Coaxial Tube Research Articles

Crashworthiness analysis of multi-configuration thin walled co-axial frusta tube structures under quasi-static loading

Abstract In the present study crashworthiness performance of monolithic and co-axial multi-wall (double, triple, and four layered) frusta tube structures was investigated under the quasi-static axial loading. The developed layered frusta tubular structures having a total equivalent thickness of 2.3 mm were made of aluminium alloy AA-1080 sheet. A series of layered configurations were simulated and analysed using non-linear finite element analysis code LS-DYNA, keeping volume approximately the same as the monolithic frusta tube. For the effectiveness of the simulated results, double-tubular structure was examined through experimental results. A parametric study was performed by keeping taper angle constant as 5.71° with the variation in height (91.6 and 82 mm for double layered, 91.6, 86 and 78 mm for triple layered and 91.6, 87, 82 and 77 mm for four layered), thickness (2.3–0.4 mm) and diameter (smaller end diameter in the range of 42.8 mm–48.4 mm while larger end diameter varied from 61 mm to 64 mm) to analyse the crushing performance of layered structures. The crashworthiness performance indicator like peak force (PF), mean force (MF), energy absorbing capacity (EAC), specific energy absorption (SEA) and crush load efficiency (CLE) which is defined as the ratio of MF to the PF, were studied for the various layered frusta tubular structures. Moreover, optimization technique GRA (Grey Relational Analysis) was employed to obtain a better combination of multi-wall layered structures. With the increase in the layer, the initial peak force was reduced compared to the monolithic frusta. The optimization technique suggested the triple-layer configuration showed better crashworthiness performance.

이중관식 열교환기가 설치된 역방향 공기 주입 방식 무화염 연소로 내 열유동 특성에 대한 연구

이중관식 열교환기가 설치된 역방향 공기 주입 방식 무화염 연소로 내 열유동 특성에 대한 연구

A high-repetition-rate, fast temperature-programmed gas chromatograph and its online coupling to a supercritical fluid chromatograph (SFC × GC).

We present a fast gas chromatographic system that can be used as a second dimension in comprehensive two-dimensional (supercritical fluid × gas) chromatography (SFC × GC). The temperature of the short (1 m long) capillary column is controlled by a resistively heated coaxial stainless-steel tube. The electrical resistance and, therefore, temperature of the stainless-steel tube are measured by continuous monitoring of the current/voltage ratio. Highly repeatable heating rates of up to 2100 °C min-1 (35 °C s-1) are obtained, which should be high enough for the most demanding fast chromatograms. To reduce the cooling time between temperature programs, the column is cooled by injecting evaporating carbon dioxide into the space between the coaxial heater and the column. This gives cooling rates of 5100 °C min-1 (85 °C s-1), which allows quick succession of temperature programs. More repeatable heating profiles with stable GC retention times together with faster cooling are significant improvements on previous SFC × GC systems. Cycle times of four gas chromatograms per minute could readily be achieved, which allows efficient coupling to high-resolution stop-flow SFC in the first dimension. We demonstrate the fast chromatograph by separating fatty acid methyl esters, yielding information that would be useful in the food and biodiesel industries.

Design of a two-stage gas-coupled high-frequency pulse tube cryocooler working around 4 K

High-frequency pulse tube cryocooler have unique advantages for aerospace and ground applications. However, it is difficult to obtain lower cooling temperature: to obtain the liquid helium temperature, three-stage or four-stage structure by thermal coupling are currently used. In order to further improve the compactness, a two-stage gas-coupled high-frequency multi-bypass coaxial pulse tube cryocooler has been designed. The simulation results indicate that the designed cryocooler can provide a cooling capacity of 25 mW@4.2 K with 416 W input electrical work. The interaction between structural parameters and operating conditions, as well as some preliminary test results will be presented in this paper.

