3D multi-phase simulation of metal bipolar plate proton exchange membrane fuel cell stack with cooling flow field

• The uniformity of gas distribution in the third and fourth fuel cells is the worst. • The local high temperature dilutes the oxygen concentration in the PEMFC stack. • Oxygen concentration in the stack is raised by 5.13% with cooling flow field. • Hydrothermal management of stack is more difficult compared to single fuel cell. • Hot spots for cooling are concentrated in the second, third and fourth fuel cells. A three-dimensional (3D) multi-phase numerical model for a full scale proton exchange membrane fuel cell (PEMFC) stack is established, including inlet and outlet manifolds, cooling flow fields, membrane electrode assembly (MEA), and gas flow fields (including gas distribution zones). The performance of six-cell metal bipolar plate (BP) stack with isothermal boundary and cooling flow field is analyzed comprehensively, respectively. The simulation results indicate that the uniformity of oxygen distribution in the third fuel cell (FC) and fourth FC flow field is the worst, and the gas velocity in the flow field is directly proportional to the concentration and inversely proportional to the volume fraction of liquid water. The local high temperature in the stack leads to the decrease of liquid water, the increase of water vapor molar concentration and the dilution of oxygen concentration in the third FC and fourth FC flow fields. The cooling flow field reduces the overall temperature of stack, and the maximum oxygen concentration increases by 5.13 %. However, it causes a large temperature difference of stack, the maximum is 21.3 K, which increases the inconsistency of temperature distribution in the flow field. When the stack has cooling effect, the working voltage of each FC is higher. When the position is the same and the thermal boundary condition is different, the temperature difference of the stack is 6.2 K, and that of the single FC is only 4.5 K. High temperature leads to the decrease of hydration degree of proton exchange membrane (PEM) and uneven local current density. The hot spots zones of cooling flow fields in stack are concentrated in second FC, third FC and fourth FC. Temperature is an important factor causing the performance difference of each single FC, and the thermal management of stack is more significant than that of single FC.