Turbulent Mixing of Hot and Cold Air in HVAC Unit for Automobile (Thermal Mixing in Planar Shear Layer)

In HVAC (Heating, Ventilating, Air Conditioning) unit used in an automobile air-conditioning system, hot air heated by a heater core and cold air cooled by an evaporator is mixed to control the air temperature blown into the compartment. In simulating numerically the temperature control characteristics of the HVAC, the modeling of turbulent mixing process of hot and cold air is a key issue for improving the performance of the simulation. Detailed knowledge on the turbulent air mixing in HVAC unit is, however, quite scarce. Hence, as the first step to make clear the air mixing process in HVAC, we have made an experimental study on trubulent thermal mixing in a simple planar shear layer. In particular, the distributions of turbulent heat fluxes and turbulent Prandtl number over the mixing layer have been measured for two velocity ratios, and based on the experimental data, the production mechanism of the turbulent heat fluxes has been examined in detail.