scholarly journals CFD Modeling of Wall Steam Condensation: Two-Phase Flow Approach versus Homogeneous Flow Approach

2011 ◽  
Vol 2011 ◽  
pp. 1-10 ◽  
Author(s):  
S. Mimouni ◽  
N. Mechitoua ◽  
A. Foissac ◽  
M. Hassanaly ◽  
M. Ouraou
Keyword(s):  
Experimental Data ◽  
Liquid Film ◽  
Dominant Role ◽  
Droplet Diameter ◽  
Homogeneous Model ◽  
Surface Tension Force ◽  
Vapor Condensation ◽  
Cfd Modeling ◽  
Two Phase ◽  
Gravitational Forces

The present work is focused on the condensation heat transfer that plays a dominant role in many accident scenarios postulated to occur in the containment of nuclear reactors. The study compares a general multiphase approach implemented in NEPTUNE_CFD with a homogeneous model, of widespread use for engineering studies, implemented inCode_Saturne. The model implemented in NEPTUNE_CFD assumes that liquid droplets form along the wall within nucleation sites. Vapor condensation on droplets makes them grow. Once the droplet diameter reaches a critical value, gravitational forces compensate surface tension force and then droplets slide over the wall and form a liquid film. This approach allows taking into account simultaneously the mechanical drift between the droplet and the gas, the heat and mass transfer on droplets in the core of the flow and the condensation/evaporation phenomena on the walls. As concern the homogeneous approach, the motion of the liquid film due to the gravitational forces is neglected, as well as the volume occupied by the liquid. Both condensation models and compressible procedures are validated and compared to experimental data provided by the TOSQAN ISP47 experiment (IRSN Saclay). Computational results compare favorably with experimental data, particularly for the Helium and steam volume fractions.

scholarly journals CFD modeling of liquid film reversal of two-phase flow in vertical pipes

2019 ◽  
Vol 9 (4) ◽  
pp. 3039-3070
Author(s):  
Mohamed M. Hussein ◽  
A. Al-Sarkhi ◽  
H. M. Badr ◽  
M. A. Habib
Keyword(s):  
Liquid Film ◽  
Two Phase Flow ◽  
Cfd Modeling ◽  
Phase Flow ◽  
Two Phase

Computational Fluid Dynamics Modeling of Gas–Liquid Cylindrical Cyclones, Geometrical Analysis

2018 ◽  
Vol 140 (9) ◽  
Author(s):  
Juan Carlos Berrio ◽  
Eduardo Pereyra ◽  
Nicolas Ratkovich
Keyword(s):  
Fluid Dynamics ◽  
Experimental Data ◽  
Computational Fluid Dynamics ◽  
Cfd Modeling ◽  
Nozzle Geometry ◽  
Geometrical Parameters ◽  
Experimental Setup ◽  
Dynamics Modeling ◽  
Two Phase ◽  
Mean Square Errors

The gas–liquid cylindrical cyclone (GLCC) is a widely used alternative for gas–liquid conventional separation. Besides its maturity, the effect of some geometrical parameters over its performance is not fully understood. The main objective of this study is to use computational fluid dynamics (CFD) modeling in order to evaluate the effect of geometrical modifications in the reduction of liquid carry over (LCO) and gas carry under (GCU). Simulations for two-phase flow were carried out under zero net liquid flow, and the average liquid holdup was compared with Kanshio (Kanshio, S., 2015, “Multiphase Flow in Pipe Cyclonic Separator,” Ph.D. thesis, Cranfield University, Cranfield, UK) obtaining root-mean-square errors around 13% between CFD and experimental data. An experimental setup, in which LCO data were acquired, was built in order to validate a CFD model that includes both phases entering to the GLCC. An average discrepancy below 6% was obtained by comparing simulations with experimental data. Once the model was validated, five geometrical variables were tested with CFD. The considered variables correspond to the inlet configuration (location and inclination angle), the effect of dual inlet, and nozzle geometry (diameter and area reduction). Based on the results, the best configuration corresponds to an angle of 27 deg, inlet location 10 cm above the center, a dual inlet with 20 cm of spacing between both legs, a nozzle of 3.5 cm of diameter, and a volute inlet of 15% of pipe area. The combination of these options in the same geometry reduced LCO by 98% with respect to the original case of the experimental setup. Finally, the swirling decay was studied with CFD showing that liquid has a greater impact than the gas flowrate.

