Evaporation Modeling for Polydisperse Spray in Turbulent Flow

Based on an overview of existing vaporization models, a suggestion for capturing phase transition in a turbulent two phase flow is made. Focus is put on the Uniform Temperature Model (UTM). Comparison between equilibrium and non-equilibrium evaporation models to experimental data is highlighted. Two configurations with different fuels, i.e. different thermodynamic properties, are investigated and the results of both models are validated with the measurements. The configurations exhibit completely different boundary conditions and polydisperse turbulent multiphase flows with different classes and probability distribution of the droplet diameters. Large eddy simulation (LES) and Reynolds averaged numerical simulation (here RANS) models are used to capture the turbulence. In both configurations, results show that non-equilibrium effects influence the vaporization significantly. The UTM with the extension of non-equilibrium, by Langmuir and Knudsen, capture the vaporization well, whereas the equilibrium model over-predicts the volume flux of the liquid phase, i.e. the vaporization process is developing slower in case of equilibrium model. Worth to notice that the mean droplet diameter is between 20 and 40 µm. Thus the ratio of surface to volume is important if compared to larger droplets. Non-equilibrium effects are then correspondingly important and the equilibrium model is not able to describe the phase transition process well.