Un refrigerante es un producto químico líquido o gaseoso, fácilmente licuable, que es utilizado como medio transmisor de calor entre otros dos en una máquina térmica. Los principales usos son los refrigeradores y los acondicionadores de aire.
El principio de funcionamiento de algunos sistemas de refrigeración se basa en un ciclo de refrigeración por compresión, que tiene algunas similitudes con el ciclo de Carnoty utiliza refrigerantes como fluido de trabajo.
Contenido[ocultar] |
[editar]Historia
Cuando comenzaron las preocupaciones por la capa de ozono, los refrigerantes más usados eran los clorofluorocarbonos R-12 y R22. El primero era empleado principalmente para aire acondicionado de vehículos y para pequeños refrigeradores; el segundo para aire acondicionado, refrigeradores, y congeladores comerciales, residenciales y ligeros. Algunos de los primeros sistemas emplearon el R-11 por su bajo punto de ebullición, lo que permitía construir sistemas de baja presión.
La producción de R-12 cesó en Estados Unidos en 1995, y el R-22 fue eliminado posteriormente [2010]. Se está empleando el R-134a y ciertas mezclas (que no atentan contra la capa de ozono) en remplazo de los compuestos clorados. El R410a (comúnmente llamada por su nombre comercial Puron®) es una popular mezcla 50/50 de R-32 y R-125 que comienza a sustituir al R-22.
[editar]Características de los refrigerantes
- Punto de congelación. Debe de ser inferior a cualquier temperatura que existe en el sistema,para evitar congelamientos en el evaporador.
- Calor específico. Debe de ser lo más alto posible para que una pequeña cantidad de líquido absorba una gran cantidad de calor.
- Volumen específico.- El volumen específico debe de ser lo más bajo posible para evitar grandes tamaños en las líneas de aspiración y compresión
- Densidad. Deben de ser elevadas para usar líneas de líquidos pequeñas.
- La temperatura de condensación, a la presión máxima de trabajo debe ser la menor posible.
- La temperatura de ebullición, relativamente baja a presiones cercanas a la atmosférica.
- Punto crítico lo más elevado posible.
- No [deben*] ser líquidos inflamables, corrosivos ni tóxicos.
- Dado que deben interaccionar con el lubricante del compresor, deben ser miscibles en fase líquida y no nocivos con el aceite.
- Los refrigerantes, se aprovechan en muchos sistemas para refrigerar también el motor del compresor, normalmente un motor eléctrico, por lo que deben ser buenos dieléctricos, es decir, tener una bajaconductividad eléctrica.
[*Existen distintos refrigerantes, ver Tipos mas abajo.]
[editar]Tipos
[editar]Por su composición química
- Los inorgánicos, como el agua o el NH3: Amoníaco
- Los de origen orgánico(hidrocarburos y derivados):
- Los CFC's, Clorofluorocarbonos, perjudiciales para la capa de ozono
- Los HCFC's.Hidrocloroflurocarbonados
- Los HFC's.
- Los HC: Hidrocarburos (alcanos y alquenos)
- Las mezclas, azeotrópicas o no azeotrópicas.
[editar]Por su grado de seguridad
- GRUPO 1: no son combustibles ni tóxicos.
- GRUPO 2: tóxicos, corrosivos o explosivos a concetraciones mayores de 3,5% en volumen mezclados con el aire.
- GRUPO 3: tóxicos, corrosivos o explosivos a concetraciones menores o iguales a 3,5% en volumen.
[editar]Por sus presiones de trabajo
- Baja:
- Media:
- Alta:
- Muy alta:
[editar]Por su función
- Primario: si es el agente transmisor en el sistema frigorífico, y por lo tanto realiza un intercambio térmico principalmente en forma de calor latente.
- Secundario: realiza un papel de intercambio térmico intermedio entre el refrigerante primario y el medio exterior. Realiza el intercambio principalmente en forma de calor sensible.
- Pueden ser perjudiciales para la capa de ozono: Índice ODP y ayudar al efecto invernadero: Índice GWP
[editar]Refrigerantes comúnmente usados
- El agua.
- El amoníaco o R717.
- El Glicol
- R11.
- R12.
- R22.
- R23.
- R32.
- R123.
- R124.
- R134a.
- R502.
- R407C.
- R410A.
- R507.
- R517.