scholarly journals Experimental and theoretical study of dryout in annular flow in small diameter channels

2011 ◽  
Vol 32 (1) ◽  
pp. 89-108 ◽  
Author(s):  
Dariusz Mikielewicz ◽  
Michał Gliński ◽  
Jan Wajs
Keyword(s):  
Experimental Data ◽  
Liquid Film ◽  
Annular Flow ◽  
Theoretical Study ◽  
Small Diameter ◽  
Infrared Camera ◽  
Equation Model ◽  
Internal Diameter ◽  
Two Phase ◽  
Liquid Film Dryout

Experimental and theoretical study of dryout in annular flow in small diameter channels In the paper the experimental analysis of dryout in small diameter channels is presented. The investigations were carried out in vertical pipes of internal diameter equal to 1.15 mm and 2.3 mm. Low-boiling point fluids such as SES36 and R123 were examined. The modern experimental techniques were applied to record liquid film dryout on the wall, among the others the infrared camera. On the basis of experimental data an empirical correlation for predictions of critical heat flux was proposed. It shows a good agreement with experimental data within the error band of 30%. Additionally, a unique approach to liquid film dryout modeling in annular flow was presented. It led to the development of the three-equation model based on consideration of liquid mass balance in the film, a two-phase mixture in the core and gas. The results of experimental validation of the model exhibit improvement in comparison to other models from literature.

CFD Modeling of Two-Phase Gas-Liquid Slug Flow Using VOF Method in Microchannels

2009 ◽  
Author(s):  
A. Mehdizadeh ◽  
S. A. Sherif ◽  
W. E. Lear
Keyword(s):  
Numerical Simulation ◽  
Liquid Film ◽  
Slug Flow ◽  
Thin Liquid Film ◽  
Liquid Films ◽  
Vof Method ◽  
Cfd Modeling ◽  
Two Phase ◽  
Mesh Resolution ◽  
Gas Volume

Despite of the fact that numerical simulation of two-phase flows in microchannels has been attempted by many investigators, most efforts seem to have failed in correctly capturing the flow physics, especially the slug flow regime characteristics. The presence of a thin liquid film in the order of 10 μm around the bubble (sometimes called gas pocket or gas slug) may be a contributing factor to the above difficulty. Typically, liquid films have a significant effect on the flow field. Thus, there is a strong motivation to employ numerical simulation methods in order to avoid some of the experimental difficulties. In this paper, the characteristics of two-phase slug flows in microchannels are calculated with the help of the Volume-of-Fluid (VOF) method. Formation of the slugs for different superficial velocities, Capillary numbers, and gas volume fractions are investigated. The minimum mesh resolution required to capture the liquid film surrounding the gas bubble is reported employing a dynamic mesh adaption methodology with interface tracking. Results are shown to be in good agreement with experimental data and empirical correlations.

Distributions of Pressure, Velocity, and Void Fraction for One-Dimensional Gas-Liquid Bubbly Flow in Horizontal Pipes

2008 ◽  
Vol 130 (9) ◽  
Author(s):  
Phu D. Tran
Keyword(s):  
Experimental Data ◽  
Void Fraction ◽  
Bubbly Flow ◽  
Homogeneous Model ◽  
Two Phase ◽  
Mixture Flow ◽  
Horizontal Pipe ◽  
Horizontal Pipes ◽  
Pressure Distributions ◽  
Flow Variables

A homogeneous model for prediction of the longitudinal distributions of pressure, velocity, and void fraction for two-phase bubbly flow in horizontal pipes is presented. The mixture flow is described by a system of two nondimensional ordinary differential equations that can be integrated numerically to yield the distributions of the flow variables along the pipe. The viscosity of the two-phase mixture is assumed to vary with the void fraction according to a polynomial form. Experimental data were obtained for a range of air-water bubbly flow in a horizontal pipe. Prediction of pressure distributions along the pipe compares favorably with experimental data, while prediction of void fraction distributions can be achieved with moderate accuracy.

