Visualization Study on Gas Bubble Break-Up and Transport Phenomena in Microchannels

2011 ◽  
Author(s):  
Dongwook Yim ◽  
Jaeyong Sung ◽  
Jung Yul Yoo
Keyword(s):  
Liquid Phase ◽  
Bubble Size ◽  
High Speed ◽  
Silicone Oil ◽  
Flow Patterns ◽  
Flow Rate Ratio ◽  
Gas Bubble ◽  
Two Phase ◽  
Flow Rates ◽  
Break Up

In the present research, a visualization study is carried out to understand the flow patterns and break-up formation in flow-focusing microfludic device, which usually involve gas-liquid two-phase flow patterns such as bubbly flow, slug flow, and annular flow. High-speed camera and fluorescence microscopy are used to the characterize microscale gas-liquid two-phase flows in 191.64 μm × 200 μm rectangular PDMS microchannel which are fabricated by using soft lithography technique. N2 and Silicone oil serve as the gas and liquid phases, respectively. The influence of gas and liquid flow rates and the viscosity of the liquid phase on the bubble size, flow patterns, and generating frequency are experimental studied. This study is focused on viscosity of liquid phase. In order to influence of viscosity of liquid phase, various viscosity silicone oils are used in this study. The breakup mechanism, bubble generating rate, and gas bubble making time are investigated at the cross junction. The gas bubble size and space of between bubbles are dependent on the flow rates of the liquid and gas, and viscosity of liquids. The slug length L is also dependent on the flow rates of the liquid and gas in such a manner that the ratio of slug length to the channel width is a function of the flow rate ratio of gas to liquid.

Water-Silicone Oil Two-Phase Flow Hydrodynamics in a Square Glass Microchannel

2018 ◽  
Author(s):  
Zan Wu ◽  
Astrid Svensson ◽  
Jin-yuan Qian ◽  
Bengt Sunden
Keyword(s):  
Flow Regime ◽  
Slug Flow ◽  
Two Phase Flow ◽  
Silicone Oil ◽  
Sodium Dodecyl ◽  
Flow Patterns ◽  
Flow Rate Ratio ◽  
Phase Flow ◽  
Dimensionless Numbers ◽  
Two Phase

This work visualized water-silicone oil two-phase flow patterns both at the inlet cross-junction and in the main square microchannel with a channel width of 400 μm. Tubing/threading, dripping and jetting were identified at the inlet junction while annular, slug and droplet flows were categorized in the main microchannel at 50 mm downstream of the junction. Flow patterns were represented in terms of superficial velocities and dimensionless numbers. Compared to water-silicone oil flow, addition of surfactant sodium dodecyl sulfate (SDS) in water, with a dilute SDS concentration of 1000 ppm, narrows the dripping regime and widens the jetting regime at the inlet junction, while narrows the slug flow regime and widens the droplet flow regime in the main microchannel. A decrease in dynamic interfacial tension due to SDS addition is supposed to be the reason for such a flow pattern modification. Besides, for slug flow, the slug length can be scaled as a power law of the flow rate ratio and the Capillary number of the organic phase. The slug velocity is linearly dependent on the bulk average velocity for both cases with and without SDS addition.

Mixing Characteristics of an Axial-Flow Rotor: Experimental and Numerical Study

2005 ◽  
Vol 3 (1) ◽  
Author(s):  
Fouzi Kerdouss ◽  
Laszlo Kiss ◽  
Pierre Proulx ◽  
Jean-Francois Bilodeau ◽  
Claude Dupuis
Keyword(s):  
Flow Structure ◽  
Bubble Size ◽  
High Speed ◽  
Numerical Study ◽  
Axial Flow ◽  
Three Dimensions ◽  
Water Model ◽  
Two Phase ◽  
Gas Dispersion ◽  
Break Up

In the metallurgical industry, various types of rotors are used for the injection and distribution of gas and for homogenizing molten metal. In the present work, the liquid-gas two-phase flow around an axial type impeller is studied in a water model, in order to analyze the bubble break-up and coalescence and metal mixing. Details like primary and secondary vortex structure, gas flooding between the blades and gas dispersion are recorded by using high speed photography.A mathematical model that takes into account the combined effect of bubble break-up and coalescence is implemented in the commercial computational fluid dynamics (CFD) software FLUENT. In the proposed work, the impeller is explicitly described in three dimensions using Multiple Reference Frame Model. Dispersed gas and bubbles dynamics in the turbulent water are modeled using an Eulerian-Eulerian approach with dispersed k-epsilon turbulent model. The model predicts spatial distribution of gas hold-up, average bubble size and flow structure. Good qualitative agreement between physical model and simulation is achieved when comparing the bubble size distribution, flow structure and mixing.

