Condensation Rate of Nitrogen and Oxygen at Cryogenic Temperature by Molecular Dynamics Simulations
JIAOU SONG, Joe Berry, Eirini Goudeli, The Univeristy of Melbourne
Abstract Number: 320
Working Group: Aerosol Physics
Abstract
Condensation of N2 and O2 occurs at cryogenic conditions in a range of engineering processes, such as liquefaction plants, or during uncontrolled release. Quantification of the condensation rate of N2 and O2 is crucial to better control the quality of N2/O2 liquefaction and to evaluate the safety of cryogenic hydrogen leaks. However, experimental data on the condensation of air and its dependence on temperature, supersaturation, and cluster properties are limited. So, modelling condensation relies on theoretical condensation models [1,2,3] that lack rigorous validation at deep cryogenic conditions, especially for small supercritical clusters.
Here, classical molecular dynamics (MD) simulations are implemented to model the condensation of N2 and O2 vapor on N2 and O2 droplets of various sizes (4 - 60 Å). Steady-state condensation rates are calculated by tracking the number of vapor species condensed on the droplet surface as a function of time for temperatures of 40 to 100 K, and vapor densities of 4.46 to 446 mol/m3, equivalent to 0.1 to 10 times the atmospheric density. The MD-obtained condensation rate is compared to theoretical condensation models, revealing 2-3 orders of magnitude differences, attributed to the limitations of existing models. The proposed approach allows for “ab initio” development of condensation rate equations, which can be readily used in computation fluid dynamics to improve the accuracy of the predicted condensation rates in various engineering applications.
[1] Gyarmathy G. 1960. Dissertation.
[2] Fuchs NA, Sutigin AG. Ann Arbor: Ann Arbor Science; 1970.
[3] Young JB. PhysicoChem Hydrodyn 1982;3:57–82.