Bundle Configurations Research Articles

A new LMR steam generator free from SWR with a double tube bundle configuration

This paper describes the activities made at KAERI to develop an advanced liquid metal reactor (LMR) steam generator which is free from a sodium water reaction (SWR) to resolve the concern of the SWR possibility and improve the economic features of the LMR. The steam generator design houses two tube bundles that are functionally different and its tube bundle region is radially or vertically divided into two. The SG is equipped with hot and cold fluid tube bundles, a medium fluid and a pump. It prevents the occurrence of the sodium water reaction while sodium is still used as the coolant for the primary heat transport system. The feasibility of using the SG with a double tube bundle for an actual use in a LMR plant is evaluated by setting up the skeleton of the NSSS for various possible configurations of the SG tube bundles. Analysis was made for various types of the new steam generator with a double tube bundle. Since the heat transfer in the SG is made among three different fluids, it has unique heat transfer characteristics. The analysis showed the possibility of the occurrence of an undesirable reversed heat transfer not only in the integrated single-region bundle type but also in the integrated double-region bundle type. The performance analysis revealed practical performance characteristics for the various bundle configurations. Also the feasibility study for the various NSSS configurations with the new SG is described.

Tensile and compressive properties of carbon nanotube bundles

Molecular dynamics (MD) simulations were used to calculate the tensile and compressive properties of carbon nanotube (CNT) bundles, with the atomic interactions modeled by the short-range Brenner potential coupled with the long-range van der Waals potential. The dependence of the tensile and compressive properties of various configurations of CNT bundles was investigated. The critical strains, failure and buckling loads were determined and presented for the different configurations of CNT bundles. The average failure load of each single-walled carbon nanotube (SWCNT) in a CNT bundle can be used to determine the failure load of the entire CNT bundle of any sizes. The MD simulations also reveal that CNT bundles comprising bigger SWCNTs will exhibit higher strength. The average buckling load of each SWCNT was computed and compared with earlier reported buckling loads for individual SWCNTs and it was found that the presence of intratube van der Waals interactions tend to weaken the CNT bundles.

Vertical, Bubbly, Cross-Flow Characteristics over Tube Bundles

Two-phase flow over tube bundles is commonly observed in shell and tube-type heat exchangers. However, only limited amount of data concerning flow pattern and void fraction exists due to the flow complexity and the difficulties in measurement. The detailed flow structure in tube bundles needs to be understood for reliable and effective design. Therefore, the objective of this study was to clarify the two-phase structure of cross-flow in tube bundles by PIV. Experiments were conducted using two types of models, namely in-line and staggered arrays with a pitch-to-diameter ratio of 1.5. Each test section contains 20 rows of five 15 mm O.D. tubes in each row. The experiment’s data were obtained under very low void fraction (α<0.02). Liquid and gas velocity data in the whole flow field were measured successfully by optical filtering and image processing. The structures of bubbly flow in the two different configurations of tube bundles were described in terms of the velocity vector field, turbulence intensity and void fraction.

Monte Carlo simulations of hydrogen adsorption in alkali-doped single-walled carbon nanotubes

Monte Carlo simulations and Widom's test particle insertion method have been used to calculate the solubility coefficients (S) and the adsorption equilibrium constants (K) in single-walled (10,10) armchair carbon nanotubes including single nanotubes, and nanotube bundles with various configurations with and without alkali dopants. The hydrogen adsorption isotherms at room temperature were predicted by following the Langmuir adsorption model using the calculated constants S and K. The simulation results were in good agreement with experimental data as well as the grand canonical Monte Carlo simulation results reported in the literature. The simulations of nanotube bundle configurations suggest that the gravimetric hydrogen adsorption increases with internanotube gap size. It may be attributed to favorable hydrogen-nanotube interactions outside the nanotubes. The effect of alkali doping on hydrogen adsorption was studied by incorporating K+ or Li+ ions into nanotube arrays using a Monte Carlo simulation. The results on hydrogen adsorption isotherms indicate hydrogen adsorption of 3.95 wt% for K-doping, and 4.21 wt% for Li-doping, in reasonable agreement with the experimental results obtained at 100 atm and room temperature.

