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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 67 (1996), S. 1850-1857 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Double Helmholtz acoustic resonators, first proposed by Greenspan for measuring the viscosity of gases, were tested with helium, argon, and propane. Two different resonators were tested extensively with all three gases. For each of these instruments, the results for the viscosities of the three gases were consistent within ±0.5% at pressures spanning the range 25–1000 kPa. Without calibration, the viscosities deduced from one viscometer were systematically 1% larger than data from the literature; the viscosities from the second viscometer were systematically 3% larger than data from the literature. If the systematic differences were removed for each viscometer by calibration with a single gas at a single temperature and pressure, then nearly all the results for both instruments would have fallen within ±0.5% of the data from the literature. In these viscometers, the test gases are in contact with robust metal parts only; thus, these instruments are applicable to a very wide variety of gases over a very wide range of temperatures.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 62 (1991), S. 2213-2217 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Accurate measurements of the speed of sound in gases are often made using metal resonators with small transducers that perturb the resonance frequencies in minor and predictable ways. We extend this method to gases that may be corrosive and to high temperatures by using remote transducers coupled to a resonator by acoustic waveguides. Thin metal diaphragms separate the waveguides from the resonator. Thus, only metal parts come into contact with the test gas. In the present apparatus, any gas compatible with gold and stainless steel can be studied.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Journal of low temperature physics 75 (1989), S. 349-359 
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The chemical potentials as a function of He coverage have been determined from He adsorption isotherms measured at 1.72 K for the following thick substrates: Ne, Ar, and CO2-plated Cu, and bare Cu. The adsorption isotherm data were analyzed self-consistently using the modified Brunauer-Emmett-Teller method for low coverages and the Frenkel-Halsey-Hill vapor pressure relation at high coverages. The analysis establishes the surface area, chemical potential constant, Γ=−μd 3, and capacity increases and heats of adsorption of the first and second monolayers of He for each adsorbent. The measured chemical potentials follow the expected inverse-cube law for coverages greater than 2.5 layers, but differ substantially for smaller coverages. We use results of the isotherm analysis to interpret measurements of third sound velocities, and to make precision measurements of the He inert (nonsuperfluid) layer coverages on these substrates
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Journal of low temperature physics 78 (1990), S. 157-163 
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Precision measurements of third sound in atomically thin4He films on Ne, Ar, and CO2 substrates reveal a periodic structure not corresponding to whole layers. Treating the He film as an incompressible, continuous fluid, the data indicate that the chemical potential has a contribution proportional to l−6, where l is the He coverage in layers, which is modulated at intervals of 0.62±0.04 layers and which weakens the van der Waals potential. Alternatively the data indicates the existence in the film of a damped smectic density wave with a 0.54±0.40 layer periodicity.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Journal of low temperature physics 78 (1990), S. 325-334 
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Using vortex pair motion, we have measured the vortex diffusivity below the Kosterlitz-Thouless transition temperature (T KT) in atomically thin superfluid helium films on both argon and neon substrates. The diffusivities are on the order ofħ/m nearT KT and then fall rapidly to10 −3 ħ/m near0.1 K for argon and to0.03 ħ/m for neon. However, for the thinnest helium film on neon, the diffusivity is large and independent of temperature. At small flow velocities, dissipation due to unpaired vortices indicates a vortex lifetime on the order of seconds for a neon substrate near0.1 K.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Journal of low temperature physics 61 (1985), S. 173-183 
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A model is presented describing the onset of nonlinear dissipation in two-dimensional helium films for allT〈T KT, whereT KT is the Kosterlitz-Thouless transition temperature. The superfluid velocity is included in the renormalization equations of Kosterlitz and Thousless, and it is shown that the model predicts a characteristic velocity for a given temperature, film thickness, and frequency where onset occurs. No “critical velocity” is predicted except atT=0. The model neglects the effects of prinning, and preliminary measurements seem to substantiate this assumption.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    International journal of thermophysics 17 (1996), S. 1305-1324 
    ISSN: 1572-9567
    Keywords: acoustics virial coefficient ; gas densities: equation of state ; speed of sound ; thermodynamic properties ; virial coefficients
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The relationships between the first three density virial coefficients (B, C, and D) and the first four acoustic virial coefficients (β a ,γ a ,δ a andε a are rederived and a published error relatingD toδ a is corrected. We observe that even it thenth and higher-density virial coefficients of a hypothetical gas are identifically zero, thenth and higher acoustic virial coefficients are not zero; they depend on the temperature derivatives of the 1st through (n-1)th density virial coefficients. Thus, two density virial coefficients may suffice for a fit to acoustic data with a cubic pressure dependence. These results are exploited by extending the pressure range of fits to preciously published speed-of-sound data without either introducing additional parameters or degrading the fits. We deduce gas densities from fits to speed-of-sound data with acoustic virial coefficients having the temperature dependencies calculated from square-well potentials. The estimated densities differ from independent measurements be a few tenths of a percent in an important range of conditions, These estimates require nop p T data whatsoever.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    International journal of thermophysics 21 (2000), S. 983-997 
    ISSN: 1572-9567
    Keywords: acoustic resonator ; argon ; Greenspan viscometer ; helium ; helium-xenon mixture ; methane ; nitrogen ; speed of sound ; viscosity of gases ; xenon
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract An improved Greenspan acoustic viscometer (double Helmholtz resonator) was used to measure the viscosity of gases at temperatures from 250 to 400 K and at pressures up to 3.4 MPa. The improvements include a vibration damping suspension and the relocation of the fill duct. The fill duct, which is needed to supply gas to the resonator, was connected to the center of the resonator to eliminate acoustic coupling between the resonator and the manifold. In anticipation of handling corrosive gases, all surfaces of the apparatus that are exposed to the test gas are made of metal. The viscometer was tested with argon, helium, xenon, nitrogen, and methane. Isothermal measurements were carried out at 298.15 and 348.15 K and at pressures up to 3.2 MPa. Without calibration, the results differed from published viscosity data by −0.8% to +0.3% (0.47% r.m.s.). These results are significantly better than previous results from Greenspan viscometers. The measurements also yielded the speed of sound, which differed from literature data by +0.16% to +0.20% (0.18% r.m.s.). Adding empirical effective-area and effective-volume corrections to the data analysis decreased the r.m.s. deviations to 0.12% for the viscosity and to 0.006% for the speed of sound. No unusual phenomena were encountered when the viscometer was tested with a helium-xenon mixture between 250 and 375 K.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1572-9567
    Keywords: 2-difluoromethoxy-1,1,1-trifluoroethane ; difluoromethoxy-difluoromethane ; E134: E245 ; heat capacity ; speed of sound
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We present measurements of the speed of sound in gaseous difluoromethoxy-difluoromethane (CHF2-O-CHF2) and 2-difluoromethoxy-1,1,1-trifluoroethane (CF3-CH2-O-CHF2). These measurements were performed in an all-metal apparatus between 255 and 384 K. We have obtained ideal-gas heat capacities and second acoustic virial coefficients from analysis of these measurements. Two methods of correlating the second acoustic virial coefficients, a square well model of the intermolecular interaction and a function due to Pitzer and Curl, are presented.
    Type of Medium: Electronic Resource
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