Fuel cell performance equation

One of the central, steady-state fuel cell performance equations is thus given by... 

Fuel Cell Energy presented a computer model for predicting carbonate fuel cell performance at different operating conditions. The model was described in detail at the Fourth International Symposium on Carbonate Fuel Cell Technology, Montreal, Canada, 1997 (93). The model equations are listed as follows ... 

Bearing in mind that phenomena occurring in nature are too complex to be completely described by mathematical equations, the required details to be described by the model must be goal-driven, i.e. the complexity of the model, and the related results, must be strictly connected to the main goal of the analysis itself. When, for example, the main purpose of the model is to provide the fuel cell performance, in order to analyze the whole system in which it is embedded, the spatial variation in the physical and chemical variables (such as gas concentration, temperature, pressure and current density, for example) are not relevant however the performances, in terms of efficiency, electrical and thermal power and input requirements are important [1-4],... 

Mass transport within the electrodes is of particular importance in determining the reflection of the porous media structure on the fuel cell performance. In fact, the main results of mass transport limitation is that the reactant concentrations (H2 and CO for the anode, and O2 for the cathode) at the reaction zone are lower than in the gas channel. When applying Equations (3.40) and (3.42), the result is that the lower the concentration of the reactants, the lower the calculated cell performance. The loss of voltage due to the mass transport of the gas within the electrodes is also referred to as concentration overpotential. Simplified approaches for determining concentration overpotential include the calculation of a limiting current, i.e. the maximum current obtainable due to mass transport limitation (cf. Appendix A3.2). 

The analysis of the conditions within a gas channel can also be assumed to be onedimensional given that the changes in properties in the direction transverse to the streamwise direction are relatively small in comparison to the changes in the stream-wise direction. In this section, we examine the transport in a fixed cross-sectional area gas channel. The principle conserved quantities needed in fuel cell performance modeling are energy and mass. A dynamic equation for the conservation of momentum is not often of interest given the relatively low pressure drops seen in fuel cell operation, and the relatively slow fluid dynamics employed. Hence, momentum, if of interest, is normally given by a quasi-steady model,... 

The fuel cell performance drop due to the change in internal resistance between two temperatures at a constant current density can also be estimated roughly based on Equation 6.20 ... 

Figure 6.57 shows the fuel cell performance changes due to a temperature increase from 80°C to 120°C, based on Equation 6.22, as a function of current density. The... 

L. Kim, S-M Lee, S. Srinivasan, CE Chamberlin, Modeling of proton exchange membrane fuel cell performance with an empirical equation, J. Electroch. Soc., 142 (1995) 2670-2674... 

A CFD model that describes a complete single cell was introduced by Lobato et al. [33]. The MEA was implemented as a single plane separating the anode and cathode. The model considers only the cathodic part of the overpotential from the Butler-Vohner equation and the simulation results are presented for operation with pure hydrogen and oxygen. The impact of three different flow field designs, serpentine-like, parallel, and pin-type, on the overall fuel-cell performance were investigated. The best performance was observed for serpentine-like and pin-type flow fields. It should be noted that the bad performance of the selected parallel... 

The Nemst equation provides a relationship between the ideal standard potential (E°) for the cell reaction and the ideal equilibrium potential (E) at other partial pressures of reactants and products. For the overall cell reaction, the cell potential increases with an increase in the partial pressure (concentration) of reactants and a decrease in the partial pressure of products. For example, for the hydrogen reaction, the ideal cell potential at a given temperature can be increased by operating at higher reactant pressures, and improvements in fuel cell performance have, in fact, been observed at higher pressures. This will be further demonstrated in Chapters 3 through 7 for the various types of fuel cells. 

High protonic and electronic conductivity are highly desirable to optimize the CL structure with respect to high fuel cell performance. The measured fuel eell voltage ( ceii) alternatively expressed as Equation 21.33 ... 

Fuel cell performance (cell voltage versus current density) in the absence of contaminants has been described by both theoretical and empirical expressions, among which the semiempirical equation (3.18) is the most simplified [40,41]. 

In our published work [29], we concluded from AC impedance measurements and resistance data analysis that toluene caused fuel cell performance degradation mainly through a kinetic effect, i.e., the blocking of the active Pt sites via toluene adsorption. Therefore, an empirical model taking into account only the effect of toluene on the kinetics was constructed to describe the cell voltage under the influence of toluene, as shown in equation (3.21) ... 

Besides the kinetic models we discussed above, the other cathode contamination models available in the literature are the empirical model and the competitive adsorption model [4,57]. Empirical models have been successfully used to describe FEM fuel cell performance at different temperatures and pressures [55,56]. Equation (6.73) was proposed by Kim et al. [56] ... 

It is no longer economical to operate a fuel cell or fuel cell system. Power is the third central equation for fuel cell performance. General expressions can be derived for fuel cell performance involving the variables E, J, mF, pressure, and fuel flow rate to explore the full envelope of fuel cell operation. 

From Equation 10.1 it is evident that water vapor pressure increases exponentially with rising temperature. When gas enters the fuel cell stack, the gas temperature will increase. Under certain circumstances, if a constant inlet pressure and RH are maintained, the water vapor intake will increase and that the amount of reactive gas will decrease, which may cause fuel cell material deficiencies as well as flooding phenomena the latter will lead to a decline in fuel cell performance. 

There is a great variety of approaches to fuel cell performance modeling. The simplest approach used in system simulations deals with the semiempirical polarization curves of the cell or stack under investigation. Such curves are obtained by fitting a simple analytical model equation to measured data. This philosophy is very useful in the optimization of FC systems with numerous peripheral components (blowers. 

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