Coaxial Tube Research Articles

An efficient miniature 120 Hz pulse tube cryocooler using high porosity regenerator material

A 1.22 kg coaxial miniature pulse tube cryocooler (MPTC) has been fabricated and tested in our laboratory to provide cooling for cryogenic applications demanding compactness, low mass and rapid cooling rate. The geometrical parameters of regenerator, pulse tube and phase shifter are optimized. The investigation demonstrates that using higher mesh number and thinner wire diameter of stainless steel screen (SSS) can promote the coefficient of performance (COP) when the MPTC operates at 120 Hz. In this study, the 604 mesh SSS with 17 μm diameter of mesh wire is constructed as filler of regenerator. The experimental results show the MPTC operating at 120 Hz achieves a no-load temperature of 53.5 K with 3.8 MPa charging pressure, and gets a cooling power of 2 W at 80 K with 55 W input electric power which has a relative Carnot efficiency of 9.68%.

A Versatile Laminar Flow Atmospheric Pressure Plasma Jet Using a Double Coaxial Glass Tube

We report the characteristics of laminar flow atmospheric pressure plasma jets (APPJs) using a double coaxial glass tube. Two gases can be introduced independently into the tube, and the gas and plasma flows form a laminar flow and then interact outside of the glass tube. In the case of helium (He) as an inner gas flow with an outer nitrogen (N2) gas flow, emission lines of nitric oxide, the first negative and second positive system bands of N2 were observed, while only the second positive system band was observed in the case of argon (Ar) as the inner one. Considering the Penning effects of each excited state, the metastable state of He has a higher energy than that of Ar, resulting in energetic nitrogenous productions in the former case. The excited state in the core plasma is one of the important conditions to determine the characteristics of the APPJ produced with a double coaxial glass tube.

Distribution of the temperature in the coaxial tube heat exchanger with spherical end

A solution is presented for flow inside a heat exchanger. An analytical approach is developed and validated with a numerical simulation using ANSYS CFX code module taking account different boundary condition in the inlet. The temperature distribution of the laminar flow is presented, which is related to Reynolds number and the hydraulic diameter of the heat exchanger.

A New Dynamic Powder Consolidation Technique Using Shock Waves

Techniques for shock consolidation of powders have been developed for different purposes, including the synthesis of diamond from carbon powder. In this work, a new device configuration for dynamic consolidation is proposed. It consists of three coaxial tubes, with a conical cover made of explosive at the top of the device. The inner tube contains the powder to be compacted. The second is accelerated towards the first in order to promote its collapse. The third confines the explosive. A conical cap at the top of the device triggers the explosive. For a preliminary evaluation, two types of explosives, TNT and Composition B, were used. Preliminary analytical results by the impedance matching method indicate that maximum pressures of 35.44 GPa and 48.16 GPa could be achieved using TNT and Composition B, respectively. Maximum temperatures around 1,600 K and 2,500 K for TNT and Composition B, respectively, are expected. These pressure and temperature values are adequate for transforming graphite into diamond. Preliminary Rietveld refinement indicated that nanodiamond is a fraction of approximately 54% of the detonation resulting powder.

Study of Performance of Coaxial Vacuum Tube Solar Collector on Ethanol Distillation Process

Coaxial vacuum tube solar collectors can generate heat up to 80°C is possibly used for ethanol distillation process that required temperature 79°C only. This study reviews the performance of coaxial collector vacuum tube used for ethanol distillation process. This experimental research was conducted in a closed space using a halogen lamp as a solar radiation simulator. We had done on three different of the radiation values, i.e. 998 W/m2, 878 W/m2 and 782 W/m2. The pressure levels of vacuum tube collector cavity in the research were 1; 0.5; 0.31; 0.179; and 0.043 atmospheres. The Research upgraded the 30% of ethanol to produce the concentration of 77% after distillation. The result shows that the performance of coaxial collector vacuum tube used for ethanol distillation process has the negative correlation to the level of the collector tube cavity pressure. The productivity will increase while the collector tube cavity pressure decreased. Therefore, the collector efficiency has the negative correlation also to the level of collector tube cavity pressure. The best performance achieved when it operated at a pressure of 0.043 atmosphere with radiation intensity 878 W / m2, and the value of efficiency is 57.8%.

