Hexagonal Tubes Research Articles

Design a new energy absorber longitudinal member and compare with S-shaped design to enhance the energy absorption capability

A numerical investigation study of both direct and oblique crush loading was implemented. The study used ductile metallic alloy (mild steel A36) and magnesium alloy (AZ31). The study used hexagonal tube as longitudinal members. The current design consists of two parts, the inner tube which is the longitudinal and the outer is the supporting system which is the telescope. Aluminum foam incorporated to the design to enhance the crashworthiness performance. The design is subjected to impact speed of 54 km/h with the impact mass of 1100 kg using three different collision directions: direct, 40 per cent offset and oblique direction with 30 degrees.From the SEA results it can be concluded that the current design (made of steel) enhanced the specific energy absorption by 194% from the highest design used. While the current design made up of magnesium alloy increased the SEA by 255% from the best design which was foam filled s-shaped with square section. The decelerations of the current design for the three directions were at the low permit level which will put the compartment car at the low level of deformation during collision.

Impact of heat exchanging internals configurations on the gas holdup and bubble properties in a bubble column

The effect of the vertical heat-exchanging tube bundle configurations on local gas holdup and bubble dynamics, including specific gas-liquid interfacial area, bubble chord length, bubble rise velocity, and bubble passage frequency have been studied using the 4-point optical fiber probe technique. Two different tube bundle configurations were investigated, circular tube bundle and hexagonal tube bundle. 30 internal tubes, each with a diameter of 0.5 inches (0.013 m), were used in each configuration occupying 25% of the column cross-section area to represent the heat exchanging tubes utilized in the Fischer–Tropsch process. The experimental work was performed in a 0.14 m inner diameter Plexiglas bubble column using an air-water system. The applied superficial gas velocities were based on the free cross-sectional area of the column available for fluid flow and were in the range of 0.02 to 0.45 m/s covering bubbly, transition, and churn turbulent flow regimes. Although the size and the number of the tubes in both configurations were similar, their effects on the hydrodynamics were found to be different. When compared to bubble column without internals, the circular tube bundle showed a significant increase in the local gas holdup in the core region and a decrease in the wall regions. Simultaneously, a substantial increase in the bubble chord length and bubble velocity was seen. Another important observation was the decrease in the interfacial area while using circular tube bundle. A distinct asymmetrical effect on the radial profiles of gas holdup and the specific interfacial area was observed when the hexagonal configuration was used. The gas holdup and interfacial area significantly increased on one side of the column and decreased on the other side. The bubble chord length and bubble rise velocity decreased, exhibiting a narrower distribution with smaller values, in comparison to the bubble column without internals.

Direct shear tests of glass fiber reinforced polymer connectors for use in precast concrete sandwich panels

The precast concrete sandwich panel (PCSP) is a popular structural type used for prefabricated construction. In this study, three kinds of glass fiber reinforced polymer (GFRP) connector, including a flat plate, a corrugated plate, and a hexagonal tube connector, were investigated for potential use in PCSPs. In-plane direct shear tests were conducted to evaluate the performance of the connectors based on a typical push-out configuration (i.e., three concrete wythes linked with connectors and two rigid foam layers in between). Twenty-five specimens were tested, and the parameters investigated consisted of GFRP laminate thickness, projected length, and shear force direction. The shear force vs. relative slip relationships and failure modes of all types of connector were compared and are discussed in detail in this paper. Meanwhile, finite element (FE) analysis was conducted to reproduce the test results. All three types of GFRP connector exhibited a progressive failure manner in spite of the linear brittle nature of the FRP materials; the corrugated plate connector achieved higher deformability than the flat plate connector, particularly when the GFRP laminate thickness was small; and the hexagonal tube connector exhibited similar behavior along two orthogonal directions, making them well suited for use as two-way connectors. The developed FE model was able to well predict the peak shear load and stiffness of all types of connector based on comparisons with the test results.

