Fuel and oxidant delivery

Contrary to traditional fuel cells, biocatalytic fuel cells are in principle very simple in design [1], Fuel cells are usually made of two half-cell electrodes, the anode and cathode, separated by an electrolyte and a membrane that should avoid mixing of the fuel and oxidant at both electrodes, while allowing the diffusion of ions to/from the electrodes. The electrodes and membrane assembly needs to be sealed and mounted in a case from which plumbing allows the fuel and oxidant delivery to the anode and cathode, respectively, and exhaustion of the reaction products. In contrast, the simplicity of the biocatalytic fuel cell design rests on the specificity of the catalyst brought upon by the use of enzymes. 

Other components necessary for fuel cell system operation include subsystems for fuel and oxidizer delivery, voltage regulation and electronic confiol, fuel and possibly oxidizer storage, fuel recirculation/consumption, stack temperature control, and system sensing of control parameters. For the PEFC, separate humidification systems are also needed to ensure optimal performance and stability. A battery is often used... 

Fuel, oxidant, and water delivery subsystem This subsystem consists mainly of blowers/compressors and valves/orifices to deliver required reactants to the fuel processor and fuel and oxidant to the SOFC stack. 

Combustor The combustor/burner can be either a catalytic type or a more conventional, diffusion-type combustor. In an operating SOFC system, the combustor is expected to perform over a wide range of fuel and oxidant flows from moderately lean to extremely lean mixtures. Flow rates for each stream may vary by as much as 10-fold. Operating temperatures of the combustor are expected to be very high (especially at low stack FU), with Utde or no available supplementary cooHng air. Furthermore, the pressure drop must be kept low, so as to not affect adversely the air delivery power requirements and, subsequently, the net system efHciency. 

Microfluidic fuel cells, also known as membraneless fuel cells or laminar flow-based fuel cells, represent an emerging fuel cell technology capable of integration and operation within the framework of a microfluidic chip. In microfluidic fuel cells, all functions and components related to reactant delivery, reaction sites, and electrode structures are confined to a single microfluidic channel. Microfluidic fuel cells predominantly operate using co-laminar flow of fuel and oxidant electrolytes without a physical barrier, such as a membrane, to separate the two half-cells. 

To avoid confusion the reader should be aware that other symbols for stoichiometty, besides A, are commonly used in the literature, including f and The theoretical rate of reactant required is calculated by Faraday s law, and the actual rate of reactant dehvered is a funchon of the fuel or oxidizer delivery system. One important point is worth mentioning Fuel cells must always have an anode and cathode stoichiometry greater than 1. For a value less than unity, the current specified could not be produced. For reasons explained in Chapter 4, a stoichiometry of exactly 1 is not possible either, so that a Faradic efficiency of 100% is not possible on the anode or cathode for a single pass of reactant. ... 

Reactant Storage, Delivery, and Recycling This includes the pumps and blowers required to supply the stack with prescribed flow rates of fuel and oxidizer and to recycle unused fuel back into the anode inlet stream. Typically only fuel storage and recycling are needed as air is used as the oxidant. 

The first bombs developed by the US Navy, CBU-55, were used in Vietnam, and tests to perfect an advanced version of the weapons system have continued. The CBU-55B air-to-surface free-fall cluster bombs were developed for helicopter.and siow-speed fixed-wing aircraft delivery to clear helicopter landing zones of mines booby traps. This FAE bomb was designed to disperse a mixt of vaporized fuel (ethylene oxide, propylene oxide, m e thy lacetylene/propa diene/pro pane and others) in a cloud 50 ft in dram and approx 8 ft thick. It has three 100-lb individual canisters 13.6 inches in diam by 21 inches long, each containing ca 72 lbs of fuel. The canisters separate from the dispenser after... 

Surfactant-based synthesis of mesoporous metal oxides and metal sulfides emerged about four years after the initial report of MCM-41 [21-36]. High surface area and thermally robust mesoporous metal oxides and sulfides represent a new class of materials with diverse opportunities for the development of improved fuel and solar cells, batteries, membranes, chemical delivery vehicles, heavy metal sponges, sensors, magnetic devices and new catalysts. All of these applications could benefit from tailorable Bronsted and Lewis acidity and basicity, flexible oxidation states, and tunable electronic, optical and magnetic properties. 

In patients with hypothyroidism, the stimulatory effect of thyroid hormone on the oxidation of fuels is diminished. As a consequence, the generation of ATP is reduced, causing a sense of weakness, fatigue, and hypokinesis. The reduced metabolic rate is associated with diminished heat production, causing cold intolerance and decreased sweating. With less demand for the delivery of fuels and oxygen to peripheral tissues, the circulation is slowed, causing a reduction in heart rate and, when far advanced, a reduction in blood pressure. 

Figure 33.2 is a cutaway view of an R D thermal oxidizer test burner that is equipped with a number of NO, reduction methods so many NO, reduction techniques can be evaluated using a single burner. The test burner NOx reduction methods include primary, secondary, and tertiary fuel gas injection in addition to an internal fuel gas ring in a secondary air annulus around the main burner to allow testing of premixed fuel and air. All of the fuel gas delivery methods contained in the test burner would not typically be used simultaneously, but rather external valving is used to direct fuel gas to various combinations of delivery points and at different percentages. 

Fuel, oxidant, and water delivery Fuel metering valve, fuel startup valve Water metering valve, water filter Air blower, air orifice for fuel reformer, air filter... 

Fuel, oxidant, and water delivery Natural gas compressor, anode recycle blower/compressor, cathode recycle blower/compressor, startup water pump, valves... 

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