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Wikipedia

Coolant

January 24, 2023

A coolant is a substance, typically liquid, that is used to reduce or regulate the temperature of a system. An ideal coolant has high thermal capacity, low viscosity, is low-cost, non-toxic, chemically inert and neither causes nor promotes corrosion of the cooling system. Some applications also require the coolant to be an electrical insulator.

While the term "coolant" is commonly used in automotive and HVAC applications, in industrial processing heat-transfer fluid is one technical term more often used in high temperature as well as low-temperature manufacturing applications. The term also covers cutting fluids. Industrial cutting fluid has broadly been classified as water-soluble coolant and neat cutting fluid. Water-soluble coolant is oil in water emulsion. It has varying oil content from nil oil (synthetic coolant).

This coolant can either keep its phase and stay liquid or gaseous, or can undergo a phase transition, with the latent heat adding to the cooling efficiency. The latter, when used to achieve below-ambient temperature, is more commonly known as refrigerant.

Gases

Air is a common form of a coolant. Air cooling uses either convective airflow (passive cooling), or a forced circulation using fans.

Hydrogen is used as a high-performance gaseous coolant. Its thermal conductivity is higher than all other gases, it has high specific heat capacity, low density and therefore low viscosity, which is an advantage for rotary machines susceptible to windage losses. Hydrogen-cooled turbogenerators are currently the most common electrical generators in large power plants.

Inert gases are used as coolants 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 for cooling and insulating of some high-voltage power systems (circuit breakers, switches, some transformers, etc.).

Steam can be used where high specific heat capacity is required in gaseous form and the corrosive properties of hot water are accounted for.

Two-phase

Some coolants are used in both liquid and gas form in the same circuit, taking advantage of the high specific latent heat of boiling/condensing phase change, the enthalpy of vaporization, in addition to the fluid's non-phase-change heat capacity.

Refrigerants are coolants used for reaching low temperatures by undergoing phase change between liquid and gas. Halomethanes were frequently used, most often R-12 and R-22, often with liquified propane or other haloalkanes like R-134a. Anhydrous ammonia is frequently used in large commercial systems, and sulfur dioxide was used in early mechanical refrigerators. Carbon dioxide (R-744) is used as a working fluid in climate control systems for cars, residential air conditioning, commercial refrigeration, and vending machines. Many otherwise excellent refrigerants are phased out for environmental reasons (the CFCs due to ozone layer effects, now many of their successors face restrictions due to global warming, e.g. the R134a).

Heat pipes are a special application of refrigerants.

Water is sometimes employed this way, e.g. in boiling water reactors. The phase change effect can be intentionally used, or can be detrimental.

Phase-change materials use the other phase transition between solid and liquid.

Liquid gases may fall here, or into refrigerants, as their temperature is often maintained by evaporation. Liquid nitrogen is the best known example encountered in laboratories. The phase change may not occur at the cooled interface, but on the surface of the liquid, to where the heat is transferred by convective or forced flow.

Liquids

 
Device to measure the temperature to which the coolant protects the car from freezing

Water is the most common coolant. Its high heat capacity and low cost make it a suitable heat-transfer medium. It is usually used with additives, like corrosion inhibitors and antifreeze. Antifreeze, a solution of a suitable organic chemical (most often ethylene glycol, diethylene glycol, or propylene glycol) in water, is used when the water-based coolant has to withstand temperatures below 0 °C, or when its boiling point has to be raised. Betaine is a similar coolant, with the exception that it is made from pure plant juice, and is not toxic or difficult to dispose of ecologically.[1]

Polyalkylene glycol (PAG) is used as high temperature, thermally stable heat transfer fluids exhibiting strong resistance to oxidation. Modern PAGs can also be non-toxic and non-hazardous.[2]

Cutting fluid is a coolant that also serves as a lubricant for metal-shaping machine tools.

Oils are often used for applications where water is unsuitable. With higher boiling points than water, oils can be raised to considerably higher temperatures (above 100 degrees Celsius) without introducing high pressures within the container or loop system in question.[3] Many oils have uses encompassing heat transfer, lubrication, pressure transfer (hydraulic fluids), sometimes even fuel, or several such functions at once.

