Fuel cell design problem

In this section we examine the primary transient phenomena that are of interest to SOFC analysis, and provide the fundamental model equations for each one. Examples for the use of these models are given in later sections. While the focus is on reduced-order models (lumped and one-dimensional), depending on the needs of the fuel cell designer, this may, or may not be justifiable. Each fuel cell model developer needs to ensure that the solution approach taken will provide the information needed for the problem at hand. For the goal of calculating overall cell performance, however, it is often that one-dimensional methods such as outlined below will be viable. 

Wagner refused lucrative consulting offers from industry, but studied problems posed to him alone. Sometimes this would result in a letter containing calculations and suggestions. In this way, he initiated study of the three-phase boundary in fuel cell electrodes at the Pratt and Whitney company in the 1950s. His idea became the basis (with electrocatalysis) of successful fuel cell design. 

Some fuel cell designs have attempted to boost fuel utilization and reduce system parasitic losses with a dead-ended hydrogen fuel compartment. That is, the hydrogen flow channels have no exit, and fuel is either continuously or sporadically supplied at the consumption rate required for suitable performance. A major drawback of this approach is that inerts and poisons in the flow stream build up in the dead end over time, and at least periodic purging is needed. In low-temperature systems, liquid accumulation is also a common problem, and some flow in the channels is beneficial to remove liquid droplet accumulations [20]. 

Mesh—Metallic meshes and screens of various sizes are successfully being used in the electrolyzers. The uniformity may greatly be affected by positioning of the inlet manifolds. The researchers at Los Alamos National Lab successfully incorporated metal meshes in fuel cell design [23]. The problems with this design are introduction of another component with tight tolerances, corrosion, and interfacial contact resistance. 

A fuel cell vehicle requires only 1/10 the parts needed for internal combustion models. A change to fuel cell power could end overcapacity problems for GM. It would no longer have to consider different state or country environmental regulations. Fuel cells also free designers and allow them to be more creative with styles and body designs. 

A more normal shutdown sequence would first flush the fuel cell, reformer, and scrubber with nitrogen or C02 (if it is safe for the cell design). This step is followed by a slow bleed of air and nitrogen to repassivate the fuel cell and reformer under temperature control. If this is not done gradually, the reformer can reach temperatures high enough to violate its containment (meltdown) and become unrecoverable. The reformer performance does decrease after this treatment, but over 90% of its capacity can be retained. Similar problems are present when reforming the fuel cells themselves. 

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