| The fuel cell is an electrochemical device that employs electrochemical reaction to produce electricity and thermal energy with water as the by-product. Because of its zero-emission nature, it plays a more and more important role in future energy conversion system. Among the various types of fuel cells, the proton-exchange membrane fuel cell (PEMFC) has been considered as a promising choice for the automobile since it operates at near-room temperature.; In this thesis, a two-dimensional water and heat management model has been developed to simulate the energy, fluid and mass transfer processes inside a PEM fuel cell unit. Since there is water transport across the membrane, the energy balance equation involves the following items: the electro-chemical reaction released energy, output electrical energy, sensible heat carried by flow, latent heat associated with water evaporation and condensation in the flow channel, cooling heat and the heat loss to environment. Based on this model, the fluid parameters can be predicted along the channels of both cathode and anode sides, such as: pressure drop, air temperature, hydrogen temperature, stack temperature, relative humidity, water vapor mole fraction, water liquid fraction, density, viscosity, Reynolds number, velocity volume flowrate, required pumping power, current density, output voltage and so on.; The simulation results in this research are verified very well by experiments under the similar working conditions. It shows that this model can effectively describe the flow behavior inside the PEM fuel cell. It has the potential to be a useful engineering tool for PEM fuel analysis and design. In addition, the simulations indicate that factors like the relative humidity, the liquid water and temperature distribution play important roles in attaining high performance. |
