scholarly journals The Effect of Fins on Fluidelastic Instability in In-Line and Rotated Square Tube Arrays

2010 ◽  
Vol 132 (5) ◽  
Author(s):  
Robert H. Lumsden ◽  
David S. Weaver
Keyword(s):  
Finned Tube ◽  
Experimental Program ◽  
Effective Diameter ◽  
Process Industries ◽  
Finned Tubes ◽  
Tube Arrays ◽  
Fluidelastic Instability ◽  
The Stability ◽  
Tube Pitch ◽  
Bare Tube

An experimental program was conducted to examine fluidelastic instability in in-line and rotated square finned tube arrays. Three arrays of each geometry type were studied: two with serrated, helically wound finned tubes of different fin densities and the third is a bare tube, which had the same base diameter as the finned tubes. The finned tubes under consideration were commercial finned tubes of a type typically used in the fossil and process industries. The addition of fins to tubes in heat exchangers enhances heat transfer due to the increased surface area and the turbulence produced by the flow moving over the fins. The resulting flow pattern/distribution due to the fins is, therefore, more complex than in bare tube arrays. Previous research has shown that an effective diameter of a finned tube is useful in the prediction of vortex shedding. This concept is used to compare the finned tube results with the existing bare tube array guidelines for fluidelastic instability. All of the tube arrays in the present study have the same tube pitch and have been scaled to have the same mass ratio. The results for rotated square arrays suggest that the use of an effective diameter is beneficial in the scaling of fluidelastic instability and the finned tube results are found to fit within the scatter of the existing data for fluidelastic instability. For in-line square arrays, the results indicate that fins significantly increase the stability threshold. An earlier version of this paper appeared at the ASME 2007 PVP Division Conference, PVP2007-26597.

Fluidelastic Instability in Normal and Parallel Triangular Arrays of Finned Tubes

2012 ◽  
Vol 134 (2) ◽  
Author(s):  
J. Wang ◽  
D. S. Weaver
Keyword(s):  
Finned Tube ◽  
Effective Diameter ◽  
Process Industries ◽  
Finned Tubes ◽  
Triangular Arrays ◽  
Tube Bundles ◽  
Fluidelastic Instability ◽  
The Difference ◽  
The Stability ◽  
Bare Tube

An experimental study was carried out to investigate fluidelastic instability in finned tube bundles in normal and parallel triangular arrays. Three arrays of each geometry type were studied experimentally: two arrays with serrated, helically wound finned tubes of different fin densities, and a bare tube array with the same base diameter as the finned tubes. All six tube arrays studied had the same tube pitch. The finned tubes under consideration were commercial finned tubes typically used in the fossil and process industries. For the purpose of the present investigation, the concept of “effective diameter” of a finned tube, as previously used to predict vortex shedding, was used to compare the finned tube results with other finned tube results as well as the existing bare tube world data. The experimental results for the triangular arrays show that the fin’s structure strongly influences the fluidelastic stability of finned tube bundles and the fin pitch is demonstrated to reduce the difference in the stability threshold between the tube array geometries as the fin density increases. Overall, the effect of serrated fins on fluidelastic instability is very complex and array geometry dependent, stabilizing some arrays and destabilizing others. Clearly, the effect of fins cannot be accounted for by the simple use of an effective diameter of an equivalent bare tube. An earlier version of this paper appeared at the ASME 2010 FSI Conference, FEDSM-ICNMM2010-30223.

The Effect of Fins on Fluidelastic Instability in In-Line and Rotated Square Arrays

2007 ◽  
Author(s):  
Robert H. Lumsden ◽  
David S. Weaver
Keyword(s):  
Heat Exchangers ◽  
Cross Flow ◽  
Finned Tube ◽  
Experimental Program ◽  
Effective Diameter ◽  
Finned Tubes ◽  
Increased Risk ◽  
Tube Arrays ◽  
Fluidelastic Instability ◽  
Bare Tube

