End Geometry Research Articles

Experimental study of the effect of pipe length and pipe-end geometry on flooding

The onset of flooding is thought to be highly sensitive to the end geometry of the test channel and its high sensitivity is an important cause of data scattering. In the present work, the effect of end geometry on flooding is experimentally investigated. Observation shows that flooding definition also causes the data scattering and that flooding should be classified into two modes according to the location where it occurs. With the sharp liquid entrance geometry, both entrance flooding and exit flooding are able to take place while only exit flooding does when entrance is smooth. In the range of low liquid flow rates, exit flooding always takes place and flooding gas velocities for the same exit geometry are nearly the same regardless of liquid entrance geometry. When air is injected into the test tube through a nozzle, even if the liquid exit is sharp, flooding gas velocities are nearly the same as those with smooth exit geometry. The present experiments show that the length effect is significantly affected by the pipe-end geometry. It is small in the range of low liquid flow rates but becomes significant as the liquid flow rate increases.

An absolute falling tube viscometer

A structurally simple absolute viscometer, the falling tube viscometer, with a large measurement range for viscosity from 0.5 to 10 9 cP (5 × 10 −4 to 10 6 N s/m 2), has been extensively investigated. The flow field, shear rate, and pressure distribution in the viscometer have been obtained numerically to determine the entrance and exit effects. The viscometer was characterized by two variables, the geometry number Ge and the end correction factor. The former is exclusively determined by the dimension-less tube diameters and length and reflects the ratio of tube driving force to resistance. The latter is defined as the ratio of the actual to ideal geometry numbers. The results presented allow the prediction of end effects and geometry number without resorting to empirical corrections or instrument calibration. The agreement between the analytical and experimental results on the geometry number, the measured viscosity of standard fluids, repeatability, and accuracy is well within 1% in all cases. A correlation equation from which the geometry number can be calculated is presented that can be used to design viscometers for particular applications. Both the theoretical analysis and the experimental data indicate that falling tube viscometers based on the correlated equation are absolute viscometers with an accuracy within ± 1.0%.

Different modes of plasma sheath motion in the radial compression and pinch phases in plasma focus

Two distinct modes of plasma sheath (PS) motion, the stable mode and the instability mode, in the radial compression and pinch phases in a small Mather-type plasma focus device (20 kV, 18 kJ) have been observed using laser differential interferometry. The two modes occur randomly from shot to shot in consecutive discharges and their probabilities are much influenced by the anode end structures. The instability mode is characterized by the rapid radial movement of the sliding front of the PS along the anode (centre electrode) end surface. The two modes show very different sheath and pinch configurations according to their different ways of motion. They also have notable influences on the neutron yield, in that the instability mode always produces a lower one and the stable mode a higher one. The mean neutron yield for consecutive discharges is made low and largely deviated by the co-existence of the two modes. The instability mode is found to be caused by the anode end geometry with a small transition arc, whose nature is of the m = 0 MHD type but only with a half wavelength, occurring at the plasma - electrode layer. The instability can be either avoided by a hemispherical-ended anode with a larger transition arc or stabilized by the stagnation of the radial movement of the sliding front of the PS in the initial radial compression by the hollow edge and the stable mode formed. The magnetic field introduced in front of the PS by the anode end discharge that occurs from the very beginning of the main discharge is also found to act as a stabilization mechanism for the instability and to cause some of the stable mode.

Experimental studies of flooding in nearly horizontal pipes

To investigate the flooding phenomenon in nearly horizontal pipes, experimental studies are performed for air and water countercurrent flow in a test section with a length of 2160 mm, with three different inner diameters of 40, 60 and 70 mm, with different types of end geometry, and with various inclination angles. The effects of the pipe diameter, end geometry and inclination angle on flooding are examined. Two mechanisms governing the transition to flooding are proposed: inner flooding and entrance flooding. The inner flooding is initiated by unstable wave growth, i.e. slugging, at the inner location of the pipe. The entrance flooding is always observed to take place at the entrance of the water flow without slugging. The effect of the inclination angle on flooding is predominant within quite a narrow range of inclination (0° < θ < 1°). A small deviation of the inclination angle from the horizontal plane causes a large deviation of the required air flow rates for flooding. Two local void fractions are measured by parallel wire probes and a scale marked rule in two regions (sub- and super-critical regions). The local effects of the void fraction on slug formation models are investigated. It is found that the differences in the exponents of the void fraction terms of the existing slug formation models mainly result from the definition of the void fraction used. When the void fraction measured in the sub-critical region is used in the slug formation model, Mishima et al.'s model well predicts the trend of the present data. However, if the void fraction measured in the super-critical region is used, Taitel et al.'s model better predicts the present data.

