Effect of Flow Regime and Void Fraction on Tube Bundle Vibration

2001 ◽  
Vol 123 (4) ◽  
pp. 407-413 ◽  
Author(s):  
C. E. Taylor ◽  
M. J. Pettigrew
Keyword(s):  
Heat Exchanger ◽  
Flow Regime ◽  
Void Fraction ◽  
Flow Regimes ◽  
Design Guidelines ◽  
Two Phase ◽  
Fluid Forces ◽  
Drift Flux Model ◽  
Test Loop ◽  
Fraction Models

Two-phase cross flow occurs in industrial heat exchangers such as condensers, boilers, and steam generators. Under certain flow regimes and fluid velocities, the fluid forces result in tube vibration and possibly tube damage due to fretting or fatigue. Prediction of these fluid forces requires an understanding of the flow regimes found in heat exchanger tube bundles. Measurements of void fraction within a tube array were taken as an initial step in determining the two-phase flow patterns. The tests were conducted in a Freon 134a test loop at about 1 MPa and 30°C. The measurements were compared against void fraction models commonly used in heat exchanger thermalhydraulic simulation codes and against available flow regime maps. Not surprisingly, the results indicate that a drift-flux model more accurately predicts the void fraction within a tube array. The measurements also confirm the existence of nonuniform void fraction radially around the tube. Based on these measurements and available literature, appropriate void fraction models for use in flow-induced vibration design guidelines are discussed.

scholarly journals Application of Wavelet Feature Extraction and Artificial Neural Networks for Improving the Performance of Gas–Liquid Two-Phase Flow Meters Used in Oil and Petrochemical Industries

Polymers ◽  
2021 ◽  
Vol 13 (21) ◽  
pp. 3647
Author(s):  
Siavash Hosseini ◽  
Osman Taylan ◽  
Mona Abusurrah ◽  
Thangarajah Akilan ◽  
Ehsan Nazemi ◽  
...  
Keyword(s):  
Feature Extraction ◽  
Wavelet Transform ◽  
Flow Regime ◽  
Void Fraction ◽  
Low Frequency ◽  
Flow Regimes ◽  
Discrete Wavelet ◽  
Two Phase ◽  
Flow Meters ◽  
Petrochemical Industries

Measuring fluid characteristics is of high importance in various industries such as the polymer, petroleum, and petrochemical industries, etc. Flow regime classification and void fraction measurement are essential for predicting the performance of many systems. The efficiency of multiphase flow meters strongly depends on the flow parameters. In this study, MCNP (Monte Carlo N-Particle) code was employed to simulate annular, stratified, and homogeneous regimes. In this approach, two detectors (NaI) were utilized to detect the emitted photons from a cesium-137 source. The registered signals of both detectors were decomposed using a discrete wavelet transform (DWT). Following this, the low-frequency (approximation) and high-frequency (detail) components of the signals were calculated. Finally, various features of the approximation signals were extracted, using the average value, kurtosis, standard deviation (STD), and root mean square (RMS). The extracted features were thoroughly analyzed to find those features which could classify the flow regimes and be utilized as the inputs to a network for improving the efficiency of flow meters. Two different networks were implemented for flow regime classification and void fraction prediction. In the current study, using the wavelet transform and feature extraction approach, the considered flow regimes were classified correctly, and the void fraction percentages were calculated with a mean relative error (MRE) of 0.4%. Although the system presented in this study is proposed for measuring the characteristics of petroleum fluids, it can be easily used for other types of fluids such as polymeric fluids.

Measurement of Void Fraction and Pressure Drop of Air-Oil Two-Phase Flow in Horizontal Pipes

2004 ◽  
Vol 126 (1) ◽  
pp. 107-118 ◽  
Author(s):  
J. L. Pawloski ◽  
C. Y. Ching ◽  
M. Shoukri
Keyword(s):  
Pressure Drop ◽  
Flow Regime ◽  
Void Fraction ◽  
High Speed ◽  
Two Phase Flow ◽  
Flow Regimes ◽  
Phase Flow ◽  
Two Phase ◽  
Wide Range ◽  
Flow Regime Maps

The void fractions, flow regimes, and pressure drop of air-oil two-phase flow in a half-inch diameter pipe over a wide range of test conditions have been investigated. The flow regimes were identified with the aid of a 1000 frames per second high-speed camera. A capacitance sensor for instantaneous void fraction measurements was developed. The mean and probability density function of the instantaneous void fraction signal can be used to effectively identify the different flow regimes. The current flow regime data show significant differences in the transitional boundaries of the existing flow regime maps. Property correction factors for the flow regime maps are recommended. The pressure drop measurements were compared to the predictions from four existing two-phase flow pressure drop models. Though some of the models performed better for certain flow regimes, none of the models were found to give accurate results over the entire range of flow regimes.

