*2.4. Boundary Conditions and Convergence Criteria*

Unlike other high-temperature-resistant materials, graphite does not soften as the temperature rises; in fact, its strength increases [37]. At the working temperature of a fuel cell, graphite has great thermal conductivity, allowing waste heat from the bipolar plate to be effectively transferred to the coolant. Because the volume of graphite varies little when the temperature changes quickly, it has good thermal shock resistance [38]. It possesses strong chemical stability and corrosion resistance at the same time [37,39]. Therefore, graphite is used as the material of the coolant and cooling plate. The model uses computational fluid dynamics software Fluent to analyze the heat transfer performance. The material of the cooling plate is graphite. The energy equation has been introduced and the SIMPLE algorithm is used to solve the continuity equation. The pressure term adopts the standard discrete format. The K-epsilon turbulence model is adopted for the flow of the coolant. A first-order slip boundary is used, the Navier-Stokes equations is used to calculate

the flow iteratively, and the numerical simulation results are obtained. We set the inlet and outlet pressure, temperature and flow monitors to cooperate with the residual monitoring to determine that the solution is completed, and initialize with standard initialization. The residual errors of all parameters are below 10−<sup>4</sup> as the iterative convergence judgment standard, and the calculated boundary conditions are shown in Table 2.

**Table 2.** Boundary conditions.

