Modeling the Transfer Properties of Helium and Hydrogen Isotopes by Thermodynamics and Molecular Dynamics Methods

This paper analyzes the analytical expressions available in the literature for calculating the coefficient of viscosity and thermal conductivity obtained from the Chapman–Enskog kinetic theory. A modification of the expressions is proposed taking into account the calculated value of the compressibility factor Z = PV/RT, obtained as a result of thermodynamic calculations using a theoretical model of the equation of state based on perturbation theory. To validate the modified expressions, the Green–Kubo model for modeling transport properties by the molecular dynamics method is considered. This model enables simultaneous calculation of both the viscosity and thermal conductivity within one calculation, having previously performed the statization of the system in the NpT ensemble. Molecular dynamics and thermodynamic simulation of the transport properties of individual helium and hydrogen isotopes are carried out in the pressure range of 1–2000 atm and in the temperature range of 200–3000 K. The viscosity and thermal conductivity coefficients are determined in the considered pressure and temperature range. It is shown that the use of modified analytical expressions for transfer coefficients makes it possible to calculate the viscosity and thermal conductivity of helium and hydrogen isotopes, taking the real pressure in the system in accordance with experimental data and the results of molecular dynamics simulation in a wide range of pressures and temperatures, including the supercritical region, into account.