engleski

Development of numerical models within the liquid film and Lagrangian spray framework

Liquid film flow sheared by an external air flow field is a physical phenomenon encountered in many engineering applications such as: burners, rain on vehicle windows and aircraft wings, rocket nozzles, mist eliminators, heat exchangers, steam turbine blades and especially internal combustion (IC) engines. Specifically, liquid wall films affect chemical composition of the gas phase and wall thermal behaviour of these systems. The goal of this research is additional improvement of the Eulerian liquid wall film model through further development and implementation of numerical models with the ultimate aim of achieving more accurate and computationally efficient calculations. The research hypothesis is that improved, adopted and newly developed numerical models are going to enable numerical simulations of multicomponent liquid wall films, and that they could be then used in industrial applications. The first objective was adaptation and implementation of semi-empirical wall film rupturing model to the numerical computational fluid dynamics (CFD) framework, as well as the seven step reaction mechanism for SNCR process modelling. Furthermore, two multicomponent liquid film evaporation models were developed, the first one on the basis of analogy between momentum and mass transfer, and the second one employing modified wall functions which take into account influence of the evaporation on boundary layer above liquid film. Particular scientific contribution is in implementation of the UNIFAC method for activity coefficients calculation, which is employed for the first time in the area of liquid wall films. Finally, the suitable kinetical model of urea thermal decomposition was adjusted and incorporated into existing numerical framework as a step in the process of description of urea deposits influence on overall domain of the real flue gas aftertreatment system. Developed mathematical models were implemented by employing FORTRAN-based user functions that are connected to the main solver of the commercial CFD code Fire. Coupling between the liquid wall film and the gas phase is achieved through the source terms in the mass, energy, species and momentum conservation equations. The ultimate goal was to obtain results of all relevant chemical and physical phenomena that are satisfactory on both qualitative and quantitative basis. The accuracy of numerical modelling, where possible, was determined by comparison with available and relevant experimental data. Results show satisfactory agreement with experiments and encourage future applications of implemented models in industrial CFD applications.

analytical force balance; catalyst; computational fluid dynamics; Eulerian approach; film roughness; film rupturing; gas aftertreatment; Lagrangian spray; multicomponent evaporation; NOx reduction; reaction kinetics; selective catalytic reduction; selective non-catalytic reduction; turbulent boundary layer; UNIFAC method; urea deposits; urea thermal decomposition; urea water solution; wall function; wall film

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