scholarly journals Experimental Techniques for Bubble Dynamics Analysis in Microchannels: A Review

2013 ◽  
Vol 135 (2) ◽  
Author(s):  
Mahshid Mohammadi ◽  
Kendra V. Sharp
Keyword(s):  
Bubble Dynamics ◽  
Measurement Techniques ◽  
Fluorescent Microscopy ◽  
Experimental Studies ◽  
Experimental Techniques ◽  
Confocal Scanning Laser Microscopy ◽  
Microfluidic Systems ◽  
Two Phase ◽  
Micro Particle Image Velocimetry ◽  
Micro Piv

Experimental studies employing advanced measurement techniques have played an important role in the advancement of two-phase microfluidic systems. In particular, flow visualization is very helpful in understanding the physics of two-phase phenomenon in microdevices. The objective of this article is to provide a brief but inclusive review of the available methods for studying bubble dynamics in microchannels and to introduce prior studies, which developed these techniques or utilized them for a particular microchannel application. The majority of experimental techniques used for characterizing two-phase flow in microchannels employs high-speed imaging and requires direct optical access to the flow. Such methods include conventional brightfield microscopy, fluorescent microscopy, confocal scanning laser microscopy, and micro particle image velocimetry (micro-PIV). The application of these methods, as well as magnetic resonance imaging (MRI) and some novel techniques employing nonintrusive sensors, to multiphase microfluidic systems is presented in this review.

scholarly journals Wavelet analysis techniques in cavitating flows

2018 ◽  
Vol 376 (2126) ◽  
pp. 20170242 ◽  
Author(s):  
Paul A. Brandner ◽  
James A. Venning ◽  
Bryce W. Pearce
Keyword(s):  
Wavelet Transform ◽  
Continuous Wavelet Transform ◽  
High Speed ◽  
Large Scale ◽  
Bubble Dynamics ◽  
Measurement Techniques ◽  
Continuous Wavelet ◽  
High Speed Imaging ◽  
Two Phase ◽  
Ultrasonic Sensing

Cavitating and bubbly flows involve a host of physical phenomena and processes ranging from nucleation, surface and interfacial effects, mass transfer via diffusion and phase change to macroscopic flow physics involving bubble dynamics, turbulent flow interactions and two-phase compressible effects. The complex physics that result from these phenomena and their interactions make for flows that are difficult to investigate and analyse. From an experimental perspective, evolving sensing technology and data processing provide opportunities for gaining new insight and understanding of these complex flows, and the continuous wavelet transform (CWT) is a powerful tool to aid in their elucidation. Five case studies are presented involving many of these phenomena in which the CWT was key to data analysis and interpretation. A diverse set of experiments are presented involving a range of physical and temporal scales and experimental techniques. Bubble turbulent break-up is investigated using hydroacoustics, bubble dynamics and high-speed imaging; microbubbles are sized using light scattering and ultrasonic sensing, and large-scale coherent shedding driven by various mechanisms are analysed using simultaneous high-speed imaging and physical measurement techniques. The experimental set-up, aspect of cavitation being addressed, how the wavelets were applied, their advantages over other techniques and key findings are presented for each case study. This paper is part of the theme issue ‘Redundancy rules: the continuous wavelet transform comes of age’.

A Numerical Study on Flow Boiling in Parallel Microchannels

2008 ◽  
Author(s):  
Jinho Jeon ◽  
Woorim Lee ◽  
Youngho Suh ◽  
Gihun Son
Keyword(s):  
Heat Transfer ◽  
Contact Angle ◽  
Bubble Dynamics ◽  
Numerical Study ◽  
Reverse Flow ◽  
Flow Boiling ◽  
Experimental Studies ◽  
Two Phase ◽  
Flow And Heat Transfer ◽  
Parallel Microchannels

Flow boiling in parallel microchannels has received attention as an effective cooling method for high-power-density microprocessor. Despite a number of experimental studies, the bubble dynamics coupled with boiling heat transfer in microchannels is still not well understood due to the technological difficulties in obtaining detailed measurements of microscale two-phase flows. In this study, complete numerical simulation is performed to further clarify the physics of flow boiling in microchannels. The level set method for tracking the liquid-vapor interface is modified to include the effects of phase change and contact angle. The method is further extended to treat the no-slip and contact angle conditions on the immersed solid. Also, the reverse flow observed during flow boiling in parallel microchannels has been investigated. Based on the numerical results, the effects of channel shape and inlet area restriction on the bubble growth, reverse flow and heat transfer are quantified.

Local Bubble Dynamics in Two-Phase Flows

2002 ◽  
Author(s):  
Michael Schlu¨ter ◽  
So¨ren Scheid ◽  
Norbert Ra¨biger
Keyword(s):  
Mass Transfer ◽  
Multiphase Flows ◽  
Chemical Engineering ◽  
Bubble Dynamics ◽  
Measurement Techniques ◽  
Continuous Phase ◽  
Detailed Knowledge ◽  
Two Phase Flows ◽  
Two Phase ◽  
Exact Design

For the development of environmentally sustainable processes e.g. in chemical engineering or biotechnology detailed knowledge of hydrodynamics and mass transfer is essential. A calculation of the exact design layout of reactors and processes required for multiphase flows has been impossible to achieve because of the complex transient coupling between the continuous and dispersed phases. Due to the lack of exact models to describe local and transient phenomena the calculation of hydrodynamics and mass transfer is over-simplified by using time- and space-averaged data, thus neglecting important facts. Recently developed measurement techniques allow the investigation of these local effects in multiphase flows and indicate that e.g. the behavior and slip velocity of fluid particles in a particle swarm differ from the behavior of single particles and depend on particle hold-up and flow conditions of the continuous phase. Measurements in two-phase flows in co-current and counter-current flow have shown that generally used models for homogeneous flow are dissatisfying.

