Lattice Boltzmann simulation in components of polymer electrolyte fuel cell

A polymer electrolyte fuel cell (PEFC) is a very promising energy conversion device that generates electricity from hydrogen. The gas diffusion layer (GDL) is one of the main components in PEFC. On the cathode side, the liquid water is produced under the operating temperature (around 70 ∘ C). The liquid water flows through the GDL and is removed in the gas channel by the gaseous reactant to ensure the fuel cell work continuously. The situation on theGDL surface when water breaking through the GDL is very important to be studied in detail. The liquid water flowing through GDL process is simulated by the lattice Boltzmann (LB) ShanChen model. Because it is a capillary force dominated process the density ratio and viscosity ratio between two phases can be negligible. The multiple-relaxation time (MRT) approach and exact difference method (EDM) force scheme are implemented on the present model. The present LB ShanChen MRT-EDM two-phase model is validated by some tests. Different force schemes with single relaxation time (SRT) and MRT approach are compared in the external force driving Poiseuille flow test. Some model limitations, the lattice and relaxation time dependence are discussed in the flat interface test. The droplet test and contact angle test determine the model parameters to control the phase separation and material wettability. The open boundary condition is implemented on the outlet boundary for water flowing through the GDL simulations. The model is applied on the water flowing through the GDL which is fully covered with hydrophobic material. Some basic effects are studied including buffer space thickness, domain size, capillary number, geometry and wettability effects. It can be concluded that these factors have effects on the water flow behaviors. Under a specific capillary number condition, the results are consistent in quality with the theory of capillary force dominated process. Waterwill break through the GDL due to specified a velocity condition on inlet. The stochastic GDL geometries causes irregular water droplets are randomly formed on the GDL surface. The apparent contact angles and breakthrough point distances (BPD) for the formed water droplets are analyzed statistically. For the local apparent contact angles, they vary with different view directions and positions along different geometries. They are different to the idealized contact angles by symmetric simplification. For the breakthrough point distances, they are analyzed statistically in two ways. The distribution of distances are evaluated statistically by the Lilliefors test. It is concluded that the BPD can be described by the normal distribution with certain statistic characteristics. Information of the apparent contact angle and the shortest neighbour breakthrough point distance can be the input modeling setups on the cell-scale simulations in the field of PEFC simulations. Basic influences of polytetrafluoroethylene (PTFE) on the water flow are studied. Different PTFE content and PTFE distributions (along in-plane and through-plane directions in different sections) are applied on a GDL geometry. It is concluded that the PTFE content and its distribution have impact on the water flow behavior. The water is flowing preferably through the no-PTFE region. Different shapes of water saturation curves along the through-plane direction are observed on different PTFE distributions