Recognition Statistic and Analysis of Bubbles in Flow Boiling

2014 ◽  
Author(s):  
Zhongyi Wang ◽  
Pu-zhen Gao ◽  
Dali Yu ◽  
Zheng Yang ◽  
Hanying Chen ◽  
...  
Keyword(s):  
Void Fraction ◽  
High Speed ◽  
Flow Boiling ◽  
Measuring Method ◽  
Narrow Channel ◽  
High Speed Camera ◽  
Fraction Measurement

Void fraction measurement is very important in the thermal-hydraulic experiments. In this work, a new measuring method was proposed to detect the bubbles’ size and sketch by using the high-speed camera. To check the accuracy of this method, flow boiling condition in the vertical rectangular narrow channel was considered. Firstly, boiling phenomenon was observed in the test pipe. Then recognition and statistic of bubbles were performed to obtain the bubbles’ quantity, size and speed. The conclusion of this work is that the bubble images can be divided into nearly round bubbles and irregular bubbles and this method have a good performance in the bubble s’ recognition and statistic.

Experimental Investigation on the Effect of Bubble Behavior on Flow Boiling Pressure Drop in Narrow Channel

2012 ◽  
Author(s):  
Deqi Chen ◽  
Ren Song ◽  
Liang-ming Pan
Keyword(s):  
Experimental Investigation ◽  
Pressure Drop ◽  
Void Fraction ◽  
High Speed ◽  
Channel Wall ◽  
Flow Boiling ◽  
Narrow Channel ◽  
High Speed Camera ◽  
Bubble Behavior ◽  
Channel Dimension

Bubble behavior in narrow channel can be quite different with that in conventional channel. When the bubble reaches a size which is comparable with the channel dimension, the bubble is confined by the channel wall. This influences the bubble evolution significantly in the narrow channel. Then the characteristics of pressure drop in the narrow channel is affected significantly. In order to investigate the effect of bubble behavior on flow boiling pressure drop, a visual study was carried out with a high speed camera (5,000 frame per second was used) to record the bubble behavior. It is found that the OSV (Onset of Significant Vapor) emerges much earlier in narrow channel when comparing with that in conventional channel. A revised correlation for prediction of the real void fraction is proposed based on the experimental investigation. It is also found that the bubble behavior affects the pressure drop in narrow channel significantly, and the channel will be blocked easily when the confined vapor cluster appears. The pressure drop, however, dose not increase linearly with increasing void fraction, and the minimum pressure drop occurs with 60% void fraction. With increasing void fraction, the bubble behavior is more intense and turbulent, which induces more severe fluctuation in pressure drop.

Flow Boiling in a Parallel Strip Fin Heat Sink With Nonuniform Heat Flux Conditions

2020 ◽  
Vol 142 (12) ◽  
Author(s):  
Kexian Ren ◽  
Ze Miao ◽  
Bo Yang ◽  
Tongzhi Yang ◽  
Weixing Yuan
Keyword(s):  
Heat Flux ◽  
Heat Sink ◽  
Thermal Load ◽  
High Speed ◽  
Flow Boiling ◽  
Uniform Heat Flux ◽  
High Speed Camera ◽  
Pressure Drops ◽  
Boiling Process ◽  
Parallel Strip

Abstract This study investigates the thermal performance of a parallel strip fin heat sink (PSFHS) under various heat flux conditions at a flowrate of 100 ml/min, including uniform heat flux and nonuniform heat flux. The heat sink consists of 150 fins with a width of 1 mm, a height of 5.5 mm, and a pitch of 1 mm and has a Z-type inlet/outlet arrangement. Nine separate heaters offer thermal load to the heat sink in order to provide a uniform or nonuniform heat flux. The flow boiling process is captured by a high-speed camera. The temperatures of the heaters have been measured under the uniform and nonuniform heat flux conditions. In addition, the pressure drops inside the heat sink are also obtained. A minichannel heat sink (MCHS) with the same channel dimensions and inlet/outlet configuration is tested too. A comparison between MCHS and PSFHS is discussed in detail, which helps to understand the flow boiling characteristic in PSFHS.

