Mutual diffusion coefficients of heptane isomers in nitrogen: a molecular dynamics study

Area of Science:

• Chemical Engineering
• Physical Chemistry
• Computational Fluid Dynamics

Background:

• Accurate transport properties are crucial for designing chemical and mechanical systems involving mass, momentum, and energy transfer.
• Understanding fluid mixture behavior is essential for process optimization and safety.

Purpose of the Study:

• To determine mutual diffusion coefficients of heptane isomer and nitrogen mixtures.
• To compare molecular dynamics (MD) simulations with the Chapman-Enskog (C-E) equation for predicting these properties.
• To investigate the influence of molecular structure on diffusion in these mixtures.

Main Methods:

• Utilized molecular dynamics (MD) simulations with fully atomistic intermolecular potentials.
• Employed the Green-Kubo formula to compute mutual diffusion coefficients.
• Compared MD results with the Chapman-Enskog (C-E) equation using Lennard-Jones (LJ) potential parameters.

Main Results:

• MD simulations showed a maximum difference of 6% among isomers, while the C-E equation showed 3% in the 500-1000 K range.
• MD simulations identified heptane isomer structure as the primary factor influencing mutual diffusion coefficients.
• Computed cross interaction potential parameters (collision diameter σ(12) and well depth ɛ(12)) for the mixtures.

Conclusions:

• MD simulations provide accurate mutual diffusion coefficients for heptane isomer and nitrogen mixtures.
• The corresponding state principle is applicable to models weakly affected by anisotropic potentials.
• Molecular structure plays a significant role in the diffusion behavior of complex polyatomic molecules.