Coolant is a substance, usually liquid or gas, which is used to reduce or regulate the temperature of a system. The ideal cooler has a high thermal capacity, low viscosity, low cost, non-toxic, chemically inert, and does not cause or increase corrosion in the cooling system. Some applications also require a cooler to be an electrical insulator.
While the term cooler is commonly used in automotive and HVAC applications, in industrial processing fluid heat transfer is one of the more commonly used technical terms in high temperatures as well as low temperature manufacturing applications.. The term also includes fluid cutting.
The coolant can keep the phase and remain liquid or gas, or it can undergo phase transitions, with latent heat adding to cooling efficiency. The latter, when used to achieve under-environmental temperature, is more commonly known as refrigerant.
Video Coolant
Gas
Air is a common form of cooling. Air cooling uses convective airflow (passive cooling), or forced circulation using a fan.
Hydrogen is used as a high performance gas cooler. Thermal conductivity is higher than all other gases, it has a high specific heat capacity, low density and hence low viscosity, which is an advantage for rotary engines susceptible to windage losses. The hydrogen-cooled turogenerator is currently the most common electric generator in large power plants.
Inert gas is used as a coolant in gas-cooled nuclear reactors. Helium has a low tendency to absorb neutrons and become radioactive. Carbon dioxide is used in Magnox and AGR reactors.
Sulfur hexafluoride is used to cool and isolate some high voltage power systems (circuit breakers, switches, some transformers, etc.).
Steam can be used where high specific heat capacity is required in the form of gases and the corrosive properties of hot water are taken into account.
Maps Coolant
Fluid
The most common coolant is water. Its high heat capacity and low cost make it a suitable heat transfer medium. Usually used with additives, such as corrosion inhibitors and antifreeze. Antifreeze, the corresponding organic solution (most often ethylene glycol, diethylene glycol, or propylene glycol) in water, is used when a water-based coolant must withstand temperatures below 0 ° C, or when its boiling point must be raised. Betaine is a similar coolant, with the exception that it is made from pure plant extracts, and is therefore non-toxic or difficult to ecologically dispose of.
Deionized water is very pure, due to its relatively low electrical conductivity, used to cool some electrical appliances, often high-powered transmitters and high-powered vacuum tubes.
Heavy water is a moderator of neutrons used in some nuclear reactors; it also has a secondary function as their cooler. Light water reactor, both boiling water and the most common type pressure water reactor, use plain water (light).
Polyalkylene glycol (PAG) is used as a high temperature, thermally stable heat transfer fluid exhibits strong resistance to oxidation. Modern PAGs can also be non-toxic and harmless.
The cutting fluid is a refrigerant that also serves as a lubricant for metal forming machine tools.
Oil is often used for applications where water does not fit. With a higher boiling point than water, the oil can be raised to a much higher temperature (above 100 degrees Celsius) without including high pressure in the container or loop system in question.
- Mineral oil works well as a coolant and lubricant in many mechanical gears. Castor oil is also used. Because of its high boiling point, mineral oil is used in portable electric-style heating radiators in residential applications, and in closed-loop systems for industrial heating and cooling processes. Mineral oil is often used in PC systems submerged because it is not conductive and therefore will not be shorted or damaged any part.
- Silicone oil and fluorocarbon oil (such as fluorinert) are preferred because of their wide operating temperature range. However their high cost limits their applications.
- The transformer oil is used for additional electrical cooling and insulation from high-powered power transformers.
A waterless cooler is used as an alternative to conventional water coolers and ethylene glycol. With a boiling point higher than water (about 370F), cooling technology does not boil. The liquid also prevents corrosion.
Fuel is often used as a cooler for the engine. Cold fuel flows in parts of the engine, absorbing the heat of the waste and heating it before it is burned. Kerosene and other jet fuel often function in this role in aviation engines.
Freon is often used for deep cooling for example. electronic.