Hydrodynamics and Mass Transfer Simulation in Airlift Bioreactor with Settler using Computational Fluid Dynamics

2017 ◽  
Vol 15 (4) ◽  
Author(s):  
Oscar M. Hernández-Calderón ◽  
Marcos D. González-Llanes ◽  
Erika Y. Rios-Iribe ◽  
Sergio A. Jiménez-Lam ◽  
Ma.del Carmen Chavez-Parga ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Experimental Data ◽  
Mass Transfer ◽  
Computational Fluid Dynamics ◽  
Liquid Velocity ◽  
Fluid Dynamic ◽  
Gas Holdup ◽  
Airlift Bioreactor ◽  
Cfd Modeling ◽  
Two Phase

Abstract In this work, the effect of inlet-gas superficial velocity over the circulation liquid velocity, gas holdup and mass transfer, from an airlift bioreactor with settler were studied by Computational Fluid Dynamics (CFD) modeling and contrasted with experimental results. Multiphase mixture model and κ-ε turbulence model were used to describe the two phases gas-liquid flow pattern in airlift bioreactor. The hydrodynamic parameters such as liquid circulation velocity and gas holdup were computed by solving the governing equations of continuity, moment and turbulence transport using the finite volume method. Global mass transfer coefficient was evaluated through the Higbie’s penetration theory and the two-phase fluid dynamic theory. Comparison between our numerical data and experimental data previously reported in the literature was done. Numerical and experimental data were very close, and the differences found were discussed in terms of the limitations of this study.

Analysis of Cavitating High Speed Liquid Flow Through a Converging-Diverging Nozzle

2015 ◽  
Author(s):  
William E. Asher ◽  
Steven J. Eckels
Keyword(s):  
Experimental Data ◽  
High Speed ◽  
Power Plants ◽  
Control Volume ◽  
Homogeneous Model ◽  
Cavitating Flow ◽  
Shear Stresses ◽  
Variable Cross ◽  
Two Phase ◽  
Integral Forms

Cavitation is an important and common phenomena in fluid flow in which a fluid becomes two-phase through pressure variation. In devices such as valves, orifices, and metering devices, as well as loss of coolant situations in power plants, cavitation can be of interest due to erosion, energy efficiency, safety, and other concerns. It is possible for a cavitating flow to become sonic, accelerating and imposing additional energy losses that would not have occurred had the flow remained below the speed of sound. Models of this aspect of two-phase flow have not been fully explored and often have only been developed for the case of constant area. In the present paper, the homogeneous equilibrium model is developed by applying the integral forms of the conservation of mass, momentum, and energy equations to a control volume of variable cross-sectional area with adiabatic walls. The developed model is then applied to experimental data with R-134a as the fluid of interest for an instrumented converging-diverging nozzle for which mass flow, pressure, and temperature are measured. Applying the model to the experimental data yields interesting results in both the relationship between velocity and void fraction and in the predicted shear stresses down the length of the nozzle. The model predicts negative shear stresses near the nozzle’s throat an order of magnitude higher than those seen elsewhere in the nozzle. For this reason, the homogeneous model is likely not sufficient to accurately describe this variant of cavitating flow.

scholarly journals Experimental Investigation of Acoustic Atomization in Liquid Loading Horizontal Gas Wells

