Effect Of Tube Geometry Research Articles

Cryogenic Failure Behaviors of Al–Mg–Si Alloy Tubes in Bulging Process

Abstract Cryogenic medium pressure forming has been developed to form the complex-shaped tubular components, in which the needed shape and tube diameter directly determine the complex evolution of biaxial stress in bulging process. The superposition of biaxial stress and cryogenic temperature complicates the deformation behaviors, especially for the final fracture and bulging limit, which determine the forming quality of components. Therefore, the effects of tube geometry on failure orientation and fracture strain of Al–Mg–Si alloy tubes under cryogenic biaxial stress were elucidated, by utilizing cryogenic free bulging with different length–diameter ratios. The failure orientations and corresponding damage modes under different bulging geometric conditions were revealed. The influence mechanism of tube geometry and temperature on the failure mode was analyzed theoretically. A fracture model was established to predict the fracture strain in cryogenic bulging. The failure mode changes from circumferential cracking to axial cracking with the decreasing length–diameter ratio, owing to the stress sequence reversal induced by the significant nonlinearity of the stress path under a small length–diameter ratio. The failure mode can inverse under a larger length–diameter ratio of 1.0 at −196 °C because of the enhanced nonlinearity, which is promoted by the improved plasticity at cryogenic temperature. The established model based on the more accurate assessment of hardening ability during deformation can accurately predict the fracture strain with an average deviation of 10.6% at different temperatures. The study can guide deformation analysis and failure prediction in the cryogenic forming of aluminum alloy tubular parts.

Comparative Study of Different Tube Geometries of Evacuated Tube Solar Collector

Abstract This study investigates the thermal performance of an evacuated U-tube solar collector (ETSC) using different tube geometrical configurations. The effect of tube geometry on the overall collector efficiency is numerically analyzed and compared with experimental results. Three different ETSC configurations made of copper viz., Model 1 (M1) having one inlet and two outlets, Model 2 (M2) having one inlet and three outlets, and Model 3 (M3) having one inlet and four outlets are considered. An overall rise in temperature of heat transfer fluid at the outlets for each model is predicted and compared with a conventional U-tube (CT) for different mass flowrates and solar insolations to evaluate the collector performance. In comparison with the CT, the outlet temperature of the M3 and M1 is higher by 46.2% and 40.3%, respectively. M2 gives a nearly similar fluid outlet temperature as M1. A maximum of 35.4% enhancement in heat gain compared to the CT is observed for M3 (which is best among modified configurations) under similar operating conditions. However, at 788 W/m2 solar insolation and a constant mass flowrate of 0.0167 kg/s, the estimated thermal efficiency of M1 is higher among the three models which is 33.5% higher than the CT. The experimental results closely approximate the numerical predictions with a deviation of ± 1.1 °C. From the economic evaluation of the modified collectors, a minimum payback period of 2.5 years was observed for Model 1 which is the shortest among the investigated ETSC systems.

Numerical Investigation on the Effect of Tube Geometry and Feeder Height on the Heat Transfer Performance of Horizontal Tube Falling Film Evaporation

Abstract This paper discusses about the effect of tube geometry and liquid feeder height on the heat transfer performance of falling film evaporation over the horizontal heated plain tubes. To investigate this, a two-dimensional computational fluid dynamics (CFD) model was developed, compared, and validated with published data available in the literature. A numerical simulation was carried out for varying liquid load, tube diameter, liquid feeder height, and corresponding changes in the heat transfer co-efficient (HTC), and mass transfer rate was recorded and analyzed. An attempt was also made to measure the thickness of the film around the tubes from the simulation model. Mechanisms that control the factors such as HTC, film thickness, and mass transfer were numerically investigated and discussed in this work. Numerical results indicated that low value of liquid film thickness appears approximately at the angular position of the range between 90 deg and 125 deg. Also the numerical investigation revealed that liquid film thickness decreases and HTC and mass transfer rate increases with the increase of feeder height. No remarkable change in film thickness was observed with increase in the tube diameter. This numerical study also proved that the prediction of thermally developed boundary region on the circumference of the tube could be possible in terms of mass transfer rate. It was also observed from the numerical study that the highest mass transfer rate takes place between the angle 135–165 deg near to the bottom of the tube.

