Showing papers in "Advances in cryogenic engineering in 1986"
TL;DR: In this article, the authors compared three types of pulse tubes with each other and with common refrigerators such as Joule-Thomson and Stirling refrigerators, and compared the intrinsic behavior of the different types from temperatures of about 30 K to 300 K.
Abstract: Pulse tube or thermoacoustic refrigerators require only one moving part—an oscillating piston or diaphragm at room temperature. Refrigeration occurs within a tube connected to the pressure wave generator when the thermal relaxation time between gas and tube is comparable to a half period. Three types have been discussed in the literature recently by Gifford, by Mikulin, and by Wheatley. A record low temperature of 60 K was achieved in our work using a single stage pulse tube similar to that of Mikulin. Previously 105 K was the lowest temperature achieved. Because of only one moving part, all three types have the potential for long life, but their efficiency and intrinsic limitations have never been investigated. This paper compares the three types with each other and with common refrigerators such as Joule-Thomson and Stirling refrigerators. An apparatus is described which can measure the intrinsic behavior of the different types from temperatures of about 30 K to 300 K. Overall cycle efficiency as well as sources of loss such as conduction and regenerator ineffectiveness are discussed and the advantages of various phase shifting techniques to increase refrigeration capacity are compared.
121 citations
TL;DR: In this article, the authors describe the development, from a previously proven design approach, of a robust and simple Stirling cycle cooler with long life potential, for use in a spacecraft borne infra-red radiometer.
Abstract: This paper describes the development, from a previously proven design approach, of a robust and simple Stirling cycle cooler with long life potential. The need for a closed cycle refrigerator for use in a spacecraft borne infra-red radiometer is explained. The refrigerator is to supply 1 watt of cooling at 80 K for less than 80 watts of input power, be able to survive the launch environment and subsequently run for 26000 hours. Clearance seals achieved with a spring suspension developed from earlier space proven mechanisms have led to the production of a linear split Stirling cycle machine with no apparent life limiting features. A servo control system, in conjunction with moving coil motors and LVDT position sensors, permits running of balanced pairs of mechanisms. The working fluid, helium at a pressure of 1.2 MPa, is contained within titanium bodies having gold O-ring seals. A vacuum bakeout procedure, based upon experience and outgassing trials, reduces residual contaminant release to acceptable levels. A prototype refrigerator has been subjected to a vibration test and has subsequently run for 6000 hours with no detectable change in performance.
60 citations
TL;DR: In this paper, a new correlation using a fundamental equation (equation of state) explicit in Helmholtz energy, which provides for the calculation of derived thermodynamic properties by differentiation, is presented.
Abstract: The published experimental data on the thermodynamic properties of neon have been used as the basis for a new thermodynamic property formulation for neon. The new correlation uses a fundamental equation (equation of state) explicit in Helmholtz energy, which provides for the calculation of derived thermodynamic properties by differentiation. The fundamental equation for neon is a subset of a larger comprehensive function which has also been used in developing thermodynamic property formulations for other fluids of cryogenic interest including oxygen, nitrogen, argon, and ethylene. In addition, new equations for the vapor pressure, saturated liquid density, and saturated vapor density are presented. The formulation presented here may be used to calculate pressure, density, temperature, enthalpy, entropy, internal energy, isochoric and isobaric heat capacities, and velocity of sound for neon. Summary comparisons of properties calculated with the new formulation for neon with selected experimental data are included to verify the accuracy of the fundamental equation for calculation of thermodynamic properties.
49 citations
TL;DR: The performance of the Oxford Cryocooler is summarised in this paper, where the power budget for the compressor and the losses in the displacer are discussed and Graphs of the cold end temperature vs. compressor input power and cooling power are presented.
Abstract: The performance of the Oxford Cryocooler is summarised. This cooler has been developed for space use by the Rutherford Appleton Laboratory and the Departments of Atmospheric Physics and Engineering Science at Oxford University. The design goal of 1/2 watt of cooling power at 80 K for 30 W electrical input power has been exceeded by a substantial amount. The power budget for the compressor and the losses in the displacer are discussed. Graphs of the cold end temperature vs. compressor input power and cooling power are presented.
