Increasing Tube Diameter Research Articles

Theoretical Investigation of Gas Filling and Leaking in Inertial Confinement Fusion Hohlraum

The gas filling and retention of inertial confinement fusion (ICF) hohlraum is an important issue in ICF studies. In this study, a theoretical model of gas filling and leaking processes for ICF hohlraum is developed based on the unified flow theory. The effects of the fill tube size and the filling pressure on the gas filling and leaking performance are investigated. The results indicate that an increase in the variation rate of the filling/leaking pressure leads to a larger maximum pressure difference between the inside and outside of the ICF hohlraum during the filling/leaking process. The critical pressure difference of the filling process is nearly equal to that of the leaking process. Increase in fill tube diameter and decrease in its length both lead to a lower probability of the rupture of polymeric films at two ends of the hohlraum, and thus increases the security of the hohlraum. In addition, a departure in cross sectional shape of fill tube from circle to rectangle triggers an increase in pressure difference between the inside and outside of the ICF hohlraum, which raises the risk of polymeric films rupture and decreases the security of the hohlraum structure.

Evaluation of a precision air-supply system in naturally ventilated freestall dairy barns

A good ventilation system is critical to the success of any commercial cattle raising operation. Most dairies rely on natural ventilation systems, with supplemental cooling systems (e.g. cooling fans, ceiling ventilation, polytube cooling, etc.) to help mitigate the heat stress imposed on the cows when natural ventilation proves insufficient, usually during hot, humid and windless situations. However, the effects of these supplemental cooling are insufficient in many cases. Therefore, the current study assessed an alternative supplemental cooling system, referred to as a precision air supply system (PASS), with respect to how effectively it could remove excess heat from cows inside barns. The effects of three key parameters (i.e. supply-air speed, distribution tube diameter, and air-supply angle) on the performance of PASS were evaluated with respect to both a standing cow and a reclining cow, by means of a response surface methodology and a series of properly validated computational fluid dynamics (CFD) simulations. The results showed that PASS performed better when the bulk air was still and that all three investigated parameters helped to improve heat dissipation. A perturbation plotting indicated that adjusting the air-supply angle may well be the best first option when seeking to improve the cooling performance of PASS, followed by increasing tube diameter as the next best option. When serving as a supplemental cooling system deployed in a freestall, naturally ventilated barn, PASS should work well to mitigate heat stress when the temperature and humidity index (THI) increases beyond the threshold value (i.e., THI > 68).

Numerical Study on Choked Flow of CO2 Refrigerant in Helical Capillary Tube

This paper presents a numerical study on an adiabatic helical capillary tube employing homogenous and choked flow conditions of a CO2 transcritical system. The theoretical model is based on the fundamental principle of fluid dynamics and thermodynamics. The result of the present model validates with the previously published data. The influence of operating and geometric parameters on the performance of the capillary tube has been evaluated. Flow characterizations of choked and unchoked flow conditions are determined. As the evaporator pressure drops, from unchoked condition to choked state, the percentage change in mass flow rate is minimal. A simulation graph is developed which has been helpful for the design of the helical capillary tube. The choked flow condition in a capillary tube is avoided by either increasing tube diameter of the fixed length tube or decreasing the length of the fixed tube diameter.

Nanomechanics model for properties of carbon nanotubes under a thermal environment

This paper proposes a modified molecular mechanics model in which the covalent bond is treated as a beam element, and a theoretical prediction of the thermal environment effect on the elastic properties of single-walled carbon nanotubes (SWCNTs) is reported. The influence of the temperature on Young’s modulus of both armchair and zigzag SWCNTs is investigated. The study shows that the moduli decrease with the increase in temperature, but Poisson’s ratio is not dependent on the temperature. The temperature-dependent Young’s modulus increases with the increase in tube diameter. According to the principle of elasticity theory and energy consistent theory, a temperature-dependent continuum shell model of strain energy is also established. It is found that the deviation between the potential energy of carbon nanotubes and the strain energy of a continuum shell is significantly reduced based on the molecular mechanics model proposed in this study.

Experimental study on the hysteretic behavior of ECC-encased CFST columns

Concrete-encased concrete-filled steel tube (concrete-encased CFST) columns, which is a conjunction of normal steel reinforced concrete (RC) and CFST columns, have been widely used in structural engineering. However, the outer RC component tends to crush in the early stage due to the significantly different mechanical performance of outer concrete and inner CFST. In this paper, it is proposed to substitute outer concrete with engineered cementitious composite (ECC) to form ECC-encased CFST columns. This paper presents an experimental study on the hysteretic behavior of ECC-encased CFST columns. Eleven specimens, including seven ECC-encased CFST columns and four concrete-encased CFST columns were tested under cyclic loading. According to the test results, ECC-encased CFST columns exhibited stable ductile behavior and the cumulative energy dissipation is about twice as much as that of concrete-encased CFST columns with same geometry. Also, the increase of steel tube diameter and stirrup ratio have positive effects on the hysteretic behavior of ECC- encased CFST columns.