Area-Averaged Void Fraction Analysis of Flow Boiling in a Microscale Branching Channel Network

2007 ◽  
Author(s):  
Douglas Heymann ◽  
Younghoon Kwak ◽  
Lee Edward ◽  
Vinod Narayanan ◽  
James Liburdy ◽  
...  
Keyword(s):  
Void Fraction ◽  
Heat Sink ◽  
High Speed ◽  
Flow Boiling ◽  
Buffer Size ◽  
Image Processing Algorithm ◽  
Channel Network ◽  
Convective Boiling ◽  
Mass Fluxes ◽  
Scale Ratio

Area-averaged void fraction images of convective boiling in a branching channel heat sink were acquired with a high speed high resolution camera at a rate of 1,000 frames per second for one second. Data sets are limited by the buffer size of the camera. Test conditions include a flow rate of 30 g/min, 30 W of energy added, and a subcooling of approximately 11°C. Time-varying area-based void fraction data were estimated using an image processing algorithm designed to minimize noise. Conditions for upstream bubble growth are reported as are liquid momentum, evaporation momentum, and surface tension forces for two extreme mass fluxes through the channels. Mass fluxes vary for each branching level as well as with the amount of vapor present in the heat sink. The heat sink is 38.1 mm in diameter with a radial branching flow pattern. The ratio of daughter-to-mother branching lengths is equal to 1.4, which is in contrast to a previous investigation in which the length scale ratio was 0.70.

scholarly journals Novel Twofold Use of Photographic Technique for Simultaneous Flow Boiling Image Recording and Void Fraction Computation in a Mini-Channel Experiment

Energies ◽  
2021 ◽  
Vol 14 (15) ◽  
pp. 4478
Author(s):  
Krzysztof Płaczkowski ◽  
Mirosław Grabowski ◽  
Mieczysław E. Poniewski
Keyword(s):  
Void Fraction ◽  
High Speed ◽  
Flow Boiling ◽  
Video Camera ◽  
Two Phase ◽  
Data Set ◽  
Photographic Technique ◽  
Image Recording ◽  
High Speed Video Camera ◽  
High Measurement

The paper presents a novel twofold use of the photographic technique for flow boiling heat transfer investigation in the horizontal mini-channel. The dedicated measurement system was constructed to record basic thermal and flow parameters, i.e., boiling liquid inlet and outlet temperatures and pressures, and also temperatures inside the heating block to calculate heat flux going into the liquid. A high-speed video camera equipped with synchronous movement system was applied to combine the recording of two-phase flow images with simultaneous local void fraction measurements both based on the same photographic data set. The data were collected, managed, and refined with the scripts developed in the MathWorks Matlab 2019b environment. The synchronous use of two intelligent techniques in the scripts, i.e., the background subtraction technique and the statistical analysis of individual pictures allowed obtaining reliable experimental results. The proposed method of the void fraction determination ensures high measurement accuracy.

scholarly journals Study on Measure Approach of Void Fraction in Narrow Channel Based on Fully Convolutional Neural Network

2021 ◽  
Vol 9 ◽  
Author(s):  
Wenjun Chu ◽  
Yang Liu ◽  
Liqiang Pan ◽  
Hongye Zhu ◽  
Xingtuan Yang
Keyword(s):  
Neural Network ◽  
Convolutional Neural Network ◽  
Void Fraction ◽  
High Speed ◽  
Nuclear Power ◽  
Flow Boiling ◽  
Image Features ◽  
High Speed Photography ◽  
Flow State ◽  
Narrow Channels

Void fraction is one of the key parameters for gas-liquid study and detection of nuclear power system state. Based on fully convolutional neural network (FCN) and high-speed photography, an indirect void fraction measure approach for flow boiling condition in narrow channels is developed in this paper. Deep learning technique is applied to extract image features and can better realize the identification of gas and liquid phase in channels of complicated flow pattern and high void fraction, and can obtain the instantaneous value of void fraction for analyzing and monitoring. This paper verified the FCN method with visual boiling experiment data. Compared with the time-averaged experimental results calculated by the energy conservation method and the empirical formula, the relative deviations are within 11%, which verifies the reliability of this method. Moreover, the recognition results show that the FCN method has promising improvement in the scope of application compared with the traditional morphological method, and meanwhile saves the design cost. In the future, it can be applied to void fraction measurement and flow state monitoring of narrow channels under complex working conditions.

