Density and viscosity of a polyol ester lubricant: Measurement and molecular dynamics simulation
LN Lin and MA Kedzierski, INTERNATIONAL JOURNAL OF REFRIGERATION-REVUE INTERNATIONALE DU FROID, 118, 188-201 (2020).
This paper presents new experimental data and detailed molecular dynamics (MD) simulations of density and viscosity for a typical, pure polyol ester, pentaerythritol tetrahexanoate (PEC6). The density and Newtonian viscosity of PEC6 were measured over 258.15 K to 373.15 K at atmospheric pressure and predicted by MD for the same temperature range and a wide range of pressure (0.1 MPa to 1 GPa). The viscosity was calculated primarily by nonequilibrium molecular dynamics (NEMD), while equilibrium molecular dynamics (EMD) simulations were also performed for comparison. In NEMD, the Newtonian viscosity was obtained by fitting the shear viscosities at different strain rates (10(7) s(-1) to 10(10) s(-1)) computed by NEMD simulations to a rheological model (Eyring or Carreau). Three force fields (OPLS, LOPLS, and DREIDING) were benchmarked in terms of their density and viscosity prediction accuracy of PEC6. The predictions were compared with the present measurements for 0.1 MPa and literature data for high pressures. Overall, LOPLS is the most accurate force field for PEC6. It predicts the density of PEC6 to within I 3%, and Newtonian viscosity to within 50% for the range of simulation conditions. The LOPLS force field and the presented computation techniques are expected to apply to other polyol esters and perhaps other classes of lubricants. Published by Elsevier Ltd.
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