Influence of cutting technology on initial fixation strength and thread quality of different bone pins

A comparison of the fixation strength was made for the Steinmann, Denham, and the Apex commercial bone pins, which have different drilling end geometry and self-tapping thread design. Additional tests were made to assess the effects of pre-drilling with an orthopaedic twist drill bit prior to pin insertion. Peak pull-out force and pin displacement were measured for these pins inserted into the distal metaphysis of human cadaveric tibiae. The quality of thread reproduction in the bone resulting from the cutting process was assessed from thread profiles of negative moulds cast into the threaded holes. The Apex pins had similar pull-out forces to the Denham pins, despite their smaller diameter. Values for both pins were significantly greater than those for the Steinmann pin. The thread profiles showed that the Denham pin caused substantial damage to the cortical bone and formed poor quality threads in the cancellous bone. The Apex pin formed a better thread, which was improved further by the use of a pre-drilled pilot hole.

An Experimental and Analytical Investigation of Composite Drive Shafts with Non-Circular End Cross-Sections

An optimization methodology is presented for the selection of the end cross-sectional shape of composite torque tubes (drive shafts) with noncircular end geometries. In a typical application, metal inserts are adhesively bonded in the ends of the tubes to allow for torque transmission. The worst case scenario of bond failure with subse quent torque transmission via insert-tube contact is considered. Optimization of the tube end cross-sectional shape under this worst case situation is the goal of this study. Employ ing facets of elasticity and the finite element method, a two step methodology is estab lished to predict the failure torque of a tube with a range of selected end cross-sections. This methodology is verified through comparison with experimental data. Results ob tained from the analytical and experimental studies indicate a spline-like cross-sectional shape as the optimal design. Failure torques on the order of 70% of the circular cross- sectional failure torque are shown to be possible.

Measurements of Pressure Distributions and Force Coefficients in a Squeeze Film Damper Part I: Fully Open Ended Configuration

Experimental measurements of pressure distributions and force coefficients obtained from a squeeze film damper lest rig executing a circular centered orbit are presented. The test rig has been designed to study the effect of fluid inertia on the pressure field and dynamic force response on a damper configuration with a relatively large clearance. Past measurements of the squeeze film damper force characteristics have been carried out at squeeze film Reynolds numbers not exceeding a value equal to 10. In the present paper, following contemporary applications, operations at Reynolds numbers up to fifty are tested for CCO's with an orbit radius = 0.8 (Re ≤ 10 at ε = 0.5). The results obtained from a fully open ended damper are presented in detail. The effects of fluid inertia, cavitation and the open end geometry on the pressure distributions and force coefficients are discussed.

Effects of fiber orientation on the stress distribution in model composites

AbstractA Raman‐mechanical technique was used to study the relationship between stress distribution and fiber orientation in model composites. Our experimental data generally were consistent with most simplistic mechanical models. A more complete analysis, using the Eshelby equivalent inclusion method, fitted our experimental data exceptionally well. For large applied strains, compressive failure occurred for fibers which were oriented at high angles relative to the draw direction. This occurred because of the lateral shrinkage associated with the matrix when the sample was stretched. The effect of fiber end geometry on the stress distribution for these misaligned fibers was the same as observed earlier. Tapered‐end fibers generally carried loads more efficiently in composites than blunt‐end fibers.

Compressive strength, burst proneness, and failure modes of model coal pillars related to the end constraint and geometry: Babcock, C O Proc 28th US Symposium on Rock Mechanics, Tucson, 29 June–1 July 1987P173–180. Publ Rotterdam: A A Balkema, 1987

Compressive strength, burst proneness, and failure modes of model coal pillars related to the end constraint and geometry: Babcock, C O Proc 28th US Symposium on Rock Mechanics, Tucson, 29 June–1 July 1987P173–180. Publ Rotterdam: A A Balkema, 1987

Influence of the muscle fibre end geometry on the extracellular potentials.

