Measurement and calculation of densities and viscosities of PEC7 and PEC9 using molecular dynamics simulation

Abstract

To better understand the lubrication characteristics of refrigeration-compressor mechanical moving parts, the thermophysical properties of lubricants in a wide operating range of pressure should be well known, especially viscosity and density. However, the experimental data are always limited, particularly for higher pressures where experiments are difficult to implement. To obtain viscosity and density of lubricants in extreme pressures using a more cost-effective method, the densities and viscosities of pentaerythritol tetraheptanoate (PEC7) and pentaerythritol tetranonanoate (PEC9) were calculated using molecular dynamics (MD) simulations at the temperature range from 263.15 to 343.15 K and pressure range from 0.1 to 1.0 GPa. Compared to the experimental data at low pressures, the maximum relative deviations for density simulations of PEC7 and PEC9 are respectively 0.65 % and 0.70 %. The maximum relative deviations for viscosity simulations of PEC7 and PEC9 are respectively 18.9 % and 5.82 %. MD simulations combined with COMPASS forcefield can successfully calculate the densities and viscosities of pentaerythritol esters.