Modelling and Testing of Air Flow in a HVAC Module

Airflow through an automotive air conditioning unit was mathematically modelled and validated using data from an experimental model. The domain of the model was limited to the HVAC module, including the heater and evaporator cores, subsequent mixing chamber and outlet ducting (which was of a simplified geometrical nature). The blower fan and scroll were not included and instead replaced, in the experimental and theoretical models by a fully developed flow entering the HVAC through a straight duct. The Computational Fluid Dynamics (CFD) code FLUENT 5.0 was used as the basic mathematical modelling tool.

Overall, the CFD model predictions showed the same trends as the experimental model at the outlets and across selected internal planes although some of the CFD predictions were outside the desired tolerance level when compared to the measured data. Nevertheless, considering the very torturous paths imposed on the airflow by the compact nature of the HVAC module, the level of predictive accuracy achieved was encouraging. It is felt that, with the level of modelling complexity adopted here, useful exploration of design alternatives can be carried out using CFD to indicate the likely nature of changes to the flow. Absolute values of flow parameters for final design decisions should be established by confirmation with experimental measurements on prototype HVAC modules.