Experimental

Analysis of cell exhaust gas

Configuration of the short stack used in this work is as follows: the electrode area of 2000cm2 (square shaped), the gas cross flow type, the construction of 6cells/cooIer, the average current density of 300mA/cm2 (the load current of 600A), the average cell temperature of 190°C, the operating pressure of atmosphere. To obtain the exhaust gas from gas channel, sampling tubes were put into the outlet gas manifold as shown in Fig. 1. Gas compositions were measured in dry base under several operating conditions with changing temperature distribution of cooling plate, oxygen utilization and hydrogen utilization. The temperature distributions of cooling plate are shown in Fig.2. In the easel, temperature distribution was uniform, in the case2 and the case3, there were some tendency along with air flow.

Method of simulation

The algorithm of the present simulation is schematically shown in Fig.3 where Vcell is the stating cell voltage, S(x,y,z) the current densities, PH2(x.y.z) and P02(.v,y,z) the hydrogen and oxygen concentrations, respectively, T(x,y,z) the temperature, APfuel and APair the pressure losses through the fuel and air channels respectively [1], The model stack consists of 6cells, and each cell was divided into 400 elements (20x20) for the finite difference method. The feature of our simulation is that the analysis is based on actual V-I output characteristics of a small area (approximately 3cm2) PAFC. To cover the variation in a

Fuel V

m sampling tube manifold.

Fig.l A schematic diagram of an apparatus for gas sampling.

Distance from Air inlet

Fig.2 Temperature distribution of cooling plate.

Distance from Air inlet

Fig.2 Temperature distribution of cooling plate.

'© calculation ol J, PHj. and POj ^ under a constant vottago condmonj

'© calculation ol J, PHj. and POj ^ under a constant vottago condmonj

Fig.3 Algorithm of simulation.

PAFC stack, the V-I characteristics are taken under a wide range of various conditions. In the measurement, both flow rates for fuel and air are so determined that the gas velocities over the small cell are equal to those in a large area fuel cell stack. Due to the high flow rates for the small cell, the hydrogen and oxygen concentrations are practically uniform over the electrode.

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