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The behavior of flow within a rotating finite length cylinder has been investigated. For low rotational speeds, the flow is characterized by a non-uniform thickness i.e., rimming flow. Above a critical rotational speed, the flow transitions to annular flow. Correlations developed from the experimental data are presented for the three regimes: onset of annular flow, complete annular flow, and collapse of annular flow. The correlation for the collapse of annular flow compared well with a previously presented, theoretically developed correlation. Given that the heat transfer characteristics of rotating heat pipes depend upon the film thickness of the fluid charge, the correlations presented here will be valuable in determining regular operating conditions. [DOI: 10.1115/1.1411967]

Forced convection two-phase flow and its complete condensation in a miniature tube are discussed. A physical and mathematical model of annular film condensation in such a tube has been developed. The liquid flow in the model is coupled with the vapor flow along the liquid-vapor interface through the interfacial temperature, shear stress, heat flux, and pressure sump conditions because of surface tension effects. The model predicts the shape of the liquid-vapor interface along the condenser and the length of the two-phase flow region. Findings show complete condensation of the incoming vapor is possible at comparatively low heat loads.

Serpentine tubes with strip-type inserts and with refrigerant-134a are discussed relative to evaporative heat transfer and enhancement performance. Nucleate boiling from a heated wall with a strip-type insert has not been well understood in these circumstances and flow boiling tests were conducted in a 7-pass serpentine test tube 10.6 mm in insider diameter in a hot water bath.

A semi-analytical method is developed to solve the elliptic heat transfer equation in an eccentric annular fin circumscribing a circular tube. Both convective and insulated conditions at the fin tip are taken into account in the analysis. Results demonstrate that eccentric annular fins can be designed to have lesser volumes compared to concentric annular fins above a certain heat transfer duty particularly when space restriction is imposed on one side of the tube.

Investigation of environmental cracking of a 1100-MPa yield strength A 723 steel cannon tube subjected to prototype firings is described. Metallographic results show cracking of the steel beneath a 0.12-mm protective layer of chromium. Cracks undermine and remove sections of chromium and lead to localized erosion that ruins the cannon. Key features of the firing thermal damage and cracking are: (i) recrystalization of the chromium to a depth of up to 0.08 mm; (ii) steel transformation to 0.19 mm below the chrome surface; (iii) two different periodic arrays of cracks normal to the hoop and axial directions, with mean depths of 0.23 and 0.46 mm, respectively. Time-temperature-depth profiles for the firing cycle were derived via bi-material finite difference analysis of a semi-infinite solid which incorporated cannon combustion gas temperatures and material properties that vary as a function of temperature. The temperature and depth associated with the steel transformation were used to solve iteratively for the convective heat transfer coefficient. This value was further confirmed by the depths of chromium recrystalization and of the crack arrays in the two orientations. A profile of maximum temperature versus depth is used to determine the near-bore applied and residual stress distributions within the tube. The measured volume change of steel transformation is used to determine an upper limit on applied and residual stresses. These stresses are used to determine crack-tip stress intensity factors for the observed crack arrays, and hence provide some explanation for the differential depths of cracking. The near-bore temperature and residual stress distributions are used to help determine the cause of hydrogen cracking and measures to prevent cracking. Compressive yielding due to thermal loading produces near-bore tensile residual stresses, and thereby causes hydrogen cracking. Prevention of cracking is discussed in relationship to hydrogen crack growth rate tests of alternative alloys and coatings.

This paper describes numerical analysis of collapsible tube flow based on the one-dimensional distributed parameter model of Hayashi. In the present model the effect of flow separation at the collapsed part is replaced with simple viscous friction along the tube, so no ad-hoc modeling for flow separation in former studies is required. A stable semi-implicit numerical procedure based on the SIMPLE method is developed for the problem of flow and tube interaction. The numerical result for a characteristic self-excited oscillation agrees qualitatively with the experimental result. Nonlinear stability of the steady state dependent on the amplitude of the disturbance is numerically investigated and the result is compared with the linear stability analysis based on the former lumped parameter model. Finally, initiation of the self-excited oscillation is examined by applying the initial disturbance at the upstream end of the tube. The disturbance propagates in the downstream direction and is amplified to the self-excited oscillation.

