Absorption refrigerator

Absorption refrigerator

Overview
An absorption refrigerator is a refrigerator
Refrigerator
A refrigerator is a common household appliance that consists of a thermally insulated compartment and a heat pump that transfers heat from the inside of the fridge to its external environment so that the inside of the fridge is cooled to a temperature below the ambient temperature of the room...

 that uses a heat source (e.g., solar
Solar thermal energy
Solar thermal energy is a technology for harnessing solar energy for thermal energy . Solar thermal collectors are classified by the United States Energy Information Administration as low-, medium-, or high-temperature collectors. Low-temperature collectors are flat plates generally used to heat...

, kerosene-fueled flame, waste heat from factories or district heating systems) to provide the energy needed to drive the cooling system. Absorption refrigerators are a popular alternative to regular compressor refrigerators
Vapor-compression refrigeration
Vapor-compression refrigeration is one of the many refrigeration cycles available for use. It has been and is the most widely used method for air-conditioning of large public buildings, offices, private residences, hotels, hospitals, theaters, restaurants and automobiles...

 where electricity is unreliable, costly, or unavailable, where noise from the compressor is problematic, or where surplus heat is available (e.g., from turbine exhausts or industrial processes, or from solar plants).

For example, absorption refrigerators powered by heat from the combustion
Combustion
Combustion or burning is the sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat and conversion of chemical species. The release of heat can result in the production of light in the form of either glowing or a flame...

 of liquefied petroleum gas are often used for food storage in recreational vehicle
Recreational vehicle
Recreational vehicle or RV is, in North America, the usual term for a Motor vehicle or trailer equipped with living space and amenities found in a home.-Features:...

s.
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Encyclopedia
An absorption refrigerator is a refrigerator
Refrigerator
A refrigerator is a common household appliance that consists of a thermally insulated compartment and a heat pump that transfers heat from the inside of the fridge to its external environment so that the inside of the fridge is cooled to a temperature below the ambient temperature of the room...

 that uses a heat source (e.g., solar
Solar thermal energy
Solar thermal energy is a technology for harnessing solar energy for thermal energy . Solar thermal collectors are classified by the United States Energy Information Administration as low-, medium-, or high-temperature collectors. Low-temperature collectors are flat plates generally used to heat...

, kerosene-fueled flame, waste heat from factories or district heating systems) to provide the energy needed to drive the cooling system. Absorption refrigerators are a popular alternative to regular compressor refrigerators
Vapor-compression refrigeration
Vapor-compression refrigeration is one of the many refrigeration cycles available for use. It has been and is the most widely used method for air-conditioning of large public buildings, offices, private residences, hotels, hospitals, theaters, restaurants and automobiles...

 where electricity is unreliable, costly, or unavailable, where noise from the compressor is problematic, or where surplus heat is available (e.g., from turbine exhausts or industrial processes, or from solar plants).

For example, absorption refrigerators powered by heat from the combustion
Combustion
Combustion or burning is the sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat and conversion of chemical species. The release of heat can result in the production of light in the form of either glowing or a flame...

 of liquefied petroleum gas are often used for food storage in recreational vehicle
Recreational vehicle
Recreational vehicle or RV is, in North America, the usual term for a Motor vehicle or trailer equipped with living space and amenities found in a home.-Features:...

s. Absorptive refrigeration can also be used to air-condition
Air conditioning
An air conditioner is a home appliance, system, or mechanism designed to dehumidify and extract heat from an area. The cooling is done using a simple refrigeration cycle...

 buildings using the waste heat from a gas turbine
Gas turbine
A gas turbine, also called a combustion turbine, is a type of internal combustion engine. It has an upstream rotating compressor coupled to a downstream turbine, and a combustion chamber in-between....

 or water heater. This use is very efficient, since the gas turbine produces electricity
Electricity
Electricity is a general term encompassing a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena, such as lightning, static electricity, and the flow of electrical current in an electrical wire...

