Coaxial Tube Research Articles

Experimental study of the influence of cold heat exchanger geometry on the performance of a co-axial pulse tube cooler

Improving the performance of the pulse tube cooler is one of the important objectives of the current studies. Besides the phase shifters and regenerators, heat exchangers also play an important role in determining the system efficiency and cooling capacity. A series of experiments on a 10W @ 77K class co-axial type pulse tube cooler with different cold heat exchanger geometries are presented in this paper. The cold heat exchangers are made from a copper block with radial slots, cut through using electrical discharge machining. Different slot widths varying from 0.12mm to 0.4mm and different slot numbers varying from around 20–60 are investigated, while the length of cold heat exchangers are kept the same. The cold heat exchanger geometry is classified into three groups, namely, constant heat transfer area, constant porosity and constant slot width. The study reveals that a large channel width of 0.4mm (about ten times the thermal penetration depth of helium gas at 77K, 100Hz and 3.5MPa) shows poor performance, the other results show complicated interaction effects between slot width and slot number. These systematic comparison experiments provide a useful reference for selecting a cold heat exchanger geometry in a practical cooler.

Coaxial (tubular) glow discharge in electronegative gases

The positive-column plasma of a low- and medium-pressure electronegative glow discharge initiated in the gap between two coaxial cylindrical tubes has been considered (the current is directed along the tube axis). It is assumed that the gas mixture contains halogens, and ion diffusion is not negligibly weak. It is found that the coaxial discharge is characterized by plasma separation into three coaxial regions with different compositions in the direction transverse to the current. It has been shown that the ionization and excitation frequencies of atoms are higher than in the purely cylindrical case, even for a small (0.05–0.15) ratio of the radii of the inner and outer walls. An asymptotic analysis of the continuity equations yields analytic expressions that make it possible to rapidly and easily estimate the geometrical parameters of the spatial distributions of charge particle concentrations, as well as energy parameters of the plasma for the radii ratio that exceed 0.3. The conditions for the applicability of analytic relations and their accuracy are established from a comparison of the results of analytic and numerical calculations.

Development of a compact cryocooler system for high temperature superconductor filter application

Seeking a higher specific power of the pulse tube cryocooler is an important trend in recent studies. High frequency operation (100Hz and higher), combined with co-axial configuration, serve as a good option to meet this requirement. This paper introduces a high efficiency co-axial pulse tube cryocooler operating at around 100Hz. The whole system weighs 4.3kg (not including the radiator) with a nominal input power of 320W, namely, power density of the system is around 74W/kg. The envelop dimensions of the cold finger itself is about 84mm in length and 23mm in outer diameter. Firstly, numerical model for designing the system and some simulation results are briefly introduced. Distributions of pressure wave, the phase difference between the pressure wave and the volume flow rate and different energy flow are presented for a better understanding of the system. After this, some of the characterizing experimental results are presented. At an optimum working point, the cooling power at 80K reaches 16W with an input electric power of 300W, which leads to an efficiency of 15.5% of Carnot.

CFD modeling and experimental verification of a single-stage coaxial Stirling-type pulse tube cryocooler without either double-inlet or multi-bypass operating at 30–35 K using mixed stainless steel mesh regenerator matrices

This paper presents the CFD modeling and experimental verifications of a single-stage inertance tube coaxial Stirling-type pulse tube cryocooler operating at 30–35K using mixed stainless steel mesh regenerator matrices without either double-inlet or multi-bypass. A two-dimensional axis-symmetric CFD model with the thermal non-equilibrium mode is developed to simulate the internal process, and the underlying mechanism of significantly reducing the regenerator losses with mixed matrices is discussed in detail based on the given six cases. The modeling also indicates that the combination of the given different mesh segments can be optimized to achieve the highest cooling efficiency or the largest exergy ratio, and then the verification experiments are conducted in which the satisfactory agreements between simulated and tested results are observed. The experiments achieve a no-load temperature of 27.2K and the cooling power of 0.78W at 35K, or 0.29W at 30K, with an input electric power of 220W and a reject temperature of 300K.