Generation of cold atmospheric plasma jet by a coaxial double dielectric barrier reactor

In this study, the generation of cold atmospheric plasma jet was investigated in a coaxial double dielectric barrier configuration conjugated with a microsecond voltage pulse generator. The advanced reactor comprised two coaxial dielectric tubes of different diameters with two ring-shaped electrodes covering outside the larger tube. The electrodes were immersed in a liquid dielectric (i.e. transformer oil) in order to isolate them from the ambient air, which completely prevented the direct sparks formation between them within the investigated range of the applied voltage. The He discharge gas was fed to the inner tube while either air, N2, or O2 as a shielding gas was introduced into the gap between the two dielectrics. The result revealed that with these shielding gases, the unwanted abnormal discharge in the inter-dielectric gap was extinguished and the plasma discharge occurred only in the He gas in the inner tube. Consequently, the electrical power delivered to the He discharges maintained at a level of around 1 W with a considerable variation in the applied voltage. Meanwhile, the discharge power of the unshielded jet was almost tripled as the applied voltage was increased from 7 to 10 kV. Interestingly, the cold plasma jet generated by the alternative reactor design in this study, which had the electron density up to 2.5 × 1013 cm−3, consumed relatively less He gas with less restriction on the high voltage range applied. The design also enhanced the possibility to control the plasma chemistry and jet temperature by changing the shielding gas. Therefore, the reactor is capable of producing a cold atmospheric plasma jet for the emerging plasma application such as plasma medicine and bio-applications.

Numerical modelling of a coaxial Stirling pulse tube cryocooler with an active displacer for space applications

A numerical model for a coaxial Stirling pulse tube cryocooler with an active displacer has been developed. An active displacer, in place of an inertance tube, has already demonstrated good efficiency in an in-line pulse tube, but incorporating this design into a coaxial configuration permits better access to the cold head. A model of the coaxial cold head was developed to include the radial flow and cooling in this region. The sub-assembly models were validated with flow testing of the physical sub-units of the cryocooler. The performance has been predicted for the cryocooler as a function of: fill pressure, operating frequency, and phase angle between the position of the linear compressor and displacer. The projected difference in performance and efficiency of the coaxial configuration was compared to the in-line design. The coaxial cryocooler numerically simulates 6 W of cooling at 80 K with an input power of 85 W, at a fill pressure of 28 bar, an operating frequency of 60 Hz, and a compressor-displacer phase angle of 41°. Overall, the coaxial cryocooler outperforms the in-line design in terms of cooling power, but not in terms of efficiency.

Confined jets in co-flow: effect of the flow rate ratio and lateral position of a return cannula on the flow dynamics

Co-axial tubes have been used to produce a co-flowing confined jet similar to that found in an Extracorporeal Membrane Oxygenation return cannula flow configuration. Particle Image Velocimetry was used to investigate the flow rate ratio between jet and co-flow as well as changes in flow characteristics due to cannula position. The flow was found to be dominated by three main structures: lateral flow entrainment, shear layer induced vortices and backflow along the wall. An increase in cannula flow rate amplified entrainment and recirculation, resulting in a decrease in length required to reach a fully developed flow. Changing cannula position relative the outer cylinder induced a significant reduction in recirculation zone as well as vortex formation on the side to which the cannula was tilted towards, whereas on the other side, the recirculating flow region was enhanced. Proper Orthogonal Decomposition demonstrated that the dominating structure found in the flow is the backflow, composing of several structures having different oscillation frequencies. The significance of the observed and measured flow structures is in enhancing mixing.

Optimization of Heat Losses of Concentric Coaxial Glass Tube Solar Air Collector

Optimization of Heat Losses of Concentric Coaxial Glass Tube Solar Air Collector

Continuously Variable Stiffness Mechanism Using Nonuniform Patterns on Coaxial Tubes for Continuum Microsurgical Robot

Variable stiffness enables the safe and effective operation of the minimally invasive surgical instruments. In this article, we propose a continuously variable stiffness mechanism of the scalable tubular structure. The mechanism consists of multiple coaxial nitinol tubes, and each tube has an anisotropic distribution of flexural stiffness created by nonuniform through-hole patterning. The stiffness of the mechanism is varied by relative rotation and translation among the tubes, resulting in flexural stiffness difference up to 7.2 times in the direction of load. Its flexural stiffnesses along principal axes are independently controlled by the suggested counterrotation algorithm. The stiffness change is validated through analytical modeling, FEM simulation, and the experiments. Thanks to its physically embodied intelligence, the mechanism has a simple scalable structure and the response time is immediate. We applied this mechanism to control the stiffness of the steerable needle. Varying the stiffness grants the additional degree of freedom to control the needle's trajectory, which can expand the workspace of the steerable needle.

