scholarly journals Gas-liquid slug formation at a rectangular microchannel T-junction: A CFD benchmark case

2011 ◽  
Vol 1 (4) ◽  
Author(s):  
Rafael Santos ◽  
Masahiro Kawaji
Keyword(s):  
Experimental System ◽  
Velocity Slip ◽  
Liquid Slug ◽  
Two Phase ◽  
Experimental Conditions ◽  
Rectangular Microchannel ◽  
Flow Rates ◽  
Frictional Pressure Drop ◽  
Vof Model ◽  
Computational Fluid Dynamics Cfd

AbstractComputational fluid dynamics (CFD) is an important tool for development of microfluidic systems based on gasliquid two-phase flow. The formation of Taylor slugs at microchannel T-junctions has been studied both experimentally and numerically, however discrepancies still exist because of difficulties in correctly representing experimental conditions and uncertainties in the physics controlling slug flow, such as contact line and velocity slip. In this paper detailed methods and results are described for the study of Santos and Kawaji [1] on the comparison of experimental results and numerical modeling. The system studied consisted of a rectangular microchannel Tjunction nominally 100 μm in hydraulic diameter, used to generate Taylor slugs from air-water perpendicular flow. The effect of flow rates on parameters such as slug length, velocity slip, void fraction and two-phase frictional pressure drop were studied. Numerical simulation was performed using FLUENT volume-of-fluid (VOF) model. It is proposed in this paper that this microfluidic problem be taken up by researchers in the field as a benchmark case to test other numeric codes in comparison to FLUENT on the prediction of micro-scale multiphase flow, and also to model in more detail the experimental system described to obtain greater accuracy in prediction of microfluidic slug formation.

Model for Choking of Subcooled Flashing Flow Through a Steam Generator Tube Crack

2012 ◽  
Author(s):  
Brian Wolf ◽  
Shripad T. Revankar ◽  
Jovica R. Riznic
Keyword(s):  
Steam Generator ◽  
Mechanistic Model ◽  
Channel Length ◽  
Saturation Curve ◽  
Two Phase ◽  
Experimental Conditions ◽  
Flow Rates ◽  
Frictional Pressure Drop ◽  
Flow Through ◽  
Non Equilibrium

Recently there is some database available on choking flow through cracks relevant to steam generator (SG) tubes to model the critical flow. A one dimensional mechanistic model was developed to model two-phase choking flow through slits from conservation principles. The model takes into account channel entrance loss as well as frictional pressure drop for single-phase subcooled liquid. Flashing criteria are defined and temperature and pressure of the fluid are assumed to follow the saturation curve. The two-phase mixture was treated as a quasi-fluid with mixture properties and both homogenous equilibrium (HE) and homogeneous non-equilibrium models were considered. The models were compared with the choking flow rates for various experimental conditions for subcooled flashing flow through narrow slits with L/D varying from small values ( 5) to large values (100). Results are presented on the effects of thermal non-equilibrium on the choking flow for small L/D channels. A comparison of model results to experimental data shows that the HE based models grossly under predict choking flow rates in such geometries. As subcooling increases, and channel length decreases the non-equilibrium effects play a greater role in the choking phenomenon, therefore the difference in model predictions and experimental results increases for HE case.

Numerical Simulation of Bubble Formation in Co-Flowing Mercury

2008 ◽  
Author(s):  
Ashraf Ibrahim ◽  
Mark Wendel ◽  
David Felde ◽  
Bernard Riemer
Keyword(s):  
Acoustic Waves ◽  
Bubble Growth ◽  
Gas Flow ◽  
Bubble Formation ◽  
Science Center ◽  
Proton Radiography ◽  
Two Phase ◽  
Vof Model ◽  
Computational Fluid Dynamics Cfd ◽  
Bubble Sizes

In this work, we present computational fluid dynamics (CFD) simulations of helium bubble formation and detachment at a submerged needle in stagnant and co-flowing mercury. Since mercury is opaque, visualization of internal gas bubbles was done with proton radiography (pRad) at the Los Alamos Neutron Science Center (LANSCE2). The acoustic waves emitted at the time of detachment and during subsequent oscillations of the bubble were recorded with a microphone. The Volume of Fluid (VOF) model was used to simulate the unsteady two-phase flow of gas injection in mercury. The VOF model is validated by comparing detailed bubble sizes and shapes at various stages of the bubble growth and detachment, with the experimental measurements at 1.66 mg/min helium gas flow rate and different mercury velocities. The experimental and computational results show a two-stage bubble formation in stagnant mercury. The first stage involves growing bubble around the needle, and the second follows as the buoyancy overcomes wall adhesion. The comparison of predicted and measured bubble sizes and shapes at various stages of the bubble growth and detachment is in good agreement.

