Vibration and Work-Rate Measurements of Steam-Generator U-Tubes in Air-Water Cross-Flow

2002 ◽  
Author(s):  
Victor P. Janzen ◽  
Erik G. Hagberg ◽  
James N. F. Patrick ◽  
Michel J. Pettigrew ◽  
Colette E. Taylor ◽  
...  
Keyword(s):  
Cross Flow ◽  
Work Rate ◽  
Vibration Response ◽  
Fretting Wear ◽  
Steam Generators ◽  
Two Phase ◽  
Void Fractions ◽  
Vibration Properties ◽  
Wide Range ◽  
Fluidelastic Instability

In nuclear power plant steam generators, the vibration response of tubes in two-phase cross-flow is a general concern that in some cases has become a very real long-term wear problem. This paper summarizes the results of the most recent U-bend vibration-response tests in a program designed to address this issue. The tests involved a simplified U-tube bundle with a set of flat-bar supports at the apex, subjected to two-phase air-water cross-flow over the mid-span region of the U-bend. Tube vibration properties and tube-to-support interaction in the form of work-rates were measured over a wide range of flow velocities for homogeneous void fractions from zero to 90%, with three different tube-to-support clearances. The measured vibration properties and work-rates could be characterized by the relative influence of the two most important flow-induced excitation mechanisms at work, fluidelastic instability and random-turbulence excitation. As in previous similar tests, strong effects of fluidelastic instability were observed at zero and 25% void fraction for pitch velocities greater than approximately 0.5 m/s, whereas random turbulence dominated the tube vibration and work-rate response at higher void fractions. In both cases, a link between vibration properties and the effect of the flat-bar supports could be established by comparing the vibration crossing frequency, extracted from time-domain vibration signals, to the participation of the lowest few vibration modes and to the measured work-rate. This approach may be useful when fluidelastic instability, random turbulence and loose supports all combine to result in high work-rates. Such a combination of factors is thought to be responsible for excessive U-tube fretting-wear in certain types of operating steam generators.

Improved Flow-Induced Vibration and Work-Rate Measurements of Steam-Generator Tubes

2003 ◽  
Author(s):  
V. P. Janzen ◽  
B. A. W. Smith ◽  
L. Brunet ◽  
S. Fernando ◽  
D. Fingas
Keyword(s):  
Dynamic Properties ◽  
Flow Characteristics ◽  
Cross Flow ◽  
Work Rate ◽  
Fretting Wear ◽  
Steam Generators ◽  
Flow Induced Vibration ◽  
Two Phase ◽  
Software Analysis ◽  
Wide Range

In the past, the excessive fretting-wear of U-bend tubes observed in some nuclear steam generators has led to increased tube inspections, unexpectedly high numbers of plugged tubes and the prospect of degraded performance if left unchecked. In this paper, recent vibration and work-rate experiments that have attempted to address this problem are summarized, including tests of two-span U-tubes in air-water and straight tubes in two-phase Freon. Tube bundles were subjected to two-phase cross-flow over a wide range of flow conditions, measuring tube vibration, flow characteristics in the bundle, and the dynamic interaction (work-rate) between tubes and supports that gives rise to fretting-wear. Developments in vibration and work-rate instrumentation and software analysis tools are also presented. The result is an improved ability to measure dynamic properties and, thus, to better predict the vibration response and fretting-wear performance of steam generators.

Fluidelastic Instability and Periodic Fluid Forces in a Normal Triangular Tube Bundle Subjected to Air-Water Flow

2010 ◽  
Author(s):  
G. Ricciardi ◽  
M. J. Pettigrew ◽  
N. W. Mureithi
Keyword(s):  
Two Phase Flow ◽  
Tube Bundle ◽  
Fatigue Cracks ◽  
Cross Flow ◽  
Fretting Wear ◽  
Phase Flow ◽  
Steam Generators ◽  
Two Phase ◽  
Fluid Forces ◽  
Void Fractions

