Flow-Induced Vibrations of Heat Exchanger U-Tubes: A Simulation to Study the Effects of Asymmetric Stiffness

1983 ◽  
Vol 105 (1) ◽  
pp. 67-75 ◽  
Author(s):  
D. S. Weaver ◽  
D. Koroyannakis
Keyword(s):  
Heat Exchanger ◽  
Natural Frequencies ◽  
Symmetric Case ◽  
Triangular Array ◽  
Water Tunnel ◽  
Out Of Plane ◽  
Flow Induced Vibrations ◽  
Pitch Ratio ◽  
The Difference

A water tunnel study was conducted to study the effect of asymmetric stiffness on a parallel triangular array of tubes with a pitch ratio of 1.375. The tubes were cantilevered from rectangular support rods so that the stiffness, and hence natural frequencies, were different in directions parallel and transverse to the flow. This arrangement was designed to simulate the difference in in-plane and out-of-plane natural frequencies of curved tubes. A test was conducted with symmetric stiffness for datum purposes and then eight tests were run with differences between streamwise and transverse frequencies ranging from 6.3 to 57 percent. It was found that the critical reduced velocity based on the lower frequency was increased only slightly over the symmetric case. This effect is essentially independent of the difference in frequency and the direction of the lower frequency relative to the flow.

The Effect of Flat Bar Supports on the Crossflow Induced Response of Heat Exchanger U-Tubes

1983 ◽  
Vol 105 (4) ◽  
pp. 775-781 ◽  
Author(s):  
D. S. Weaver ◽  
W. Schneider
Keyword(s):  
Heat Exchanger ◽  
Wind Tunnel ◽  
Flow Velocity ◽  
Triangular Array ◽  
Induced Response ◽  
Elastic Instability ◽  
Pitch Ratio ◽  
Wind Tunnel Study

A wind tunnel study was conducted to determine the effect of flat bar supports on the crossflow induced response of heat exchanger U-tubes. The 13-mm-dia tubes formed a triangular array with a pitch ratio of 1.57 and a mean U-bend diameter of about 1.5 m. A 0.3-m-long section of the array was exposed to a flow parallel to the plane of the U-bends. Experiments were conducted with no supports, with one set of flat bars at the apex, and with two sets of flat bar supports at the apex and 45 deg points. In each case, the tube response was monitored to a flow velocity beyond that required for fluid elastic instability. Limited experiments were also conducted to examine the effect of tube support clearance on tube response. Conclusions are drawn regarding the effectiveness of flat bars as U-bend antivibration supports.

scholarly journals Vibration Analysis and Optimization of a Rectangular Plate with Flanging Hyperellipse Cutout

2018 ◽  
Vol 2018 ◽  
pp. 1-12 ◽  
Author(s):  
Wensheng Wang ◽  
Sier Deng ◽  
Song Zhang ◽  
Da Geng
Keyword(s):  
Rectangular Plate ◽  
Vibration Analysis ◽  
Natural Frequencies ◽  
Great Influence ◽  
Optimum Frequency ◽  
Out Of Plane ◽  
Nature Frequency ◽  
Parametric Studies ◽  
The Difference ◽  
Vibration Performance

Vibration analysis and optimization of a rectangular plate with a flanging hyperellipse cutout is investigated in this paper, numerically. In the analysis, finite element method (FEM) is applied to perform parametric studies on various plates in different boundary conditions, addressing the influence of different cutout parameters (area, shape, flanging height, position, and rotation) on the first- and second-order natural frequencies of the rectangular plate and providing references for the optimum frequency design. Then, maximization of frequency or the difference of two consecutive frequencies of the rectangular plate is carried out using Multi-island Genetic Algorithm, aiming to achieve the best dynamic characteristics. The results show that different cutout parameters have great influence on vibration performance of the plate, the existing of the flanging increases the out-of-plane stiffness of the plate. Additionally, the nature frequency of the plate has been improved obviously for different models with the optimal design of the cutout.

The Effect of Approach Flow Direction on the Flow-Induced Vibrations of a Triangular Tube Array

1983 ◽  
Vol 105 (1) ◽  
pp. 76-81 ◽  
Author(s):  
H. C. Yeung ◽  
D. S. Weaver
Keyword(s):  
Heat Exchangers ◽  
Small Amplitude ◽  
Flow Direction ◽  
Triangular Array ◽  
Incident Flow ◽  
Stability Threshold ◽  
Flow Induced Vibrations ◽  
Pitch Ratio ◽  
Flow Directions ◽  
The Stability

Water tunnel experiments were conducted on an equilateral triangular array of tubes with a pitch ratio of 1.5. Eight tests were run with different array orientations so that the effects of incident flow direction on crossflow induced vibrations could be studied. Small amplitude vorticity response was observed for all orientations except the parallel triangular array. A Strouhal number of 0.57 based on pitch velocity and independent of incident flow directions was found. The fluidelastic threshold for the normal triangular array was found to be about twice that of the parallel triangular array. However, the stability threshold for the normal triangular array was found to be quite sensitive to incident flow direction suggesting that advantage of this higher threshold should not be taken in the design of heat exchangers.

