Tube Shape Research Articles

Compact electromagnetic pulse forming system based on the trigger vacuum switch

Electromagnetic pulse forming (EMPF) is a type of electromagnetic manufacturing technology which produces a powerful Lorentz force to change the shape or form of a work piece. In this paper, a 6.75-kJ/15-kV compact EMPF system based on the RVU-43 trigger vacuum switch is designed, fabricated and tested. The RVU-43 has good performance in a high-voltage discharge process that can withstand 25 kV and conduct 400 kA. A trigger source for the RVU-43 based on a pulse transformer and a solid-state switch can generate a rectangular trigger pulse of an adjustable amplitude of 0–5 kV and a pulse width of 0–5 μs. A simulation model is built in PSPICE to analyze the parameters affecting the performance of the EMPF. The results show that the system inductance can affect the peak current and the rise time, while the system resistance can affect the peak current. Connecting the capacitors in parallel, reducing the discharge loop area and designing a single-turn forming coil with a 30-degree field shaper are used to reduce the influence of the system parameters. The results of experiments for changing the shape of an aluminum alloy tube suggest that the EMPF system can form and process the metal tube successfully.

Geometric Reconstruction of the Drawn Tube Shape

Technological processes have a significant influence on the properties of the metallic formed pieces during production. Due to the plastic deformation, the shape of the component is changed and the degree of the structural anisotropy is increased - the orientation of the grain boundaries in the different parts of the component. It is important to identify these changes, to analyse them and optimize the technological processes. We get an important knowledge of relationship “technological parameters – microstructure – properties”. The article presents the results of the solution of a partial task from this area. It deals with changing of the geometric shape of the component when it is deformed. Specifically, the tubes (material EN SPT 360, STN 411 353) were drawn through the dies with different reduction angles. The dimensions (length and angle), roundness, cylindricity, coaxiality and surface roughness were evaluated.

Study of the heat transfer capacity of thermosyphon cooling system under the inclined condition

Machine applications with superconductors attract much interest in the industry. It is crucial to maintaining the operating temperature range between 28 K and 40 K for high-temperature superconductor (HTS) field poles. A thermosyphon (TS) is a suitable choice for HTS applications’ cooling system. The cryo-mechanical system composition is simple, lightweight and based on natural convection therefore not using any mechanical pump. Considering the rotating application, an adiabatic tube is necessary to carry the cryogen from the vertical condenser portion toward the horizontal evaporator part. However, this tube shape prevents the natural convection when in an inclined configuration which can occur for applications such as ship propulsion and electrical aircraft motors or generators. In this work, we focused on and investigated the heat transfer capacity of TS for inclinations. The results show that the TS cooling system employing the coaxial tubes architecture maintained the natural convection even under inclined conditions

Definitive Resolution of the Shape of Geotextile Tubes: Numerical Approach Based on Pumping Pressure P0

Geotextile tubes are severally used more and more in maritime field as systems of beaches protection against coastal erosion. The prediction of their dimensions is very important, because these they govern the stability against several site conditions of wave and current. There are many studies that have calculated the dimensions of geotextile tubes, but they require the running of a computer program and this limits their access to a larger public of designers. The most popular one is the approach presented by Leshchinsky and the computer program GeoCoPS 2.0. In this paper, and in addition to the approach established by Amallas and Ajdor 2018, another numerical approach is established in order to calculate definitively dimensions of geotextile tubes regarding the pumping pressure P0 (kPa) and the material density γ (kN/m3). The most useful formulas for the direct calculation of filled geotextile tube dimensions, depending on P0 (kPa), material density γ (kN/m3) and the circumference of tube L (m) are given for the large public designers without further resort to have computer programs. The comparison between values calculated by these formulas, the ones given by the established program and the ones given by the existing methods, highlights a very good agreement.

