You’ve probably heard about fuel cells. In 2003, President Bush announced a program called the Hydrogen Fuel Initiative (HFI) during his State of the Union Address. This initiative, supported by legislation in the Energy Policy Act of 2005 (EPACT 2005) and the Advanced Energy Initiative of 2006, aims to develop hydrogen, fuel cell and infrastructure technologies to make fuel-cell vehicles practical and cost-effective by 2020. The United States has dedicated more than one billion dollars to fuel cell research and development so far.
So what exactly is a fuel cell, anyway? Why are governments, private businesses and academic institutions collaborating to develop and produce them? Fuel cells generate electrical power quietly and efficiently, without pollution. Unlike power sources that use fossil fuels, the by-products from an operating fuel cell are heat and water. But how does it do this?
If you want to be technical about it, a fuel cell is an electrochemical energy conversion device. A fuel cell converts the chemicals hydrogen and oxygen into water, and in the process it produces electricity.
The other electrochemical device that we are all familiar with is the battery. A battery has all of its chemicals stored inside, and it converts those chemicals into electricity too. This means that a battery eventually "goes dead" and you either throw it away or recharge it.
With a fuel cell, chemicals constantly flow into the cell so it never goes dead -- as long as there is a flow of chemicals into the cell, the electricity flows out of the cell. Most fuel cells in use today use hydrogen and oxygen as the chemicals.
Sir William Grove invented the first fuel cell in 1839. Grove knew that water could be split into hydrogen and oxygen by sending an electric current through it (a process called electrolysis). He hypothesized that by reversing the procedure you could produce electricity and water. He created a primitive fuel cell and called it a gas voltaic battery. After experimenting with his new invention, Grove proved his hypothesis. Fifty years later, scientists Ludwig Mond and Charles Langer coined the term fuel cell while attempting to build a practical model to produce electricity.
There are several different types of fuel cells, each using a different chemistry. Fuel cells are usually classified by their operating temperature and the type of electrolyte they use. Some types of fuel cells work well for use in stationary power generation plants. Others may be useful for small portable applications or for powering cars. The main types of fuel cells include:
Polymer exchange membrane fuel cell (PEMFC)
The Department of Energy (DOE) is focusing on the PEMFC as the most likely candidate for transportation applications. The PEMFC has a high power density and a relatively low operating temperature (ranging from 60 to 80 degrees Celsius, or 140 to 176 degrees Fahrenheit). The low operating temperature means that it doesn't take very long for the fuel cell to warm up and begin generating electricity.
Solid oxide fuel cell (SOFC)
These fuel cells are best suited for large-scale stationary power generators that could provide electricity for factories or towns. This type of fuel cell operates at very high temperatures (between 700 and 1,000 degrees Celsius). This high temperature makes reliability a problem, because parts of the fuel cell can break down after cycling on and off repeatedly. However, solid oxide fuel cells are very stable when in continuous use. In fact, the SOFC has demonstrated the longest operating life of any fuel cell under certain operating conditions. The high temperature also has an advantage: the steam produced by the fuel cell can be channeled into turbines to generate more electricity. This process is called co-generation of heat and power (CHP) and it improves the overall efficiency of the system.
Alkaline fuel cell (AFC)
This is one of the oldest designs for fuel cells; the United States space program has used them since the 1960s. The AFC is very susceptible to contamination, so it requires pure hydrogen and oxygen. It is also very expensive, so this type of fuel cell is unlikely to be commercialized.
Molten-carbonate fuel cell (MCFC)
Like the SOFC, these fuel cells are also best suited for large stationary power generators. They operate at 600 degrees Celsius, so they can generate steam that can be used to generate more power. They have a lower operating temperature than solid oxide fuel cells, which means they don't need such exotic materials. This makes the design a little less expensive.
Phosphoric-acid fuel cell (PAFC)
The phosphoric-acid fuel cell has potential for use in small stationary power-generation systems. It operates at a higher temperature than polymer exchange membrane fuel cells, so it has a longer warm-up time. This makes it unsuitable for use in cars.
Direct-methanol fuel cell (DMFC)
Methanol fuel cells are comparable to a PEMFC in regards to operating temperature, but are not as efficient. Also, the DMFC requires a relatively large amount of platinum to act as a catalyst, which makes these fuel cells expensive.
Source : How Stuff Works , Wikipedia
Showing posts with label Chemistry Behind Substances. Show all posts
Showing posts with label Chemistry Behind Substances. Show all posts
Saturday, April 07, 2007
Friday, March 16, 2007
Artificial Snow
Once upon a time, making snow was a straightforward craft. One could simply grind up large blocks of ice and spread the pulverized material where desired or use a basic stand-in material such as cellulose powder or bits of paper. Nowadays, with the advent of better materials and machinery--and because the fluffy white stuff fascinates people to no end--there are myriad ways to pull off a big snow job for indoor or outdoor use using machine-made snow or artificial snow.
