Transient thermodynamic analysis of a fuel cell system

This presentation is concerned with the development of an analytical model capable of accurately predicting the transient temperature and voltage response characteristics of a fuel cell system. The Apollo fuel cell system was selected for analysis. For a given space mission, a complete time history of fuel cell temperature and voltage must be obtained before launch to determine (1) whether there are sufficient reactants aboard the spacecraft available for fuel cell consumption to complete the objectives of the mission-reactants consumed depend on the efficiency of the fuel cell, which is a function of operating temperature; (2) whether fuel cell voltage is always within its specification voltage band of 29 +-2 volts. In order to obtain the necessary relations for the variation of fuel cell temperature and voltage with time, a control volume was set up around the fuel cell stack, or heart of the system. Heat and mass balances were then used, time derivatives taken, and appropriate boundary and initial conditions applied. Due to the complexity of the system, it was necessary to introduce a set of simplifying assumptions in order to hold the number of varying parameters to a minimum. A certain amount of empirical (test) data was also needed. [...]