Structural stability and vibrational analysis of beryllium sulfide BeS from the bulk to the (n,0) nanotubes. An ab initio description

Beryllium sulfide (BeS) in different forms from molecule, bulk, monolayer (h-BeS), to the single-walled nanotube obtained by wrapping the h-BeS monolayer along the (n,0) hexagonal lattice vector for n varying from n = 6 to 64, has been examined. Density functional theory (DFT) with an all electron basis set and the hybrid DFT/B3LYP level have been applied to compute energetic and geometrical, electronic and vibrational, elastic and piezoelectric properties, where the trend towards the hexagonal monolayer (h-BeS) in the limit of large tube radius is obtained. The vibrational properties including Raman spectra and polarizabilities are evaluated via the Coupled Perturbed Hartree–Fock and Kohn–Sham (CPHF/KS) computational schemes. For the first time, the IR vibrational modes at higher tube diameter and their convergence to the h-BeS monolayer limit are reported where the vibrational and electronic contributions to both perpendicular and parallel components of polarizability tensor are additionally discussed. For the (n,0) BeS nanotube family, three ranges of IR active phonon modes are determined. The first one located in the 0–300 cm−1frequency domain, goes regularly to zero when the tube diameter increases. Both the second (300–400 cm−1) and the third (700–800 cm−1) ones tend smoothly with different slope, towards the two optical vibrational modes of the h-BeS layer. These theoretical models can be extended to investigate further issues, such as the effect caused by the addition of a dopant, the influence of the substitutional fraction of nanotube atoms and the interaction of molecules outside and/or inside of the nanotube.

Experimental study on spontaneous ignition and subsequent flame development caused by high-pressure hydrogen release: Coupled effects of tube dimensions and burst pressure

Combined effects of tube dimensions and burst pressure on the spontaneous ignition caused by high-pressure hydrogen release into a semi-confined space are investigated experimentally. An important finding is that the influence of tube diameter on spontaneous ignition shows complex behavior. For tubes with different diameters, the minimum burst pressure for spontaneous ignition depends on not only the strength of the shock wave but also the mixing of hydrogen and air. A dimensionless parameter of tubes, L/D—which is defined as the ratio of the tube length to the tube diameter—is introduced to describe the effect of tube size. The results show that the possibility of spontaneous ignition increases with increasing L/D. Under appropriate conditions, spontaneous ignition leads to flame development. As the flame propagates into a semi-confined space, it first forms an envelope structure in front of the hydrogen jet. Since some amount of a partially premixed combustible mixture, created by the hydrogen jet, exists in the semi-confined space, the flame subsequently undergoes deflagration. The overpressure caused by deflagration is significantly greater than that caused by the leading shock wave. In addition, both the deflagration overpressure and the shock-wave overpressure increase with increasing tube diameter and initial release pressure.

Structural and Electronic Properties of α2-Graphyne Nanotubes: A Density Functional Theory Study

Another form of carbon-based two-dimensional material in the graphene family, named the α2-graphyne sheet, was predicted very recently. The α2-graphyne sheet was created by doubling each acetylenic linker in an α-graphyne sheet. It exhibited semimetallic Dirac point features similar to graphene and α-graphyne sheets. In the present work, single -walled carbon nanotubes based on an α2-graphyne sheet was introduced. The structural and electronic properties of these nanotubes were studied using density functional theory. It was found that armchair α2-graphyne nanotubes showed metallic behavior, while zigzag α2-graphyne nanotubes were found to have semiconducting or metallic properties depending on tube size. The energy band gap of zigzag α2-graphyne nanotubes decreased with increasing tube diameter. The results indicated that the α2-graphyne sheet and its nanotubes can be proper materials for future nanoelectronics.

