Relationship between Viscosity Coefficients and Volumetric Properties:  Measurements and Modeling for Pentaerythritol Esters

Abstract

A rolling ball viscometer has been used in this work to determine the temperature and pressure dependencies of the dynamic viscosity of two pentaerythritol ester-based lubricants: pentaerythritol tetrapentanoate (PEC5) and pentaerythritol tetraheptanoate (PEC7). The viscosity measurements were performed along the six isotherms from 303.15 K to 353.15 K and at pressures up to a maximum of 60 MPa with an experimental uncertainty of (3%. It has been observed that the dynamic viscosity increases as the size and branching of the chains of the pentaerythritol esters each increase. Based on the viscosity experimental data, the pressure and temperature viscosity coefficients, together with the viscosity index, have been determined for these fluids. The experimental viscosity values, together with literature data of other pentaerythritol esters, 2,3-dimethylpentane, and squalane were analyzed with several models, based on free-volume or hard-sphere concepts. Furthermore, we have analyzed one of the expressions proposed by Schmelzer et al. [J. Chem. Phys. 2005, 122, 074511/1-074511/ 11] that relates the pressure-viscosity coefficient with the thermal expansion coefficient, the isothermal compressibility, and the temperature-viscosity coefficient. The Schmelzer et al. relation is valid for 2,3dimethylpentane but not for the other compounds. A more-general relation is proposed, which can explain the cases where the Schmelzer et al. equation fails.

The Pressure–Viscosity Coefficient of Several Ionic Liquids

“…The constant c reflects the intensity of the intermolecular and intramolecular interactions. In a very recent work, we have combined the thermodynamic scaling of the viscosity with the relation of Pensado et al [65,66] to derive an expression for the viscosity-pressure derivative (qg/qp) T , which includes the scaling exponent c:…”

High‐pressure viscosity and density of carbon dioxide + pentaerythritol ester mixtures: Measurements and modeling

“…17,22,23 The viscosity of the pure compounds is described satisfactorily with AADs ranging from 0.3% for CO 2 to 2.3% for PEC9. The parameters for pure CO 2 and POE lubricants are reported in Table 7, together with the deviations with which this model represents the dynamic viscosities of these compounds.…”

“…For pure carbon dioxide, the experimental viscosity values between 303.15 and 353.15 K and from 10 to 60 MPa were taken from a previous work of Pensado et al 17 For PEC5, PEC7, PEC9, and PEB8 the g values already measured between 303.15 and 353.15 K and from 0.1 to 60 MPa were used. 22,23 The models considered range from the simple classical mixing laws by Grunberg and Nissan 31 and Katti and Chaudhri 32 through empirical general correlations, such as the self-referencing model, 63 to recent approaches with a physical and theoretical background, such as the hard-sphere scheme 36,37,39 and the free-volume model.…”

“…The V 0 and R g parameters for the pure lubricants have been taken from a work of Pensado et al, 23 and for pure carbon dioxide they were determined by fitting the viscosity data previously reported. 17 The hardsphere model represents the viscosity of pure CO 2 with an AAD of 0.1%, a MD of 0.5%, and a Bias of 20.001%.…”

“…At present, our research group is studying the density [19][20][21] and viscosity [22][23][24] in broad ranges of temperature and pressure of pentaerythritol esters considered as precursors of POE oils (i.e., as components of refrigerant commercial oils), the solubility 25 of carbon dioxide in pentaerythritol esters, and the density and viscosity 17 of mixtures containing POE lubricants and CO 2 .…”