The acoustic wave attenuation performance of Venturi tubes with zero mean fluid flow is investigated by: (1) combining analytical solutions for one-dimensional wave propagation in conical reducers, diffusers, and straight ducts; (2) employing a computational time-domain technique; and (3) conducting experiments in an extended impedance tube setup with four fabricated Venturi tubes and matching contraction chambers. The results from both analytical and computational approaches compare well with each other and the experimental data. The numerical technique is also applied to address the effects of a compressible mean flow on the acoustic behavior. Finally, the flow performance of the fabricated Venturi tubes is measured and the trade-offs are discussed between flow efficiency and acoustic performance.

The local aerodynamic and heat transfer performance were measured in a rib-roughened square duct as a function of the rib pitch to height ratio. The blockage ratio of these square obstacles was 10 or 20 percent depending on whether they were placed on one single (1s) or on two opposite walls (2s). The Reynolds number, based on the channel mean velocity and hydraulic diameter, was fixed at 30,000. The aerodynamic description of the flow field was based on local pressure distributions along the ribbed and adjacent smooth walls as well as on two-dimensional LDV explorations in the channel symmetry plane and in two planes parallel to the ribbed wall(s). Local heat transfer distributions were obtained on the floor, between the ribs, and on the adjacent smooth side wall. Averaged parameters, such as friction factor and averaged heat transfer enhancement factor, were calculated from the local results and compared to correlations given in literature. This contribution showed that simple correlations derived from the law of the wall similarity and from the Reynolds analogy could not be applied for the present rib height-to-channel hydraulic diameter ratio (e/[D.sub.h] = 0.1). The strong secondary flows resulted in a three-dimensional flow field with high gradients in the local heat transfer distributions on the smooth side walls.

Heat transfer research shows that a straight tube of elliptical cross section achieves the maximum average Nusselt number when placed in a vertical position in an initially quiescent fluid of infinite extent. Heat exchange experiments measuring the velocity and thermal fields over time were devised to assess the effects of tube orientation, Rayleigh number and axis ratio. A sharp increase in tube surface temperature occurs before equal heat exchange is established.

A newly developed flow tracer composed of shear-thickening and high extensional-viscosity fluids was used in a visualization study of flow around circular-cylinder groupings resembling tube banks, at Reynolds numbers ranging from 500 to 13,000. The photos confirm traditional ideas on the effect of flow on heat transfer, pressure drop and vibration aspects in tube banks. Many of the photos also show the organization of the flow into a large bluff-body wake.

Two tubes in tandem and normal to flow were studied on the basis of the unsteady-flow theory. Motion-dependent fluid forces were measured in a water channel and the pitch-to-diameter ratio was 1.35. From the measured fluid forces, fluid damping and stiffness were calculated as a function of reduced flow velocity and several Reynolds numbers. Once the fluid-damping and fluid-stiffness coefficients are known, coupled vibration and stability of the two tubes in cross-flow can be predicted.

This paper presents an unsteady-flow theory for flow-induced vibration of tubes in cross-flow. It includes a general description of motion-dependent fluid forces, characteristics of fluid-force coefficients, and mathematical models. Detailed results are presented for the constrained mode in the lift direction for various tube arrangements.

When dealing with the probabilistic estimation of the peak response of an offshore structure dynamically responding under excitation by unidirectional irregular waves, it becomes apparent that nonlinearities introduced by the wave-structure interaction, and principally associated with the drag contribution of the Morison force model that has been traditionally used to describe this forcing, leads to non-Gaussian statistical properties of not only the forcing, but also the response. However, it is also apparent that for lightly damped structures, the response under certain circumstances can be very 'narrow-banded,' and hence its statistical description would then approach the Gaussian form irrespective of whether the forcing associated with the response is itself highly non-Gaussian or otherwise. This paper treats both a numerical and experimental investigation of the peak response characteristics of compliant bottom-pivoted surface-piercing cylinders subjected to hydrodynamic excitation by unidirectional Pierson-Moskowitz (P-M) irregular waves and modeled as single-degree-of-freedom (SDOF) oscillators with a fixed 'straight line' mode shape (the result of the bottom-pivoted support condition). Conditions under which the response can reasonably be approximated as Gaussian are identified via an upcrossing investigation for the likely peak response in a storm of a nominated period of duration.

