Kinetic nucleation model for free expanding water condensation plume simulations

Abstract

Recent direct simulation Monte Carlo (DSMC) simulations of homogeneous condensation in free expansion water plumes [Z. Li, J. Zhong, D. A. Levin, and B. Garrison, AIAA J. 47, 1241 (2009)] show that the nucleation rate is a key factor for accurately modeling condensation phenomenon. In this work, we use molecular dynamics (MD) simulations of a free expansion to explore the microscopic mechanisms of water dimer formation and develop collision models required by DSMC. Bimolecular and termolecular dimer cluster formation mechanisms are considered and the former is found to be the main mechanism in expanding flows to vacuum. MD simulations between two water molecules using the simple point charge intermolecular potential were performed to predict the bimolecular dimer formation probability and the probability was found to decrease with collision energy. The formation probabilities and postcollisional velocity and energy distributions were then integrated into DSMC simulations of a free expansion of an orifice condensation plume with different chamber stagnation temperatures and pressures. The dimer mole fraction was found to increase with distance from the orifice and become constant after a distance of about two orifice diameters. Similar to experiment, the terminal dimer mole fraction was found to decrease with chamber stagnation temperatures and increase linearly with chamber stagnation pressures which is consistent with a bimolecular nucleation mechanism.

Nucleation is Second Order: An Apparent Kinetically Effective Nucleus of Two for Ir(0)nNanoparticle Formation from [(1,5-COD)IrI·P2W15Nb3O62]8–Plus Hydrogen

“…Noteworthy here is that these hints of the broader generality of bimolecular to termolecular nucleation encompass relatively weak bonding/associating chemical interactions such as those present in the protein aggregation and H 2 SO 4 nucleation systems. • Worth mentioning here is that there is also computational evidence for bimolecular nucleation as a preferred process in water condensation in expanding/cooling water plumes 69 and of simulated nucleation populations that drop off by ∼10 7.5 as one goes from dimers to 10-mers in a glassy solid crystallization system. 70 The protein aggregation simulations by Stryer come to mind here as well, Stryer showing that dimer formation is favored over all other aggregates in the monomeraddition mechanism 39 since only the dimer grows with a quadratic dependence on [A].…”

Modeling of CO2Homogeneous and Heterogeneous Condensation Plumes

“…The importance of the model versus CNT for argon was demonstrated in ref 5 and has recently been applied to modeling homogeneous water condensation. 29 In the kinetic nucleation model, the initial clusters and dimers are created by triple collision processes. Two molecules, denoted as M and M, first form a metastable collision complex, M 2 * .…”

“…In this work, we adopted a kinetic nucleation model based on previous research as an alternate approach to the CNT nucleation rate. The importance of the model versus CNT for argon was demonstrated in ref and has recently been applied to modeling homogeneous water condensation …”

Nanoparticle Nucleation Is Termolecular in Metal and Involves Hydrogen: Evidence for a Kinetically Effective Nucleus of Three {Ir3H2x·P2W15Nb3O62}6– in Ir(0)n Nanoparticle Formation From [(1,5-COD)IrI·P2W15Nb3O62]8– Plus Dihydrogen

“…Computational evidence also exists suggestive of bimolecular nucleation as a preferred process in water condensation in expanding/cooling water plumes and in simulated nucleation populations that drop off by ∼10 7.5 as one goes from dimers to decamers in a glassy solid crystallization system . In addition, Stryer has shown in protein aggregations that dimer formation is favored over all other aggregates in the monomer-addition mechanism since only dimers grow as a quadratic dependence on [ A ] .…”