Modeling of Free-Expanding Argon Condensation Flow with a Unimolecular Evaporation Model

Zhong, Jian; Moghe, Nilesh; Fliflet, Deborah Levin

doi:10.2514/6.2008-1182

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“…The total energy, E c,int , has been conserved to within 0.1%, as seen by the evolution of E c,int , kinetic E c,kin , and potential E c,pot energy of a single trimer cluster as a function of time. 23 Since the total energy and mass of the cluster without evaporation are constant, we may describe the cluster as being in an equilibrium state during which the internal kinetic energy and temperature fluctuate frequently. Calvo et al 24 proposed that the distribution of argon atom kinetic energy inside a cluster, e k,i , has the following analytical form:…”

Section: B Cluster Kinetic Binding and Dissociation Energiesmentioning

confidence: 99%

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

Zhong

Moghe

et al. 2009

Physics of Fluids

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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.

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Section: B Cluster Kinetic Binding and Dissociation Energiesmentioning

confidence: 99%