Phase field modeling of Taylor flow in mini/microchannels, Part II: Hydrodynamics of Taylor flow parasitic currents or pressure oscillations with phase field model (original) (raw)
Related papers
2013
Multiphase heat and mass transfer in microscale devices is a growing field of research due to the potential of these devices for use in various engineering applications. Before the heat and mass transport phenomena in such systems can be modeled, the hydrodynamics of adiabatic multiphase flow, in the absence of specie transport across interfaces, must be accurately predicted. In the present paper, a finite element implementation of the phase field method is applied to simulate Taylor flow in mini/microchannels. Channels with characteristic dimensions ranging from 100 to 500 mm are modeled and criteria present in the literature for domain discretization are assessed. The effects of phase field parameters, namely mobility and interface thickness, on the predicted flow features are discussed. The predicted Taylor bubble lengths are compared against empirical correlations as well as available experimental data in the literature. The predicted gas void fraction data for different channel dimensions are compared with numerous experimental studies. The present results indicate a linear variation of gas void fraction with respect to volumetric flow ratio for all channel sizes.
On the CFD modelling of Taylor flow in microchannels
Chemical Engineering Science, 2009
With the increasing interest in multiphase flow in microchannels and advancement in interface capturing techniques, there have recently been a number of attempts to apply computational fluid dynamics (CFD) to model Taylor flow in microchannels. The liquid film around the Taylor bubble is very thin at low Capillary number (Ca) and requires careful modelling to capture it. In this work, a methodology has been developed to model Taylor flow in microchannel using the ANSYS Fluent software package and a criterion for having a sufficiently fine mesh to capture the film is suggested. The results are shown to be in good agreement with existing correlations and previous valid modelling studies. The role played by the wall contact angle in Taylor bubble simulations is clarified.
Numerical Simulation of Taylor Flow in the Entrance Region of Microchannels
2020
Computational Fluid Dynamics (CFD) has been widely employed by investigators to simulate Taylor flow in microchannels. High-resolution images captured by numerical techniques reveal significant details of an ultra-thin liquid film around the gas bubble. The interface between the liquid and the gas phases is a decisive factor in order to determine the flow pattern, the gas bubble profile, the bubble length–separation distance, the slug length, and so forth. Since the thickness of the liquid film is on the order of 10-15 μm for low capillary number flows, the mesh generation requires careful modeling to capture it and transport phenomena, such as momentum and heat. The present study is to develop a model of a transient Taylor flow in a two-dimensional microchannel using commercial ANSYS Fluent software. The Volume of Fluid (VoF) method was employed to simulate the interface between two phases, i.e., air and water. A comprehensive grid study was carried out to identify a sufficiently f...
Processes
Taylor flow is a strategy-aimed flow to transfer conventional single-phase into a more efficient two-phase flow resulting in an enhanced momentum/heat/mass transfer rate, as well as a multitude of other advantages. To date, Taylor flow has focused on the processes involving gas–liquid and liquid–liquid two-phase systems in microchannels over a wide range of applications in biomedical, pharmaceutical, industrial, and commercial sectors. Appropriately micro-structured design is, therefore, a key consideration for equipment dealing with transport phenomena. This review paper highlights the hydrodynamic aspects of gas–liquid and liquid–liquid two-phase flows in microchannels. It covers state-of-the-art experimental and numerical methods in the literature for analyzing and simulating slug flows in circular and non-circular microchannels. The review’s main objective is to identify the considerable opportunity for further development of microflows and provide suggestions for researchers in...
Hydrodynamics of gas–liquid Taylor flow in rectangular microchannels
Microfluidics and Nanofluidics, 2012
The effect of fluid properties and operating conditions on the generation of gas-liquid Taylor flow in microchannels has been investigated experimentally and numerically. Visualisation experiments and two-dimensional numerical simulations have been performed to study bubble and slug lengths, liquid film hold-up and bubble velocities. The results show that the bubble and slug lengths increase as a function of the gas and liquid flow rate ratios. The bubble and slug lengths follow the model developed by and , however the model coefficients appear to be dependent on the liquid properties and flow conditions in some cases. The ratio of the bubble velocity to superficial two-phase velocity is close to unity, which confirms a thin liquid film under the assumption of a stagnant liquid film. Numerical simulations confirm the hypothesis of a stagnant liquid film and provide information on the thickness of the liquid film.
C-2011 PHASE FIELD METHOD FOR SIMULATION OF MULTIPHASE FLOW.pdf
The present paper reports a comprehensive study on the numerical simulation of Taylor flow in microchannels by the phase field method. Additionally, a comparative study was also performed against an alternative volume of fluid model based on which the phase field method was found to be more advantageous in key aspects such as the absence of unphysical interfacial pressure oscillations and the ability to account for variations in the surface tension force and thus predict several bubble lengths under constant flow conditions while observing the physics of homogeneous two-phase flow. Different bubble formation mechanisms were simulated and compared against experimental findings in literature. The simulation of a thin liquid film at the channel wall was found to be a limitation of most works pertaining to Taylor flow, including the present. This was ascribed to be more likely due to limited dimensional and spatial resolution as well as inaccurate contact angle dynamics rather than limitations of the modeling approach itself. The effect of wall adhesion was studied with respect to the flow and pressure field in the channel. A validation of the model was achieved through a favorable comparison of the numerically predicted gas void fraction and bubble lengths with existing models and correlations. On the whole, the phase field method was concluded to have improved predictive accuracy with respect to certain aspects as compared to conventional multiphase flow models.
Film Thickness and Pressure Drop for Gas-Liquid Taylor Flow in Microchannels
Journal of Fluid Flow, Heat and Mass Transfer
This paper investigates the hydrodynamics of gasliquid two-phase flow in an axisymmetric microchannel with a circular cross-sectional area. ANSYS Fluent was employed to simulate Taylor flow using the Volume of Fluid model to predict the interfacial phenomena between the two phases. Film thickness, bubble curvature, pressure drop, bubble/slug lengths are determined to investigate gas-liquid Taylor flow in micro capillaries. The results show that the liquid film thickness remains almost constant, but the length of the flat film region increases as the air bubble proceeds downstream. The predictions are validated with theoretical and experimental data in the literature, which show a good agreement.
Modeling the motion of a Taylor bubble in a microchannel through a shear-thinning fluid
E3S Web of Conferences, 2021
Applications of multiphase flows in microchannels as chemical and biological reactors and cooling systems for microelectronic devices typically present liquid slugs alternated with bubbles of elongated shape, the Taylor bubbles. These occupy almost entirely the cross-section of the channel and present a hemispherical front and a liquid layer, the lubrication film, which separates the gas from the tube wall. The Taylor bubble perturbs the surrounding fluids activating many transport mechanisms in the proximity of the gas-liquid interface; therefore, the bubble motion significantly influences the heat and mass transfer rates. Although many works deeply investigate the bubble hydrodynamics in Newtonian fluids, the knowledge about the relation between bubble hydrodynamics and rheological properties is insufficient, and studies where the continuous phase exhibits a shear-thinning behavior are missing. Our numerical analysis tries to fill this gap by investigating the motion of a Taylor b...
Analysis of local pressure gradient inversion and form of bubbles in Taylor flow in microchannels
Chemical Engineering Science
h i g h l i g h t s Local inversion of the pressure gradient by the gas-liquid Taylor flow is theoretically explained. In the film around the bubble an inverse flow of liquid exists. Inverse flow of fluid is caused by the inverse pressure gradient in the film. Pressure oscillations near the ends of the bubble reasons are explained. Form of Taylor bubbles is explained theoretically at qualitative level.