Two-phase flow in power plant steam generators can induce tube vibrations, which may cause fretting-wear and even fatigue cracks. It is therefore important to understand the relevant two-phase flow-induced vibration mechanisms. Fluidelastic instabilities in cross-flow are known to cause the most severe vibration response in the U-bend region of steam generators. This paper presents test results of the vibration of a normal triangular tube bundle subjected to air-water cross-flow. The test section presents 31 flexible tubes. The pitch-to-diameter ratio of the bundle is 1.5, and the tube diameter is 38 mm. Tubes were flexible in the lift direction. Seven tubes were instrumented with strain gauges to measure their displacements. A broad range of void fractions (from 10% to 90%) and fluid velocities (up to 13 m/s) were tested. Fluidelastic instabilities were observed for void fractions between 10% and 60%. Periodic fluid forces were also observed. The results are compared with those obtained with the rotated triangular tube bundle, showing that the normal triangular configuration is more stable than the rotated triangular configuration.

Fluidelastic Instability and Work-Rate Measurements of Steam-Generator U-Tubes in Air–Water Cross-Flow

2005 ◽  
Vol 127 (1) ◽  
pp. 84-91 ◽  
Author(s):  
V. P. Janzen ◽  
E. G. Hagberg ◽  
M. J. Pettigrew ◽  
C. E. Taylor
Keyword(s):  
Tube Bundle ◽  
Cross Flow ◽  
Two Phase ◽  
Void Fractions ◽  
Wide Range ◽  
Fluidelastic Instability ◽  
Out Of Plane ◽  
Plane Direction ◽  
First Time ◽  
Support Work

The dynamic response of U-tubes to two-phase cross-flow has been studied in tests involving a simplified U-tube bundle with a set of flat-bar supports at the apex, subjected to air–water cross-flow over the mid-span region. Tube vibration and the interaction between tubes and supports were measured over a wide range of void fractions and flow rates, for three different tube-to-support clearances. The vibration properties and tube-to-support work-rates could be characterized in terms of the relative influence of fluidelastic instability and random-turbulence excitation. For the first time, in a U-bend tube bundle with liquid or two-phase flow, fluidelastic instability was observed both in the out-of-plane and in the in-plane direction. This raises the possibility of higher-than-expected tube-to-support work-rates for U-tubes restrained by flat bars, particularly if fluidelastic instability, random turbulence and loose supports combine adversely.

Time Domain Simulation of the Vibration of a Steam Generator Tube Subjected to Fluidelastic Forces Induced by Two-Phase Cross-Flow

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
Téguewindé Sawadogo ◽  
Njuki Mureithi
Keyword(s):  
Steam Generator ◽  
Two Phase Flow ◽  
Work Rate ◽  
Fretting Wear ◽  
Phase Flow ◽  
Reference Case ◽  
Two Phase ◽  
Steam Generator Tube ◽  
Wide Range ◽  
Instability Regime

Having previously verified the quasi-steady model under two-phase flow laboratory conditions, the present work investigates the feasibility of practical application of the model to a prototypical steam generator (SG) tube subjected to a nonuniform two-phase flow. The SG tube vibration response and normal work-rate induced by tube-support interaction are computed for a range of flow conditions. Similar computations are performed using the Connors model as a reference case. In the quasi-steady model, the fluid forces are expressed in terms of the quasi-static drag and lift force coefficients and their derivatives. These forces have been measured in two-phase flow over a wide range of void fractions making it possible to model the effect of void fraction variation along the tube span. A full steam generator tube subjected to a nonuniform two-phase flow was considered in the simulations. The nonuniform flow distribution corresponds to that along a prototypical steam-generator tube based on thermal-hydraulic computations. Computation results show significant and important differences between the Connors model and the two-phase flow based quasi-steady model. While both models predict the occurrence of fluidelastic instability, the predicted pre-instability and post instability behavior is very different in the two models. The Connors model underestimates the flow-induced negative damping in the pre-instability regime and vastly overestimates it in the post instability velocity range. As a result the Connors model is found to underestimate the work-rate used in the fretting wear assessment at normal operating velocities, rendering the model potentially nonconservative under these practically important conditions. Above the critical velocity, this model largely overestimates the work-rate. The quasi-steady model on the other hand predicts a more moderately increasing work-rate with the flow velocity. The work-rates predicted by the model are found to be within the range of experimental results, giving further confidence to the predictive ability of the model. Finally, the two-phase flow based quasi-steady model shows that fluidelastic forces may reduce the effective tube damping in the pre-instability regime, leading to higher than expected work-rates at prototypical operating velocities.

