Surface tension and density of dielectric heat transfer fluids of HFE type-experimental data at 0.1 MPa and modeling with PC-SAFT equation of state and density gradient theory

Abstract

Hydrofluoroethers (HFEs) belong to a family of promising fluids that find application potential both in scientific research and in many industrial areas. These include electronics cooling, cascade refrigeration, heat transfer fluids, lubricant carriers or even rinsing agents. However, the thermophysical properties of HFEs required for an effective design of technical applications are only vaguely described and the available experimental data for thermodynamic and transport properties are still limited. In order to improve the description of HFEs, new experimental measurements of liquid density and surface tension at pressure of 0.1 MPa and temperatures from 260 to 338 K were carried out with a series of five HFEs; namely HFE-7000, HFE-7100, HFE-7200, HFE-7300, and HFE-7500. Liquid density was determined from a single sinker buoyancy method with an expanded uncertainty of 0.50 kg•m−3. The Wilhelmy plate method and the du Noüy ring method were used for the measurement of surface tension with expanded uncertainties of 0.068 mN•m−1 and 0.18 mN•m−1, respectively. In the modelling part, a consistent fluid property model was developed based on the physically based equation of state PC-SAFT. Additionally, regarding polarity of HFEs, empirical correlation for dipole moment was addressed. In case of larger HFE molecules, it was determined that the polar modification named PCP-SAFT, provides only marginal correction. The equations were combined with the density gradient theory (DGT) in order to model vapor-liquid phase interface and predict the surface tension. DGT+PC-SAFT was found to provide good predictions for the surface tension of the five selected HFEs.