Inter- and intradiffusion in liquid mixtures of methane andn-decane

The interdiffusion coefficient,D ₁₂, has been measured by Mach-Zehnder interferometry for liquid mixtures of methane andn-decane at 303 K. The mole fraction of methane was from 0.11 to 0.96 and the pressure was from 30 to 60 MPa. This includes measurements in the critical region, the critical locus being approached from supercritical pressures to within 0.4 MPa. The accuracy inD ₁₂ is estimated to be from 3 to 10%, depending on the composition. Our data are compared with the Sigmund correlation, which is widely used to estimate diffusion coefficients in hydrocarbons at high pressures. The deviation between estimate and measurement is one order of magnitude for some of the states. We have also compared with a more recent correlation used by Erkey, but this one is not found to be applicable to the compositions studied in the present work. Our data were related to recently measured intradiffusion coefficients,D ₁ andD ₂, at the same state points. On this basis, we have evaluated different mixing rules for obtaining the interdiffusion coefficient from intradiffusion coefficients, both close to and away from the critical region. It is found that the so-called Darken and Adamson relations have the right qualitative behavior.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, U.S.A.     

Heat transfer in liquid nitrogen—methane mixtures under pressure

Heat transfer in nitrogen—methane mixtures (0 to 100 molar per cent CH₄) was studied in the bubble boiling range under pressures up to 3.5 MPa.For a given heat flux density in all mixtures the temperature differences are higher than in the adjacent pure componentThe maximum heat flux densities have a maximum between 90 and 70 molar per cent methane (for lower and higher pressures, respectively) with the absolute values being higher than for the pure components     

Diffusion measurements in binary liquid mixtures by Raman spectroscopy

It is shown that Raman spectroscopy allows determination of the molar fractions in mixtures subjected to molecular diffusion. Spectra of three binary systems, benzene/n-hexane, benzene/cyclohexane, and benzene/acetone, were obtained during vertical (exchange) diffusion at several different heights (z) as a function of time. A procedure to determine time-dependent concentration profiles and diffusion coefficients is described in detail for one system, and results are given for the two other cases. For the system benzene/cyclohexane, much lower diffusion coefficients than reported in the literature were found, even in a thermostatically controlled diffusion cell, recording spectra through circulating water. For the system benzene/acetone, the determined diffusion coefficients were in good agreement with the literature data. The limitations of the Raman method are discussed, and it is concluded that many more systems ought to be studied. It is pointed out that diffusion profiles can be obtained in ternary and higher systems, where proper measurements are almost nonexistent.     

Electron attachment of oxygen in a drift chamber filled with xenon + 10% methane

The existence of O₂ contamination attenuates the pulse height and degrades its resolution in a drift chamber filled with xenon-methane (90/10) gas. The first measurement of the electron attachment coefficient due to oxygen in such a mixture is reported.     

High-pressure cylindrical acoustic resonance diffusion measurements of methane in liquid hydrocarbons

A novel cylindrical acoustic resonance method for the measurement of gas diffusion into liquids at high pressures is described. The measurements were per formed in a vertically oriented cylindrical acoustic resonator containing both the liquid solvent and gaseous diffusant while under high-precision isothermal and isobaric control. Individual resonance modes of the liquid column, the gas column, and the two-phase coupled fluid are resolved in the fast Fourier trans form acoustic-resonance spectrum (FFT-ARS). High-resolution acoustic spectra measured at frequent time intervals reveal the changes which accompany the diffusion fusion of gas into the liquid phase. One change, namely, the growth in length of the liquid column, results in a systematic shift to higher frequencies of axial modes in the gas column. The temporal behavior of this moving boundary, together with quantitative measurement of the flow to the gas column required to sustain the constant pressure, permits determination of the gas-into-liquid diffusion coefficient. Diffusion coefficients were determined from the change in frequency as a function of time of axial resonance modes in the gas-phase virtual cylinder as the surface of the underlying liquid phase advanced due to gas absorption. Measurements of the systems methane/n-octane, methane/n-nonane, and methane/n-decane were performed as a function of temperature at a pressure of 250 psia. Comparisons is made to results obtained elsewhere and by other methods but at the same temperatures and pressure.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, U.S.A.     

Electron attachment to oxygen,water, and methanol,in various drift chamber gas mixtures

Attachment of electrons to oxygen, water, and methanol molecules has been studied in various gas mixtures based on argon, methane and isobutane, a class of gases often used to operate large drift chambers. The measurements were performed using a drift chamber in which the conditions prevailing in large experiments could be closely reproduced. Attachment coefficients were extracted as a function of the gas composition and pressure, the drift field, and the concentration of the molecules under investigation. The observed effects are compared to other measurements, and are discussed within the frame of physical models.     