Direct fabrication of metal tubes with high-quality inner surfaces via droplet deposition over soluble cores

Droplet-based 3D printing is very promising for the fabrication of complex thin-wall microwave devices such as antenna horns and waveguide tubes since it can print a shell by utilizing only several layers of droplets. However, due to the naturally scalloped shape of metal droplets, conventional droplet-based 3D printing methods cannot produce thin-wall tubes with high-quality inner surfaces that can meet the requirement of electromagnetic transmission. Here, combining the conventional casting procedure and droplet printing, a hybrid printing process is proposed. Uniform aluminum droplets were first rotationally deposited on a soluble core, and then the core was dissolved and left behind a tube with a high-quality inner surface. The deposition parameters (i.e., number of layers and deposition frequency) were adjusted according to the rotation of the core to form a dense shell over its surface. A hexagonal metal tube was fabricated by using the proposed method to prove its effectiveness. The standard Archimedes test shows that the density of the formed part was up to 98.89%. The industrial CT scanning results also prove a porosity-free inner structure. The inner surface roughness (Ra) was measured to be 4.38 μm by using a laser confocal microscope scanning, and the roughness is only 0.37% of the droplet diameter.

Design and Analysis of Impact Attenuator for a Formula Student Car: A Study between Singular and Bi-tubular Tubes of Varying Geometries

The viability of thin-walled energy absorbers as impact attenuators for Formula Student car was examined in this study, specifically the crashworthiness of singular and bi-tubular tubes of varying geometries. 12 designs were lumped into 4 groups, consisting of 3 singular tubes and 9 bi-tubular tubes of varying shapes and dimensions, and they were axially crush-simulated in LS-DYNA. The tubes were set to 50mm long and made of aluminium 6061-T6. The LS-DYNA settings were validated using published experimental data of similar studies. The singular tubes were found to have the highest values of specific energy absorption (SEA), with the singular hexagonal tube design recording the highest value of SEA compared to the other designs. It was also observed that square-shaped geometries were the best in absorbing energy, especially a bi-tubular tube with outer and inner square geometries.

Combination of Taper and Hierarchy to Improve Crushing Efficiency of Thin-Walled Tubes

To improve the energy absorption capacity of thin-walled tubular structures and simultaneously reduce their initial peak force (IPF), hierarchical hexagonal tapered tube (HHTT) is proposed combining advantages of the hierarchical hexagonal tube (HHT) and the tapered tube (TT), for HHTs can greatly improve the mean crushing force (MCF) while TTs can reduce the IPF. Crushing behaviors of HHTTs under quasi-static compression are investigated through numerical simulations and theoretical analyses. According to the folding modes, a theory to predict the MCF of the HHTT is proposed. According to the research, it is found that the combination of hierarchy and tapering improves the MCF of the tubular structure and the crushing force efficiency (CFE), defined by the ratio of the MCF to the IPF. It is also found that increasing the tapered angle, the wall thickness and the cell number of the lattice wall can effectively improve the CFE of the HHTT.

Seismic performance of concrete-encased column base for hexagonal concrete-filled steel tube: numerical study

The seismic performance of concrete-encased column base for hexagonal concrete-filled steel tube (CFST) columns was investigated through finite element analysis (FEA) modeling. A FEA model for the seismic analysis of the column base was first established and verified with test results. The numerical model was subsequently used to study the mechanical behavior of the column base, including the typical failure modes, the load transfer mechanisms, and the interaction among components and the internal force distribution. Finally, a parametric study was carried out to investigate the effect of salient parameters on the behavior of the column base. It was found that the parameters of the outer RC component, as well as the axial load level, have significant effects on the seismic behavior of the column base, while the effects of the parameters of the CFST column and the base plate connection were moderate within the investigated parameter range. In addition, the accuracy of a simplified strength model for the column base proposed by the authors was verified with the FEA model.

Experimental and theoretical study on crashworthiness of star-shaped tubes under axial compression

Thin-walled tubes play a very important role in energy absorbing for car crash. Current studies mainly focus on the design theory and performance improvement by proposing different structures. However, the practical performances might be influenced by manufacturing process, but few studies on this aspect could be found. In this paper, the crashworthiness of several star-shaped tubes, i.e., the hexagonal, octagonal and twelve corners, which were made with different material and fabrication methods, are compared through the experimental analysis. It is found that the energy absorption of octagonal star-shaped tubes is the best and that of the twelve corners star-shaped tubes is the lowest. Under quasi-static compression, the Pm of the octagonal star-shaped tubes increases by 7.94% with respect to the hexagonal star-shaped tubes, while the Pm of star-shaped tubes with twelve corners decreases by 15.75% with respect to the octagonal star-shaped tubes. The star-shaped tubes manufactured by different processing methods have some influence on the deformation mode, but the effect on overall crashworthiness is limited. Finally, the axial mean crushing force of the star-shaped tubes was analyzed theoretically based on the simplified Super Folding Element theory. A theoretical solution for the mean crushing force of the star-shaped tubes was derived, and the theoretical solutions show an excellent agreement with the experimental results.

