De-icing is the process of removing snow, ice or ice from the surface. Anti-icing is understood as a chemical application that not only removes ice but also remains on the surface and continues to delay ice reform for a certain period of time, or preventing ice adhesion to make mechanical removal easier.
Video Deicing
Approach
De-icing can be achieved by mechanical methods (scratching, pushing); through the application of heat; by using dry or liquid chemicals designed to lower the freezing point of water (various salts or brines, alcohols, glycols); or with a combination of these different techniques.
Rail and rail switches
Trains and train switches in the arctic area have big problems with snow and ice piling up. They need a constant heat source in the cold days to ensure functionality. In trains it is mainly brakes, suspensions and couplers that require heating for de-icing. On the rails are mainly switches that are sensitive to ice. This high-powered electric heater efficiently prevents the formation of ice and melts the rapidly-formed ice.
The heater is preferably made of PTC material, eg PTC Rubber, to avoid overheating and potentially damaging the heater. This heater is self-limiting and does not require electronic set up; they can not overheat and do not require overheating protection.
Planes
On the ground, when there are frozen conditions and rainfall, de-icing of aircraft is very important. Frozen contaminants cause critical control surfaces to become rough and uneven, disrupting smooth airflow and greatly decreasing the ability of the wings to generate lift, and increasing barriers. This situation can cause crashes. If large pieces of ice are separated when the plane is in motion, they can be digested in the engine or pressing the blades and causing catastrophic failure. Frozen contaminants may inhibit the control surface, preventing it from moving properly. Because of this potentially severe consequence, de-icing is performed at airports where the temperature may be around 0 Ã, Â ° C (32 Ã, Â ° F).
In flight, super cold water droplets are often present in stratiform and cumulus clouds. They are formed into ice when they are struck by the wing of a passing plane and suddenly crystallize. This disrupts the airflow above the wing, reducing lift, so the aircraft expected to fly in such conditions is equipped with a de-icing system.
The de-icing technique is also used to ensure that the engine inlets and various sensors outside the aircraft are free of ice or snow.
Chemical de-icing
The de-icing fluid comprising propylene glycol (PG) and additives is widely used by airlines for aircraft de-icing. Ethylene glycol (EG) liquids are still used for de-icing aircraft in some parts of the world because they have lower operational operating temperatures (LOUT) than PG. However, PG is more common because it is more toxic than ethylene glycol.
When applied, most de-icing fluids do not stick to the plane surface, and fall to the ground. Airports usually use a containment system to capture the fluid used, so it can not seep into the ground and water. Although PG is classified as non-toxic, it pollutes waterways because it consumes oxygen in large amounts as it decomposes, causing aquatic life to suffocate. ( View Environmental impacts and mitigation.)
Anti-icing aircraft is achieved by applying a protective coating, using a viscous liquid called anti-ice fluid , above the surface to absorb contaminants. All anti-ice fluids offer only limited protection, depending on the type of frozen contaminants and prevailing weather conditions. The liquid has failed when it can no longer absorb the contaminants and is essentially the contaminant itself. Even water can be a contaminant in this sense, because water melts anti-ice substances until they are no longer effective.
Heating de-icing heat
Direct infrared heating has also been developed as an aircraft de-icing technique. This heat transfer mechanism is substantially faster than the conventional heat transfer mode used by conventional de-icing (convection and conduction) due to the air-cooling effect on the de-icing fluid spray.
One infrared de-icing system requires that the heating process takes place inside specially constructed hangars. This system has limited interest among airport operators, due to the space and associated logistic requirements for hangars. In the United States, this type of infrared de-icing system has been used, on a limited scale, at two major hub airports and one small commercial airport.
Other infrared systems use truck-driven heating units that do not require the use of hangars. Manufacturers claim that this system can be used for both fixed-wing and helicopter aircraft, although it does not mention examples of its use on commercial aircraft.
Airport sidewalk
De-icing operations for airport pavements (runways, taxiways, apron, taxiway bridges) may involve several types of liquid and solid chemical products, including propylene glycol, ethylene glycol and other organic compounds. Chloride-based compounds (eg salts) are not used at airports, due to their corrosive effects on planes and other equipment.
The urea mixture has also been used for making ice cubes, because the price is cheap. However, urea is a significant pollutant in waterways and wildlife, as it is degraded into ammonia after application, and has been largely removed at US airports. In 2012, the US Environmental Protection Agency (EPA) banned the use of urea-based deicers in most commercial airports.
