A review of experimental methods for solid solubility determination in cryogenic systems

Over the past years, there have been a number of serious explosions in air industry, which have resulted in workers injuries and fatalities. At the same time, there has been an increase in the use of air separation products for industrial activities.The quality of air entering an air separation plant is of crucial importance for its safe and reliable operation and the interest in the solubility data of solids in cryogenic liquid solvents is closely connected to the problem of impurities accumulation in the process plant and storage tanks. Such accumulations, especially in liquid oxygen, may cause fouling and blockage in heat exchangers and pipelines and they may eventually cause serious explosions. For this reason the air contaminants composition in liquid oxygen must be determined with great precision.This paper aims at reviewing experimental methods for determining the solubility of solid compounds that may be present in the cryogenic liquefaction processing of air distillation. A review of the literature data on solubility of solids in liquid oxygen and nitrogen is included as well.Emphasis is given to the difficulties in setting-up measuring apparatuses working at extreme conditions, i.e. low compositions and low temperatures.     

Recommended values for the thermal conductivity of aluminium of different purities in the cryogenic to room temperature range, and a comparison with copper

The thermal conductivity of pure aluminium at cryogenic temperatures varies by many orders of magnitude depending on purity and treatment, and there is little information in the literature on the likely values to be obtained for samples of a given purity. A compilation of measurements from the literature has been assembled and used to provide recommended ranges of values for aluminium of different purities (4N, 5N and 6N) in the normal (non superconducting) state. The number of direct thermal conductivity measurements is too limited to be used alone. Electrical resistivity measurements have thus also been used by converting to thermal conductivity using the Wiedemann-Franz law, which is shown to be valid. Since low temperature measurements can easily be extrapolated to higher temperatures, the results cover the range from 1.2 K (the superconducting transition temperature) to room temperature. Values for 5N purity copper have also been examined in a similar manner, to allow a comparison between the two materials. The main application of these results is in the design of cryogenic thermal links; a discussion of the advantages and disadvantages of both materials for this use is given. The use of silver is also investigated briefly. Trends in the behaviour of the conductivity of aluminium in the superconducting state (to temperatures as low as 50 mK) are also discussed.     

Thermal design of the CFRP support struts for the spatial framework of the Herschel Space Observatory

Thermal finite element (FE) models, of low thermal conductance struts which are required to provide support for the low temperature components of the Herschel Space Observatory, have been validated by measurements at temperatures below 20 K. The Herschel Space Observatory structure is introduced. FE modelling of two designs of support strut is briefly discussed and the final designs presented. Validation of the design models was made in two experiments. The first of these provided specific thermal conductivity data for component CFRP materials, whose composition was initially designed on the basis of data available in the literature. The second experiment was performed to confirm the thermal conductance (Q′/ΔT), of the completed struts. The validation test rigs are described together with details of the experimental methods employed. Values of conductance were at the level of 5 × 10⁻⁵ W/K at a mean temperature of 6 K. The measured data are presented and discussed with reference to the thermal models. Sources of measurement inaccuracy, are also discussed.     

Performance evaluation of the ITER Toroidal Field Model Coil phase I: Part 2: M&M analysis and interpretation

The ITER Toroidal Field Model Coil (TFMC), a large (2.7 m × 3.8 m × 0.8 m) superconducting (Nb₃Sn) DC coil designed and constructed in collaboration between EU industries and laboratories coordinated by EFDA, has been tested during 2001 in the TOSKA cryogenic facility at Forschungszentrum Karlsruhe, Germany, achieving the nominal 80 kA at 7.8 T peak field and 86 MJ stored energy as a standalone coil (Phase I). The results of the current sharing temperature (T_CS) measurements at I=80, 69 and 57 kA, presented in a companion paper (Part 1), are evaluated here using the M&M code. The critical properties best fitting the experimental voltage-inlet temperature characteristic of the P1.2 pancake are deduced from the TFMC data under the assumption of an ideal collective behaviour of the strands. The TFMC results are compared first with the expected conductor performance, showing that at the maximal current the performance was borderline with what was expected, while at the minimal current tested it was better than expected. Second, they are compared with the performance of the single strand as measured in the lab, showing that, in order to reproduce the TFMC data, one has to invoke that some degradation, larger at higher current, occurred when going from the strand to the cable.     