Operational Control of Mixing Enhancement and Far-Field Jet Noise Suppression Using Downstream Fluidic Injection

Abstract A novel fluid injection scheme is analyzed for its ability to suppress the far-field jet noise using multiple radial microjets placed downstream from the nozzle exhaust. Contrary to other previous research studies, which injected fluid either inside the nozzle or just at the nozzle exhaust, this injection scheme uses a coaxial injector tube to inject multiple equally spaced microjets perpendicular to the jet axis at an axial location downstream from the nozzle exhaust. Microjet injection closer to the jet axis leads to the formation of a counter rotating vortex pair (CVP) close to the injection location which subsequently breaks down into streamwise vortices as the microjet bends and follows the flow direction. Microjet injection pressure and angle of injection play a crucial role in determining the jet trajectory, penetration, and the strength of the CVP formed. The effect of these parameters on the far-field acoustic radiation is evaluated in this study. Detailed large eddy simulations are performed for a nozzle–injector setup operating at Mach 0.9 jet with Reynolds number ≈106 to help understand the aerodynamic and acoustic features of the interaction of this fluid injection scheme with the main jet.

Influence of Varying Temperature and Concentration on MHD Peristaltic Transport for Jeffrey Fluid with Variable Viscosity through Porous Channel

The present paper deals with the peristaltic motion of Jeffrey fluid with varying temperature and concentration through a porous medium in a coaxial uniform circular tube. The fluid is assumed to be non-Newtonian, namely Jeffrey fluid. The inner tube is uniform, while the outer flexible tube has a sinusoidal wave traveling down its wall. The analytical formulas of the velocity and temperature have been obtained in terms of the Bessel function of first and second kinds. The numerical formula of the axial velocity, temperature and concentration are obtained as functions of the physical parameters of the problem (Darcy number, magnetic parameter, thermal Grashof number, Reynolds number, Prandtl number, and Schmidt number) with other physical parameters are obtained. The Influence of physical parameters of the problem on this formula are discussed numerically and illustrated graphically through a set of figures.

Effect of the Variable Viscosity on the Peristaltic Flow of Newtonian Fluid Coated with Magnetic Field: Application of Adomian Decomposition Method for Endoscope

In the present analysis, peristaltic flow was discussed for MHD Newtonian fluid through the gap between two coaxial tubes, where the viscosity of the fluid is treated as variable. In addition, the inner tube was considered to be at rest, while the outer tube had the sinusoidal wave traveling down its motion. Further, the assumptions of long wave length and low Reynolds number were taken into account for the formulation of the problem. A closed form solution is presented for general viscosity using the Adomian decomposition method. Numerical illustrations that show the physical effects and pertinent features were investigated for different physical included phenomenon. It was found that the pressure rise increases with an increase in Hartmann number, and frictional forces for the outer and inner tube decrease with an increase in Hartmann number when the viscosity is constant. It was also observed that the size of the trapping bolus decreases with an increase in Hartmann number, and increases with an increase in amplitude ratio when the viscosity is parameter.

DC/AC magnetohydrodynamic-micropump of a generalized Burger's fluid in an annulus

The article describes a new model for investigating the effect of a uniform magnetic field and an imposed electric field through two coaxial tubes on a flow of DC and AC-operated micropumps. Assumptions are made in order to reach to closed-form solutions. Expressions for the velocity, flow rate, magnitude of pressure gradient, and shear stress are derived by means of Laplace transforms along with numerical inversion algorithms. Graphical results are presented for the physical variables with different parameters involved in the flow field. Comparisons are made with the other non-Newtonian fluids and discussed graphically. Critical values for the magnetic and material parameters are found around which the flow velocity is reversed for the DC magnetohydrodynamic-micropump. The present study might provide a reference for controlling and manipulating small non-Newtonian fluid volumes.

