High Pressure Annular Two-Phase Flow in a Narrow Duct: Part II—Three-Field Modeling

2000 ◽  
Vol 122 (2) ◽  
pp. 375-384 ◽  
Author(s):  
Ranganathan Kumar ◽  
Thomas A. Trabold
Keyword(s):  
High Pressure ◽  
Void Fraction ◽  
Annular Flow ◽  
Predictive Capability ◽  
Two Phase ◽  
Modeling Approach ◽  
Field Modeling ◽  
Hot Film ◽  
Vertical Duct ◽  
Narrow Duct

This paper outlines the development of a three-field modeling approach in annular flow and the predictive capability of an analysis code. Models have been developed here or adapted from the literature for the thin film near the wall as well as the droplets in the vapor core, and have been locally applied in a fully developed, two-phase adiabatic boiling annular flow in a duct heated at the inlet at high pressure. Numerical results have been obtained using these models that are required for the closure of the continuity and momentum equations. The two-dimensional predictions are compared with local void fraction and droplet velocity (using a hot film anemometer), and average void fraction (using gamma densitometry) for a refrigerant fluid flowing in a narrow vertical duct with a cross-section aspect ratio of 22.5. Predicted results match the experimental data well for high void fraction annular flows, validating the overall modeling approach. [S0098-2202(00)01002-6]

Two-Phase Friction Factor Obtained From Various Void Fraction Models During Condensation of R134A in Vertical Downward Flow at High Mass Flux

2008 ◽  
Author(s):  
Ahmet Selim Dalkilic ◽  
Suriyan Laohalertdecha ◽  
Somchai Wongwises
Keyword(s):  
Void Fraction ◽  
Annular Flow ◽  
Smooth Tube ◽  
High Mass ◽  
Two Phase ◽  
Void Fractions ◽  
Mass Fluxes ◽  
Friction Factors ◽  
Flow Void ◽  
Fraction Models

Void fractions are determined in vertical downward annular two-phase flow of R134a inside 8.1 mm i.d. smooth tube. The experiments are done at average saturated condensing temperatures of 40 and 50°C. The average qualities are between 0.84–0.94. The mass fluxes are around 515 kg m−2s−1. The experimental setup is explained elaborately. Comparisons between the void fraction determined from 35 void fraction correlations are done. According to the use of various horizontal and vertical annular flow void fraction models together with the present experimental condensation heat transfer data, similar void fraction results were obtained mostly for the smooth tube. The experimental friction factors obtained from void fraction correlations are compared with the friction factors determined from graphical information provided by Bergelin et. al. Effect of void fraction alteration on the momentum pressure drop is also presented.

Flow Characteristics of Adiabatic Gas-Liquid Two-Phase Flow in a Horizontal Flat Rectangular Microchannel

2011 ◽  
Author(s):  
Hideo Ide ◽  
Kentaro Satonaka ◽  
Tohru Fukano
Keyword(s):  
Void Fraction ◽  
Slug Flow ◽  
Annular Flow ◽  
Two Phase Flow ◽  
Flow Characteristics ◽  
Flow Patterns ◽  
Phase Flow ◽  
Similar Data ◽  
Two Phase ◽  
The Mean

Experiments were performed to obtain, analyze and clarify the mean void fraction, the mean liquid holdup, and the liquid slug velocity and the air-water two-phase flow patterns in horizontal rectangular microchannels, with the dimensions equal to 1.0 mm width × 0.1 mm depth, and 1.0 mm width × 0.2 mm depth, respectively. The flow patterns such as bubble flow, slug flow and annular flow were observed. The microchannel data showed similar data patterns compared to those in minichannels with the width of 1∼10mm and the depth of 1mm which we had previously reported on. However, in a 1.0 × 0.1 mm microchannel, the mean holdup and the base film thickness in annular flow showed larger values because the effects of liquid viscosity and surface tension on the holdup and void fraction dominate. The remarkable flow characteristics of rivulet flow and the flow with a partial dry out of the channel inner wall were observed in slug flow and annular flow patterns in the microchannel of 0.1 mm depth.

scholarly journals CFD modelling of two-phase gas–liquid annular flow in terms of void fraction for vertical down- and up-ward flow

2019 ◽  
Vol 1 (11) ◽  
Author(s):  
A. Pinilla ◽  
E. Guerrero ◽  
D. H. Henao ◽  
D. V. Reyes ◽  
E. Pereyra ◽  
...  
Keyword(s):  
Void Fraction ◽  
Annular Flow ◽  
Cfd Modelling ◽  
Two Phase

Flow Pattern, Void Fraction and Pressure Drop During Adiabatic Two-Phase Gas-Liquid Flow in Vertical Micro-Channel

2012 ◽  
Author(s):  
Sira Saisorn ◽  
Somchai Wongwises
Keyword(s):  
Pressure Drop ◽  
Flow Pattern ◽  
Void Fraction ◽  
Test Section ◽  
Annular Flow ◽  
Fused Silica ◽  
Working Fluid ◽  
Micro Channel ◽  
Two Phase ◽  
Churn Flow

