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.

Recent Progress in the Studies of Gas-Liquid Two-Phase Flows at Microgravity Conditions

2003 ◽  
Author(s):  
Tomoji Takamasa ◽  
Takashi Hibiki
Keyword(s):  
Recent Progress ◽  
Interfacial Area ◽  
Phase System ◽  
Two Phase Flows ◽  
Two Phase ◽  
Interfacial Area Transport ◽  
Drift Flux ◽  
Wide Range ◽  
Microgravity Conditions ◽  
Heat Loads

In a thermal system of spacecraft, two-phase flow system now is an excellent alternative to the conventional single-phase system in transporting large amount of thermal energy at a uniform temperature regardless of variations in the heat loads. In addition, two-phase flows exist in a wide range of applications and enabling technologies in space. This report outlines recent progress in the studies of gas-liquid two-phase flows at microgravity conditions, especially for which regarding to interfacial area transport and drift flux.

scholarly journals Исследование реакции поверхности жидкости на импульсное воздействие наклонной газовой струи при малых числах Рэйнольдса

2022 ◽  
Vol 92 (2) ◽  
pp. 216
Author(s):  
А.П. Савенков ◽  
В.А. Сычёв
Keyword(s):  
Drag Force ◽  
Liquid Surface ◽  
Dynamic Properties ◽  
Liquid System ◽  
Gas Jet ◽  
Viscous Drag ◽  
Phase System ◽  
Two Phase ◽  
Automatic Control Theory ◽  
Viscous Drag Force

A mathematical description of the motion of a cavity on the liquid surface under an oblique action of a gas jet is obtained using the well-known expressions for the movement of a gas bubble in a liquid. The boundary of the viscous drag force domination over the form drag force is determined. The impingement of the gas jet on the liquid surface is considered as a dynamic object of the automatic control theory. It is found that the dynamic properties of the two-phase system "gas jet - liquid" are described by the integrator equations. Using a specially designed setup, the transient response of the "gas jet - liquid" system were experimentally obtained for the aerodynamic action at angles of 20º and 50º to the surfaces of liquids with the viscosities of 0.71 and 26.1 Pa•s (Reynolds number Re < 2). The research results are necessary for the analysis of the non-contact aerodynamic method of liquid viscosity measurements.

scholarly journals Thermodynamics of phase equilibrium in solid-liquid and solid-gas systems

2021 ◽  
Vol 83 (1) ◽  
pp. 30-35
Author(s):  
Y. I. Shishatskii ◽  
A. A. Derkanosova ◽  
S. A. Tolstov
Keyword(s):  
Driving Force ◽  
Cheese Whey ◽  
Extraction Process ◽  
Liquid System ◽  
Average Concentration ◽  
Phase System ◽  
Gibbs Equation ◽  
Two Phase ◽  
Thermodynamic Potentials ◽  
Solid Liquid

The thermodynamic equilibrium of a two-phase system is described by the Gibbs equation, which includes state parameters. On the basis of the Gibbs equation and the combined equation of the first and second laws of thermodynamics, thermodynamic potentials are written: internal energy, enthalpy and Gibbs free energy. If the two phases are in equilibrium, then the temperatures, pressures and chemical potentials of these phases are equal to each other. Equalities express the conditions of thermal and mechanical equilibrium, as well as the condition for the absence of a driving force for the transfer of a component across the interface. For a two-phase system, the Gibbs-Duhem equation connects the volume and entropy of 1 mole of the mixture, the content of any component, expressed in mole fractions. Extraction from lupine particles with cheese whey (solid-liquid system) is considered. The driving force of the extraction process in the solid-liquid system is the difference between the concentration of the solvent at the surface of the solid C and its average concentration C0 in the bulk of the solution. The concentration at the interface is usually taken to be equal to the concentration of a saturated solution of Cn, since equilibrium is established rather quickly near the surface of a solid. Then the driving force of the process is expressed as Cn – C0. A curve for the extraction of extractives from lupine with cheese whey was plotted by superimposing low-frequency mechanical vibrations.