Structural and electronic properties of nitrogenated holey nanotubes: A density functional theory study

The structural and electronic properties of nanotubes based on C2N sheet known as nitrogenated holey graphene are investigated using density functional theory. The cohesive and strain energies, electronic band structures, total and partial density of states of the armchair and zigzag nanotubes constructed by rolling up nitrogenated holey graphene are calculated. The calculated cohesive energies indicate that the zigzag nitrogenated holey nanotubes are more stable than the armchair ones. The energetic stability of the considered nanotubes increases with increasing tube diameter. It is found that both armchair and zigzag nitrogenated holey nanotubes show semiconducting properties similar to nitrogenated holey graphene sheet. The semiconducting properties of nitrogenated holey nanotubes are dependent on the tube size and chirality. The results provide new insight into nanomaterials for use in emerging nanoelectronic devices.

Analyses of Sampling Disturbance of the Lunar Surface in Direct Push Sampling Method

The study of direct push sampling characteristics forms the theoretical basis for deep sampling tool design. In this paper, a ground test of the direct push sampling was carried out to analyze three influencing factors: tube diameter; friction coefficient; and soil plug length. Using the discrete element method software, EDEM, a lunar subsurface direct push sampling model was established. We propose a vortex structure of the particle displacement field in the sampling tube and establish a connection between the three influencing factors and the structure disturbance of the soil plug. The EDEM simulation revealed the microscopic mechanism of penetration sampling disturbance. The results show that the soil plug in the compressive state had a small disturbance and a high degree of sequence retention and that the internal stress was changed compared to that in the in-situ state. The structure disturbance of the soil plug in the stick-slip state was large, while the parts of the soil plug that are away from the center line of the tube were in disorder. In the center line of the tube, the in-situ sequence state was gradually restored with the increase in tube diameter or decrease in soil plug length. Increasing the friction coefficient would change the soil plug from the compression state to the stick-slip or adhesion state. In case of the stick-slip state or adhesion, reducing the diameter of the tube or increasing the length of the soil plug would change the soil plug from the stick-slip state or adhesion state to the compression state.

Phase change in spiral coil heat storage systems

Since new technology in residential buildings encourages the implementation PCM heat storage systems and as far as larger heat transfer surface can be provided using spiral coil heat storage systems, it is aimed to introduce this enhancement via a numerical study.In this ‎study, spiral coil tube is considered in a shell and tube heat storage unit and numerical ‎simulations are performed to predict the effect of geometrical and operational parameters such as spiral coil ‎diameter, tube diameter, HTF mass flow rate and HTF inlet temperature on heat transfer characteristics and thermal behavior of Paraffin ‎RT50 as phase change material during melting process in the shell and spiral coil tube heat ‎exchanger while HTF flows inside the tube and PCM fill the space between shell and tube. ‎Simulation results showed that spiral coil diameter plays an important role in melting process ‎and heat transfer procedure. By increasing spiral coil diameter from 50 mm to 70 mm, total ‎melting time will reduce up to 71.4%. In contrast, tube diameter has little effect on melting ‎process. It is indicated that for larger spiral coil diameter, increasing tube diameter has a ‎reverse impact on reduction of total melting time.‎

Denting the oil pipelines by a rigid cylindrical indenter with conical nose by the numerical and experimental analyses

The present research discusses indentation process on the oil pipelines using a rigid indenter in the quasi-static condition by the experimental and numerical analyses. This article investigates influences of internal pressure, diameter and wall thickness of pipes and geometrical characteristics of rigid cylindrical indenters with conical nose such as cone angle, conical nose diameter and cylindrical part diameter on mechanical behavior of the circular steel pipes under concentrated lateral loading (denting). In the experimental part, some specimens made from the steel API5L L245 were prepared and they laterally compressed by a rigid cylindrical indenter with the conical nose to perform the indentation process on them. In the numerical part, some finite element models were prepared and indentation process was simulated on different models with various tube and indenter geometries in different conditions of internal pressure. By comparing the numerical and experimental results, precision and accuracy of the simulations were affirmed. The discussed results show that when tube diameter increases, bending moment arm of the concentrated applied load around the formed plastic hinge lines enhances; therefore, lower lateral load can create a certain plastic deformations in the tube wall; and also, total absorbed energy by the tube enhances. Results demonstrate that when a conical projectile with a certain mass and initial velocity laterally compresses a circular tube, increment of tube diameter causes reduction of probability of the tube failure. The results show that when cone angle of conical indenter decreases and reaches to a certain value that called critical angle, the penetration occurs during the indentation process. Furthermore, it is found that by increasing the diameter of cylindrical part of the indenter, lateral indentation load increases; and when applied internal pressure on the tube increases, ultimate lateral displacement of the indenter decreases; but, the maximum load for the tube wall fracture enhances.