Effect of Vacuum Level on Heating Speed on Ethanol Destillation Process Using Coaxial Vacuum Tube Solar Collector

Vacuum tube collectors that could produce heat up to a temperature of 80°C could be used to process ethanol distillation, because the evaporation process of ethanol only requires a temperature of 79°C at 1 atm. Vacuum tube collectors in terms of many types of heat absorbers, each type had a different heat absorption ability. This study will review the performance of the coaxial vacuum tube collector used for the process of ethanol distillation. The study was carried out in space using halogen lamps as solar radiation simulators. In the study conducted with three radiation variations, namely 998 W/m2, 878 W/m2, and 782 W/m2. The pressure / vacuum level of the collector tube cavity varies from 0.043 atm, 0.179 atm, 0.315 atm, 0.5atm, and 1 atm. Ethanol research material with 30% content using water as a distillation cooling medium. The results of this research could be known the effect of the vacuum level on the speed of achieving temperature in the distillation process using a solar collector coaxial vacuum tube.

Wastewater treatment by dielectric barrier discharge plasma

This paper presents the influence of atmospheric non-thermal plasma on household wastewater by using dielectric barrier discharge (DBD) plasma generator. The model was designed in a vertical coaxial tube shape. The high voltage was supplied from high frequency AC power supply to the model for plasma generation at 0 (control group), 10, and 15 kV. Wastewater was released from the top of glass tube passing through DBD corona discharges that was generated between the needle tips and the glass tube, flowed down to the storage tank, and pumped to the top of the model again. The treatment process was operated for 30 minutes with the flow rate of water at 2 min/L. From the experimental results, it shows that all plasma treatment conditions could improve the wastewater quality. The best results were found at 15 kV plasma treated wastewater; the alkalinity, dissolved oxygen (DO), and conductivity were increased from the control group for 10.48%, 10.09%, and 17.79%, respectively. In addition, biochemical oxygen demands (BOD), and chemical oxygen demand (COD) were decreased from the control group for 7.5 times and 37.5%, respectively. An offensive odor of wastewater could be also improved.

A new analytical heat transfer model for deep borehole heat exchangers with coaxial tubes

Deep borehole heat exchangers (DBHE) provide an effective solution for ground coupled heat pump (GCHP) systems in cold climate region where heating is dominant. Concerning the analytical heat transfer models, the simplification that borehole wall temperature is constant along the depth of ground heat exchangers (GHE) which the existing quasi-three-dimensional models have assumed in the application of shallow borehole GHE, can no longer be accepted in the application of DBHE due to the geothermal gradient in deep ground. Making this simplification cannot give the real temperature distribution of circulating fluid along the depth of DBHE. Therefore, this paper developed a new analytical model for DBHE with coaxial pipes by successfully addressing the increasing borehole wall temperature using the convolution theorem, so that the widely employed quasi-three-dimensional models for shallow borehole GHE is extended for DBHE with coaxial pipes for the first time. The new analytical model is validated by comparing with an existing numerical model. Using the newly developed analytical model, the trends revealing the relationships between thermal performance of DBHE and various parameters are firstly plotted. Because of the high accuracy and quick calculation, this new analytical model can be used as a benchmark for numerical models. More importantly, the proposed analytical model can be an effective tool for the design and optimization of DBHE, since current numerical models are always calculation-demanding, time-consuming and difficult for engineers and designers to use. Also, the method this paper proposed to address the varying borehole wall temperature can certainly be employed to improve the existing quasi-three-dimensional models for shallow borehole GHE so that they can be applicable in some other cases, for example, GHE installed in layered soils, or affected by underground seepage flow in partial depth.

Development by robocasting and mechanical characterization of hybrid HA/PCL coaxial scaffolds for biomedical applications

Porous structures consisting of a tetragonal three-dimensional mesh of interpenetrating coaxial tubes were fabricated by robocasting from hydroxyapatite (HA) inks. After sintering the structures, polycaprolactone (PCL) was infiltrated within the tubes core by injection of a polymer solution. The addition of the polymer enhanced the mechanical performance in terms of toughness over dense- and hollow-strut all-ceramic scaffolds, specially under bending stresses. PCL impregnation improved also the compressive strength over hollow-strut scaffolds —although dense-strut structures remained stronger especially in compression. Thus, this coaxial core-shell strut configuration combines the best features of each material: the necessary stiffness and excellent osteoconductivity of the bioceramic, with the high toughness and ductility of the biopolymer; and allows the fabrication of hybrid scaffolds with the interconnected macroporosity necessary for cell ingrowth. Hence, this work successfully provides a proof-of-concept of this novel strategy for the mechanical enhancement of bioceramic-based scaffolds while preserving their osteoconductive properties.

