Development of Homogeneous Water Condensation Models Using Molecular Dynamics

A condensation phenomenon in free expansion plumes has been observed and studied in the past several decades. To model homogeneous condensation of small, polar molecules produced in the combustion products of chemical propellants, such as water, accurate microscopic cluster models need to be developed. In this work, the molecular dynamics method is used to develop a model of water cluster sizes, cluster–monomer collisions, and sticking probabilities necessary for the study of water homogeneous condensation in a plume expanding to low pressure, space conditions. The molecular dynamics results are integrated into a direct-simulation Monte Carlo simulation and the simulated Rayleigh scattering intensities are compared with experimental data to test the models and direct-simulation Monte Carlo simulation results. Nomenclature b = impact parameter, m bi;m = cluster maximum impact parameter, m bm = maximum impact parameter, m cp = specific heat capacity, J=kg K cr = relative collision velocity, m=s cref = reference relative collision velocity, m=s