Abstract: The oxidation reactor plays the key role in the chloride process for producing titanium dioxide (TiO₂).The design of the initial mixing zone has direct influence on the quality of TiO2 products (i.e., particle size and its distribution).A detailed study was carried out on the hydrodynamics in gas cross-flow mixing zone by the non-intrusive measurement technique,particle imaging velocimetry(PIV).The effects of momentum ratio, width of jet aperture and the angle between bulk flow and jet flow were investigated.The results showed that larger momentum ratio, narrower width of the aperture, and 90° angle between wall jet and axial flow promoted a better flow field in the mixing zone.The computational fluid dynamics (CFD) technique was also used to study the above processes in theoretical modeling and numerical simulation.The CFD predictions had very good agreement with the PIV experimental data, which demonstrated the predictability of the proposed model for the cold-model flows.