Liquid-Phase Speed of Sound and Vapor-Phase Density of Difluoromethane

Abstract

Difluoromethane (HFC-32, DFM), with a global warming potential (GWP) of 677, is of interest as a pure refrigerant and as a component in low-GWP refrigerant mixtures. Additionally, difluoromethane has recently been identified as a safe, liquefied-gas electrolyte material in batteries. Using state-of-the-art instruments for measurements, this paper presents new liquid-phase speed of sound and vapor-phase density data for difluoromethane. Two hundred and nine liquid-phase speed of sound values were measured using a dual-path pulse-echo instrument at temperatures from 230 to 345 K and pressures from 2.1 to 70 MPa. Accounting for all sources of uncertainty, the relative expanded combined uncertainty (k = 2) in the speed of sound ranged from 0.035 to 0.17%. One hundred and thirty-eight vapor-phase density values were measured using a two-sinker densimeter at temperatures from 240 to 340 K and pressures from 0.1 to 1.61 MPa with an uncertainty of 0.011 to 0.12%. These experimental data will be valuable in the ongoing development of a new fundamental thermodynamic equation of state for difluoromethane.

A Dual-Path Pulse-Echo Instrument for Liquid-Phase Speed of Sound and Measurements on p-Xylene and Four Halogenated-Olefin Refrigerants [R1234yf, R1234ze(E), R1233zd(E), and R1336mzz(Z)]

“…Related to the uncertainty in the calibration of the path-length difference is the mechanical stability of the overall assembly comprising the crystal, spacers, and reflectors. Repeated measurements on propane taken over the course of 25 months revealed average differences of less than 0.005% as reported by Rowane et al, 29 and we take 0.005% as the standard uncertainty associated with the mechanical stability of the path lengths. Any corrosion of the reflector faces, especially corrosion that affected one reflector more than the other, would alter the effective path length difference.…”

“…This is the reason that we measured propane first. After repairs, subsequent measurements with this instrument required a full repetition of the path-length calibration (which was different than the one reported here), as discussed by Rowane et al…”

Report from the Extreme Ultraviolet (EUV) Lithography Working Group Meeting :

“…The speed of sound (SoS) is a particularly useful material property because it can be combined with density and isobaric heat capacity data at a single (T, p) point allowing one to derive the additional thermophysical properties of density, isobaric expansivity, and isobaric heat capacity at any temperature, T, and pressure, 𝑝. The value of the SoS measurement has been shown by researchers at NIST for refrigerant materials [31]. Accurate SoS measurements are crucial to reaching the ultimate goal of modeling a material's thermodynamic properties by use of an equation of state (EoS) [32].…”

“…A US patent on the instrument design and operation was submitted in October 2022 [34]. The new metal SoS instrument is an extension of an existing instrument at NIST that operates at less extreme temperatures and pressures [31]. The new instrument is currently under development, and additional dedicated resources are necessary to make tin measurements.…”

Journal of Chemical & Engineering Data: Introducing the Inaugural Early Career Board (ECB)

“…and Ph.D. degrees from the University of Washington-Seattle, all in mechanical engineering. She has investigated thermophysical properties’ usefulness in sustainable nanomaterial synthesis manufacturing and is now focused on the speed of sound metrology of materials . In addition to her technical publications, Dr. Rasmussen has given over 30 invited technical presentations and holds four U.S. patents.…”