Vibration of a Tube Bundle in Two-Phase Freon Cross-Flow

1995 ◽  
Vol 117 (4) ◽  
pp. 321-329 ◽  
Author(s):  
M. J. Pettigrew ◽  
C. E. Taylor ◽  
J. H. Jong ◽  
I. G. Currie
Keyword(s):  
Two Phase Flow ◽  
Tube Bundle ◽  
Density Ratio ◽  
Cross Flow ◽  
Flow Regimes ◽  
Phase Flow ◽  
Two Phase ◽  
Void Fractions ◽  
Fluidelastic Instability ◽  
First Results

Two-phase cross-flow exists in many shell-and-tube heat exchangers. The U-bend region of nuclear steam generators is a prime example. Testing in two-phase flow simulated by air-water provides useful results inexpensively. However, two-phase flow parameters, in particular surface tension and density ratio, are considerably different in air-water than in steam-water. A reasonable compromise is testing in liquid-vapor Freon, which is much closer to steam-water while much simpler experimentally. This paper presents the first results of a series of tests on the vibration behavior of tube bundles subjected to two-phase Freon cross-flow. A rotated triangular tube bundle of tube-to-diameter ratio of 1.5 was tested over a broad range of void fractions and mass fluxes. Fluidelastic instability, random turbulence excitation, and damping 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. Generally, random turbulence excitation forces are much lower in Freon than in air-water. Damping is very dependent on void fraction, as expected.

Vibration Analysis of Steam Generators and Heat Exchangers: An Overview — Part II: Vibration, Response, Fretting-Wear, Guidelines

2002 ◽  
Author(s):  
Michel J. Pettigrew ◽  
Colette E. Taylor
Keyword(s):  
Heat Exchangers ◽  
Vibration Analysis ◽  
Response Prediction ◽  
Design Guidelines ◽  
Vibration Response ◽  
Fretting Wear ◽  
Steam Generators ◽  
Flow Induced Vibration ◽  
Two Phase ◽  
Service Water

Design guidelines were developed to prevent tube failures due to excessive flow-induced vibration in shell-and-tube heat exchangers. An overview of vibration analysis procedures and recommended design guidelines is presented in this paper. This paper pertains to liquid, gas and two-phase heat exchangers such as nuclear steam generators, reboilers, coolers, service water heat exchangers, condensers, and moisture-separator-reheaters. Part 2 of this paper covers forced vibration excitation mechanisms, vibration response prediction, resulting damage assessment, and acceptance criteria.

Streamwise Dynamics of a Tube Array Subjected to Two-Phase Cross-Flows

2015 ◽  
Author(s):  
Stephen Olala ◽  
Njuki W. Mureithi
Keyword(s):  
Phase Measurement ◽  
Cross Flow ◽  
Economic Loss ◽  
Two Phase ◽  
Void Fractions ◽  
Measurement Results ◽  
Fluidelastic Instability ◽  
Coupling Force ◽  
Important Input ◽  
Excitation Mechanisms

Nuclear steam generator tubes in two-phase cross-flow may vibrate due to excitations that emanate from various sources. Of these excitation mechanisms, fluidelastic instability is the most dominant cause of tube failures in the short-term. These failures, other than leading to unscheduled plant shutdowns, may result in leakage of radioactive materials that may ultimately cause accidents and economic loss. Very limited work has been dedicated to investigating purely streamwise fluidelastic instability in tube arrays. However, recent observations of tube failure caused by streamwise or in-plane instability confirm the importance of streamwise fluidelastic instability analysis. In the present study, we present detailed dynamic cross-coupling force and phase measurement results for a central cluster of tubes in a rotated triangular tube array of Pitch-to-Diameter ratio (P/D)=1.5 subjected to air-water two-phase cross-flow, for homogeneous void fractions of 0% and 60%. The measured dynamic forces together with previously measured quasi-steady forces are necessary to estimate the time delay which is an important input for the quasi-steady fluidelastic instability model.