Data from two experimental programs have been analyzed to determine the characteristics of the random excitation forces associated with two-phase cross-flow in tube bundles. Large-scale air-water flow loops in France and Canada were used to generate the data. Tests were carried out on cantilevered, clamped-pinned, and clamped-clamped tubes in normal-square, parallel-triangular, and normal-triangular configurations. Either strain gages or force transducers were used to measure the vibration response of a centrally located tube as the tube array was subjected to a wide range of void fractions and flow rates. Power spectra were analyzed to determine the effect of parameters such as tube diameter, frequency, flow rate, void fraction, and flow regime on the random excitation forces. Normalized expressions for the excitation force power spectra were found to be flow-regime dependent. In the churn flow regime, flow rate and void fraction had very little effect on the magnitude of the excitation forces. In the bubble-plug flow regime, the excitation forces increased rapidly with flow rate and void fraction.

This paper deals with geosynthetic tubes that are made of several geosynthetic sheets sewn together to form a shell capable of confining pressurized slurry. The slurry is sufficiently fluid so that it is possible to hydraulically fill the tube. After pumping the slurry in, the geosynthetic shell acts as a 'cheese cloth,' allowing seepage of liquid out and retaining the solid particles. The availability of a wide selection of geosynthetics in terms of strength, durability, and permeability enables the use of hydraulically filled tubes in many applications, some of which may be considered critical (e.g., encapsulate contaminated soil). This paper presents an overview of an analysis to calculate both stresses in the geosynthetic and geometry of the tube. It also verifies the correctness and validity of the results obtained from a computer program developed to solve the problem. An instructive parametric study implies that the most critical factor needed to assure successful construction is the pumping pressure; a slight accidental increase in this pressure may result in a very significant stress increase in the encapsulating geosynthetic. Pressure increase beyond a certain level, however, has little influence on the storage capacity of the tube. Guidance in selecting an adequate geosynthetic, including partial safety factors and filtration properties, is also presented. Design aspects associated with required spacing of inlets and head loss of the slurry as it flows through the tube are considered outside the scope of this paper.

Severe noise emission due to acoustical resonance can occur in conduits or chambers containing large tube arrays subjected to fluid cross flow, as is the case in many heat exchangers and steam generators. A theoretical basis obtained from updated literature is used to assess excitation and damping forces. Whether acoustical resonance is to be expected or not depends upon the relative magnitude of both forces. A calculation method is proposed for the prediction of acoustical resonance and its frequency. The method has been checked by using geometrical and experimental data for Moisture Separator Reheaters of two different power plants. Results show reasonable agreement between predictions and measurements. Two methods are suggested for the suppression of existing resonance.

The electrohydrodynamical (EHD)-extraction phenomenon can be achieved more effectively with an externally enhanced tube than with a smooth tube. A smooth copper tube and an externally enhanced copper tube are used to study the EHD enhanced condensation heat transfer. Refrigerant-113 is the working fluid. The condensation heat transfer coefficient results are compared to the Nusselt solution for laminar condensation and the Kutateladze correlation. The results are a significant improvement over the earlier studies using smooth tubes.

Experimental analysis of the heat transfer of air/water two-phase flow in helicoidal pipes in axially horizontal, vertical, and inclined orientations shows that tube diameter significantly influences the average heat transfer. Orientation influences heat transfer in the large-tube-diameter coil but has no impact on the small-tube-diameter coil. Experimental data is used to plot the average heat transfer coefficient ratio against the liquid superficial Reynolds number and the Lockhart-Martinelli parameter.

The critical heat flux (CHF) of a two-phase thermosyphon containing a liquid film and a vapor flow in a countercurrent annular flow is studied analytically. The CHF point is calculated from the maximum falling liquid rate fed to the thermosyphon. Estimation of the maximum falling liquid rate is based on momentum equations for liquid and vapor flows. The CHF values calculated using the maximum liquid rate agrees well with the experimental data.