Algorithmes simples pour l'évaluation rapide des propriétés des mélanges binaires de fluides frigorigènesSimple algorithms for the rapid evaluation of properties of binary refrigerant mixtures

The paper describes a calculation to predict equilibrium thermodynamic properties of binary refrigerant mixtures and provides simple algorithms with only a few calculation steps (1400) for small pocket calculators. The Peng-Robinson equation of state is chosen; the data needed are critical temperature and pressure and acentric factor for pure refrigerants and the interaction parameter which characterizes the binary mixture under consideration. The proposed programs lead to the calculation of the equilibrium properties (temperatures, pressure and phase compositions) and of the enthalpy h, entropy s and specific v of each phase with a precision of the order of 1–2% for h, s and v_vapour and 5% for v_liquid. The main interest of such algorithms is to provide a tool for those involved in the estimation of performance of refrigerating equipment or heat pumps under given working conditions with a given refrigerant mixture. This interest is ever more acute due to the fact that the utilization of mixtures is one of the means of reducing CFC emissions of refrigerants which deplete the ozone layer.     

A coupled numerical analysis of shield temperatures, heat losses and residual gas pressures in an evacuated super-insulation using thermal and fluid networks: Part II: Unsteady-state conditions (cool-down period)

This paper analyses the cool-down period of a 300 L super-insulated cryogenic storage tank for liquid nitrogen. Storage tank and evacuated shields are the same as described in part I of this paper where stationary states were investigated. The aim of the present paper is to introduce thermal resistance networks as a tool to quantitatively understand and control also unsteady-states like cool-down of super-insulations. Numerical simulations using thermal resistance networks have been performed to determine time dependence of local shield temperatures and heat loss components. Coupling between radiation and solid conduction is investigated under these conditions. Using the numerical results, we have checked an experimental method suggested in the literature to separate heat losses through the insulation from losses through thermal bridges by measurement of unsteady-state evaporation rates. The results of the simulations confirm that it takes the outer shields much longer to reach stationary temperature; cool-down does not proceed uniformly in the super-insulation. Coupling between different heat transfer modes again is obvious. Thermal emissivity is important also during the early phase of cool-down. Using the obtained numerical results, the experimental method to separate heat loss components could only roughly been confirmed for thick metallic foils.     

Experimental investigation and thermodynamic calculation of the Ga–Sb–Zn phase diagram

Phase equilibrium of ternary Ga–Sb–Zn system was investigated by applying CALPHAD method and using literature thermodynamic data for constitutive binary systems. The liquidus surface and isothermal section at 673 K were calculated. Calculated results were verified experimentally on the alloys samples with the compositions corresponding to the characteristic vertical sections: SbZn (1:1)–Ga; GaZn(1:1)–Sb; and GaSb(1:1)–Zn. Phase transitions temperatures were determined by differential thermal analysis and differential scanning calorimetry. Microstructure and phase composition investigation were investigated by using scanning electronic microscopy with energy dispersive spectrometry. The experimental and analytical results showed good agreement, concerning the temperatures of phase transitions and phase compositions of alloys concerned.     

Forced flow boiling heat transfer of liquid hydrogen for superconductor cooling

Heat transfer from inner side of a heated vertical pipe to liquid hydrogen flowing upward was first measured at the pressure of 0.7 MPa for wide ranges of flow rates and liquid temperatures. The heat transfer coefficients in non-boiling regime for each flow velocity were well in agreement with the Dittus–Boelter equation. The heat fluxes at the inception of boiling and the departure from nucleate boiling (DNB) heat fluxes are higher for higher flow velocity and subcooling. It was found that the trend of dependence of the DNB heat flux on flow velocity was expressed by the correlation derived by Hata et al. based on their data for subcooled flow boiling of water, although it has different propensity to subcooling.     

