Viscosity Of He Research Articles

Heat Transfer Mechanisms in Arcs of Various Gases at Atmospheric Pressure

This work expands findings about the dominant heat transfer mechanisms in argon and helium arcs at atmospheric pressure for monoatomic (Ar, He, 50% Ar–50% He), diatomic (air, {hbox{N}}_{2}, {hbox{O}}_{2}, {hbox{F}}_{2}, {hbox{Cl}}_{2}), and triatomic ({hbox{CO}}_{2}) gases. The objective is to understand the dominant mechanisms in atmospheric plasmas through validated numerical modeling for GTAW welding process. Arcs of all gases have lengths of 10 mm and 200 A current. Five heat transfer mechanisms are considered: Joule heating, convection, radiation, conduction, and Thomson effect. Results indicate that the general structure of the arcs and dominant mechanisms are qualitatively similar for all gases; sizes change depending on the gas. The dominant energy input near the cathode is Joule heating, while that near the anode is convection. The dominant energy output always follows the same sequence: Thomson effect next to the cathode followed by convection, radiation in the arc column, and conduction near the anode. Joule heating is the most significant in Ar, while in He, it has the lowest significance. This is due to differences in electric conductivity of He (higher up to 21,000 K and lower beyond 21,000 K than other gases) and high viscosity of He, which creates a small Joule heating versus a large convection region. He transfers the most heat towards the anode by convection while {hbox{N}}_{2} has the lowest; due to the high enthalpy and viscosity of He compared to {hbox{N}}_{2}. Finally, Ar has the most significant radiative emission and He the smallest due to their net emission coefficient.

Statistical properties of homogeneous and isotropic turbulence in He II measured via particle tracking velocimetry

Despite being a quantum two-fluid system, superfluid helium-4 (He II) is observed to behave similarly to classical fluids when a flow is generated by mechanical forcing. This similarity has brought up the feasibility of utilizing He II for high Reynolds number classical turbulence research, considering the small kinematic viscosity of He II. However, it has been suggested that the non-classical dissipation mechanism in He II at small scales may alter its turbulent statistics and intermittency. In this work, we report our study of a nearly homogeneous and isotropic turbulence (HIT) generated by a towed grid in He II. We measure the velocity field using particle tracking velocimetry with solidified deuterium particles as the tracers. By correlating the velocities measured simultaneously on different particle trajectories or at different times along the same particle trajectory, we are able to conduct both Eulerian and Lagrangian flow analyses. Spatial velocity structure functions obtained through the Eulerian analysis show scaling behaviors in the inertial subrange similar to that for classical HIT but with enhanced intermittency. The Lagrangian analysis allows us to examine the flow statistics down to below the dissipation length scale. Interestingly, strong deviations from the classical scaling behaviors are observed in this regime. We discuss how these deviations may relate to the motion of quantized vortices in the superfluid component in He II.

Additional mass from a quartz tuning fork vibrating in He II

The additional mass caused by vibrations of tuning forks in He II with resonant frequencies of 6.7, 8.5, 12.1, 25, and 33 kHz is studied experimentally. The additional mass coefficient, given by the ratio of the additional mass to the mass of the fluid displaced by the tuning fork, is determined from the measured temperature and pressure dependences of the resonance frequencies of the tuning forks. These studies were made at temperatures from 2.2 to 0.1 K and the pressure dependences of the tuning forks were found for pressures from 1 to 24.8 atm at a constant temperature of 0.365 K. It is shown that for temperatures below 0.7 K, where the viscosity of He II is negligible, the resonance frequency of the tuning fork oscillations is determined by the additional mass of the fluid. It is found that measurements of the resonance frequencies as a function of pressure can be used to determine the additional mass coefficient with an accuracy that is almost an order of magnitude higher than when the temperature dependences are used. The additional mass coefficient is observed to depend on frequency and decreases as the frequency is raised.

Viscosity and relaxation processes in the phonon-roton system of He II

The viscosity of He4 in the temperature range 0.1–2.2K has been measured using a vibrating quartz tuning fork. A quantitative comparison is made of the experimental data and the conclusions of the modern theory of the phonon-roton system of superfluid helium. The complex hierarchy of relaxation processes is analyzed and the role and contribution of each process to the coefficient of viscosity are determined. Agreement between the experiments and theory is obtained in the hydrodynamic region. The transition from the hydrodynamic to the ballistic regime of phonon flow is analyzed and the effective viscosity of He II at such temperatures is found. It is shown that the position of the maximum of the temperature dependence of the effective viscosity, obtained using different methods of measurement, correlates with the characteristic size of the measuring apparatus.

