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Physics

Thermodynamics

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Displaying 26 - 50 of 437

Dynamic acoustic optimization of pulse tube refrigerators for rapid cooldown

April 23, 2024
Author(s)
Ryan Snodgrass, Vincent Kotsubo, Scott Backhaus, Joel Ullom
Pulse tube refrigerators are a critical enabling technology for many disciplines that require low temperatures. These refrigerators dominate the total power consumption of most modern cryostats, including those that reach millikelvin temperatures using

The Four-sinker Densimeter: A New Instrument for the Combined Investigation of Accurate Densities and Sorption Phenomena of Gases and Gas Mixtures

February 29, 2024
Author(s)
Luca Bernadini, Reiner Kleinrahm, Katharina Moritz, Mark O. McLinden, Markus Richter
An apparatus for high-accuracy gas density and adsorption measurements over the range of temperature from (193 to 423) K and pressure from (0 to 15) MPa is described. This instrument is based on the two-sinker densimetry principle and incorporates a

Optical n(p, T_90) measurement suite 1: He, Ar, and N_2

November 23, 2023
Author(s)
Patrick Egan, Yuanchao Yang
An n(p, T90) measurement suite is reported for the gases helium, argon, and nitrogen. The methodology is optical refractive-index gas metrology, operating at laser wavelength 633 nm and covering the temperature range (293 T 433) K and pressures p 0.5

Small Corrections to 1989 NIST Constant-Volume Gas Thermometry Data

November 17, 2023
Author(s)
Allan H. Harvey
Constant-volume gas thermometry data published in 1989 for the difference between the thermodynamic temperature and the International Practical Temperature Scale of 1968 are corrected in two ways. A refined estimate of the thermal expansivity of the

Ab initio Calculation of Fluid Properties for Precision Metrology

September 12, 2023
Author(s)
Giovanni Garberoglio, Christof Gaiser, Roberto Maria Gavioso, Allan H. Harvey, Robert Hellmann, Bogumil Jeziorski, Karsten Meier, Michael R. Moldover, Laurent Pitre, Krzysztof Szalewicz, Robin Underwood
Recent advances regarding the interplay between ab initio calculations and metrology are reviewed, with particular emphasis on gas-based techniques used for temperature and pressure measurements. Since roughly 2010, several thermophysical quantities – in

An Equation of State for the Thermodynamic Properties of Helium

August 10, 2023
Author(s)
Diego Ortiz Vega, Kenneth Hall, James Holste, Allan H. Harvey, Eric W. Lemmon
This report documents the equation of state for fluid helium implemented in Version 10 of NIST's REFPROP Standard Reference Database. The equation of state is expressed as the molar Helmholtz energy as a function of temperature and density, and is valid

Quantum Entropic Effects in the Liquid Viscosities of Hydrogen, Deuterium, and Neon

July 26, 2023
Author(s)
Ian Bell, Jacob Leachman, Albert Rigosi, Heather Hill
The extreme conditions have limited the availability and accuracy of experimental thermophys- ical property measurements for cryogens, particularly transport properties. Traditional scaling techniques such as corresponding states theory have long been

pH response of sequence-controlled polyampholyte brushes

May 31, 2023
Author(s)
Xin Yuan, Harold Hatch, Jacinta Conrad, Amanda Marciel, Jeremy Palmer
We use molecular simulation to investigate the pH response of sequence-controlled polyampholyte brushes (PABs) with polymer chains consisting of alternating blocks of weakly acidic and basic monomers. Changes in the ionization state, height, lateral

Reference materials for phase equilibrium studies. 2. Solid-liquid equilibria (IUPAC Technical Report)

January 11, 2023
Author(s)
Ala Bazyleva, William E. Acree, Vladimir Diky, Glenn T. Hefter, Johan Jacquemin, M. Clara F. Magalhaes, Joe W. Magee, Kirk Nordstrom, John O'Connell, James D. Olson, Ilya Polishuk, Kurt A. G. Schmidt, John M. Shaw, J. P. Martin Trusler, Ronald D. Weir
This article is the second of three projected IUPAC Technical Reports on reference materials for phase equilibrium studies. The goal of this project was to select reference systems with critically evaluated property values for the verification of

Entropy Scaling of Viscosity for Molecular Models of Molten Salts

January 9, 2023
Author(s)
Jeffrey Young, Ian Bell, Allan H. Harvey
Entropy scaling relates dynamic and thermodynamic properties by reducing the viscosity to be a function of only the residual entropy. Molecular simulations are used to investigate the entropy scaling of the viscosity of three models of sodium chloride and

Physics-based Models for photonic thermometers

December 1, 2022
Author(s)
Zeeshan Ahmed
Resistance thermometry, meticulously developed over the last century, provides a time-tested method for taking temperature measurements. However, fundamental limits to resistance-based approaches along with a desire to reduce the cost of sensor ownership

Role of Non-Temperature-Gradient Power Flow Terms in Low-Temperature Regenerators

December 1, 2022
Author(s)
Ryan Snodgrass, Joel Ullom, Scott Backhaus
The total power flow through cryocooler regenerators is key to their performance because it reduces the cooling available at the cold heat exchanger. At temperatures near 4 K, the real-fluid properties of helium and the finite-heat-capacity of regenerator

Connecting entropy scaling and density scaling

August 17, 2022
Author(s)
Ian Bell, Robin Fingerhut, Jadran Vrabec, Lorenzo Costigliola
It is shown that the residual entropy (entropy minus that of the ideal gas at the same temperature and density) is mostly synonymous with the independent variable of density scaling, identifying a direct link between these two approaches. The residual
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