A fundamental equation of state for the (R134a + triethylene glycol dimethyl ether) mixture

Abstract

in Wiley InterScience (www.interscience.wiley.com).The thermodynamic properties of the mixture of 1,1,1,2-tetrafluoroethane (R134a) and triethylene glycol dimethyl ether (TriEGDME) have been modeled with equations of state in an extended corresponding states format. A recent equation of state for pure R134a was assumed as the reference while the scale factors have been obtained in neural network form by regression of experimental data for the mixture. The modeling was focused on the liquid phase, considering the possible application of such a mixture in a refrigeration plant; since the vapor pressure of pure TriEGDME is negligible over the considered temperature range, the vapor phase of the mixture at vapor-liquid equilibrium condition is almost pure R134a. Two fundamental equations are proposed herein. The first one, developed from a limited amount of experimental data is valid for R134a mole fractions greater than 0.94. The second equation was obtained from a wider data base; it has a larger number of free parameters to regress and covers the R134a mole fractions greater than 0.59. 2007 American Institute of Chemical Engineers AIChE J, 53: [1349][1350][1351][1352][1353][1354][1355][1356][1357][1358][1359][1360][1361] 2007 Keywords: extended corresponding states, neural networks, R134a, refrigerant þ lubricant mixtures, thermodynamic properties, TriEGDME IntroductionThe environmental problems connected with the use of chlorofluorocarbon (CFC) refrigerants, in particular the depletion of the stratospheric layer of ozone, have imposed the phase-out of such substances and their replacement with less harmful fluids. Consequently, the study of alternative refrigerants and of their properties has become a fundamental task for scientific and technical research.Nowadays, the fluids mainly used in the refrigeration and air-conditioning plants are hydrofluorocarbons (HFC) that show better environmental behavior, thanks to the absence of chlorine atoms in their molecules. Among the substances of this family, 1,1,1,2-tetrafluoroethane (R134a) is widely used, because of its favorable thermodynamic performances in compression cycles and its compatibility with the existing refrigeration plants designed for CFC refrigerants.The identification of a suitable alternative refrigerant does not completely solve the technical problem: in fact, in the compression plants, the working fluid is not a pure refrigerant (or a mixture of refrigerants), but a certain amount of lubricant, compatible and soluble with the refrigerant, must be added. Because the mineral oils that were used with CFCs for years show low solubility in HFC refrigerants, it is necessary to propose alternative lubricants. The problems posed by the selection of the lubricant have been widely studied in recent years; a partial review is given by Marsh and Kandil.1 Guidance for the choice of the most efficient lubricant for specific technical applications, as for instance the design of a refrigeration plant, requires the knowledge of the thermophysical properties of t...

Kirkwood correlation factors in liquid mixtures from an extended Onsager–Kirkwood–Fröhlich equation

“…In another interesting development, Mehrotra and co-workers [48][49][50] surmised that g A and g B in a mixture might be related by a common factor to g à A and g à B , respectively. Again, in view of eqn (19) this conjecture is dismissed by our results, even for ideal mixtures.…”

“…Eqn (19) expresses the dependence of g id A on composition through the change of e id r . At x A = 1, g id A equals g à A , as expected.…”

“…In order to better appreciate this dependency, from eqn (19) we worked out the following expression for the difference g id A À g à A :…”

“…Equations similar to eqn ( 19)-( 21) hold for constituent B. However, a word of caution should be said about the applicability of eqn (4) and ( 5), and hence of eqn ( 16) and (19). This is because in the event the difference e id r À ðn à A Þ 2 becomes negative we would be faced by a meaningless negative correlation factor g id A .…”

“…Glymes find application to stabilise solvates in high-energy rechargeable lithium batteries 15,16 and as synthetic lubricants in refrigerant-lubricant environment-friendly fluid mixtures. [17][18][19][20] There are numerous reports of experimental thermophysical properties of binary liquid systems containing glymes, for example with water, 21,22 alkanes, [23][24][25][26][27][28] haloalkanes 29 or dialkyl carbonates. 30 In turn, 2,2,2-trifluoroethanol is an amphiprotic hydroxilic solvent with high relative permittivity and dipole moment.…”