Cell stack assembly

As many as 400 membrane electrode assemblies or stacks are applied together to make up a fuel cell. Alignment of the cells will be required to be within 5 pm of one another [12], Stress will be lowered by the tighter requirements and the fragile carbon assembly will gain some necessary protection. This requirement will make speed of assembly difficult, which in turn will result in higher cost. 

http //www.pharmaceutical-echnology.com/contractors/lab%5Fequip/whitehouse/ 

http //www.inrf.uci.edu/research/posters/Nanoparticle Synthesis with Air-Assisted Ultrasonic Spray Pyrolysis Prof Chen Tsai UCI 949-824-5144 HJ Yoo.pdf 

Santos, P. S. Santos, M. L. A. Temperini, V. W. Brar, M. A. Pimenta, and M. S. Dresselhaus. 2004. Characterization of single wall carbon nanotubes filled with silver and with chromium compounds. Chemical Physics Letters 383 475. 

Filling of multi-walled carbon nanotubes with tin (UV) oxide. Carbon 42 3251. 

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PAFC. The weaknesses of this technology include the need to limit as much as possible the presence of sulfur in the fuel feed and in the reformate stream, in order to avoid catalyst poisoning and frequent corrosion problems at the primary cell stack coolant circuit, and the need to increase electrical generation efficiencies of cell stack assembly lifetime to at least 40,000 hours (5 years) furthermore, an increase in power densities is an area where technical development is necessary (see Lane et al., 1995). 

The power section consists of twenty cell-stack assemblies (CSAs). Each CSA contains approximately 450 individual Tuel cells, stacked one above the other. Manifolds on the CSAs direct the fuel gas to the anode side of the fuel cells and the air to the cathode side. Electrochemically. the CSAs convert the hydrogen and oxygen inlo direct-current power according to the following reaction ... 

Although time-pressure, auger, and piston systems are the most commonly used methods of needle dispensing, some other pump designs exist. For the purposes of fuel cell stack assembly, however, the considerations listed above apply to most technologies. 

The fuel for the PAFC is either naphtha or natural gas. These fuels must first be reformed to produce hydrogen and C02> and treated to remove any CO or H2S which would poison the platinum catalyst. Thus it is necessary to have a fuel processor unit proceeding the fuel cell stack. The electricity produced is, of course, D.C. and so for many applications it is necessary to invert the output to A.C. Thus a complete fuel cell plant consists of three units - a fuel reformer, a cell stack assembly and an electrical invertor. The cost of the two auxiliary units is by no means insignificant. 

The cell stack assembly is the heart of the power plant which produces both electrical and thermal energy by electrochemically combining H2 in fuel and O2 in air. The basic description of a phosphoric acid fuel cell is shown in Fig. 12.2. 

The main components of a PAFC are bipolar plates, gas diffusion layers, catalyst layers, and matrix layer [3]. Typical cell designs include a sandwich of these layers as arranged in Fig. 12.2 between coolers. Multiple cells per cooler designs are generally employed to improve power density and this unit is called a sub stack. A cell stack assembly consists of multiple sub stacks held between two pressure plates tmder compression to minimize reactant leakage and contact resistance losses. 

Non-repeat components. The components described in the previous section are usually referred to as repeat components since every cell has those components with multiple cells present in a cell stack. Non-repeat components are those that are used only once in a cell stack. The main non-repeat components in a cell stack assembly are pressure plates, coolant inlet and outlet manifolds, reactant inlet and outlet manifolds, and manifold seals. Multiple cells placed between coolers are stacked between two stainless steel pressure plates and loaded axially to arotmd 60 psi with the help of tie rods that run the entire length of the cell stack. Reactant manifolds are then assembled onto the cell stack with manifold seals placed between the cell stack and the manifold. These reactant manifolds are made of stainless steel and coated with PTFE coating to prevent phosphoric acid attack of the manifolds. It is very essential to ensure that there are no pin holes in the PTFE coating for the same reason mentioned above. In phosphoric acid fuel cells, manifold seals made... 

Bonk, S.P, M. Krasij, and C.A. Reiser. 2002. Fuel cell stack assembly with edge seal. U.S. Patent 6399234. 

Table 51.25 Union Carbide sealed nickel-cadmium button cell stack assemblies (jacketed with plastics tubing)...

Fig. 2 Fuei cell stack assembly (from Costamagna 2002).

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