The study of fluidelastic instability in tube arrays has been ongoing for four decades. Although much research has been conducted, a full understanding of the mechanisms involved is still not available. Designers of cross-flow heat exchangers must depend on experience and empirical data from laboratory studies. As new designs are developed, which differ from these experimental facilities, there is an increased risk of failure due to fluidelastic instability. An experimental program was conducted to examine fluidelastic instability in in-line and rotated square finned tube arrays. Three arrays of each geometry type were studied; two with serrated, helically wound finned tubes of different fin densities, and the third, a bare tube which had the same base diameter as the finned tubes. The finned tubes under consideration were commercial finned tubes of a type typically used in the fossil and process industries. The addition of fins to tubes in heat exchangers enhances heat transfer due to the increased surface area and the turbulence produced by the flow moving over the fins. The resulting flow pattern/distribution due to the fins is therefore much more complicated than in bare tube arrays. Previous research has shown that an effective diameter of a finned tube is useful in the prediction of vortex shedding. This concept is used to compare the finned tube results with the existing bare tube array guidelines for fluidelastic instability. All of the tube arrays in the present study have the same tube pitch, and have been scaled to have the same mass ratio. Results for the rotated square arrays show that the use of an effective diameter is beneficial in the scaling of fluidelastic instability and the finned tube results are found to fit within the scatter of the existing data for fluidelastic instability. For in-line square arrays, the results indicate that fins significantly increase the stability threshold.

Fluidelastic Instability in Normal and Parallel Triangular Arrays of Finned Tubes

2010 ◽  
Author(s):  
J. Wang ◽  
D. S. Weaver
Keyword(s):  
Finned Tube ◽  
Effective Diameter ◽  
Process Industries ◽  
Finned Tubes ◽  
Triangular Arrays ◽  
Tube Bundles ◽  
Fluidelastic Instability ◽  
The Difference ◽  
The Stability ◽  
Bare Tube

An experimental study was carried out to investigate fluidelastic instability in finned tube bundles in normal and parallel triangular arrays. Three arrays of each geometry type were studied experimentally: two arrays with serrated, helically wound finned tubes of different fin densities, and a bare tube array with the same base diameter as the finned tubes. All six tube arrays studied had the same tube pitch. The finned tubes under consideration were commercial finned tubes typically used in the fossil and process industries. For the purpose of the present investigation, the concept of “effective diameter” of a finned tube, as previously used to predict vortex shedding, was used to compare the finned tube results with other finned tube results as well as the existing bare tube world data. The experimental results for the triangular arrays show that the fin’s structure strongly influences the fluidelastic stability of finned tube bundles and the fin pitch is demonstrated to reduce the difference in the stability threshold between the tube array geometries as the fin density increases. Overall, the effect of serrated fins on fluidelastic instability is very complex and array geometry dependent, stabilizing some arrays and destabilizing others. Clearly, the effect of fins cannot be accounted for by the simple use of an effective diameter of an equivalent bare tube.

Flow-Induced Vibration in Spiral Finned Gas Tube Bundle Heat Exchangers

2003 ◽  
Author(s):  
Michael Fischer
Keyword(s):  
Heat Exchangers ◽  
Tube Bundle ◽  
Practical Importance ◽  
Acoustic Resonance ◽  
Finned Tube ◽  
Flow Induced Vibration ◽  
Finned Tubes ◽  
The Past ◽  
Short Period ◽  
Fluidelastic Instability

In the past finned tube bundle heat exchangers were often subject of severe damages due to flow-induced vibration followed by high amounts of loss for the operator. A case of practical importance is the design of spiral finned gas tube bundle heat exchangers that still have been investigated in literature only seldom. Both acoustic resonance and fluidelastic instability can lead to tube rupture within a short period of operation. In this paper analytic calculation methods for tube Eigenfrequencies are extended to spiral finned tubes. The results are in agreement with static and vibrational experiments. Stability criteria for fluidelastic instability are derived by flow channel experiments extending Connor’s equation to the design of spiral finned tube bundles. A number of cases of damage is described. The importance of correct damping values is demonstrated. The scheme reported in this paper is able to avoid damages in spiral finned tube bundle heat exchangers due to fluidelastic instability.