Optimized Gun Barrel Based on Numerical Simulation to Produced Oil With Low BSW Content

2020 ◽  
Author(s):  
Silvia Araujo Daza ◽  
Urbano Montañez Villamizar
Keyword(s):  
Flow Rate ◽  
Operating Conditions ◽  
Water Mixture ◽  
Two Phase ◽  
Ansys Fluent ◽  
Inlet Flow ◽  
Gun Barrel ◽  
Vof Model ◽  
Inlet Flow Rate ◽  
Computational Fluid Dynamics Cfd

Abstract This work presents the methodology and results of the optimization of the internals (Inlet distributor, oil and water collectors) of a 20,000 BPD (0.037 m3/s) gun-barrel tank starting from an existing design. Computational fluid dynamics (CFD) was applied to simulate and evaluate the performance of various internal configurations. These simulations were performed to determine the best configuration to ensure efficient separation of the oil-water mixture and oil with a low BSW content < 2% at the outlet. The simulations were carried out using the commercial software ANSYS Fluent under the two-phase flow VOF model and k-ε realizable turbulence model. Further CFD simulations were performed to evaluate the behavior of the gun barrel tank under different operating conditions (Different inlet flow rate) and to determine the maximum operation flow which allows obtaining the crude-oil with a maximum BSW content of 0.5%. From the simulation results, an operating curve (operating flow vs retention time) was constructed. This information allows, in practice, to identify the inlet flow rate based on the desired content of BSW in the separated oil.

Applicability of Choking Flow Models for Subcooled Flashing Flow Through Tube Cracks

2011 ◽  
Author(s):  
Brian Wolf ◽  
Shripad T. Revankar ◽  
Jovica R. Riznic
Keyword(s):  
Mechanistic Model ◽  
Channel Length ◽  
Two Phase ◽  
Experimental Conditions ◽  
Flow Rates ◽  
Flow Models ◽  
Model Predictions ◽  
Flow Through ◽  
The Difference ◽  
Non Equilibrium

Recently there is some database available on choking flow through cracks relevant to steam generator (SG) tubes to model the critical flow. These data are used in assessing the key choking flow models. Based on this assessment a mechanistic choking model is developed. The model is used to predict the choking flow rates for various experimental conditions for subcooled flashing flow through narrow slits with L/D varying from small values (∼5) to large values (100). Results are presented on the effects of thermal and mechanical non-equilibrium on the choking flow for small L/D channels. A mechanistic model was developed to model two-phase choking flow through slits. A comparison of model results to experimental data shows that the homogeneous equilibrium based models markedly under predict choking flow rates in such geometries. As subcooling increases, and channel length decreases the non-equilibrium effects play a greater role in the choking phenomenon, therefore the difference in model predictions and experimental results increases.

Quantification of Mixing in RIM Using a Non-Diffusive Two-Phase Flow Numerical Model

2011 ◽  
Vol 9 (1) ◽  
Author(s):  
Cláudio P. Fonte ◽  
Ricardo J. Santos ◽  
Madalena M. Dias ◽  
José Carlos B. Lopes
Keyword(s):  
Fluid Dynamics ◽  
Reynolds Number ◽  
Two Phase Flow ◽  
Phase Flow ◽  
Linear Scale ◽  
Cfd Simulations ◽  
Two Phase ◽  
Vof Model ◽  
Mixing Chamber ◽  
Computational Fluid Dynamics Cfd

Mixing in RIM is made mainly by advective mechanisms, rather than diffusion. In this paper, the advective mechanisms that enable reducing the mixing scales down to the values required for the complete chemical reaction of the two monomers inside the RIM mixing chamber are identified and studied. From Computational Fluid Dynamics (CFD) simulations of non-diffusive two-phase flow using the Volume-of-Fluid (VOF) model, a linear scale of segregation is determined as a measure of the degree of mixing and the effect of the Reynolds number is studied.

