An experimental study was conducted on the promotion and control of turbulent mixing of hot and cold airflows in a rectangular channel with a T-junction, which simulated an HVAC unit for automobile air-conditioning system. A delta-wing row was installed on the bottom wall of the main channel before the T-junction to promote and control the turbulent thermal mixing. The mean temperature and velocity distributions were measured in several cross sections after the flow merging by thermocouples and PIV, respectively, and the flow in the mixing region was visually observed as well. The development of the thermal mixing layer was promoted effectively by delta wings and the degree of thermal mixing could be controlled by changing the angle of attack of wings. Longitudinal vortices produced by delta wings disappeared just after the merging of two flows, but high turbulence generated by the interaction of those vortices and the branch flow was maintained to further downstream cross sections. The proper orthogonal decomposition analysis was applied to the fluctuating concentration and the fluctuating velocity fields to extract the dominant spatial structures in the T-junction. It was suggested that longitudinal vortices with clockwise and counter-clockwise rotations were shed alternately just behind each delta wing.