Experimental investigation of transparent parabolic trough collector based on gas-phase nanofluid

An experimental study on new high temperature parabolic trough collector (PTC), with transparent receiver tube, based on gas-phase nanofluid, has been carried out for the first time in this work. Two-axes solar tracking PTC, with 4m2 reflecting surface has been realized. Besides, two coaxial quartz tubes, with vacuum in the inner space were used as receiver pipe, with air-dispersed CuO nano-powders as working fluid. The aim of this work was to investigate the technological issues related to the use of gas-based nanofluid coupled with transparent quartz receiver and to evaluate the performance of the first prototype, comparing numerical and experimental results. The experimental campaign highlighted a critical issue related to nanopowder deposition within the receiver pipe, due to humidity. Moreover, in a day of measurement, the fluid temperature higher than 145°C has been maintained for about 10h, reaching a maximum value of 180°C, with a mean efficiency of about 65%.

Using atmospheric plasma to increase wettability, imbibition and germination of physically dormant seeds of Mimosa Caesalpiniafolia

In this study, we analyzed seed wettability as well as imbibition and germination after treatment with atmospheric pressure cold plasma (APCP) using dielectric barrier discharge (DBD) in seeds that have very low germination rates. To aid industrial applications, several seeds were simultaneously treated with plasma within a space between two coaxial glass tubes sandwiched by two metal mesh screens that produced high-voltage pulses at 17.5kV with a frequency of 990Hz. Three treatment times (3min, 9min and 15min) as well as untreated seeds were used to conduct the wettability, imbibition and germination tests. The wettability and imbibition were found to be directly related to the treatment duration, but saturation of the imbibition was found for treatment durations greater than 9min. Plasma treatment was also effective in improving germination, but shorter treatment duration presented greater germination. This apparent contradiction is explained by the cell damage caused by the increased exposure to plasma, as observed in other studies. The results suggest that there must be an optimal wettability and imbibition condition that ensures that excessive moisture does not harm the germination process.

Experimental study on the performance of capacitance-type meters for slush nitrogen measurement

Slush nitrogen, a cryogenic fluid with solid particles suspended in liquid, is considered a potential coolant for high temperature superconductors. In this study, the capacitance-type meters, which are adopted for measuring the density, liquid level and flow velocity of slush nitrogen, are improved with their accuracy and reliability by optimizing the measurement components and mechanical structure. For density measurement, a capacitance-to-digital converter with high accuracy and resolution is used. The liquid level meter is equipped with a coaxial shielding tube, which is earth grounded to protect the electrodes from mechanical disturbance and electromagnetic interference, to strengthen the mechanical support and to improve the stability. The capacitors with double-circular curved-plate electrodes are adopted in the flowmeter to improve its sensitivity. According to the calibration results, the densimeter and the liquid level meter have high sensitivity and good linearity, with the improved accuracy of ±0.16% and ±1.0%, respectively. Besides, the flow velocity can be calculated from the capacitors’ mounting spacing and the delay time of density fluctuation analyzed by cross-correlation function, which turns out to have a relative error within ±7.5% compared with that calculated by the measured variation of liquid level.

Open-Type Magnetic Shields for Optical Fiber Coil Protection With Coaxial Foil Tubes

To decrease the considerable nonreciprocal phase drift caused by environmental magnetic fields in fiber-optic gyroscope (FOG), magnetic shields on optical fiber coil (OFC) are necessarily used in medium- and high-accuracy FOG protection. Cubic boxes and spherical shells without any gaps have been widely adopted for decades in shields, posing challenge for tradeoff between weight limitation of shields and its shielding demand yet. Here, an open-type magnetic shields (OMSs) with several coaxial permalloy foil tubes in few hundred micrometers thickness is proposed, overlaying on the winding process of fiber coil and finally combining with OFC as an integration module (OFC-OMS). The shielding effectiveness (SE) and longitudinal availability were adjustable by changing permalloy tubes’ thickness, intervals between coaxial foil tubes, and extended length in endcaps. The optimized result showed that an OMS set with six coaxial permalloy foil tubes achieved a longitudinal availability of 82.6% for SE above 20dB in both axial and radial magnetic field and further revealed anisotropic shielding effect in axial magnetic field remarkably resulting in a 40-dB longitudinal availability of 70.1%. Total mass of OMS reduced by around 75% comparing with the conventional magnetic shields for OFC, which showed immense potentials on reduction of FOG size and processing cost.