Dynamic viscosity of gases over a wide range of temperatures. I

The results are presented of a generalization of the experimental data on the viscosities of He, Ne, Ar, Kr, Xe, and N2 at atmospheric pressure over the range of temperatures from the boiling point at atmospheric pressure to 2000 K using polynomial approximating relationships.

Preparation of Fe-, Co-, and Ni-Based amorphous alloy powders by high-pressure gas atomization and their structural relaxation behavior

By using newly constructed high-pressure gas atomization equipment, the effect of atomizing gas (Ar, N2, or He) on the formation tendency of amorphous alloy powders and their Curie temperature(Tc), structural relaxation, glass transition(Tg), and crystallization(Tx) was examined for Fe-P-C, Fe-Si-B, Fe-Cr-Mo-P-C, Co-Si-B, Ni-Si-B, Ni-Pd-P, and Cu-Zr alloys with easy glass-forming capacity. Amorphous powders are formed in all the alloy systems and the critical diameter for the formation of amorphous powders is 25 to 44 µm for Ar and 44 to 100 µm for He. The average particle size is considerably smaller for He than for Ar and N2, probably because of large kinematic viscosity of He. No appreciable differences inTc,Tg, andTx of Fe77P13C10 amorphous powders with the kind of atomizing gas are seen and these values are the same as those of the amorphous ribbon with 20 µm thickness. However, He-atomized Fe77P13C10 powders exhibit a lower onset temperature of relaxation and larger heats of relaxation and crystallization as compared with the Ar- and N2-atomized powders, and the values of the He-atomized powders are comparable to those of the ribbon sample, indicating that He-gas atomization has a higher cooling capacity and results in the formation of a more disordered amorphous structure. This difference agrees with the tendency estimated under the assumption that heat removal from atomized droplets occurs by Newtonian cooling caused only by the convective heat transfer. Accordingly, the greater heat removal capacity of He gas is concluded to be a dominant factor for the formation of amorphous alloy powders with a more unrelaxed atomic configurations.

Gas exchange during constant flow ventilation with different gases.

To investigate the mechanisms of CO2 transport during constant flow ventilation, we measured arterial blood gases using air, 80% He-20% O2 (He) or 80% SF6-20% O2 (SF6) as the insufflating gas. At any given flow rate (0.2 to 1.0 L/s), PaCO2 was greatest with He and lowest with SF6. Data for all gases could be described by the equation PaCO2/Pb = 0.044 V-0.64 v0.23, where Pb = barometric pressure, PaCO2 is in mm Hg, V = insufflated flow in L/s, and v = kinematic viscosity (cm2/s). At any given flow rate, the AaPO2 was greater using SF6 than using He. These results are consistent with a 2-zone model of gas transport in which the enhancement of gas transport as V increases may be due to an increase in the turbulent diffusivity in zone I (the region affected by the jet). The decreased gas transport with He compared to air and SF6 at any V may be due to either the decreased penetration depth of zone I caused by the greater kinematic viscosity of He, or the decreased rate of gas transport in the region affected by cardiogenic oscillations (zone II) secondary to the higher molecular diffusivity of He.

The roton viscosity of He II under pressure

The roton viscosity of superfluid liquid 4He has been measured as a function of pressure in both hydrodynamic and non-hydrodynamic regimes.

Viscosities of binary gas mixtures at high temperatures

The viscosities of He + Ar, Ar + Kr and CH4+ CF4 binary gas mixtures have been measured over the temperature range 293–1600 K using a capillary flow technique. The results are in good agreement with existing data both for the pure components (up to 1600 K) and for the inert gas mixtures (up to 1000 K). They have been analyzed in terms of the so-called interaction viscosity, η12, which is characteristic of the unlike pair interactions and essentially independent of composition. The application of this quantity of the estimation of other transport properties for gas mixtures and to the direct determination of pair potential energy functions for unlike molecules is discussed.

Viscosity of He–Ar and He–Kr Binary Gaseous Mixtures in the Temperature Range 25–720°C

Measurements were made of the viscosity of helium, argon, krypton, and the mixture pairs helium–argon and helium–krypton to elevated temperature. The viscosity of the pure gases was measured to a temperature of about 850°C, whereas that of the mixtures was measured to 720°C. The instrument used was that of an oscillating-disk type, and absolute measurements were obtained. The data on the pure gases showed good agreement with previous work on oscillating viscometers but did not agree well with the older capillary-flow measurements. It is contended that the present results enjoy a higher confidence level. The pure-gas results were used to find optimum force parameters for the interaction potential. It was found that argon and krypton are best represented by the conventional Lennard-Jones (6–12) potential, but helium is best represented by a (6–9.5) potential model. Due to the extremely shallow depth of the potential well for helium, the present viscosity data are inadequate to yield meaningful values for the force parameters for it. Consequently, force parameters derived from measured binary diffusion coefficients were used to test proposed combination rules. The combination rules were found to be moderately successful. The viscosity data were then used to calculate diffusion coefficients of the mixtures. These values were in good agreement with reliable correlations referred to in the paper. The viscosity of the pure components as well as that of the mixtures was used to generate skeleton tables for thermal conductivity; the interpolation scheme for them is described in the paper. In cases when these values can be compared with direct measurements, the agreement is good.