K-value predictions for the methane-ethane-propane system

Vapour-liquid equilibrium distribution coefficients at widely ranging pressures, temperatures, and compositions are essential data for process engineering calculations in the natural gas separation and petroleum processing industries. Computational methods for the accurate prediction of these data using only pure component properties are presented in this paper. The validity of the method has been tested for the system methane-ethane-propane at low temperatures and high pressures. The agreement between the predicted values and the corresponding experimental data taken from the literature illustrates the accuracy of the prediction method and justifies its applicability to working separation systems.     

A new apparatus for mechanical Q-factor measurements between 5 and 300 K

Today’s laser interferometric gravitational wave detectors are sensitivity limited by thermal noise of the optical components within the detection band of about 0.1-1 kHz. Cooling down these parts to cryogenic temperatures is a promising technique to increase the sensitivity of the gravitational wave detectors by at least one to two orders of magnitudes. Cooling substantially increases the material Q-factor contributing to reduced thermal noise. This article describes a new cryogenic apparatus which allows the measurement of the mechanical Q-factor - as a measure of internal losses - in a temperature range from 5 K up to 300 K. The requirements for cryogenic Q-factor measurements and their realization are shown. The measuring technique as well as the key parameters are discussed. Exemplary, measurements on crystalline quartz and silicon (1 0 0) are given to characterize the setup.     

Crystallization of lithium magnesium zinc silicates

Subsolidus phase equilibria in the system Li₄SiO₄-Zn₂SiO₄-Mg₂SiO₄-SiO₂ have been studied and seventeen quaternary subsolidus phase volumes identified. The crystalline orthosilicate phases are solid solutions, and their compositions or ranges of composition in the various quaternary volumes have been determined. Perspective drawings are used to show the relationship between quaternary subsolidus phase volumes at about 850°C. An unusual feature of the phase distribution is that all quaternary compositions, even those highest in silica content, will yield a ternary -type orthosilicate phase at equilibrium. This phase is structurally related to Li₃PO₄. Examples are given of the calculation of the phase composition at equilibrium for various quaternary volumes.The crystallization of quaternary glasses is compared with the equilibrium phase diagram. At crystallization temperatures approaching the solidus, the equilibrium phases are readily obtained. At lower temperatures, about 500 to 600°C, metastable phases are formed. These include lithium disilicate having a variable LiSi ratio, the Proto - phase which has a wurtzite-like structure and metastable orthosilicates. These phases persist indefinitely at lower temperatures, but readily convert to the equilibrium phases on reheating to higher temperatures.     

Real gas choked flow conditions at low reduced-temperatures

Real gas choked mass flux is calculated for a frictionless stream expanding isentropically until it reaches the speed of sound and without phase changes. The other parameters associated with the choked state are the pressure, density, temperature ratios, and the speed of sound. Departure of the choked mass flux from the ideal gas model is discussed first in absolute terms and then in relative terms, using the Principle of Corresponding States, for gases with boiling points in the low temperature range. Reduced-stagnation pressures are examined up to values of 30 for hydrogen, neon, nitrogen, argon, methane, krypton, xenon, and R-14 and up to 100 for ⁴He. The corresponding reduced-stagnation temperatures go down to 1.4 and in some cases down to 1.2 for nitrogen and argon. Also discussed are the limiting values of stagnation parameters for which no phase change occurs in the choked state. Compared to the ideal gas, the mass flux may almost double and the critical pressure ratio may decrease by an order of magnitude. The relevance of results is discussed qualitatively and quantitatively for Joule-Thomson cryocooling.     

