FUEL CELLS PRESENTED BY GANESH.M

ABSTRACT   According to the Merriam-Webster dictionary, engineering is the application of science and mathematics, by which the properties of matter and the sources of energy in nature are made useful to people. The development of the fuel cell since 1839 has been a long and thought out engineering process. Making alternative sources of energy useful to people, the engineering accomplishment of the development of fuel cells have very practical vehicle applications. By replacing the Internal Combustion engine, fuel cells could dramatically reduce urban air pollution, decrease oil imports, reduce the trade deficit and produce American jobs. The electrochemical processes inside the cells, the mathematical calculations about the effect fuel cells will have on the economy, the reworking and constant engineering to produce a better product, communication between many organizations, and ethical decisions about if the high priced vehicle is actually worth the improvements in the environment, show the integration of chemistry, math, science, communications, and ethics in development of fuel cell vehicles.

FUEL CELLS ORIGIN: 1840-1890 Despite their modern high-tech aura, “fuel cells” actually have been known to science for more than 150 years. Though generally considered a curiosity in the 1800s, fuel cells became the subject of intense research and development during the 1900s.   WHAT IS A FUEL CELL? “A fuel cell is a device that generates electricity by a chemical reaction. Every fuel cell has two electrodes, one positive and one negative, called, respectively, the cathode and anode. The reactions that produce electricity take place at the electrodes.” Every fuel cell also has an electrolyte, which carries electrically charged particles from one electrode to the other, and a catalyst, which speeds the reactions at the electrodes. One detail of terminology: a single fuel cell generates a tiny amount of direct current (DC) electricity. In practice, many fuel cells are usually assembled into a stack. Cell or stack, the principles are the same.  

CHARACTERIZATION OF FUEL CELL TECHNOLOGY   CHARACTERIZATION OF FUEL CELL TECHNOLOGY Fuel cell technology can be viewed as a series of technologies that are used individually or in combination to make new applications and to better understand science  The fuel cell technology can be characterized as follows; Fuel Flexibility Fuel cells are capable of operating on hydrogen, or hydrogen reformed from any of the common fossil fuels available today. High Power Densities The amount of power a fuel cell can generate within a given volume is usually given in kWh/liter. These numbers continue to rise as manufacturers continue research and development on their respective products. Low Operating Temperatures and Pressures Fuel cells operate at 80<sup>o C to over 1,000<sup>o C, depending on the type of fuel cell. These numbers might seem high, but the temperature inside your vehicle's internal combustion engine can reach over 2,300<sup>o C. Site Flexibility Fuel cells, with their inherently quiet operation, zero to minimal emissions and reduced permitting requirements, can be located in a variety of areas, both residential and commercial, inside and outside.

  Cogeneration Capability : When the waste heat from the fuel cell's electrochemical reaction is captured, it can be utilized for water, space heating and cooling. With cogeneration capabilities, the efficiencies achieved by a fuel cell system approach 90%. Quick Response to Load Variations: To receive additional energy from a fuel cell, more fuel is introduced into the system. Fuel cell load response is analogous to depressing the gas pedal in your vehicle, more fuel more power. Engineering simplicity: Fuel cells do not contain any moving parts. The lack of movement allows for a simpler design, higher reliability’s, Quite operation and a system that is less likely to fail. .

TYPES OF FUEL CELLS: Phosphoric Acid. Molten Carbonate. Solid Oxide. Alkaline. Direct Methanol fuel cells. Regenerative fuel cells. Proton Exchange Membrane or Solid Polymer Above all these types this paper deals with “alkaline fuel cells”, construction, working and its applications.  

ALKALINE FUEL CELLS Hydrogen is the basic fuel, but fuel cells also require oxygen. One great appeal of fuel cells is that they generate electricity with very little pollution—much of the hydrogen and oxygen used in generating electricity ultimately combine to form a harmless byproduct, namely water.

CONSTRUCTION OF ALKALINE FUEL CELLS:  The following diagram shows a model of an alkaline fuel cell:

PRINCIPLE The purpose of a fuel cell is to produce an electrical current that can be directed outside the cell to do work, such as powering an electric motor or illuminating a light bulb or a city. The chemical reactions that produce this current are the key to how a fuel cell works.

ALKALI FUEL CELL APPLICATIONS AERONAUTICAL APPLICATIONS: NASA selected alkali fuel cells for the Space Shuttle fleet, as well as the Apollo program, mainly because of power generating efficiencies that approach 70 percent. Alkali cells also provide drinking water for the astronauts. The cells are expensive -- perhaps too expensive for commercial applications -- but several companies are examining ways to reduce costs and improve the cells' versatility. Most of these alkali fuel cells are being designed for transport applications. MILITARY APPLICATIONS: Fuel cells help the military reduce the cost of battlefield logistics, provide a source of energy for the modern soldier, save money and reduce pollution at military installations and on board ships and terrestrial vehicles, and most importantly, save lives and materiel by reducing telltale heat and noise.

ADVANTAGES CONTINUOUS SOURCE OF ENERGY: HIGH EFFICIENCY:   CONTINUOUS SOURCE OF ENERGY: There is no electrode material to be replaced as in ordinary battery. The fuel is continuously supplied to produce power. HIGH EFFICIENCY: The fuel cell converts the energy of a fuel directly into electricity; they are more efficient (70%) than the conventional methods (40%) of generating electricity. POLLUTION FREE WORKING: There are no by-products; hence they do not cause pollution problems (like noise, vibration, heat transfer, thermal pollutions).

DISADVANTAGES The basic workings of a fuel cell may not be difficult to illustrate. But, Building inexpensive. Efficient. Reliable fuel cells. Is a far more complicated business? Scientists and inventors have designed many different types and sizes of fuel cells in the search for greater efficiency, and the technical details of each kind vary. The “design of electrodes”, for example, and the materials used to make them depend on the electrolyte. Today, the main electrolyte types are alkali, molten carbonate, phosphoric acid, proton exchange membrane (PEM) and solid oxide. The first three are liquid electrolytes; the last two are solids. The type of fuel also depends on the electrolyte. Some cells need pure hydrogen, and therefore demand extra equipment such as a “reformer” to purify the fuel. So, they are “electrolyte dependent”. The type of electrolyte also dictates a cell’s operating temperature–“molten” carbonate cells run hot, just as the name implies.

CONCLUSION     Solid fuels will become increasingly important in the future, but present conversion systems for solid fuels are inherently inefficient. So new conversion systems for solid fuels with higher efficiency are possible; ultimately a flexible hydrogen and power producing system-converting heat into power can be conceived. Thus FUEL CELL TECHNOLOGY is a key technique. This particular fields growth should be contained between certain limits, so that this doesn’t pose any threat to human race. So we need to tame this particular field in such a way that we get the maximum use of it.

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