41 citations
TL;DR: In this paper, the properties of aluminum-lithium alloy 2090-T8E41 were evaluated at 298 K, 77 K, and 4 K. This alloy exhibits substantially improved properties at cryogenic temperatures; the strength, elongation, fracture toughness and fatigue crack growth resistance all improve simultaneously as the testing temperature decreases.
Abstract: The mechanical properties of aluminum-lithium alloy 2090-T8E41 were evaluated at 298 K, 77 K, and 4 K. Previously reported tensile and fracture toughness properties at room temperature were confirmed. This alloy exhibits substantially improved properties at cryogenic temperatures; the strength, elongation, fracture toughness and fatigue crack growth resistance all improve simultaneously as the testing temperature decreases. This alloy has cryogenic properties superior to those of aluminum alloys currently used for cryogenic applications.
31 citations
TL;DR: In this article, the authors investigated the magnetocaloric properties of the Ericsson type magnetic refrigerators in the range below 77 K and reported the first report of experimental results of the refrigeration character.
Abstract: We investigated the Ericsson type magnetic refrigerators in the range below 77 K This is the first report of experimental results of the refrigeration character, especially the magnetocaloric character of RAl2, where R is a rare earth atom
31 citations
TL;DR: In this paper, a study of forced convection heat transfer in superfluid helium (He II) is initiated to better understand the physical behavior of this process and to compare it with the more familiar He II heat transfer mechanism of internal convection.
Abstract: A study of forced convection heat transfer in superfluid helium (He II) is initiated to better understand the physical behavior of this process and to compare it with the more familiar He II heat transfer mechanism of internal convection. An experimental assembly is designed to achieve fluid flow by a motor-driven hydraulic pump which utilizes two stainless steel bellows. Each bellows is connected to one end of a copper tube, 3 mm in diameter and 2 m long. The system allows measurements of one dimensional heat and mass transfer where the measured quantities include: temperature profile and pressure drop. The variable quantities are the helium bath temperature, flow velocity and heat input. The helium bath is held at 1.8 K and under saturation pressure. The flow tube is heated at the middle and the flow velocity is varied up to 97 cm/s. The helium pressure is monitored at both ends of the tube and a friction factor is estimated for He II. Temperature measurements are made at seven evenly spaced locations along the tube. The experimental temperature profile is compared with a numerical solution of an analytical model developed for the problem under study.
27 citations
TL;DR: In this paper, a gas-gap heat switch is constructed from OFHC copper, separated by a thin gap which is filled with helium gas from a heater-activated getter, and the temperature of the getter controls the pressure of the gas in the switch.
Abstract: A cryogenic thermal switch has been designed, assembled, and tested over a range of temperatures. The switch has no moving parts and has a thermal resistance which can vary about a factor of 3000 on demand by the actuation of a heater. The switch resistance can be varied continuously between “on” and “off” values. This device is a gas-gap heat switch filled and evacuated by a heater-activated getter. The switch contains two end pieces constructed from OFHC copper, separated by a thin gap which is filled with helium gas from the getter. The temperature of the getter controls the pressure of the gas in the switch. A thermal model of the device was set up to predict its performance for various temperatures and gas pressures. Tests down to liquid-helium temperatures verified the predicted resistance ratios between “off” and “on”.
23 citations
TL;DR: In this paper, the total heat transfer from approximately to 77 K was experimentally studied for a series of different arrangements of multilayer insulation (MLI) on black painted and aluminum taped copper surfaces.
Abstract: The total heat transfer from approximately to 77 K was experimentally studied for a series of different arrangements of multilayer insulation (MLI) on black painted and aluminum taped copper surfaces. The heat flux as a function of the number of MLI layers and of the overall vacuum level was measured. The flux to a painted surface was 24.7 W/m2 with no MLI and 0.64 W/m2 with 30 layers, both at a vacuum of 1.5 × 10−5 torr. The corresponding values to a taped surface were 4.8 W/m2 and 0.52 W/m2. At 1.5 × 10−5 torr, the use of aluminum tape permits one to use approximately one-half as many layers for the same heat flux. The heat flux was measured for six insulation systems from 1.5 x 10−5 torr to ∿ 1 × 10−3 torr. The temperature distribution through the MLI was measured as a function of vacuum level. It was deduced that the apparent thermal conductivity increases with the distance from the cold surface. The effect of cracks in a paint-MLI system was studied by cutting 6-mm wide cracks through a 90-layer blanket. The heat load increased by more than three times the value calculated from the exposed area only.