Enhancement of UV photoluminescence in ZnO tubes grown by metal organic chemical vapour deposition (MOCVD)

We have synthesized ZnO tubes, without any catalyst, on Al2O3 (001) substrates by metal organic chemical vapor deposition (MOCVD) at different growth temperatures, pressures and Zn-O ratios. The results confirm that the growth temperature, reactor pressure and Zn-O ratio play important roles in the formation of hexagonal ZnO tubes. Scanning electron microscopy (SEM) images indicated that, at a growth temperature of 500 °C, reactor pressure of 75 Torr and Zn-O ratio of 10/75 are an appropriate condition to obtain hexagonal and well-aligned ZnO tubes. High-resolution, double crystal XRD analysis shows a symmetric ω-scan rocking curve, with a full width at half maximum (FWHM) of 1.1°. It confirms the ZnO tubes have highly c-axis orientation on Al2O3 substrate. Subsequently, room temperature photoluminescence (PL) studies confirm that the enhancement of UV emissions from ZnO tubes is due to increasing Zn-O ratios.

Structural response and performance of hexagonal thin-walled grooved tubes under dynamic impact loading conditions

This paper numerically investigates the structural response and crashworthiness performance of a hexagonal thin-walled grooved tube subjected to axial and oblique impact loading conditions. First, an analytical formulation that estimates the mean crushing force and total energy absorption are obtained for both hexagonal and circular tubes subjected to high dynamic impact loading conditions. The solutions of the analytical model are used to verify and compare the approximate solutions of the finite element model. The inclusion of grooves to the conventional hexagonal thin-walled tubes shows the great potential for improving the crashworthiness performance such as the energy absorption capacity, crushing force efficiency and specific energy absorption. In further, parametric studies are performed, deformation modes of different models are obtained and their crushing force-displacement characteristics are described. The improved crashworthiness performance of the hexagonal thin-walled grooved tubes make them good candidate used as energy absorbers.

A Mathematical Model Development for the Lateral Collapse of Octagonal Tubes

Many researches has been done on the lateral collapse of tube. However, the previous researches only focus on cylindrical and square tubes. Then a research has been done discovering the collapse behaviour of hexagonal tube and the mathematic model of the deformation behaviour had been developed [8]. The purpose of this research is to study the lateral collapse behaviour of symmetric octagonal tubes and hence to develop a mathematical model of the collapse behaviour of these tubes. For that, a predictive mathematical model was developed and a finite element analysis procedure was conducted for the lateral collapse behaviour of symmetric octagonal tubes. Lastly, the mathematical model was verified by using the finite element analysis simulation results. It was discovered that these tubes performed different deformation behaviour than the cylindrical tube. Symmetric octagonal tubes perform 2 phases of elastic - plastic deformation behaviour patterns. The mathematical model had managed to show the fundamental of the deformation behaviour of octagonal tubes. However, further studies need to be conducted in order to further improve on the proposed mathematical model.

Energy Storage by Melting Commercial Change Phase Materials in Hexagonal-Shaped Heat Exchangers

A two-dimensional melting of a technical-grade phase-change material is modeled. The phase-change material is placed in the annular space formed by an outer regular hexagonal tube and an inner tube. A nonorthogonal boundary fitted coordinate method is implemented on a staggered grid arrangement. The mushy region of the impure phase-change material has been accommodated through the enthalpy-porosity scheme. A set of parametric studies is carried out. Selected results are presented as a function of time for the velocity and temperature fields, the cumulatively stored energy, the total melt fraction, and the average Nusselt number on the inner tube. The oblate-shaped inner tube results in the highest melting rate and stores the maximum energy among the studied units irrespective of the shape and vertical position of the inner tube. Among the three vertical positions of the inner circular tube, when the center of the inner tube is placed at one-third height from the base of the outer tube, it shows the greatest thermal efficiency, and the worst performance is obtained for the upper position of the inner tube at the two-thirds height of the outer tube. With the increase in the Rayleigh number (wall temperature), the amount of energy storage is enhanced.

