CFD Simulations and Potential of Nanofluids for PEM Fuel Cells Cooling

Polymer Electrolyte Membrane Fuel Cells (PEMFCs) are undergoing a rapid development, due to the ever-growing interest towards their use to decarbonize power generation applications. In the transportation sector, a key technological challenge is their thermal management, i.e. the ability to preserve the membrane at the optimal thermal state to maximize the generated power. This corresponds to a narrow temperature range of 75-80°C, possibly uniformly distributed over the entire active surface. The achievement of such a requirement is complicated by the generation of thermal power, the limited exchange area for radiators, and the poor heat transfer performance of conventional coolants (e.g., ethylene glycol). The interconnection of thermal/fluid/electrochemical processes in PEMFCs renders heat rejection as a potential performance limiter, suggesting its maximization for power density increase. To this aim, suspensions of coolants and nanoparticles (nanofluids) have been proposed for PEMFCs cooling, although their characterization has often been limited to the superior thermal conductivity, overlooking a comprehensive understanding, and leaving a relevant research gap. In this paper, nanofluids cooling is simulated using 3D-CFD in a small laboratory scale (25 cm2) model of a hydrogen-air PEMFC with a liquid cooling circuit. The variation of the coolant fluid is studied considering flow uniformity, heat rejection, pressure losses, and power generation, ultimately leading to a high-level analysis on the trade-off between heat transfer/storage, relevant for coolant channels in PEMFCs. The study elucidates the membrane conditions and the compositional requirements for ethylene glycol and water based nanofluids to lead to a net gain in the generated power density, modelled in the range of +5/10% for high particle loading (10%) and envisaged to reach +15% for hypothesized ideal compositions. The study clarifies the role of nanofluids for PEMFC cooling and redefines their enabler contribution in the development of high power density PEMFCs, indicating guidelines for their application-designed formulation.