Fluidelastic Instability of a Single Flexible Tube in a Rigid Tube Array

2010 ◽  
Author(s):  
Ahmed Khalifa ◽  
David Weaver ◽  
Samir Ziada
Keyword(s):  
Nuclear Power ◽  
Power Plants ◽  
Precise Control ◽  
Flexible Tube ◽  
Tube Arrays ◽  
Fluidelastic Instability ◽  
Excitation Mechanisms ◽  
The Stability ◽  
Square Array ◽  
Special Case

Tube and shell heat exchangers are commonly used in both fossil and nuclear power plants. The unexpected failure for such components is expensive and potentially dangerous. Of the various excitation mechanisms which can cause excessive tube vibration, fluidelastic instability is the most dangerous and therefore has received the most attention. The present study reviews the experimental work published in the open literature which involves the use of a single flexible tube in a rigid array to study fluidelastic instability. The data are categorized based on the array geometry into four main groups, parallel triangular, normal triangular, rotated square, and square array patterns. It is concluded from this review that the simplification of using a single flexible tube in a rigid array to study fluidelastic instability should be done with great care, and precise control of some parameters is essential to obtain reliable and repeatable results. Fluidelastic instability of a single flexible tube in a rigid array may occur in some cases, and may be used to improve our understanding of the phenomenon. However, it must be noted that this behavior is a special case and not generally useful for determining the stability of tube arrays.

Effect of Tube-to-Tube Ties on Fluidelastic Instability of Tube Arrays Exposed to Crossflow

1998 ◽  
Vol 120 (2) ◽  
pp. 179-185 ◽  
Author(s):  
F. L. Eisinger ◽  
M. M. Rao
Keyword(s):  
Numerical Simulation ◽  
Unsteady Flow ◽  
Flow Theory ◽  
Single Tube ◽  
Tube Arrays ◽  
Fluidelastic Instability ◽  
Critical Velocities ◽  
The Stability ◽  
Stability Limits

Tube-to-tube ties and their arrangement within the tube array are shown to affect the onset of fluidelastic instability. The influence of tie arrangement for a single tube row and for an in-line tube array is obtained by numerical simulation using S. S. Chen’s unsteady flow theory. Maps of dimensionless critical velocities for groups of tubes consisting of two, three, four, and five tubes tied to each other are developed for several design configurations. It is shown that the stability limits can be raised by appropriate choice of tube group and tie location.

Pitch and Pattern Effects on Streamwise Fluidelastic Instability in Tube Arrays

2019 ◽  
Author(s):  
Marwan Hassan ◽  
David Weaver
Keyword(s):  
Los Angeles ◽  
Channel Model ◽  
High Mass ◽  
Flow Induced Vibration ◽  
Geometric Patterns ◽  
Small Pitch ◽  
Tube Arrays ◽  
Fluidelastic Instability ◽  
Pitch Ratio ◽  
The Stability

Abstract Fluidelastic instability (FEI) is well known to be a critical flow-induced vibration concern for the integrity of the tubes in nuclear steam generators. Traditionally, this has been assumed to occur in the direction transverse to the direction of flow but the tube failures at San Onofre Nuclear Generating Station (SONGS) in Los Angeles proved that this assumption is not generally valid. A simple tube-in-channel theoretical model was previously developed to predict streamwise as well as transverse FEI in a parallel triangular tube array. This predicted that this array geometry was particularly sensitive to streamwise FEI for high mass-damping parameters and small pitch ratios, the conditions in which the SONGS failures occurred. The advantage of this simple modelling approach is that no new empirical data are required for parametric studies of the effects of tube pattern and pitch ratio on FEI. The tube-in-channel model has been extended to in-line square, normal triangular and rotated square tube arrays and the stability of these geometric patterns are analyzed for the effects of varying pitch ratio and the mass-damping parameter. The results are compared with the available experimental data and conclusions are drawn regarding the relative vulnerability of these different tube array geometries to streamwise FEI.