21 citations
TL;DR: The formation of the stoichiometric Nb3Al phase by a solid state reaction of thin Nb/Al multilayers is basically determined by the intermediate formation of a metastable NbAl solid solution as mentioned in this paper.
Abstract: The formation of the stoichiometric Nb3Al phase by a solid state reaction of thin Nb/Al multilayers is basically determined by the intermediate formation of a metastable NbAl solid solution. If the nucleation of Nb2Al is avoided, the homogeneity range of the A15 phase can be extended metastably up to about 28 at.% Al. The temperature dependence of the metastable Al-rich A15 phase boundary can be determined by the respective (free) enthalpy curves of the A15 and the bcc phase calculated from the phase diagram.
21 citations
TL;DR: In this article, the HERA proton magnet ring must provide 6.775 kW of refrigeration at 4.3 K plus 20.5 g/s of helium at 2.5 bar and 4.5 K for leads cooling.
Abstract: Each of the three refrigerators for the HERA proton magnet ring must provide 6.775 kW of refrigeration at 4.3 K plus 20.5 g/s of helium at 2.5 bar and 4.5 K for leads cooling and 20 kW of refrigeration at 40–80 K for shield cooling.
TL;DR: In this article, a new fundamental equation for correlation of thermodynamic property data for fluids is presented, which is explicit in Helmholtz energy and is readily adapted to system analysis applications.
Abstract: A new fundamental equation for correlation of thermodynamic property data for fluids is presented. The fundamental equation (equation of state) is explicit in Helmholtz energy and is readily adapted to system analysis applications. All thermodynamic properties are derived by differentiation of the fundamental equation. A comprehensive function containing up to 100 terms provides the basis for the correlation. The fundamental equation for a specific fluid is a subset of this comprehensive function. The individual terms of the comprehensive function may be easily changed by varying exponents of the functions of the independent variables. Functions for the calculation of derivative properties are given, and the incorporation of calorimetric information via ideal gas heat capacity equations is discussed. Applications to fluids of cryogenic interest include oxygen, nitrogen, argon, ethylene and neon. Coefficients for calculation of thermodynamic properties of these fluids taken from formulations published elsewhere are given.
TL;DR: In this paper, an overview of recent neutron irradiation experiments on superconductors is presented, focusing on those materials which are considered as candidates for fusion reactor magnets, and to an irradiation environment which is closely related to the magnet operating conditions over the lifetime of a fusion reactor.
Abstract: An overview of recent neutron irradiation experiments on superconductors is presented. Special attention is paid to those materials which are considered as candidates for fusion reactor magnets, and to an irradiation environment which is closely related to the magnet operating conditions over the lifetime of a fusion reactor. The results on a variety of NbTi superconductors may be summarized as follows: 1) the influence of irradiation temperature is very small, if thermal cycles following low temperature irradiations are included; 2) the influence of the metallurgical starting conditions becomes very small at high fields (≥ 7 T) indicating saturation effects for flux pinning and and an increasing influence of Hc2 on critical current densities jc; 3) the overall degradation of jc does not exceed 20% over the lifetime of a fusion magnet. The experimental results on A15 superconductors, in particular Nb3Sn with small additions of Ti, show the normal increase of critical current densities with neutron fluence followed by a sharp decrease of jc. However, the peak of jc is shifted to much lower fluences in the alloyed samples as compared to pure Nb3Sn. Finally, a comment on the resistivity change of “magnet” copper is made indicating that a considerable increase of resistivity (~60% at 8 T) has to be taken into account, if “reasonable” operating conditions of the magnet (i.e. only occasional annealing cycles to room temperature) are taken as a basis.
TL;DR: In this article, the authors developed a NbTi composite conductors with very fine filaments for the Superconducting Super Collider (SSC), which required 40,000 or more filaments.
Abstract: The present interest in NbTi composite conductors with very fine filaments has developed because of the requirements of the Superconducting Super Collider. The Fermilab Tevatron utilizes wire with 8 μm diameter filaments; the SSC may require wire with less than 3 μm diameter filaments. The reduction in filament diameter means that, while Fermilab wire required 2,000 filaments, a similar size wire for the SSC will require 40,000 or more filaments. Conventional techniques of billet assembly will no longer suffice.