The effect of tube geometry on the chiral plasma

A chiral plasma plume has recently been reported inside a circular quartz tube without the use of an external magnetic field. It is believed that the quartz tube plays an important role in the formation of the chiral plasma plume. In this paper, to better understand how this interesting structure is generated, the effect of the tube geometry on the chiral plasma is investigated. First, the effect of the thickness of the tube wall on the chiral plasma is investigated. It is interesting to find that a too thin or too thick tube wall is not favorable for generating the chiral plasma. The chiral plasma plume can be obtained only at the tube wall thickness of 2 mm. Second, the effect of the diameter of the tube on the chiral plasma is investigated. It is found that, when a tube with an inner diameter of 2 mm is connected with a tube with an inner diameter of 4 mm and the high voltage electrode is placed in the tube with an inner diameter of 2 mm, a diffuse plasma is generated in the tube with an inner diameter of 2 mm, it propagates into the tube with an inner diameter of 4 mm, and a chiral plasma can be obtained at a distance of about 2 cm away from the joint of the two tubes. Third, to further understand how the tube diameter affects the appearance of the chiral plasma, horn shaped tubes with different opening angles are tested. It is found that, when the opening angle is 5°, the chiral plasma formation in the straight part of the tube can maintain the chiral shape and keep propagating in the horn shaped tube but with a much longer pitch. Fourth, to disrupt the axial symmetry, square quartz tubes are used. No chiral plasma can be obtained in the square quartz tubes under all experimental conditions. In addition, when a circular quartz tube is connected with a square tube, the chiral plasma formation in the circular quartz tube changes to a straight plasma plume in the square tube. Finally, the high voltage electrode is placed away from the center of the circular tube to disrupt its symmetry, and it is found that the chiral plasma plume can always be seen even if the high voltage is placed next to the inner wall of the tube.

Numerical Study of Creeping Flow Through Sinusoidally Periodic Tube

There has been renewed interest in the flow behaviour within tubes with periodically varying cross-section with the recognition that they can be used as particle separation devices. In this paper, we present a numerical study of the effect of tube geometry on creeping flow of viscous incompressible fluid through sinusoidally constricted periodic tube which is axisymmetric but longitudinally asymmetric. The boundary element method is used to solve for the flow in the tube by specifying the pressure drop across the ends of the tube. The boundary element equations have been formulated for ­an infinite periodic tube by writing the velocity in terms of the integrals over the tube boundary and is used to calculate the force on the tube boundary, to obtain the detailed velocity distribution within the tube and to determine the effect of amplitude and wavelength of corrugation on the structure of the flow. We have found that the highest axial velocity is at throat region and lowest axial velocity is at expansion region. Also, we have discovered that the maximum radial velocity occurs at diverging cross-section and minimum radial velocity occurs at converging cross-section. The tangential force on the tube wall is examined for different amplitudes and wavelengths of corrugation and observed that the tangential force is greater in the constricted region than in the expansion region. The physical quantities (such as velocity and force) increase with increasing amplitude and decrease with increasing wavelength. Finally, we have compared our results with the work of Hemmat and Borhan [3] and have found good agreement with them.

Dynamic Instability of Anisotropic Cylinders in a Pressurized Limited-Energy Underwater Environment

A fundamental experimental study was conducted to understand the physical phenomena resulting from the dynamic instability of carbon/epoxy composite tubes in an underwater pressurized tubular confining environment. The confining nature of the environment limits the potential energy available to drive instability, resulting in a decrease in hydrostatic pressure with the onset of instability and allowing the carbon/epoxy composite tubes to recover. Unsupported tube length and tube diameter were varied in order to determine the effect of tube geometry on the failure mechanisms of the tube and pressure waves emitted throughout the confining chamber during the instability event. High-speed photography coupled with Digital Image Correlation techniques were employed alongside the acquisition of pressure-history data from each experiment to relate specimen displacement behavior to resulting pressure pulses. Tubes of 55 mm diameter experienced partial implosion, in which the walls of the specimen oscillated radially with no wall contact. This resulted in pressure oscillations of the same frequency throughout the confining chamber, with oscillations increasing in amplitude with distance from the axial center. Amplitude of pressure and radial structural oscillations were found to be dependent on pressure just prior to instability. Tubes of 35 mm diameter experienced full implosion, which resulted in water-hammer pressure spikes at the ends of the confining chamber due to the formation and subsequent collapse of large cavitation bubbles. Longer tubes were observed to undergo significantly more damage during full implosion, reducing their ability to recover radially and thus effectively reducing the strength of hammer pulses.

