Analysis of PEM System Architectures That Enable Unification of the Aspiration and Cooling Into a Single System

In this work, a fuel cell cooling methodology is explored where excess oxidizer is sent to the fuel cell stack. With enough excess flow, the temperature increase of the oxidizer can fully account for the heat rejection by the fuel cell, thus potentially eliminating both the need for separate cooling channels in the stack, as well as the need for separate cooling hardware such as circulation pumps or blowers. To perform this work, a system model was generated consisting of a 1D PEMFC component model, as well as several 0D component models. Initially, two system models were generated: one with a recuperator and turbine, and a simply aspirated system without these components for when the stack pressure and oxidizer temperature is low. Eventually, these models were refined to incorporate 1D models of the fuel cell oxidizer channels to appropriately model the pressure drop through the stack. The outcome of these analyses is that this cooling methodology can be thermodynamically feasible even for low-temperature PEMFCs, although for LT-PEMFC there would be additional challenges with humidification of the membrane that are not explicitly considered here. A simply aspirated system is preferrable given the increase in compressor work at high oxidizer flow rates. For this methodology, the oxidizer channels must be sufficiently sized to limit pressure losses. To cool the analyzed stack to 80 °C (a typical stack temperature in low-temperature PEMFC applications), it was found that oxidizer channels with a 2.5 × 2.5 mm cross section would be required, which is a slightly larger cross section than what is typically used in PEMFC applications. The outcome of this work also shows that for high-temperature PEMFCs, the aspiration cooling scheme is advantageous and documents the thermodynamic and fluid dynamic parameters under which it would operate.