Non-nulling protocols for fast, accurate, 3-D velocity measurements in stacks.

The authors present protocols for making fast, accurate, 3D velocity measurements in the stacks of coal-fired power plants. The measurements are traceable to internationally-recognized standards; therefore, they provide a rigorous basis for measuring and/or regulating the emissions from stacks. The authors used novel, five-hole, hemispherical, differential-pressure probes optimized for non-nulling (no-probe rotation) measurements.

Facility for Calibrating Anemometers as a Function of Air Velocity Vector and Turbulence.

NIST calibrates anemometers as a function of airspeed vector and turbulence intensity (). The vector capability (sometimes called "3-D") is particularly important for calibrating multi-hole differential-pressure probes that are often used to quantify pollution emitted by smokestacks of coal-burning electric power plants. Starting with a conventional "1-D" wind tunnel, we achieved vector and capabilities by installing translation/rotation stages and removable turbulence generators (grids or flags).

Erratum: Improved First-Principles Calculation of the Third Virial Coeffcient of Helium.

[This corrects the article on p. 729 in vol. 116.

Refractive-index gas thermometry.

The principles and techniques of primary refractive-index gas thermometry (RIGT) are reviewed. Absolute primary RIGT using microwave measurements of helium-filled quasispherical resonators has been implemented at the temperatures of the triple points of neon, oxygen, argon and water, with relative standard uncertainties ranging from 9.1 × 10 to 3.

Progress Towards a Gas-Flow Standard using Microwave and Acoustic Resonances.

We describe our progress in developing a novel gas flow standard that utilizes 1) microwave resonances to measure the volume, and 2) acoustic resonances to measure the average gas density of a collection tank / pressure vessel. The collection tank is a 1.85 m, nearly-spherical, steel vessel used at pressures up to 7 MPa.

Energy accommodation coefficient extracted from acoustic resonator experiments.

We review values of the temperature jump coefficient determined from measurements of the acoustic resonance frequencies of helium-filled and argon-filled, spherical cavities near ambient temperature. We combine these values of with literature data for tangential momentum accommodation coefficient (TMAC) and the Cercignani-Lampis model of the gas-surface interaction to obtain measurement-derived values of the normal energy accommodation coefficient (NEAC). We found that NEAC ranges from 0 to 0.

Advances in thermometry.

The last 25 years have seen tremendous progress in thermometry in the moderate temperature range (1 K to 1235 K). Various primary thermometers - based on different physics -have uncovered errors in the International Temperature Scale of 1990 and set the stage for the planned redefinition of the kelvin.

Improved First-Principles Calculation of the Third Virial Coefficient of Helium.

We employ state-of-the-art pair and three-body potentials with path-integral Monte Carlo (PIMC) methods to calculate the third density virial coefficient C(T) for helium. The uncertainties are much smaller than those of the best experimental results, and approximately one-fourth the uncertainty of our previous work. We have extended our results in temperature down to 2.

Shear thinning near the critical point of xenon.

We measured shear thinning, a viscosity decrease ordinarily associated with complex liquids, near the critical point of xenon. The data span a wide range of reduced shear rate: 10(-3) View Article and Find Full Text PDF

Theory of the Greenspan viscometer.

We present a detailed acoustic model of the Greenspan acoustic viscometer, a practical instrument for accurately measuring the viscosity eta of gases. As conceived by Greenspan, the viscometer is a Helmholtz resonator composed of two chambers coupled by a duct of radius rd. In the lowest order, eta=pi f rho(rd/Q)2, where f and Q are the frequency and quality factor of the isolated Greenspan mode, and rho is the gas density.

Design and Uncertainty Analysis for a PVTt Gas Flow Standard.

A new pressure, volume, temperature, and, time (PVTt) primary gas flow standard at the National Institute of Standards and Technology has an expanded uncertainty (k = 2) of between 0.02 % and 0.05 %.

Can a Pressure Standard be Based on Capacitance Measurements?

We consider the feasibility of basing a pressure standard on measurements of the dielectric constant and the thermodynamic temperature of helium near 0 °C. The pressure of the helium would be calculated from fundamental constants, quantum mechanics, and statistical mechanics. At present, the relative standard uncertainty of the pressure () would exceed 20 × 10, the relative uncertainty of the value of the molar polarizability of helium calculated .