Thermophysical properties of n-dodecane over a wide temperature and pressure range via molecular dynamics simulations with modification methods

The working range of hydrocarbon fuel has gradually expanded to high pressure/high temperature con-ditions above the critical point with the proposal of "dual carbon" strategy. The calculation accuracy of fuel thermophysical properties in the power systems has become a major difficulty. In this study, the density, internal energy, enthalpy, entropy, thermal conductivity and viscosity of n-dodecane molecular system were calculated using the SKS-UA force field in the isothermal-isobaric (NPT) ensemble via molecular dynamics (MD) simulations in the range of temperatures from 298 K to 2000 K and pressures from 1.2773 atm to 3000 atm. Three modification methods in terms of stability modification, kernel den-sity estimation (KDE) modification and zero potential energy surface modification were proposed to improve the calculation accuracy. Average absolute relative deviation (AARD) and standard error (SE) were employed to perform error and uncertainty analysis on existing and non-existent thermophysical properties data of n-dodecane, respectively. The results indicated that the modified results for the six thermophysical properties are better than the original ones. The modified density, internal energy, enthalpy, entropy, and thermal conductivity were in good agreement with the experimental values, while the viscosity is underestimated at low temperature. The change in thermophysical properties was enor-mous near the critical point. Among the conditioned factors, pressure had a greater impact on density and thermal conductivity, while internal energy, enthalpy and entropy were more sensitive to temperature. Viscosity changed significantly when the temperatures were below the critical point. This modification method offers high-precision calculation results, inspiring the prediction of thermophysical properties over a wide temperature and pressure range.(c) 2022 Elsevier B.V. All rights reserved.