The Effect of Angle of Attack on the Fluidelastic Instability of Tube Bundle Subjected to Two-Phase Cross-Flow

2009 ◽  
Author(s):  
T. F. Joly ◽  
N. W. Mureithi ◽  
M. J. Pettigrew
Keyword(s):  
Tube Bundle ◽  
Angle Of Attack ◽  
Cross Flow ◽  
Diameter Ratio ◽  
Test Results ◽  
Two Phase ◽  
Void Fractions ◽  
Fluidelastic Instability ◽  
Flexible Tubes ◽  
Existing Data

Tests were done to study the effect of angle of attack on the fluidelastic instability of a fully flexible tube bundle subjected to two-phase (Air-Water) cross-flow. A test array having nineteen flexible tubes in a rotated triangular configuration with a pitch-to-diameter ratio of 1.5 was tested. Four different angles of attack ranging for 0 degree (inline flexibility) through 30 and 60 degrees to 90 degrees (transverse flexibility) were studied. For each angle of attack several homogeneous void fractions have been tested (70%, 80%, 90%, and 95%). Stability test results show that the angle of attack strongly affect the tube bundle dynamic behavior. The different mechanisms underlying the fluidelastic instability are highlighted and the results compared to existing data on fluidelastic instability.

Streamwise Fluidelastic Instability of Tube Arrays in Two-Phase Cross Flow

2014 ◽  
Author(s):  
Stephen Olala ◽  
Njuki W. Mureithi
Keyword(s):  
Nuclear Power ◽  
Single Phase ◽  
Cross Flow ◽  
Force Measurements ◽  
Two Phase Flows ◽  
Two Phase ◽  
Fluid Force ◽  
Void Fractions ◽  
Tube Arrays ◽  
Fluidelastic Instability

In-plane instability of tube arrays has not been a major concern to steam generator designers until recently following observations of streamwise tube failure in a nuclear power plant in U.S.A. However, modeling of fluidelastic instability in two-phase flows still remains a challenge. In the present work, detailed steady fluid force measurements for a kernel of an array of tubes in a rotated triangular tube array of P/D=1.5 subjected to air-water two-phase flows for a series of void fractions and a Reynolds number (based on the pitch velocity), Re = 7.2 × 104 has been conducted. The measured steady fluid force coefficients and their derivatives, with respect to streamwise static displacements of the central tube, are employed in the quasi-steady model [1, 2], originally developed for single phase flows, to analyze in-plane fluidelastic instability of multiple flexible arrays in two-phase flows. The results are consistent with dynamic stability tests [3].

Fluidelastic Instability in a Normal Triangular Tube Bundle Subjected to Air-Water Cross-Flow

2011 ◽  
Vol 133 (6) ◽  
Author(s):  
G. Ricciardi ◽  
M. J. Pettigrew ◽  
N. W. Mureithi
Keyword(s):  
Tube Bundle ◽  
Cross Flow ◽  
Diameter Ratio ◽  
Tube Diameter ◽  
Void Fractions ◽  
Fluid Velocities ◽  
Wide Range ◽  
Fluidelastic Instability

This paper presents the results of tests on the vibration of a normal triangular tube bundle subjected to air–water cross-flow. The pitch-to-diameter ratio of the bundle is 1.5, and the tube diameter is 38 mm. The tubes were preferentially flexible in one direction. Both the lift and the drag direction were tested. A wide range of void fractions and fluid velocities was tested. Fluidelastic instabilities and tube resonances were observed. The resonances induced significant vibration amplitudes at high void fractions in the lift direction. The results are compared with those obtained with a rotated triangular tube bundle. They show that the normal triangular configuration is more stable than the rotated triangular configuration.

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