Characterisation of Air-Water Two-Phase Flow Using a Wire-Mesh Sensor

2011 ◽  
Author(s):  
Carlos E. F. do Amaral ◽  
O´liver B. S. Scorsim ◽  
Eduardo N. Santos ◽  
Marco Jose´ da Silva ◽  
Marco Germano Conte ◽  
...  
Keyword(s):  
High Speed ◽  
Gas Flow ◽  
Two Phase Flow ◽  
Flow Patterns ◽  
Industrial Applications ◽  
Wire Mesh ◽  
Phase Flow ◽  
Two Phase ◽  
Flow Rates ◽  
Piping Systems

Two phase flow occurs in many industrial applications, mainly in the transport of mixtures. Many patterns can be produced according to the liquid and gas flow rates. The identification of these patterns is very important in the design of piping systems and equipments. This work proposes an experimental study to identify multiphase flow patterns of water and air in horizontal pipes. The study was developed using an experimental circuit of 26 mm diameter and 9.2 m length pipe, at Thermal Sciences Lab (LACIT) at the Federal University of Technology - Parana´. To characterize the flow patterns, an intrusive mesh electrodes sensor was used, which allows the detailed visualization of the phases distribution. Tests were made using several experimental settings of water and gas flow rates. Measurements were compared to images obtained by high speed camera and the temporal void fraction series which were analyzed with the use of PDF and PSD functions, showing the singularities for each two-phase flow pattern.

High Speed Imaging and Two-Phase Flow Patterns During Flow Boiling in a Single Microchannel

2008 ◽  
Author(s):  
Jacqueline Barber ◽  
Khellil Sefiane ◽  
David Brutin ◽  
Lounes Tadrist
Keyword(s):  
High Speed ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Pressure Sensors ◽  
Flow Patterns ◽  
Bubble Nucleation ◽  
Phase Flow ◽  
Vapour Bubble ◽  
Two Phase ◽  
Over Time

Boiling in microchannels remains elusive due to the lack of full understanding of the mechanisms involved. A powerful tool in achieving better comprehension of the mechanisms is detailed imaging and analysis of the two phase flow at a fundamental level. We induced boiling in a single microchannel geometry (hydraulic diameter 727 μm), using a refrigerant FC-72, to investigate several flow patterns. A transparent, metallic, conductive deposit has been developed on the exterior of rectangular microchannels, allowing simultaneous uniform heating and visualisation to be conducted. The data presented in this paper is for a particular case with a uniform heat flux of 4.26 kW/m2 applied to the microchannel and inlet liquid mass flowrate, held constant at 1.33×10−5 kg/s. In conjunction with obtaining high-speed images and videos, sensitive pressure sensors are used to record the pressure drop profiles across the microchannel over time. Bubble nucleation, growth and coalescence, as well as periodic slug flow, are observed in the test section. Phenomena are noted, such as the aspect ratio and Reynolds number of a vapour bubble, which are in turn correlated to the associated pressure drops over time. From analysis of our results, images and video sequences with the corresponding physical data obtained, it is possible to follow visually the nucleation and subsequent both ‘free’ and ‘confined’ growth of a vapour bubble over time.

Vapour explosion under hot water depressurization

2016 ◽  
Vol 812 ◽  
pp. 65-128
Author(s):  
Oleg E. Ivashnyov ◽  
Marina N. Ivashneva
Keyword(s):  
Compression Wave ◽  
High Speed ◽  
Saturation Pressure ◽  
Pressure Rise ◽  
Hot Water ◽  
Hyperbolic Model ◽  
Two Phase ◽  
Saturation State ◽  
Break Up ◽  
Bubble Fragmentation

