Numerical simulation of mixing of coaxial air flows with condensation

Abstract

A numerical model is described for the flow and cloud formation processes during co-current mixing of cold dry air and warm moist air in a large-diameter flow chamber. This numerical model solves for the flow pattern and the distributions of temperature, water vapor, and liquid water droplets in the chamber. The computational scheme uses a two-equation turbulence model ( k−3, model), which has been modified to include the effects of buoyancy and droplet condensation. The turbulent transport of momentum, heat, species, and droplets are simultaneously determined. The model also incorporates a treatment of the droplet growth and sedimentation mechanisms during the cloud formation process. Samples of the streamlines, isotherms, and contours of constant droplet and species concentrations obtained for a matrix of running conditions are presented. Results from this numerical model indicate that the wall of the cylindrical chamber (oriented vertically) has a very strong influence on the flow field and on the temperature distribution inside the chamber. The model predictions are shown to be in good agreement with limited experimental observations of a coaxial mixing process. The strengths and limitations of the model are also discussed.