Vibration In Heat Exchangers Research Articles

Fluid-elastic Instability Effect of Groove Cylinder in Heat Exchanger

The fluidelastic instability impact of groove cylinders in heat exchangers are investigated in this study, and explores associated phenomena of flow-induced vibration and fluidelastic instability. The primary focus is on investigating the performance of various rows of tubes in the tube bundle, with a particular emphasis on the largest instability identified in the third row. The analysis also considers the impact of a triangular arrangement of tubes within the tube bundle. The addition of groove tubes in the heat exchanger proved to greatly delay the onset of fluidelastic instability, lowering the possibility of flow induced vibration. Despite the improved impact of groove cylinders, the study found that the third row of tubes in the tube bundle had a higher degree of instability than the other rows. This result emphasizes the significance of tube location and arrangement throughout the design phase in reducing fluidelastic behavior. Overall, this study shows that groove tubes may delay fluidelastic instability and reduce the frequency of flow-induced vibration in heat exchangers. The design may significantly improve the operating efficiency and reliability of the heat exchanger by using groove cylinders and carefully studying tube designs and optimize heat exchanger performance.

Study on Behavior of the Heat Exchanger with Conically-Corrugated Tubes and HDD Baffles

Baffles with holes in different diameters (or HDD baffles) and conically-corrugated tubes are respectively longitudinal flow baffle and high-efficiency heat exchange tubes proposed by the author. In this paper, vibrations of tube bundles with HDD baffles and fluid flow as well as heat transfer inside conically-corrugated tubes were numerically simulated, and the heat exchanger with conically-corrugated tubes and HDD baffles was tested for the heat transfer efficiency. It is found that compared with the traditional segmental baffles, tube bundle vibrations in heat exchangers, if using the HDD baffles, can be significantly reduced. Regarding heat transfer efficiency, conically-corrugated tubes are much better than smooth tubes and even better than other high-efficiency heat transfer tubes. Compared with the traditional heat exchangers, heat exchangers constructed with conically-corrugated tubes and the HDD baffles can provide better heat transfer efficiency and less tube bundle vibration.

EFFICIENCY OF TUBE-IN-TUBE HEAT EXCHANGER

Actual problems of heat exchangers efficiency are considered. It is assumed that the use of ultrasonic vibrations in heat exchangers will help to increase the of heat exchange efficiency, and to reduce the amount of deposits and spume in tube side. Ultrasonic cleaning, as a method of cleaning the surface from solids in washing liquids, in which ultrasonic vibrations are introduced into the liquid in one way or another, is a known technological technique. Application of ultrasound usually significantly speeds up the cleaning process and improves its quality. At the same time, it is possible to replace flammable and toxic solvents with safer detergents without loss of clean- ing quality. Cleaning is due to the combined effect of various non-linear effects arising in the liquid under the influence of powerful ultrasonic vibrations. These effects are cavitation, acoustic currents, sound pressure, sound-capillary effect, among which cavitation plays a decisive role. Pulsating and col- lapsing near contaminants cavitational bubbles destroy them. This effect is known as cavitation erosion. As is known, ultrasonic action leads to a decrease in the viscosity of the medium and, correspondingly, a decrease in the hydraulic resistance, an increase in the flow velocity, which makes it possible to use more viscous media in tube side of heat exchangers. It is also possible to increase the heat transfer due to the internal friction of the molecules of the substance in the ultrasonic field. The passage of ultrasound in media is accompanied by their heating due to the conversion of acoustic energy into thermal energy as a result of ultrasound absorption. The thermal effect is inextricably linked with the mechanical action of ultrasound, since one of the possibilities of heat formation is the conver- sion of mechanical energy into thermal energy as a result of absorption. In the CFX module of the ANSYS software complex, modeling of heat exchange with a change in viscosity was carried out, which is caused by ultrasound effect. The calculations results draw conclusions about the positive effect of ultrasonic oscillations of the medium on heat transfer.

Parametric study of flow-induced vibrations in cylinder arrays under single-phase fluid cross flows using POD-ROM

Modeling numerically Flow-Induced Vibrations in heat exchangers at a microscopic scale requires high computational resources and time which are still unreachable. Therefore model reduction is investigated in the present work in order to address the issue of simulation computational time reduction. In the framework of POD-Galerkin projection methods, the purpose is to propose optimal a posteriori reduction strategies enabling error control on approximation as well as Reduced-Order Model (ROM) interpolation to deal with sensitivity analysis of solutions to parameter perturbations. A multi-phase fluid–solid POD-Galerkin-based method is proposed for modeling flows and vibrations in cylinder arrangements under single-phase fluid cross-flows. Moreover a single-POD basis method is evaluated in the context of ROM interpolation. This work is a first step in the development of robust ROM describing fluid and solid dynamics in the presence of turbulence, heat transfer effects and large magnitude structure displacements and deformations.

