Fuel cell system is an advanced power system for the future that is sustainable, clean and environmental friendly. Fuel cells are electrochemical devices that convert the chemical energy of hydrogen and oxygen directly into electrical energy. Fuel cells are growing in importance as sources of sustainable energy and will doubtless form part of the changing program of energy resources in the future. Small fuel cells have provided significant advantages in portable electronic applications over conventional battery systems. Competitive costs, instant recharge, and high energy density make fuel cells ideal for supplanting batteries in portable electronic devices. For portable applications like laptops, camcorders, and mobile phones the requirements of the fuel cell systems are even more specific than for stationary and vehicular applications. The requirements for portable applications are mostly focused on size and weight of the system as well as the temperature. The CFD models in this book would allow the creation of powerful computational fuel cell engineering tools that lead to dramatic reductions in lead times and development costs, and spur innovative design.