General models of optical-fiber-bundle displacement sensors

General models of optical-fiber-bundle displacement sensors are presented and their design and implementation are described. They are applicable to various bundle configurations and light sources. Moreover, they can be easily expanded to any combined bundles. A double concentric fiber-bundle sensor is constructed for verifying our developed models. Good agreement between the experimental and theoretical results shows the theoretical models are accurate. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 47: 494–497, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21209

Transverse mechanical properties of carbon nanotube crystals. Part II: sensitivity to lattice distortions

Perfect crystals of carbon nanotubes tend to form aligned bundles that assume a hexagonal packing configuration in a minimum energy state. The theoretical constitutive relation for these defect-free crystals is highly anisotropic with a large axial stiffness due to a network of strong delocalized carbon–carbon bonds and transverse properties that are orders of magnitude lower due to a sole dependence on non-bonding van der Waals forces. The assemblage of a large number of collimated nanotubes may be expected to exhibit a distribution of lattice sites containing imperfections caused by packing faults or inclusions that will function as ‘weak-links’ and adversely affect local stiffness and strength. The present study is therefore directed towards quantifying the effects of distorted bundle configurations on mechanical properties. To illustrate distortion sensitivity, the transverse shear and bulk moduli are calculated by considering various magnitudes of random perturbations in nanotube packing. Monte Carlo simulations are performed to obtain a statistical distribution of predicted moduli. The present analysis demonstrates that even small perturbations to the lattice geometry give rise to large variations in transverse moduli, and suggests that chemical functionalization to improve nanotube bundle cohesion may be required for successful structural applications.

A Modified Cryo-Jaw for in Vitro Biomechanical Testing of Tendons

The purpose of this study was to develop a new device, which represents a modification of the Cryo-Jaw described by Riemersa and Schamhardt and modified by Hamner et al., for in vitro biomechanical testing of tendons which allows the lower clamp to move in every direction and thus simulate a pathological dislocation of the knee. Tendons are fixed to the device by freezing the clamped part with dry ice. After fixation of their free ends, the lower clamp was rotated 45°, translated 1 cm, and angled 40° to simulate a knee sprain. Various configurations of bundles were tested: parallel, twisted, and braided. Tests were performed on 10 paired bovine bifurcated digital extensor tendons and 6 paired human hamstring tendons. Grafts were then tested to failure subjected to impulsive load, using a servohydraulic machine. The highest ultimate load recorded for parallel bundles was 4662 ± 565.71 N for bovine bifurcated digital extensor tendons, and 3057 ± 475.44 N for human hamstring tendons. In any case, the tendons ruptured midway, well clear of the frozen part; in no case was slippage of the tendons observed. Thus the device proposed allows one to test what happens to the graft of an ACL reconstructed knee during physiological and pathological movements because it can be easily displaced in every direction.

Magnetic field exposures for UK live-line workers

Dosimetry is evaluated for live-line workers exposed to 50 Hz non-uniform magnetic fields from typical high-voltage transmission lines in the United Kingdom. The configurations involve twin-, triple- and quadruple-conductor transmission line bundles. Scenarios include three worker postures for the twin and triple bundles, and four postures for the quadruple bundle. The postures are selected to simulate worst case scenarios representative of work practices and result in highest values of dosimetric measures in critical organs. Only single-phase bundles are considered, as adjacent bundles of differing phase result only in a small reduction of the dosimetric measures. Reported data include various measures of the electric field and current density induced in tissues, as well as of the current density averaged over 1 cm2 areas normal to the current flow. A value of this latter quantity of 10 mA m−2 is suggested as a threshold for neural tissue in the UK and international regulations. Critical tissues considered in this study include the retina, spinal cord, brain and cerebrospinal fluid. Some discussion is devoted to problems associated with the concept of current-density averaging, and two algorithms are considered. For a nominal load of 1 kA per subconductor, averaged current densities exceed the guideline bounds, only for a small number of postures and bundle configurations, in the brain, retina and cerebrospinal fluid. Non-averaged current densities in the cerebrospinal fluid exceed the suggested bound for all scenarios modelled, as well as in the retina for three postures involving a quadruple bundle.

The Effects of Bundle Geometry on Heat Exchanger Tube Vibration in Two-Phase Cross Flow

Many shell-and-tube heat exchangers operate in two-phase flows. This paper presents the results of a series of experiments done on tube bundles of different geometries subjected to two-phase cross flow simulated by air-water mixtures. Normal (30 deg) and rotated (60 deg) triangular, and normal (90 deg) and rotated (45 deg) square tube bundle configurations of pitch-to-diameter ratio of 1.2 to 1.5 were tested over a range of mass fluxes from 0 to 1000 kg/(m2s) and void fraction from 0 to 100 percent. The effects of tube bundle geometry on vibration excitation mechanisms such as fluidelastic instability and random turbulence, and on dynamic parameters such as damping and hydrodynamic mass are discussed.