Influence of heat transfer on the peristaltic transport of Walters B fluid in an inclined annulus

The aim of the present analysis is to investigate the effects of endoscope and heat transfer on the peristaltic flow of an incompressible Walters B fluid in an inclined tube. The fluid fills the gap between coaxial uniform tubes, such that the inner tube is rigid, circular and outer tube has sinusoidal wave travelling down its wall. The governing equations for Walters B fluid model are considered in cylindrical polar coordinates in moving frame of reference. The governing coupled partial differential equations are solved analytically employing regular perturbation method. The graphical results have been discussed for velocity, pressure gradient, pressure difference, frictional force, temperature and trapping phenomena. Four different wave forms have been considered for investigation. Trapping phenomena has been presented for different wave forms. It is observed that the pressure gradient is an increasing function of volume flow rate, heat generation parameter and inclination angle. The pumping rate increases from horizontal tube to vertical tube. Best pumping can be seen when the radius of the endoscope increases. The size of the trapping bolus increases with increase of wave amplitude ratio.

Experimental investigation of mixing of non-isothermal water streams at BWR operating conditions

In this experimental investigation, wall surface temperatures have been measured during mixing of three water streams in the annular gap between two coaxial stainless-steel tubes. The inner tube, with an outer diameter of 35mm and a thickness of 5mm, holds six K-type, ungrounded thermocouples with a diameter of 0.5mm, which measured surface temperatures with a sampling rate of either 100Hz or 1000Hz. The tube was rotated from 0 to 360° and moved in a range of 387mm in the axial direction to allow measurements of surface temperatures in the whole mixing region. The outer tube has an inner diameter of 80mm and a thickness of 10mm to withstand a water pressure of 9MPa. A water stream at a temperature of either 333K or 423K and a Reynolds number between 1657 and 8410 rose vertically in the annular gap and mixed with two water streams at a temperature of 549K and a Reynolds number between 3.56×105 and 7.11×105. These two water streams entered the annulus radially on the same axial level, 180° apart. Water pressure was kept at 7.2MPa. Temperature recordings were performed at five axial and eight azimuthal locations, for each set of boundary conditions. Each recording lasted 120s to provide reliable data on the variance, intermittency and frequency of the surface temperature time series at hand. Thorough calculations indicate that the uncertainty in the measured temperature is of 1.58K. The mixing region extends up to 0.2m downward of the hot inlets. In most cases, measurements indicate non-uniform mixing in the azimuthal direction, because of asymmetries in either geometry or mass flow rates at the hot inlets. Due to the measurement accuracy and a relatively simple geometry, an experimental database has been obtained for validation of computational methods to predict thermal mixing and fatigue. Furthermore, these data can provide new insight into turbulent mixing at BWR operating conditions and, more generally, into mixing coupled to the dynamics, also termed level-2 mixing.

Simulation of Heat-Exchange Processes in Coaxial Flues at Abnormally Low Temperatures

AbstractMathematical modeling (simulation) of the movement of the air mixture in the combustion of natural gas was performed for coaxial flue tubes with countercurrent flow for conditions of extrem...

Acoustic gas oscillations in coaxial tubes

Pulsating combustion is one of the possible solutions to improve energy efficiency of combustors that use hydrocarbon fuels. In this paper analysis of gas oscillations in coaxial tubes is provided. An influence of geometric parameters of the combustion chamber and the resonance tube on the installation frequency is considered.

О ЗАДАЧЕ ИДЕНТИФИКАЦИИ НАЧАЛЬНОГО ГИДРОДИНАМИЧЕСКОГО УЧАСТКА ПРИ ЛАМИНАРНОМ ТЕЧЕНИИ НЬЮТОНОВСКОЙ ЖИДКОСТИ В ГОРИЗОНТАЛЬНОМ КОЛЬЦЕВОМ КАНАЛЕ