Experimental Study of Turbulence and Entrained Air Characteristics in a Plunging Breaking Solitary Wave

2020 ◽  
Vol 03 (01n02) ◽  
pp. 2050001
Author(s):  
Lian Tang ◽  
Yun-Ta Wu ◽  
Onyx. W. H. Wai ◽  
Pengzhi Lin
Keyword(s):  
Solitary Wave ◽  
Void Fraction ◽  
High Speed ◽  
Surf Zone ◽  
Phase Speed ◽  
Breaking Waves ◽  
High Speed Camera ◽  
Ensemble Averaging ◽  
The Mean ◽  
Entrained Air

The entrained air and turbulence characteristics under a breaking solitary wave on a 1:20 sloping beach are investigated through laboratory measurement. Free surface elevation is obtained from wave gauge measurements. Wave breaking process is captured in detail by a high-speed camera. The bubble image velocimetry (BIV) is used to measure the velocity and the fiber optic reflectometer (FOR) is used to capture instantaneous void fraction in the aerated region. The mean void fraction and velocities in the aerated region are obtained by ensemble averaging over 22 repetitions. Results show that the maximum mean void fraction is 0.6 in the collapsing cavity region and is 0.35 in the splash up region. The time series of the mean void fraction has good synchronization with the instantaneous images taken by high-speed camera. The maximum horizontal velocity occurs in the splash up region and reaches 1.17C shortly after the plunging jet hits the water surface, with C being the phase speed of the primary wave. The turbulence intensities over the entire aerated region are presented and discussed. The measured data can be used for the calibration and verification of the numerical model for aerated flows simulation under breaking waves in the surf zone.

Dependence of Vapor Void Fraction on Fundamental Bubble Parameters in Subcooled Flow Boiling

2006 ◽  
Author(s):  
Hayato Kubota ◽  
Tatsuhiro Ishida ◽  
Tomio Okawa ◽  
Isao Kataoka ◽  
Michitsugu Mori
Keyword(s):  
Heat Flux ◽  
Void Fraction ◽  
Bubble Size ◽  
High Speed ◽  
Flow Boiling ◽  
Bubble Diameter ◽  
Nucleate Boiling ◽  
Vapor Generation ◽  
Subcooled Flow Boiling ◽  
Subcooled Flow

A visual study of water subcooled flow boiling was conducted to clarify the mechanism of triggering the net vapor generation (NVG). The test section was a transparent sapphire grass tube of 20 mm in inside diameter; a high-speed camera was used to capture the behavior of vapor bubbles. In the present experiments, the vapor void fraction in the heated tube was expressed as the function of the following bubble parameters: nucleation site density, frequency of bubble release, bubble lifetime, and bubble size. Among these four bubble parameters, the bubble size had a particularly strong influence on the vapor void fraction: the void fraction was approximately proportional to the forth power of mean bubble diameter. Consequently, mean bubble diameter should be large enough for the vapor void fraction to increase rapidly with the wall heat flux. In low flowrate experiments, bubbles generated at nucleation sites were relatively large at the onset of nucleate boiling (ONB). The heat flux at ONB hence appeared the reasonable approximation of that at NVG. Whereas, in high flowrate experiments, bubbles were small at ONB and much higher heat flux was necessary to obtain large bubbles. Thus, the heat flux required to trigger NVG was much higher than that at ONB. It was concluded in the present experimental conditions that accurate evaluation of mean bubble diameter was of significant importance in predicting the onset of net vapor generation.

Experimental Data Acquisition System for Flow Boiling in Mini Channels

2015 ◽  
Vol 797 ◽  
pp. 263-273 ◽  
Author(s):  
Mirosław Grabowski ◽  
Mieczysław Poniewski ◽  
Sławomir Alabrudziński ◽  
Krzysztof Płaczkowski
Keyword(s):  
Heat Flux ◽  
Void Fraction ◽  
High Speed ◽  
Flow Boiling ◽  
Channel Length ◽  
Temperature Profiles ◽  
Inverse Heat Conduction ◽  
Flow Parameters ◽  
Mini Channels ◽  
Inverse Heat Conduction Problems

The study discusses experiments on ethanol flow boiling in mini-channels. Pre-set thermal and flow parameters (pressure and temperature at the inlet, mass flux, the heat flux delivered to the heater) and temperature, pressure and void fraction measurements obtained in the experiment provided data for further simulation computations. On the basis of high-speed camera images, void fraction in the mini-channel was determined. Thermograms of the heater surface and the surface in the adiabatic part of the mini-channel allowed producing temperature profiles along the channel length. The read and computed parameters satisfy the expected dependences (especially that for void fraction as a function of volume flux and heat flux). Those were used to solve inverse heat conduction problems.

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