  • Mineral oils serve as both coolants and lubricants in many mechanical gears. Some vegetable oils, e.g. castor oil are also used. Due to their high boiling points, mineral oils are used in portable electric radiator-style space heaters in residential applications, and in closed-loop systems for industrial process heating and cooling. Mineral oil is often used in submerged PC systems as it is non-conductive and therefore won't short circuit or damage any parts.
    • Polyphenyl ether oils are suitable for applications needing high temperature stability, very low volatility, inherent lubricity, and/or radiation resistance. Perfluoropolyether oils are their more chemically inert variant.
    • A eutectic mixture of diphenyl ether (73.5%) and biphenyl (26.5%) is used for its wide temperature range and stability to 400°C.
    • Polychlorinated biphenyls and polychlorinated terphenyls were used in heat transfer applications, favored due to their low flammability, chemical resistance, hydrophobicity, and favorable electrical properties, but are now phased out due to their toxicity and bioaccumulation.
  • Silicone oils and fluorocarbon oils (like fluorinert) are favored for their wide range of operating temperatures. However their high cost limits their applications.
  • Transformer oil is used for cooling and additional electric insulation of high-power electric transformers. Mineral oils are usually used. Silicone oils are employed for special applications. Polychlorinated biphenyls were commonly used in old equipment, which now can possess risk of contamination.

Fuels are frequently used as coolants for engines. A cold fuel flows over some parts of the engine, absorbing its waste heat and being preheated before combustion. Kerosene and other jet fuels frequently serve in this role in aviation engines. Liquid hydrogen is used to cool nozzles of rocket engines.

Waterless coolant is used as an alternative to conventional water and ethylene glycol coolants. With higher boiling points than water (around 370F), the cooling technology resists boil over. The liquid also prevents corrosion. [4]

Freons were frequently used for immersive cooling of e.g. electronics.

Molten metals and salts

See also: Nuclear reactor coolant and Thermal energy storage § Molten salt technology

Liquid fusible alloys can be used as coolants in applications where high temperature stability is required, e.g. some fast breeder nuclear reactors. Sodium (in sodium cooled fast reactors) or sodium-potassium alloy NaK are frequently used; in special cases lithium can be employed. Another liquid metal used as a coolant is lead, in e.g. lead cooled fast reactors, or a lead-bismuth alloy. Some early fast neutron reactors used mercury.

For certain applications the stems of automotive poppet valves may be hollow and filled with sodium to improve heat transport and transfer.

For very high temperature applications, e.g. molten salt reactors or very high temperature reactors, molten salts can be used as coolants. One of the possible combinations is the mix of sodium fluoride and sodium tetrafluoroborate (NaF-NaBF4). Other choices are FLiBe and FLiNaK.

Liquid gases

Liquified gases are used as coolants for cryogenic applications, including cryo-electron microscopy, overclocking of computer processors, applications using superconductors, or extremely sensitive sensors and very low-noise amplifiers.

Carbon Dioxide (chemical formula is CO2) - is used as a coolant replacement[5] for cutting fluids. CO2 can provide controlled cooling at the cutting interface such that the cutting tool and the workpiece are held at ambient temperatures. The use of CO2 greatly extends tool life, and on most materials allows the operation to run faster. This is considered a very environmentally friendly method, especially when compared to the use of petroleum oils as lubricants; parts remain clean and dry which often can eliminate secondary cleaning operations.

Liquid nitrogen, which boils at about -196 °C (77K), is the most common and least expensive coolant in use. Liquid air is used to a lesser extent, due to its liquid oxygen content which makes it prone to cause fire or explosions when in contact with combustible materials (see oxyliquits).

Lower temperatures can be reached using liquified neon which boils at about -246 °C. The lowest temperatures, used for the most powerful superconducting magnets, are reached using liquid helium.

Liquid hydrogen at -250 to -265 °C can also be used as a coolant. Liquid hydrogen is also used both as a fuel and as a coolant to cool nozzles and combustion chambers of rocket engines.

Nanofluids

A new class of coolants are nanofluids which consist of a carrier liquid, such as water, dispersed with tiny nano-scale particles known as nanoparticles. Purpose-designed nanoparticles of e.g. CuO, alumina,[6] titanium dioxide, carbon nanotubes, silica, or metals (e.g. copper, or silver nanorods) dispersed into the carrier liquid enhance the heat transfer capabilities of the resulting coolant compared to the carrier liquid alone.[7] The enhancement can be theoretically as high as 350%. The experiments however did not prove so high thermal conductivity improvements, but found significant increase of the critical heat flux of the coolants.[8]

Some significant improvements are achievable; e.g. silver nanorods of 55±12 nm diameter and 12.8 µm average length at 0.5 vol.% increased the thermal conductivity of water by 68%, and 0.5 vol.% of silver nanorods increased thermal conductivity of ethylene glycol based coolant by 98%.[9] Alumina nanoparticles at 0.1% can increase the critical heat flux of water by as much as 70%; the particles form rough porous surface on the cooled object, which encourages formation of new bubbles, and their hydrophilic nature then helps pushing them away, hindering the formation of the steam layer.[10] Nanofluid with the concentration more than 5% acts like non-Newtonian fluids.