The influence of water vapour on the viscosity of He, Ar, N2 and CO2 at 30°C

The changes in the viscosity of He, Ar, N 2 , and CO 2 resulting from the addition of a defined fraction of water vapour have been investigated at 30°C and at atmospheric pressure. For all gases a decrease in the velocity was found, with the exception of He, which showed a maximum increase of 0.2% at 1 vol. % of water vapour. The experimental results have been compared with those calculated on the basis of a first order approximation to the viscosity of a binary polar-nonpolar gas mixture.

Calculation of the roton-roton contribution to the viscosity of liquid he II

A new potential, which accounts for roton-roton interaction is proposed. Using this potential without any adjustable parameters, the calculated roton-roton contribution to the viscosity of He II in the temperature range between 1.35 °K and 1.9 °K is found to be in qualitative agreement with the experimental value.

Gaseous Diffusion. The Systems He–Ar, Ar–Xe, and He–Xe

Relative values of the diffusion coefficients of the systems He–Ar, Ar–Xe, and He–Xe have been determined over the temperature range 0° to 120°C by a two-bulb method. The experimental diffusion coefficients, at 1 atm pressure, can be described by the following equations: He–Ar: log10D=1.684log10T−4.2902,Ar–Xe: log10D=1.955log10T−5.7807,He–Xe: log10D=1.720log10T−4.5251. The apparatus was calibrated with the He–Ar diffusion data; the results for the system Ar–Xe are in essential agreement with the data reported by other workers, but the He–Xe diffusion coefficients are about 9% lower than previously published values. The present He–Xe coefficients are in good agreement, however, with results which have been determined from a consideration of the composition dependence of the viscosities of He–Xe mixtures.

Viscosity of Helium, Oxygen, Helium-Oxygen, Helium-Steam, and Oxygen-Steam Mixtures at High Temperatures and Pressures.

S>The first phase of this investigation was the determination of the viscosity of He and O/sub 2/ at elevated pressures over a temperature range of 200 to 450 deg C. The second phase was the determination of the viscosity of He - O/sub 2/, steam-He, and steam-O/sub 2/ mixtures at elevated pressures and temperatures. (W.L.H.)

The viscosity of gaseous He, Ne, H 2 and D 2 below 80°K

Measurements are reported of the coefficient of viscosity of He, Ne, H2 and D2 between 20 and 80°K, using an oscillating disc viscometer. A simple thermostat, developed for this purpose, is also described. The results are in good agreement with the existing data below 20°K and above 60°K. In the course of the measurements a heretofore omitted correction of the oscillating disc measurements was found. With the aid of this correction, the existing discrepancies in the viscosity data below 4°K could be greatly reduced. Corrected values for the viscosity coefficient are given. The experimental results are compared with theoretical predictions based on the quantum-mechanical modification of the law of corresponding states. The first term of the series expansion of the reduced viscosity in powers of the De Broglie parameter is determined from the experimental data. Furthermore, the data are compared with calculations, based on different models for the intermolecular potential.

Thermal conductivity of gaseous helium

In this paper the experimental values for λ 1) and 28) are compared with the theoretical relations: λ = f η c υ ; λ = λ( T); λ = λ( p). To control the first relation the available data concerning the viscosity of He are discussed. The theoretical value for f = 2,5 is in good agreement with the available data for all temperature regions. Calculations of De Boer 27) concerning λ = λ( T) proved to be in accordance with the experimental data. From investigations in the third relation λ = λ( p) no decisive conclusions could be drawn, not enough theoretical data being available.

Thermal conductivity of gaseous helium

In this paper the experimental values for λ1) and 28) are compared with the theoretical relations: λ = f η cυ; λ = λ(T); λ = λ(p). To control the first relation the available data concerning the viscosity of He are discussed. The theoretical value for f = 2,5 is in good agreement with the available data for all temperature regions. Calculations of De Boer 27) concerning λ = λ(T) proved to be in accordance with the experimental data. From investigations in the third relation λ = λ(p) no decisive conclusions could be drawn, not enough theoretical data being available.