TL;DR: For the measurement of temperatures between 1 K and 300 K, there are available a wide variety of sensors and several dc, ac, and pulse techniques as mentioned in this paper, and the choice of measurement system depends on a number of factors, including the required precision, cost, speed of response, sensor size and availability, and the effect of high magnetic fields.
Abstract: For the measurement of temperatures between 1 K and 300 K, there are available a wide variety of sensors and several dc, ac, and pulse techniques. The choice of measurement system depends on a number of factors, including the required precision, cost, speed of response, sensor size and availability, and the effect of high magnetic fields. When the most significant of those factors have been identified and quantified, it should then be possible to select the thermometer(s) that best meet those requirements. To aid in the selection procedures, some pertinent characteristics of a number of useful thermometers are presented. A brief discussion of high magnetic field sensors useful at low temperatures is included.
TL;DR: In this article, a three-parameter pseudo-cubic equation of state is proposed to describe the critical isotherms of argon, carbon dioxide, and water.
Abstract: A three-parameter pseudo-cubic equation of state is proposed. The pseudo-cubic equation of state is a sixth power polynomial equation in volume, which may be solved in a manner similar to conventional cubic equations. The proposed equation has a maximum of three positive roots. The proposed equation has successfully described the critical isotherms of argon, carbon dioxide, and water. The three adjustable equation-of-state parameters have been treated both as a function of temperature and as constants. Performance comparisons with other three parameter equations of state are given. The results of the comparisons indicate the proposed equation or state to be superior in a number of ways, especially in the prediction of liquid densities. The proposed equation of state has also been successfully applied to the correlation of high pressure vapor-liquid equilibria of cryogenic fluid mixtures.
TL;DR: In this article, experimental investigations of liquid helium heat transfer from a channel configuration are reported, where four model test sections are constructed each consisting of a rectangular cross section channel 127 mm in length and 12.7 mm wide with a narrow gap of dimension 0.5, 1, 2 and 3 mm.
Abstract: Experimental investigations of liquid helium heat transfer from a channel configuration are reported. Four model test sections are constructed each consisting of a rectangular cross section channel 127 mm in length and 12.7 mm wide with a narrow gap of dimension 0.5, 1, 2 and 3 mm respectively. The channels are open at both ends to permit natural circulation of the helium coolant. Variables within the experiment include bath temperature and channel orientation. Values for the peak heat flux are compared to available correlations. An empirical fit to the angular dependence of the peak heat flux is suggested.
TL;DR: In this paper, the diffusion process between Cu and Nb-Ti has been studied in a well-bonded composite, and three distinct layers were seen, two of these were intermetallic compounds of approximate composition Ti2Cu7 and (TixNb1-x)Cu, where x is ~ 0.5.
Abstract: The diffusion process between Cu and Nb-Ti has been studied in a well-bonded composite. Interdiffusion studies were performed between 500° and 650°C and three distinct layers were seen. Two of these were intermetallic compounds of approximate composition Ti2Cu7 and (TixNb1-x)Cu, where x is ~ 0.5. A significant diffused region of Cu with grain boundary precipitation was seen in the NbTi solid solution. The growth rates of the layers were quite well-behaved and diffusion parameters for the process are presented.
TL;DR: The TORE SUPRA refrigerator design and manufacture have both been governed by several strict design criteria as mentioned in this paper, including reliable operation over long periods (8,000 hours per year), pulsed thermal loads at 1.75 K and 4.0 K (every 4 minutes), fully automatic control in the various operating modes, low operating costs and acting as a technical demonstration so that larger future designs could be extrapolated from this base.
Abstract: The TORE SUPRA refrigerator design and manufacture have both been governed by several strict design criteria. These include reliable operation over long periods (8,000 hours per year), pulsed thermal loads at 1.75 K and 4.0 K (every 4 minutes), fully automatic control in the various operating modes, low operating costs and acting as a technical demonstration so that larger future designs could be extrapolated from this base. The paper reviews these criteria, and presents the current status.