Machine-made snow has been substantially refined by the ski industry over the years. Snowmaking serves to extend the ski season or can rescue a dry winter, but it also has become important for controlling snow conditions as the number of skiers has increased and the mode of enjoying the slopes has evolved to include tubing, sledding, and snowboarding. Machine snow is also used in labs to learn how to forecast avalanches.
To make snow, water cooled to just above its freezing point is pumped under high pressure through the nozzles of a "snow gun." Compressed air or electric fans are usually used to help atomize the water into fine droplets and to disperse them over a wide area where they hopefully will freeze before they hit the ground. If not, the snow will be too wet. Other ways to make snow include using a combination of water and compressed air that is frozen by liquid nitrogen, a method used primarily for indoor sports centers. Snow also can be made from carbon dioxide.
Critical to snowmaking for skiing is getting the right combination of temperature and humidity--the lower the humidity, the higher the outdoor temperature can be to form snow. With untreated water, an air temperature of about –8 °C (18 °F) is needed. Another important factor is the need to generate sufficient nucleation sites for ice crystals to form. Nucleation sites can be a few water molecules that coalesce alone; calcium, magnesium, or other ions; or an impurity such as a clay particle or organic matter.
When the temperature isn't quite cold enough--above about –5 °C (23 °F)--snowmakers need little helpers in the form of seed materials added to the water to generate nucleation sites. Silver iodide, kaolin, soaps and detergents, and fungi or lichens are among the materials that have been used.
Currently, the most popular additive is Snomax, a freeze-dried protein powder sold by York Snow, Victor, N.Y. Snomax is derived from Pseudomonas syringae, a common bacterium found on grasses, trees, and vegetable crops. In the 1970s, plant pathologists studying the frost sensitivity of corn plants at the University of Wisconsin, Madison, discovered that the bacteria were responsible for initializing ice crystallization [Nature, 262, 282 (1976)].
A newer seeding product taking the market by storm is called Drift, a liquid polyether-substituted trisiloxane produced by Aquatrols in Cherry Hill, N.J. Drift works as a surfactant to decrease the level of hydrogen bonding in water so the water can freeze more quickly, according to the company.
When it comes to artificial snow, ice, or frost, there are more than 100 different materials that can be used, according to Snow Business, a U.K.-based company that supplies ersatz snow for movie sets. Different classes of materials include paper, plastic, starch and cellulose, or foam.
On movie sets, several products generally will be used in combination or with machine-made snow to create the desired effect. Machine snow is usually avoided because it melts and doesn't look flaky when it's falling. Paper, starch, and cellulose are good materials for falling snow. They can be sprinkled down onto a scene and kept aloft by fans blowing air from the edges of the set. A problem with fans, however, is that the noise may interfere with dialogue. During snow scenes there often will be no dialogue, only music, or the dialogue will be dubbed over.
Paper is one of the most versatile materials because it's weatherproof. Starch and cellulose can give the effect of a light dusting of snow or frost on plants and the ground, but they can be slippery to walk on and can generate a sticky mess. Shredded plastic snow is good for small-scale uses in a studio, although it's more expensive. Firefighting foam works well for deep snow and is fast and inexpensive to use, but it can't be walked on.
A favored material is instant mashed potato flakes. From a distance, the flake snow looks pretty real. The drawback: If it starts raining or the ground somehow gets wet, there's mashed potato slush to slog through. Also, in a close-up shot, potato flakes look like potato flakes, and on moist lips they could present a problem--pass the gravy!
One final type of artificial snow is called dryslope. This is a group of wood, metal, or plastic materials, usually laid down as latticework with void spaces, that is used to ski on out of season or in regions where it does not snow. One downside is the hard materials can lead to a greater risk of injury.
A newer type of dryslope that aims to curb injuries is a multilayer polymer composite matting that resembles carpeting. Two products are Snowflex, made by Briton Engineering Developments, Yorkshire, England, and Powderpak, made by an Atlanta-based company with the same name.
Snowflex, for example, has a slippery polybutylene terephthalate fiber surface layer that sits atop a shock-absorbing pad that has a woven backing. Water piped through the layers exits recessed nozzles and mists the surface, which helps reduce friction even further. This new type of dryslope can be laid out like carpet and cut to fit features such as moguls. It has been used indoors and outdoors to make half pipes and short slopes for freestyle (acrobatic) or downhill skiing and snowboarding.