Experimental Visualization and Analysis of Multiphase Immiscible Flow in Fractured Micromodels Using Micro-Particle Image Velocimetry

2021 ◽  
pp. 1-25
Author(s):  
Najrul Haque ◽  
Anugrah Singh ◽  
Ujjwal K. Saha
Keyword(s):  
Oil Recovery ◽  
Single Phase ◽  
Preferential Flow ◽  
Two Phase Flow ◽  
Phase Flow ◽  
Single Phase Flow ◽  
Immiscible Flow ◽  
Two Phase ◽  
Micro Particle Image Velocimetry ◽  
Micro Piv

Abstract The study of fluid flow through fractured porous media has drawn immense interest in the fields of soil hydrology, enhanced oil recovery (EOR) and others. In this work, a low cost fractured micromodel with regular pore geometry is fabricated and visualization experiments are performed to study the flow field produced by single-phase and two-phase immiscible flow. The fractured micromodel is fabricated using Polydimethylsiloxane (PDMS) substrate. The micro-PIV method is applied to map the flow velocity, both at the throat and near the fracture region of micromodel. In two-phase flow, imbibition flow experiments are performed to investigate the effects of fracture on the front migration caused by the trapping mechanism of residual fluid (displaced phase). The velocity distribution obtained for the two-phase flow revealed many peculiarities that are completely different from the single-phase flow pattern. These peculiarities create instabilities that yield random preferential flow paths near the pockets of stagnant fluid. Such dynamic events are quantified by mapping the velocity magnitude of flow fields. No effects of fracture are seen in the single-phase flow where uniform flow patterns are observed in the porous region. However, for the two-phase flow, more pockets of trapped fluids are found at the junction of two fractures.

Velocity Measurements in Microscopic Two-Phase Flows by Means of Micro PIV

2008 ◽  
Author(s):  
Ulrich Miessner ◽  
Ralph Lindken ◽  
Jerry Westerweel
Keyword(s):  
Liquid System ◽  
Index Of Refraction ◽  
Refractive Indices ◽  
Phase System ◽  
Velocity Measurements ◽  
Two Phase Flows ◽  
Two Phase ◽  
Spherical Droplet ◽  
Micro Particle Image Velocimetry ◽  
Micro Piv

This article examines the velocity distributions of microscopic liquid-liquid two-phase flows by means of micro particle image velocimetry (micro-PIV). Aqueous droplets are dispersed into an oil bulk at the T-junction of a micro fluidic Polydimethylsiloxane (PDMS) device. The channel geometry is rectangular (H: 100μm, W: 100μm). The flow is pressure driven. Tracer particles (D: 0.5–1.2μm) are added to either phase, enabling simultaneous measurements in both phases. However, the use of immiscible liquids causes optical disturbances due to a difference in refractive indices of the two liquids and due to a curved interface geometry. Particle images are thus imaged in a distorted field of view. The results of a PIV analysis will be inaccurate in scaling as well as in location of the velocity vectors — depending on the mismatch of the refractive index. We present a basic analysis on the effect of mismatched refractive indices on the precision of the velocity measurements. The estimation is based on Snell’s law and the simplified geometry of a spherical droplet. Furthermore, we propose a method to match not only the index of refraction accurately but also to leave one additional degree of freedom to set an additional property of the liquid-liquid system, e.g. viscosity ratio or density ratio. The latter ensures that properties of the modified liquid-liquid system are close to those of the non-modified two-phase system. The findings of this study are part of the design of a Lab-on-a-Chip device. It performs a DNA analysis in an online quality control application. The miniaturization of a two-phase flow combines the benefits of confined sample compartments (i.e. droplets) with the easy-to-control process parameters of a miniaturized device (e.g. temperature, pressure). Thus band broadening of the sample by Taylor-Aris dispersion is avoided and the processes can be set accurately.

scholarly journals Bubble Dynamics in a Two-Phase Bubbly Mixture

2010 ◽  
Author(s):  
Arvind Jayaprakash ◽  
Sowmitra Singh ◽  
Georges Chahine
Keyword(s):  
Void Fraction ◽  
High Speed ◽  
Bubble Dynamics ◽  
Bubble Radius ◽  
Discharge Voltage ◽  
Large Bubble ◽  
Water Mixture ◽  
Two Phase ◽  
Mixture Density ◽  
Bubbly Medium

The dynamics of a primary relatively large bubble in a water mixture including very fine bubbles is investigated experimentally and the results are provided to several parallel on-going analytical and numerical approaches. The main/primary bubble is produced by an underwater spark discharge from two concentric electrodes placed in the bubbly medium, which is generated using electrolysis. A grid of thin perpendicular wires is used to generate bubble distributions of varying intensities. The size of the main bubble is controlled by the discharge voltage, the capacitors size, and the pressure imposed in the container. The size and concentration of the fine bubbles can be controlled by the electrolysis voltage, the length, diameter, and type of the wires, and also by the pressure imposed in the container. This enables parametric study of the factors controlling the dynamics of the primary bubble and development of relationships between the bubble characteristic quantities such as maximum bubble radius and bubble period and the characteristics of the surrounding two-phase medium: micro bubble sizes and void fraction. The dynamics of the main bubble and the mixture is observed using high speed video photography. The void fraction/density of the bubbly mixture in the fluid domain is measured as a function of time and space using image analysis of the high speed movies. The interaction between the primary bubble and the bubbly medium is analyzed using both field pressure measurements and high-speed videography. Parameters such as the primary bubble energy and the bubble mixture density (void fraction) are varied, and their effects studied. The experimental data is then compared to simple compressible equations employed for spherical bubbles including a modified Gilmore Equation. Suggestions for improvement of the modeling are then presented.

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