Experimental study on cross-flow induced vibrations in heat exchanger tube bundle

Vibration in heat exchangers is one of the main problems that the industry has faced over last few decades. Vibration phenomenon in heat exchangers is of major concern for designers and process engineers since it can lead to the tube damage, tube leakage, baffle damage, tube collision damage, fatigue, creep etc. In the present study, vibration response is analyzed on single tube located in the centre of the tube bundle having parallel triangular arrangement (60°) with P/D ratio of 1.44. The experiment is performed for two different flow conditions. This kind of experiment has not been reported in the literature. Under the first condition, the tube vibration response is analyzed when there is no internal flow in the tube and under the second condition, the response is analyzed when the internal tube flow is maintained at a constant value of 0.1 m/s. The free stream shell side velocity ranges from 0.8 m/s to 1.3 m/s, the reduced gap velocity varies from 1.80 to 2.66 and the Reynolds number varies from 44500 to 66000. It is observed that the internal tube flow results in larger vibration amplitudes for the tube than that without internal tube flow. It is also established that over the current range of shell side flow velocity, the turbulence is the dominant excitation mechanism for producing vibration in the tube since the amplitude varies directly with the increase in the shell side velocity. Damping has no significant effect on the vibration behavior of the tube for the current velocity range.

Fluid Excitation Forces on a Tightly Packed Tube Bundle Subjected in Cross-Flow

Fluid excitation forces acting on stationary cylinders with cross-flow are the coupling of vortex shedding and turbulence buffeting. Those forces are significant in the analytical framework of fluid-induced vibration in heat exchangers. A bench-scale experimental setup with an instrumented test bundle is constructed to measure fluid excitation forces acting on cylinders in the normal triangular tube arrays (P/D = 1.28) with water cross-flow. The lift and drag forces on stationary cylinders are measured directly as a function of Reynolds number with a developed piezoelectric transducer. The results show that the properties of fluid excitation forces, to a great extent, largely depend upon the locations of cylinders within bundle by comparison to the inflow variation. A quasi-periodic mathematical model of fluid excitation forces acting on a circular cylinder is presented for a tightly packed tube bundle subjected to cross-flow, and the bounded noise theory is applied between fR = 0.01 and fR = 1. The developed model is illustrated with lots of identification results based on the dominant frequency, the intensity of random frequency, and the amplitude of fluid excitation forces. A second model has been developed for fluid excitation forces between fR = 1 and fR = 6 with the spectrum index introduced. Although still preliminary, each model can predict the corresponding forces relatively well.

Numerical investigation on heat transfer performance of planar elastic tube bundle by flow-induced vibration in heat exchanger

This study numerically investigated the heat transfer enhancement of planar elastic tube bundle by flow-induced vibration based on a two-way fluid structure interaction (FSI) model in the range of inlet velocity 0.2–0.5m/s. This two-way FSI calculation involved the unsteady, three-dimensional incompressible Navier–Stokes equation solved with finite volume approach and the dynamic equilibrium equation of tube bundle solved with finite element method combined with dynamic mesh scheme, which was verified by comparing with the published experimental results. Then the Nusselt number of the circumference of tube, local position, single tube and the overall tube bundle was presented. The performance evaluation criterion (PEC) was selected to study the heat transfer performance of planar elastic tube bundle. Results show that vibration frequency dominates the heat transfer enhancement at the local position near the mass-block. In the middle of tube bundle, vibration amplitude plays a significant role on heat transfer enhancement. Therefore, the average heat transfer enhancement of 12.97% and 4.58% at the middle two tubes is higher than that of 5.37% and 2.4% at the innermost and outermost tubes when the inlet velocity is 0.2m/s and 0.5m/s, respectively. In the range of inlet velocity 0.2–0.5m/s, flow-induced vibration contributes to enhancing the heat transfer of planar elastic tube bundle at low inlet velocity, resulting in the heat transfer enhancement of 8.26%, 6.07%, 5.67% and 3.91% respectively. Compared to the mechanical vibration strengthening heat transfer technology, flow-induced vibration plays an advantage on energy conversion to improve heat transfer. PEC indicates that the higher inlet velocity is sometimes more acceptable to obtain a higher heat transfer coefficient in the industry production.

