Contenido

El agua es el refrigerante más común dada su alta capacidad calorífica y su bajo costo. Por lo general, se usa con aditivos, como inhibidores de corrosión y anticongelantes (generalmente etilenglicol, dietilenglicol o propilenglicol). Un anticongelante se usa cuando el refrigerante a base de agua tiene que soportar temperaturas por debajo de 0 °C (32 °F; 273 K), o cuando se deba elevar su punto de ebullición. La betaína es un refrigerante similar, con la excepción de que está hecho de jugo de plantas puro, que no es tóxico ni difícil de desechar ecológicamente.

El polialquilenglicol (PAG) se utiliza como fluidos de transferencia de calor térmicamente estables y de alta temperatura que exhiben una fuerte resistencia a la oxidación. Los PAG modernos también pueden ser no tóxicos y no peligrosos.[1]​.

El fluido de corte es un refrigerante que también sirve como lubricante para máquinas herramienta de conformado de metales.

Los aceites se utilizan a menudo para aplicaciones en las que el agua no es adecuada. Con puntos de ebullición más altos que el agua, los aceites pueden elevarse a temperaturas considerablemente más altas por encima de los 100 °C (212 °F; 373 K), sin introducir altas presiones dentro del recipiente o sistema de circuito en cuestión.[2]​ Muchos aceites tienen usos que abarcan transferencia de calor, lubricación, transferencia de presión (fluidos hidráulicos), a veces incluso combustible, o varias funciones similares a la vez.

Los combustibles se utilizan con frecuencia como refrigerantes para motores. Un combustible frío fluye sobre algunas partes del motor, absorbiendo su calor residual y precalentándose antes de la combustión. El queroseno y otros combustibles para aviones cumplen con frecuencia esta función en los motores de aviación. El hidrógeno líquido se utiliza para enfriar las toberas de los motores de cohetes.

El refrigerante sin agua se utiliza como alternativa a los refrigerantes convencionales de agua y etilenglicol. Con puntos de ebullición más altos que el agua de alrededor de 370 °C (698 °F; 643 K), la tecnología de enfriamiento resiste la ebullición. El líquido también previene la corrosión.[3]​.

Los freones se usaban con frecuencia para la refrigeración por inmersión.

Salts and molten metals

Liquid fusion alloys can be used as coolants in applications where high temperature stability is required, for example 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 used. Another liquid metal used as a coolant is lead, for example in fast reactors cooled by lead or a lead-bismuth alloy. Some of the first fast neutron reactors used mercury ("Mercury (element)").

For certain applications, automotive poppet valve stems may be hollow and filled with sodium to improve heat transport and transfer.

For very high temperature applications, for example molten salt reactors or very high temperature reactors, molten salts can be used as coolants. One of the possible combinations is the mixture of sodium fluoride and sodium tetrafluoroborate (NaF-NaBF). Other options are FLiBe and FLiNaK.

liquid gases

Liquefied 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.

CO: used as a coolant replacement[4]​ for cutting fluids. CO can provide controlled cooling at the cutting interface, so that the cutting tool and workpiece are kept at room temperature. Using CO greatly extends tool life and, in most materials, allows the operation to run faster. It is considered an environmentally friendly method and at the same time keeps the pieces clean and dry, reducing secondary cleaning operations.

Liquid nitrogen: The most common and least expensive refrigerant in use, it boils at −196 °C (−321 °F; 77 K). Liquid air is used to a lesser extent due to its liquid oxygen content which makes it prone to causing fires or explosions when it comes into contact with combustible materials.

Liquefied Neon: Lower temperatures can be achieved using boiling at approximately −246 °C (−411 °F; 27 K). The lowest temperatures used by superconducting magnets are achieved using liquid helium.

Liquid hydrogen −250 to −265 °C (−418 to −445 °F) (23 to 8 K) can also be used as a refrigerant. Liquid hydrogen is also used as fuel and as a coolant to cool the nozzles and combustion chambers of rocket engines.