Experimental Observations of Nonlinear Nonplanar Oscillations of a Cantilever Beam

2007 ◽  
Author(s):  
Haider N. Arafat ◽  
Ali H. Nayfeh ◽  
Bashar K. Hammad
Keyword(s):  
Cantilever Beam ◽  
Natural Frequencies ◽  
Excitation Frequency ◽  
Low Frequency ◽  
Harmonic Load ◽  
Bending Vibrations ◽  
Out Of Plane ◽  
Frequency Components ◽  
Plane Bending ◽  
The Difference

The dynamics of a thin cantilever beam undergoing combined torsion and bending vibrations are examined experimentally. The beam’s fundamental natural frequencies in the two orthogonal bending motions and in torsion are fv1 = 5.719 Hz, fw1 = 189.730 Hz, and fφ1 = 138.938 Hz, respectively. A base-excitation shaker imparts a harmonic load that acts parallel to the width of the beam. First, the response of the beam is examined when the excitation frequency is equal to the fundamental torsion natural frequency (i.e., f = 138.9 Hz). For low levels of excitation, the motion consists mainly of hardly noticeable twisting vibrations. For high levels of excitation, the energy of the first torsion mode excites the first out-of-plane bending mode. In this case, the beam responses exhibit modulated vibrations containing both high-frequency and low-frequency components. Second, the beam is excited at the frequency f = 132.0 Hz, which is in the neighborhood the difference of these two natural frequencies. For large excitation levels, the beam vibrates with large-amplitude out-of-plane bending motions that exhibit chaotically intermittent behaviors.

Elimination of outlier measurements for damage detection of structures under changing environmental conditions

2021 ◽  
pp. 147592172199847
Author(s):  
William Soo Lon Wah ◽  
Yining Xia
Keyword(s):  
Damage Detection ◽  
Multiple Regression ◽  
Natural Frequencies ◽  
Detection Method ◽  
Detection Methods ◽  
Structure Model ◽  
Bridge Structure ◽  
Beam Structure ◽  
Dependent Variables ◽  
The Difference

Damage detection methods developed in the literature are affected by the presence of outlier measurements. These measurements can prevent small levels of damage to be detected. Therefore, a method to eliminate the effects of outlier measurements is proposed in this article. The method uses the difference in fits to examine how deleting an observation affects the predicted value of a model. This allows the observations that have a large influence on the model created, to be identified. These observations are the outlier measurements and they are eliminated from the database before the application of damage detection methods. Eliminating the outliers before the application of damage detection methods allows the normal procedures to detect damage, to be implemented. A multiple-regression-based damage detection method, which uses the natural frequencies as both the independent and dependent variables, is also developed in this article. A beam structure model and an experimental wooden bridge structure are analysed using the multiple-regression-based damage detection method with and without the application of the method proposed to eliminate the effects of outliers. The results obtained demonstrate that smaller levels of damage can be detected when the effects of outlier measurements are eliminated using the method proposed in this article.

Thermodynamic Estimate of Minimal Dissipation for Heat Exchange System

2008 ◽  
Author(s):  
Andrei A. Akhremenkov ◽  
Anatoliy M. Tsirlin ◽  
Vladimir Kazakov
Keyword(s):  
Heat Exchanger ◽  
Heat Exchange ◽  
Heat Load ◽  
Point Of View ◽  
Exchange System ◽  
Heat Exchange System ◽  
Heat Exchange Surface ◽  
Minimal Dissipation ◽  
The Difference ◽  
Exchange Surface

In this paper we consider heat exchange system from point of view of Finite-time thermodynamics. At first time the novel estimate of the minimal entropy production in a general-type heat exchange system with given heat load and fixed heat exchange surface is derived. The corresponding optimal distribution of heat exchange surface and optimal contact temperatures are also obtained. It is proven that if a heat flow is proportional to the difference of contacting flows’ temperatures then dissipation in a multi-flow heat exchanger is minimal only if the ratio of contact temperatures of any two flows at any point inside heat exchanger is the same and the temperatures of all heating flows leaving exchanger are also the same. Our result based on those assumptions: 1. heat transfer law is linear (17); 2. summary exchange surface is given; 3. heat load is given; 4. input tempretures for all flows are given; 5. water equivalents for all flows are given.

scholarly journals Out-of-Plane Vibration of Curved Uniform and Tapered Beams with Additional Mass

