FCS Characterization Effect of Operative Parameters

The experimental characterization of the FCS described in the previous paragraph is first performed using the operative conditions recommended by the manufacturer for maximum stack performance. 

The tests are run at the temperature of 346 K and reactant pressures of 250 kPa. The air flow rate is set for each load value in order to assure the correct stack operation and minimize air compressor power consumption and water flow rate necessary for the humidification. This regulation of oxidant flow rate determines a value of R ranging from 6 at low load to 2 at full load. An excess of air with respect to the stoichiometric requirement is always necessary due to the mass transport limitations on the cathode side (see Sect. 4.3). The stack humidification is performed by saturating the inlet air stream at the temperature value approximately equal to the measured one at the cathode outlet. 

In Figs. 7.4 and 7.5, the voltages of the individual cells are reported for the open circuit and full load, respectively. It can be noted that a rather uniform distribution of voltage is obtained also in severe operative conditions when the stack works at maximum power, with no endangering of the optimal stack operation. 

The different terms involved in the generation of power are reported in Fig. 7.6 as a function of stack current. In this figure, Pstack is the electric power produced by the stack, P, 

which corresponds to maximum load), and the constant and negligible consumption of 110 W is due to the cooling water pump. 

---