Investigation of Characteristics of Gas-Liquid Two-Phase Flows in a Rectangular Microchannel With Return Bends

2011 ◽  
Author(s):  
Akimaro Kawahara ◽  
Michio Sadatomi ◽  
Hideki Matsuo ◽  
Satoshi Shimokawa
Keyword(s):  
Void Fraction ◽  
Scaling Law ◽  
Bubble Velocity ◽  
Liquid Slug ◽  
Two Phase Flows ◽  
Two Phase ◽  
Rectangular Microchannel ◽  
Drift Flux Model ◽  
Bubble Length ◽  
Length Data

Gas-liquid two-phase flows in a horizontal rectangular microchannel with return bends have been investigated. The width and the depth of the microchannel are 240 μm and 230 μm, respectively. T-junction type gas-liquid mixer was used to introduce gas and liquid in the channel. In order to know the effects of liquid properties, distilled water, pure ethanol, 49wt% ethanol aqueous solution and HFE7200 were used as the test liquids, while nitrogen gas as the test gas. The flow pattern, the bubble velocity, the bubble length and the liquid slug length were measured, and the void fraction was determined as the ratio of the gas superficial velocity to the bubble velocity. The bubble velocity at a downstream position from the bend is faster than that at an upstream position, and thus the void fraction is smaller at a downstream position. The bubble velocity data were well correlated with the well-known drift flux model with Kawahara et al.’s distribution parameter correlation. The bubble length data at the upstream and the downstream positions are also correlated with the scaling law proposed by Garstecki et al., irrespective of the test liquids. The liquid slug length data are correlated with an exponential function of the void fraction. The ratio of the bubble length to the bubble pitch is also well correlated with a linear function of the homogeneous void fraction.

Influence of Jordanian zeolite on the performance of a solar still: experiments and CFD simulation studies

2016 ◽  
Vol 16 (6) ◽  
pp. 1700-1709 ◽  
Author(s):  
Yazan Taamneh
Keyword(s):  
Experimental Data ◽  
Phase Change ◽  
Cfd Simulation ◽  
Volume Fraction ◽  
Solar Still ◽  
Cfd Simulations ◽  
Two Phase ◽  
Vof Model ◽  
Computational Fluid Dynamics Cfd ◽  
Good Agreement

Computational fluid dynamics (CFD) simulations were performed for experiments carried out with two identical pyramid-shaped solar stills. One was filled with Jordanian zeolite-seawater and the second was filled with seawater only. This work is focused on CFD analysis validation with experimental data conducted using a model of phase change interaction (evaporation-condensation model) inside the solar still. A volume-of-fluid (VOF) model was used to simulate the inter phase change through evaporation-condensation between zeolite-water and water vapor inside the two solar stills. The effect of the volume fraction of the zeolite particles (0 ≤ ϕ ≤ 0.05) on the heat and distillate yield inside the solar still was investigated. Based on the CFD simulation results, the hourly quantity of freshwater showed a good agreement with the corresponding experimental data. The present study has established the utility of using the VOF two phase flow model to provide a reasonable solution to the complicated inter phase mass transfer in a solar still.

PRESSURE DROP CHARACTERISTICS OF R410A-OIL MIXTURE FLOW BOILING IN SMALL SMOOTH TUBES

2010 ◽  
Vol 18 (02) ◽  
pp. 109-116 ◽  
Author(s):  
YIFENG GAO ◽  
BIN DENG ◽  
GUOLIANG DING ◽  
HAITAO HU ◽  
XIANGCHAO HUANG
Keyword(s):  
Pressure Drop ◽  
Flow Boiling ◽  
Smooth Tube ◽  
Two Phase ◽  
Experimental Conditions ◽  
Mixture Flow ◽  
Frictional Pressure Drop ◽  
New Correlation ◽  
Smooth Tubes ◽  
Local Properties

This study presents experimental frictional pressure drop for R410A/oil mixture flow boiling in small horizontal smooth tubes with inside diameters of 4.18 mm and 2.0 mm. Experimental conditions cover nominal oil concentrations from 0 to 5%. The test results show that the presence of oil enhances two-phase frictional pressure drop about 0–120% and 0–90% at present test conditions for 4.18 mm I.D. smooth tube and 2.0 mm I.D. smooth tube, respectively, and the enhanced effect is more evident at higher vapor qualities where the local oil concentrations are higher. A new correlation to predict the local frictional pressure drop of R410A/oil mixture flow boiling inside conventional size and small smooth tubes is developed based on local properties of refrigerant–oil mixture, and the experimental data of 4.18 mm I.D. and 2.0 mm I.D. smooth tubes and that of 6.34 mm I.D. smooth tube (Hu et al., 2008) are well-correlated with the new correlation.

