On Acoustic Propagation and Critical Mass Flux in Two-Phase Flow

1971 ◽  
Vol 93 (4) ◽  
pp. 413-421 ◽  
Author(s):  
D. F. D’Arcy
Keyword(s):  
Void Fraction ◽  
Single Phase ◽  
Flow Model ◽  
Two Phase Flow ◽  
Separated Flow ◽  
Propagation Speed ◽  
Critical Flow ◽  
Phase Flow ◽  
Two Phase ◽  
Void Fractions

Theoretical values for the propagation speed of small pressure disturbances through two-phase fluid have been derived by a method analogous to the well-known method for single-phase fluids and using the well-known separated-flow model of two-phase flow. Since the liquid and vapor phases in general flow at different mean speeds, it is appropriate to compute the propagation speed relative to the laboratory frame of reference, not relative to the fluid as is usually done in single phase. With the extra degree of freedom in two-phase flow, two distinct speeds are found for propagation both upstream and downstream, each representing compatible thermodynamic behavior of both phases. Comparisons between calculations based on the model, and several published sets of experimental values of the speed of sound, tend to confirm the theory at low and at high void fractions. Both propagation speeds have been observed in experiments. Also by analogy with the single-phase case, critical flow is predicted to occur when the upstream propagation speed relative to the laboratory is zero, i.e., when pressure waves cannot travel into the opening from which the flow issues. Flow calculations based on the model under these conditions show agreement with published experimental critical-flow measurements in the regions of low and high void fractions. Thus, a satisfactory explanation of the critical-flow phenomenon in two-phase fluids is obtained in these regions. From the analytical–experimental comparisons it appears that of the two propagation speeds and critical flows, one is observed at low void fraction, and the other at high void fraction. In the intermediate range, the theory and experiment differ and it is probable that the separated-flow model does not adequately represent the flow regimes occurring in this range.

Damping and Hydrodynamic Mass of a Cylinder in Simulated Two-Phase Flow

1980 ◽  
Vol 102 (3) ◽  
pp. 597-602 ◽  
Author(s):  
L. N. Carlucci
Keyword(s):  
Flow Regime ◽  
Void Fraction ◽  
Single Phase ◽  
Two Phase Flow ◽  
Phase Flow ◽  
Single Phase Flow ◽  
Two Phase ◽  
Mixture Density ◽  
Void Fractions ◽  
Fixed Cylinder

This paper describes the results of experiments conducted to determine the damping and hydrodynamic mass characteristics of a fixed-fixed cylinder both in liquid and in simulated two-phase flows. It was observed that damping was significantly higher in two-phase flow than in single phase flow, and that, depending on the flow regime, it exhibited a maximum or maxima at void fractions of 30% to 60%. The hydrodynamic mass was observed to decrease with increasing void fraction but at a higher rate than that of the mixture density.

scholarly journals Experimental Investigation and Prediction on Pressure Drop during Flow Boiling in Horizontal Microchannels

Micromachines ◽  
2021 ◽  
Vol 12 (5) ◽  
pp. 510
Author(s):  
Yan Huang ◽  
Bifen Shu ◽  
Shengnan Zhou ◽  
Qi Shi
Keyword(s):  
Pressure Drop ◽  
Flow Model ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Separated Flow ◽  
Heat Fluxes ◽  
Phase Flow ◽  
Vapor Quality ◽  
Two Phase ◽  
Gas Flux

In this paper, two-phase pressure drop data were obtained for boiling in horizontal rectangular microchannels with a hydraulic diameter of 0.55 mm for R-134a over mass velocities from 790 to 1122, heat fluxes from 0 to 31.08 kW/m2 and vapor qualities from 0 to 0.25. The experimental results show that the Chisholm parameter in the separated flow model relies heavily on the vapor quality, especially in the low vapor quality region (from 0 to 0.1), where the two-phase flow pattern is mainly bubbly and slug flow. Then, the measured pressure drop data are compared with those from six separated flow models. Based on the comparison result, the superficial gas flux is introduced in this paper to consider the comprehensive influence of mass velocity and vapor quality on two-phase flow pressure drop, and a new equation for the Chisholm parameter in the separated flow model is proposed as a function of the superficial gas flux . The mean absolute error (MAE ) of the new flow correlation is 16.82%, which is significantly lower than the other correlations. Moreover, the applicability of the new expression has been verified by the experimental data in other literatures.