Solids

In some applications, solid materials are used as coolants. The materials require high energy to vaporize; this energy is then carried away by the vaporized gases. This approach is common in spaceflight, for ablative atmospheric reentry shields and for cooling of rocket engine nozzles. The same approach is also used for fire protection of structures, where ablative coating is applied.

Dry ice and water ice can be also used as coolants, when in direct contact with the structure being cooled. Sometimes an additional heat transfer fluid is used; water with ice and dry ice in acetone are two popular pairings.

Sublimation of water ice was used for cooling the space suit for Project Apollo.

References

  1. ^ Betaine as coolant 2011-04-09 at the Wayback Machine
  2. ^ Duratherm Extended Life Fluids
  3. ^ Paratherm Corporation
  4. ^ Sturgess, Steve (August 2009). "Column: Keep Your Cool". Heavy Duty Trucking. Retrieved April 2, 2018.
  5. ^ ctemag.com
  6. ^ . Archived from the original on November 13, 2013. Retrieved November 13, 2013.
  7. ^ Wang, Xiang-Qi; Mujumdar, Arun S. (December 2008). "A review on nanofluids - part II: experiments and applications". Brazilian Journal of Chemical Engineering. 25 (4): 631–648. doi:10.1590/S0104-66322008000400002.
  8. ^ scienceblog.com January 5, 2010, at the Wayback Machine
  9. ^ Oldenburg, Steven J.; Siekkinen, Andrew R.; Darlington, Thomas K.; Baldwin, Richard K. (9 July 2007). "Optimized Nanofluid Coolants for Spacecraft Thermal Control Systems". SAE Technical Paper Series. Vol. 1. pp. 2007–01–3128. doi:10.4271/2007-01-3128.
  10. ^ mit.edu

External links

 
Look up coolant in Wiktionary, the free dictionary.