The experimental investigation is performed to study two-phase flow pattern, void fraction and pressure drop characteristics in a vertical micro-channel. The test section is a fused silica tube with a diameter of 0.53 mm and a length of 320 mm. Air and water are used as working fluid which is introduced to the test section in vertical upward direction. The test runs are done at superficial velocities of gas and liquid ranging respectively from 0.375 to 21.187 m/s and 0.004 to 2.436 m/s. Stereozoom microscope mounted together with camera are employed to conduct flow visualization from which slug flow, throat-annular flow, churn flow, annular flow and annular-rivulet flow are observed. Based on image analysis, void fraction data are obtained and found to be linear relationship with volumetric quality. The frictional pressure drop is relatively high when the formation of churn flow is established. Besides, the two-phase frictional multiplier is found to be strongly dependent on both mass flux and flow pattern.

Experimental Study of Dispersed Droplets in High-Pressure Annular Flows

1999 ◽  
Vol 121 (4) ◽  
pp. 924-933 ◽  
Author(s):  
T. A. Trabold ◽  
R. Kumar ◽  
P. F. Vassallo
Keyword(s):  
Void Fraction ◽  
High Pressures ◽  
Liquid Droplet ◽  
Droplet Velocity ◽  
Laser Doppler Velocimeter ◽  
Two Phase ◽  
R 134A ◽  
Gamma Densitometer ◽  
Density Ratios ◽  
Hot Film

Local measurements were made in a droplet-laden vapor core in upward R-134a annular flow in a high aspect ratio vertical duct. These detailed measurements are unique in that they were performed at high pressures and low liquid-to-vapor density ratios. Using a gamma densitometer, hot-film anemometer and laser Doppler velocimeter, profiles of void fraction, liquid droplet frequency, and droplet velocity were acquired across the narrow test section dimension. At relatively high flows, the measured void fraction was highest near the wall, due to the thinning of the liquid film. The dip in the void fraction in the vapor core at these flows suggests significant droplet entrainment. The entrainment fractions for these refrigerant flows fall in the range measured for pressurized steam-water systems. The average drop size, calculated from direct measurements of void fraction, droplet velocity, and frequency, compares favorably with previous experimental results from the literature. These data are useful for developing an improved understanding of practical two-phase flows, and for assessment of advanced two-fluid computer codes.

Bubble size and system pressure effects on the phase distribution for two-phase turbulent bubbly flows

2001 ◽  
Vol 215 (1) ◽  
pp. 121-132 ◽  
Author(s):  
T-C Kuo ◽  
A-S Yang ◽  
C-C Chieng
Keyword(s):  
High Pressure ◽  
Void Fraction ◽  
Bubble Size ◽  
Phase Distribution ◽  
Pressure Effects ◽  
Bubbly Flows ◽  
Two Phase ◽  
System Pressure ◽  
Transport Behaviour ◽  
Pressure Transport

The coupled Eulerian-Lagrangian approach was used to study the effects of bubble size and high-pressure transport behaviour on the phase distribution mechanisms in vertically upward air-water two-phase bubbly flows. The approach solves the conservation equations of liquid phase in Eulerian space and equations of motion in conjunction with the random walk method for dispersed air bubbles in Lagrangian space. Numerical calculations were performed under conditions of three bubble diameters (2.8, 4.0 and 5.0 mm) and two different pressure levels (0.1 and 7.17 MPa) to explore the flow and void fraction development phenomena. Simulation results indicate the tendency of higher slip ratios and the movement of the void fraction peak towards the flow core for larger gas bubbles. In the pressure range 0.1-7.17 MPa, predictions reveal that the effect of high-pressure transport behaviour on the phase distribution is insignificant.

Pressure Drop and Void Fraction in Steam-Water Two-Phase Flow at High Pressure

2013 ◽  
Vol 135 (8) ◽  
Author(s):  
Wei Liu ◽  
Hidesada Tamai ◽  
Kazuyuki Takase
Keyword(s):  
High Pressure ◽  
Pressure Drop ◽  
Void Fraction ◽  
Two Phase Flow ◽  
Water Pressure ◽  
Homogeneous Model ◽  
Test Fluid ◽  
Phase Flow ◽  
Two Phase ◽  
Drift Flux Model

For a steam generator (SG) in a commercialized sodium-cooled fast breeder reactor (FBR), flow instability in the water side is one of the most important items needing research. As the first step of this research, thermal-hydraulic experiments using water as the test fluid were performed under high pressure conditions at the Japan Atomic Energy Agency (JAEA) by using a circular tube. Void fraction, pressure drop, and heat transfer coefficient data were obtained under 15, 17, and 18 MPa. This paper discusses the steam-water pressure drop and void fraction. Using the obtained data, we evaluated existing correlations for void fraction and two-phase flow multipliers under high pressure. As a result, the drift flux model implemented in the TRAC-BF1 code was confirmed to suitably predict the void fraction well under the present high pressure conditions. For the two-phase flow multiplier, the Chisholm correlation and the homogeneous model were confirmed to be the best under the present high-pressure conditions.

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