Computer aided fuel cell design and scale-up,comparison between model and experimental results

The present work illustrates the employment of an Automatic Scale-up Algorithm (ASA) to design a 200 cm² multiple serpentine (MS) flow field for a Polymer Electrolyte Fuel Cell (PEFC). With a fixed fuel cell active area and total pressure drop, the algorithm provides the flow-field design solution characterized by a specific set of parameters including channel width, rib width, channel height, covering factor, number of switchbacks, Reynolds number and pressure drop. It is known that a correlation exists between the mass flow passing through the electrode and the pressure drop, influencing the fuel cell performance. A pressure drop range from 5 to 45 kPa with steps of 5 kPa has been investigated. Numerical simulations performed on each geometry set have permitted a comparison of the flow-field total pressure drop with the analytical compressible calculation, and to evaluate the mass flow rate passing through the electrode and in the flow field channels separately. A comparison between ASA and CFD results has highlighted that the methodology is able to find a flow-field geometry that matches target geometrical and fluid dynamic requirements. A better agreement between the Automatic Scale-up Algorithm and direct CFD pressure drop calculation has been obtained taking into account the gas compressibility effects. The increase of the mass flow rate vs flow-field total pressure drop is also reported. A better understanding of the gas shorting phenomenon has been achieved by CFD post-processing, in terms of gas velocity profiles and pressure drop between adjacent channels. Since the gas shorting is a pressure driven effect, the total mass flow rate percentage passing through the porous backing has been related to the shorting velocity and geometrical parameters of the porous backing; moreover proportionality between “shorting” pressure drop and ratio of flow field total pressure drop and switchback number has been highlighted.