Rapid synthesis of CNTs@MIL-101(Cr) using multi-walled carbon nanotubes (MWCNTs) as crystal growth accelerator

In this work, hybrid material CNTs@MIL-101(Cr) was synthesized in 2h using multi-walled carbon nanotubes (MWCNTs) as the crystal growth accelerator with hydrothermal method. The characteristic differences between the crystals of CNTs@MIL-101(Cr) and MIL-101 were investigated by N2 adsorption–desorption isotherms, X-ray diffraction (XRD), scanning electron microscope (SEM) and thermogravimetric analyzer (TGA). The results showed that MWCNTs embedding in the hybrid material provide more mesoporous volumes than that of MIL-101. Moreover, the fast synthesized crystals of CNTs@MIL-101(Cr) still preserve the octahedral shape like MIL-101 and have a larger size ranging from 1.5 to 2.0μm which were approximately three times larger than that of MIL-101. In the proposed mechanism, the roles of MWCNTs played in the crystallization were discussed where MWCNTs can be seen as coaxial cylindrical tubes composed of multi-layer graphenes and the place where nucleation and crystal growth processes occur at the tubes' out surface. Then, a crystal seeding layer bonding with the MWCNTs may be easily formed which accelerates the growth rate of MIL-101 crystals. Thus, larger crystals of CNTs@MIL-101(Cr) were formed due to the faster crystal growth rate of MIL-101.

A novel coupled VM-PT cryocooler operating at liquid helium temperature

This paper presents experimental results on a novel two-stage gas-coupled VM-PT cryocooler, which is a one-stage VM cooler coupled a pulse tube cooler. In order to reach temperatures below the critical point of helium-4, a one-stage coaxial pulse tube cryocooler was gas-coupled on the cold end of the former VM cryocooler. The low temperature inertance tube and room temperature gas reservoir were used as phase shifters. The influence of room temperature double-inlet was first investigated, and the results showed that it added excessive heat loss. Then the inertance tube, regenerator and the length of the pulse tube were researched experimentally. Especially, the DC flow, whose function is similar to the double-orifice, was experimentally studied, and shown to contribute about 0.2K for the no-load temperature. The minimum no-load temperature of 4.4K was obtained with a pressure ratio near 1.5, working frequency of 2.2Hz, and average pressure of 1.73MPa.

Commercial Pulse Tube Cryocoolers Producing 330 W and 1000 W at 77 K for Liquefaction

Fabrum Solutions and Callaghan Innovation have been developing large pulse tube cryocoolers based on Callaghan Innovation's diaphragm pressure wave generators (DPWGs). The pulse tube's lack of moving parts in combination with the DPWG's metal diaphragms produces a cost-effective, long-life, and robust cryocooler. The DPWG has had ten years of development, resulting in a series of DPWGs ranging in input powers from 0.5 to 30 kW that have been coupled to a variety of inline and coaxial pulse tubes. Two DPWGs have each had in excess of 7000 h running to date. A 330-cc DPWG was designed and manufactured to run with an inline pulse tube with a target refrigeration power of 330 W at 77 K. Absolut System carried out the pulse tube design, and manufacture was done by Fabrum Solutions, with integration and testing by Callaghan Innovation. Over 450 W of cooling power at 77 K was achieved from the cryocooler. A sealed condensation chamber was added to the cold head and connected to a Dewar via vacuum insulated lines for nitrogen liquefaction. Three such pulse tubes were combined on a single 1000-cc DPWG to produce over 1000 W at 77 K. This paper details the development of the PTC330 and PTC1000 cryocoolers from initial laboratory prototypes to commercial products, integrated into liquefiers and ready for use in applications such as liquid nitrogen production, reliquefaction of storage tank boiloff, or cooling of high-temperature superconductor applications.

