow, and the wavy-annular flow. The interaction of the bubble with the pin fins during nucleate boiling from G=350 kg/m2 s to G=827 kg/m2 s and wall heat fluxes from 10 W/cm2 to 110 W/cm2 is detailed.

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