Fluid Phase Equilibria 275 (2009) 152–158 Contents lists available at ScienceDirect Fluid Phase Equilibria journal homepage: www.elsevier.com/locate/fluid Dielectric properties of 1,1,1-trifluoroethane (HFC-143a) in the liquid phase Anélia N. Gurova a , Ana P.C. Ribeiro a,b , Carlos A. Nieto de Castro a,b,∗ , Umesh V. Mardolcar a,c a Centro de Ciências Moleculares e Materiais, Faculdade de Ciências da Universidade de Lisboa, Campo Grande, 1749-016 Lisboa, Portugal b Departamento de Química e Bioquímica, Faculdade de Ciências da Universidade de Lisboa, Campo Grande, 1749-016 Lisboa, Portugal c Instituto Superior Técnico, Departamento de Fisica e Núcleo de Termofísica, Av. Rovisco Pais, 1049-001 Lisboa, Portugal article info Article history: Received 23 July 2008 Received in revised form 29 September 2008 Accepted 29 September 2008 Available online 15 October 2008 Keywords: Dipole moment HFC-143a Liquid state Relative permittivity 1,1,1-Trifluoroethane abstract The relative permittivity (ε r ) data of 1,1,1-trifluoroethane (HFC-143a), (CAS N# 420-46-2), a hydrofluoro- carbon (HFC) developed as a refrigerant that has zero ozone depletion potential, is reported. The relative permittivity of HFC-143a in the liquid phase was measured using a direct capacitance method at temper- atures from T = 218 to 294 K and at pressures up to P = 15 MPa, for a frequency of 10 kHz. The uncertainty of the ε r measurements is estimated to be better than ±1.2 × 10 -2 . A complete set of tables of experimental data as a function of temperature, pressure and density, is presented that covers the dielectric property needs for most engineering applications. To study the dependence of ε r on density and temperature on a molecular basis, the theory developed by Vedam et al. and adapted by Diguet was applied to analyse the data. The Kirkwood modification of the Onsager equation was used to obtain the value of its dipole moment in the liquid phase (*). The apparent dipole moment obtained was * = 3.293 D. The effective dipole in the liquid state predicted by the Kirkwood–Frölich theory is 2.530D. The measured values are compared with density functional and density functional self-consistent calculations (SCIPCM) of the electronic distribution and of the dipole moment of HFC-143a. Finally, the values of the isobaric thermal expansion and isothermal compressibility were estimated from the reported measurements. © 2008 Elsevier B.V. All rights reserved. 1. Introduction The prohibition to use working fluids in heat pumps, refriger- ation plants and air conditioning for environmental reasons, and the selection of alternative replacement fluids justifies the need for their properties, namely those necessary for an optimum tech- nological design. Pure HFC’s and mixtures of HFC’s can be used, but there are some restrictions related with finding compressor oil that is compatible with the working fluid. Many important fac- tors when selecting successful compressor oil are dependent on the working fluid’s solubility in the compressor oil and its dielectric properties. To minimize costly experimentation, new thermody- namic tools that can predict the behavior of HFCs and compressor oils will be very useful. Relative permittivity (ε r ) provides information about the behav- ior of molecules under an electrical field and it is dependent on chemical structure and molecular interactions [1]. It also repre- sents the electric properties of the compressor lubricants where the refrigerants are soluble. HFC-143a mixed with HFC-125 can replace ∗ Corresponding author at: Departamento de Química e Bioquímica, Faculdade de Ciências da Universidade de Lisboa, Campo Grande, 1749-016 Lisboa, Portugal. Tel.: +351 217 500 918; fax: +351 217 500 088. E-mail address: cacastro@fc.ul.pt (C.A. Nieto de Castro). R502 1 in commercial refrigeration (supermarket freezers and dis- play cases, transport refrigeration, cold stores) and in industrial refrigeration plants [1]. Due to its flammability, HFC-143a is not used yet as a pure substance. It is the purpose of this paper to report measurements on the electrical permittivity of 1,1,1-trifuoroethane, HFC-143a in the liquid state, as a function of temperature and pressure, and to con- tribute to the understanding of the molecular interactions in the liquid state, by calculating the dipole moments using available statistical mechanics theories of Kirkwood and Kirkwood–Frölich [2–4], as well as the Vedam formalism, applying the concept of Eulerian deformation, also named Eulerian strain, developed by Vedam et al. [5,6] and adapted by Diguet [7]. Recent studies of the measurement of the ε r in the liquid state and the interpretation of neutron scattering spectral data in conjunction with molecular dynamics simulations have been attempted to elucidate the liquid state structure of these systems. The present calculations of the electronic distribution and of the dipole moment in the liquid state for several alternative refrigerants were reported recently [8,9], and will be integrated in the present discussion. Finally, a recent attempt 1 R502 is the azeotropic mixture of HCFC-22 (chlorodifluoromethane) and CFC- 115 (chloropentafluoroethane) (48.8% HCFC-22). 0378-3812/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.fluid.2008.09.022