In the frameworks of physical linearization of the Navier-Stokes equations in a cylindrical coordinates system on the one-way axial force-feed laminar flow of Newtonian fluid, a mathematical model of the flow development in the entrance region of a horizontal annular channel is formulated. The unknown constant gradient of pressure along the channel is connected with the equation of continuity written in an integral form of stability of liquid flow in any cross section of a channel. Use of the one-way integral Laplace transformation along the longitudinal coordinate allowed to obtain an analytical expression of the local hydrodynamic field at the entrance region and determine pressure losses coincided with the classic data. Analysis of the characteristic structure of the hydrodynamic field of dimensionless velocities at the entrance region showed that for small values of the ratio of the radii of the inner and outer coaxial cylindrical tubes constituting the annular channel, asymmetry of the longitudinal velocity profile is observed with a shift of the maximum value towards the surface of a coaxial cylinder of smaller radius, and an increase in the Reynolds number practically linearly increases the length of the hydrodynamic entrance region. Assumption about the absence of drift of the radial coordinate of the maximum velocity in the entrance hydrodynamic region, limited to the so-called "regular" regime, made it possible to identify the length of the entrance hydrodynamic region in the annular channel by the completed expression in an explicit form that correlates with the classical estimates obtained as a result of computational experiments. It is noted that when the ratio of the radii of the inner and outer coaxial cylinders approaches zero or infinity (corresponding to particular cases of a circular tube and a flat channel), the known results for the lengths of the entrance hydrodynamic regions are obtained. Difference between velocity values calculated by the proposed model and experimental values in the region adjacent to the entry section is explained by the fact that kinetic energy of the liquid flow is not accounted for by leveling the pressure inhomogeneity along the channel cross-section. Nonetheless, it is shown that it does not have a significant influence on the length of hydrodynamic entrance region.

Numerical Optimization of Double Tube GHE for Ground Source Heat Pump

In this paper, a two-dimensional axisymmetric numerical simulation model was developed for optimization of double (coaxial) tube vertical ground heat exchangers (GHEs) in cooling mode. Details of the heat transfer rates and pressure drops for each model are presented and analyzed. The results of the numerical study of optimization of double tube vertical GHEs have been done by considering heat transfer rates and pressure drops. The effect of different inlet and outlet tube diameters, and mass flow rates were numerically investigated. Effect of the different materials on heat transfer and longtime operation also discussed. The double tube vertical GHEs are more effective in laminar flow condition considering balance between heat transfer and pressure drop. The results indicate that since in laminar flow condition, pressure drop is not significantly high, it is possible to reduce the inlet and outlet diameter of double tube GHEs if double tube GHEs operate in laminar flow condition. The heat transfer rate decreased only 17% but diameter of the inlet tube can be reduced from 130 mm to 40 mm with fixed outlet diameter 20 mm. Heat transfer rate can also be enhanced by reducing the outlet tube diameter for a fixed inlet tube diameter. Long time operation suggested the possibility of installation of multiple double tube GHE at 2.0 m apart.

Study on Thermal Resistance of Coaxial Tube Boreholes in Ground-Coupled Heat Pump Systems

Taking the fluid temperature distribution along the borehole depth and thermal short-circuiting into account, a new model for coaxial tube borehole heat exchangers has been established, which provides a better understanding of the heat transfer processes in the ground heat exchangers. On this basis the borehole resistance and efficiency of the borehole heat exchanger have been defined, and their analytical expressions derived. Impacts of different constructional and operational parameters on borehole performance are analyzed and discussed. The concept and explicit expression of thermal resistance of the coaxial tube borehole provides an essential and appropriate means for thermal analysis and engineering design of the ground-coupled heat pump systems with coaxial tube boreholes.