Fluidelastic Vibration Analysis of Normal Square Finned Tube Arrays in Water Cross Flow

2019 ◽  
Vol 141 (3) ◽  
Author(s):  
Sandeep R. Desai ◽  
Aslam A. Maniyar
Keyword(s):  
Vortex Shedding ◽  
Fluid Velocity ◽  
Cross Flow ◽  
Finned Tube ◽  
Instability Threshold ◽  
Experimental Program ◽  
Triangular Arrays ◽  
Array Pattern ◽  
Tube Arrays ◽  
Pitch Ratio

An experimental program was carried out by subjecting normal square finned tube arrays to gradually increasing water cross flows. In all, total six tube arrays were tested—three having pitch ratio 2.1 and remaining three of pitch ratio 2.6. Under each category, three arrays tested were: plain array, coarse finned array, and fine finned array. The objective of the research was to determine the fluid velocity at which each of the six arrays becomes fluidelastically unstable. The experiments were started with tests on plain arrays to establish them as a datum case by comparing their test results with published results on plain arrays having lower pitch ratios. This was then followed by testing of finned arrays to study the effect of fins on the instability threshold. The tubes were subjected to a gradually increasing flow rate of water from 10 m3/h to the point where instability was reached. The results of the present work are compared with author's earlier published results for parallel triangular arrays in water. The research outcomes help to study the effect of pitch ratio, tube array pattern, and fin density on the instability threshold. The results show that instability is delayed due to the addition of the fins. It is also concluded that normal square arrays should be preferred over parallel triangular arrays to avoid fluidelastic vibrations. The vortex shedding behavior studied for all the arrays shows that small peaks before fluidelastic instability are due to vortex shedding.

Numerical Estimation of Fluidelastic Instability in Tube Arrays

2010 ◽  
Vol 132 (4) ◽  
Author(s):  
Marwan Hassan ◽  
Andrew Gerber ◽  
Hossin Omar
Keyword(s):  
Unsteady Flow ◽  
Stokes Equations ◽  
Navier Stokes ◽  
Arbitrary Lagrangian Eulerian ◽  
Navier Stokes Equations ◽  
Fluid Forces ◽  
Tube Arrays ◽  
Fluidelastic Instability ◽  
Viable Approach ◽  
The Stability

This study investigates unsteady flow in tube bundles and fluid forces, which can lead to large tube vibration amplitudes, in particular, amplitudes associated with fluidelastic instability (FEI). The fluidelastic forces are approximated by the coupling of the unsteady flow model (UFM) with computational fluid dynamics (CFD). The CFD model employed solves the Reynolds averaged Navier–Stokes equations for unsteady turbulent flow and is cast in an arbitrary Lagrangian–Eulerian form to handle any motion associated with tubes. The CFD solution provides time domain forces that are used to calculate added damping and stiffness coefficients employed with the UFM. The investigation demonstrates that the UFM utilized in conjunction with CFD is a viable approach for calculating the stability map for a given tube array. The FEI was predicted for in-line square and normal triangle tube arrays over a mass damping parameter range of 0.1– 100. The effect of the P/d ratio and the Reynolds number on the FEI threshold was also investigated.

Pitch and Pattern Effects On Streamwise Fluidelastic Instability in Tube Arrays

2021 ◽  
Author(s):  
Marwan A. Hassan ◽  
David S. Weaver
Keyword(s):  
Los Angeles ◽  
Channel Model ◽  
High Mass ◽  
Flow Induced Vibration ◽  
Geometric Patterns ◽  
Small Pitch ◽  
Tube Arrays ◽  
Fluidelastic Instability ◽  
Pitch Ratio ◽  
The Stability

Abstract Fluidelastic instability (FEI) is well known to be a critical flow-induced vibration concern for the integrity of the tubes in nuclear steam generators. Traditionally, this has been assumed to occur in the direction transverse to the direction of flow but the tube failures at San Onofre Nuclear Generating Station (SONGS) in Los Angeles proved that this assumption is not generally valid. A simple tube-in-channel theoretical model was previously developed to predict streamwise as well as transverse FEI in a parallel triangular tube array. This predicted that this array geometry was particularly sensitive to streamwise FEI for high mass-damping parameters and small pitch ratios, the conditions in which the SONGS failures occurred. The advantage of this simple modelling approach is that no new empirical data are required for parametric studies of the effects of tube pattern and pitch ratio on FEI. The tube-in-channel model has been extended to in-line square, normal triangular and rotated square tube arrays and the stability of these geometric patterns are analyzed for the effects of varying pitch ratio and the mass-damping parameter. The results are compared with the available experimental data and conclusions are drawn regarding the relative vulnerability of these different tube array geometries to streamwise FEI.

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