Nucleation Rate and Critical Cluster Size of Nitrogen and Oxygen at Cryogenic Temperature from Molecular Dynamics Simulations
JIAOU SONG, Joe Berry, Eirini Goudeli, The Univeristy of Melbourne
Abstract Number: 319
Working Group: Aerosol Physics
Abstract
Controlling the quality of N2/O2 liquefaction and evaluating the safety of cryogenic hydrogen leaks requires an understanding and quantification of their rate of nucleation at cryogenic conditions. Despite the wide use of the Classical Nucleation Theory (CNT) and Mean-field Kinetic Nucleation Theory (MKNT) for the prediction of nucleation rate of aerosols, significant deviations are observed from nucleation measurements in cryogenic supersonic nozzles [1].
Here, classical molecular dynamics (MD) simulations are used to investigate the homogeneous nucleation of N2 and O2, using H2 and He as carrier gas at isothermal conditions at cryogenic temperatures (T = 30 – 80 K) and initial monomer concentrations between 5.65×1024–2×1027 m-3 [2]. A Lennard-Jones potential is employed to describe interatomic interactions, validated based on the pressure and temperature of N2 during steady-state nucleation experiments in cryogenic supersonic nozzles.
Increasing temperature and decreasing concentration of the nucleating vapor leads to larger critical cluster sizes formed during nucleation. A nucleation rate is derived by MD for N2 and O2. The proposed nucleation rate is in agreement with the CNT at temperatures below 60 K, but 3−7 orders of magnitude higher at temperatures >70 K. Contrary to CNT, MKNT underpredicts the nucleation rate compared to MD by up to 6 orders of magnitude at all temperatures. The proposed MD approach enables direct tracking of nucleation at temperature ranges where limited property data are available, allowing for accurate determination of the nucleation rate and improving the accuracy of nucleation theories.
[1] Bhabhe, A., & Wyslouzil, B. (2011). J Chem Phys, 135(24), 244311.
[2] Song, Berry, Goudeli (2023).