, hot water and air-conditioning (called trigeneration
Trigeneration
Trigeneration, also called CCHP , refers to the simultaneous generation of electricity, useful heating and useful cooling from the same original heat source such as fuel or solar energy...

).

Both absorption and compressor refrigerators use a refrigerant with a very low boiling point
Boiling point
The boiling point of an element or a substance is the temperature at which the vapor pressure of the liquid equals the environmental pressure surrounding the liquid....

 (less than 0 °F (-17.8 °C)). In both types, when this refrigerant evaporates (boils), it takes some heat away with it, providing the cooling effect. The main difference between the two types is the way the refrigerant is changed from a gas back into a liquid so that the cycle can repeat. An absorption refrigerator changes the gas back into a liquid using a different method that needs only heat, and has no moving parts. The other difference between the two types is the refrigerant used. Compressor refrigerators typically use an HCFC
Chlorofluorocarbon
A chlorofluorocarbon is an organic compound that contains carbon, chlorine, and fluorine, produced as a volatile derivative of methane and ethane. A common subclass are the hydrochlorofluorocarbons , which contain hydrogen, as well. They are also commonly known by the DuPont trade name Freon...

 or HFC, while absorption refrigerators typically use ammonia
Ammonia
Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...

 or water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

.

The standard for the absorption refrigerator is given by the ANSI/AHRI standard 560-2000.

Principles


Absorptive refrigeration uses a source of heat
Heat
In physics and thermodynamics, heat is energy transferred from one body, region, or thermodynamic system to another due to thermal contact or thermal radiation when the systems are at different temperatures. It is often described as one of the fundamental processes of energy transfer between...

 to provide the energy needed to drive the cooling process.
The absorption cooling cycle can be described in three phases:
  1. Evaporation: A liquid refrigerant evaporates in a low partial pressure
    Partial pressure
    In a mixture of ideal gases, each gas has a partial pressure which is the pressure which the gas would have if it alone occupied the volume. The total pressure of a gas mixture is the sum of the partial pressures of each individual gas in the mixture....

     environment, thus extracting heat from its surroundings – the refrigerator.
  2. Absorption: The gaseous refrigerant is absorbed – dissolved into another liquid - reducing its partial pressure in the evaporator and allowing more liquid to evaporate.
  3. Regeneration: The refrigerant-laden liquid is heated, causing the refrigerant to evaporate out. It is then condensed through a heat exchanger to replenish the supply of liquid refrigerant in the evaporator.

Simple salt and water system


A simple absorption refrigeration system common in large commercial plants uses a solution of lithium bromide
Lithium bromide
Lithium bromide, or LiBr, is a chemical compound of lithium and bromine. Its extreme hygroscopic character makes LiBr useful as a desiccant in certain air conditioning systems.-Production and properties:...

 salt and water. Water under low pressure is evaporated from the coils that are being chilled. The water is absorbed by a lithium bromide/water solution. The water is driven off the lithium bromide solution using heat.

Water spray absorption refrigeration



Another variant, depicted to the right, uses air, water, and a salt water solution. The intake of warm, moist air is passed through a sprayed solution of salt water. The spray lowers the humidity but does not significantly change the temperature. The less humid, warm air is then passed through an evaporative cooler, consisting of a spray of fresh water, which cools and re-humidifies the air. Humidity is removed from the cooled air with another spray of salt solution, providing the outlet of cool, dry air.

The salt solution is regenerated by heating it under low pressure, causing water to evaporate. The water evaporated from the salt solution is re-condensed, and rerouted back to the evaporative cooler.


Single pressure absorption refrigeration



A single-pressure absorption refrigerator uses three substances: ammonia
Ammonia
Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...

, hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

 gas, and water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

. At standard atmospheric conditions, ammonia is a gas with a boiling point of -33°C, but a single-pressure absorption refrigerator is pressurised to the point where the ammonia is a liquid. The cycle is closed, with all hydrogen, water and ammonia collected and endlessly reused.