Atomistic-continuum modeling of vibrational behavior of carbon nanotubes using the variational differential quadrature method

A numerical approach is adopted for the multiscale analysis of vibrations of single-walled carbon nanotubes (SWCNTs). The SWCNT is modeled by a hyperelastic membrane whose kinematics is described using the higher-order Cauchy-Born rule. The constitutive model is formulated exclusively in terms of the interatomic potential, so, it inherits the atomistic information and involves no other phenomenological input. The variational differential quadrature (VDQ) method is employed in which the continuum model is discretized using DQ, and a weak form of equation of motion is obtained via a variational approach. VDQ is computationally advantageous since it has a fast rate of convergence and can reproduce the results of molecular dynamics simulations. Detailed investigations into frequencies and mode shapes of SWCNTs with different geometrical parameters, boundary conditions and chiralities are carried out. It is found that short nanotubes display a coupling between the axial/torsional and bending modes. Also, as the tube diameter or length increases, mode transitions are made at several critical points. If the edge supports are more flexible and tube length is longer, the critical diameters are larger. Eventually, the vibration characteristics of axially strained nanotubes are analyzed, and it is concluded that SWCNTs with smaller radii have higher strain sensitivity.

Spermine Regulates Pollen Tube Growth by Modulating Ca2+-Dependent Actin Organization and Cell Wall Structure.

Proper growth of the pollen tube depends on an elaborate mechanism that integrates several molecular and cytological sub-processes and ensures a cell shape adapted to the transport of gametes. This growth mechanism is controlled by several molecules among which cytoplasmic and apoplastic polyamines. Spermine (Spm) has been correlated with various physiological processes in pollen, including structuring of the cell wall and modulation of protein (mainly cytoskeletal) assembly. In this work, the effects of Spm on the growth of pear pollen tubes were analyzed. When exogenous Spm (100 μM) was supplied to germinating pollen, it temporarily blocked tube growth, followed by the induction of apical swelling. This reshaping of the pollen tube was maintained also after growth recovery, leading to a 30–40% increase of tube diameter. Apical swelling was also accompanied by a transient increase in cytosolic calcium concentration and alteration of pH values, which were the likely cause for major reorganization of actin filaments and cytoplasmic organelle movement. Morphological alterations of the apical and subapical region also involved changes in the deposition of pectin, cellulose, and callose in the cell wall. Thus, results point to the involvement of Spm in cell wall construction as well as cytoskeleton organization during pear pollen tube growth.

Molecular dynamics study on radial deformation of armchair single-walled boron nitride nanotubes

Radial deformation of boron nitride nanotubes (BNNTs) plays a significant role in the performances of BNNT-based applications. By performing molecular dynamics simulations, the radial deformation of armchair single-walled BNNTs was investigated. The deformation energy barrier was found to follow a decreasing trend with increasing tube diameter. Two threshold diameters were identified that demarcate three stability regimes for the deformed single-walled BNNTs. Whereas the van der Waals interaction was simply favorable for radial deformation, the electrostatic interaction had a complex effect; it prevented deformation from the initial cylindrical shape but promoted collapse when the opposing tube wall came into proximity.

R32 flow boiling in horizontal mini channels: Part I. Two-phase flow patterns

The two-phase flow patterns of R32 flow boiling in horizontal mini channels were investigated. The working conditions cover 1 and 2mm channel inner diameters, 10–20°C saturation temperatures, 50–600kgm−2s−1 mass fluxes, 10–30kWm−2 heat fluxes and 0–1 vapor qualities. Slug flow, churn flow, annular flow, dryout, mist flow and stratified flow were observed. The slug flow region is smaller with increasing mass flux and is larger with increasing tube diameter, saturation temperature or heat flux; the annular flow region is smaller with increasing tube diameter, saturation temperature, mass flux or heat flux; the mist flow region is larger with increasing saturation temperature, mass flux or heat flux and is smaller with increasing tube diameter. The existing flow-pattern maps cannot well predict the flow patterns of R32 flow boiling in mini channels. By adopting the existing correlations and introducing Bo number, a new flow-pattern map was established and it agrees 97.6% of the experimental data in this study.