Fundamental Issues Related to the Numerical Simulation of Two-Phase Flows With Phase-Change

2006 ◽  
Author(s):  
Didier Jamet
Keyword(s):  
Numerical Simulation ◽  
Phase Change ◽  
Bubbly Flow ◽  
Nucleate Boiling ◽  
Phase System ◽  
High Heat Flux ◽  
Two Phase Flows ◽  
Miscible Fluids ◽  
Two Phase ◽  
Phase Change Phenomena

In direct numerical simulation (DNS) of two-phase flows, all the interfaces of the two-phase system are tracked individually. If this technique is computationally expensive, it is also very powerful, especially to study basic phenomena. In particular, it helped to better understand fundamental issues such as the forces acting on a single bubble (e.g. [1]) or the interaction of a couple of bubbles in a bubbly flow (e.g. [2,3]) and it now begins to be used to assess average models in detail ([4]). Currently, most of the basic phenomena studied involve non-miscible fluids, where no mass transfer between the phases occurs (air and water for instance). However, in many applications of industrial interest, phase-change phenomena are very important because high heat flux can be achieved with moderate temperature gradients (since the energy exchange through latent heat occurs at a constant temperature). It is thus widely used in the energy industry (nuclear energy in particular) and it is used to design compact heat exchangers (e.g. heat pipes for space or electronic devices). Moreover, basic phenomena related to phase-change are, to a large extent, still misunderstood, which make phase-change phenomena of fundamental interest as well. For instance, despite several decades of valuable scientific studies, the boiling crisis, which is an instability of the nucleate boiling regime, is still misunderstood from a fundamental point of view. It is one of the very few fundamental issues that are still open in fluid mechanics. Since DNS has already been successful to study fundamental issues in two-phase flows of non-miscible fluids, it should be successful to study these issues as well. However, the DNS of two-phase flows with phase-change is more difficult than that of two-phase flows involving non-miscible phases. These issues are both numerical and physical and some of them are discussed in this paper.

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.

ON SIMULATIONS OF HIGH-DENSITY RATIO FLOWS USING COLOR-GRADIENT MULTIPHASE LATTICE BOLTZMANN MODELS

2013 ◽  
Vol 24 (04) ◽  
pp. 1350021 ◽  
Author(s):  
HAIBO HUANG ◽  
JUN-JIE HUANG ◽  
XI-YUN LU ◽  
MICHAEL C. SUKOP
Keyword(s):  
Density Ratio ◽  
High Density ◽  
Density Contrast ◽  
Two Phase Flows ◽  
Two Phase ◽  
Spherical Droplet ◽  
Two Fluids ◽  
Spherical Bubbles ◽  
Color Gradient ◽  
Density Ratios

Originally, the color-gradient model proposed by Rothman and Keller (R–K) was unable to simulate immiscible two-phase flows with different densities. Later, a revised version of the R–K model was proposed by Grunau et al. [D. Grunau, S. Chen and K. Eggert, Phys. Fluids A: Fluid Dyn. 5, 2557 (1993).] and claimed it was able to simulate two-phase flows with high-density contrast. Some studies investigate high-density contrast two-phase flows using this revised R–K model but they are mainly focused on the stationary spherical droplet and bubble cases. Through theoretical analysis of the model, we found that in the recovered Navier–Stokes (N–S) equations which are derived from the R–K model, there are unwanted extra terms. These terms disappear for simulations of two-phase flows with identical densities, so the correct N–S equations are fully recovered. Hence, the R–K model is able to give accurate results for flows with identical densities. However, the unwanted terms may affect the accuracy of simulations significantly when the densities of the two fluids are different. For the simulations of spherical bubbles and droplets immersed in another fluid (where the densities of the two fluids are different), the extra terms may not be important and hence, in terms of surface tension, accurate results can be obtained. However, generally speaking, the unwanted term may be significant in many flows and the R–K model is unable to obtain the correct results due to the effect of the extra terms. Through numerical simulations of parallel two-phase flows in a channel, we confirm that the R–K model is not appropriate for general two-phase flows with different densities. A scheme to eliminate the unwanted terms is also proposed and the scheme works well for cases of density ratios less than 10.

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.

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