Effect of Venturi Tube Shape on Reaction Performance by Hydrodynamic Cavitation

Effect of Venturi Tube Shape on Reaction Performance by Hydrodynamic Cavitation

Enhancement of thermal and hydraulic performance of compact finned-tube heat exchanger using vortex generators (VGs): A parametric study

In this study, a numerical analysis is conducted to investigate the influence of interrupted surfaces on compact heat exchangers (CHXs). The performance of CHXs in terms of heat transfer enhancement and pressure drop can be augmented by incorporating innovative passive techniques. In relation to that the influence of delta winglet vortex generators (DWVGs) on thermal-hydraulic features of heat exchanger is elucidated. The effect of vortex generators (VGs) with different number of rows (N), attack angles (θ) and configuration on heat transfer performance (j) and pressure drop (f) are demonstrated. Moreover, the influence of tube arrangements such as inline and staggered placement of tubes and different tube shape (circular, oval and rectangular) are also deduced. The optimum attack angle (θop) of VGs is concluded i.e. 1650, which provides higher transfer performance at moderate pressured drop (ΔP). Array of winglet rows gives comparatively higher heat transfer rate than one row of winglets and also common flow down (CFD) configuration of winglets are preferable over common flow up (CFU) configuration of winglets. Moreover, staggered tubes arrangement tends to provide relatively better thermodynamic features as compared to inline arrangement of tubes. Finally, it is concluded that oval and circular tubes deliver quite comparative act in terms of thermal and hydraulic performance as compared to rectangular tubes.

Numerical investigation of enhancement in melting process of PCM by using internal fins

This paper presents numerical investigation of melting N-eicosane as phase change material (PCM). Effect of using innovative tube shape, in which internal fin had been added to HTF tube, in melting process in cylindrical container had been investigated. For understanding the effect of HTF tube shape in melting rate, different number of fin had been added to HTF tube, and also for understanding this effect more clearly, effect of different number of fin had been investigated for two different situations: (1) ratio of A/P which is ratio of HTF perimeter to area that PCM had occupied had been considered fix and (2) outer diameter had been considered fix and by changing the HTF tube shape, does not change. Also, inner tube had been considered as hot tube and outer tube as insulated. Numerical results were shown by increasing the fin to inner tube; rate of melting increases.

A shriveled rectangular carbon tube with the concave surface for high-performance enzymatic glucose/O2 biofuel cells

In this study, a novel carbon tube was prepared by carbonizing a rectangular polypyrrole (RPPy) tube at a high temperature for the construction of enzymatic biofuel cells with high performance. SEM and TEM images clearly showed that the initial PPy presented a rectangular tube shape, while the carbonized PPy became a shriveled rectangular tube with a concave surface, which might be beneficial for enzyme immobilization and electrochemical applications. The glucose oxidase (GOx)- or laccase (Lac)-modified electrodes based on carbonized RPPy exhibited excellent bioelectrochemical performance. In addition, a biofuel cell (GOx, glucose/O2, Lac) was assembled, and the open-circuit voltage reached 1.16 V. The maximum power density was measured to 0.350 mW cm−2, which correlated to the gravimetric power density of 0.265 mW mg−1 (per mg of GOx) at 0.85 V. The constant-current discharge method was used to further evaluate the continuous discharge capacity. The discharge time reached 49.9 h at a discharge current of 0.2 mA before the voltage was lower than 0.8 V. Furthermore, three of the fabricated biofuel cells in series were able to continually light up a white light-emitting diode (LED) whose turn-on voltage was ca. 2.4 V for more than 48 h. This study suggests that carbonized conducting polymers may become a useful electrode material for the development of enzymatic biofuel cells.

Vortex tube shape optimization for hot control valves through computational fluid dynamics

A vortex tube (VT) is a thermofluidic device that generates cold and hot streams from a single injection of compressed gas. This interesting phenomenon of energy separation is due to fluid dynamic effects. In this study, the optimization of the VT geometry was performed to investigate the potential applications of the VT as an expansion device in natural gas processing and air separation industries. A steady-state computational fluid dynamics (CFD) model with the standard k–ɛ turbulence was used to solve the hydrodynamics of the highly compressible, turbulent, and swirling flow within the VT. Velocity streamlines and temperature distributions of the separated air stream were obtained for different control valve shapes located at a hot end. The CFD results showed the effects of the control valve shape, cone valve geometry, and nozzle inlet pressures on the VT performance. A truncated cone control valve with an optimized geometry was found to be the best choice for thermal performance enhancement of the VT. The CFD results were validated with experimental data, and the difference in the cold temperatures between the numerical and experimental values were less than 4.12% for the 2D and 2.3% for the 3D vortex tube models.