An optical version of the naphthalene sublimation technique gives local mass transfer data for circular-finned tubes in staggered and in-line two-row bundles. Local variations in the heat transfer coefficient do not lead to significant fin efficiency deviations from Gardner's analytical solution to the problem of finned tubes. The Reynolds number ranges from 5000 to 28,000. Local mass transfer results provide values of local heat transfer coefficients. The numerical solution of the heat equation, obtained using these data, gives the true fin efficiency.

Capillary tubes are used widely in small refrigeration systems. It is necessary to design the capillary tube, but there does not exist any analytical equation which allows the determination of capillary tube length or mass flow rate for all refrigerants. In this work, an analytical equation is derived which allows to design the capillary tubes. The comparison with existing methods and experimentally obtained values using the refrigerants R12, R22, R113, R114, R134a, and R600a has turned out to be satisfactory.

In this work, the fluidelastic instability of a tube placed in an array subjected to two-phase crossflow has been studied. For the determination of fluidelastic instability, acrylic tubes 2.2 cm or 2.37 cm in diameter and 20 cm in length were arranged in a triangular array with pitch to diameter ratio of 1.4 and 1.3. The test tube was flexibly supported with two cantilever beams. By installing cantilever beams horizontally and vertically, drag and lift direction tube vibration were studied. The total damping ratio is found to increase as the liquid gap velocity or void fraction increases. It has been found that the effective spring constant decreases rapidly with increase of liquid gap velocity or void fraction just prior to the onset of instability. For the range of parameters studied in this work, the onset of fluidelastic instability is associated with a rapid decrease of the effective spring constant because for a given applied force the amplitude of the tube vibration is inversely proportional to the spring constant.

A tube array supported by baffle plates in cross-flow may be subjected to fluidelastic instability in the tube-support-plate-inactive mode. An experimental study is presented to characterize the tube motion. Three series of tests were performed to measure tube displacements as a function of flow velocity for differing clearances. The motion was examined by root-mean-square values of tube displacements, power spectral densities, phase planes, Poincare maps, and Lyapunov exponents. The experimental data agree reasonably well with an analytical model based on the unsteady flow theory.

Tube arrays exposed to air, gas or liquid cross-flow can vibrate due to vortex-shedding, turbulence, or fluidelastic instability. The major emphasis of this paper is on the phenomenon of fluidelastic instability (or fluidelastic vibration). A numerical model is applied to the simulation of fluidelastic vibration of representative tubes in a tube bundle, based on S. S. Chen's unsteady flow theory. The results are validated against published data based on linear cases. The model is then applied to a nonlinear structure of a U-bend tube bundle with clearances at supports, and the computed results compared to those obtained by experimental testing. The numerical studies were performed using the ABAQUS-EPGEN finite element code using a special subroutine incorporating fluidelastic forces. It is shown that the results of both the linear and nonlinear modeling are in good agreement with experimental data.

Flow in a bifurcating tube system typifying a major bronchial bifurcation is studied experimentally with a two color, two velocity component laser Doppler anemometer. The flow loop is composed of a pumping station, flow stratifiers and a constant head pressure tank; it can accommodate steady, pulsatile or oscillatory flow. The test section is a symmetric bifurcation of constant cross sectional area and has a branching angle of 70 deg. The test section is a cast of clear silicon rubber in a plexiglass room that was milled on a numerically controlled milling machine. The flow division ratio from the parent to daughter branches is about unity. Steady flow results that model the inspiratory phase at Reynolds numbers of 518, 1036 and 2089, corresponding to Dean numbers of 98, 196 and 395, show that in the bifurcation plane velocity profiles in the daughter branches are skewed toward the inner wall. In the transverse plane, 'm' shaped velocity profiles are found with low velocity at the center. Secondary flow patterns, which are responsible for such phenomena, are first observed at the axial position where the flow begins to turn. Flow separation was not observed at any point in the bifurcation.

This paper presents an extension of the previous analyses on the collapsible tube-flow problem using a simplified model based on a two-dimensional channel conveying a one-dimensional flow. The main objective of the paper is to exploit the static and dynamic behavior of the model, by comparing with available experimental data and examining the accuracy of calculated results obtained for different numerical resolutions. The main revision from the previous analyses is the incorporation of a universal 'tube' law that is valid for a wide range of positive and negative transmural pressure. Most of the numerical results agree qualitatively with the experimental observations. Self-excited high-frequency oscillation with very small amplitude of the membrane wall is, however, predicted to occur in a flow range where the slope of the pressure drop curve is positive. It is seen that the high-frequency oscillation is associated with the motion of the separation point of the flow.

