Turbulent Mixing of Hot and Cold Airflows in Automobile HVAC Unit

Characteristics of Velocity and Temperature Fields in Mixing T-junction

Abstract

In this paper, experimental results are reported on turbulent mixing of hot and cold airflows in a T-junction, which models the HVAC unit used in an automobile air conditioning system. Experiments were conducted keeping Reynolds number and temperature of the main flow at 2.5×10⁴ and 12°C, respectively, and the velocity of the branch flow (60°C) was changed for three velocity ratios of 0.5, 1, and 2. The influence of the channel aspect ratio on the flow characteristics was also investigated. The flow entering the main channel from the branch is separated at the edge of the T-junction and forms a large separation bubble. Longitudinal vortices are formed around this separation bubble, thus the flow field has a complex three-dimensional structure. In spite of such a complex flow field, the mean temperature of the airflow in the mixing layer shows quite uniform distributions in the spanwise direction of the channel. It was also found that the strong turbulence produced around the separation bubble does not work effectively to the thermal mixing of hot and cold airflows.