Numerical studies of complex reacting flows

This work is a numerical study of the design and operation of three reactor systems that represent great potential in their respective fields. As the design of reacting flow systems becomes more and more complex, it becomes infeasible to build and experimentally verify new ideas. Numerical simulation has demonstrated the ability to evaluate design geometries and operation without the investment in time, money, and safety hazards associated with developing new reactor designs. Reaction-transport models based on the fundamental conservation equations are solved using the Finite Element Method to predict the fluid flow, heat, and species concentration profiles within the reactors. A counterflow jet reactor (CJR) is being developed to study the homogeneous thermal decomposition of precursors related to Metalorganic Vapor Phase Epitaxy (MOVPE) and for particle nucleation studies. A proposed flow and heat transfer model of the CJR was validated through flow visualization. The geometry and operating conditions were evaluated with the model to locate optimal reactor configurations for the kinetic studies. A massively parallel 2D/3D bifurcation and stability analysis was undertaken which identified regions of multiplicity and oscillatory behavior with respect to the geometry and operating parameters. The design of vertical stagnation flow and rotating-disk reactors for the MOVPE of GaN has been studied. A fundamental reaction-transport model describing the MOVPE of GaN from trimethyl gallium and ammonia has been developed. This model has been tested against experimental data from research-scale and industrial-scale reactors. A reduced mechanism applied in 3D simulations accurately predicted the spatial variation of the deposition rate observed in the experimental data. Subsequent analysis revealed the sensitivity of growth rate uniformity to the position of obstructions in the gas inlets of the reactor. A parameter space study of a vertical reactor has revealed the underlying variables and phenomena that control growth rate uniformity under transport limited growth conditions. 3D studies of a multi-tube showerhead inlet were performed to examine precursor back diffusion effects, flow recirculation effects near the inlets, and the possible existence of multiple stagnation flow steady states. Finally, a parametric study of the conversion of ethane to ethylene in a short contact time reactor has been performed. Various operating conditions and geometries were studied to find the optimal conditions for the production of ethylene based on carbon conversion, selectivity to ethylene, and pollutant production.