Advanced validation of the developed PEM Model was carried out using a Full Coupled Fuel Cell (Fig. 9(b)) at various relative humidities at the cathode inlet. The computational geometry consists of four parts: the first part is the main part of the co-simulation, containing fuel cell and gas channels with 677,264 computational cells. In the first part of the simulation cell the mass transport is calculated, in the other three parts mainly the heat transport between the cell elements is computed. More detailed descriptions of the simulation procedure of PEMFC by CFD Code AVL FIRE are found in Refs.