Flow-Induced Void Fraction Transition Phenomenon in Two-Phase Flow

2010 ◽  
Author(s):  
Xiuzhong Shen ◽  
Kaichiro Mishima ◽  
Hideo Nakamura
Keyword(s):  
Void Fraction ◽  
Two Phase Flow ◽  
Flow Direction ◽  
Flow Regimes ◽  
Phase Flow ◽  
Vertical Pipe ◽  
Two Phase ◽  
Transition Phenomenon ◽  
Drift Flux Model ◽  
Slug Flows

The flow-induced void fraction transition phenomenon was observed in an upward air-water two-phase flow in a vertical pipe with inner diameter D = 200 mm and height z = 25 m. As the two-phase flow develops in a vertical pipe, the void fraction increases firstly in the flow direction in bubbly flow, then decreases in the flow direction, finally increase again. The flow-induced void fraction transition shows an N-shaped changing manner. The present experimental investigation revealed that this phenomenon was attributed to the formation and the growth of local dominant large bubbles in the flow. According to the bubble sizes and behaviors observed in the experiment, the flow regimes were classified into bubbly, churn and slug flows in a vertical large-diameter pipe. The drift velocities in the three flow regimes were measured in this paper. New constitutive equation for drift velocities in bubbly, churn and slug flows was proposed and confirmed in this study. The flow-induced void fraction transition in N-shaped manner can be predicted by using the drift flux model with the newly developed constitutive equations.

Measurement of Void Fraction and Pressure Drop of Air-Oil Two-Phase Flow in Horizontal Pipes

2002 ◽  
Author(s):  
J. Pawloski ◽  
C. Ching ◽  
M. Shoukri
Keyword(s):  
Pressure Drop ◽  
Flow Regime ◽  
Void Fraction ◽  
High Speed ◽  
Two Phase Flow ◽  
Flow Regimes ◽  
Average Error ◽  
Phase Flow ◽  
Two Phase ◽  
Wide Range

The flow regimes and pressure drop of air-oil two-phase flow in a half-inch diameter pipe over a wide range of test conditions have been investigated. The flow regimes were identified with the aid of a 1000 frames per second high-speed camera. The current flow regime data show significant differences in the transitional boundaries from the flow regime maps of Mandhane et al. (1974), Taitel and Dukler (1974) and Spedding and Nguyen (1980). The pressure drop measurements were compared to the predictions from four existing pressure drop models: Homogeneous, Martinelli (1948), Chisolm (1973) and Olujic (1985). The Chisolm and Martinelli models were found to be the most accurate, with an average error of about 35 percent. A capacitance sensor for instantaneous void fraction measurement was developed. Results indicate the data from the sensor could be used to identify the different flow regimes.

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.

Countercurrent Two-Phase Flow Regimes and Void Fraction in Vertical and Inclined Channels

1995 ◽  
Vol 119 (3) ◽  
pp. 182-194 ◽  
Author(s):  
S. M. Ghiaasiaan ◽  
K. E. Taylor ◽  
B. K. Kamboj ◽  
S. I. Abdel-Khalik
Keyword(s):  
Void Fraction ◽  
Two Phase Flow ◽  
Flow Regimes ◽  
Phase Flow ◽  
Two Phase ◽  
Inclined Channels

scholarly journals On Damping and Fluidelastic Instability in a Tube Bundle Subjected to Two-Phase Cross-Flow

2007 ◽  
Author(s):  
Joaquin E. Moran ◽  
David S. Weaver
Keyword(s):  
Flow Regime ◽  
Void Fraction ◽  
Tube Bundle ◽  
Damping Ratio ◽  
Pressure Fluctuations ◽  
Cross Flow ◽  
Phase Changes ◽  
Working Fluid ◽  
Two Phase ◽  
Fluidelastic Instability