TL;DR: In this article, the main purpose of the present paper is to discuss the magnetic and thermal properties necessary for these refrigerants and to report recent investigations, which can be expediently divided into two groups, one for the Carnot type magnetic refrigerator below 20 K and the other for the Ericsson-type refrigerator.
Abstract: In development of the magnetic refrigerator, an important problem is selection of magnetic materials as refrigerants. The main purpose of the present paper is to discuss the magnetic and thermal properties necessary for these refrigerants and to report recent investigations. Magnetic refrigerants can be expediently divided into two groups, one for the Carnot-type magnetic refrigerator below 20 K and the other for the Ericsson-type refrigerator. The required physical properties of refrigerants in each type of the magnetic refrigerator are first discussed. And then, the results of recent investigations on the magnetic, thermal and magnetocaloric characters of several promising magnetic refrigerants are shown. Finally, a brief prospect of the magnetic refrigerants and refrigerators is given.
TL;DR: In this article, an attempt has been made to increase the chemical homogeneity of Nb3Sn layers in a conventional bronze-process composite with excess Sn through extended time reaction heat treatments at high temperature (> 750°C).
Abstract: An attempt has been made to increase the chemical homogeneity of Nb3Sn layers in a conventional bronze-process composite with excess Sn through extended time reaction heat treatments at high temperature (> 750°C). This study has included measurements of Jc, Bc2, local chemical composition, and grain size and morphology. The local bronze/Nb ratio has been found to influence the local chemical composition even after extensive reaction times. The dependence of Bc2 on local composition variation is uncertain. Critical current densities at high magnetic fields have been improved up to 50% over those obtained for heat treatments at 700°C. These increases are attributed to increased values of Bc2, but they are accompanied by a reduction in JQ below 12 T. Drastically reduced Jc is found with overaging, despite a quite high value of Bc2. Grain size is found to increase strongly with heat treatment temperature and a large variation is found above 750°C. Equiaxed morphologies have been found at all temperatures between 650°C and 800°C.
TL;DR: In this article, the authors developed a test facility for superconducting magnet suspension systems and multi-layer insulation (MLI) systems with a functional end in which test components of differing geometrical configurations could be installed and evaluated.
Abstract: Heat leak measurements of superconducting magnet suspension systems, and multi-layer insulation (MLI) systems are important for the optimum design of magnet cryostats. For this purpose, a versatile cryogenic test facility was developed having a functional end in which test components of differing geometrical configurations could be installed and evaluated.
TL;DR: In this paper, the system RNi2 (R=Dy, Ho and Er) is verified to be promising as magnetic refrigerant in the wide temperature range below 35 K.
Abstract: The system RNi2 (R=Dy, Ho and Er) is verified to be promising as magnetic refrigerant in the wide temperature range below 35 K. We prepared these compounds and measured the temperature variation of the specific heat and the magnetization in magnetic field up to 5 T. From these results we determined the total entropy and the magnetic entropy change by a magnetic field. It is made clear that these compounds are applicable to the magnetic refrigerants using an Ericsson-type cooling cycle below 35 K.
TL;DR: In this article, a new type of non-contacting direct current meter that can measure large currents (in this case up to 25 kA) with an accuracy of 0.1% of full scale is presented, consisting of a superconducting toroidal transformer that encloses the unknown current flowing through the aperture, a shielded field sensing coil which is connected to the transformer but positioned in a weak magnetic field, and a control unit that presents a reading of the measured current.
Abstract: An accurate measurement of direct currents in closed superconducting circuits is often difficult to perform, especially if the circuit is exposed to time dependent and/or high stationary magnetic fields. In this paper a new type of non-contacting direct current meter that can measure large currents (in this case up to 25 kA) with an accuracy of 0.1% of full scale is presented. The device consists of a superconducting toroidal transformer that encloses the unknown current flowing through the aperture, a shielded field sensing coil which is connected to the transformer but positioned in a weak magnetic field, and a control unit that presents a reading of the measured current.
TL;DR: In this paper, the heat transfer from thin wires to He II has been investigated at low hydrostatic pressures on ground and at milligravity on board of the NASA KC-135 aircraft.