Vibrating-wire measurements in vacuum,liquid3He and liquid3He-4He mixtures

In order to overcome the 200µK - barrier in the refrigeration of liquid ³ He- ⁴ He mixtures we have constructed an experimental cell using only pure materials to minimize possible origins for heat leaks into the liquid. With this arrangement we were able to cool a saturated6.8%- mixture to a temperature of 150µK. A vibrating wire which was immersed in pure ³ He floating on top of the phase-separated mixture was used as a thermometer. This wire was calibrated in a second experiment with pure ³ He only in the cell. In superfluid ³ He-B at T0.15 mK the damping of the wire due to the quasiparticles becomes very small, and we observe typical characteristics of the vacuum damping of the wire which was extensively examined before filling any liquid into the cell.     

The prediction of vapour–liquid equilibrium behaviour of HFC blend–oil mixtures from commonly available data

This paper addresses the problem of achieving accurate calculations for vapour–liquid equilibrium behaviour in the presence of the (new) oils in use with HFC refrigerants by introducing a correlation which depends only on the gas constant, critical temperature and molecular weight of the blend constituent and the molecular weight of the oil; i.e. the method depends on commonly available data and not a specialised measurements. The work is believed to be of value to plant designers and research workers.     

Transient surface velocity measurements in a liquid by an active ultrasonic probe

A high sensitive ultrasonic method for measuring the surface velocity in a liquid is described. This method is based on the detection of the phase of a high frequency continuous ultrasonic wave (probe beam) reflected from the moving surface. The analysis shows that the main phenomenon is the interaction, through the acoustic nonlinearity parameter B/A of the fluid, between the reflected carrier wave and the low frequency pressure wave transmitted by the moving surface in the liquid. This interaction produces a phase-shift of the carrier proportional to the surface velocity and to the time delay undergone by the probe beam. Results of experiments carried out in water with a 30-MHz focused transducer probe are in good agreement with the analysis. Surface velocity smaller than 0.04 mm/s (i.e., mechanical displacements down to 3 pin) can be detected in a 5 MHz bandwidth. Lateral resolution of 0.5 mm has been achieved. Compared to optical techniques, this method has the advantages of compactness and of a low sensitivity to surface roughness.     

The sound velocity in liquid binary mixtures of <Emphasis Type="Italic">n</Emphasis>-alkanes

The method of direct measurement of the time of pulse transmission is used for investigating the sound velocity in liquid binary mixtures of n-alkanes, namely, n-hexane + n-hexadecane, n-octane + n-hexadecane, and n-decane + n-hexadecane in the range of temperatures from 298 to 433 K and pressures from 0.1 to 100.1 MPa. The maximal error of measurements is 0.1%. It is for the first time that experimental data for mixtures of n-octane + n-hexadecane and n-decane + n-hexadecane are obtained.     

Measurements of the viscosity of compressed gaseous and liquid nitrogen + methane mixtures

The shear viscosity coefficients of three compressed gaseous and liquid nitrogen + methane mixtures have been measured at temperatures between 100 and 300 K and at pressures to about 30 MPa (4350 psia) with a piezoelectric quartz crystal viscometer. The precision of the measurements ranges from about 0.5% at high densities to about 1% at low densities. The estimated experimental error ranges from about 2% at high densities to about 4% at densities near the critical density and at supercritical temperatures near the critical temperature. The measurements have been compared with an extended corresponding states model, previously proposed for calculating the viscosities of fluid mixtures. Differences between the measured and calculated viscosities are discussed.     

Electron parameters in Xe-Ne mixtures

The effect made by xenon concentration and by reduced electric field on the parameters of electrons in Xe-Ne mixtures is numerically studied. It is demonstrated that the increase in xenon concentration in mixture leads to a decrease in the average electron energy, to an increase in the frequency of collisions of electrons with gas atoms, and to variation of the transport coefficients of electrons. The increase in xenon concentration in mixture above ≈10% leads to an abrupt slowing down of the rates of excitation of xenon atoms. The efficiency of ionization increases with the xenon concentration increasing to ≈7%. The fraction of electron energy spent for excitation of xenon decreases with increasing electric field, and more energy is put into the ionization of xenon and into excitation and ionization of neon. The results of calculation of parameters of electrons make it possible to limit the search for xenon concentrations in Xe-Ne mixture, which are optimal for vacuum ultraviolet radiation, to the range of 1–10%.     

Studying average electron drift velocity in pHEMT structures

Technical Physics Letters - Small-signal characteristics of pseudomorphic high-electron-mobility transistors based on donor–acceptor doped heterostructures (DA-pHEMTs) are compared to those...     

