Double-walled Tube Research Articles

Finite element analysis of tube inversion process with radiused dies

The extended rmin technique has been incorporated in the incremental updated Lagrangian formulation (ULF) of an elasto-plastic finite element computer code in order to handle the contact boundary condition when analyzing the axisymmetric tube inversion process with a quarter fillet die radius. A fillet die applies an axial compressional load onto a thin tube so that the inside or outside of the tube inverts totally making the central axis of the original tube the same as a new double-walled tube. This is called an inside-out or outside-in inversion process. This study employs an elasto-plastic finite element method to simulate and analyze inside-out inversion. The objective is to examine how different process factors, such as the geometry and material modulus, influence metal tube inversion. This study also simulates a quarter fillet radius of the die to analyze the tube forming condition and range that can be applied in engineering under these requirements. In addition, the axial compressional load under inside-out inversion stability to be suitable for a personal computer, so it can be effectively analyzed and evaluated on line instantaneously.

Length-independent inter-tube conductance in double-wall carbon nanotubes

Conductance due to inter-tube transfer in incommensurate double-wall tubes is numerically studied. The conductance is usually much smaller than e 2 / π ℏ and its average and fluctuation are independent of the length. This behavior arises because the inter-tube transfer oscillate around zero in a complex plain as a function of position in a quasi-periodic manner and therefore cancel each other when being summed up except near tube edges.

Impact of ivermectin on the ultrastructure of the testis of Argas (Persicargas) persicus (Ixodoidea: Argasidae)

Mated male Argas persicus were dissected 1 and 2 weeks after feeding on untreated and ivermectin (IVM)-treated pigeons. One week after feeding, testes of untreated ticks were filled with rounded spermatids with subplasmalemmal vesicles and cytoplasmic organelles, but lacking in treated ticks. Two weeks after feeding, testes were crowded with elongated spermatozoa supported by double-walled cisternal tubes. The tubes consisted of two opposite walls, each with outer-fringed processes and inner elongated cisternae. Both were supported with electron dense striated plates in the middle of the spermatozoon. Internally, the cisternal tubes contained mitochondria and vacuoles. The nuclei were elongated dense masses between the tubes and the cell membranes. Subcutaneous inoculation of IVM at the dose 400 microg/kg pigeon resulted in extensive alterations in the testis of A. persicus. IVM prevented the development of new spermatids. There was a break down of cell membranes and cytoplasmic organelles of spermatozoa. Multivesicular bodies and numerous vacuoles were noticed in their cytoplasm. Double membranes of elongated cisternae and striation of electron dense plates became indistinct. IVM caused granulation and vacuolization of the nucleus as well as injury of mitochondrial cristae. The results suggest that IVM may bind to the neurotransmitter or the hormone involved in the process of sperm development or may be toxic to the germinal cells of A. persicus testis.

Gold tubes membrane with novel morphology replicated from ZnO template

Gold tubes membrane with novel morphology was fabricated on glass substrate by electroless plating gold on ZnO crystals array, and then annealing and removing the ZnO template by acid erosion. The morphology and size of the gold tubes membrane were decided by ZnO template. Hexagonal gold tubes membrane and double-wall gold tubes membrane were obtained, which enjoys some potential usage in electrode modification or chemical separation due to their huge surface area and unique geometric structure. SEM images show that those gold tubes in membrane are hollowed hexagonal columns with a closed head and an open bottom. Further researches found that two main factors determined the success of replication: the gold seeds (4–5 nm in diameter) immobilized on ZnO surface through APTMS (3-Aminopropyl-trimethoxysilane) before gold electroless plating and the annealing condition after electroless plating.

Double-Walled Reactor Tube with Molten Salt Thermal Storage for Solar Tubular Reformers

This paper proposes a novel-type of “double-walled” reactor tube with molten-salt thermal storage at high temperatures for use in solar tubular reformers. The prototype reactor tube is demonstrated on the heat-discharge and chemical reaction performances during cooling mode of the reactor tube at laboratory scale. The Na2CO3 composite material with MgO ceramics was filled into the outer annulus of the double-walled reactor tube while the Ru-based catalyst particles were filled into the inner tube. The heat discharge form the molten Na2CO3 circumvented the rapid temperature change of the catalyst bed, which resulted in the alleviation of decrease in chemical conversion during cooling mode of the reactor tube. The application of the new reactor tubes to solar tubular reformers is expected to help realize stable operation of the solar reforming process under fluctuating insolation during a cloud passage.

