Numerical simulations of mixing for gas exhaust treatment

Sammanfattning: According to the World Health Organisation, nine out of ten people live in places with sub par air quality. Therefore, the study of the treatment of polluted air is from a global point of view of great importance, and a matter of life quality for both humans and as well as animals. There are several di erent methods to treat polluted air, this study focuses on treatment of gas exhausts through ozonation. In the ozonation pro-cess, ozone is injected into the air stream, reacting and degrading the pollutants. The mixing phenomena of ozone in air is highly important for the process, being the focus of this study.To study the mixing, a computational fluid dynamic study was commit-ted on the injection process, with geometries base on industrial applica-tions. The Finite Volume Method was implemented in the simulation software OpenFOAM, on a highly turbulent incompressible flow. To depict the turbulence, Reynolds average RNG k − ε with wall functions and the Large Eddy Simulation (LES) with Wall-Adapting Local Eddy-viscosity (WALE) models were utilized and compared. The mixing is implemented through the transport equation for a passive scalar. For the steady state simulations the Simple-implicit Method for Pressure Linked Equation (SIMPLE) solver was used, and the PIMPLE algo-rithm for the transient cases.First, the flow through a 90 degree elbow pipe bend was investigated. A secondary flow, perpendicular to the pipe, was induced by the pipe bend making the flow three dimensional. Both turbulence models showed great similarities to previous experimental results, and were deemed suÿcient in terms of depicting the flow behaviour. The intensity of the secondary flow depends on the curvature radius, whereas a change in Reynold’s number has negligible e ects on the flow. After the valida-tion, a study of the injection after the pipe bend was conducted, where the position of the injection showed the greatest e ect on the mixing quality. Due to the position being important, it was shown that the secondary flow highly correlates with the quality of mixing, where a high intensity yields a better mixing.