Stack leakage model

One of the first models to examine transients in polymer-electrolyte fuel cells was a stack-level model by Amphlett et al. Their model is mainly empirical and examines temperature and gas flow rates. They showed that transient behavior lasts for a few minutes in a stack before a new steady state is reached. In a similar stack-level analysis, Yerramalla et al.2 9 used a slightly more complicated single-cell model and examined the shape of the transients. They noticed voltage behavior that had oscillations in it and some leakage current. Their overall analysis was geared to the development of a controller for the stack. 

Defects include (dust) particles on or within suspended interdigitated seismic masses, leading to electrical shorts and to deviations in moments of inertia. Another example relates to the appearance of crystallographic defects such as dislocations or stacking faults in epitaxial superstructures, causing leakage currents that might impair sensor reliability in the field. Defect densities may of course vary within a wafer, from wafer to wafer, and from lot to lot. Unfortunately, at present not many models are available that link tolerance bands of functional parameters to specific defects and their tolerable density distributions. 

Since the above-core calculations represented an infinite array of fuel channels, they did not include those parts of the pressure vessel in the vicinity of the hot gas duct penetration and therefore no account was taken in the above-core calculation of the neutrons wMch scatter around the top comer of the graphite stack and enter the hot gas duct penetration area. The neutron fluxes in the vicinity of the hot duct entrances were therefore takai to be equal to the fluxes calculated for the side shield model with a contribution added to account for the top-core leakage component. This component was scaled fi om the sub-core results and is considered to probably result in pessimistically high flux values for the hot gas duct pen ration since the neutron flux levels below the core are generally higher than those above. 

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