Fundamental heat and mass transfer analysis in a quasi-counter flow parallel-plate three-fluid membrane contactor

A quasi-counter flow parallel-plate three-fluid membrane contactor with cooling tubes installed in the solution channels (QCPMCC) is used for air/solution/water exchange. The air and the solution streams are separated by the selectively permeable membranes. Absorption heat generated in the solution can be taken away by the water flow in the cooling tubes. A three-dimensional mathematical model describing the heat and mass transports in the membrane contactor is built based on an element including a piece of the plate membrane, half of the air channel, half of the neighboring solution channel, and half of the row of the tubes. The momentum, energy and mass conservation equations are simultaneously solved. The mean product of friction factor and Reynolds number (fRe)m, Nusselt number and Sherwood number under the conjugate heat and mass transfer boundary conditions are then obtained. Effects of the tube numbers, tube outer diameters, Reynolds numbers, and various tube shapes on the basic data are analyzed. It can be found that both the tube numbers and the tube outer diameters have small influences on the mean Nusselt numbers and Sherwood numbers for the air stream, while they have large effects on those for the solution stream.

Intraluminal three-dimensional optical coherence tomography – a tool for imaging of the Eustachian tube?

The cause of Eustachian tube dysfunction often remains unclear. Therefore, this study aimed to examine the feasibility and possible diagnostic use of optical coherence tomography in the Eustachian tube ex vivo. Two female blackface sheep cadaver heads were examined bilaterally. Three conditions of the Eustachian tube were investigated: closed (resting position), actively opened and stented. The findings were compared (and correlated) with segmented histological cross-sections. Intraluminal placement of the Eustachian tube with the optical coherence tomography catheter was performed without difficulty. Regarding the limited infiltration depth of optical coherence tomography, tissues can be differentiated. The localisation of the stent was accurate as was the lumen. The application of optical coherence tomography in the Eustachian tube under these experimental conditions is considered to be a feasible, rapid and non-invasive diagnostic method, with possible diagnostic value for determining the luminal shape and superficial lining tissue of the Eustachian tube.

Justicia carajensis, a new species of Acanthaceae from the Serra dos Carajás, Pará, Brazil

A new species, Justicia carajensis, is described from the Serra dos Carajás as part of the ongoing taxonomic study of Justicia from the state of Pará in northern Brazil. Morphologically, it belongs to Justicia sect. Chaetothylax, and differs from other species by a combination of characters of calyx lobe length and indumentum, corolla tube shape, anther morphology, and ovary and fruit indumentum.

Production of bistable fully closed metallic shells by introducing residual stresses during bending processes

Bistable fully closed metallic shells are of great interest as lightweight construction components, which could be transported without enclosure and unfolded at the construction place. The effect of bistability in metallic shell structures is achieved by a specific distribution of residual stresses over the shell thickness, which can be introduced by bending processes. So far no fully closed structures have been achieved in metallic shells. Hence, the aim of this paper is the identification of suitable bending radii combinations in order to produce a bistable shell with a fully closed tube shape in the deployed state. Therefore, a Finite Element (FE) model was established to determine whether bistability occurs in dependence on the bending radii. The numerical model indicates, that bistability can be achieved for 0.2 mm thick spring steel 1.1274 (AISI 1095) by applying two die-bending operations with small bending radii of 6–8 mm. Accompanying experiments with a closed-die incremental bending tool were performed. A good transferability of the numerical results regarding the occurrence of bistability and the calculated residual stresses is shown. For the second aspect, X-ray diffraction measurements of residual stresses were used for comparison. Finally, the present work presents a process route to generate a bistable shell with a fully closed tube shape structure in the deployed state, having a radius of 40.95 mm.