Intra- and extracellular action potentials of isolated frog muscle fibres were recorded at different distances to the end of the fibre. The first and second time derivatives of the intracellular action potentials were also recorded. The intracellular action potentials and their first and second time derivatives were almost the same regardless of the place of recording. With the decrease in the axial distance to the end the extracellular action potentials changed gradually in a complicated manner from a shape similar to the second time derivative into a shape similar to the first time derivative. Extracellular potentials, having two negative maxima, were recorded over the terminal taper part of the fibres. These alterations were simulated by a mathematical model. It was shown that the changes in the shape of the extracellular action potentials around the end of the fibres were mainly due to the existence of the fibre end though a better correspondence of the experimentally recorded and the calculated extracellular action potentials was obtained when the morphology of the fibre end was taken into consideration.

Stress Distribution of Aligned Short-Fiber Composites Under Axial Load

The objective of this paper is to investigate the normal and interfacial shear stress distribution of short-fiber composites under a force either parallel to the fiber or mak ing some angle with the fiber. Different geometrical shapes of fiber end were taken into account. The geometrical shapes under investigations were: rectangular, semi-circular, V-shaped and wedge-shaped respectively. Analytical solutions of this problem were achieved by using finite-element numerical scheme. For the cases when the applied load is parallel to the fiber, very small triangular constant strain elements were used near the fiber tip and rectangular elements were used throughout the rest of the region. For the cases of off-axis loading parabolic-isoparametric elements were used throughout the entire domain. Depending upon the fiber volume fractions and fiber end geometry, the total time of calculation for each case is around 18 seconds. Numerical results of normalized normal stress σf and shear stress τ were plotted as a function of the coordinate along the fiber direction. It was observed that, the distribu tions of σ f and τ were in good agreement with existing results obtained experimentally by using photoelasticity method. It was also observed that shear stress concentration is very high near the fiber tip. This phenomenon is particularly true for wedge and V-shaped fiber ends. A possible application of this investigation is to optimize internal damping of short- fiber composites by properly adjusting fiber end geometry. It is believed that the presence of high shear stress concentration at numerous fiber ends in short-fiber com posites will transfer to the viscoelastic matrix. The viscoelastic matrix will then dissipate energy and thus improve internal damping of the composites.

Air-water countercurrent annular flow

Experimental results on investigation of countercurrent air-water flows in vertical circular tubes of a range of diameters are reported. Based on the influence of tube end geometries on measured countercurrent fluxes, liquid fraction, and pressure gradients, analogies between countercurrent gas-liquid flow and other more familiar flows in internal geometries are indicated. Interfacial momentum transfer between the phases is characterised by empirical friction factors. The dependence of interfacial friction factors on tube diameter is used to suggest a basis for generalizing the results using a dimensionless correlation involving surface tension.

Fuel characteristics required for LWR fuel rod calculations

BELGONUCLEAIRE gradually increasing in-reactor experience has enabled to assess the relative importance of attributes defined in specifications and drawings for both UO 2 and MO 2 fuels. On the basis of that experience, design codes have been benchmarked and were thereafter applied to cover the range of parameters and irradiation histories to be encountered or evaluated. To illustrate the effects of fuel characteristics on fuel behaviour, sensitivity calculations were performed on the basis of actual fuel irradiated in BWR's (DODEWAARD, GARIGLANO and OYSTER CREEK) and PWR's (BR3, DOEL, SENA, TIHANGE and MAINE YANKEE). The major characteristics are : fuel structure, UO 2 versus mixed oxide fuel; fuel accomodation (depending on the fuel microstructure and chemical composition); fuel density and densification stability; open porosity; pellet end geometry; pellet L/D ratio, gap size. Although the influence of the various parameters is not additive, these examples enable to determine the relative influence of each characteristic and to conclude to what accuracy it should be measured (in demo fuel) or controlled (in production fuel).

