Nonstationary performance model

The goal is to formulate the nonstationary performance model for the cathode side of such a cell. The main assumptions are as follows ... 

The time-dependent CCL performance model is obtained if time derivatives are added to the system of Equations 4.7 through 4.9. The nonstationary version of this system is... 

Below, the model for DMFC cathode impedance is presented, assuming the electrochemical mechanism of MOR on the cathode side (Kulikovsky, 2012b). In this section, the nonstationary version of the DMFC cathode performance model (the section Cathode Catalyst Layer in a DMFC ) is used to calculate the cathode impedance. As discussed in the section Cathode Catalyst Layer in a DMFC, the model takes into account spatial distribution of the MOR and ORR, through the cathode thickness. It is shown below that the spatial separation of MOR and ORR, discussed in the section Cathode Catalyst Layer in a DMFC, leads to the formation of a separate semicircle in the impedance spectrum. 

In this section, a model for the PEFC cathode impedance is discussed, including oxygen transport in the channel (Kulikovsky, 2012d). The model is based on the transient CCL performance model from the section Basic Equations linked to the nonstationary extensions of the models for oxygen transport in the GDL and in the channel, discussed in the section Performance Modeling of a Fuel Cell. ... 

The hydraulic performance of sewer pipes can be described at different levels. In the case of nonstationary, nonuniform flow, the Saint Venant Equations should be applied. However, under dry-weather conditions, the Manning Equation is an adequate description of the wastewater flow in a gravity sewer pipe when considering the prediction of wastewater quality changes under transport. There are no grounds for using advanced hydraulic models because of the uncertainties in the prediction of the microbial transformations of the wastewater. 

This chapter will focus on practicable methods to perform both the model specification and model estimation tasks for systems/models that are static or dynamic and linear or nonlinear. Only the stationary case win be detailed here, although the potential use of nonstationary methods will be also discussed briefly when appropriate. In aU cases, the models will take deterministic form, except for the presence of additive error terms (model residuals). Note that stochastic experimental inputs (and, consequently, outputs) may stiU be used in connection with deterministic models. The cases of multiple inputs and/or outputs (including multidimensional inputs/outputs, e.g., spatio-temporal) as well as lumped or distributed systems, will not be addressed in the interest of brevity. It will also be assumed that the data (single input and single output) are in the form of evenly sampled time-series, and the employed models are in discretetime form (e.g., difference equations instead of differential equations, discrete summations instead of integrals). 

Recently, nonstationary experiments on the microkinetics of typical reactions on Pt/Ce/y-AbOs three-way catalyst were performed (Harmsen et al., 2(XX), 2(X)la,b). Their results were evaluated in the form of detaUed reaction schema. Mukadi and Hayes (2(X)2) used these kinetic expressions in the model of TWC monolith converter. They pointed to the significance of the effects of diffusion in the catalytic washcoat on the performance... 

In this section, the analysis is based on a nonstationary model for the CCL performance with the Butler-Volmer conversion function. The steady-state version of this model has been discussed in Chapter 4. 

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