engleski

Development of Numerical Models Within the Liquid Film and Lagrangian Spray Framework

Different environmental regulations impose ever stringent limitations on flue gas emissions from industry and transport as a part of the air pollution and global warming problem solution and with it connected climate changes. Fossil fuel combustion emissions are influenced by the quality of mixing process between combustion air and fuel and flue gas aftertreatment system efficiency. From the above it is clear that the industry and transport are facing major challenges which can be only met by the development of new and more efficient systems using advanced tools for product development, one of which is computational fluid dynamics. This research is going to address three different areas all of which could be found within different industrial applications – liquid film rupturing, multicomponent liquid film evaporation and urea deposit formation and its chemical kinetics.This work will numerically describe liquid wall film phenomena through further upgrade of the existing mathematical framework based on the conservation laws of physical quantities. Within the commercial software package for computational fluid dynamics based on the method of control volume which will be used for research, spray droplets are described using the Lagrangian formulation, whilst the gaseous phase and wall film are solved by the Eulerian formulation. Developed mathematical models are going to be implemented by employing FORTRAN-based user functions that are connected to the main solver. It is expected that this research will define models for liquid wall film rupturing, multicomponent evaporation and chemical kinetics of urea deposits. After coding and implementation of all user functions, validation simulations are defined. They include generation of computational mesh, setting of initial and boundary conditions and selection of the appropriate differencing schemes and other relevant parameters of the solver. Verification of the film rupturing criterion was obtained through qualitative check of cell position where separation occurred and through manual calculation of separation criterion for activated cells. Urea thermal decomposition model was implemented in commercial CFD code and tested on the experiment where biuret was heated up in a test tube from room temperature with a heat rate of 2 K/minute. The validation of the multicomponent evaporation model was performed on two experimental set-ups, namely evaporation of two component liquid mixture in quiescent environment and strongly turbulent air flow conditions over the multicomponent film surface in the narrow gap (3.9 mm). Implemented model qualitatively captures behavior of liquid components in quiescent case but the evaporation rate is underestimated, whilst the evaporation in narrow gap case is satisfactorily described. The developed numerical framework in the area of liquid wall films has been proved to be sufficiently accurate on the series of selected validation cases and can be used as a tool in the modern development process of various industrial devices. Recommendation for future work should entail employing more detailed description of liquid wall film temperature and composition and its comparison versus currently developed model in terms of result’s accuracy and computational demands.

computational fluid dynamics; wall film rupturing; selective catalytic reduction; urea thermal decompo-sition; multicomponent evaporation

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