Calculation of spacer compression for bundle lines under short-circuit

In a recent Institute paper, the authors presented experimental results on spacer compression, which showed clearly, that the simplified analytical calculation method used today, the so called Manuzio formula, leads to severe underestimation of spacer compression and thus to faulty spacer design. In this paper, further test results are presented covering today's practical range of bundle configurations, subspan lengths, sagging tensions and short-circuit levels for transmission lines. Based on these results, the authors present a new calculation method for spacer compression, which builds up on well accepted IEC standards.

Bundle-Flowline Thermal Analysis

Summary The bundle flowline involves packaging multiple flowlines, control, and injection lines within a single carrier pipe. A bundle is claimed to provide an effective means of insulating flowlines by use of low-cost materials; however, no rigorous heat transfer analysis of bundled flowline systems has been offered by the literature or the vendors. For this reason, the thermal performance of bundle- insulated flowlines has been studied with a general-purpose, finite- element, partial-differential equation solver. Steady-state and transient cooldown performance were analyzed for six different bundle configurations. Overall heat transfer coefficients for individual flowlines within a bundle have been determined in addition to cooldown performance for different insulation levels and pipe sizes. These results have been compared with results obtained for the simple bundle geometry of a pipe-in-pipe system, and found comparable. To expedite the calculation of overall heat transfer coefficients for bundle flowlines, simplified heat transfer calculations were developed as an approximation to the finite-element solutions. These approximations are on the average within 5% of the finite- element solution.

Overhead electrical transmission line galloping. A full multi-span 3-DOF model, some applications and design recommendations

A full multi-span three-degree-of-freedom (3-DOF) iced power transmission line model is presented. This new model is applicable for describing the galloping phenomena of both single and bundle lines, for performing static and dynamic analysis, and predicting the galloping behavior of iced power transmission lines, as well as for performing checks against field experience. Some applications for overhead power transmission lines design are detailed. Some original recommendations for the design of multi-span bundle configurations are also proposed.

Fluid-Damping Controlled Instability in Tube Bundles Subjected to Air Cross-Flow

There are different excitation mechanisms that cause fatal damages due to undesirable vibrations in heat exchanger tube bundles subjected to cross-flow. One of them is the fluid-damping-controlled instability (galloping) that is characterised by a sudden appearance of large amplitudes of the tubes exclusively in cross-flow direction. This paper reports on investigations using an experimental set-up in a wind tunnel where the galloping mechanism in a tube bundle can be observed as an isolated phenomenon. The apparatus allows to realise several tube bundle configurations and geometry's of real heat exchangers. The position of a flexible test tube with a linear iso-viscoelastic mounting inside the tube array is variable. The test tube is equipped with dynamical pressure sensors which are placed directly under pressure holes inside the tube. For the investigation of the acting fluid forces the non-stationary pressure distribution is measured simultaneously at 30 points on the circumference in mid plane and at 15 points in line along the tube together with the tube motion. The acting fluid forces are determined by integration of the whole pressure field process. The study gives insights into the effect of the fluid-damping-controlled instability that is still not fully understood. Moreover, a flow visualization gives an impression of the mechanism at relevant Reynolds-numbers. The results show that in case of instability due to galloping the correlation length of the forces acting along the tube axis increases suddenly to large values. The fluid forces are correlated well for the whole tube when galloping is dominant. The exciting fluid forces show harmonic character and lead to a classical resonance behaviour. Instead of a simple free vibration test in vacuum or still air, which is done mostly for fluid excited structures, the damping coefficient of the oscillating system is determined under operating conditions on the basis of the measured fluid forces. A comparison of the results with those of a free vibration test in still air is shown.

The Prediction of Wear in Fluidized Beds

Abstract A procedure is formulated to model impact and abrasion wear of surfaces exposed to a fluidized bed. A methodology adapting a single-particle wear model and the kinetic theory of gases to granular flows is used to develop a model accounting for impact wear from all possible particle collisions. Abrasive wear is modeled using a single-particle abrasion model adapted to describe the effects of many abrading particles. Parameters describing granular flow are necessary for evaluation of the resulting wear expressions. They are determined by numerical solution of the conservation equations describing fluidized-bed hydrodynamics. Additional parameters appear in the wear expressions which describe the contact between individual fluidized particles and the wearing surface. These are determined by an optimization procedure which minimizes error between predicted and measured wear rates. The modeling procedure was used to analyze several bubbling and turbulent fluidized bed experiments with single-tube and tube bundle configurations. Quantitative agreement between the measured and predicted wear rates was found, with some exceptions for local wear predictions. This work demonstrates a methodology for wear predication in fluidized beds.