Nanofluids

A new class of coolants are nanofluids that consist of a carrier liquid, such as water, dispersed with small nanometer-scale particles known as nanoparticles. Specially designed nanoparticles of, for example, CuO "Copper(II) Oxide"), alumina,[5]​ titanium dioxide "Titanium(IV) Oxide"), carbon nanotubes, silica "Silicon(IV) Oxide") or metals (e.g., copper or silver nanorods) dispersed in the carrier liquid improve the heat transfer capabilities of the resulting coolant compared to the carrier liquid alone.[6]​ The improvement can theoretically be as high like 350%. However, the experiments did not demonstrate such high improvements in thermal conductivity, but found a significant increase in the critical heat flux of the coolants.

Some significant improvements can be achieved; for example, silver nanorods of 55±12 nm in diameter and 12.8 µm in average length at 0.5 vol%. increased the thermal conductivity of water by 68% and 0.5% vol. of silver nanorods increased the thermal conductivity of the ethylene glycol-based coolant by 98%.[7]​ 0.1% alumina nanoparticles can increase the critical heat flux of water by up to 70%; The particles form a rough porous surface on the cooled object, which encourages the formation of new bubbles, and their hydrophilic nature helps to push them away, making it difficult for the vapor layer to form.[8]​ Nanofluid with a concentration greater than 5% acts as non-Newtonian fluids.

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

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

Sublimation of water ice was used to cool the Apollo Project spacesuit.

Some refrigerants are used in both liquid and gaseous forms in the same circuit, taking advantage of the high specific latent heat of the boiling/condensation phase change, the enthalpy of vaporization, as well as the non-phase change heat capacity of the fluid.

Refrigerant refrigerants are refrigerant liquids that are used to reach low temperatures by undergoing a phase change between liquid and gas. Halomethanes were frequently used, most commonly R-12 and R-22, often with liquefied propane or other haloalkanes such as R-134a. Anhydrous ammonia is frequently used in large commercial systems and sulfur oxide was used in early mechanical refrigerators. CO (R-744) is used as a working fluid in automotive climate control systems, residential air conditioning, commercial refrigeration, and vending machines. Many refrigerants are phased out for environmental reasons (CFCs due to ozone layer effects, many of their successors now face restrictions due to global warming, for example R134a).

Heat pipes are a special application of refrigerants.

Water is sometimes used in this way, for example in boiling water reactors. The phase shift effect can be used intentionally or it can be detrimental.

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

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

Contenido

El agua es el refrigerante más común dada su alta capacidad calorífica y su bajo costo. Por lo general, se usa con aditivos, como inhibidores de corrosión y anticongelantes (generalmente etilenglicol, dietilenglicol o propilenglicol). Un anticongelante se usa cuando el refrigerante a base de agua tiene que soportar temperaturas por debajo de 0 °C (32 °F; 273 K), o cuando se deba elevar su punto de ebullición. La betaína es un refrigerante similar, con la excepción de que está hecho de jugo de plantas puro, que no es tóxico ni difícil de desechar ecológicamente.

El polialquilenglicol (PAG) se utiliza como fluidos de transferencia de calor térmicamente estables y de alta temperatura que exhiben una fuerte resistencia a la oxidación. Los PAG modernos también pueden ser no tóxicos y no peligrosos.[1]​.

El fluido de corte es un refrigerante que también sirve como lubricante para máquinas herramienta de conformado de metales.

Los aceites se utilizan a menudo para aplicaciones en las que el agua no es adecuada. Con puntos de ebullición más altos que el agua, los aceites pueden elevarse a temperaturas considerablemente más altas por encima de los 100 °C (212 °F; 373 K), sin introducir altas presiones dentro del recipiente o sistema de circuito en cuestión.[2]​ Muchos aceites tienen usos que abarcan transferencia de calor, lubricación, transferencia de presión (fluidos hidráulicos), a veces incluso combustible, o varias funciones similares a la vez.

