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The mixing characteristics of a passive scalar in the turbulent fl ow of a selective catalytic reduction process were numerically and experimentally investigated, focusing especially on an injection nozzle with multiple holes for the reducing agent. The multihole injection nozzle studied has six holes that are perpendicular to the ambient fl ue gas fl ow and are located near the tip of the nozzle. Large eddy simulation was applied to the turbulent fl ow and mixing fi elds to elucidate the mixing mechanism of the proposed nozzle compared with the single-hole nozzle that is commonly used in the conventional selective catalytic reduction process. From the results, there exist broader regions of higher turbulent intensities for the multihole nozzle than for the conventional single-hole nozzle. These regions are well matched with the positions of high vorticity in the near upstream region of the jet fl ow issuing from the multiple holes of the nozzle. Consequently, the high turbulent intensities and vorticity magnitudes lead to intensifi ed mixing between the fl ue gas and the reducing agent. Hence, the most suitable molar ratio between NOx and the reducing agent for the catalytic reaction can be easily obtained within a shorter physical mixing length as a result of the enhanced scalar mixing. Finally, the numerical results were applied to a trial design version of a multihole nozzle, and this nozzle was experimentally tested to confi rm its mixing performance.

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