An Experimental Investigation of the Dynamics of a Loosely Supported Tube Array

2017 ◽  
Author(s):  
Amro Elhelaly ◽  
Marwan Hassan ◽  
Atef Mohany ◽  
Soha Moussa
Keyword(s):  
Experimental Investigation ◽  
Impact Force ◽  
Cross Flow ◽  
Open Loop ◽  
Diameter Ratio ◽  
Force Level ◽  
Steam Generators ◽  
Flow Induced Vibration ◽  
System Integrity ◽  
Tube Bundles

The integrity of tube bundles is very important especially when dealing with high-risk applications such as nuclear steam generators. A major issue to system integrity is the flow-induced vibration (FIV). FIV is manifested through several mechanisms including the most severe mechanism; fluidelastic instability (FEI). Tube vibration can be constrained by using tube supports. However, clearances between the tube and their support are required to allow for thermal expansion and for other manufacturing considerations. The clearance between tubes may allow frequent impact and friction between tube and support. This in turn may cause fatigue and wear at support and potential for catastrophic tube failure. This study aims to investigate the dynamics of loosely supported tube array subjected to cross-flow. The work is performed experimentally in an open-loop wind tunnel to address this issue. A loosely-supported single flexible tube in both triangle and square arrays subjected to cross-flow with a pitch-to-diameter ratio of 1.5 and 1.733, respectively were considered. The effect of the flow approach angle, as well as the support clearance on the tube response, are investigated. In addition, the parameters that affect tube wear such as impact force level are presented.

Modeling and Simulation of Cross-Flow Induced Vibration in a Multi-Span Tube Bundle

2004 ◽  
Author(s):  
Shahab Khushnood ◽  
Zaffar M. Khan ◽  
M. Afzaal Malik ◽  
Zafarullah Koreshi ◽  
Mahmood Anwar Khan
Keyword(s):  
Heat Exchanger ◽  
Tube Bundle ◽  
Cross Flow ◽  
Fatigue Cracking ◽  
Acoustic Resonance ◽  
Computer Code ◽  
Variable Geometry ◽  
Flow Induced Vibration ◽  
Two Phase ◽  
Tube Bundles

Flow-induced vibration in steam generator and heat exchanger tube bundles has been a source of major concern in nuclear and process industry. Tubes in a bundle are the most flexible components of the assembly. Flow induced vibration mechanisms, like fluid-elastic instability, vortex shedding, turbulence induced excitation and acoustic resonance results in failure due to mechanical wear, fretting and fatigue cracking. The general trend in heat exchanger design is towards larger exchangers with increased shell side velocities. Costly plant shutdowns have been the motivation for research in the area of cross-flow induced vibration in steam generators and process exchangers. The current paper focuses on the development of a computer code (FIVPAK) for the design (natural frequencies, variable geometry, tube pitch & pattern, mass damping parameter, reduced velocity, strouhal and damage numbers, added mass, wear work rates, void fraction for two-phase, turbulence and acoustic considerations etc.) of tube bundles with respect to cross flow-induced vibration. The code has been validated against Tubular Exchanger Manufacturers (TEMA), Flow-Induced Vibration code (FIV), and results on an actual variable geometry exchanger, specially manufactured to simulate real systems. The proposed code is expected to prove a useful tool in designing a tube bundle and to evaluate the performance of an existing system.

Flow-Induced Vibration of Tube Arrays With Various Pitch-to-Diameter Ratios

1982 ◽  
Vol 104 (3) ◽  
pp. 168-174 ◽  
Author(s):  
H. Tanaka ◽  
S. Takahara ◽  
K. Ohta
Keyword(s):  
Fluid Dynamic ◽  
Cross Flow ◽  
Diameter Ratio ◽  
Flow Induced Vibration ◽  
Threshold Velocity ◽  
Unsteady Forces ◽  
Practical Applications ◽  
Tube Arrays ◽  
Dynamic Forces ◽  
Unsteady Fluid

Tube arrays in cross flow start to vibrate abruptly when the flow reaches at a certain velocity. The threshold flow velocity depends upon the geometrical arrangement of tubes. It is very important for practical applications to understand the relations between the threshold velocity and pitch-to-diameter ratio of tube array. Unsteady fluid dynamic forces on a tube array with a pitch-to-diameter ratio of 2.0 were clarified experimentally and the characteristics of the threshold velocity were revealed by calculating the velocity with the unsteady forces. By comparing the threshold velocities of tube arrays of pitch-to-diameter ratio of 2.0 and 1.33, the characteristics of threshold velocity with respect to pitch-to-diameter ratio were clarified.

