Page 336 - High Temperature Solid Oxide Fuel Cells Fundamentals, Design and Applications

3 12 High Temperature Solid Oxide Fuel Cclls: Fundamentals, Design and Applications

generation calculated. In an approximate 3-D cell or stack model, it is customary
to use a lumped electrochemical heat generation: that is, one assumes a uniform
distribution of the reversible and irreversible heat generation over the respective
electrode. Using a more advanced electrode-level model, the distribution of heat
generation in the electrodes can be analysed, which may yield important
information for structural stability of the electrodes and their interfaces with the
electrolyte and the current collector/gas channel profiles.
The heat source terms discussed above are used in the energy balance
equations of the flow and thermal models for both cell and stack simulations. To
manage the computation cost, most simulations avoid the full CFD treatment of
the flow. However, full CFD treatments provide more accurate and detailed
information on the flow in an SOFC system. With increased computing power,
more and more full CFD simulations are expected to appear.
Figure 11.5 shows sample cell modelling results: the steady-state temperature,
current density, and species concentration distributions. As can be seen by
comparison with Figure 11.2, the steady-state temperature distribution is quite
different from that during the rapid startup.
Figure 11.6 shows the steady-state modelling results for a tubular SOFC
design, as reported by Ferguson et al. [29]. Clearly, the characteristic operating

) HI mass fraction

(4 0: mass fraction (e) PEN temperature \.) HJQ massfraction

Figure 11.5 Sample results for planar SOFC in cross-flow configuration: a, air temperature, max. 899"C,
min. 625°C; b. current, A/cm2: max. = 1.46. min. = 0.300; c, H, mass fraction. kglkg: max. 0.0385, min.
0.00472 (CO distribution similar); d, 02 mass fraction. kglkg: max. 0.231, min. 0.182; e, PEN
temperature. "C: max. 911, min. 643; f, H20 mass fraction, kglkg: max. 0.224. min. 0.0387 (CO,
distribution similar ).