    January 24, 2023
    coolant, coolant, substance, typically, liquid, that, used, reduce, regulate, temperature, system, ideal, coolant, high, thermal, capacity, viscosity, cost, toxic, chemically, inert, neither, causes, promotes, corrosion, cooling, system, some, applications, al. A coolant is a substance typically liquid that is used to reduce or regulate the temperature of a system An ideal coolant has high thermal capacity low viscosity is low cost non toxic chemically inert and neither causes nor promotes corrosion of the cooling system Some applications also require the coolant to be an electrical insulator While the term coolant is commonly used in automotive and HVAC applications in industrial processing heat transfer fluid is one technical term more often used in high temperature as well as low temperature manufacturing applications The term also covers cutting fluids Industrial cutting fluid has broadly been classified as water soluble coolant and neat cutting fluid Water soluble coolant is oil in water emulsion It has varying oil content from nil oil synthetic coolant This coolant can either keep its phase and stay liquid or gaseous or can undergo a phase transition with the latent heat adding to the cooling efficiency The latter when used to achieve below ambient temperature is more commonly known as refrigerant Contents 1 Gases 2 Two phase 3 Liquids 3 1 Molten metals and salts 3 2 Liquid gases 3 3 Nanofluids 4 Solids 5 References 6 External linksGases EditAir is a common form of a coolant Air cooling uses either convective airflow passive cooling or a forced circulation using fans Hydrogen is used as a high performance gaseous coolant Its thermal conductivity is higher than all other gases it has high specific heat capacity low density and therefore low viscosity which is an advantage for rotary machines susceptible to windage losses Hydrogen cooled turbogenerators are currently the most common electrical generators in large power plants Inert gases are used as coolants 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 for cooling and insulating of some high voltage power systems circuit breakers switches some transformers etc Steam can be used where high specific heat capacity is required in gaseous form and the corrosive properties of hot water are accounted for Two phase EditSome coolants are used in both liquid and gas form in the same circuit taking advantage of the high specific latent heat of boiling condensing phase change the enthalpy of vaporization in addition to the fluid s non phase change heat capacity Refrigerants are coolants used for reaching low temperatures by undergoing phase change between liquid and gas Halomethanes were frequently used most often R 12 and R 22 often with liquified propane or other haloalkanes like R 134a Anhydrous ammonia is frequently used in large commercial systems and sulfur dioxide was used in early mechanical refrigerators Carbon dioxide R 744 is used as a working fluid in climate control systems for cars residential air conditioning commercial refrigeration and vending machines Many otherwise excellent refrigerants are phased out for environmental reasons the CFCs due to ozone layer effects now many of their successors face restrictions due to global warming e g the R134a Heat pipes are a special application of refrigerants Water is sometimes employed this way e g in boiling water reactors The phase change effect can be intentionally used or can be detrimental Phase change materials use the other phase transition between solid and liquid Liquid gases may fall here or into refrigerants as their temperature is often maintained by evaporation Liquid nitrogen is the best known example encountered in laboratories The phase change may not occur at the cooled interface but on the surface of the liquid to where the heat is transferred by convective or forced flow Liquids Edit Device to measure the temperature to which the coolant protects the car from freezing Water is the most common coolant Its high heat capacity and low cost make it a suitable heat transfer medium It is usually used with additives like corrosion inhibitors and antifreeze Antifreeze a solution of a suitable organic chemical most often ethylene glycol diethylene glycol or propylene glycol in water is used when the water based coolant has to withstand temperatures below 0 C or when its boiling point has to be raised Betaine is a similar coolant with the exception that it is made from pure plant juice and is not toxic or difficult to dispose of ecologically 1 Very pure deionized water due to its relatively low electrical conductivity is used to cool some electrical equipment often high power transmitters and high power vacuum tubes Heavy water is a neutron moderator used in some nuclear reactors it also has a secondary function as their coolant Light water reactors both boiling water and pressurised water reactors the most common type use ordinary light water Some designs e g CANDU reactor use both types heavy water in the nonpressurized calandria tank as the moderator and a supplementary coolant and light water as the primary heat transfer fluid Polyalkylene glycol PAG is used as high temperature thermally stable heat transfer fluids exhibiting strong resistance to oxidation Modern PAGs can also be non toxic and non hazardous 2 Cutting fluid is a coolant that also serves as a lubricant for metal shaping machine tools Oils are often used for applications where water is unsuitable With higher boiling points than water oils can be raised to considerably higher temperatures above 100 degrees Celsius without introducing high pressures within the container or loop system in question 3 Many oils have uses encompassing heat transfer lubrication pressure transfer hydraulic fluids sometimes even fuel or several such functions at once Mineral oils serve as both coolants and lubricants in many mechanical gears Some vegetable oils e g castor oil are also used Due to their high boiling points mineral oils are used in portable electric radiator style space heaters in residential applications and in closed loop systems for industrial process heating and cooling Mineral oil is often used in submerged PC systems as it is non conductive and therefore won t short circuit or damage any parts Polyphenyl ether oils are suitable for applications needing high temperature stability very low volatility inherent lubricity and or radiation resistance Perfluoropolyether oils are their more chemically inert variant A eutectic mixture of diphenyl ether 73 5 and biphenyl 26 5 is used for its wide temperature range and stability to 400 C Polychlorinated biphenyls and polychlorinated terphenyls were used in