Compositional changes in minor phases present in 12CrMoVNb steels during thermal exposure at 550°C and 600°C

Abstract

One of the techniques considered promising in the assessment of the time–temperature history of creep resistant power plant steels is based on studies of compositional changes occurring in the minor phases during service exposure. Chemical compositions of alloy carbides and/or nitrides precipitated during quality heat treatment of high alloy steels are expected to be very close to equilibrium. However, since in practice the operating temperatures for these steels are usually much lower than the tempering temperatures used in their original heat treatments, changes in the compositions of their minor phases are likely to occur during service exposure. These changes depend on the differences between the respective equilibrium compositions of the minor phases at the tempering and service temperatures. The greater the difference between these temperatures, the greater will be the expected changes in the compositions of the minor phases during exposure at the service temperature. Since these changes are dependent on the time and temperature of exposure, any minor phase, which is present in the microstructure in the as received condition, as well as after prolonged service exposure, represents a potential indicator of time–temperature history of the material. In this paper the results of quantitative microstructural studies are reported on a series of martensitic 12CrMoVNb steels in their as received heat treated condition and following long term exposure at 550 and 600°C. The results of minor phase composition changes are discussed in terms of the equilibrium minor phase compositions calculated using the MTDATA computer program and the SGTE database, and their potentials as in service time–temperature history indicators for the materials are evaluated.     

Thermal conductivity of subcooled liquid oxygen

The thermal conductivity of liquid oxygen below 80 K and pressures up to 1 MPa has been measured using a horizontal, guarded, flat-plate calorimeter. The working equation of the calorimeter is based on the one-dimensional Fourier’s law. The gap between the calorimeter plates was measured in situ from a capacitance measurement. The cooling power to the calorimeter is provided by a two-stage Gifford-McMahan cryocooler. The absolute temperatures are measured using platinum resistance thermometers. The results are compared to existing data and analytical models.     

Liquid-vapour phase equilibria in the N2CH4 system from 130 to 180 K

Isothermal composition measurements for both the equilibrium liquid and vapour phases have been determined for the nitrogen + methane system at eight temperatures between 112.00 and 180.00 K, and at pressures from 1 to 49 atm (1 to 50 bar). The internal consistency of these data is checked by comparing experimental and calculated thermodynamically consistent vapour phase compositions. Derived Henry's constants are used to provide a comparison between these data and those of other investigators.     

An automated flow calorimeter for heat capacity and enthalpy measurements

An automated flow calorimeter has been developed for the measurement of heat capacity and latent enthalpies of fluids at elevated temperatures (300–700 K) and pressure (<30M Pa) with a design accuracy of 0.1%. The method of measurement is the traditional electrical power input flow calorimeter, utilizing a precision metering pump, which eliminates the need for flow-rate monitoring. The calorimeter cell uses a unique concentric coil design with passive metal radiation shields and active guard heaters to minimize heat leakage, eliminate the traditional constant-temperature bath, and facilitate easy component replacement. An additional feature of the instrument is a complete automation system, greatly simplifying operation of the apparatus. A novel multitasking software scheme allows a single microcomputer simultaneously to control all system temperatures, provide continuous monitoring and updates on system status, and log data. Preliminary results for liquid water mean heat capacities show the equipment to be performing satisfactorily, with data accuracies of better than ±0.3%. Minor equipment modifications and better thermometry are required to reduce systemic errors and to achieve the designed operational range.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

A high frequency cascade thermoacoustic engine

A miniature cascade thermoacoustic engine, which consisted of one standing-wave stage and one traveling-wave stage in series, was built and tested, which length was about 1.2 m, operating at 470 Hz using helium as working gas. The cascade modeling, the simulation and the primary experimental results are described in this paper. Four different configurations of the miniature cascade thermoacoustic engines had been designed and compared. According to the analysis, the diameter ratio of stages was designed to extend the traveling-wave region, which optimized value was about 1.69. The peak-to-peak value of the acoustic pressure was predicted to arrive to 3 bar at the 3 MPa mean pressure of helium when 300 W heating power was the input. The features of the engine were predicted delivering 68 W acoustic power with a thermal efficiency of up to 22.74% (the ratio of acoustic power to heater power). Due to careful designing, the engine self-excited the oscillation smoothly from the first experiment. An onset temperature gradient of about 4.5 K/mm was achieved, and the peak-to-peak acoustic pressure was 48 KPa at the 2 MPa mean pressure when 200 W heating power was the input. The design computation and experimental results showed a rather good agreement between the measured and calculated pressure phasor and temperatures distributions in the cascade thermoaoustic engine.     