Vibration of Tube Bundles in Two-Phase Cross-Flow: Part 1—Hydrodynamic Mass and Damping

Abstract Two-phase cross-flow exists in many shell-and-tube heat exchangers, such as condensers, reboilers and nuclear steam generators. An understanding of damping and of flow-induced vibration excitation mechanisms is necessary to avoid problems due to excessive tube vibration. Accordingly, we have undertaken an extensive program to study the vibration behavior of tube bundles subjected to two-phase cross-flow. In this paper we present the results of experiments on four tube bundle configurations; namely, normal triangular of pitch over diameter ratio, p/d, of 1.32 and 1.47, and parallel triangular and normal square of p/d of 1.47. The bundles were subjected to air-water mixtures to simulate realistic mass fluxes and vapor qualities corresponding to void fractions from 5 to 99 percent. Hydrodynamic mass and damping are discussed in Part 1 of this series of three papers. We found that hydrodynamic mass is roughly related to the homogeneous mixture density. The damping characteristics of all tube bundles are generally similar. Damping is maximum between 40 and 80 percent void fraction where the damping ratio reaches about 4 percent. The effect of mass flux is generally weak. Design guidelines are proposed for hydrodynamic mass and for damping.

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.

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.

Vibration of Tube Bundles in Two-Phase Cross-Flow: Part 2—Fluid-Elastic Instability

Abstract An extensive experimental program was carried out to study the vibration behavior of tube bundles subjected to two-phase cross-flow. Fluid-elastic instability is discussed in Part 2 of this series of three papers. Four tube bundle configurations were subjected to increasing flow up to the onset of fluid-elastic instability. The tests were done on bundles with all-flexible tubes and on bundles with one flexible tube surrounded by rigid tubes. Fluid-elastic instabilities have been observed for all tube bundles and all flow conditions. The critical flow velocity for fluid-elastic instability is significantly lower for the all-flexible tube bundles. The fluid-elastic instability behavior is different for intermittent flows than for continuous flow regimes such as bubbly or froth flows. For continuous flows, the observed instabilities satisfy the relationship V/fd = K(2πζm/ρd2)0.5 in which the minimum instability factor K was found to be around 4 for bundles of p/d = 1.47 and significantly less for p/d = 1.32. Design guidelines are recommended to avoid fluid-elastic instabilities in two-phase cross-flows.

Shellside Waterflow Pressure Drop Distribution Measurements in an Industrial-Sized Test Heat Exchanger

Throughout the life of a heat exchanger, a significant part of the operating cost arises from pumping the heat transfer fluids through and past the tubes. The pumping power requirement is continuous and depends directly upon the magnitude of the pressure losses. Thus, in order to select an optimum heat exchanger design, it is is as important to be able to predict pressure drop accurately as it is to predict heat transfer. This paper presents experimental measurements of the shellside pressure drop for 24 different segmentally baffled bundle configurations in a 0.6-m (24-in.) diameter by 3.7-m (12-ft) long shell with single inlet and outlet nozzles. Both plain and finned tubes, nominally 19-mm (0.75-in.) outside diameter, were arranged on equilateral triangular, square, rotated triangular, and rotated square tube layouts with a tube pitch-to-diameter ratio of 1.25. Isothermal water tests for a range of Reynolds numbers from 7000 to 100,000 were run to measure overall as well as incremental pressure drops across sections of the exchanger. The experimental results are given and correlated with a pressure drop versus flowrate relationship.

Flow-Induced Vibration in Shell-and-Tube Heat Exchangers with Double-Segmental Baffles

One of the techniques used by designers of shell-and-tube heat exchangers when they encounter a potential flow-induced vibration problem is to shift from a tube bundle with segmental baffles to one with double-segmental baffles. This results in a split of the flow into either half of the shell with lower velocities and makes it possible to reduce the unsupported tube span length while keeping below a given allowable pressure drop. Tests were performed as a part of a systematic study of water flow-induced vibration in industrial-size heat exchangers. Results for nine different double-segmental baffled bundle configurations are presented. Comparison of the results with those for similar segmental baffled bundles shows that higher flows can be tolerated without developing damaging flow-induced vibration.