January 19,2004
Volume 82, Number 03
CENEAR 82 03 p. 72
ISSN 0009-2347
STEVE RITTER
Machine-made snow has been substantially refined by the ski industry over the years. Snowmaking serves to extend the ski season or can rescue a dry winter, but it also has become important for controlling snow conditions as the number of skiers has increased and the mode of enjoying the slopes has evolved to include tubing, sledding, and snowboarding. Machine snow is also used in labs to learn how to forecast avalanches.
To make snow, water cooled to just above its freezing point is pumped under high pressure through the nozzles of a "snow gun." Compressed air or electric fans are usually used to help atomize the water into fine droplets and to disperse them over a wide area where they hopefully will freeze before they hit the ground. If not, the snow will be too wet. Other ways to make snow include using a combination of water and compressed air that is frozen by liquid nitrogen, a method used primarily for indoor sports centers. Snow also can be made from carbon dioxide.
Critical to snowmaking for skiing is getting the right combination of temperature and humidity--the lower the humidity, the higher the outdoor temperature can be to form snow. With untreated water, an air temperature of about –8 °C (18 °F) is needed. Another important factor is the need to generate sufficient nucleation sites for ice crystals to form. Nucleation sites can be a few water molecules that coalesce alone; calcium, magnesium, or other ions; or an impurity such as a clay particle or organic matter.
When the temperature isn't quite cold enough--above about –5 °C (23 °F)--snowmakers need little helpers in the form of seed materials added to the water to generate nucleation sites. Silver iodide, kaolin, soaps and detergents, and fungi or lichens are among the materials that have been used.
Currently, the most popular additive is Snomax, a freeze-dried protein powder sold by York Snow, Victor, N.Y. Snomax is derived from Pseudomonas syringae, a common bacterium found on grasses, trees, and vegetable crops. In the 1970s, plant pathologists studying the frost sensitivity of corn plants at the University of Wisconsin, Madison, discovered that the bacteria were responsible for initializing ice crystallization [Nature, 262, 282 (1976)].
A newer seeding product taking the market by storm is called Drift, a liquid polyether-substituted trisiloxane produced by Aquatrols in Cherry Hill, N.J. Drift works as a surfactant to decrease the level of hydrogen bonding in water so the water can freeze more quickly, according to the company.
When it comes to artificial snow, ice, or frost, there are more than 100 different materials that can be used, according to Snow Business, a U.K.-based company that supplies ersatz snow for movie sets. Different classes of materials include paper, plastic, starch and cellulose, or foam.
On movie sets, several products generally will be used in combination or with machine-made snow to create the desired effect. Machine snow is usually avoided because it melts and doesn't look flaky when it's falling. Paper, starch, and cellulose are good materials for falling snow. They can be sprinkled down onto a scene and kept aloft by fans blowing air from the edges of the set. A problem with fans, however, is that the noise may interfere with dialogue. During snow scenes there often will be no dialogue, only music, or the dialogue will be dubbed over.
Paper is one of the most versatile materials because it's weatherproof. Starch and cellulose can give the effect of a light dusting of snow or frost on plants and the ground, but they can be slippery to walk on and can generate a sticky mess. Shredded plastic snow is good for small-scale uses in a studio, although it's more expensive. Firefighting foam works well for deep snow and is fast and inexpensive to use, but it can't be walked on.
A favored material is instant mashed potato flakes. From a distance, the flake snow looks pretty real. The drawback: If it starts raining or the ground somehow gets wet, there's mashed potato slush to slog through. Also, in a close-up shot, potato flakes look like potato flakes, and on moist lips they could present a problem--pass the gravy!
One final type of artificial snow is called dryslope. This is a group of wood, metal, or plastic materials, usually laid down as latticework with void spaces, that is used to ski on out of season or in regions where it does not snow. One downside is the hard materials can lead to a greater risk of injury.
A newer type of dryslope that aims to curb injuries is a multilayer polymer composite matting that resembles carpeting. Two products are Snowflex, made by Briton Engineering Developments, Yorkshire, England, and Powderpak, made by an Atlanta-based company with the same name.
Snowflex, for example, has a slippery polybutylene terephthalate fiber surface layer that sits atop a shock-absorbing pad that has a woven backing. Water piped through the layers exits recessed nozzles and mists the surface, which helps reduce friction even further. This new type of dryslope can be laid out like carpet and cut to fit features such as moguls. It has been used indoors and outdoors to make half pipes and short slopes for freestyle (acrobatic) or downhill skiing and snowboarding.
January 19,2004
Volume 82, Number 03
CENEAR 82 03 p. 72
ISSN 0009-2347
STEVE RITTER
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