Study of neon heat flux in thermosyphon cooling system for high-temperature superconducting machinery

High-temperature superconductors (HTS) applied to rotating machine draw much interest in the shipbuilding industry as the urge to get high-power density and efficient electric propulsion systems. To achieve an optimal performance of HTS field pole magnets in ship propulsion motors, it is crucial to regulate the operating temperature under 40 K and a simple and reliable cooling system is necessary. A thermosyphon (TS) is highly suitable since its operation principle consists in using natural convection without the intervention of mechanical circulation pump. The system composition is simple and light-weight. The TS benefits from a high heat transfer coefficient thanks to latent heat. The available temperature for TS depends on the saturation temperature of the refrigerant, which provides adequate controllable cooling for cryogenic machine application. A TS system using neon enables us to supply cooling temperatures of 28–40 K range. To determine the optimal gas-liquid state operation for HTS motors, a scaled model of a 20 MW motor TS cooling system was designed and constructed. This enabled us to visualize any phenomena and transient state change inside the evaporator part of the rotor. We studied heat transfer capacity under heat load for different neon quantities. Neon heat flux was then calculated to determine the heat transfer area for effective cooling. The boiling curve leads to the refined evaporator design with optimal heat transfer area. Introducing coaxial tubing between condenser and evaporator, possible sustainable liquid-gas circulation has been achieved without interruption under inclined condition required for ship operation. The present results contribute to the next stage HTS ship propulsion motor and superconducting machine design.

Relativistic Charged-Particle Beam Space-Charge Limited Current in Finite Length Coaxial Drift Tube

In the strong axial (guide) magnetic field and uniform beam density approximations, we calculate scalar potential distribution induced by axisymmetric annular relativistic charged-particle beam in a finite-length coaxial drift tube. This scalar potential distribution allows us to find an approximate radial position at which the extremum of the scalar potential is attained in the coaxial drift tube inside the annular relativistic charged-particle beam. By knowing the approximate extremal radial position, we obtain the analytical estimate for the space-charge limited (SCL) current of axisymmetric annular (finite thickness) relativistic charged-particle beam propagating in strong axial magnetic field in a finite length coaxial drift tube and establish a simple correspondence of this result to that in a long coaxial drift tube. A comparison of numerical nonlinear calculations and the analytical estimate for the SCL current in the finite-length coaxial drift tube is also given.

One Dimensional Van Der Waals Heterostructures Wrapped Around Single-Walled Carbon Nanotubes

We have synthesized a new coaxial nanotube structure, in which mono- or few-layer hexagonal boron nitride nanotube (BNNT) seamlessly wrap around a single-walled carbon nanotube (SWCNT), and result in an atomically smooth coaxial tube consisting two different materials, as shown in Fig. 1(a). TEM-EELS clearly demonstrated the BNNT-SWCNT coaxial structure. We have tried various morphologies of SWCNTs as starting material, e.g. vertically aligned array, horizontally aligned array, suspended SWCNTs, and dry-deposited random network films. We can clearly observe the coaxial structure from originally isolated SWCNTs. We found no correlation between chiral angle of inner SWCNT and outer BNNT for ‘double-walled’ SWCNT-BNNT shown in Fig. 1(b). We concluded that these are one-dimensional van der Waals heterostructure. We have further developed the 1D coating CVD for transition metal dichalcogenide nanotubes, such as MoS2 nanotube as shown in Fig. 1 (c). We can grow MoS2 nanotubes around relatively large diameter SWCNT or SWCNT@BNNT [1]. We will discuss properties of the 1D heterostructures though optical absorption, Raman scattering, photoluminescence, FT-IR, and cathode luminance. Reference: [1] Rong Xiang et al., arXiv:1807.06154 (2018). Figure 1