A unimolecular evaporation model for simulating argon condensation flows in direct simulation Monte Carlo

Abstract

In previous work, a cluster evaporation model was derived from the classical nucleation theory ͑CNT͒ to simulate condensation in free expanding plumes using the direct simulation Monte Carlo ͑DSMC͒ method. However, the use of a CNT evaporation model, especially in a low temperature environment, is problematic because macroparameters such as cluster surface tension and vapor saturation pressure are not physical for small cluster sizes. In this work, we propose a kinetic based evaporation model obtained from unimolecular dissociation theory ͑UDT͒ to model argon cluster evaporation processes in a free expanding plume. The UDT argon cluster evaporation model has been directly verified by molecular dynamics and quasiclassical trajectory simulations. It is found that although there is about one order of magnitude difference in the CNT and UDT evaporation rates, these two theories predict similar cluster evaporation rate trends as a function of cluster size and temperature. The verified new UDT evaporation model, as well as the previous CNT model, are applied to a free expanding argon condensation plume simulated with DSMC. The simulation results show that although there are some differences in cluster number density and average cluster size using the CNT and UDT evaporation models, the condensation onset conditions and Rayleigh scattering intensity for both models agree reasonably well with experimental data.

Modeling of CO2Homogeneous and Heterogeneous Condensation Plumes

“…A hybrid MD-DSMC approach was developed to construct a kinetic nucleation model for generating initial dimer clusters from a triple collision process . Finally, in ref , a kinetics-based evaporation model was obtained from unimolecular dissociation theory and directly verified by molecular dynamics (MD).…”

“…A homogeneous condensation model has been developed in previous work to simulate a free expanding argon (a Lennard-Jones system similar to CO 2 ) condensation plume using the direct simulation Monte Carlo (DSMC) method. − Our previous work can be briefly summarized as follows. On the basis of the mass, momentum, and energy conservation relationship, a comprehensive DSMC condensation model, including nucleation, cluster-monomer sticking and nonsticking collision, and cluster evaporation model, was developed .…”

Probing Phase Transitions with Supersonic Beams – A Joint Experimental and Theoretical Study

“…Moreover, the calculations of collision integrals require extensive numeric efforts and are not feasible at elevated densities even today. As importantly, calculations on a molecular scale [36][37][38] require the knowledge of temperature-dependent cross sections and unimolecular as well as bimolecular reaction rates; however, especially for molecular systems this information is largely missing.…”

Precision Velocity Measurements of Pulsed Supersonic Jets

“…The condensation of supersaturated gases also is of fundamental relevance in a number of research fields, such as, for instance, atmospheric and environmental chemistry, chemical engineering, and process technology. Recently, this subject has experienced a remarkable renaissance owing to urging questions in climate research and fascinating applications in materials science and also due to significant progress achieved in computer-based molecular simulations − and modern experimental methods. − Despite a great deal of theoretical and experimental work, open questions remain, including, for example, the gas−liquid phase transition close to the critical point and rapid nonequilibrium processes.…”