Thermophysical Properties of Some Selected Alternative Refrigerants

A summary of a thermophysical properties program for six candidate alternative. refrigerants is given. This work has been performed recently at the National Institute of Standards and Technology (U.S.A.), Thermophysics Division, in Gaithersburg, Maryland. Properties measured include gas and liquid·phase PVT, vapo~ pressures, surface tension, index of ~efraction, dielect~ie eons~ant, gas phase speed of sound, critical parameters and materials compatibility. Results have been obtained for R 123, R 125, R 134, R 134a, R 14lb, and E 134 (some properties only). INTRODUCTION The ASHRAE 1989 CFC Technology Conference was held at the NIST laboratories in Gaithersburg MD in September 1989. There, it was pointed out that published informacion on the chermophysical properties of che potential alternati~e refrigerants was at besc spotty and in many cases, nonexis~ent. Only for R l34a and several mixtures do the published measurements approach those available for the present refrigerants, For R 123 the lack of publications was particularly notable. The information reported on the ethers is of mixed quality; some of it would be of limit@d usefulness for the c&leulation of accurat8 ~h@rmodynamic proper~ies. This assessment dces not, however, reflect the level of experimental effort being expended on these measurements worldwide. Due to th~ normal delays which occur between measurem~nt and publieacion, much of this work has not appeared in print. This paper gives a brief survey of the experimental measurements that have been made in the Thermophysics Division at NIST in Gaithersburg, Maryland during the past two years. Some of this work has been published, but much remains unpublished at present, Although I will concentrate on my own measurements, on R 134a, R 123 and R 14lb, I ~ill show some typical examples of the other results from our group, particularly where they overlap or complement my work. MEASUREMENTS The Gaithersburg portion of the Thermophysics Division has a wide variety of experimental capabilities. many of which have been turned to m~asurements on refrig8rants. The Appendix gives a brief summary of each appara~us along with its operating range and its accuracy. So~e resul~s can be obtain~d relatively quickly, and the number of systems studied has gone far beyond the leading three candidates which have been measured in Lhe slo~~ classical gas-phase PVT apparatus. Not all of Lhe results ~re comprehensive, however, that is they do not yet cover Lhe whole range of pressure and temperature of interest. The compressed liquid PVT measurements are at present limited to T<373 K; che index of refraction measure~en~s were made on saturated liquid and vapor only; speed of sound has been ~easured fer the gas phas~ at temperatures below 65 °C for Rl34a and Rl23 ~nd below 40°C for R14lb; dielec·tric constant has b8an ~easured only in the gas phase. The compatibility tests were of the sealed ampule type. They were used to determine compatibility with various metals at elevated temperatures, [1]. The measurements which we make, that are applicable to refrigerants, are as follows. Ih~ index of !efraction ,n, can be used to-calculate the density hy m@ans of the Lorenz-Lorentz relationship: (n -l)/(n2+2) -A P which holds surprisingly well, (1) The value_of A (the ~olecular polarizabflity) can