UREA-WATER DROPLET PHASE CHANGE AND REACTION MODELLING: MULTI-COMPONENT EVAPORATION APPROACH

Urea-water solution droplet evaporation is modelled using multi-component droplet evaporation approach. The heat and mass transfer process of a multi-component droplet is implemented in the Langrangian framework through a custom code in ANSYS-Fluent R15. The evaporation process is defined by a convection-diffusion controlled model which includes the effect of Stefan flow. A rapid mixing model assumption is used for the droplet internal physics. The code is tested on a single multi-component droplet and the predicted evaporation rates at different ambient temperatures are compared with the experimental data in the literature. The approach is used to model the injection of urea-water solution spray in a duct carrying hot air to predict the urea to ammonia conversion efficiency. Thermolysis reaction of the evaporated urea and the hydrolysis of the byproduct iso-cyanic acid are solved as volumetric reactions in the Eulerian framework using laminar finite rate approach. The spray simulation results are compared with the experimental data and the numerical results of surface reaction based direct thermolysis approach available in the literature.