The Flow-Structure Couplings of Fluidelastic Instability and the Effect of Frequency Detuning in Triangular Tube Bundles Subjected to a Two-Phase Flow

Journal of Pressure Vessel Technology ◽

10.1115/1.4053381 ◽

2021 ◽

Author(s):

Omar Sadek ◽

Atef Mohany ◽

Marwan A. Hassan

Keyword(s):

Void Fraction ◽

Two Phase Flow ◽

Phase Flow ◽

Frequency Detuning ◽

Two Phase ◽

Stability Threshold ◽

Damping Parameter ◽

Tube Bundles ◽

The Stability ◽

Air Void

Abstract For decades, fluidelastic instability (FEI) has been known to cause dramatic mechanical failures in tube bundles. Therefore, it has been extensively studied to mitigate its catastrophic consequences. Most of these studies were conducted in controlled experiments where significant simplifications to the geometry and flow conditions were utilized. One of these simplifications is the assumption that all tubes have the same dynamic characteristics. However, in steam generators with U-bend tube configuration, the natural frequencies of tubes are nonuniform due to manufacturing tolerances and tubes' curvature in the U-bend region. Thus, this investigation aims to understand the rule of frequency variation (detuning) on FEI in two-phase flow. This includes investigating the effect of detuning on transverse and streamwise FEI for air-water mixture flow. The role of FEI damping and stiffness couplings was investigated over the entire range of air void fraction, or equivalently, the mass-damping parameter. It was found that frequency detuning could elevate the stability threshold caused by either coupling at high air void fraction in the case of transverse FEI. Furthermore, the frequency detuning had a marginal effect on the stability threshold for water flow. It was observed that the mass-damping parameter has a critical impact on FEI under detuning conditions.

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A New Capacitance Sensor for Measuring the Void Fraction of Two-Phase Flow Through Tube Bundles

Sensors ◽

10.3390/s20072088 ◽

2020 ◽

Vol 20 (7) ◽

pp. 2088

Author(s):

Wael Ahmed ◽

Adib Fatayerji ◽

Ahmed Elsaftawy ◽

Marwan Hassan ◽

David Weaver ◽

...

Keyword(s):

Void Fraction ◽

Two Phase Flow ◽

Tube Bundle ◽

Local Variation ◽

Phase Flow ◽

Capacitance Sensor ◽

Two Phase ◽

Element Analysis ◽

Tube Bundles ◽

The Stability

Evaluating the two-phase flow parameters across tube bundles is crucial to the analysis of vibration excitation mechanisms. These parameters include the temporal and local variation of void fraction and phase redistribution. Understanding these two-phase parameters is essential to evaluating the stability threshold of tube bundle configurations. In this work, capacitance sensor probes were designed using finite element analysis to ensure high sensor sensitivity and optimum response. A simulation-based approach was used to calibrate and increase the accuracy of the void fraction measurement. The simulation results were used to scale the normalized capacitance and minimize the sensor uncertainty to ±5%. The sensor and required conditioning circuits were fabricated and tested for measuring the instantaneous void fraction in a horizontal triangular tube bundle array under both static and dynamic two-phase flow conditions. The static calibration of the sensor was able to reduce the uncertainty to ±3% while the sensor conditioning circuit was able to capture instantaneous void fraction signals with frequencies up to 2.5 kHz.

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Numerical Prediction of Two-Phase Flow in Tube Bundles with a CFD Porous Media Approach Based on Mixture Model and a Void Fraction Correlation

E3S Web of Conferences ◽

10.1051/e3sconf/202132101002 ◽

2021 ◽

Vol 321 ◽

pp. 01002

Author(s):

Claire Dubot ◽

Vincent Melot ◽

Claudine Béghein ◽

Cyrille Allery ◽

Clément Bonneau

Keyword(s):

Porous Media ◽

Mixture Model ◽

Void Fraction ◽

Two Phase Flow ◽

Numerical Prediction ◽

Phase Flow ◽

Two Phase ◽

Mixture Density ◽

Tube Bundles ◽

Phase Mixture

Being able to predict the void fraction is essential for a numerical prediction of the thermohydraulic behaviour in steam generators. Indeed, it determines two-phase mixture density and affects two-phase mixture velocity which enable to evaluate the pressure drop of heat exchanger, the mass transfer and heat transfer coefficients. In this study, the flow is modelled by coupling Ansys Fluent with an in-house code library where a CFD porous media approach is implemented. In this code, the two-phase flow has been modelled so far using the Eulerian model. However, this two-phase model requires interaction laws between phases which are not known and/or reliable for a flow within a tube bundle. The aim of this paper is to use the mixture model, for which it is easier to implement suitable correlations for tube bundles. By expressing the relative velocity, as a function of slip, the void fraction model of Feenstra et al. developed for upward cross-flow through horizontal tube bundles is introduced. With this method, physical phenomena that occur in tube bundles are taken into consideration in the mixture model. The developed approach is validated based on the experimental results obtained by Dowlati et al.

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DYNAMICS OF TWO-PHASE FLOW ACROSS HORIZONTAL TUBE BUNDLES - A REVIEW

Revista de Engenharia Térmica ◽

10.5380/ret.v4i2.5404 ◽

2005 ◽

Vol 4 (2) ◽

Author(s):

G. Ribatskia ◽

J. R. Thome

Keyword(s):

Void Fraction ◽

Two Phase Flow ◽

Experimental Studies ◽

Horizontal Tube ◽

Prediction Methods ◽

Phase Flow ◽

Two Phase ◽

Pressure Drops ◽

Frictional Pressure Drop ◽

Tube Bundles

This paper presents a state-of-the-art review of the hydrodynamic aspects of two-phase flow across horizontal tube bundles. The review covers studies related to the evaluation of void fraction, two-phase flow behaviors and pressure drops on the shell side of staggered and in-line tube bundles for upward, downward and side-to-side flows. This study of the literature critically describes the proposed flow pattern maps and semi-empirical correlations for predicting void fraction and frictional pressure drop. These predicting methods are generally based on experimental results for adiabatic air-water flows. A limited number of experimental studies with R-11 and R-113 were also carried out in the past. The review shows noticeable discrepancies among the available prediction methods. Finally, this study suggests that further research focusing on the development of representative databanks and new prediction methods is still necessary.

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

Journal of Pressure Vessel Technology ◽

10.1115/1.1462045 ◽

2002 ◽

Vol 124 (2) ◽

pp. 144-153 ◽

Cited By ~ 32

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.

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