Reduced Model of a Vehicle Cabin for Transient Thermal Simulation 2018-37-0022

In the proposed work the transient thermal modeling of a vehicle cabin has been performed. Therefore, a reduced model has been developed based on a one-node discretization of the cabin air. The conduction in the solid parts is accounted for by a one-dimensional heat transfer approach, the radiation exchange between the surfaces is based on view factors adopted from a 3D reference and the convective heat transfer from the cabin surfaces to the cabin air is conducted with the help of heat transfer coefficients calculated in a 3D reference simulation. The cabin surface is discretized by planar wall elements, including the outer shell of the cabin and inner elements such as seats. Each wall element is composed of several homogeneous material layers with individual thicknesses. Investigations have been conducted on the temporal and spatial resolution of the layer structure of these wall elements, for the 3D model as well as for the reduced one. The cabin air is discretized as one thermal mass, which acts as a reference temperature for both the convective heat fluxes at the inside surfaces of the cabin and zonal air temperatures. These are derived based on a distribution approach of the overall energy balance of the cabin air. The convective heat fluxes on the outside surfaces of the cabin are calculated by means of Nusselt correlations dependent on the vehicle velocity. Verification of this reduced model is conducted by comparison of calculated transient temperatures at the cabin air thermal mass, inside and outside surfaces of the two load cases “Heatup” and “Cooldown” with the full transient 3D conjugate heat transfer model results, which are in good agreement and show only small local temperature deviations.