Motion-dependent fluid forces acting on a tube array were measured as a function of excitation frequency, excitation amplitude, and flow velocity. Fluid-damping and fluid-stiffness coefficients were obtained from measured motion-dependent fluid forces as a function of reduced flow velocity and excitation amplitude. The water channel and test setup provide a sound facility for obtaining key coefficients for fluidelastic instability of tube arrays in crossflow. Once the motion-dependent fluid-force coefficients have been measured, a reliable design guideline, based on the unsteady flow theory, can be developed for fluidelastic instability of tube arrays in crossflow.

We present a Preston tube device that combines both total and static pressure readings for the measurement of wall shear stress. As such, the device facilitates the measurement of wall shear stress under conditions where there is streamline curvature and/or over surfaces on which it is difficult to either manufacture an array of static-pressure taps or to position a single tap. Our 'Preston-static' device is easily and conveniently constructed from commercially available regular and side-bored syringe needles. The pressure difference between the total pressure measured in the regular syringe needle and the static pressure measured in the side-bored one is used to determine the wall shear stress. Wall shear stresses measured in pipe flow were consistent with independently determined values and values obtained using a conventional Preston tube. These results indicate that Preston-static tubes provide a reliable and convenient method of measuring wall shear stress.

Correlations for the critical heat flux (CHF) condition in two-phase crossflow through multitube bundles are valid for tube rows after the third row in the bundle. Scatter plot comparison studies reveal that the data is representative, randomly distributed and does not follow any particular trend. The CHF does not depend on its position in the bundle as heat flux increases.

A porous substrate approach-based study of heat transfer and fluid flow in spirally fluted tubes yielded predictions for friction factor and heat transfer that agreed well with results obtained from the application of a numerical model to the tubes. The study conditions included the assumption that the tubes and the porous substrates influenced the flow in a similar manner.

Two-phase flow exists in many engineering systems and is a dominant type of flo in heat exchangers, steam generators, and condensers. A flowing two-phase fluid is a source of energy that can cause vibration of tube bundles of these systems A simple correlation is presented to predict the response of tube bundles in two-phase flow. The model correlates with experimental data reasonably well and is a useful tool in the prediction of tube response.

Re-evaluation results show that the modeling of dispersion effect for air and water flows should be different. A non-linear dispersive conductivity with Peclet number is used for water flow. The predicted values of Nusselt number agree with the present data for water flow for low Peclet number.

The topic of this study concerns principally representative models of some elliptical thin-walled anatomic vessels and polymeric tubes under uniform negative transmural pressure p (internal pressure minus external pressure). The ellipse's ellipticity k(sub o), defined as the major-to-minor axis ratio, varies from 1 up to 10. As p decreases from zero, at first the cross-section becomes somewhat oval, then the opposite sides touch in one point at the first-contact pressure p(sub c). If p is lowered beneath p(sub c), the curvature of the cross-section at the point of contact decreases until it becomes zero at the osculation pressure or the first line-contact pressure p(sub l). For p < p(sub l), the contact occurs along a straight-line segment, the length of which increases as p decreases. The pressures p(sub c) and p(sub l) are determined numerically for various values of the wall thickness of the tubes. The nature of contact is especially described. The solution of the related nonlinear, two-boundary-values problem is compared with previous experimental results which give the luminal cross-sectional area (from two tubes), and the area of the mid-cross-section (from a third tube).

The continuity equation and Navier-Stokes equations derived from a non-orthogonal helical coordinate system are solved by the Galerkin finite-element method in an attempt to study the torsion effect on the fully developed laminar flow in the helical square duct. Since high-order terms of curvature and torsion are considered, the approach is also applicable to the problems with finite curvature and torsion. The interaction effects of curvature, torsion, and the inclined angle of the cross section on the secondary flow, axial velocity, and friction factor in the helical square duct are presented. The results show that the torsion has more pronounced effect on the secondary flow rather than the axial flow. In addition, unlike the flow in the toroidal square duct, Dean's instability of the secondary flow, which occurs near the outer wall in the helical square duct, can be avoided due to the effects of torsion and/or inclined angle. In such cases, a decrease of the friction factor is observed. However, as the pressure gradient decreases to a small value, the friction factor for the toroidal square duct is also applicable to the helical square duct.