2017 ◽  
Vol 2017 ◽  
pp. 1-8 ◽  
Author(s):  
Hamdi Alper Özyiğit ◽  
Mehmet Yetmez ◽  
Utku Uzun
Keyword(s):  
Finite Element ◽  
Free Vibration ◽  
Boundary Conditions ◽  
Natural Frequencies ◽  
Variable Cross ◽  
Additional Mass ◽  
Inertia Effects ◽  
Tapered Beam ◽  
Out Of Plane ◽  
Good Agreement

As there is a gap in literature about out-of-plane vibrations of curved and variable cross-sectioned beams, the aim of this study is to analyze the free out-of-plane vibrations of curved beams which are symmetrically and nonsymmetrically tapered. Out-of-plane free vibration of curved uniform and tapered beams with additional mass is also investigated. Finite element method is used for all analyses. Curvature type is assumed to be circular. For the different boundary conditions, natural frequencies of both symmetrical and unsymmetrical tapered beams are given together with that of uniform tapered beam. Bending, torsional, and rotary inertia effects are considered with respect to no-shear effect. Variations of natural frequencies with additional mass and the mass location are examined. Results are given in tabular form. It is concluded that (i) for the uniform tapered beam there is a good agreement between the results of this study and that of literature and (ii) for the symmetrical curved tapered beam there is also a good agreement between the results of this study and that of a finite element model by using MSC.Marc. Results of out-of-plane free vibration of symmetrically tapered beams for specified boundary conditions are addressed.

Spiral-Plate Heat Exchanger Effectiveness With Equal Capacitance Rates

2005 ◽  
Author(s):  
Louis C. Burmeister
Keyword(s):  
Heat Exchanger ◽  
Plate Heat Exchanger ◽  
Close Approximation ◽  
Transfer Coefficients ◽  
Plate Heat ◽  
Heat Transfer Coefficients ◽  
Outer Periphery ◽  
Large Heat ◽  
The Difference ◽  
Spiral Plate

A formula is derived for the dependence of heat exchanger effectiveness on the number of transfer units for a spiral-plate heat exchanger with equal capacitance rates. The difference-differential equations that describe the temperature distributions of the two counter-flowing fluids, neglecting thermal radiation, are solved symbolically to close approximation. Provision is made for offset inlet and exit of the hot and cold fluids at the outer periphery and for large heat transfer coefficients in entrance regions. The peak effectiveness and the number of transfer units at which it occurs are predicted.

Vibrations of an Intermediately Supported U-Bend Tube

1975 ◽  
Vol 97 (1) ◽  
pp. 23-32 ◽  
Author(s):  
L. S. S. Lee
Keyword(s):  
Natural Frequency ◽  
Natural Frequencies ◽  
Experimental Tests ◽  
Bending Stiffness ◽  
Stiffness Ratio ◽  
Plane Vibration ◽  
Straight Beam ◽  
Out Of Plane ◽  
Straight Segments ◽  
Good Agreement

Vibrations of an intermediately supported U-bend tube fall into two independent classes as an incomplete ring of single span does, namely, the in-plane vibration and the coupled twist-bending out-of-plane vibration. Natural frequencies may be expressed in terms of a coefficient p which depends on the stiffness ratio k, the ratio of lengths of spans, and the supporting conditions. The effect of the torsional flexibility of a curved bar acts to release the bending stiffness of a straight beam and hence decrease the natural frequency. Some conclusions for an incomplete ring of single span may not be equally well applicable to the U-tube case due to the effects of intermediate supports and the presence of the supporting straight segments. Results of the analytical predictions and the experimental tests of an intermediately supported U-tube are in good agreement.

On-Line Fuzzy Logic Temperature Control of a Concentric-Tubes Heat Exchanger Facility

2006 ◽  
Author(s):  
Claudia Ruiz-Mercado ◽  
Arturo Pacheco-Vega ◽  
Kevin Peters
Keyword(s):  
Heat Exchanger ◽  
Temperature Control ◽  
Fuzzy Controller ◽  
Fuzzy Rule ◽  
Outlet Temperature ◽  
Single Input Single Output ◽  
Single Output ◽  
On Line ◽  
The Difference ◽  
Two Stages

We develop a fuzzy rule based controller to perform on-line temperature control of a concentric-tubes heat exchanger facility. The rules were derived from dynamical values of the mass flow rates and fluid temperatures in the heat exchanger. The controller was embedded in a closed-loop single-input single-output system to control the outlet temperature of the cold fluid. The controller was constructed in two stages, the difference between them being the amount of information provided to the controller. To validate the fuzzy controller two sets of tests were carried out for maintaining a constant value of the outlet temperature under different perturbations. Results from this analysis demonstrate that the fuzzy-based controller is able to achieve control of the system, and that the information about the system provided to it is important in terms of accuracy and efficiency.

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