Highway
De-icing of the street has traditionally been done with salt, propagated by snowplows or dump trucks designed to spread it, often mixed with sand and gravel, on slippery roads. Sodium chloride (rock salt) is usually used, because it is cheap and available in large quantities. However, since salt water still freezes at -18 Â ° C (0 Â ° F), it is useless when the temperature falls below this point. It also has a strong tendency to cause corrosion, rusting of steel used in most vehicles and rebar on concrete bridges. Depending on the concentration, it can be toxic to some plants and animals, and some urban areas have moved away from it as a result. Newer snowmelters use other salts, such as calcium chloride and magnesium chloride, which not only suppress the freezing point of water to a much lower temperature, but also produce exothermic reactions. They are somewhat safer for sidewalks, but the excess still has to be removed.
Recently, organic compounds have been developed that reduce the environmental problems associated with salt and have a longer residual effect when scattered on the road, usually along with salt water or salt solids. These compounds are produced as a by-product of agricultural operations such as sugar beet refining or distillation processes that produce ethanol. In addition, mixing of common rock salts with some organic compounds and magnesium chloride produces a dispersible material which are both effective for many cooler temperatures (-34 Â ° C or -29 Â ° F) as well as at a lower overall rate of deployment per area units.
The solar road system has been used to keep the road surface above the freezing point of water. Array pipes embedded in road surfaces are used to collect solar energy in the summer, transferring heat to the thermal banks and restoring heat to roads in the winter to maintain surfaces above 0 Ã, Â ° C (32 Ã, Â ° F). This automatic form of collecting, storing and delivering renewable energy avoids environmental problems using chemical contaminants.
It is recommended in 2012 that a superhydrophobic surface capable of holding water can also be used to prevent the accumulation of ice that causes icephobicity. However, not every superhydrophobic surface is icephobic and the method is still under development.
Chemical de-icers
All chemical de-icers share a common working mechanism: they chemically prevent water molecules from binding above a certain temperature that depends on concentration. This temperature is below 0 ° C, the freezing point of pure water. Occasionally, there is an exothermic dissolution reaction that allows for a stronger melting strength. The following list contains the most commonly used de-icing chemicals and typical chemical formulas.
- Inorganic salt
- Sodium chloride (NaCl or table salt, the most common de-icing chemical)
- Magnesium chloride ( MgCl
2 , often added to salt to lower its working temperature) - Calcium chloride ( CaCl
2 , often added to salt to lower its working temperature) - Potassium chloride (KCl)
- Organic compounds
- Calcium magnesium acetate ( CaMg
2 (CH
3 COO) < span>
6 - Potassium acetate ( CH
3 COOK ) - Potassium formers ( CHO
2 )
2 )
2 ), general fertilizer
- Alcohol, diol and polyol
(this is an antifreeze agent and rarely used on the road)
- Metanol ( CH
4 O ) - Ethylene glycol ( C
2 H
6 O
2 ) - Propylene glycol ( C
3 H < span>
8 O
2 ) - Glycerol ( C
3 H
8 O
3 )
Liquid type
There are several types of fluid de-icing aircraft, falling into two basic categories:
- De-icing fluid: Hot glycol is diluted with water for ice and snow/ice removal, also called Newton fluid (because the viscous flow is similar to water)
- Anti-icing fluid: , an unheated propylene glycol liquid, which has thickened (think of a half-set of gelatin), also referred to as a non-Newtonian liquid (due to a typical viscous flow), is applied to slow the development of ice in the future or to prevent the falling snow or hail from accumulation. Anti-icing fluid provides barrier protection against ice formation when the aircraft is stationary on the ground. However, when subjected to shear forces such as airflow over the surface of the fluid, when an aircraft accelerates to take off, the entire liquid rheology changes and it becomes thinner, running to leave a clean, smooth aerodynamic surface to the wing.
In some cases both types of fluid are applied to the plane, first a heated glycol/water mixture to remove contaminants, followed by heated unheated liquids to keep the ice from altering before the plane takes off. This is called a "two-step procedure".
De-es methanol fluids have been used for years to surface wings and small de-es tails from small to medium common aircraft and are commonly used with small hand-held sprayers. Methanol can only remove frozen and mild ice soil before flying.