Effect of Tube Geometry and Curvature on Film Condensation in the Presence of a Noncondensable Gas

Based on the double boundary layer theory, a generalized mathematical model was developed to study the distributions of gas film, liquid film, and heat transfer coefficient along the tube surface with different geometries and curvatures for film condensation in the presence of a noncondensable gas. The results show that: (i) for tubes with the same geometry, gas film thickness, and liquid film thickness near the top of the tube decrease with the increasing of curvature and the heat transfer rate increases with it. (ii) For tubes with different geometries, one need to take into account all factors to compare their overall heat transfer rate including gas film thickness, liquid film thickness and the separating area. Besides, the mechanism of the drainage and separation of gas film and liquid film was analyzed in detail. One can make a conclusion that for free convection, gas film never separate since parameter A is always positive, whereas liquid film can separate if parameter B becomes negative. The separating angle of liquid film decreases with the increasing of curvature.

Effect of tube geometry and ply-angle on energy absorption of a circular glass/epoxy crush tube – A numerical study

The superior specific energy absorption characteristics of long fiber composite structures as compared to aluminum and steel are well established. Due to cost and time involved in testing of composites, it is imperative to develop numerical solution of the crushing phenomenon. The work presented here reports work to better understand the energy absorption characteristics of glass–fiber circular crush tubes. The effect of tube diameter and ply orientation on the energy absorption has been extensively investigated. Numerical results are compared with experiments performed elsewhere and the correlation between the two is encouraging.

Laboratory Simulation of Field Sampling: Comparison With Ideal Sampling and Field Data

Tube sampling disturbance effects are investigated in this paper based on the results of constant rate of strain consolidation tests and unconsolidated undrained triaxial compression tests conducted on resedimented Boston blue clay sampled in the laboratory using a specifically designed device and employing various tubes differing in size, diameter to thickness ratio, and tip geometry. The effects of tube geometry were assessed based on comparison of the residual effective stresses, the reconsolidation strains, the undrained strength, and the one-dimensional drained compression behavior. Increasing degradation in the engineering properties was observed with decreasing diameter to thickness ratio (B∕t) , and the negative impact of a blunt tip geometry could not be compensated for even by a substantial increase in B∕t . Comparison of these results to those obtained from triaxial element tests in which disturbance was simulated according to the ideal sampling approach (ISA), indicated that tube sampling is a...

Numerical simulations comparing nonlinear acoustic effects in straight and tapered tubes

In their efforts to improve the efficiency of an orifice pulse tube refrigerator, Olson and Swift [Cryogenics 37, (769–776 (1997)] reported on the benefit of using an optimal taper angle in the construction of the conical pulse tube. They concluded that this geometry effectively suppressed nonlinear acoustic streaming which was interfering with the desired heat transfer within the device. To investigate further the effects of tube geometry on streaming, a numerical simulation is developed for a tube with varying degrees of taper angle. This 2-D finite-difference model, based on the work of Sparrow and Raspet [J. Acoust. Soc. Am. 90, 2683–2691 (1991)], compares nonlinear acoustic propagation in a straight cylindrical tube with that in a tapered conical tube. Development of the model equations in cylindrical and spherical coordinates as well as refinement of the computational grid near the boundaries are considered. [Work supported in part by ONR.]

TUBE GEOMETRY EFFECTS ON QUANTUM TRANSPORT IN CARBON NANOTUBE ELECTRON RESONATORS

The effect of tube geometry on quantum transport in carbon nanotube electron resonators is studied analytically by developing a transfer matrix method. The conductance of metallic chiral nanotubes not only shows oscillating variations as a function of gate voltage with rapid and slow periods, but also exhibits a conductance gap and some resonance conductance peaks in the gap region. These features depend on to a high degree on both tube diameter and chirality and thus provide an experimental means for structure appraisal of the nanotube devices.

Determination of food particle residence time distributions in coiled tube and straight tube with bends at high temperature using correlation analysis

The effects of tube geometry (coiled and straight), particle concentration (0–30% v/v), average product flow rate, and carrier fluid temperature (96–124 °C) on residence time distributions of model food particles in the holding section of an aseptic processing system were investigated by means of correlation analysis. Hold tube geometry and flow rate exerted significant effects on the mean normalized residence time. Minimum normalized residence time was significantly influenced by the fluid temperature and the interaction between hold tube geometry and particle concentration. In the coiled tube, standard deviation of normalized residence time decreased with an increase in particle concentration. The fastest-moving particles in the coiled tube possessed a velocity of 1.96 times the average product velocity, whereas the velocity of fastest-moving particle in the straight tube was 1.8 times the average product velocity. Based on empirical expressions of the residence time parameters as functions of particle concentration and dimensionless groups ( Fr f, Re gp, and Ar f), variable influence of several forces on particle residence time of particulate food suspensions in different settings was deduced.

