|
|
|
|
|
DeicingDeicing is the process of removing ice from a surface. Most commonly referring to liquids applied to the wings of aircraft, deicing can also be done by other means and on other surfaces. Aircraft When there are freezing conditions and precipitation, it is critical that an airplane be deiced. Failure to do so means the airplane's wings will be too rough to be aerodynamic, thereby causing a loss of lift, and resulting in a crash to the ground. Because of the potentially severe consequence, deicing is done at just about any airport where temperatures are likely to dip below the freezing point. Deicing is usually done with a pink liquid such as propylene glycol, a very close relative of the ethylene glycol used in an automobile's antifreeze. While less toxic than its counterpart, it still must have a containment system in place to capture all of the used liquid, so that it cannot seep into the water. (In one case, a significant snow in Atlanta in early January 2002 caused an overflow of such a system, briefly contaminating the Flint River downstream of the Atlanta airport.) Roads Deicing of roads has traditionally been done with salt, spread by snowplows or other dump trucks designed to spread it, along with sand and gravel, on slick roads. Sodium chloride (table salt) is normally used, as it is cheap and readily available in large quantities. However, since saltwater still freezes at -18°C or 0°F (the basis for Fahrenheit's thermometer scale), it is of no help when the temperature reaches below this point. It also has a strong tendency to cause corrosion, rusting the steel used in most vehicles, and leading the northern U.S. to be called the "Rust Belt". More recent snowmelters use other salts, such as calcium chloride and potassium chloride, which not only lower the freezing point of water much lower, but actually create heat by reacting with it. They are somewhat safer for concrete sidewalks, but excess should still be removed. Since the 1990s, liquid chemical melters have been catching on, being sprayed on roads by nozzles instead of a spinning spreader. These have the advantage of soaking down through snow and spreading evenly across ice. While these are environmentally safer and also more effective, they are also much more expensive. In Nagano, Japan, relatively inexpensive hot water bubbles up through holes in the pavement to melt snow, though this solution is only practical within a city or town. Some individual buildings may melt snow and ice with electric heating elements buried in the pavement, or even on a roof to prevent ice jams under the shingles, or to keep massive chunks of snow and dangerous icicles from collapsing on anyone below.
|
 |
|
| Copyright 2005-2009 OnPedia.com. All Rights Reserved |
|
|