Formation and electronic properties of double-walled boron nitride nanotubes

The electronic and structural properties of double-walled boron nitride (BN) nanotubes are studied using the first principle pseudopotential density functional method. It is shown that zigzag-type tubes have a larger formation energy for the double-walled configuration than the armchair-type structure, and that interwall stacking plays a significant role for intertube interactions and in the formation of multiwall BN nanotubes. The fundamental energy gap of double-walled BN nanotubes was found to be smaller than that of single-walled tubes mostly due to band shift. It is shown that the electronic properties of double-walled BN tubes exhibit a slight but noticeable difference for the zigzag and armchair type tubes studied.

NEWS OF THE WEEK

Although often overshadowed by their single-and multiwalled siblings, double-walled carbon nanotubes (DWNTs) are predicted to have superior mechanical properties, thermal conductivity, and structural stability. However, scientists have found it difficult to create DWNTs in the pure, highly crystalline form needed to study the tubes' properties in depth. Now,an international team led by Morinobu Endo,an engineering professor at Shinshu University in Nagano, Japan,as developed a process for making highly pure DWNTs[Nature, 433,476 (2005)]. They isolate the material in sheets as a tough buckypaper that is flexible enough to fold into a tiny paper airplane. Endo and coworkers envision more high-tech applications for the material in the future, such as nanotube bi-cables and electronic devices. Endos group makes DWNTs using a standard chemical vapor deposition procedure. They employ a molybdenum conditioning catalyst to favor formation of double-walled tubes over single-walled ones. Next, they purify the DWN...

FEM numerical simulation of tube axial drawing process

Tube inversion by the axial drawing is an advanced forming process for manufacturing double-walled tubes with high quality, high efficiency, and low consumption. However, to realize forming process depends on producing the tearing in deforming zone, which has a close relationship with forming load. So in this paper, the influence of forming condition parameters on the deforming force and the process is investigated by rigid-plastic FEM numerical simulation. The results show that: (1) during the whole forming process, the shape of the tube remains unchanged when the radius of the core die is larger than a certain value, so a precision forming can be easily realized; (2) for a given r/ d 0 or t 0/ d 0, the deforming force depends mainly on the value of r/ t 0, and there is a critical parameter k, when r/ t 0 < k, the steady forming force decreases with an increase of r/ t 0; on the contrary, when r/ t 0 > k, the steady forming force increases with an increase of r/ t 0; (3) the material hardening exponent n of the tube and the friction coefficient μ have a remarkable influence on the deforming force. The smaller the value of n and the larger the value of μ the larger the forming force.

A molecular motor constructed from a double-walled carbon nanotube driven bytemperature variation

A new molecular motor is theoretically constructed from a double-walled carbon nanotubewhose inner tube is a long (8, 4) single-walled carbon nanotube (SWNT) and whoseouter tube a short (14, 8) SWNT. The interaction between the inner and outertubes is derived by summing the Lennard-Jones potentials between atoms inthe inner and outer tubes. It is proved that the molecular motor in a thermalbath exhibits a directional motion with the temperature variation of the bath.

Simple and double walled Krasnikov tubes: II. Primordial microtubes and homogenization

First we take a look at the behaviour of geodesics initially directed at a Krasnikov tube of small mass. We show that superluminal shifting is a generic property of geodesics aimed at the tube, not just of those entering the tube by its mouths. Then we show that if present in sufficient numbers, microtubes could be put to task in achieving an inflationless predecoupling homogenization of an open neighbourhood of our particle horizon.

Lattice dynamics and symmetry of double wall carbon nanotubes

Stable configurations and full symmetry groups of double wall carbon nanotubes aredetermined. These are used to calculate phonon bands for commensurate tubes. Inparticular, the modes with rigid walls are analysed and weak interlayer interaction isconfirmed. Taking infra-red measurements is found to be a suitable method forcharacterizing double wall tubes. The heat capacity in the low temperature region ispredicted to be lower than for single wall layers.