heat transfer applications favored due to their low flammability chemical resistance hydrophobicity and favorable electrical properties but are now phased out due to their toxicity and bioaccumulation Silicone oils and fluorocarbon oils like fluorinert are favored for their wide range of operating temperatures However their high cost limits their applications Transformer oil is used for cooling and additional electric insulation of high power electric transformers Mineral oils are usually used Silicone oils are employed for special applications Polychlorinated biphenyls were commonly used in old equipment which now can possess risk of contamination Fuels are frequently used as coolants for engines A cold fuel flows over some parts of the engine absorbing its waste heat and being preheated before combustion Kerosene and other jet fuels frequently serve in this role in aviation engines Liquid hydrogen is used to cool nozzles of rocket engines Waterless coolant is used as an alternative to conventional water and ethylene glycol coolants With higher boiling points than water around 370F the cooling technology resists boil over The liquid also prevents corrosion 4 Freons were frequently used for immersive cooling of e g electronics Molten metals and salts Edit See also Nuclear reactor coolant and Thermal energy storage Molten salt technology Liquid fusible alloys can be used as coolants in applications where high temperature stability is required e g some fast breeder nuclear reactors Sodium in sodium cooled fast reactors or sodium potassium alloy NaK are frequently used in special cases lithium can be employed Another liquid metal used as a coolant is lead in e g lead cooled fast reactors or a lead bismuth alloy Some early fast neutron reactors used mercury For certain applications the stems of automotive poppet valves may be hollow and filled with sodium to improve heat transport and transfer For very high temperature applications e g molten salt reactors or very high temperature reactors molten salts can be used as coolants One of the possible combinations is the mix of sodium fluoride and sodium tetrafluoroborate NaF NaBF4 Other choices are FLiBe and FLiNaK Liquid gases Edit Liquified gases are used as coolants for cryogenic applications including cryo electron microscopy overclocking of computer processors applications using superconductors or extremely sensitive sensors and very low noise amplifiers Carbon Dioxide chemical formula is CO2 is used as a coolant replacement 5 for cutting fluids CO2 can provide controlled cooling at the cutting interface such that the cutting tool and the workpiece are held at ambient temperatures The use of CO2 greatly extends tool life and on most materials allows the operation to run faster This is considered a very environmentally friendly method especially when compared to the use of petroleum oils as lubricants parts remain clean and dry which often can eliminate secondary cleaning operations Liquid nitrogen which boils at about 196 C 77K is the most common and least expensive coolant in use Liquid air is used to a lesser extent due to its liquid oxygen content which makes it prone to cause fire or explosions when in contact with combustible materials see oxyliquits Lower temperatures can be reached using liquified neon which boils at about 246 C The lowest temperatures used for the most powerful superconducting magnets are reached using liquid helium Liquid hydrogen at 250 to 265 C can also be used as a coolant Liquid hydrogen is also used both as a fuel and as a coolant to cool nozzles and combustion chambers of rocket engines Nanofluids Edit A new class of coolants are nanofluids which consist of a carrier liquid such as water dispersed with tiny nano scale particles known as nanoparticles Purpose designed nanoparticles of e g CuO alumina 6 titanium dioxide carbon nanotubes silica or metals e g copper or silver nanorods dispersed into the carrier liquid enhance the heat transfer capabilities of the resulting coolant compared to the carrier liquid alone 7 The enhancement can be theoretically as high as 350 The experiments however did not prove so high thermal conductivity improvements but found significant increase of the critical heat flux of the coolants 8 Some significant improvements are achievable e g silver nanorods of 55 12 nm diameter and 12 8 µm average length at 0 5 vol increased the thermal conductivity of water by 68 and 0 5 vol of silver nanorods increased thermal conductivity of ethylene glycol based coolant by 98 9 Alumina nanoparticles at 0 1 can increase the critical heat flux of water by as much as 70 the particles form rough porous surface on the cooled object which encourages formation of new bubbles and their hydrophilic nature then helps pushing them away hindering the formation of the steam layer 10 Nanofluid with the concentration more than 5 acts like non Newtonian fluids Solids EditIn some applications solid materials are used as coolants The materials require high energy to vaporize this energy is then carried away by the vaporized gases This approach is common in spaceflight for ablative atmospheric reentry shields and for cooling of rocket engine nozzles The same approach is also used for fire protection of structures where ablative coating is applied Dry ice and water ice can be also used as coolants when in direct contact with the structure being cooled Sometimes an additional heat transfer fluid is used water with ice and dry ice in acetone are two popular pairings Sublimation of water ice was used for cooling the space suit for Project Apollo References Edit Betaine as coolant Archived 2011 04 09 at the Wayback Machine Duratherm Extended Life Fluids Paratherm Corporation Sturgess Steve August 2009 Column Keep Your Cool Heavy Duty Trucking Retrieved April 2 2018 ctemag com Noghrehabadi Bibliography Archived from the original on November 13 2013 Retrieved November 13 2013 Wang Xiang Qi Mujumdar Arun S December 2008 A review on nanofluids part II experiments and applications Brazilian Journal of Chemical Engineering 25 4 631 648 doi 10 1590 S0104 66322008000400002 scienceblog com Archived January 5 2010 at the Wayback Machine Oldenburg Steven J Siekkinen Andrew R Darlington Thomas K Baldwin Richard K 9 July 2007 Optimized Nanofluid Coolants for Spacecraft Thermal Control Systems SAE Technical Paper Series Vol 1 pp 2007 01 3128 doi 10 4271 2007 01 3128 mit eduExternal links Edit Look up coolant in Wiktionary the free dictionary CO2 as a natural coolant FAQs Retrieved from https en wikipedia org w index php title Coolant amp oldid 1133162000, wikipedia, wiki, book, books, library,

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