This paper continues a series of works developing a model for a high-speed boiling flow capable of describing different fluxes with no change in the model coefficients. Refining the interfacial area transport equation in partial derivatives, we test the ability of the model to describe phenomena that cannot be simulated by models that average the interfacial interaction. In the previous version, the possibility for bubble fragmentation was considered, which permitted us to reproduce an explosive boiling in rarefaction shocks moving at a speed of ${\sim}10~\text{m}~\text{s}^{-1}$ fixed in experiments on hot water decompression. The shocks were shown to be caused by a chain bubble fragmentation leading to a sharp increase in the interphase area (Ivashnyov et al., J. Fluid Mech., vol. 413, 2000, pp. 149–180). With no change in the free parameters (the initial number of boiling centres in the flow bulk and the critical Weber number) chosen for a tube decompression, the model gave close predictions for critical flows in long nozzles, $L/D\sim 100$. The formation of a boiling shock in the nozzle was shown to be the reason for the onset of autovibrated regimes (Ivashnyov & Ivashneva, J. Fluid Mech., vol. 710, 2012, pp. 72–101). However, the previous model does not simulate the phenomenon of a vapour explosion at a primary stage of a hot water decompression, when the first rarefaction wave is followed by an extended, 1 m width, several MPa amplitude compression wave in which the pressure reaches a plateau below a saturation value. The model proposed assumes initial boiling centre origination at the channel walls. Due to overflowing, the wall bubbles break up, with their fragments passing into the flow. On growing up, the flow bubbles can break up in their turn. It is shown that an extended compression wave is caused by the fragmentation of wall bubbles, which leads to the increase in the interphase area, boiling intensification and the pressure rise. The pressure reaches a plateau before a saturation state is reached due to flow momentum loss accelerating the fragments of wall bubbles. The phenomenon of pressure ‘oscillation’ fixed in some experimental oscillograms when the pressure in the compression wave increases up to a saturation pressure and then drops to the plateau value has been explained as well. The ‘illposedness’ defect of the generally accepted model for two-phase two-velocity flow with a compressible carrying phase, which lies in its complex characteristics, has been rectified. The calculations of a stationary countercurrent liquid-particle flow in a diffuser with the improved hyperbolic model predicts a critical regime with a maximal liquid mass flux, while the old non-hyperbolic model simulates the supercritical regimes with ‘numerical instabilities’. Calculations of a transient upward flow of particles have shown the formation of a superslow ‘creeping’ shock wave of particles compacting.

scholarly journals Numerical Research on Performance of High-Speed Partial Emission Pump

2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Qingjiao Shui ◽  
Ting Jiang ◽  
Binghui Pan ◽  
Tianxing Yang ◽  
Wei Pan
Keyword(s):  
Liquid Phase ◽  
High Speed ◽  
Phase Particle ◽  
Characteristic Curve ◽  
Particle Diameter ◽  
Two Phase ◽  
Factors Affecting ◽  
External Characteristic ◽  
Numerical Simulation Methods ◽  
Small Flow

The high-speed partial emission pump is a small flow and high-head pump, which has been widely used. To study the main factors affecting the performance of high-speed partial emission pumps, numerical simulation methods were used to calculate the performance parameters of high-speed partial emission pumps with and without inducers, and the external characteristic parameters were verified through comparison test values. The results show that the head of the high-speed partial emission pump with inducer is nearly 15 m higher than that of the high-speed partial emission pump without inducer. Considering the influence of air in the high-speed partial emission pump on the working performance, the two-phase flow with different flow rates, different particle sizes, and different concentrations was calculated, and the different liquid phase distributions, liquid phase velocity vector diagrams, and external characteristic curve were compared. The results show that under the same flow condition, the gas-phase particle diameter has the most severe influence on the external characteristic.

Two-Phase Upward Flow in a Slightly Deviated Pipe

2014 ◽  
Vol 136 (5) ◽  
Author(s):  
Abolore Abdulahi ◽  
Barry J. Azzopardi
Keyword(s):  
Void Fraction ◽  
Silicone Oil ◽  
Flow Characteristics ◽  
Flow Patterns ◽  
Visual Observation ◽  
Wire Mesh ◽  
Vertical Position ◽  
Upward Flow ◽  
Two Phase ◽  
Observation Methods

This study was undertaken to look at the effect of a slight inclination of pipe on upward flow characteristics especially at 10 deg from vertical position. Air-silicone oil flows in a 67 mm diameter pipe have been investigated using a capacitance wire mesh sensor (WMS) and electrical capacitance tomography (ECT). They provide time and cross-sectionally resolved data on void fraction. Superficial gas and liquid velocities of 0.05–1.9 and 0.05–0.5 were studied. Statistical methods and visual observation methods were used to characterize the fluid flows obtained into different flow patterns. From the output results from the tomography instruments, flow patterns were identified using both the reconstructed images as well as the characteristic signatures of Probability density function (PDF) plots of the time series of cross-sectionally averaged void fraction. Bubbly, cap bubble, slug, and churn flows were observed when the pipe was deviated by 10 deg from vertical pipe for the range of superficial gas velocities considered.

