Numerical Modeling of Heat Transfer and Water Shedding in Automotive Evaporator Louvered Fins

A mathematical model has been developed to simulate mass and heat transfer of humid air flows at the airside of automobile air conditioning evaporators. The phenomenon of water condensation and water shedding in louvered fins are modeled based on extension of the existing Eulerian two-fluid method which treats water and air as two continuous media. A species transport equation for the mass fraction of water vapor in humid air is solved. The condensation of water from the air mixture translates into a sink term for the vapor transport equation and an equal source in the continuity equation for the volume fraction of liquid water in the two-fluid system of equations. A critical element in modeling the condensate transport in louvered fins calls for a surface tension force sub-model, since the surface tension force is the primary resistance against water shedding and draining. A formulation is proposed to evaluate the surface tension force based on searching for the most probable liquid-air interface where sharp gradient of water volume fraction exists. Numerical aspect of the implementation is discussed. In order to validate the model and demonstrate the applicability of the present methodology, a six-louver two-dimensional test case is established. The relative influence of the stopping force on liquid distribution pattern and flow was illustrated. The simulation is then carried out on a full-scale 2-D louvered fin design for different operating conditions. This study has demonstrated the feasibility of modeling “wet” heat transfer and water shedding in evaporator fins with an Eulerian two-fluid based method.