Characterization of dynamic fluctuations of CO2 fluid parameters at critical regions near the pseudo-critical line

Abstract

Dynamic parameter fluctuations of a fluid in the critical region exhibit abnormal phase behaviors. Explanation of the pseudo-critical line, even at the supercritical region, shows difficulties in the continuous traveling and crossing process of the near-by region. The present study shows molecular dynamics simulation of CO2 fluid near the pseudo-critical line, using an updated set of CO2 parameter-set in all-atom optimized potentials for liquid simulations forcefield. Standard deviation analysis has been employed to analyze the regularity and characteristic of CO2 existence near its pseudo-critical line. Different from the conventional phase-analogy method, the nonequilibrium supercritical CO2 fluid shows asymmetry behavior around the pseudo-line ridge, which indicates the uneven parameter distribution at two sides. Instead of a simple “mixture” explanation, local distribution parameters illustrate the intermolecular aggregation and structural transformation across the near-pseudo-critical line region. At the far-away region, fluctuation amplitude decreases and the transient aggregation phenomenon vanishes.