Narrow diameter double-wall carbon nanotubes: synthesis, electron microscopy andinelastic light scattering

Double-wall carbon nanotubes are the molecular analogues to coaxial cables. Narrowdiameter double-walled carbon nanotubes (DWNTs) have been obtained by catalyticchemical vapour deposition process with high yield and characterized by scanning andtransmission electron microscopy. We examine the inelastic light scattering spectrum ofmostly DWNTs with internal tubes of subnanometre diameter. We observe particularlynarrow radial breathing modes corresponding to the internal tubes of diameter lessthan 0.7 nm of double-walled tubes. The D band is found to be strongly helicitydependent and the tangential modes in narrow diameter DWNTs are found to be oftendown-shifted.

On the nuclear response of the water-cooled Pb–17Li test blanket module for ITER-FEAT

Within the European Fusion Technology Programme, the Water-Cooled Lithium Lead (WCLL) DEMO breeding blanket line was selected in 1995 as one of the two EU lines to be developed in the next decades, in particular with the aim of manufacturing a Test Blanket Module (TBM) to be tested in ITER-FEAT. The present paper is focused on the study of the WCLL-TBM nuclear response in ITER-FEAT, being specifically oriented to the investigation of the local effects due to the typical C-shaped tubes of the breeder zone, since they could play a pivotal role in the module-relevant thermo–mechanical design. A 3D heterogeneous model of the WCLL-TBM, realistically simulating its new lay out and taking into account 9% Cr martensitic steel as reference structural material, has been set-up. A particular attention has been paid to the simulation of the characteristic ‘C’ shape of the breeder zone double walled tubes, which have been realistically reproduced. The WCLL-TBM model has been inserted into an existing ITER-FEAT 3D semi-heterogeneous model accounting for a proper D–T neutron source. Analyses have been performed by means of MCNP-4C code running on a cluster of four workstations through the implementation of a parallel virtual machine. For each analysis a large number of histories (>10.000.000) have been simulated, obtaining statistical uncertainties on the results lower than 3%. The main features of the WCLL-TBM nuclear response have been determined focusing the attention on power deposition density, material damage through DPA and He and H production rate, daily tritium production and tritium production rate radial distribution in the module. The obtained results are herewith presented and critically discussed.

In-pile performance of a double-walled tube and a tritium permeation barrier

In two recent irradiation experiments in the HFR Petten, tritium permeation rates through representative materials to be used as cooling tubes of the water-cooled lithium-lead blanket have been measured in-pile. These latest experiments in the EXOTIC 8 series (E 8.9 and E 8.10) are made of a double wall tube (DWT) and a T91 tube with an Fe–Al/Al 2O 3 layer acting as tritium permeation barrier (TPB). These tubes contain annular pebble beds of ceramic breeder materials for the helium-cooled pebble bed concept blanket as tritium breeding material. Both experiments are built up of two concentric and independently purged containments allowing on-line tritium release rate and permeation rate measurements. In-pile operation has ended in March 2001 after 450 full power days and resulted in an irradiation damage of approximately 2.6 and 3.2 dpa, respectively in T91 steel. This paper reports on the experimental results obtained for in-pile tritium permeation and discusses the influence of purge gas compositions, temperature and irradiation on tritium permeation through the DWT and TPB.

Status of the design and performances of the WCLL test blanket module for ITER-FEAT

The water-cooled lithium–lead (WCLL) DEMO blanket is one of the two European blanket lines to be further developed with the aim, in the short term, of manufacturing a DEMO blanket mock-up, named the test blanket module (TBM) to be tested in ITER-FEAT. This blanket line is based on reduced-activation ferritic-martensitic steel of the 9% Cr class as structural material, the liquid alloy Pb–17Li as breeder and neutron multiplier and water at typical PWR conditions as coolant. The WCLL TBM is expected to use all technologies required for that concept and is essentially formed by a directly cooled steel box having the function of Pb–17Li container and by a double-walled C-shaped tube bundle, immersed in the liquid metal, in which the water coolant circulates. The design of the TBM and its ancillary circuits is described. Conceptual studies have shown that, in the range of the foreseen heat flux and neutron wall loading in ITER-FEAT, DEMO relevant testing conditions could be reached with a unique reference TBM design by properly adjusting the thermal–hydraulic conditions in both the breeder zone and segment box. A tentative test plan in ITER has been established with the overall objective to evaluate the TBM behavior (e.g. functional, thermal, mechanical, neutronic) in conditions which are, as much as possible, relevant to DEMO.

