PEFC model process-level

This section deals with multi-scale models for the PEFC and consists of three subsections, 4.1,4.2, and 4.3, that relate to molecular-level models, bridging models between scales and device/process level models, respectively. The objectives of these subsections are to survey the development and application of these models. 

At the process level, efficient flowsheet optimization strategies based on lumped parameter models are now widely used in practice (Biegler et al., 1997). At this scale, the PEFC is embedded within a power plant flowsheet model, as shown in Figure 3. The process comprises... 

Process-scale models represent the behavior of reaction, separation and mass, heat, and momentum transfer at the process flowsheet level, or for a network of process flowsheets. Whether based on first-principles or empirical relations, the model equations for these systems typically consist of conservation laws (based on mass, heat, and momentum), physical and chemical equilibrium among species and phases, and additional constitutive equations that describe the rates of chemical transformation or transport of mass and energy. These process models are often represented by a collection of individual unit models (the so-called unit operations) that usually correspond to major pieces of process equipment, which, in turn, are captured by device-level models. These unit models are assembled within a process flowsheet that describes the interaction of equipment either for steady state or dynamic behavior. As a result, models can be described by algebraic or differential equations. As illustrated in Figure 3 for a PEFC-base power plant, steady-state process flowsheets are usually described by lumped parameter models described by algebraic equations. Similarly, dynamic process flowsheets are described by lumped parameter models comprising differential-algebraic equations. Models that deal with spatially distributed models are frequently considered at the device... 

Specific processes involved in the ORR will be dealt with in the section Electrocatalysis of the Oxygen Reduction Reaction at Platinum in Chapter 3. Here, the focus is on basic phenomenological concepts that are required to incorporate electro-catalytic reactions in device-level modeling of PEFCs. For a more detailed treatment of fundamental concepts in electrocatalysis, see the recent edition of the textbook by Schmickler and Santos (2010), as well as the classical textbook by Bard and Faulkner (2000). 

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