Two-Phase Flow Through Square and Circular Microchannels—Effects of Channel Geometry

2004 ◽  
Vol 126 (4) ◽  
pp. 546-552 ◽  
Author(s):  
Peter M.-Y. Chung ◽  
Masahiro Kawaji ◽  
Akimaro Kawahara ◽  
Yuichi Shibata
Keyword(s):  
Pressure Drop ◽  
Void Fraction ◽  
Two Phase Flow ◽  
Flow Characteristics ◽  
Separated Flow ◽  
Phase Flow ◽  
Two Phase ◽  
Channel Geometry ◽  
Frictional Pressure Drop ◽  
Channel Shape

An adiabatic experiment was conducted to investigate the effect of channel geometry on gas-liquid two-phase flow characteristics in horizontal microchannels. A water-nitrogen gas mixture was pumped through a 96 μm square microchannel and the resulting flow pattern, void fraction and frictional pressure drop data were compared with those previously reported by the authors for a 100 μm circular microchannel. The pressure drop data were best estimated using a separated-flow model and the void fraction increased non-linearly with volumetric quality, regardless of the channel shape. However, the flow maps exhibited transition boundaries that were shifted depending on the channel shape.

Estimation of Average Void Fraction for Gas-Liquid, Two-Phase Flow in an Industrial Nozzle Assembly Using a Quick-Closing-Valve

2008 ◽  
Author(s):  
Mohammad A. Rahman ◽  
Johana Gomez ◽  
Ted Heidrick ◽  
Brian A. Fleck ◽  
Jennifer McMillan
Keyword(s):  
Void Fraction ◽  
High Speed ◽  
Two Phase Flow ◽  
Video Camera ◽  
Synchronization Error ◽  
Phase Flow ◽  
Closing Time ◽  
Two Phase ◽  
Void Fractions ◽  
Atomization Performance

Experimentally accurate void fraction measurements are a challenge in an air/water, two-phase flows through an industrial nozzle assembly, as a highly non-uniform void fraction exists in the feeding conduit prior to the nozzle. In this study, average void fractions were measured by isolating a section in the feeding conduit of a horizontal nozzle assembly, termed as the quick-closing-valve (QCV) technique. A high-speed video camera was utilized to capture the asynchronization closing time, tac. The average closing time and asynchronization for the pneumatically controlled valves were 200 ms and 2 ms, respectively. Based on the equation of 100umtac (1−α)/αlc, the synchronization error between the two valves was 1.12%, 1.26%, and 1.79% for the 1%, 2% and 4% ALR cases, respectively; here um is the mixture velocity, α is the void faction, and lc is the closing length. Higher synchronization error at 4% ALR occurs due to enhanced momentum in the flow regime. Experimental results indicate that the average α over the 33.4 cm feeding conduit (6.25 mm ID) was 76% (αtheoretical = 75%) for the 2% ALR, and 85% (αtheoretical = 83%) for the 3.3% ALR. In the two-phase, two-component flow the α affects the drop size and stability of the spray produced from an industrial nozzle assembly. Learning from this study will yield insights and conceptual understanding of two-phase flow phenomena in conduit, which would affect stability, pulsation tendency, and possibly atomization performance of the nozzle downstream. Two-phase flow nozzles have wide applications in the industries, e.g. petrochemical, pharmaceutical, and others.

Towards Understanding Two-Phase Flow Induced Vibration of Piping Structure With a U-Bend

2019 ◽  
Author(s):  
Olufemi E. Bamidele ◽  
Wael H. Ahmed ◽  
Marwan Hassan
Keyword(s):  
Void Fraction ◽  
Vibration Amplitude ◽  
Two Phase Flow ◽  
Bubbly Flow ◽  
Phase Flow ◽  
Flow Conditions ◽  
Flow Induced Vibration ◽  
Two Phase ◽  
Void Fractions ◽  
Flow Induced Vibrations

Abstract The current work investigates two-phase flow induced vibrations in 90° U-bend. The two-phase induced vibration of the structure was investigated in the vertical, horizontal and axial directions for various flow patterns from bubbly flow to wavy and annular-dispersed flow. The void fractions at various locations along the piping including the fully developed void fraction and the void fraction at the entrance of the U-bend were fully investigated and correlated with the vibration amplitude. The results show that the excitation forces of the two-phase flow in a piping structure are highly dependent on the flow pattern and the flow conditions upstream of the bend. The fully developed void fraction and slip between phases are important in modelling of forces in U-bends and elbows.

Development of Sodium Two-Phase Flow Model for KALIMER Core Analysis

2002 ◽  
Author(s):  
W. P. Chang ◽  
Dohee Hahn
Keyword(s):  
Liquid Metal ◽  
Single Phase ◽  
System Analysis ◽  
Flow Model ◽  
Two Phase Flow ◽  
Water System ◽  
Phase Flow ◽  
Two Phase ◽  
Applicable Range ◽  
Further Development

An algorithm for sodium boiling is developed in order to extend the applicability of SSC-K, which is a main system analysis code for the KALIMER (Korea Advanced LIquid MEtal Reactor) conceptual design. As the capability of the current SSC-K version is limited to simulation of only a single-phase sodium flow, its applicable range should not be enough to assess the fuel integrity under some of HCDA (Hypothetical Core Disruptive Accident) initiating events where sodium boiling is anticipated. The two-phase flow model similar to that used for the light water system is known to be no more effective directly to liquid metal reactors, because the phenomena observed between two reactor coolant systems are definitely different. The developing algorithm is based on a multiple-bubble slug ejection model, which allows a finite number of bubbles in a channel at any time. The present work is a continuous effort following the former study to confirm a qualitative acceptance on the model. Since the model has been applied only to the active fuel region in the former study, a part of its qualification seems to have already been demonstrated. For its application to the whole KALIMER core channel, however, the model needs to be examined the applicability to the fuel regions other than the active fuel. The present study primarily focuses on that point. In a result, although the model may be improved in a sense through the present study over the previous modeling, a clear limitation is also confirmed with the validity of the model. The further development, therefore, is required for this model to achieve its goal by resolving such limitations.

