Numerical Investigation of the Heat Transfer Characteristics and Wall Film Formation of Spray Impingement in SCR Systems

This work established a numerical model to investigate the heat transfer characteristics and wall film formation of spray impinging on the wall in the selective catalytic reduction (SCR) system. The model is developed by the Eulerian-Lagrangian approach, where the Lagrangian approach is used to represent the spray generated by a commercial non-air-assisted pressure-driven injector and the Eulerian approach is adopted to represent exhaust gas. The Stochastic Kuhnke Model is applied to spray/wall interaction. The model considers relevant processes, which include mass transfer, momentum transfer, heat transfer, droplet phase change, spray/wall interaction, and wall film formation. The numerical results compared with that of the experiment indicate that the model can accurately estimate the heat transfer characteristics of the wall surface during the spray impingement. Based on the numerical results, the causes of the spray local cooling effect and the rapid cooling effect are analyzed. The correlation between the critical transition temperature and the critical heat flux temperature for wall film formation is derived from the trends of wall temperature and heat flux. In this work, the Stochastic Kuhnke Model is applied and compared with the Kuhnke Model, which proves that it can improve the disadvantage of sudden change during the wall film formation. When the wall temperature is below the critical transition temperature, the wall film mass is sensitive to the wall temperature and increases as the wall temperature decreases.