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.

Onset of Nucleate Boiling and Active Nucleation Site Density During Subcooled Flow Boiling

2002 ◽  
Vol 124 (4) ◽  
pp. 717-728 ◽  
Author(s):  
Nilanjana Basu ◽  
Gopinath R. Warrier ◽  
Vijay K. Dhir
Keyword(s):  
Heat Flux ◽  
Contact Angle ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Nucleation Site ◽  
Subcooled Flow Boiling ◽  
Site Density ◽  
Wall Superheat ◽  
Subcooled Flow ◽  
Nucleation Site Density

The partitioning of the heat flux supplied at the wall is one of the key issues that needs to be resolved if one is to model subcooled flow boiling accurately. The first step in studying wall heat flux partitioning is to account for the various heat transfer mechanisms involved and to know the location at which the onset of nucleate boiling (ONB) occurs. Active nucleation site density data is required to account for the energy carried away by the bubbles departing from the wall. Subcooled flow boiling experiments were conducted using a flat plate copper surface and a nine-rod (zircalloy-4) bundle. The location of ONB during the experiments was determined from visual observations as well as from the thermocouple output. From the data obtained it is found that the heat flux and wall superheat required for inception are dependent on flow rate, liquid subcooling, and contact angle. The existing correlations for ONB underpredict the wall superheat at ONB in most cases. A correlation for predicting the wall superheat and wall heat flux at ONB has been developed from the data obtained in this study and that reported in the literature. Experimental data are within ±30 percent of that predicted from the correlation. Active nucleation site density was determined by manually counting the individual sites in pictures obtained using a CCD camera. Correlations for nucleation site density, which are independent of flow rate and liquid subcooling, but dependent on contact angle have been developed for two ranges of wall superheat—one below 15°C and another above 15°C.

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.

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.

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.

Nucleate Pool Boiling on Ribbed Surfaces With Micro-Roughness at Low and Moderate Heat Flux

1999 ◽  
Vol 121 (2) ◽  
pp. 376-385 ◽  
Author(s):  
S.-S. Hsieh ◽  
C.-J. Weng ◽  
J.-J. Chiou
Keyword(s):  
Heat Flux ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Nucleation Site ◽  
Nucleate Pool Boiling ◽  
Site Density ◽  
R 134A ◽  
Microlayer Evaporation ◽  
Two Parameters ◽  
Nucleation Site Density

Nucleate pool boiling correlation was developed for five different rib-type roughened tube geometries (including plain tube) with different rib angles of 30 deg, 45 deg, 60 deg, and 90 deg for both distilled water and R-134a as the working media. A scanning electron micrograph (SEM) examination was made for these horizontal roughened tubes. Bubble departure diameter, frequency of bubble emission, and the active nucleation site density with the influence of the rib angle for this type of roughened surface were obtained. Boiling heat flux incorporating natural convection, nucleate boiling, and microlayer evaporation mechanisms following Benjamin and Balakrishnan (1996) was predicted. Heat transfer correlation was also developed in terms of the degree superheat and active nucleation site density. The dependence for these two parameters was found in favorable agreement with that of previous study for smooth surfaces.

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.

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