A refrigerant is a liquid or gaseous chemical, easily liquefiable, which is used as heat transfer medium between two other in a heat engine. The main uses are as refrigerators and air conditioners.The principle of operation of some refrigeration systems is based on a compression refrigeration cycle, which has some similarities with the refrigerant cycle Carnoty used as working fluid.Contents [hide]1 History2 Characteristics of refrigerants3 Types3.1 By their chemical composition3.2 For their security3.3 For their work pressures3.4 In its role4 commonly used refrigerants5 See also[Edit]
When concerns began the ozone layer, the most widely used refrigerants were chlorofluorocarbons R-12 and R22. The first was used mainly for vehicle air conditioning and small refrigerators, the second for air conditioners, refrigerators, and freezers, commercial, residential and light. Some early systems used R-11 for its low boiling point, allowing low pressure systems build.The production of R-12 in United States ceased in 1995, and R-22 was subsequently removed [2010]. You are using the R-134a and certain blends (not threaten the ozone layer) in replacement of chlorinated compounds. The R410a (commonly known by its trade name Puron ®) is a popular 50/50 mixture of R-32 and R-125 begins to replace R-22.[Edit] Characteristics of refrigerants
Freezing. Must be below any temperature that exists in the system to avoid freezing in the evaporator.Specific heat. Should be as high as possible so that a small amount of fluid absorbed a large amount of heat.Specific volume. - The specific volume should be as low as possible to avoid large sizes in the suction lines and compressionDensity. Must be elevated to use small fluid lines.The condensation temperature at the maximum working pressure should be as small as possible.The boiling temperature, relatively low pressures close to atmospheric.Critical point as high as possible.Not [must *] be flammable, corrosive or toxic.Since they must interact with the lubricant of the compressor must be miscible in the liquid phase and not deleterious to the oil.Refrigerants, is utilized in many systems to cool also the compressor motor, usually an electric motor, so that should be good dielectric, ie, having an electric bajaconductividad.[* There are different refrigerants, see Types below.][Edit] Types
[Edit] On the chemical compositionInorganics, such as water or NH3: AmmoniaThe organic origin (hydrocarbons and derivatives):CFCs, chlorofluorocarbons, harmful to the ozone layerHCFC's. HidrocloroflurocarbonadosThe HFC's.HC: hydrocarbons (alkanes and alkenes)Mixtures, azeotropic or azeotrope no.[Edit] On the level of safetyGROUP 1: non-combustible or toxic.GROUP 2: toxic, corrosive or explosive concetraciones greater than 3.5% by volume mixed with air.GROUP 3: toxic, corrosive or explosive concetraciones less than or equal to 3.5% by volume.[Edit] For his work pressuresLow:Media:Added:Very high:[Edit] By functionPrimary: if the transmitting agent in the refrigeration system, and therefore performs a heat exchange mainly in the form of latent heat.Secondary: performs a role of intermediate heat exchange between the coolant and the external environment. Make the exchange mainly in the form of sensible heat.- Can be harmful to the ozone layer: ODP index and help the greenhouse effect: GWP index[Edit] Commonly used Refrigerants
Water.Ammonia or R717.The glycolR11.R12.R22.R23.R32.R123.R124.R134a.R502.R407C.R410A.R507.R517.
When concerns began the ozone layer, the most widely used refrigerants were chlorofluorocarbons R-12 and R22. The first was used mainly for vehicle air conditioning and small refrigerators, the second for air conditioners, refrigerators, and freezers, commercial, residential and light. Some early systems used R-11 for its low boiling point, allowing low pressure systems build.The production of R-12 in United States ceased in 1995, and R-22 was subsequently removed [2010]. You are using the R-134a and certain blends (not threaten the ozone layer) in replacement of chlorinated compounds. The R410a (commonly known by its trade name Puron ®) is a popular 50/50 mixture of R-32 and R-125 begins to replace R-22.[Edit] Characteristics of refrigerants
Freezing. Must be below any temperature that exists in the system to avoid freezing in the evaporator.Specific heat. Should be as high as possible so that a small amount of fluid absorbed a large amount of heat.Specific volume. - The specific volume should be as low as possible to avoid large sizes in the suction lines and compressionDensity. Must be elevated to use small fluid lines.The condensation temperature at the maximum working pressure should be as small as possible.The boiling temperature, relatively low pressures close to atmospheric.Critical point as high as possible.Not [must *] be flammable, corrosive or toxic.Since they must interact with the lubricant of the compressor must be miscible in the liquid phase and not deleterious to the oil.Refrigerants, is utilized in many systems to cool also the compressor motor, usually an electric motor, so that should be good dielectric, ie, having an electric bajaconductividad.[* There are different refrigerants, see Types below.][Edit] Types
[Edit] On the chemical compositionInorganics, such as water or NH3: AmmoniaThe organic origin (hydrocarbons and derivatives):CFCs, chlorofluorocarbons, harmful to the ozone layerHCFC's. HidrocloroflurocarbonadosThe HFC's.HC: hydrocarbons (alkanes and alkenes)Mixtures, azeotropic or azeotrope no.[Edit] On the level of safetyGROUP 1: non-combustible or toxic.GROUP 2: toxic, corrosive or explosive concetraciones greater than 3.5% by volume mixed with air.GROUP 3: toxic, corrosive or explosive concetraciones less than or equal to 3.5% by volume.[Edit] For his work pressuresLow:Media:Added:Very high:[Edit] By functionPrimary: if the transmitting agent in the refrigeration system, and therefore performs a heat exchange mainly in the form of latent heat.Secondary: performs a role of intermediate heat exchange between the coolant and the external environment. Make the exchange mainly in the form of sensible heat.- Can be harmful to the ozone layer: ODP index and help the greenhouse effect: GWP index[Edit] Commonly used Refrigerants
Water.Ammonia or R717.The glycolR11.R12.R22.R23.R32.R123.R124.R134a.R502.R407C.R410A.R507.R517.
No hay comentarios:
Publicar un comentario