Degradation behaviour of sputtered Co–Al coatings on superalloy

Degradation behaviour of sputtered Co–Al coatings on Superni-718 substrate has been investigated. Cyclic high temperature oxidation tests were conducted on uncoated and coated samples at peak temperatures of 900 °C for up to 100 thermal cycles between the peak and room temperatures. The results showed that a dense scale formed on the coated samples during thermal cycling at the peak temperature of 900 °C. The external scale exhibited good spallation resistance during cyclic oxidation testing at both temperatures. The improvement in oxide scale spallation resistance is believed to be related to the fine-grained structure of the coating. Nanostructured Co–Al coatings on Superni-718 substrate were deposited by DC/RF magnetron sputtering. FE-SEM/EDS, AFM, and XRD were used to characterize the morphology and formation of different phases in the coatings, respectively. The Co–Al coating on superalloy substrate showed better performance of cyclic high temperature oxidation resistance due to its possession of β-CoAl phase as Al reservoir and the formation of Al₂O₃ and spinel phases such as CoCr₂O₄ and CoAl₂O₄ in scale. The oxidation results confirmed an improved oxidation resistance of the Co–Al coating on superalloy as compare to bare substrate in air at 900 °C temperature up to 100 cycles.     

The crystallization characteristics of Mg-Zn metallic glasses from Mg80Zn20 to Mg60Zn40

Using the conventional melt-spinning technique we have been able to double the range over which Mg-Zn has hitherto been made amorphous. The crystallization characteristics of the alloys have been investigated through differential scanning calorimetry (DSC), X-ray photography and measurement of electrical resistance and magnetic susceptibility. The crystallization of amorphous Mg-Zn is initiated at lower temperatures by the precipitation of fine-grained, distorted Mg₅₁Zn₂₀ crystals which grow into regular Mg₅₁Zn₂₀ crystals at the end of the crystallization process. Mg is also precipitated for the Mg-rich alloys. The mechanism for further recrystallization at higher temperatures depends on whether the alloy is Mg-rich or Zn-rich with respect to Mg₅₁Zn₂₀. Both recrystallization steps are shown to be in qualitative agreement with the equilibrium phase diagram. For all compositions, upon crystallization, the electrical resistivity decreases while the valence magnetic susceptibility increases, as expected for a simple s-p system. The value of the magnetic susceptibility for the composition Mg₇₀Zn₃₀ is in excellent agreement with the prediction of the free electron model. The deviations from the free electron model for the other compositions may be due to the simple subtraction of the large core diamagnetism (filled d-band) of Zn.     

A very light and thin liquid hydrogen/deuterium heat pipe target for COSY experiments

A liquid hydrogen/deuterium heat pipe (HP) target is used at the COSY external experiments TOF, GEM and MOMO. The target liquid is produced at a cooled condenser and guided through a central tube assisted by gravitation into the target cell. An aluminum condenser is used instead of copper, which requires less material, improves conductivities and provides shorter cooling down time. Residual condenser temperature fluctuations in the order of ≈0.4 K are reduced by using thermal resistances between the cooling machine and the condenser of the heat pipe combined with a controlled heating power. A new design with only a 7-mm-diameter HP has been developed. The diameter of the condenser part remains at 16 mm to provide enough condensation area. The small amount of material ensures short cooling down times. A cold gas deuterium HP target has been designed and developed which allows protons with energy ?1 MeV to be measured. A 7-mm-diameter HP is used to fill a cooling jacket around the D₂ gas cell with LH₂. The D₂ gas is stabilized at 200 mbar to allow for thin windows. Its density is increased by factor 15 compared to room temperature.