An experimental study was conducted to investigate damping and fluidelastic instability in tube arrays subjected to two-phase cross-flow. The purpose of this research was to improve our understanding of these phenomena and how they are affected by void fraction and flow regime. The working fluid used was Freon 11, which better models steam-water than air-water mixtures in terms of vapour-liquid mass ratio as well as permitting phase changes due to pressure fluctuations. The damping measurements were obtained by “plucking” the monitored tube from outside the test section using electromagnets. An exponential function was fitted to the tube decay trace, producing consistent damping measurements and minimizing the effect of frequency shifting due to fluid added mass fluctuations. The void fraction was measured using a gamma densitometer, introducing an improvement over the Homogeneous Equilibrium Model (HEM) in terms of density and velocity predictions. It was found that the Capillary number, when combined with the two-phase damping ratio (interfacial damping), shows a well defined behaviour depending on the flow regime. This observation can be used to develop a better methodology to normalize damping results. The fluidelastic results agree with previously presented data when analyzed using the HEM and the half-power bandwidth method. The interfacial velocity is suggested for fluidelastic studies due to its capability for collapsing the fluidelastic data. The interfacial damping was introduced as a tool to include the effects of flow regime into the stability maps.

scholarly journals Damping Measurements in Tube Bundles Subjected to Two-Phase Cross Flow

2006 ◽  
Author(s):  
Joaquin E. Moran ◽  
David S. Weaver
Keyword(s):  
Flow Regime ◽  
Void Fraction ◽  
Mass Flux ◽  
Damping Ratio ◽  
Logarithmic Decrement ◽  
Working Fluid ◽  
Exponential Fitting ◽  
Two Phase ◽  
Tube Bundles ◽  
Half Power

An experimental study was conducted to investigate two-phase damping in tube arrays. The objective was to compare different measurement methodologies in order to obtain a more reliable damping estimate. This will allow for improved guidelines related to failures due to fluidelastic instability in tube bundles. The methods compared were the traditionally used half-power bandwidth, the logarithmic decrement and an exponential fitting to the tube decay response. The working fluid used was Refrigerant 11 (Freon), which better models the real steam-water problem, as it allows for phase change. The void fraction was measured using a gamma densitometer, introducing an improvement over the traditional Homogeneous Equilibrium Model (HEM) in terms of velocity and density predictions. The results obtained by using the half-power bandwidth method agree with data previously reported for two-phase flow. The experiments showed that the half-power bandwidth produces higher damping values than the other two, but only up to a certain void fraction. After that point, the results obtained from the three methods are very similar. The exponential fitting proved to be more consistent than the logarithmic decrement, and it is not as sensitive as the half-power bandwidth to the frequency shifting caused by the change in added mass around the tube. By plotting the damping ratio as a function of void fraction, pitch mass flux and flow regime, we were able to verify that damping is more dependent on void fraction and flow regime than on mass flux.

Flow Regime Identification Under Adiabatic Upward Two-Phase Flow in a Vertical Rod Bundle Geometry

2011 ◽  
Vol 133 (9) ◽  
Author(s):  
Sidharth Paranjape ◽  
Shao-Wen Chen ◽  
Takashi Hibiki ◽  
Mamoru Ishii
Keyword(s):  
Flow Regime ◽  
Two Phase Flow ◽  
Flow Regimes ◽  
Distribution Functions ◽  
Flow Channel ◽  
Cumulative Probability ◽  
Phase Flow ◽  
Spacer Grid ◽  
Two Phase ◽  
Rod Bundle

Flow regime maps were obtained for adiabatic air-water two-phase flow through a flow channel with 8 × 8 rod bundle, which simulated a typical rod bundle in a boiling water reactor. Impedance void meters were used to measure the area averaged void fraction at various axial locations in the flow channel. The Cumulative Probability Distribution Functions of the signals from the impedance meters were utilized along with self organizing neural network methodology to identify the flow regimes. The flow regimes were identified at five axial locations in the channel in order to understand the development of the flow regimes in axial direction. The experimental flow regime transition boundaries for bubbly to cap-bubbly and part of the cap-turbulent to churn-turbulent agreed with the theoretical boundaries of bubbly to slug and slug to churn-turbulent in round pipes. In addition, the two impedance void meters located across a spacer grid, revealed the nature of change in the flow regime across the spacer grid.

Sign in / Sign up

Export Citation Format

Share Document