Peristaltic Transport of Couple Stress fluids In a Uniform and Non-Uniform Annulus

The aim of the present investigation is to study the peristaltic transport through the gap between coaxial tubes, where the outer tube is non uniform and the inner tube is rigid. The necessary theoretical results such as viscosity, pressure gradient and friction force on the inner and outer tubes have been obtained in terms of couple stress parameter. Out of these theoretical results the numerical solution of pressure gradient, outer friction, inert friction and flow rate are shown graphically for the better understanding of the problem.

Fabrication of polystyrene fibers with tunable co-axial hollow tubing structure for oil spill cleanup

Hollow tubing polystyrene (PS) fibers (HFs) with porous shell were successfully fabricated through co-axial electrospinning and selectively dissolving and removing polyvinyl pyrrolidone (PVP) core of the co-axial PS/PVP fibers using C2H5OH at room temperature. The size of co-axial hollow tubing structure (CHTS) and the thickness of shell can be controlled by varying the feed rate ratio of the core solution to the shell solution. The oil-sorption results show that the oil-sorption capacity increases with the increasing of the size of CHTS in the HFs, and the HFs have higher oil-sorption capacities than the porous PS fibers (PFs) without CHTS. It is noticeable that the diesel sorption capacity (66g/g) of the HFs is approximately 1.74 times as much as that (38g/g) of the PFs. The motor oil sorption capacity (147g/g) of the HFs is approximately 1.55 times as much as that (95g/g) of the PFs. It is suggested that the HFs have a better oil-sorption performance than the PFs, especially for the low viscosity oil, which is contributed to large CHTS and high porosity.

Busbar arcs at large fusion magnets: Model experiments on busbar arcing in a double-walled feeder tube with the LONGARC device

Electric arcs moving along the power cables (the so-called busbars) of the toroidal field (TF) coils of large fusion devices like DEMO and ITER may reach and penetrate the cryostat wall. The present work concludes a series of model experiments studying the propagation and destruction mechanisms of such busbar arcs in small scale. While it went clear from previous findings that the inner feeder tube of a busbar would not withstand a powerful arc, the present work investigated the impact of the arc on the second, coaxial outer feeder tube. The key finding is that the outer feeder tube will stay intact in any case, proving the robustness of the ITER TF busbar confinement concept. As the basic DEMO magnet concept will be “ITER-like”, the knowledge of weaknesses and strengths of the ITER TF busbar feeder design may be helpful in the preparation phase of a detailed DEMO magnet feeder design.

Study on Relationship between Dielectric Constant and Water Content of Rock-Soil Mixture by Time Domain Reflectometry

It is important to test water content of rock-soil mixtures efficiently and accurately to ensure both the quality control of compaction and assessment of the geotechnical engineering properties. To overcome time and energy wastage and probe insertion problems when using the traditional calibration method, a TDR coaxial test tube calibration arrangement using an upward infiltration method was designed. This arrangement was then used to study the influence of dry density, pore fluid conductivity, and soil/rock ratio on the relationship between water content and the dielectric constant of rock-soil mixtures. The results show that the empirical calibration equation forms for rock-soil mixtures can be the same as for soil materials. The effect of dry density on the calibration equation has the most significance and the influence of pore fluid conductivity can be ignored. The impact of variation of the soil/rock ratio can be neutralized by considering the effect of dry density in the calibration equation for the same kind of soil and rock. The empirical equations proposed by Zhao et al. show a good accuracy for rock-soil mixtures, indicating that the TDR method can be used to test gravimetric water content conveniently and efficiently without calibration in the field.

Preparation of morphologically controlled zirconia particles using a coaxial tube reactor

Preparation of morphologically controlled zirconia particles using a coaxial tube reactor

CFD simulation of a miniature coaxial Stirling-type pulse tube cryocooler operating at 128 Hz

A two-dimensional axis-symmetric CFD model of a miniature coaxial Stirling-type pulse tube cryocooler with an overall weight of 920g operating at 128Hz is established, and systematic simulations of the performance characteristics at different temperatures are conducted. Both thermal equilibrium and non-equilibrium mechanisms for the porous matrix are considered, and the regenerator losses including the gas and solid conduction, the pressure drop and the imperfect interfacial heat transfer are calculated, respectively. The results indicate that the pressure drop loss is dominant during the first 85% and 78% of regenerator length for the thermal equilibrium and non-equilibrium models, respectively, and it decreases monotonously from warm to cold end due to the steadily decreasing Darcy and Forchheimer terms, whereas other entropy generations share similar changing tendencies, going up gradually near the warm end, increasing dramatically from about 60% of length and then decreasing sharply near the cold end. The reasons for these entropy variations are discussed.