Mono-ethylene, di-ethylene and propylene glycol are non-flammable petroleum products and similar products most commonly found in automotive refrigeration systems. Glycols have excellent de-icing properties and flight rates are referred to as SAE/ISO/AEA Type I (AMS 1424 or ISO 11075). it is usually applied to water-diluted contaminated surfaces at 95 degrees Fahrenheit (35 ° C) using a cherry picker on a truck containing 1,500 to 2,000 gal US (5,680 to 7,570 Â ° L; 1,250 to 1,670 Â ° C) for Application of runway entry point -ramp or departure. The dyed-colored liquid is preferred as it can be confirmed easily with visual observations that the aircraft has received a de-es application. Type I liquid extraction seems to change the pinkish tinge, hence the term "pink snow." Otherwise, all Type I fluids are orange.
In 1992, Dead Sea Works began marketing ice icer based on salt and minerals from the Dead Sea.
Maps Deicing
In-flight aircraft de-icing
Pneumatic system
The accumulation of ice in the plane is most common on wingtips, tails, and engines (including propellers or fan blades). Low speed aircraft often use pneumatic pneumatic boots on the wingtips and tail for the ice melting in the air. Rubber cover periodically increases, causing cracking and peeling ice. Once the system is activated by the pilot, the inflation/deflation cycle is controlled automatically. In the past, it was considered such a system could be defeated if they increased prematurely; if the pilot does not allow a thick layer of ice to form before pumping the boots, the boots will only create a gap between the leading edge and the formed ice. Recent research shows "bridging" does not happen with modern boots.
Electrical system
Some aircraft can also use electrically heated resistive elements embedded in cemented rubber sheets to the wing edges and the leading tail surfaces, the front edges of propellers, and the edges of the helicopter rotor blades. This de-icing system was developed by the US Rubber Company in 1943. Such systems usually operate continuously. When ice is detected, they first function as a de-icing system, then as anti-icing system for advanced flights under icing conditions. Some aircraft use a chemical de-icing system that pumps antifreeze such as alcohol or propylene glycol through a small opening on the wing surface and at the roots of the blades, melting the ice, and making the surface unfriendly to ice formation. The fourth system, developed by NASA, detects ice on the surface by sensing changes in resonant frequency. Once the electronic control module has determined that the ice has been formed, a large current spike is pumped into the transducer to produce a sharp mechanical shock, crack the ice sheet and cause it to be flaked by the slipstream.
Exhaust system
Many modern civilian civil wing transport aircraft use anti-ice systems on the cutting edge wings, engine inlets and air data probes using warm air. It is detonated from the engine and channeled into the cavity beneath the surface for anti-ice. Warm air heats the surface to some degree above 0 ° C (32 ° F), prevents ice from forming. The system can operate independently, switched on and off when the aircraft enters and leaves the icing condition.
Environmental impacts and mitigation
Salt de-icing such as sodium chloride or calcium chloride seeps into the soil, where the ions (especially cations) can accumulate and eventually become toxic to organisms and plants that grow on this soil. Chemicals can also reach water bodies in concentrations that are toxic to ecosystems. Increased salinity has been observed in lakes and rivers in the United States, due to road salt. The organic compounds decompose and can cause oxygen depletion problems. Tidal rivers and long rotation pools are especially vulnerable.
Ethylene glycol and propylene glycol are known to exert high levels of biochemical oxygen demand (BOD) during degradation at the water surface. This process can affect aquatic life by consuming the oxygen needed by aquatic organisms to survive. A large amount of dissolved oxygen (DO) in the water column is consumed when the microbial population decomposes propylene glycol.
Sufficient levels of dissolved oxygen on the surface of the water are essential for the survival of fish, macroinvertebrates, and other aquatic organisms. If the concentration of oxygen falls below the minimum level, the organism emigrates, if able and possible, to areas with higher oxygen levels or eventually dies. This effect can drastically reduce the amount of aquatic habitats that can be used. DO level reductions can reduce or eliminate bottom feeder populations, create conditions that support changes in the profile of community species, or alter critical food-web interactions.
In one case, significant snow in Atlanta in early January 2002 caused an overflow of such systems, which briefly pollute the Flint River downstream of Atlanta airport.
Some airports recycle using de-icing fluids, separating water and solid contaminants, allowing the reuse of fluids in other applications. Other airports have on-site wastewater treatment facilities, and/or deliver collected liquids to municipal sewage treatment plants or commercial waste water treatment facilities.
Toxicity of de-icing fluid is another environmental problem, and research is underway to find less toxic alternatives (ie non-glycols).
See also
- The atmospheric layer
- Ice protection system
- Icephobicity
- The pitot tube
- The pitot-static system
References
Source of the article : Wikipedia
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