Two-Phase Flow-Induced Vibration of Parallel Triangular Tube Arrays With Asymmetric Support Stiffness

2009 ◽  
Vol 131 (3) ◽  
Author(s):  
Paul Feenstra ◽  
David S. Weaver ◽  
Tomomichi Nakamura
Keyword(s):  
Two Phase Flow ◽  
Cross Flow ◽  
Phase Flow ◽  
Heat Exchanger Tube ◽  
Flow Induced Vibration ◽  
Two Phase ◽  
Tube Arrays ◽  
Tube Bundles ◽  
Pitch Ratio ◽  
Exchanger Tube

Laboratory experiments were conducted to determine the flow-induced vibration response and fluidelastic instability threshold of model heat exchanger tube bundles subjected to a cross-flow of refrigerant 11. Tube bundles were specially built with tubes cantilever-mounted on rectangular brass support bars so that the stiffness in the streamwise direction was about double that in the transverse direction. This was designed to simulate the tube dynamics in the U-bend region of a recirculating-type nuclear steam generator. Three model tube bundles were studied, one with a pitch ratio of 1.49 and two with a smaller pitch ratio of 1.33. The primary intent of the research was to improve our understanding of the flow-induced vibrations of heat exchanger tube arrays subjected to two-phase cross-flow. Of particular concern was to compare the effect of the asymmetric stiffness on the fluidelastic stability threshold with that of axisymmetric stiffness arrays tested most prominently in literature. The experimental results are analyzed and compared with existing data from literature using various definitions of two-phase fluid parameters. The fluidelastic stability thresholds of the present study agree well with results from previous studies for single-phase flow. In two-phase flow, the comparison of the stability data depends on the definition of two-phase flow velocity.

Severed Tubes in Operating Nuclear Steam Generators: Case Analysis — I

2003 ◽  
Author(s):  
M. K. Au-Yang ◽  
Stephen Leshnoff
Keyword(s):  
Linear Theory ◽  
Fatigue Failure ◽  
Cross Flow ◽  
Ductile Failure ◽  
Integral Approach ◽  
Elastic Instability ◽  
Steam Generators ◽  
Flow Induced Vibration ◽  
Fluid Structure ◽  
Eddy Current Inspection

During a routine inspection in October 2001, it was discovered that a plugged tube in one of the steam generators at a nuclear station was completely severed at the upper tubesheet. The severed surface appeared to be fresh, clean, 360-deg. and with no evidence of necking down, ductile failure or visible flaws. Eddy current inspection revealed that the four neighboring tubes downstream of the severed tube each had wedge-shaped wear marks starting from the tubesheet end. However, there was no visible mid-span impact wear marks. Furthermore, the tube was visibly swollen due to over-pressurization. This tube was plugged in 1986 with no indications of flaw or wear marks. It was replugged later. The tube was not stabilized because there was no apparent potential for a circumferential sever to occur anywhere in the tube. Flow-induced vibration based on classic linear theory showed that this tube should have wide margin against fluid-elastic instability, turbulence or vortex-induced fatigue failure. However, it also was found that if for any reason the tube was laterally restrained (clamped) at the support plates, the margin against fluid-elastic instability would be reduced significantly. Still, this tube should have been stable and turbulence or vortex-induced vibration alone, as predicted by the classic linear theory without fluid-structure interaction, should not have caused fatigue failure. This study points out a deficiency in the classic linear turbulence-induced vibration analysis without taking into account the effect of fluid-structure coupling. When the cross-flow gap velocity is near the critical velocity, fluid-structure coupling would greatly increase the vibration amplitude over what is predicted by the classic acceptance integral approach. It is this increase in turbulence-induced vibration that caused this particular tube to fail by fatigue.

Two-Phase Flow Induced Vibration of an Array of Tubes Preferentially Flexible in the Flow Direction

2005 ◽  
Author(s):  
R. Violette ◽  
N. W. Mureithi ◽  
M. J. Pettigrew
Keyword(s):  
Natural Frequencies ◽  
Flow Direction ◽  
Cross Flow ◽  
Diameter Ratio ◽  
Phase Flow ◽  
Flow Induced Vibration ◽  
Two Phase ◽  
Array Configuration ◽  
Fluidelastic Instability ◽  
Existing Data

Tests were done to study the fluidelastic instability of a cluster of seven cylinders much more flexible in the flow direction than in the lift direction. The array configuration is rotated triangular with a pitch to diameter ratio of 1.5. The array was subjected to two-phase (air-water) cross flow. Cylinder natural frequencies of 14 and 28 Hz were tested. Fluidelastic instabilities were observed at 65, 80, 90 and 95% void fraction albeit at a somewhat higher flow velocity than that expected for axisymetrically flexible arrays. These results and additional wind tunnel results are compared to existing data on fluidelastic instability.