Electron transport in xenon-hydrogen gas mixtures

We present the results of numerical solution of the Boltzmann equation in a two-term approximation taking into account both elastic and inelastic electron collisions in Xe-H₂ gas mixtures. Using the obtained electron energy distribution functions, the electron transport properties (drift velocities, mobilities, mean and characteristic energies, diffusion coefficients) are calculated for the E/N parameter (the electric field strength to gas density ratio) ranging within several townsends. A similarity rule is derived for the properties of Xe-H₂ mixtures of various densities, which allows the electron transport coefficients to be determined for the mixtures with small (below 4%) hydrogen content.     

Shear viscosity measurements of liquid 3He-4He mixtures above 0.5 K

Simultaneous measurements of () and of the molar volume are reported for liquid mixtures of ³He in ⁴He over the temperature range between 0.5 and 2.5 K. Here is the shear viscosity and is the mass density. In the superfluid phase, the product of the normal components, _n and _n , is measured. The mixtures with ³He molefractions 0.30 < X < 0.80 are studied with emphasis on the region near the superfluid transition T and near the phase-separation curve. Along the latter, they are compared with data by Lai and Kitchens. For X > 0.5, the viscosity singularity near T becomes a faint peak, which however fades into the temperature-dependent background viscosity as X tends to the tricritical concentration X _t. Likewise, no singularity in is apparent when T _t is approached along the phase separation branches _– and ₊. Furthermore, viscosity data are reported for ³He and compared with previous work. Finally, for dilute mixtures with 0.01 X 0.05, the results for are compared with previous data and with predictions.     

多元有机混合液体声速温度系数的预测方法

根据Jacobson理论及液体声速与分子自由程的关系 ,导出了多元有机混合液体声速与各组分声速之间的关系 ;推导出多元有机混合液体声速温度特性的预测公式 ,并根据组成多元有机混合液各组分特性参量 (摩尔分数、密度、自由程、等压膨胀系数等 ) ,利用文中给出的多元有机混合液声速的温度特性预测公式 ,对由丙酮、四氯化碳、苯、甲醇组成的三元系、四元系有机混合液体的声速温度特性进行了理论值的预测 ,理论预测结果与实验测量结果符合较好     

Microstructure and properties of hercynite–magnesia–calcium zirconate refractory mixtures

Refractory manufacturers have focused their investigations on the development of chrome-free products that suitably meet the refractory lining requirements of cement rotary kilns. The experimental development of refractory mixtures based on magnesia and calcium zirconate, to which electrofused hercynite was added, was carried out in this work. Formulations, in which various amounts of hercynite were added to study its influence on MgO–CaZrO₃ microstructure and properties, were prepared. Samples were obtained by compacting powders and sintering in an industrial tunnel kiln. The samples were characterized via XRD and SEM. The strength of the refractory was determined at room temperature. Resistance to attack by cement raw meal at 1300 °C was studied. According to the results, formulations with the addition of hercynite show superior cold crushing strength compared to those without the additive, moreover, all compositions showed good chemical resistance to the presence of cement raw meal.     

Preliminary measurements of the velocity distribution in a cylinder filled with liquid He II during spin-up

In a rotating He II-filled cylinder with an aspect ratio of 4.3 the transient evolution of the vorticity fields of the normal fluid and the superfluid component during spin-up are investigated. The acoustical method of measurement used utilizes the change of propagation time of first- and second-sound signals irradiated through a slit in the middle of the cylinder. The results of the first-sound measurements within the range 1.3 T 2.1 K essentially do not depend on temperature and, for the final state, indicate a lack of about 30% of vorticity compared to solid-body rotation. On the other hand, the results of the second-sound measurements are temperature-dependent and show that the superfluid component reaches solid-body rotation, while the normal fluid fraction seems to slip at the wall. Accordingly, the velocity in the inner part of the flow field adopts a value lower than one would expect from the present velocity of the wall, thus confirming the lack of vorticity observed.     

Precise determination of the compressibility factor of methane,nitrogen, and their mixtures from refractive index measurements

We show that the absolute determination of the refractive index, when combined with an expansion technique for obtaining the higher-order coefficients of the Lorentz-Lorenz expansion, leads to precise values of density. A grating interferometer has been developed for the refractive index measurements as a function of pressure. The advantage of a grating interferometer is that it performs a reversible counting and generates a DC compensated signal from the interference fringes. The pressure is also measured with an interferometer, previously calibrated with an oil-type precision piston gauge. For the precise determination of the compressibility factor, the absolute measurement of the refractive index is combined with the differential technique to determine the refractivity virial coefficients of the Lorentz-Lorenz expansion. The compressibility factors of methane, nitrogen, and their mixtures have been determined at 323.15 K for pressures up to 335 bar. The optical method for the determination of the compressibility factor not only is shown to be precise, but also has the ability to produce numerous experimental points in a short time as compared to other methods.Paper presented at the Ninth Symposium on Thermophysical Properties, June 24–27, 1985, Boulder, Colorado, U.S.A.