In this particular model the two manifolds of the stack are represented by a 7 mm diameter tube each, which are made from PMMA for omnidirectional optical access to enable PIV measurements. These manifold tubes are interconnected by 32 flexible tubes representing the microchannels within the cathode side of the bipolar plates of the individual fuel cells. Length and diameter of these tubes are chosen to obtain a pressure drop that is typical for the laminar flow within the microchannels of the cathode-side flow field. Hence, a fuel cell stack model is gained that is able to resemble the fluidic system of a stack (compare sketch in Fig. 1). For experimental ease regarding flow velocities and seeding particles, water was used as fluid. Since electrochemical effects are neglected in this simplified model, only the fluid mechanical similarity is of importance. As long as the Reynolds number is the same as in the real fuel cell stack, any Newtonian fluid can be used for the experiment. In this first validation experiment the model stack is integrated in a circular piping system consisting of a pump, a flow straightener just before the inlet manifold, the model stack itself, a flow meter with needle valve and an open reservoir which is again connected to the pump.