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It is important to understand the influence of gas transport properties on the process of urea gas decomposition in the modeling of a urea-SCR system. The purpose of this study is to find the gas transport property that exerts the strongest influence on the process of urea gas decomposition in a urea-SCR system using a three-dimensional model with the laminar flow of incompressible viscous gas at a steady-state condition by the SIMPLE algorithm. It is found that the gas transport properties which have the strongest influence on the process of urea gas decomposition in a urea-SCR system are the density and molecular diffusivity. It is also found that the influence of density is stronger than the molecular diffusivity at low temperature ranges. In contrary, the molecular diffusivity has stronger influence at high temperature ranges comparing with the density.

A comprehensive three-dimensional modeling for a single channel of SCR monolith reactor is performed with the laminar flow of viscous gas by the SIMPLE algorithm. The main advantage of this modeling approach is that the processes in the gas phase, washcoat layer and solid substrate are calculated simultaneously by a three-dimensional steady-state simulation. The detailed simulation of SCR monolith reactor may help to understand the complex interactions between various physical and chemical processes that occur in the reactor channel. The washcoat layer is represented by a porous medium. The non-isothermal diffusion and reaction processes are calculated in the waschoat layer by suppressing the convective term of the species transport equation. The effects of pore diffusion and mass transfer on the gas phase which usually lumped into the gas-solid mass and heat transfer coefficients are directly calculated by this fully distributed model.

A three-dimensional model with the laminar flow of an incompressible viscous gas at a steady-state is developed to simulate a urea-SCR system by the SIMPLE algorithm. A porous medium coated by a metal-oxide-based catalyst is considered in this study. The flow field and chemical reactions inside the reactor are calculated simultaneously by a porous medium approach. In a urea-SCR modeling, the gas transport properties exist as parameters in each of the conservation equations. The evaluations of density, diffusion coefficients, viscosities, thermal conductivities and specific heats are required to select the most suitable gas transport properties in a numerical modeling of a multi-component gaseous mixture and chemically reacting flow.