Acoustic properties of additive manufactured narrow tube periodic structures

Quarter tube periodic resonators are used to attenuate the acoustic energy of discrete frequencies wherein their sizes can vary from narrow to large. This paper reports acoustical properties of additive manufactured, narrow tube, single and multi-periodic structures, both, theoretically and experimentally. Herein, multi-periodic structures are defined as periodically arranged unit sections of tubes, where each section is composed of periodically repeated unit cells of different sizes and shapes. Structures with hexagonal narrow tubes and octagonal narrow tubes with interfacial gaps are considered for the study, and normal absorption coefficients of these samples are measured by using impedance tube. the theoretical absorption coefficient of these structures is predicted using unit section analysis method and narrow tube theory, where shape dependent viscous and thermal losses are incorporated. Estimated theoretical absorption coefficients are in good agreement with measured results. The result shows that the frequency and amplitude of maximum absorption can be varied by altering the aperture ratio and/or the length of periodic structure. The proposed theoretical method gives an alternative approach for designing and manufacturing periodic narrow tubes for different applications such as absorbing panels, acoustic transducers, and engine filter elements.

Mapping the band structure of GeSbTe phase change alloys around the Fermi level

Phase change alloys are used for non-volatile random-access memories exploiting the conductivity contrast between amorphous and metastable, crystalline phase. However, this contrast has never been directly related to the electronic band structure. Here we employ photoelectron spectroscopy to map the relevant bands for metastable, epitaxial GeSbTe films. The constant energy surfaces of the valence band close to the Fermi level are hexagonal tubes with little dispersion perpendicular to the (111) surface. The electron density responsible for transport belongs to the tails of this bulk valence band, which is broadened by disorder, i.e., the Fermi level is 100 meV above the valence band maximum. This result is consistent with transport data of such films in terms of charge carrier density and scattering time. In addition, we find a state in the bulk band gap with linear dispersion, which might be of topological origin.

A Novel Tube Lattice Slotted Core Highly Birefringent Photonic Crystal Fiber for THz Application

A hexagonal slotted porous core tube lattice cladding photonic crystal fiber (SPC-TLC-PCF) is suggested to simultaneously achieve a very high birefringence and low transmission loss. At the operating frequency of 1 THz the pr... | Find, read and cite all the research you need on Tech Science Press

Carbon based Nanomaterials: Synthesis and Applications (A Review)

Over the last few years, carbon nanomaterials have been widely used in different applications such as, sensors, super capacitors, batteries, fabrication of composites, solar cells, fuel cells etc. the reason for such conspicuous and remarkable properties of these carbon nano materials is because it consists of same number of atoms. Although, graphite and diamond, both are made up of strong covalent linkage of carbon atoms., in graphite, each carbon atom uses its three electrons to form three single bonds to form a linear sheet. Whereas diamond usesall its four electrons to form four single bonds and resulting in a 3-D structure. Buckminster fullerene, is another carbonal-lotrope, often referred to as a buckyball, fullerene or simply C60. The carbon atoms in this highly symmetrical C60 are arranged to form a closed shell that resembles a soccer ball. In early 1990s, an incredibly new carbon allotrope in a form of a hexagonal tube was discovered which was named Carbon Nanotubes. These tubes were just rolled up sheets of graphite but had totally different properties compared to graphite. Another form of carbon, graphene, understood as 2D layered material which was just one atom thick was discovered later on. Carbon-based nanomaterials, therefore, havebeen used immensely in recent technology due to their extraordinary and exceptional electrical, thermal, chemical, mechanical, properties worldwide. They have also evolved as major and important mate-rialand reason-to-be-studied material in various applicationssuch as field emission display devices, composite materials, drug delivery, sensors, electronics, energy storage, etc.

