Speed of Sound Measurements of Binary Mixtures of 1,1,1,2-Tetrafluoroethane (R-134a), 2,3,3,3-Tetrafluoropropene (R-1234yf), and trans-1,3,3,3-Tetrafluoropropene (R-1234ze(E)) Refrigerants

Abstract

Speed of sound data measured using a dual-path pulse-echo instrument are reported for binary mixtures of 1,1,1,2-tetrafluoroethane (R-134a), 2,3,3,3-tetrafluoropropene (R-1234yf), and trans-1,3,3,3-tetrafluoropropene (R-1234ze­(E)). For each binary mixture, the speed of sound is studied at two compositions of approximately (0.33/0.67) and (0.67/0.33) mole fraction. The conditions covered in this study range in temperature from 230 to 345 K and from pressures slightly above the bubble curve up to a maximum pressure of 51 MPa. However, to avoid potential polymerization reactions, data for mixtures containing R-1234yf are limited to a maximum pressure of 12 MPa at temperatures below 295 K and 8 MPa at temperatures above 295 K. The mean uncertainty of the measured speed of sound is less than 0.1%, where relative combined expanded uncertainties at individual state points range from 0.04 to 0.4% of the measured speed of sound value. The greatest combined expanded uncertainties are encountered as the state point approaches the mixture critical region where weakened echo signals and lower speed of sound values are observed. The reported data are compared to available REFPROP mixture models, which are not adjusted using the data reported here, with average absolute deviations ranging from 0.27 to 0.75% with maximum deviations as high as 1.1%. The comparisons to the REFPROP correlations show that further adjustments to the mixture models are needed to provide a representation of the data within its experimental uncertainty.

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

“…This behavior was observed, for example, by El Hawary et al for speed of sound measurements of isopentane at an operating frequency of 8 MHz and was characterized by a significant dampening of the echo signals at lower temperatures. Such behavior was not observed for the present measurements or for those reported in our previous studies for mixtures of hydrofluorocarbons and hydrofluoroolefins. ,, …”

“…The results in Figure show that even after 2 years, the dual-path pulse-echo instrument calibration remained stable; during this time, measurements on 19 refrigerant mixtures were carried out. , Data tables containing the propane speed of sound data measured to validate the instrument are included in the Supporting Information.…”

“…The dual-path pulse-echo instrument used to measure the speed of sound has been described in detail elsewhere, and only key details are outlined here. − At the heart of the instrument, a quartz crystal, acting as both an ultrasonic signal transmitter and receiver, is immersed in the sample fluid. A 10-cycle sinusoidal tone burst from an arbitrary function generator excites the crystal at its resonance frequency of 8.00 MHz; the generated tone burst thus emitted from both faces of the crystal traverses the fluid along short and long paths of 12 and 30 mm defined by tubular spacers before returning from flat reflectors at each end of the sample volume.…”

“…The uncertainties in the temperature and pressure had a relatively small contribution to the combined uncertainty; variations between repeat determinations of the Δt [up to 12 replicates at each (T, p) state point] averaged 0.02%; details pertaining to the calculation of Δt are described elsewhere. 33 The uncertainty contribution from the composition was negligible since the samples used here had a purity of 99.99%. All speed of sound state point uncertainties reported in this study are calculated with a coverage factor, k = 2, or approximately 95% confidence level.…”

“…Such behavior was not observed for the present measurements or for those reported in our previous studies for mixtures of hydrofluorocarbons and hydrofluoroolefins. 33,35,37 The crystal/spacer/reflector assembly was housed within a type 316 stainless-steel pressure vessel, which was, in turn, situated within a liquid bath whose temperature was measured using a standard platinum resistance thermometer (SPRT) located adjacent to the cell. The temperature control of the instrument was accomplished using the thermostated bath.…”