Refrigerant is a refrigerant used to achieve a low temperature by undergoing a phase change between liquid and gas. Halomethan is often used, most often R-12 and R-22, but because environmental problems are being removed, often with liquid propane or other haloalkanes such as R-134a. Anhydrous ammonia is often used in large commercial systems, and sulfur dioxide is used in the early mechanical refrigerators. Carbon dioxide (R-744) is used as a working fluid in climate control systems for cars, residential air conditioners, commercial coolers, and vending machines.
Heat pipe is a special application of refrigerant.
Metal and liquid salt
Usable liquid mixtures can be used as coolants in applications requiring high temperature stability, eg. some fast nuclear reactor reactors. Sodium (in fast reactor-cooled sodium) or sodium-potassium NaK alloys are often used; in special cases lithium may be used. Another liquid metal used as a coolant is lead, in eg. leading a rapidly cooled reactor, or a tin-bismuth alloy. Some early early neutron reactors use mercury.
For certain applications, automotive poppet valve rods can be hollow and filled with sodium to improve transport and heat transfer.
For very high temperature applications, e.g. a liquid saline reactor or a very high temperature reactor, a molten salt may be used as a coolant. One possible combination is a mixture of sodium fluoride and sodium tetrafluoroborate (NaF-NaBF 4 ). Other options are FLiBe and FLiNaK.
Liquid gas
Liquid gases are used as coolants for cryogenic applications, including cryo-electron microscopy, overclocking computer processors, applications using superconductors, or very sensitive sensors and very low amplifier noise.
Carbon Dioxide (chemical formula CO 2 ) - used as a substitute for coolant to cut the liquid. CO 2 can provide controlled cooling at the cutting interface in such a way that cutting tools and workpieces are held at room temperature. The use of CO 2 greatly extends the life of the chisel, and in most materials allows the operation to run faster. It is considered a very environmentally friendly method, especially when compared to the use of petroleum oil as a lubricant; clean and dry parts that can often eliminate the operation of secondary cleaning.
Liquid nitrogen, which boils at about -196 ° C (77K), is the most common and most expensive coolant used. Liquid air is used for lower levels, because the liquid oxygen content which makes it vulnerable causes fire or explosion when in contact with combustible material (see oxyliquits).
Lower temperatures can be achieved by using a boiling liquid fluid at about -246 ° C. The lowest temperature, used for the strongest superconducting magnet, is achieved using liquid helium.
Liquid hydrogen at -250 to -265 Â ° C can also be used as a coolant. Liquid hydrogen is also used both as fuel and as a coolant to cool the nozzles and combustion chamber of the rocket engine.
Nanofluids
A new class of refrigerants is a nanofluid composed of carrier fluid, such as water, scattered with small nanoscale particles known as nanoparticles. Specially designed nanoparticles, for example, CuO, alumina, titanium dioxide, carbon nanotubes, silica, or metals (eg copper, or silver nanorods) dispersed into the carrier fluid increase the heat transfer capability of the resulting coolant compared to the carrier fluid alone. This increase is theoretically as high as 350%. However the experiment did not prove the increase in high thermal conductivity, but found a significant increase of the critical heat flux from the coolant.
Some significant improvements can be achieved; for example silver nanorods with a diameter of 55 Â ± 12m and an average length of 12.8 Ã,Âμm at 0.5Ã, vol.% increase the thermal conductivity of water by 68%, and 0.5 vol vol.% of silver nanorods increases thermal conductivity of ethylene glycol based on coolant of 98%. 0.1% alumina nanoparticles can increase critical water hot water by 70%; particles form a coarse porous surface on the cooled object, which encourages the formation of new bubbles, and their hydrophilic properties then help push them away, blocking the formation of the vapor layer. Nanofluids with concentrations greater than 5% act like non-Newtonian fluids.
Solids
In some applications, solid materials are used as coolants. The material requires high energy to evaporate; this energy is then carried away by the evaporating gases. This approach is common in outer space, for the ablative shift of the atmosphere shell and to cool the rocket engine nozzle. The same approach is also used for fire protection structures, where ablative coatings are applied.
Dry ice and ice water can also be used as a coolant, when in direct contact with the cooled structure.
Sublimation ice water is used to cool the space suits for the Apollo Project.
References
External links
- CO 2 as a natural cooler - FAQ
Source of the article : Wikipedia
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