Operating system optimization, fuel cell

Zhao H, Burke AF (2009) Optimization of fuel cell system operating conditions for fuel cell vehicles. J Power Sources 186 408-416... 

Optimize fuel cell hybrid vehicle system, considering a variety of energy storage options and system operating characteristics, including fuel cell idling and start-up/shut-down... 

In the development of molten carbonate fuel cells (MCFCs), many issues require mathematical models. Some of them, for example, the design of controllers and the integration of an MCFC stack in a larger plant system, can be solved with spatially lumped models. Other questions such as the analysis of an inhomogeneous current density profile or the optimal design and operation of a fuel cell with respect to temperature Hmitations, need spatially distributed models. Because the latter are usually the more complex models, this chapter is focused on these models. 

The proton conduction based on the phosphoric acid is the basis of HT-PEMFC Celanese technology [37], mostly referred to as phosphoric acid-doped PBI (polybenzimidazole) This membrane enables operation at temperatures as high as 180°C, without the need for external humidification. Heat dissipation at this temperature is much easier than at the 70-80°C operating temperature of fuel cell systems using standard PFSA membranes. The CO tolerance at 180°C is such that even 1 % CO leads to a minor loss of power density compared to that using the same membrane on pure hydrogen. The downside of this membrane is its low conductivity below 1(X)°C, making a cold start impossible, as well as the lower power density at its optimal temperature. 

To support system design and optimization. Fuel cell systems have so many unit operations and components that system models are critical for effective system design. 

The design and optimization of a fuel cell power system is very complex because of the number of required systems, components, and functions. Many possible design options and trade-offs affect unit capital cost, operating cost, efficiency, parasitic power consumption, complexity, reliability, availability, fuel cell life, and operational flexibility. Although a detailed discussion of fuel cell optimization and integration is not within the scope of this section, a few of the most common system optimization areas are examined. 

The fuel cell network which was simulated was not fully optimized. Optimization of flow geometry, operating pressure, stack fuel utilization and current, reactant conditioning, and other parameters would be expected to yield further significant increases in total system efficiency. 

However, this porosity takes into account all the open pores—even those that are not connected between each other, which are useless in fuel cell operation. Therefore, the effective porosity, which counts only the interconnected pores, is more critical when determining the optimal diffusion layer in a fuel cell. This porosity can be determined by using volume filtration techniques. For example, a porous sample is immersed in a liquid that does not enter inside the pores (e.g., mercury at low pressures) and then the total volume of the material can be determined. Next, the specimen is put inside a container of known volume that contains an inert gas, and the changed pressure is recorded. After this, a second evacuated chamber of known volume is connected to the system, and the new pressure is recorded. With these pressures and the ideal gas law, the volume of open pores and thus the effective porosity can be determined [195]. 

An important point to consider about the stack management, with reference to an electric power train operating in dynamic conditions, as determined by road requirements, is the regulation of the stack temperature together with the other control parameters of water and reactants to avoid mass transfer limitations and membrane drying out or flooding. Moreover, the interaction between stack and auxiliaries has to be balanced taking into account the optimization of fuel cell system efficiency and reliability (see Sect. 4.6). 

Microfabrication processes have been used successfully to form micro-fuel cells on silicon wafers. Aspects of the design, materials, and forming of a micro-fabricated methanol fuel cell have been presented. The processes yielded reproducible, controlled structures that performed well for liquid feed, direct methanol/Oj saturated solution (1.4 mW cm ) and direct methanol/H O systems (8 mA cm" ). In addition to optimizing micro-fuel cell operating performance, there are many system-level issues to be considered when developing a complete micro power system. These issues include electro-deposition procedure, catalyst loading, channel depth, oxidants supply, and system integration. The micro-fabrication processes that have... 

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