Vibration Of Tube Bundles Research Articles

Coulomb friction modelling in numericalsimulations of vibration and wear work rate of multispan tube bundles

The working life of heat exchanger multispan tube bundless, and similar components subjected to flow-induced virabtion, is heavily dependent on nonlinear interaction between the loosely supported tubes and their supports. Therefore, reliable wear prediction techniques must account for a number of factorscontrolling impact-sliding tube response, such as tube support gap, contact stiffness impact damping, Coulomb friction and squeeze film effect at supports. Tube fretting wear potential risk may then be adequately quantified by an equivalent wear work rate. In this paper, a simple model is presented which accounts for the key aspects of dry friction and is well suited to the efficient explicit numerical integration schemes, specifically through nonlinear modal superposition. Extensive parametric two-dimensional simulations, under random vibration induced byflow turbulence, are presented. Also, the effect of permanent tube-support preload, arising from cross flow drag, tube-support masalignment and thermal expansion, is investigated. Results show that frictional forces consistently reduce wear work rates, which decreasefor higher values of the coefficient of friction. Indeed, such reductions may be extremely important for the limiting case when preload and frictional forces rate of sufficient magnitude to overcome dynamic forces, preventing tube-support relative motion.

Vibration of Tube Bundles in Two-Phase Cross-Flow: Part 3—Turbulence-Induced Excitation

Abstract An extensive experimental program was carried out to study the vibration behavior of tube bundles subjected to two-phase cross-flow. Turbulence-induced excitation is discussed in Part 3 of this series of three papers. Random vibration response to turbulence-induced excitation is a significant vibration mechanism in heat exchanger tube bundles subjected to two-phase cross-flow. The vibration responses of centrally located tubes in four tube bundle configurations subjected to air-water cross-flow was measured. The results are presented in the form of a normalized forced-excitation spectrum which can be used as a design guideline over a void fraction range from 25 percent to 99 percent and over a practical range of flow rates. The data are further analyzed to determine the dependence of the vibration response on Reynolds number, void fraction and frequency. Measurements taken on a single tube, a row of tubes and on tubes having varying end conditions were used to assist in interpreting the bundle data.

Turbulence-Induced Vibration of Tube Bundle in Cross and Parallel Jet Mixed Flow

Abstract In the multi-tube type of heat exchanger, baffle plates are located at appropriate intervals to support the heat transfer tubes. Depending on the baffle plate type employed, the flow field in the tube bundle will consist of a mixture of the cross flow (the fluid flows at right angles to the tube bundle along the baffle plate surfaces) and the parallel jet flow (the fluid streams through channels such as the flow holes of the baffle plates in the form of jets and flows in parallel with the tube bundle). Vibrations induced by the flow can cause fretting wear and fatigue of the heat transfer tubes. Therefore, it it essential to establish a method of evaluating heat transfer tube vibrations induced by the mixed flow for the purpose of evaluating the integrity of heat exchanger tubes. In this paper, three different flows, that is, cross, parallel jet and mixed flows, were simulated in order to clarify the relationships between the flow conditions and vibration of the tube bundle, and to study a method for evaluating tube bundle vibrations induced by turbulence in the mixed flow field by using the vibration characteristics in the cross flow field and the parallel jet flow field.

Stability effects in a normal triangular cylinder array

Fluid-elastic vibrations in tube bundles are often responsible for major damage and very high shutdown costs. The onset is manifested by a rapid increase in the tube vibration amplitude at a particular critical flow velocity and is strongly dependent upon various physical parameters. In this paper, experimental results showing a second stability boundary for a flexibly mounted cylinder in an otherwise fixed cylinder array are presented. It is shown that minor variations of the array geometry affect its vibration mode. The stability boundaries, for various configurations of flexibly mounted and fixed cylinders in the array, have been measured. The resulting stability boundaries are plotted as functions of the mass-damping parameter and amplitude-diameter ratio in stability diagrams. The results are critically compared with known results from the literature. A closed-circuit wind tunnel with a 1·5 m diameter, 2·1 m long test section is used for the tests. The eighteen 80 mm × 800 mm aluminium cylinders in the multi-row normal triangular array have a pitch-to-diameter ratio of 1·25 and are, when not fixed, linear iso-viscoelastically mounted. Additionally, the linear damping of nine cylinders (4, 3 and 2 cylinders in the first, second and third cylinder row, respectively) can be continuously varied over the wide mass-damping parameter range of 10 2

Vibration of tube bundle induced by cross and parallel jet mixed flow. 1st report. The relation between flow distribution and vibration.

Vibration of tube bundle induced by cross and parallel jet mixed flow. 1st report. The relation between flow distribution and vibration.

An experimental investigation of fluid-elastic instability for a single row of tubes subjected to two-phase cross flow.

Interesting features, connected with fluid-elastic vibration of tube bundles in a cross flow, have been reported in many papers. Most of the experiments were done for single-phase (liquid or air) flow. This paper presents an experimental investigation on vibrations of a row of five circular tubes with P/D =1.33, subjected to single-phase water and two-phase (air-water) cross flow. Experiments covered mass-damping parameters from 0.9 to 5 by changing the damping ratio. Experimental results show differences in characteristics of vibration response between those for pure water and two-phase flows. Depending on conditions specified by mass-damping parameters, void fraction and reduced flow velocity, air bubbles contained in the flow destabilize the vibrations of the row of tubes or they suppress the vibrations. Further, critical flow velocity for two-phase flow induced fluid-elastic vibration has been made clear for mass-damping parameters ranging from 0.9 to 5.

Vibration of Tube Bundles Subjected to Two-Phase Cross-Flow

Two-phase cross-flow exists in many shell-and-tube heat exchangers such as condensers, reboilers and nuclear steam generators. Thus we are conducting a comprehensive program to study tube bundle vibrations subjected to two-phase cross-flow. This paper presents the results of experiments on a normal-triangular and a normal-square tube bundle, both of p/d = 1.47. The bundles were subjected to air-water mixtures to simulate realistic vapor qualities and mass fluxes. Vibration excitation mechanisms were deduced from vibration response measurements. Results on damping, hydrodynamic mass, fluid-elastic instability and random turbulence excitation in two-phase cross-flow are presented.