The strength and deformations of torispherical ends for glass-reinforced plastic pressure vessels—Part I: Effect of torus radius/cylinder diameter ratio on ends with sphere radius equal to cylinder diameter

Six glass-reinforced plastic cylindrical pressure vessels with torispherical end closures have been tested to destruction. Each vessel was of 0·01 nominal thickness/diameter ratio and had an end geometry with the spherical radius equal to the cylinder diameter of 1 m. Three different torus radii of 0·29, 0·19 and 0·1 m were used to give head heights of 0·32, 0·25 and 0·19 m, respectively (two vessels of each geometry were tested). Results from the tests were compared with those suggested by the current UK design code (BS 4994) and the predictions of a computer-based elastic stress analysis (BOSOR 4). These all confirm that maximum stresses and strains increase with decreasing knuckle radius. It was also found that, because of the high elastic strains of GRP, the change of geometry under pressure makes a significant contribution to the ultimate strength of these ends. The result of this, together with the effect of some local wall thickening, was to strengthen the ends to the extent that failure took place in the torisphere for only three of the six vessels tested.

The effect of trailing end geometry on the vibration of a circular cantilevered rod in nominally axial flow

The effect of “trailing end” geometry on the vibration of a circular cantilevered rod in nominally axial water flow is reported. Eleven different trailing end geometries were tested. For each end geometry, rms displacement response and damping were measured and are presented as functions of mean axial flow velocity. The various geometric end shapes are ordered according to their effectiveness in attenuating rod vibration. The results, which are in qualitative agreement with similar experimental results from tests on flat plates, provide the designer with empirical information that allows selecting a trailing end geometry that minimizes response to parallel flow excitation. The results have application in the design of nuclear reactor fuel pins and certain instrumentation probes.

Predicting Exit Temperature Profile from Gas Turbine Combustors

An analytical model has been developed for predicting exit radial temperature profile from gas turbine engine annular primary combustors. The model assesses the effect of changes in dilution or cooling air distribution, changes in combustor aft end geometry, or changes in combustor operating conditions. The description of the dilution air mixing process includes the effects of mixing in confined flows, closely spaced dilution jets, and elongated dilution ports, the interaction of opposing rows of dilution jets, and the effect of flow area convergence, including nonsymmetric convergence. The cooling air mixing process description includes the effects of combustor turbulence, multiple louvers, and flow area convergence. Comparison of measured exit temperature profile shifts, with the predictions of the analytical design system, shows good agreement in predicting the effects of both dilution and cooling air shifts within the combustor aft end. Nomenclature A =area C = coefficient D = diameter H = height / — momentum flux ratio M = blowing parameter (mass flux ratio) S = spacing, gap T = temperature V = velocity W =flowrate X — downstream distance Y = penetration distance d —exit temperature profile = local minus exit average temperature 7 = heat/momentum diffusivity ratio p = density = temperature profile thickness

Matrix and Interface Stresses in a Discontinuous Fiber Composite Model

The method of finite element analysis is applied to an axially symmetrical model of a single filament glass-resin composite under tension. Fiber end geometries are varied by considering ellipsoids of revolution with one axis length equal to the fiber diameter while the second varies from one-tenth to ten times the fiber diameter. Tapered tips with these same axis ratios are considered also. The results show that the best ellipsoidal end shape for minimizing matrix shear stress concentration is one having the longitudinal axis equal to twice the fiber diameter. The shear stress concentration for this geometry, however, is still greater than that of the slowly tapered end, which causes the lowest stress concentration. General stress patterns in the matrix as found by the finite element method are compared to previous analytical and experimental predictions.

Measured End Corrections for Woodwind Tone-holes

Impedance parameters of a tone-hole system are expressible in terms of geometrical hole lengths L plus added end corrections. These were estimated from frequency measurements on resonators. Account was taken of boundary-layer effects, which are small above 300 Hz. For a hole or tube of radius b, each correction is of the form ΔL=b⋅E, where E depends on the end geometry. For a tube whose flange has an outer radius (b+w), the measured end correction is Et=0.821−0.13[(w/b)+0.42]−64. A disk of radius r placed normal to the tube axis at a distance h from its end (e.g., a pad poised over its tone hole) gives Ed=0.61(r/b)0.18(b/h)0.39 for 1≤(r/b)≤4, provided Ed≥0.65. For a hole of radius b drilled through the wall of a pipe whose outside radius is R, the outer-surface correction is E0=0.64[1+0.32ln(0.3R/b)] for 1.5≤(R/b)≤7. The inner-surface correction for this hole is found using a doubly closed resonator tube of inside radius a and of variable length, into whose side is inserted an open side-branch of variable length and radius. The inner correction at 300 Hz is Ei=[1.3−0.9(b/a)] for (b/a)≤0.72.