Volumetric velocity measurements (V3V) on turbulent swirling flows

This paper presents some results of Volumetric V3V 3D3C velocity measurements on a turbulent flow from a swirl burner. The flow out from the burner used is highly three-dimensional. The study aims at using a system of instantaneous 3D velocity measurements in order to characterize the turbulent swirling flow. The burner used consists of two coaxial tubes with a swirler placed in an annular part supplying the oxidant flow. The central pipe delivers the fuel radially (in the case of reacting flow) through eight holes symmetrically distributed on the periphery of the tube. The burner is placed at the bottom of a combustion chamber and the flow develops vertically along the confinement. The Volumetric 3-component Velocimetry V3V® technique commercialized by TSI is used for 3D velocity measurements in a non reacting flow. The measurement volume above the burner is located at 1.3Db (=49.4mm) and is 50×50×22mm3. The operating conditions considered in this study are 4.67m/s of bulk velocity, Re=7531 of Reynolds number and Sn=1.4 of swirl number. There are very limited works on the application V3V technique on fluid flows. This paper presents the first results concerning an isothermal non-reacting gas flow. Instantaneous and mean velocity 3D3C volumes are measured and shown. Streamlines and velocity iso-surfaces are also analyzed together with different velocity profiles. The results are compared to previous SPIV (Stereoscopic Particle Image Velocimetry) measurements performed by the authors. A good agreement is found between the results of both techniques; the discrepancy did not exceed 10%. V3V results allowed a fine description of 3D aspects of the flow including the recirculation zone and the annular zone with swirling jet effects. The swirling part of the flow and the central recirculation zone are clearly identified by 3D fields of velocities and streamlines. Velocity volume indicates the presence of a central zone with a negative longitudinal velocity, which can reach −1m/s at the burner center. Under the swirl effect, the tangential velocity is relatively high, particularly in the annular zone of the burner. Indeed, this velocity is varied between 3 and −3m/s for a bulk velocity of 4.7m/s.

Calculation of AC loss in two-layer superconducting cable with equal currents in the layers

A new method for calculating AC loss of two-layer SC power transmission cables using the commercial software Comsol Multiphysics, relying on the approach of the equal partition of current between the layers is proposed. Applying the method to calculate the AC-loss in a cable composed of two coaxial cylindrical SC tubes, the results are in good agreement with the analytical ones of duoblock model. Applying the method to calculate the AC-losses of a cable composed of a cylindrical copper former, surrounded by two coaxial cylindrical layers of superconducting tapes embedded in an insulating medium with tape-on-tape and tape-on-gap configurations are compared. A good agreement between the duoblock model and the numerical results for the tape-on-gap cable is observed.

A canonical geometry to study wall filming and atomization in pre-filming coaxial swirl injectors

A coaxial twin counter-rotating air swirl prefilming injector with necessary optical access, is developed to visualize and quantify its internal fluid dynamics. This research injector consists of a simplex nozzle arranged at the center of two coaxial counter-rotating radial air flow swirlers, and two transparent coaxial tubes are attached, one each to the primary and secondary air swirl paths. Spray from the simplex nozzle is swirled by the primary air and impinges on the inner tube—the prefilmer, undergoes filming, and convects to the tube tip to form a liquid rim, which is sheared by the counter-rotating swirl into finer droplets. Stage-wise phase Doppler particle analyzer measurements indicate the final spray to be much finer than the simplex nozzle spray after undergoing the above processes. Time resolved laser induced fluorescence (TR-LIF) imaging techniques are applied to visualize the wall filming and primary atomization inside the injector. The simplex nozzle spray velocity under the influence of air swirl flow is measured using stereo-particle image velocimetry. The precessing vortex core from the primary swirl imparts a precessing motion to the simplex spray, which in turn induces a non-uniform filming on the prefilmer. The droplet impingement on the prefilmer leads to splashing and crater formation on the surface. The crater size distribution is obtained and compared to the droplet size of the injector spray before impingement. The film thickness variation on the prefilmer surface and the rim thickness are estimated from planar LIF experiments along with a long distance microscope. The thickness of the liquid rim is identified as a major factor in determining the final droplet size at the injector exit. These are correlated to SMD at the injector exit at different air flow rates.

Analysis of temperature fluctuations caused by mixing of non-isothermal water streams at elevated pressure

Temperatures were measured at the inner surface of an annulus between two coaxial tubes, where three water streams mixed. These temperatures were sampled at either 100Hz or 1000Hz. The acquisition time was set to 120s. Two water streams at 549K, with a Reynolds number between 3.56×105 and 7.11×105, descended in the annular gap and mixed with a water stream at 333K or 423K, with a Reynolds number ranging from 1.27×104 to 3.23×104. Water pressure was kept at 7.2MPa. Inner-surface temperatures were collected at eight azimuthal and five axial positions, for each combination of boundary conditions. To better analyze these temperatures and mixing in the vicinity of the wall, scalars estimating the mixing intensity at each measurement position were computed from detrended temperature time series. Fourier and Hilbert–Huang marginal spectra were calculated for the time series giving rise to the highest values of a mixing estimator of choice. The relationship between temperature and velocity was explored by examining the results of an LES simulation using the same boundary conditions as in one of the experimental cases.