Experimental study of shell side flow-induced vibration of conical spiral tube bundle

Conical spiral tube bundles are widely used in enhancing the heat transfer via the flow-induced vibration in heat exchangers. The shell side flow-induced vibration of the conical spiral tube bundle is experimentally investigated in this paper. The experiment table was built and the operational modes, the vibration parameters of the tube bundle were analyzed. The results show that, the operational mode frequencies of the conical spiral tube are decreased as the shell-side fluid flow velocity increases, especially for the first order frequency. Within the parameter range of this experiment, the real working frequency of the conical spiral tube is between the 1st and the 2nd operational modes, and the free end vibration amplitude of the tube bundle increases greatly when the shell side fluid flow velocity exceeds a critical value.

Study on the Conical Spiral Tube Bundle Heat Exchangers with Pulsation Flow Generator Structure

Elastic tube bundles are universally used in heat transfer enhancement by flow-induced vibration in heat exchangers, and the study of the heat transfer performance is of importance. The structure of conical spiral tube bundle heat exchanger was introduced first, and the structure of pulsation flow generator was also introduced. The frequency of pulsation flow was discussed. Finally, in condition of same shell side diameter, the heat transfer and natural frequency of the conical spiral tube bundle were compared with the planar elastic tube bundle. The results show that the natural frequency of conical spiral tube bundle was smaller, the heat transfer performance of conical spiral tube bundle was better than the planar elastic tube bundle.

Vibration Characteristics of Multiple Conical Spiral Tube Bundles in Heat Exchangers

Elastic tube bundles are universally used in heat transfer enhancement via the flow-induced vibration in heat exchangers, and the study of the tube vibration characteristic is essential. The natural vibration of multiple conical spiral tube bundles was discussed in this paper based on numerical simulation. The substructures of ten conical spiral tubes, the inlet and the outlet branch were set up individually. Then the mass matrix and the stiffness matrix of these substructures were calculated. The general matrices were obtained and the vibration equation of the overall structure was founded. The results show that the natural frequencies of the multiple conical spiral tube bundles are smaller than the traditional planar elastic tube bundles and each natural vibration mode has a frequency band, which contains several natural frequencies.

Heat transfer enhancement by flow-induced vibration in heat exchangers

The flow-induced vibration in heat exchanger is usually considered as a detrimental factor for causing the heat exchanger damage and is strictly prevented from its occurrence. Its positive role for the possible heat transfer enhancement has been neglected. In this article a novel approach is proposed to enhance the heat transfer by using the flow-induced vibration of a new designed heat transfer device. Thus the flow-induced vibration is effectively utilized instead of strictly avoiding it in the heat exchanger design. A heat exchanger is constructed with the new designed heat transfer devices. The vibration and the heat transfer of these devices are studied numerically and experimentally, and the correlation of the shell-side convective heat transfer coefficient is obtained. It is found that the new designed heat exchanger can significantly increase the convective heat transfer coefficient and decrease the fouling resistance. Therefore, a lasting heat transfer enhancement by the flow-induced vibration can be achieved.

WS4-3 熱交換器管群の流動励起振動評価の現状と課題(WS4 柱状構造物の流力振動,ワークショップ)

WS4-3 熱交換器管群の流動励起振動評価の現状と課題(WS4 柱状構造物の流力振動,ワークショップ)

Flow-Induced Vibration in Heat Exchangers

Heat exchanger tube bundles may fail due to excessive vibration or noise. The main failure mechanisms are generated by the shellside fluid that passes around and between the tubes. This fluid may be a liquid, gas or multi-phase mixture. The most severe vibration mechanism is a fluidelastic instability, which may cause tube damage after only a few hours of operation. Clearly, such extreme causes of vibration must always be avoided. In contrast buffeting due to flow-turbulence causes very little vibration. However, after many years of service such remorseless low level vibration will produce tube wall thinning, due to fretting, which may be unacceptable in a high-integrity heat exchanger. Consequently, the issues of life cycle and integrity must frequently be included in heat exchanger specification. This paper reviews the various mechanisms that cause vibration and noise. Particular attention is given to methods for achieving good tube support arrangements that minimize vibration damage. References to the most recent sources of data are given and good working practice for the design and operation of standard and high-integrity heat exchangers is discussed.

