Improving the CFD predictive accuracy of particle fate in turbulent duct flows: Four key issues and applications in in-duct UVGI system

In order to refine the CFD methodology for predicting particle fate in duct flows, this study investigated four key issues largely influencing the predictive accuracy. The flow field modeling method applicable to in-duct UVGI systems (ID-UVs) was also investigated. The particle number independence test indicated that at least 30000 particles should be released. The use of 2D duct cannot consider particle trapping at the sidewalls, thus underestimating the particle deposition behavior. The two-equation k-epsilon models significantly overestimated the fluctuation velocity perpendicular to the duct walls in the near-wall region, resulting in them providing Vd+ and eta were on average 1767.9 % and 451.3 % higher than those predicted by the RSM model, respectively. Corrections for fluctuation velocity had very limited benefit in improving the predictive accuracy of the two-equation k-epsilon model, which unexpectedly resulted in a decrease in the predictive ac-curacy of the RSM model. Therefore, it was recommended to use the uncorrected RSM model to predict the 3D duct flow field to obtain a high prediction accuracy of particle fate. Similarly, the RSM model was also recommended for modeling the flow field in ID-UVs instead of the two-equation k-epsilon model that was often used. This study also revealed that missing the "Wall Reflection Effects" would lead to confusing results and analyzed the reasons for the quantitative differences in the results obtained in previous studies. The findings presented may form a CFD methodological framework for further investigation of the in-duct air purification technologies.