The yield and flow characteristics of an initially orthotropic material under multiaxial stresses are investigated. Experiments are conducted wherein an aluminum tube is loaded axially using a hydraulic-type multiaxial stress testing machine. A load cell with strain gages fixed to its surface is used to measure the axial load and torque. Results reveal that flow stress rises to a maximum value under a proportionally combined loading of axial load,internal pressure and torsion.

Asimple and acccurate technique for determining the space-variable heat transfercoefficient or boundary heat flux from given measurements of temperature at some interior point in the body is discussed. The theory was applied to circumferential variations of horizontal tube temperature and radiantly heated tube with temperature-dependent thermal conductivity to test its efficacy. Based on the results of the two examples, the technique was found to be efficient.

The problem of transient flow stratification in vertical tube arrays, volume averaging and scaling arguments are discussed. An analytical solution produces a tube array geometry which was used to evaluate the study along with standard control-volume numerical methods and a Lagrangian tracking interface procedure. Results indicate that significant numerical diffusion and error can be introduced by control volume and upwind finite-difference numerical formulations.

Fluidelastic vibration of a tube array caused by two-phase flow has been reported in some papers. The critical flow velocity is usually estimated with a simple Connors-type criterion which is based on average flow velocity, average fluid mass density and damping in two-phase flow. However, there is no explanation why this simple criterion can be used or how the fluidelastic instability occurs by two-phase flow. This paper shows the experimental results on the fluidelastic vibration both by air-water two-phase flow and by steam-water flow in the condition of up to 7.0 MPa in pressure and to 284 degrees C in temperature, and a new criterion based on an assumption of energy balance is here introduced using a 'true' flow velocity. However, the comparison with the experimental data indicates that an intermittently rising slug speed, which has been introduced in Part 1, in slug or in froth flow region, should be used, and a modified new criteria for slug or froth flow region is derived. In addition, the new criteria is compared with the usual Connors-type criteria, which greatly depend on the estimation of the damping in two-phase flow. The agreement of both criteria is revealed to be in the vicinity of the variance of the unknown parameters in the usual criteria.

There are few published papers about the flow-induced vibration caused by two-phase flow. Especially, the experimental data at high-pressure and high-temperature conditions which corresponds to the practical phenomenon, are extremely few, and the mechanism of the two-phase flow-induced load acting on a tube in tube array has not yet been explained. This paper shows the experimental results about the turbulent buffeting force both by air-water two-phase flow and by steam-water flow of extreme conditions up to 5.8 MPa in pressure and 272 degrees C in temperature, the explanation of the mechanism of this force, and the method to evaluate the response of the tube caused by two-phase flow. Here, the main source of the buffeting force by two-phase flow in slug or froth flow pattern is recognized to be the impact force caused by the intermittently rising liquid slug. The slug speed and the fluid force acting on a tube are estimated, combined with the estimation of the intermittence of the occurrence of the liquid slug rising.

Results are presented from an experimental study conducted to determine friction coefficient behavior in OCTG connections. The study was conducted using the OCTG friction and galling tester at Texas Tech University. The tester employs tubular pin and box specimen pairs fabricated from 73-mm (2 7/8 in.) diameter OCTG tubing. Friction coefficient was determined for test specimens made of material grades L80 and J55 at loads of up to 620 kN (140,000 lb) acting on a surface area of up to 645 mm squared (1 in. squared) with sliding velocities of 0.53 and 1.78 cm/s (1 and 3.5 ft/min), and nominal surface roughnesses of 0.37, 1.2, and 1.5 micron (15, 47, and 60 micro-in.) Ra. An API Modified thread compound was used for all tests. When plotted versus the applied load, the friction coefficient behavior is seen to be highly nonlinear. In addition to load, the variables of sliding velocity, material, and surface roughness are shown to have an effect. Preliminary experiments show that the test surface geometry also has a significant effect on the friction coefficient.

