Effect of molecular elongation on the thermal conductivity of diatomic liquids

The effect of molecular elongation on the thermal conductivity of diatomic liquids has been analyzed using a nonequilibrium molecular dynamics (NEMD) method. The two-center Lennard-Jones model was used to express the intermolecular potential acting on liquid molecules. The simulations were performed using the nondimensional form of the potential so that the molecular elongation, d/sigma, was the only parameter varied in the simulation. The simulations were performed for five values of this parameter. First, the equation of state of each liquid was obtained using equilibrium molecular dynamics simulation, and the critical temperature, density, and pressure of each liquid were determined. Then, NEMD simulations of heat conduction in the five liquids were performed using values for temperature and density which were identical among the five liquids when they were reduced by their respective critical temperature and density (T=0.7 T-cr and rho=2.24 rho(cr)). Obtained thermal conductivities were reduced by the critical temperature, density, and molecular mass of each compound, and these values were compared with each other. It was found that the reduced thermal conductivity increased as molecular elongation increased. Detailed analysis of the molecular contribution to the thermal conductivity revealed that (a) the contribution of the heat flux caused by energy transport and by translational energy transfer to the thermal conductivity is independent of the molecular elongation, and (b) the contribution of the heat flux caused by rotational energy transfer to the thermal conductivity increases with the increase in the molecular elongation. (C) 2003 American Institute of Physics.