Analysis of Pressure Drop From The Air Side in Automotive Heat Exchanger Using Porous Media Approach

Abstract

Air-to-liquid heat exchangers which are used in the automotive industry are of fin and tube type. In conjunction with the heat exchanger, axial fans are used, for two main reasons: to compensate the pressure drop of air and to enhance the cooling efficiency. In design process of heat exchanger, it is necessary to choose the appropriate axial fan which will meet the demands. One of the main data set in that sense is the relationship between the air volumetric flow rate and pressure drop in the heat exchanger. In this paper, air flow through the fin and tube type heat exchanger is analyzed using steady-state numerical simulations. Since it is practically impossible to generate the numerical grid for the real, physical fins, they are modeled using the porous media approach, with Darcy-Forchheimer model, applied in defined cell zone which corresponds to fins. By this, additional sink/source term is added in momentum equation. From series of numerical computations, where the inlet flow rate is varied, the relationship between pressure drop in porous zone and flow rate is established. Flow of the air is treated as incompressible and isothermal. OpenFOAM, free and open-source software for computational fluid dynamics (CFD) is used for aforementioned computations. The control volume is modeled to match the experimental airflow test rig set up, while for the boundary conditions velocity inlet and pressure outlet are used. Symmetry boundary condition is applied at the longitudinal plane of the model, in order to reduce the mesh count. Values of coefficients in Darcy-Forchheimer model are estimated from the geometrical characteristics of the heat exchanger and available experimental data. It is concluded that porous media approach implemented in OpenFOAM software can be used as toolkit in prediction of pressure of drop from the air side in automotive heat exchanger.