The calculation of the heat transfer coefficients for tube banks is presented. The process involves steam at slightly above atmospheric pressure flowing vertically downward over a staggered tube bank. A general trend of decreasing heat transfer coefficient with depth in the bank was formed. However, 'a saw tooth' effect was superimposed with the three tube rows having higher coefficients than the other four rows.

Fluidelastic instability of loosely supported tubes, vibrating in a tube support plate (TSP)-inactive mode, is suspected to be one of the main causes of tube failure in some operating steam generators and heat exchangers. This paper presents a mathematical model for fluidelastic instability of loosely supported tubes exposed to nonuniform cross flow. The model incorporates all motion-dependent fluid forces based on the unsteady-flow theory. In the unstable region associated with a TSP-inactive mode, tube motion can be described by two linear models: TSP-inactive mode when tubes do not strike the TSP, and TSP-active mode when tubes do strike the TSP. The bilinear model (consisting of these linear models) presented here simulates the characteristics of fluidelastic instability of loosely supported tubes in stable and unstable regions associated with TSP-inactive modes. Analytical results obtained with the model are compared with published experimental data; they agree reasonably well. The prediction procedure presented for the fluidelastic instability response of loosely supported tubes is applicable to the stable and unstable regions of the TSP-inactive mode.

Due to tube-support gaps in heat-exchangers, low-frequency modes may develop and become unstable at comparatively low flow velocities. This kind of linear fluidelastic instability results in a negative modal damping value, which is a function of the flow velocity. The response amplitude of the unstable tubes increases steadily until tube-support impact becomes unavoidable. These extremely nonlinear vibratory motions have a high-risk potential, as tube velocities and impact forces can be of very considerable magnitude. This paper reports results on a series of laboratory experiments, intended to validate nonlinear calculations on vibro-impact dynamics of heat exchanger tube bundles under fluidelastic instability. The test model was designed for unidirectional motion and the results obtained should be fairly representative of the actual behavior of the U-bend portion of the heat exchanger tube bundles. The system instability is generated by a velocity feedback loop. This method presents significant advantages due to simplicity of the setup and the controllability of the system parameters, in particular concerning the negative damping ratio of the unstable model. A comparison of experimental and computed system dynamics is presented for several values of the instability growth rate and for various initial conditions of the motion. Influence of other parameters, such as tube-support gap magnitude and gap symmetry, is asserted for realistically ranged values. Results show that several steady motion regimes may arises, depending on the system parameters and initial conditions of the motion, which is a fact of engineering significance. Furthermore, a satisfactory qualitative and quantitative agreement was obtained between theoretical predictions and test data., A series of experiments were conducted to verify nonlinear computational methods for vibro-impact tube motions under fluidelastic instability. These involved using a model that produced results which simulated conditions of the U-bend portion of steam generator and heat-exchanger tube bundles. System instability was obtained through a velocity feedback loop. Experimental results when compared with numerical computation results showed agreements between the values obtained.

The geometry of collapsible latex tubes was measured while fluid flows at static loading and steady flow. Measurement of static tube laws yielded results which were in agreement with previous findings while steady state flow geometrical measurements were significantly different from theoretical models. This technique for measuring the geometry of a tube is important in understanding the field of flow through collapsible tubes and can be applied in large amplitude wave propagation or fluid dynamic behavior acrossan elastic jump.

The removal of gravitational force induced particulate radial migration produces a symmetric and normal residence time distribution (RTDs) of suspended particles in the tubular flow. The particle's radial location and initial velocity have no effect on the RTDs. The particle volumetric fraction from single to > 20% particles, and suspension Reynolds number between 6300 to 26000 influence the RTDs.

Stratification is the dominating factor at low heat flow rates in horizontal tubes. The heat flow becomes annular as mass flux increases. For a given mass flux, a higher heat flux leads to a higher heat transfer coefficient. The R-134a forced convection evaporative heat transfer coefficients, for within a horizontal microfin tube, are studied experimentally. The heat transfer coefficients are plotted against refrigerant quality as well as the mass flux in the test section.