Status of the round robin on the transport properties of R134a

Abstract

The paper contains a status report on an international project coordinated by the Subcommittee on Transport Properties of Conamissiort 1.2 of the International Union of Pure and Applied Chemistry. The project has been conducted to investigate the large discrepancies between the results reported by various authors Ibr the transport properties of RI34a. The project has involved the remeasurenaent of the transport properties of a single sample of R I34a in rdne laboratories throughout the world in order to test the hypothesis that at least part of the discrepancy could be attributed to the purity of Ihe sample. This paper provides an intercomparison of the new experimental results obtained to data in this project Ibr the viscosity and the thermal conductivity in both gaseous and liquid phases. The agreclncnt between the viscosity data from the laboratories contributing to the prc, jcct was improved with several techniques, now producirtg consistent results. This suggests that the purity of the samples of R I34a used in previous work was at least partly rcponsible Ibr the discrepancies observed. For the thermal conductivity in the liquid phasc the resuhs of the measurenlents are also more cortsistenl than before, although nut Ibr all experimental techniques. Nut all of the previous measurements suffered from ~ Invited paper presented at the Twelfth Symposium on Tllermophysical Properties. significant sample impurities, so Ihe present measurements on a consistent high-purity sample can be used to detect data sets v,,hich are outliers, possibly because of impurities. Identification of laboratories and techniques with systematic differences may require the examination of data Ibr several Iluids. The implications for future measurements of the transport properties of other refrigerants are significant.

Validation of an accurate vibrating-wire densimeter: Density and viscosity of liquids over wide ranges of temperature and pressure

“…The 1,1,1,2-tetrafluoroethane (HFC134a) used for the measurements was taken from a round-robin sample [ 13 ] of stated purity 99.9 % and was used without further purification. In all cases, the cell of the vibrating-wire densimeter was filled under vacuum through a 65-pm filter to avoid contamination or the admission of solid particles to the interior of the pressure vessel containing the densimeter.…”

“…Larger inconsistencies are observed for the densities of R134a than were for the other two liquids studied. Purity problems, which were known to exist for previous measurements with this refrigerant [ 13], are the likely cause for these errors.…”

“…The first of these contains the inertial contribution and the second the viscous drag. They are given by k= -1 +2 lm(A) k' =2 Re(A) (13) The complex quantity A depends on the modified Bessel functions Ko and K~ of a dimensionless group I2:…”

Thermophysical Property Measurements: The Journey from Accuracy to Fitness for Purpose

“…Indeed, discrepancies of up to 25% between the results of several laboratories for the viscosity of R134a [103] prompted a study by the Subcommittee on Transport Properties of the International Union of Pure and Applied Chemistry (IU-PAC) through a 'Round Robin' project to identify their causes. The principle outcome of the project was a greater consensus between laboratories on values for the various properties [104,105]. The causes for some of the original discrepancies remained unresolved however.…”

High-Pressure Viscosity Measurements of 1,1,1,2-Tetrafluoroethane

“…Measurement results published until 1992 for liquid R134a differed by up to 33 %. A round-robin project under the auspices of the former IUPAC Subcommittee on Transport Properties [3][4][5] did not identify the causes of the discrepancies [6]. They were elucidated in two NIST studies.…”