Experimental Visualization and Numerical Simulation of Liquid-Gas Two-Phase Flows in a Horizontal Pipe

2017 ◽  
Author(s):  
Milad Darzi ◽  
Chanwoo Park
Keyword(s):  
Numerical Simulation ◽  
Gas Flow ◽  
Cfd Simulation ◽  
Glass Tube ◽  
Flow Patterns ◽  
Two Phase Flows ◽  
Two Phase ◽  
Mixture Flow ◽  
Horizontal Pipe ◽  
Flow Rates

This paper presents the results of both visualization experiment and numerical simulation for two-phase (water-air mixture) flows in a horizontal tube. A visualization experimental setup was used to observe various two-phase flow patterns for different flow rates of water/air mixture flow in a glass tube of 12 mm in diameter. Total of 303 experimental data points were compared with Mandhane’s flow map. Most of the data for stratified, plug and slug flows were found to be in good agreement. However, annular flow was observed for relatively lower gas flow rates and also wavy flow occurred at relatively higher liquid flow rates in this experiment. A three-dimensional Computational Fluid Dynamics (CFD) simulation was performed using OpenFOAM employing “interFoam” as the solver to simulate the two-phase flows in horizontal pipe based on Volume-Of-Fluid (VOF) method. The simulated and experimentally observed flow patterns for the same set of superficial velocities shows acceptable similarities for stratified, wavy, plug, slug and annular flows. Also, the computed values of the void fraction and pressure drop for the numerical simulations shows reasonable agreement with well-known correlations in literature.

Development of Prediction Technology of Two-Phase Flow Dynamics Under Earthquake Acceleration — (5) Measurement of Bubble Deformation Near Wall Under Structure Vibration

2012 ◽  
Author(s):  
Kousuke Mizuno ◽  
Akiko Kaneko ◽  
Hideaki Monji ◽  
Yutaka Abe ◽  
Hiroyuki Yoshida ◽  
...  
Keyword(s):  
Liquid Phase ◽  
Flow Structure ◽  
Test Section ◽  
High Speed ◽  
Bubbly Flow ◽  
Oscillation Amplitude ◽  
Reactor Core ◽  
Two Phase ◽  
Piv Measurement ◽  
Structure Vibration

In a nuclear power plant, one of the important issues is evaluation of the safety of reactor core and its pipes when an earthquake occurs. Many researchers have conducted studies on constructions of plants. Consequently, there is some knowledge about earthquake-resisting designs. However the influence of an earthquake vibration on thermal fluid inside a nuclear reactor plant is not fully understood. Especially, there are little knowledge how coolant in a core response when large earthquake acceleration is added. Some studies about the response of fluid to the vibration were carried out. And it is supposed that the void fraction or the power of core is fluctuated with the oscillation by the experiments and numerical analysis. However detailed mechanism about a kinetic response of gas and liquid phases is not enough investigated, therefore the aim of this study is to clarify the influence of vibration of construction on bubbly flow structure. In order to investigate it, we visualize changing of bubbly flow structure in pipeline on which sine wave is applied. Bubbly flow is produced with injecting gas into liquid flow through a horizontally circular pipe. In order to vibrate the test section, the oscillating table is used. The frequency of vibration added from the table is from 1.0 Hz to 10 Hz and acceleration is from 0.4 G to 1 G (1 G = 9.8 m/s2). The test section and a high speed video camera are fixed on the table. Thus the relative velocity between the camera and the test section is ignored. In the visualization experiment, the PIV measurement is conducted. Then the motion of bubbles, for example the shape, the positions and the velocity are measured with observation. In addition, by varying added oscillation amplitude, frequency and flow rate of the fluids, the correlation between these parameters and bubble motion was evaluated. It was clarified that the behavior of liquid phase and bubble through horizontal circular pipes was affected by an oscillation. When structure vibration affects the flow, two main mechanisms are supposed. One is the addition of body force of the oscillation acceleration to liquid phase and bubble, and the other is the velocity oscillation of the test section and the effect of the boundary layer of the pipe wall. It was also found that when the added oscillation frequency and amplitude was changed, the degree of the fluctuation of liquid phase and bubble motions were changed.

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