Abstract: The heat transfer from thin wires to He II has been investigated at low hydrostatic pressures on ground and at milligravity on board of the NASA KC-135 aircraft. The peak heat flux density at low gravity is found to be less than 10% lower than the lowest laboratory values, the recovery heat flux density, however, about 50%. For the recovery heat flux density a large scatter was observed, indicating a significant drop of this quantity in the milligravity region.
TL;DR: In this article, the time evolution of a normal zone and propagation of the normal front are calculated for a cryogenically stable superconductor resembling the configuration of a UW Energy Storage Conductor laboratory prototype.
Abstract: The time evolution of a normal zone and propagation of the normal front are calculated for a cryogenically stable superconductor resembling the configuration of a UW Energy Storage Conductor laboratory prototype of 13.5 cm diameter stabilized with 400 RRR A1 carrying 765 kA in a field of 3.5 T. The coupled heat transport and current diffusion equations with temperature dependent physical properties are solved numerically. Both radial adiabatic and superfluid helium cooling cases are treated. A factor of four enhancement in the propagation velocity occurs in the adiabatic case and a transient propagation velocity in the superfluid helium cooling case exists because of the heat generation due to the transient non-uniform current distribuion in the stabilizer.
TL;DR: In this paper, the magnetic entropy of Dy3AlsO12 (DAG) was investigated for the Carnot-type magnetic refrigerator, and the results showed that DAG is a more useful refrigerant than GGG for the refrigerator having a broad temperature span from ~20 K to 4.2 K.
Abstract: We investigated the magnetic entropy of Dy3AlsO12 (DAG), which is one of the most promising refrigerants for the Carnot-type magnetic refrigerator. In the present investigation we measured the specific heat in zero magnetic field and the magnetization as a function of temperature and magnetic field, and from the analysis of these experimental results, the magnetic entropy change ΔSJ and entropy S are obtained. The values of ΔSJ and S of DAG were compared with those of Gd3Ga5O12(GGG), which is frequently used as a refrigerant for the Carnot-type magnetic refrigerator. The g-factor of the magnetic ion in DAG was shown to play a more important role in determining ΔSJ near 20 K than the J-value. It is therefore clear that DAG is a more useful refrigerant than GGG for the Carnot-type refrigerator having a broad temperature span from ~20 K to 4.2 K.
TL;DR: In this paper, the authors have succeeded in manufacturing long lengths of NbTi ultra-fine filament wires in which 50 Hertz losses are strongly reduced by using a Cu-30 At % Ni matrix between the filaments.
Abstract: Thanks to technological progress carried out in our Company for the last ten years, we have succeeded in manufacturing long lengths of NbTi ultra-fine filament wires in which 50 Hertz losses are strongly reduced. These results have been obtained by manufacturing the wires with a Cu-30 At % Ni matrix between the filaments, by reducing the filament diameter well below .5 micron and by reducing the twist pitch length to 4 times the wire diameter.
TL;DR: In this paper, a system composed of a vertical pipe and a long horizontal one was filled with Freon-113 as the test medium, and the conditions under which geysering occurred were obtained experimentally.
Abstract: In order to simulate geysering phenomena in LNG pipelines, a system composed of a vertical pipe and a long horizontal one was filled with Freon-113 as the test medium. When the system was heated by electrical heaters along the tube walls, geysering was observed under some conditions. Parameters, including feed system, pipe wall heat fluxes, and liquid velocity, were varied. The effects of these factors on geysering were studied. It was found that the geysering was characterized by the storage and release of thermal energy in the liquid column and in the long horizontal line. The conditions under which geysering occurred were obtained experimentally. The region where geysering occurred was shown as a map of heat flux and liquid velocity.
TL;DR: In this article, a Claude cycle helium refrigerator (5W at 4.5K) with two-stage expansion micro-turbines has been developed for the application of NMR-CT and Josephson computers.
Abstract: In the field of small size helium refrigerators, need for a maintenance free and vibration free system is rapidly increasing, especially for the application to cryoelectronic devices such as NMR-CT and Josephson computers. To meet this need, we have been developing a Claude cycle helium refrigerator (5W at 4.5K) with two-stage expansion micro-turbines. Other than the micro-turbines, compact size perforated- plate heat exchangers and a single-stage screw type compressor have been developed for the system. This paper describes design and test results of the major components of the system with an emphasis on the micro-turbine performance.