Commercialisation of Pulse Tube cryocoolers to produce 330 W and 1000 W at 77 K for liquefaction

Fabrum Solutions in collaboration with Callaghan Innovation has been developing large pulse tube cryocoolers based on Callaghan Innovation's diaphragm pressure wave generators (DPWG). The pulse tube's lack of moving parts in combination with the DPWG's metal diaphragms produces a cost-effective, long life and robust cryocooler. The DPWG has had 10 years of development, resulting in a series of DPWGs ranging in input powers from 0.5 kW to 30 kW that have been coupled to a variety of in-line and coaxial pulse tubes. Two DPWGs have had in excess of 7000 hours running to date. The PTC330 cryocooler is based on a new 330 cc DPWG and has produced 480 W of cooling at 77 K during testing. The PTC1000 combines three such pulse tubes on a single 1000 cc DPWG to produce 1270 W at 77 K. This paper details the development of the PTC330 and PTC1000 cryocoolers from initial lab prototypes through to commercial products, integrated into liquefiers and ready for use in applications such as: Nitrogen liquefaction, re-liquefaction of boil-off from storage tanks, or cooling of cryostats for High Temperature Superconductor applications.

Diagnosis of asymmetric mode competition in triaxial klystron amplifier

In order to meet the diagnosis requirements of asymmetric mode competition in an X-band triaxial klystron amplifier, a novel waveguide coupler with compact structure is designed, and its coupling characteristics for TE61 mode are analyzed with small-hole coupling principle and CST simulation software. A physical model is established by using PIC method to diagnose the spectrum characteristics in the TKA coaxial drift tube. Through simulation, the validity of the designed coupler to diagnose TKA asymmetric mode competition is verified.

Simulational Investigation of a High-Efficiency X-Band Magnetically Insulated Line Oscillator**supported by National Natural Science Foundation of China (No. 11075210) and the Special Financial Grant from the China Postdoctoral Science Foundation (No. 201104761)

The magnetically insulated line oscillator (MILO) is a gigawatt-class, coaxial crossed-field microwave tube, which is at present a major hotspot in the field of high-power microwaves (HPM) research. In order to improve the power conversion efficiency and eliminate or at least minimize anode plasma formation in the load region and radio frequency (RF) breakdown in the slow wave structure (SWS) section, an X-band MILO is presented and investigated numerically with KARAT code. The design idea is briefly presented and the simulation results are given and discussed. In the simulation, HPM is generated with peak power of 3.4 GW, maximum electric field of about 1 MV/cm, and peak power conversion efficiency of 14.0%, when the voltage is 559.1 kV and the current is 43.2 kA. The microwave frequency is pure and falls in the X-band of 9.0 GHz. The theoretical investigation and the simulation results are given to prove that the anode plasma formation and the RF breakdown can be effectively avoided or at least minimized, respectively.

The Effect of Convection on Microstructures and Interface Stability of Al-4.5wtpctCu Alloy Made by Directional Solidification

The effect of convection and diffusion introduced by sample size and curvatures on microstructures, stability of solid/liquid (S/L) interface, and solute distribution in an Al-4.5wtpctCu alloy was studied with growth velocity between 1 and 96 μm/s. The experiments were undertaken via directional solidification within coaxial tubes of a variety of diameters. The intent was to achieve the same temperature gradient and growth velocity but different magnitudes of convection. The results indicate that with respect to planar growth, the growth front of the smallest diameter samples (1 mm) in the inner tube is less stable than that of large diameter (7.3 mm). The samples with the smallest diameter have weak convection and show no planar growth. Because of the reduced convection, the transition from cellular-to-dendritic growth occurs at relatively slow growth rate (4 μm/s). Increasing sample sizes results in formation of a planar growth front. The interface position of the inner smaller samples is located behind that of the outer larger samples, and more interfacial Cu segregation is found in smaller samples than in larger samples because of convection reductions in small samples. The change of the curvature of the samples affects the convection. At certain conditions, small curvature results in reduced convection. Samples with smaller sizes and therefore reduced convections have larger S/L curvatures than the larger samples.