Numerical Analyses of Effects of Tube Shape on Performance of a Finned Tube Heat Exchanger

Th is article discusses the eff ects of tube geometry on the performance of a multi-row fi nned tube heat exchanger having herringbone wavy fi ns. Th e air-side heat transfer and pressure drop characteristics of the heat exchanger were predicted numerically and the tube-side heat transfer coeffi cient and pressure drop were calculated using commonly adopted equations for turbulent fl ow in a smooth tube. Th e numerical calculations were performed in three dimensions for three frontal air velocities of 1.0, 2.0, and 3.0 m/s, yielding hydraulic diameter Reynolds numbers from 297 to 999. Investigated were fi ve tube geometries, including a round tube, three elliptical oval tubes, and a fl at oval tube. Th e round tube has a 15.875 mm (⅝ ) outside diameter and serves as the baseline tube. Th e four oval tubes were made by reforming the baseline round tube and have the same perimeter as that of the round tube. Th e aspect ratios of the three elliptical tubes are 2.00, 3.00, and 4.29, respectively, and the aspect ratio of the fl at oval tube is 3.00. As the tube aspect ratio is increased, the air-side heat transfer coeffi cient and pressure drop decrease, but the water-side heat transfer coeffi cient and pressure drop increase. At 2.0 m/s frontal velocity, the 3.00 aspect ratio elliptical tube yields a 6.9% lower air-side heat transfer coeffi cient and a 45.9% lower air pressure drop than the round tube. As compared to the 3.00 aspect ratio elliptical tube, the same aspect ratio fl at tube has a 0.6% higher air-side heat transfer coeffi cient and a 2.5% higher air pressure drop.

Experimental investigation on large amplitude standing wave induced in closed tubes with varying cross section

When a gas-filled closed tube is driven near the resonant frequency of the gas-column, large amplitude standing wave is induced in the tube. The use of large amplitude standing wave in practical field is based on the exploitation of high amplitude pressure fluctuation together with the associated phenomena like acoustic streaming, thermoacoustic effect and mean pressure distribution. It is already known that shock wave appears in cylindrical tube and thereby the wave motion is limited in the peak pressure that can be generated. In shaped tubes, it is possible to avoid the problem of shock formation and as a result, large amplitude standing wave can be achieved. And also the mode of standing wave induced in shaped tubes depends on the tube geometry. For practical application of large amplitude standing wave, the selection of optimum tube shape must be required. In this report, experimental results are described for three types of tube geometry, such as conical, exponential and half cosine. HFC134a was selected as the working gas for the reason that the effects of tube geometry in the wide range of pressure amplitude can be investigated than air. The frequency responses and pressure fluctuation at closed end of each tube were monitored. The result revealed that the half cosine geometry is suitable in the case of design of the acoustic compressor.

Experimental investigation of the performance of R22, R407C and R410A in several capillary tubes for air-conditioners

The objective of this study is to present test results and to develop a dimensionless correlation on the basis of the experimental data of adiabatic capillary tubes for R22 and its alternatives, R407C (R32/125/134a, 23/25/52 wt.%) and R410A (R32/125, 50/50 wt.%). Several capillary tubes with different length and inner diameter were selected as test sections. Mass flow rate through the capillary tube was measured for several condensing temperatures and various degrees of subcooling at the inlet of each capillary tube. Experimental conditions for the condensing temperatures were selected as 40, 45 and 50°C, and the degrees of subcooling were adjusted to 1.5, 5 and 10°C. Mass flow rates of R407C and R410A were compared with those of R22 for the same test conditions. The results for straight capillary tubes were also compared with those of coiled capillary tubes. A new correlation based on Buckingham π theorem to predict the mass flow rate through the capillary tubes was presented based on extensive experimental data for R22, R407C and R410A. Dimensionless parameters were chosen considering the effects of tube geometry, capillary tube inlet conditions, and refrigerant properties. Dimensionless correlation predicted experimental data within relative deviations ranging from −12% to +12% for every test condition for R22, R407C and R410A. The predictions by the developed correlation were in good agreement with the results in the open literature.

宇宙膨張構造用ポリウレタンの減圧環境下における発泡挙動

Inflatable space structures are expected to be a promising candidate for future large-scaled space structures because of the compactness at the launch stage and the simple extension mechanism. In this paper, the feasibility of an inflatable structure was examined utilizing the expansion force of foam materials as the inflation thrust. As a trial inflatable space structure, an extensible mast, which was made of foam material covered with an aluminum sheet or a carbon fiber cloth was chosen. This paper describes foaming behavior of the material in space. As a first report of the study, intensive discussion was placed upon the effect of low pressure environment on the expansion behavior. The expansion behavior of foam material appeared to be controlled mainly by the pressure difference between the inside and outside of foams. It was found that the fracture of foams could be prevented and the density of the foam material could be controlled even in the low pressure environment by controlling the amount of blowing agent. The effect of tube geometry on the expansion behavior was also discussed.