Parametric study of the cross-section shape of aluminium tubes in dynamic three-point bending

Square and circular tubes were tested experimentally and numerically in quasi-static three-point bending. A finite element model with failure criterion was developed that correlated well with the experimental results and provided accurate simulation of top surface failure of the tubes. The model was used to conduct a parametric study of the effects of common cross-section shapes, with or without rib reinforcements, on dynamic bending performance. Results showed the reinforced shapes had higher specific energy absorption (SEA). The highest SEA was obtained for a square tube with internal parabolic shaped rib, but this was the only shape that suffered catastrophic failure.

Fine structure of the midgut epithelium of Thulinius ruffoi (Tardigrada, Eutardigrada, Parachela) in relation to oogenesis and simplex stage

Thulinius ruffoi is a small freshwater tardigrade that lives in both non-polluted and polluted freshwater environments. As a result of tardigradan body miniaturization, the digestive system is reduced and simplified. It consists of a short fore- and hindgut, and the midgut in the shape of a short tube is lined with a simple epithelium. The midgut epithelium is formed by the digestive cells and two rings of crescent-shaped cells were also detected. The anterior ring is located at the border between the fore- and midgut, while the posterior ring is situated between the mid- and hindgut. The precise ultrastructure of the digestive and crescent-shaped cells was examined using transmission electron microscopy, serial block face scanning electron microscopy and histochemical methods. We analyzed the changes that occurred in the midgut epithelial cells according to oogenesis (the species is parthenogenetic and there were only females in the laboratory culture). We focused on the accumulation of reserve material and the relationship between this and the intensity of autophagy. We concluded that autophagy supplies energy during a natural period of starvation (the simplex stage) and delivers the energy and probably the substances that are required during oogenesis. Apoptosis was not detected in the midgut epithelium of T. ruffoi.

Finite Element Analysis of Shield Pipe Structure and Stress Cone Position of 10kV Cable Intermediate Joint

The shielding tube and stress cone of the intermediate joint of XLPE cable accessory make the potential distribution along the insulation surface linearized to optimize the electric field and. By establishing the finite element model of the intermediate joint of 10kV cable accessory, the electric field distribution of different structure shielding tube and stress cone in different position of the joint is simulated and analyzed. The results show that the structure of shield tube and the position of stress cone are also a parameter characteristic which can not be ignored in the design, and they have a great influence on the distribution of the field strength of the intermediate joint. On the basis of finite element analysis, the optimum shape of shield tube and the best position of stress cone are obtained by comparing and analyzing the variation law of electric field intensity.

Electro-osmotic pumping through a bumpy microtube: Boundary perturbation and detection of roughness

To machine precision, a micro-duct cannot be fabricated without producing surface roughness. It is of essential importance to examine the effects and predict the level of roughness on electro-osmotic (EO) pumping for ducts of fundamental shapes. In this study, we consider a bumpy microtube with its wall shape modeled by the product of two sinusoidal functions. Boundary perturbation is carried out with respect to the amplitude roughness ε (relative to the Debye length) up to the second-order by considering the Debye-Hückel approximation and viscous Stokes equation for the electrolyte transport. Besides the amplitude roughness ε, the key parameters include the azimuthal wave number n and the axial wave number α of the bumpiness, as well as the non-dimensional electrokinetic width K. It is shown that the EO pumping rate Q is modified by a second-order term −ε2πχ, namely, Q = Q0 − ε2πχ, where Q0 denotes the pumping rate through the smooth tube. The net effect χ = χ1 + χ2 comprises two components: χ1 = χ1(K) < 0 increases with increasing K, representing a pure gain, while χ2 has no definite sign and is a complex function of K, n, and α. In particular, χ is negative at small α whilst being positive at large α, and the dividing line of signs also depends on K. For small α (<1), χ increases with increasing n at all K, while for large α (>1), χ decreases with increasing n at large K (>20). For a given number of oscillations Ac = nα (>1), there exists an intermediate n at which the EO pumping rate is maximized at small K (<20). Moreover, we identify a long-wavelength limit singularity in the EO pumping rate as α → 0 for all n, i.e., in the longitudinal sense. In addition, the velocity component along the tube axis is modified by a second-order term of the roughness, though the same velocity component near the wavy wall exhibits periodic behaviors in phase with the wall roughness. Physical reasoning is given to all the derived mathematical results, and their implication in practical applications as a model for predicting tube roughness is explained. As the tube shape represents a conduit of practical use, a particular emphasis is placed upon potential applications of the derived result.