Concept of a Pitot tube able to detect blockage by ice, volcanic ash, sand and insects, and to clear the tube

A conceptual coaxial Pitot tube (PT) has been developed using fiber optic sensors combined with actuators to monitor and maintain its correct operation under different environmental conditions. Experiments were performed showing that the dynamic and static tubes can be cleared of ice. It was also demonstrated that the dynamic tube could be cleared of dust and sand which was not the case for the static tube in the coaxial configuration. An approach was proposed to overcome this problem involving a conventional configuration where the static tube was operated independently orthogonal to the dynamic tube, and a second set of sensors and actuators was used. Sensors and associated actuators were developed for temperature and intensity for a linear PT. The aim of this work is to propose a solution for a problem that has caused the loss of the lives of many passengers and crew of aircraft. Resources were not available to test a full implementation of a PT incorporating the proposed modifications.

Comparative Study of the Surface Cleaning for Ar-/He-Based Plasma Jets at Atmospheric Pressure

In this study, an atmospheric-pressure He/O2 or Ar/O2 plasma jet is generated by a specially designed equipment with two coaxial quartz tubes and double power electrodes to remove lubricants from the surfaces of metals. The experimental results indicate that the cleaning performance is much better in the Ar/O2 plasma jet than in the He/O2 plasma jet under the same input power and O2 mixing ratio. It is found that more electron, more atomic oxygen, and more metastable Ar atoms generated in the Ar/O2 plasma jet result in better cleaning performance. In the He/O2 plasma jet or the Ar/O2 plasma jet, there exists an optimum O2 mixing ratio for a certain input power, at which the desirable cleaning performance can be received. And the highest removing rate is 1259.8 ng/s when the 2.1% O2 in the Ar plasma jet at an input power of 6 W. It is considered that atomic oxygen can be generated most efficiently under this optimum O2 mixing ratio.

An open port sampling interface for liquid introduction atmospheric pressure ionization mass spectrometry.

A simple method to introduce unprocessed samples into a solvent for rapid characterization by liquid introduction atmospheric pressure ionization mass spectrometry has been lacking. The continuous flow, self-cleaning open port sampling interface introduced here fills this void. The open port sampling interface used a vertically aligned, co-axial tube arrangement enabling solvent delivery to the sampling end of the device through the tubing annulus and solvent aspiration down the center tube and into the ionization source of the mass spectrometer via the commercial APCI emitter probe. The solvent delivery rate to the interface was set to exceed the aspiration rate, creating a continuous sampling interface along with a constant, self-cleaning spillover of solvent from the top of the probe. Using the open port sampling interface with positive ion mode APCI and a hybrid quadrupole time-of-flight mass spectrometer, rapid, direct sampling and analysis possibilities are exemplified with plastics, ballpoint and felt tip ink pens, skin, and vegetable oils. These results demonstrated that the open port sampling interface could be used as a simple, versatile and self-cleaning system to rapidly introduce multiple types of unprocessed, sometimes highly concentrated and complex, samples into a solvent flow stream for subsequent ionization and analysis by mass spectrometry. The basic setup presented here could be incorporated with any self-aspirating liquid introduction ionization source (e.g., ESI, APCI, APPI, ICP, etc.) or any type of atmospheric pressure sampling-ready mass spectrometer system. The open port sampling interface provides a means to introduce and quickly analyze unprocessed solid or liquid samples with the liquid introduction atmospheric pressure ionization source without fear of sampling interface or ionization source contamination.