Los combustibles se utilizan con frecuencia como refrigerantes para motores. Un combustible frío fluye sobre algunas partes del motor, absorbiendo su calor residual y precalentándose antes de la combustión. El queroseno y otros combustibles para aviones cumplen con frecuencia esta función en los motores de aviación. El hidrógeno líquido se utiliza para enfriar las toberas de los motores de cohetes.

El refrigerante sin agua se utiliza como alternativa a los refrigerantes convencionales de agua y etilenglicol. Con puntos de ebullición más altos que el agua de alrededor de 370 °C (698 °F; 643 K), la tecnología de enfriamiento resiste la ebullición. El líquido también previene la corrosión.[3]​.

Los freones se usaban con frecuencia para la refrigeración por inmersión.

Salts and molten metals

Liquid fusion alloys can be used as coolants in applications where high temperature stability is required, for example 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 used. Another liquid metal used as a coolant is lead, for example in fast reactors cooled by lead or a lead-bismuth alloy. Some of the first fast neutron reactors used mercury ("Mercury (element)").

For certain applications, automotive poppet valve stems may be hollow and filled with sodium to improve heat transport and transfer.

For very high temperature applications, for example molten salt reactors or very high temperature reactors, molten salts can be used as coolants. One of the possible combinations is the mixture of sodium fluoride and sodium tetrafluoroborate (NaF-NaBF). Other options are FLiBe and FLiNaK.

liquid gases

Liquefied 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.

CO: used as a coolant replacement[4]​ for cutting fluids. CO can provide controlled cooling at the cutting interface, so that the cutting tool and workpiece are kept at room temperature. Using CO greatly extends tool life and, in most materials, allows the operation to run faster. It is considered an environmentally friendly method and at the same time keeps the pieces clean and dry, reducing secondary cleaning operations.

Liquid nitrogen: The most common and least expensive refrigerant in use, it boils at −196 °C (−321 °F; 77 K). Liquid air is used to a lesser extent due to its liquid oxygen content which makes it prone to causing fires or explosions when it comes into contact with combustible materials.

Liquefied Neon: Lower temperatures can be achieved using boiling at approximately −246 °C (−411 °F; 27 K). The lowest temperatures used by superconducting magnets are achieved using liquid helium.

Liquid hydrogen −250 to −265 °C (−418 to −445 °F) (23 to 8 K) can also be used as a refrigerant. Liquid hydrogen is also used as fuel and as a coolant to cool the nozzles and combustion chambers of rocket engines.

Nanofluids

A new class of coolants are nanofluids that consist of a carrier liquid, such as water, dispersed with small nanometer-scale particles known as nanoparticles. Specially designed nanoparticles of, for example, CuO "Copper(II) Oxide"), alumina,[5]​ titanium dioxide "Titanium(IV) Oxide"), carbon nanotubes, silica "Silicon(IV) Oxide") or metals (e.g., copper or silver nanorods) dispersed in the carrier liquid improve the heat transfer capabilities of the resulting coolant compared to the carrier liquid alone.[6]​ The improvement can theoretically be as high like 350%. However, the experiments did not demonstrate such high improvements in thermal conductivity, but found a significant increase in the critical heat flux of the coolants.

Some significant improvements can be achieved; for example, silver nanorods of 55±12 nm in diameter and 12.8 µm in average length at 0.5 vol%. increased the thermal conductivity of water by 68% and 0.5% vol. of silver nanorods increased the thermal conductivity of the ethylene glycol-based coolant by 98%.[7]​ 0.1% alumina nanoparticles can increase the critical heat flux of water by up to 70%; The particles form a rough porous surface on the cooled object, which encourages the formation of new bubbles, and their hydrophilic nature helps to push them away, making it difficult for the vapor layer to form.[8]​ Nanofluid with a concentration greater than 5% acts as non-Newtonian fluids.

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

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

Sublimation of water ice was used to cool the Apollo Project spacesuit.