Mechanical Behavior of Multiwalled Carbon Nanotube Reinforced 7075 Aluminum Alloy Composites Prepared by Mechanical Milling and Hot Extrusion

In this paper, multiwalled carbon nanotubes (MWCNTs) were synthesized by spray pyrolysis to be used later as material reinforcement in the production of MWCNTs/Al7075 aluminum composites. Both, MWCNTs and MWCNTs/Al7075 composites were microstructurally and mechanically characterized. Scanning electron microscopy (SEM) analysis shows MWCNTs formed by multiple layers rolled on themselves forming a tube shape with lengths up to 1300 µm and diameters ranging from 55 to 120 nm. MWCNTs were added to the aluminum matrix in different concentrations up to 3.0 wt%. Their dispersion in the aluminum matrix was carried out by ultrasonic/methanol method followed by high-energy mechanical milling process. The effect of MWCNTs on the morphology and mechanical behavior of composites were evaluated. Results indicate that a homogeneous dispersion of CNTs was obtained as a consequence of the dispersion routes used in the production of composites, observing no damage on their morphology. The mechanical behavior of the composites shows a noticeable improvement for MWCNTs concentrations above 2.0 wt%, with ductility similar to that found in the literature for the Al7075 commercial alloy.

Effects of Origami Pattern Crash Box and Rectangular Pattern Crash Box on The Modelling Of MPV Car Structure on Deformation

Crash box serves as a kinetic energy absorber during collision. It has a tube shape, which is located between bumper and chasis. The crash box design requires development in order to reduce buckling mode and obtain symmetry folding mechanism, so it will achieve greater energy absortion. The researchers find a method to reduce tension due to impact by providing dents in crash box geometry. This research observed origami pattern crash box design having dents functioned as pre-folded so that collapse mode can be predicted and stable. In this research, the crash box was modeled according to the size of bumper and chassis on the MPV car. Testing simulation was performed by modelling Impactor as rigid body and crash box as flexible. Fixed support was housted in the surface of rear side of the crash box. Simulation process was started from the impactor moving to supress crash box. This Impactor collision led to deformation on the crash box. Crash box material was AA7004-T7, it was modelled as bilinier isotropic hardening. Based on the research result, the addition of pre folded pattern is able to reduce impact force at the first impact and has stable characteristic as well as predictable collapse mode.

Eliminating spikes by optimizing machining parameters in electrochemical drilling

Electrochemical drilling (ECD) is an important method for producing small holes in difficult-to-machine materials such as titanium alloys and nickel-based alloys. However, the hollow tube shape often generates spikes at the hole bottoms, and these significantly influence the flow uniformity, machining accuracy, and process stability. This paper considers the hole bottom to be spiked, flat, or pitted depending on the equilibrium gap, which can be controlled with the machining parameters of applied voltage and electrode feed rate. Consequently, the spikes can be eliminated with a suitable choice of machining parameters. An electric-field model of ECD is established and the dynamic shaping of holes is simulated. This reveals that the machining parameters affect the equilibrium gap, whereupon the hole bottom shape is determined. Experiments verify the simulation results, and the relationships between the machining parameters (applied voltage and electrode feed rate) and (i) the equilibrium gap and (ii) the bottom shape are plotted. It is found that a low voltage with a high feed rate generates a small gap and a spiked bottom, whereas a high voltage with a low feed rate produces a large gap and a flat or pitted bottom. Finally, three typical parameter groups are selected with which to drill through holes. The machining-current signals at the moment of hole punching and the tool durability indicate that the ECD stability without a spike is better than that with a spike. Optimal parameters are beneficial for eliminating spikes and enhancing the ECD process performance.