Correlation between Void Fraction and Two-Phase Flow Pattern Air-Water with Low Viscosity in Mini Channel with Slope 30 Degrees

2020 ◽  
Vol 846 ◽  
pp. 289-295
Author(s):  
Sukamta ◽  
Sudarja
Keyword(s):  
Void Fraction ◽  
High Speed ◽  
Two Phase Flow ◽  
Fluid Velocity ◽  
Flow Patterns ◽  
Superficial Velocity ◽  
Working Fluid ◽  
Phase Flow ◽  
Two Phase ◽  
Void Fractions

Two-phase flow has been used in so many industrial processes, such as boilers, reactors, heat exchangers, geothermal and others. Some parameters which need to be studied include flow patterns, void fractions, and pressure changes. Research on void fractions aims to determine the composition of the gas and liquid phases that will affect the nature and value of the flow property. The purpose of this study is to find out the characteristics of the void fraction of various patterns that occurs and to determine the characteristics of the velocity, length, and frequency of bubbly and plug. Data acquisition was used to convert the data from analog to digital so that it can be recorded, stored, processed, and analyzed. High-speed camera Nikon type J4 was used to record the flow. The condition of the study was adiabatic with variation of superficial gas velocity (JG), superficial fluid velocity (JL), and also working fluid. To determine the void fraction by using the digital image processing method. The results of the study found that the flow patterns which occurred in this study were bubbly, plug, annular, slug-annular and churn flows. It also showed that the void fraction value is determined by the superficial velocity of the liquid and air. The higher the superficial velocity of the air, the lower the void fraction value.

Vibration Behavior of Rotated Triangular Tube Bundles in Two-Phase Cross Flows

2002 ◽  
Vol 124 (2) ◽  
pp. 144-153 ◽  
Author(s):  
M. J. Pettigrew ◽  
C. E. Taylor ◽  
V. P. Janzen ◽  
T. Whan
Keyword(s):  
Void Fraction ◽  
Two Phase Flow ◽  
Flow Regimes ◽  
Intermittent Flow ◽  
Phase Flow ◽  
Two Phase ◽  
Vibration Behavior ◽  
Void Fractions ◽  
Tube Bundles ◽  
Fluidelastic Instability

The results of a series of tests describing the vibration behavior of several rotated triangular tube bundles subjected to two-phase cross flows are presented. Tube bundles with a pitch-to-diameter ratio of approximately 1.5 were tested over a broad range of void fractions and mass fluxes. Fluidelastic instability, random turbulence excitation, hydrodynamic mass, two-phase damping and local void-fraction were investigated. Well-defined fluidelastic instabilities were observed in continuous two-phase flow regimes. However, intermittent two-phase flow regimes had a dramatic effect on fluidelastic instability leading to lower than expected threshold flow velocities for instability. This effect was more pronounced in Freon two-phase flow than in air-water, and appeared well correlated to the transition between continuous and intermittent flow regimes. Generally, random turbulence excitation forces were much lower in Freon than in air-water. Although very dependent on void fraction, as expected, damping was quite similar in air-water and Freon.

Hydrodynamics of Two-Phase Flow Across Horizontal In-line and Staggered Rod Bundles

1992 ◽  
Vol 114 (3) ◽  
pp. 450-456 ◽  
Author(s):  
R. Dowlati ◽  
A. M. C. Chan ◽  
M. Kawaji
Keyword(s):  
Pressure Drop ◽  
Void Fraction ◽  
Flow Model ◽  
Two Phase Flow ◽  
Phase Flow ◽  
Gas Velocity ◽  
Rod Bundles ◽  
Two Phase ◽  
Friction Pressure Drop ◽  
Velocity Effect

The void fraction and friction pressure drop measurements have been made for vertical two-phase flow of air-water across staggered and in-line rod bundles with different pitch-to-diameter ratios. All void fraction data showed a strong mass velocity effect and were significantly less than the values predicted by a homogeneous flow model, but were well correlated using the dimensionless gas velocity, jg*. The two-phase friction multiplier data could be well correlated with the Martinelli parameter for G > 200 kg/m2s. The correlations developed for void fraction and two-phase friction multiplier were successfully tested in predicting the total pressure drop in boiling R-113 experiments.

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