In-pile tritium-permeation measurements on T91 tubes with double walls or a Fe–Al/Al 2O 3 coating

Two new irradiation projects are being performed at the HFR Petten, named EXOTIC-8.9 and EXOTIC-8.10. Issues such as tritium release from candidate ceramic breeder pebbles for the HCPB blanket and tritium permeation through cooling tubes of the WCLL blanket are investigated simultaneously. In EXOTIC-8.9, the tritium release behaviour of a Li 2TiO 3 pebble bed is measured along with the tritium-permeation rate through a double-wall tube (DWT) of T91 with a Cu interlayer. In EXOTIC-8.10, the tritium release behaviour of a Li 4SiO 4 pebble bed is measured along with the tritium permeation rate through a T91 tube with a Fe–Al/Al 2O 3 coating as tritium permeation barrier (TPB). Tritium permeation phenomena are studied by variations of temperatures and purge gas conditions. This paper reports on the results of the first 100 irradiation days.

Design of an in-pile device for testing of WCLL double wall tubes

The present paper describes irradiation devices proposed by SCK CEN to test segments of water cooled lithium–lead blankets (WCLL), and in particular their double-wall tubes (DWT), under irradiation in the BR2 reactor. The purpose of the first experiment is to assess the efficiency of a tritium permeation barrier (TPB) coating at the outer surface of the DWT. Hence, two DWT segments are plunged in a lithium–lead pool. The inside of the DWT is flushed by helium and collects the tritium permeating through the wall. One of the DWTs has received a TPB coating, the other not, so that comparative measurements are possible. For the second experiment, a DWT segment is heated by the gamma flux of BR2 and cooled at the inside by pressurised water. Hence, the temperature gradient tends to separate the two tubes. The purpose is to verify how the brazing agent performs at doses up to 3 dpa. The irradiation device is installed inside the central hole of a BR2 fuel element, in order to maximise the fast neutron component of the flux received by the target. As an attractive alternative, the utilisation of the PWR loop Callisto is also proposed.

Hydrogen and deuterium permeation measurements on the double-wall tubes material for the water-cooled Pb–17Li DEMO blanket

The aim of this study is to measure the hydrogen/deuterium transport and inventory parameters in the double-wall tubes (DWT) material for the water-cooled Pb–17Li DEMO blanket. Measurements are conducted using a time dependent permeation method over the temperature range 473–723 K, with hydrogen and deuterium driving pressures in the range 1–10 5 Pa (0.01–1000 mbar). The samples are also characterised using optical microscopy, SEM, microhardness measurements and mechanical tests. An effective permeability of about 12 times lower than 2.1 mm of bare F82H steel at 573 K and three times lower than 2.1 mm of bare F82H steel at 723 K have been measured. This result is close to the theoretical prevision (multi-layer model).

Objectives feasibility assessment of the water-cooled lithium–lead mock-up testing in ITER

This paper presents a short description of the latest design version of the water-cooled Pb–17Li test-blanket module system and the proposal for the test program to be performed during the ITER Basic Performance Phase. The present R&D program foresees to start the test on the first day of ITER operation. The test-blanket module is expected to use all technologies required for the corresponding DEMO blanket (e.g. same structural material, double-wall tubes, permeation barriers) presently under development. Main testing objectives are the demonstration of the system functionality and the validation of the predictions obtained from the theoretical analyses. The feasibility of such objectives is discussed from the point of view of instrumentation and interpretation.

Curling of thin tubes: Analytical and experimental study

The curling of thin tubes under compressive loads produces double walled tubes for many engineering applications. Experiments have been performed on annealed copper, low carbon steel, stainless steel, and aluminum tubes to determine the relationship between the curling process parameters and the tube geometry, as well as tube material properties. Effects of friction and work hardening during forming are included in the analysis. The analytical and experimental results are compared with published results to determine the validity of the proposed analytical model. The model can be used to determine the curling load and the correct die radius for successful curling. For simple and quick determination of the die radius, the present work introduces design curves, which correlate the tube geometry with the radius of the forming die.