Energy storage in a complex heat storage unit using commercial grade phase change materials: Effect of convective heat transfer boundary conditions

For the storage of latent energy in an arbitrary-shaped double-pipe heat exchanger is considered in this study. The heat exchanger is numerically modeled considering the convective heat transfer boundary condition on the inner tube. The horizontal heat exchanger is composed of an insulated outer hexagonal tube and an inner tube. The commercial grade PCM which melts over a temperature range of 8.7 °C is placed in the annular gap between the two tubes. The flow rate and the inlet temperature of the heat transfer fluid (HTF) flowing through the inner tube are varied for the low-temperature solar energy storage. The cross-sectional shapes of the inner tube as well as the vertical position of the circular tube are varied, keeping the cross-sectional area of the annular gap constant. In order to correctly account for the arbitrary-shaped boundaries, a non-orthogonal boundary-fitted coordinate technique on a staggered grid system is used. A control volume based finite difference scheme is employed to solve the non-dimensional set of equations. The predicted results of the velocity and temperature fields, the surface-averaged Nusselt number on the heat transfer surface of the inner tube, the complete and total melt fractions, and the latent and total cumulative energy stored, all as a function of time are presented and discussed. The results show that the effect of the change of the bulk temperature is much more prominent on the storage of energy compared to the change in the mass flow rate of the HTF. For the identical conditions, the oblate-shaped inner tube stores the maximum amount of energy irrespective of the studied shapes and the vertical positions of the inner tube.

Mechanism Study of Heat Transfer Enhancement Using Twisted Hexagonal Tube with Slurry from Biogas Plant

Waste-heat recovery from discharged slurries is important to improve the biogas production efficiency but still remains challenge duo to the special properties of slurries in anaerobic digestion process. In this work, numerical study was carried out to investigate the flow field, and heat transfer performance of slurry from biogas plant in the twisted hexagonal and other twisted tubes was simulated with computer fluid dynamic (CFD) for the first time. The numerical method was validated with experimental data from the literature. The heat transfer performance and flow resistance of twisted hexagon tube were calculated and compared with other types of twisted tubes. The enhancement factor of the twisted hexagonal tube reached to 2 and kept optimum at turbulence flow region compared to the twisted tubes with square and elliptical cross section. Meanwhile, the mechanism of heat transfer enhancement with different twisted tubes was further studied, and the optimal field synergy and minimum local circulation flow near the wall are the main reasons for the high performance and low flow resistance of the twisted hexagonal tube.

Synthesis of barium-strontium titanate hollow tubes using Kirkendall effect

(BaSr)TiO3 hexagonal hollow tubes was fabricated by a solid-state interfacial reaction including a Kirkendall diffusion. Using a co-precipitation and sol-gel process, a core@shell structure of (BaSr)CO3@TiO2 rods were prepared, and then converted to (BaSr)TiO3 hollow tubes at 750 °C. This was a first achievement of single-phase crystal hollow tube. Here, the inner diameter and wall thickness of hollow tube were about 700 nm and 130 nm, respectively. The fabrication of (BaSr)TiO3 hollow tubes was monitored with scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS), transmission electron microscopy (TEM), and X-ray diffraction (XRD) to investigate their formation mechanism. The present synthetic approach would provide a new insight into the design and fabrication of hollow architectures of many perovskite oxides.

Investigating the role of different reducing agents, molar ratios, and synthesis medium over the formation of ZnO nanostructures and their photo-catalytic activity

ZnO nanostructures with divergent morphologies were synthesized by a facile chemical approach using various solvents and reducing agents. The synthesized nanostructures were characterized by XRD, electron microscopic techniques and fluorescence spectroscopy. The microstructural analysis shows that different morphologies of ZnO can be formed when suitable reducing agents (RAs) and solvents are used with variation in the molar ratio (β) of zinc precursor to RAs. The morphologies observed are spindles, flowers, nanoassemblies, rods and hexagonal hollow tubes. The size of spindle-shaped ZnO nanostructures varies from 1 to 5 μm, and nanoassemblies are of around 150 ± 20 nm. Each nanoassembly is the aggregation of individual nanoparticles of sizes around 4–5 nm. The optical study shows that these ZnO nanostructures have various defect concentrations and surface properties. Furthermore, the alterations and transformations in the physical and chemical properties of ZnO nanostructures significantly influenced the photo-catalytic degradation of methylene blue (MB) dye under solar irradiation. A complete degradation of MB is observed within 130 and 60 min when treated with ZnO of suitable morphology under UV and solar light radiation. This variation in time may be attributed to the availability of higher specific surface area, large amount of defects and anisotropy in morphology.