2021 ◽  
Author(s):  
Eiman Al Munif ◽  
Jennifer Miskimins
Keyword(s):  
Experimental Data ◽  
Liquid Film ◽  
Test Section ◽  
Positive Impact ◽  
Water Injection ◽  
Acoustic Properties ◽  
Flow Loop ◽  
Gas Wells ◽  
Two Phase ◽  
Artificial Lift

Abstract Enhancing the production in liquid-loaded horizontal natural gas wells using an acoustic liquid atomizer tool is proposed as a possible artificial lift method. The more liquid that is converted to droplets, the more available gas is able to carry the liquid to the surface, resulting in an increase in production. The acoustic atomizer was selected to be the atomization device as it can create very small droplets at certain frequencies leading to a mist flow. The contribution of this research includes obtaining experimental data using different laboratory procedures for horizontal and slightly inclined tubulars. Two-phase (gas and water) injection stream lines are joined to the test section to introduce gas and water at desired rates. An ultrasonic atomizer inside the test section is used to better understand the atomization mechanism as an artificial lift technique. Several experiments with varying factors influencing the acoustic properties are tested including varying liquid and gas rates, four different frequencies, two different flow pipe inclination angles, and two different acoustic device orientations. The results show that when using frequencies of 62 and 62.5 kHz, the outcomes were almost identical for horizontal and slightly inclined pipe. Both frequencies reduced liquid film accumulation by 1% at lower (0.001 m/s) and higher (0.0168 m/s) liquid velocities while gas velocity was kept at 14 m/s. The performance of the acoustic tool was highly dependent on the orientation of the tool inside the flow loop due to its atomizer geometry, shape and size. Sprayers facing up (0°, original case) helped the droplets to be carried by the gas since the gas occupies the top portion of the pipe and did not block the atomizer. The sprayers failed to work while facing the bottom of the pipe (180°) due to water accumulating around the sprayers, plugging the atomizer and hindering it from working. Using an orientation of 90° (sprayers facing sideways) provided better results and positive impact in reducing the liquid film level. The efficiency of the tool decreases in slightly inclined wells. As more liquid quantity accumulated in the well, the atomization technique seems to be slow in reducing the liquid film height. This research presents a set of diverse experimental data to suggest acoustic atomization might be used as a possible artificial lift technique in horizontal wells. The technique shows a 1-4% improvement which might be experimental error or in experimental control. Thus, the device used in the lab needs improvement to work as efficiently as other artificial lift techniques to possibly enhance production.

Two Phase Flow CFD Modeling of a Steam Turbine Low Pressure Section: Comparison With Data and Correlations

2021 ◽  
Author(s):  
Nicola Maceli ◽  
Lorenzo Arcangeli ◽  
Andrea Arnone
Keyword(s):  
Experimental Data ◽  
Steam Turbine ◽  
Low Pressure ◽  
Performance Model ◽  
Operating Conditions ◽  
Cfd Modeling ◽  
Steam Turbines ◽  
Two Phase ◽  
Scaled Model ◽  
Application Range

Abstract Testing a sub-component or testing a scaled model are the approaches currently used to reduce the development cost of the new low-pressure (LP) section of a steam turbine. In any case, testing campaigns are run at a limited number of operating conditions. Therefore, some correlations are used to build a performance model of the LP module and expand the usage of a limited set of experimental data to cover the application range encountered in the steam turbine market. Another approach, which has become feasible during the last decade, is the usage of CFD calculations. These two approaches include a certain amount of uncertainty in the performance of the LP section, mainly related to the losses caused by the moisture content in the flow. In the present paper, the results of the analysis of a cutting-edge low-pressure section for small steam turbines are presented. The results are obtained by using a CFD commercial code with a set of user defined subroutines to model the effects of droplets nucleation and growth. Different operating conditions are considered, with different wetness at the exit and different pressure ratios, in order to clearly show the loss trend for different levels of exit moisture. The numerical results are compared with the experimental data, showing a significant improvement in the performance predictability for the considered case and demonstrating the benefit of using a CFD approach instead of using existing correlations.

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