Flow-Induced Vibration Analysis of Tube Bundles—A Proposed Section III Appendix N Nonmandatory Code

1991 ◽  
Vol 113 (2) ◽  
pp. 257-267 ◽  
Author(s):  
M. K. Au-Yang ◽  
R. D. Blevins ◽  
T. M. Mulcahy
Keyword(s):  
Vibration Analysis ◽  
Steam Generators ◽  
Flow Induced Vibration ◽  
Nuclear Plants ◽  
Tube Bundles ◽  
Operations And Maintenance ◽  
Asme Code ◽  
Excitation Mechanisms ◽  
American Society ◽  
Tube Banks

This paper presents guidelines for flow-induced vibration analysis of tubes and tube bundles such as those commonly encountered in steam generators, heat exchangers, condensers and nuclear fuel bundles. It was proposed as a nonmandatory code to be included in Section III Appendix N (N-1300 series) of the American Society of Mechanical Engineers (ASME) Boiler Code. In preparing this code, the authors tried to limit themselves to the better-defined flow excitation mechanisms—vortex-induced vibration, fluid-elastic instability and turbulence-induced vibration—and include only the more-established methods. References are, however, given for other methods whenever justified. This guideline covers only design analysis. A companion guideline on the testing and data analysis of heat exchanger tube banks was proposed as part of the ASME Code on Operations and Maintenance of Nuclear Plants. The latter is not included in this paper.

A Comparative Study of Cross-Flow Induced Vibrations in Heat Exchanger Tube Bundles Using Bond Graph Approach

2005 ◽  
Author(s):  
M. Afzaal Malik ◽  
Badar Rashid ◽  
Shahab Khushnood
Keyword(s):  
Heat Exchanger ◽  
Comparative Study ◽  
Tube Bundle ◽  
Cross Flow ◽  
Bond Graph ◽  
Heat Exchanger Tube ◽  
Flow Induced Vibration ◽  
Study Results ◽  
Tube Bundles ◽  
Exchanger Tube

Flow-induced vibration (FIV) has been a major concern in the nuclear and process industries involving steam generator and heat exchanger tube bundle design. Various techniques and models have been developed and used for the analysis of cross-flow induced vibration of tube bundles. Bond Graph approach has been applied to existing FIV excitation models, followed by a comparative study. Results have been obtained using 20-SIM software. It is expected that the current approach will give a new dimension to the FIV analysis of tube bundles.

An Experimental Investigation of Cross-Flow Turbine Efficiency

1994 ◽  
Vol 116 (3) ◽  
pp. 545-550 ◽  
Author(s):  
Venkappayya R. Desai ◽  
Nadim M. Aziz
Keyword(s):  
Experimental Investigation ◽  
Angle Of Attack ◽  
Cross Flow ◽  
Water Entry ◽  
Diameter Ratio ◽  
Geometric Parameters ◽  
Maximum Efficiency ◽  
Outer Diameter ◽  
Turbine Efficiency ◽  
The Cross

An experimental investigation was conducted to study the effect of some geometric parameters on the efficiency of the cross-flow turbine. Turbine models were constructed with three different numbers of blades, three different angles of water entry to the runner, and three different inner-to-outer diameter ratios. Nozzles were also constructed for the experiments to match the three different angles of water entry to the runner. A total of 27 runners were tested with the three nozzles. The results of the experiments clearly indicated that efficiency increased with increase in the number of blades. Moreover, it was determined that an increase in the angle of attack beyond 24 deg does not improve the maximum turbine efficiency. In addition, as a result of these experiments, it was determined that for a 24 deg angle of attack 0.68 was the most efficient inner-to-outer diameter ratio, whereas for higher angles of attack the maximum efficiency decreases with an increase in the diameter ratio from 0.60 to 0.75.

Experimental and Numerical Characterization of Flow-Induced Vibration of Multi-Span U-Tubes

2010 ◽  
Author(s):  
Atef Mohany ◽  
Victor P. Janzen ◽  
Paul Feenstra ◽  
Shari King
Keyword(s):  
Tube Bundle ◽  
Measurement Techniques ◽  
Cross Flow ◽  
Process Conditions ◽  
Steam Generators ◽  
Test Program ◽  
Flow Induced Vibration ◽  
Two Phase ◽  
Support Design ◽  
Set Up

This paper describes a test program that was developed to measure the dynamic response of a bundle of steam generator U-tubes with Anti-Vibration Bar (AVB) supports, subjected to Freon two-phase cross-flow. The tube bundle geometry is similar to the geometry used in preliminary designs for future CANDU® steam generators. This test program is one of the initiatives that Atomic Energy of Canada Limited (AECL) is undertaking to demonstrate that the tube support design for future CANDU steam generators meets the stringent requirements associated with a 60-year lifetime. In particular, the tests will address issues related to in- and out-of-plane fluidelastic instability and random turbulent excitation of a U-tube bundle with Anti-Vibration Bar (AVB) supports. Therefore, the measurements include tube vibration amplitudes and frequencies, work-rate due to impacting and sliding motion of the tubes against their supports, bulk process conditions and local two-phase flow properties. Details of the test rig set-up and the measurement techniques are described in the paper. Moreover, a numerical prediction of the U-tube vibration response to flow was performed with AECL’s PIPO-FE code. A summary of the numerical results is presented.

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