Experimental Evaluation on the Thermal Stress Due to Ice Plugging of Tubes in Nuclear Power Plant

Ice-plugging of tube in nuclear power plant has been widely used for the purpose of preventing flow of the tube temporarily like a valve. Most common plugging method employs Liquid Nitrogen Gas of . According to the change of tube materials and its dimension, the thermal stress caused from the application of the frozen gas can be varied. In this research, a series of experiments have been carried out to inspect the effect of tube geometry on thermal stresses induced due to ice-plugging. Two typical dimension of stainless and mild steels of 3 and 6 inch diameters were used for the experiments. Each critical spots were checked using strain rosette gages. Another inspection was made on the pressure and temperature of the fluid. It is shown that significant thermal stress level which can cause plastic deformation of failure has not been noticed in this series of experiments.

A Generalized Performance Prediction Method for Adiabatic Capillary Tubes

Generalized dimensionless correlations were developed to predict refrigerant mass flow rate in an adiabatic capillary tube, for both subcooled and quality inlet conditions. Dimensionless parameters were created using the Buckingham Pi Theorem. These parameters were based on the effects of tube geometry, inlet conditions, and fluid properties. The correlations were based on experimental performance data with refrigerants R-134a, R-22, and R-410A that encompass an extensive range of operating conditions, including: condensing temperatures from 79 °F to 127°F (26°C to 53°C), capillary tube inner diameters from 0.026 to 0.090 in (0.66 to 2.29 mm), capillary tube lengths from 20 to 200 in (508 to 5080 mm), and inlet conditions from 30°F (16.7°C) sub-cooled to 35% quality. Corresponding to this range of refrigerants, capillary tube geometry, and operating conditions, the experimental mass flow rate range was between 3 and 375 lbm/h (1.4 to 170 kg/h). Independent assessments of both correlations were made by comparing predictions to measured performance with R-152a. These data fell within the ±6% and ±13% prediction intervals for the subcooled inlet and quality inlet correlations, respectively. The accuracy of the subcooled inlet correlation was further assessed by comparing predicted performance to measured data reported by other investigators with refrigerants R-12, R-134a, and R-22. It was shown that the subcooled inlet correlation predicted the bulk of these flow data to within ±10%. However, when compared to reported data with R-600a (isobutane), however, the subcooled inlet correlation over-predicted mass flow rate by 0 to 20%.

The effect of geometry on the performance of the closed tube thermosyphon at low Rayleigh numbers

The results of an experimental investigation of heat transfer in the closed tube thermosyphon under laminar conditions are presented. Attention is focused on the effect of tube geometry when the Rayleigh number is low enough to create boundary layer, transitional and impeded flows. The data show that the length-diameter ratio and heated-cooled length ratio both have a monotonic effect on the heat transfer rate, the former being the greater. Results are presented for both air and water, with the latter tests including the effect of cooled wall temperatures low enough to produce an inverted flow in the cooled section.

Experimental Investigation of Noise Reduction from Two Parallel-Flow Jets

Multitube nozzles have been developed to suppress turbojet engines in a number of cases. The concept of two parallel-flow jets forms a basic element of the multitube nozzle. Hence, the acoustic characteristics of two parallel-flow jets have been investigated as a fundamental study aimed at understanding jet noise suppression mechanisms which then could lead to improved jet noise suppressors. Model-scale tests were conducted in an anechoic environment. Acoustic measurements were made in the plane containing the axis of the two jets using a far-field microphone array. The effect of tube geometry (lateral tube spacing, longitudinal tube staggering, and tube size) was studied with the same flow through both tubes. The effect of flow parameters was investigated using twin coplanar jets. Detailed acoustic test results were evaluated in terms of engineering as well as subjective units. The following general conclusions were drawn from the study: 1) two coplanar parallel-flow jets with dissimilar unmixed flow can be quieter than an equivalent fully mixed single-flow jet; 2) two parallel-flow jets with the same flow can be up to 3 dB quieter than the equivalent single-flow jet; 3) two parallel-flow jets become quieter when lateral spacing is reduced, the nozzle near the observer is staggered upstream, or a smaller nozzle is placed near the observer; and 4) for two parallel-flow jets with dissimilar flows, the noise at 90 to 110 deg from the inlet axis depends mainly on the peak jet velocity, and noise at 120 to 160 deg depends very strongly on only that part of velocity profile which the observer can see directly.