Fuel cell systems descriptions

The initial emphasis on evaluation and modeling of losses in the membrane electrolyte was required because this unique component of the PEFC is quite different from the electrolytes employed in other, low-temperature, fuel cell systems. One very important element which determines the performance of the PEFC is the water-content dependence of the protonic conductivity in the ionomeric membrane. The water profile established across and along [106]) the membrane at steady state is thus an important performance-determining element. The water profile in the membrane is determined, in turn, by the eombined effects of several flux elements presented schematically in Fig. 27. Under some conditions (typically, Pcath > Pan), an additional flux component due to hydraulic permeability has to be considered (see Eq. (16)). A mathematical description of water transport in the membrane requires knowledge of the detailed dependencies on water content of (1) the electroosmotic drag coefficient (water transport coupled to proton transport) and (2) the water diffusion coefficient. Experimental evaluation of these parameters is described in detail in Section 5.3.2. 

In this modeling work [100], Springer and co-workers have reduced the description of the complicated fuel cell system to the set of parameters that most strongly influences the behavior of the cells. These do not include anode parameters, but it should be realized that this would be true only for the conditions specified -well humidified cells with a pure H2 feed stream. The accuracy of the model depends strongly on the representation of the ORR kinetics and the authors have stressed the use of realistic ORR parameters. For well-humidified H2/air PEFCs, the model... 

Description. In July 2002, Austin Energy installed a 200 kW fuel cell system at the Rebekah Baines Johnson (RBJ) Health Center. Pictured in Figure 4 (next page), the system also produces 900,000 BTUs of usable heat per hour. 

As became obvious in the previous section, a detailed description of a complete fuel cell is computationally very demanding. The stack models thatt are discussed in this section are on a higher abstraction level. They serve mainly as one component of a complete fuel-cell system. The discussion of system simulation is beyond the scope of this chapter, and at this point only the characteristics of the stack models are mentioned. 

Life cycle assessment of SOFC technology is still uncommon due to the relatively early stage in technical development. However, several studies have been performed since the end of the 1990s. Since there is a lack of standard commercial equipment that could serve as a basis and reference point for analysis, LCA studies mostly refer to hypothetical concepts and/or extrapolate from laboratory and early market prototypes to commercial units. While the first studies had only little access to operation data at aU (for the fuel cell system itself but also for production processes), the main effort was set in the assessment of inventory data using assumptions, simplifications, and correlations [79, 80]. The main outcomes of these studies were the identification of weak points and the setting of benchmarks for further development. With more information about fuel cells available today and a simultaneous advancement in LCA methodology, the studies became more reliable and detailed, regarding system description [81] as well as the assessment of environmental impacts coimected with inputs and outputs [82]. Especially the extensive data of these two studies found their way to commercial databases for LCA [83] and thereby became available to LCA practitioners. In 2005, the Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (BMU)... 

A fuel cell stack has to be surrounded with actuators and devices which are necessary for its operation. The ensemble is called a fuel-cell system. It is not easy to genetically define a fuel-cell system and its limitations. Indeed, on the one hand, the elements contained in the system depend on the fuel-cell technology being used, the apphcation in question and the technical specifications pursued. On the other hand, a fuel-cell system is a multi-physical system because it involves chemical, electrical, fluidic and thermal phenomena whose effects are closely interrelated. Thus, the interactions between the different elements of the system and the environment are significant. Figure 3.12 offers a generic description of the elements of the system and sets the general outlines of the system [CAN 07 PER 07 HIS 09]. Besides the stack, which is the heart of the system, we can identify various different circuits ... 

This coincides with ongoing research to increase power density, improve water management, operate at ambient conditions, tolerate reformed fuel, and extend stack life. In the descriptions that follow, Ballard Power Systems fuel cells are considered representative of the state-of-the-art. 

Any governing model equations have to be supplemented by initial and boundary conditions, all together called side conditions. Their definition means imposing certain conditions on the dependent variable and/or functions of it (e.g. its derivative) on the boundary (in time and space) for uniqueness of solution. A proper choice of side conditions is crucial and usually represents a significant portion of the computational effort. Simply speaking, boundary conditions are the mathematical description of the different situations that occur at the boundary of the chosen domain that produce different results within the same physical system (same governing equations). A proper and accurate specification of the boundary conditions is necessary to produce relevant results from the calculation. Once the mathematical expressions of all boundary conditions are defined the so-called properly-posed problem is reached. Moreover, it must be noted that in fuel cell modeling there are various... 

A more detailed description of different types of batteries and other electric energy storage systems for electric vehicles can be found in Sect. 5.3, while a description of the main characteristics and properties of fuel cells for automotive application is given here, starting from some basic concepts of electrochemistry and thermodynamic, and focusing the attention on the operative parameters to be regulated to obtain the best performance in the specific application. 

As conclusion to this section, we have stressed the influence of the heterogeneous surface structure on catalyst activity. Two complementary model approaches have been presented that could be used to establish the effective value of 7 . Kinetic MC simulations provide the most versatile tool for exploring structure-reactivity relations. It allows incorporating detailed surface structures and finite mobilities of adsorbates. In the limit of high surface mobilities of adsorbates, an analytical MF model could replace the stochastic description. The MF model still accounts for the heterogeneous surface structure. It is, thus, more realistic for real catalyst systems in fuel cells than homogeneous surface models. 

Description. SWRI is an independent, nonprofit, applied engineering and research development organization. In addition to its work in other areas, SWRI "promotes innovative approaches to fuel cell construction, fueling infrastructure, waste heat utilization, and power control and storage. SWRI engineers also develop ancillary fuel cell processes such as fuel processors and fuel storage, delivery, and cleanup systems."" SWRI engineers are heavily involved in the fuel cell demonstration project at Brooks City Base. 

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