Pressure Drop for Single- and Two-Phase Flows Through a Return Bend in Horizontal Rectangular Microchannel and Minichannel

2015 ◽  
Author(s):  
Akimaro Kawahara ◽  
Michio Sadatomi ◽  
Shinichi Miyagawa ◽  
Mohamed H. Mansour
Keyword(s):  
Pressure Drop ◽  
Pressure Loss ◽  
Single Phase ◽  
Distribution Data ◽  
Micro Channel ◽  
Two Phase Flows ◽  
Two Phase ◽  
Rectangular Microchannel ◽  
Frictional Pressure Drop ◽  
Mini Channels

In this paper, single-phase liquid and two-phase gas-liquid pressure drop data through 180° return bends have been obtained for horizontal rectangular micro-channel and mini-channel. To investigate the size effects of the test channels, the hydraulic diameters were 0.25 mm and 3 mm respectively as the micro-channel and the mini-channel. The curvature radii of the bends were 0.500 mm and 0.875 mm for the micro-channel, while 6 mm for the mini-channel. To know liquid properties effects, distilled water, surfactant and glycerin aqueous solutions, ethanol and HFE (hydrofluoroether)-7200 were used as the test liquid, while nitrogen gas and air as the test gas. Pressure distributions upstream and downstream tangents of the bend were measured for the single-phase and the two-phase flows. From the pressure distribution data, the bend pressure loss was determined. By analyzing the present data, the bend loss coefficient for single-phase flow in both micro- and mini-channels could be correlated with Dean number. On the other side, the total bend pressure loss for two-phase flows were correlated by using an approach of Padilla et al., in which the total pressure loss is the sum of two pressure drop components, i.e., frictional pressure drop and singular pressure drop. The approach was found to be applicable to the present data for the micro- and the mini-channels if the frictional pressure drop was calculated by Lockhart-Martinelli method with Mishima & Hibiki’s correlation and Kawahara et al.’s correlation and the singular pressure drop was calculated by a newly developed empirical correlation.

Pressure Drop of Taylor Flow in Capillaries: Impact of Slug Length

2003 ◽  
Author(s):  
Michiel T. Kreutzer ◽  
Wei Wei ◽  
Freek Kapteijn ◽  
Jacob A. Moulijn ◽  
Johan J. Heiszwolf
Keyword(s):  
Pressure Drop ◽  
Inlet Section ◽  
Liquid Slug ◽  
Two Phase ◽  
End Effects ◽  
Taylor Flow ◽  
Frictional Pressure Drop ◽  
Independent Variation ◽  
The Difference

In a single capillary, the frictional two-phase pressure drop in Taylor flow has been measured using various liquids, and a correlation to predict the friction factor has been developed. A carefully designed inlet section for the capillary allowed the independent variation of gas bubble and liquid slug length. Gas and liquid superficial velocities were varied in the range 0.04–0.3 m/s. If the slug length was lower than 10 times the capillary diameter, the frictional pressure drop in the liquid slug increased drastically from the single phase limit (f = 16/Re). The slug length dependence is caused by a larger contribution to the pressure drop of the end effects near the bubble caps. Increased pressure drop at the ends of the slug is caused by two separate effects: (1) near the bubbles the circulation inside the liquid slug induces extra friction, and (2) the difference in curvature of the gas-liquid interface at the front and at the rear of the bubble gives rise to extra pressure drop. The use of different liquids allowed the independent variation of the Reynolds number Re and the Capillary number Ca, and an expression for the frictional pressure drop as a function of Re, Ca and the slug length was developed. The results of this work allow the determination of slug length from pressure drop measurements in closed equipment where the slug length cannot otherwise be measured easily. The applicability of the pressure drop model to estimate mass transfer is demonstrated by combined pressure drop and gasliquid measurements in a monolith, which is essentially an array of capillary channels.

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