EXPERIENCE WITH UNUSUAL ACOUSTIC VIBRATION IN HEAT EXCHANGER AND STEAM GENERATOR TUBE BANKS

Cases of atypical acoustic vibration in heat exchanger and steam generator tube banks are presented. The cases include a tubular air heater with acoustic vibration developed in the flow direction, a steam generator tube bank with vibration developed along the tubes, and a shell and tube process heat exchanger with acoustic vibration developed in the shell axial direction. The vibratory cases were compared with a number of steam generator tube banks in service which did not develop acoustic vibration. The vibration prediction methodology developed recently for heat exchangers vibrating in the transverse acoustic modes was applied to the cases studied. It is shown that this methodology is also applicable to the prediction of the unusual acoustic vibration described in this paper.

Unusual Acoustic Vibration in Heat Exchanger and Steam Generator Tube Banks Possibly Caused by Fluid-Acoustic Instability

Flow channels of heat exchangers or steam generators containing tube arrays can be subject to acoustic vibration excited by flow of air, gas, or steam tranversely across the tubes. Such vibration occurs when a flow disturbance inside the tube bank excites a strong acoustic (standing wave) mode of the channel. The acoustic modes typically excited are those related to the dimension perpendicular to both the fluid flow direction and the tube axes. Preventive measures taken in the design stage are typically directed against these commonly existing standing waves. Evidence is presented of the unusual occurrence of standing waves that develop in the flow direction and in the tube axial direction. The causes for their development and methods of suppression are discussed.

Fluid dynamic forces on vibrating tubes of heat exchangers in cross-flow

We report results on the excitation of vibration of tubes in cross-flow, and in particular, on fluctuating fluid dynamic forces which act on rigidly fixed nonvibrating tubes; this approach excludes fluidelastic excitation. The results comprise measured values of fluctuating pressure on tube surfaces, as well as fluctuating local velocities, correlation lengths of the vortex structures, fluid dynamic forces on tubes and their vibration characteristics. Numerical solutions give the fluctuating fluid dynamic forces and the effect of parameters related to shear flows on a vibrating single tube, also in the experimental investigation of forces on the tube in a bundle. The study covered the Reynolds number range from 10 3 to 2 × 105 in water and air flows. Both the analysis and the experiment suggest that with small vibration amplitudes ( Ā/d ≤ 0·2) fluid dynamic behaviour on vibrating tubes does not differ from that on stationary tubes. Average correlation lengths of the vortex structures are l c /d = 0·9 for tubes in the bundle interior, and h/d from 2 to 3 for the leading rows. This is an indication of an incomplete separation from the tubes. The coherence function between measured fluid dynamic forces on tubes and their vibration parameters shows a nearly linear relation. This suggests the possibility of using the linear equations of motion as a mathematical description of flow-induced tube vibration in heat exchangers.

Shellside Waterflow-Induced Tube Vibration in Heat Exchanger Configurations With Tube Pitch-to-Diameter Ratio of 1.42

Abstract The pitch-to-diameter ratio (P/D) of the tube layout in shell-and-tube heat exchangers is one of the major parameters with which the designer may control heat transfer and pressure drop and facilitate mechanical cleaning. As part of a comprehensive investigation of waterflow-induced tube vibration in an industrial-size research heat exchanger, various configurations characterized by different design parameters, including P/D ratio, had been investigated. To provide a comparison with previous data obtained with P/D = 1.25, this paper presents the results of a study of eight different tube bundle configurations with P/D = 1.42. Four equilaterally spaced tube layout patterns and two baffle edge orientations were investigated. The results indicate that the greater flow area of the P/D = 1.42 configuration increases flow penetration into the bundle, reduces the tube-to-tube vibration coupling and generally provides less well-defined, even though sometimes improved, fluidelastic instability thresholds.

熱交換器における管群の振動と気柱の共鳴(<小特集>流体関連振動)

熱交換器における管群の振動と気柱の共鳴(<小特集>流体関連振動)

Acoustic phenomena in a steam generating unit

With the increased capacity of modern power plants, the study of flow-induced vibrations in heat exchangers has become an important problem. Tube-banks are sources of noise. This noise can be amplified by the acoustical resonances of the circuit and induce severe stresses in the structures. In this paper, it is shown that the acoustic behaviour of a complex circuit, such as a steam generating unit, can be calculated with good accuracy.

Closure to “Discussions of ‘Modeling of Flow-Induced Vibrations In Heat Exchangers and Nuclear Reactors’” (1975, ASME J. Fluids Eng., 97, p. 395)

Closure to “Discussions of ‘Modeling of Flow-Induced Vibrations In Heat Exchangers and Nuclear Reactors’” (1975, ASME J. Fluids Eng., 97, p. 395)