A study of heat transfer scaling of supercritical pressure water in horizontal tubes

Understanding the role of the heat transfer scaling in supercritical utilities can help us obtain a better design for supercritical single phase thermosiphons. In this paper, heat transfer scaling analysis of supercritical pressure water in horizontal tubes with differential inside diameters are experimentally investigated. The operating conditions included mass flux of 100–600kg/m2s and heat flux of up to 400kW/m2. The uneven circumferential temperature distributions are discussed firstly over a broad range of heat fluxes. A significant temperature discrepancy exists between the top and bottom surface in each pipe, deteriorated heat transfer occurs on the top surface but enhanced heat transfer happens in the bottom region. With the rise of heat flux, more severe deterioration appears on the higher domain. Then a qualitatively comparison on the heat transfer characteristic of supercritical flow in different pipes are implemented. Evidently, with the increase of tube diameter, the inner-wall temperature peak is much pronounced and the degree of deterioration at the top surface much severe due to the intensification of buoyancy force. The heat transfer mechanism of horizontal pipes is further discussed by comparing the effect of buoyancy and thermal acceleration. With the augment of diameter, free convection gradually intensifies due to its steeper density variation and expanded flow space, which leads to larger temperature deviation between the bottom and top region along the circumferential direction. On the contrary, thermal acceleration plays a relatively minor role in deteriorated heat transfer. Considering the scaling effect in various pipes, two heat transfer correlations are proposed respectively in both the bottom and top region of the horizontal flows.

Ab initio investigation of pristine and doped single-walled boron nitride nanotubes as acetone sensor

The sensor properties of single-walled boron nitride nanotubes (BNNTs) towards acetone are studied by investigating the intermolecular interactions of acetone with a serials of pristine and doped BNNTs. Density-functional theory (DFT) with empirical dispersion corrected is adopted to explore the adsorption properties of acetone on the surface of BNNT. Results show that acetone binds strong to the surface of pristine BNNTs with small diameter and the adsorption energy decreases significantly as the tube diameter increases. The adsorption of acetone on serials of doped BNNTs (Al, Si, Cu, Co, Ni, Ga, and Ge) shows that the adsorption of acetone on BNNT can be strengthened by the doped impurity. With the analysis of charge density, density of states, molecular orbitals, and the noncovalent interaction index (NCI), the study shows that the sensitivity of BNNT-based chemical gas sensor towards acetone can be remarkable improved by introducing appropriate dopant. The study also reveals the potential application of BNNT as sensor for the detection of acetone molecule.

Synthesis and characterization of UHMWPE nanocomposite fibers containing carbon nanotubes coated with a PVP surfactant layer

Ultra‐high‐molecular‐weight polyethylene (UHMWPE) nanocomposite fibers were fabricated using solution spinning, consisting of surface modified single‐walled carbon nanotubes (SWCNTs) embedded into the fiber matrix. The SWCNTs were modified using polyvinylpyrrolidone (PVP) noncovalent functionalization process, which acts as a surfactant and has the ability to enhance the dispersion of CNTs in the base polymer matrix by reducing aggregation and promoting interfacial adhesion with the fiber polymer matrix. Tensile testing of fibers containing PVP‐coated SWCNTs showed substantial improvements in the tensile strength and fracture strain by 125% and 137%, respectively, compared to fibers containing pristine CNTs. The amount of PVP coated onto the surfaces of CNTs was determined to be about 32.5% using thermogravimetric analysis (TGA). Differential scanning calorimetry (DSC) analysis of the nanocomposite fibers showed significant increase in crystallinity and upshift in the melting point compared to that of neat UHMWPE fibers. Fourier transform infrared spectroscopy (FTIR) analysis showed the presence of characteristic absorbance bands of PVP functional groups (CN @ 1289 cm−1 and CO @ 1651 cm−1) on the modified CNTs. Scanning electron microscopy (SEM) imaging of modified CNTs and nanocomposite fibers showed an increase in average tube diameter and reduced aggregate formation compared to pristine CNTs, indicating the successful coating of the nanotubes with PVP. Preferential alignment of the modified CNTs along the direction of fiber extrusion and crack bridging of the fiber by nanotubes were also observed. POLYM. COMPOS., 39:E1025–E1033, 2018. © 2017 Society of Plastics Engineers

Tunable structural and electrical properties of zigzag CdS nanotubes: A density functional study

AbstractWe report structural and electrical properties such as wall thickness, binding energy, curvature energy, band‐gap energy, work function etc. of various zigzag CdS nanotubes within the framework of density functional theory. Binding energy calculation reveals that all the nanotubes studied here are stable and they follow classical elasticity law. The wall thickness, band‐gap, and work function of the tubes are found to decrease with increasing tube diameter. Quantitatively, the band‐gap may be tuned from 1.711 to 2.162 eV and from 0.871 to 1.291 eV, respectively, while the work function may be varied from 6.081 to 6.239 eV and from 4.679 to 4.911 eV, respectively, by changing parameters such as diameter and atomic arrangement of the tubes. The results may be useful in designing various nanoscale devices.