The cooling cycle starts with liquefied ammonia entering the evaporator at room temperature. The ammonia is mixed in the evaporator with hydrogen. The partial pressure
Partial pressure
In a mixture of ideal gases, each gas has a partial pressure which is the pressure which the gas would have if it alone occupied the volume. The total pressure of a gas mixture is the sum of the partial pressures of each individual gas in the mixture....

 of the hydrogen is used to regulate the total pressure, which in turn regulates the vapour pressure and thus the boiling point
Boiling point
The boiling point of an element or a substance is the temperature at which the vapor pressure of the liquid equals the environmental pressure surrounding the liquid....

 of the ammonia. The ammonia boils in the evaporator, providing the cooling required.

The next three steps exist to separate the gaseous ammonia and the hydrogen. First, in the absorber, the mixture of gasses enters the bottom of an uphill series of tubes, into which water is added at the top. The ammonia dissolves in the water, producing a mixture of ammonia solution
Solution
In chemistry, a solution is a homogeneous mixture composed of only one phase. In such a mixture, a solute is dissolved in another substance, known as a solvent. The solvent does the dissolving.- Types of solutions :...

 and hydrogen. The hydrogen is collected at the top of the absorber, with the ammonia solution collected at the bottom.

The second step is to separate the ammonia and water. In the generator, heat is applied to the solution, to distill
Distillation
Distillation is a method of separating mixtures based on differences in volatilities of components in a boiling liquid mixture. Distillation is a unit operation, or a physical separation process, and not a chemical reaction....

 the ammonia from the water. Some water remains with the ammonia, in the form of vapour and bubbles. This is dried in the final separation step, called the separator, by passing it through an uphill series of twisted pipes with minor obstacles to pop the bubbles, allowing the collected water to drain back to the generator.

Finally the pure ammonia gas enters the condenser. In this heat exchanger
Heat exchanger
A heat exchanger is a piece of equipment built for efficient heat transfer from one medium to another. The media may be separated by a solid wall, so that they never mix, or they may be in direct contact...

, the hot ammonia gas is cooled to room temperature and hence condenses to a liquid, allowing the cycle to restart.

History


Absorption cooling was invented by the French scientist Ferdinand Carré
Ferdinand Carré
Ferdinand Philippe Edouard Carré was a French engineer, born at Moislains on 11 March 1824. Carré is best known as the inventor of refrigeration equipment used to produce ice...

 in 1858. The original design used water and sulfuric acid.

In 1922 Baltzar von Platen
Baltzar von Platen (1898-1984)
Baltzar von Platen , together with Carl Munters, was the inventor of the gas absorption refrigerator in 1922 while they were both Swedish engineering students at the Royal Institute of Technology in Stockholm, Sweden. The technique produced "cold" from a heat source such as propane, electricity, or...

 and Carl Munters
Carl Munters
Carl Georg Munters was a Swedish inventor, most known for inventing together with Baltzar von Platen the gas absorption refrigerator now sold by Electrolux...

, while they were still students at the Royal Institute of Technology
Royal Institute of Technology
The Royal Institute of Technology is a university in Stockholm, Sweden. KTH was founded in 1827 as Sweden's first polytechnic and is one of Scandinavia's largest institutions of higher education in technology. KTH accounts for one-third of Sweden’s technical research and engineering education...

 in Stockholm
Stockholm
Stockholm is the capital and the largest city of Sweden and constitutes the most populated urban area in Scandinavia. Stockholm is the most populous city in Sweden, with a population of 851,155 in the municipality , 1.37 million in the urban area , and around 2.1 million in the metropolitan area...

, Sweden
Sweden
Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....

, enhanced the principle with a 3 fluids configuration. This "Platen-Munters" design can operate without a pump.

Commercial production began in 1923 by the newly formed company AB Arctic, which was bought by Electrolux
Electrolux
The Electrolux Group is a Swedish appliance maker.As of 2010 the 2nd largest home appliance manufacturer in the world after Whirlpool, its products sell under a variety of brand names including its own and are primarily major appliances and vacuum cleaners...

 in 1925. In the 60s the absorption refrigeration saw a renaissance due to the substantial demand for refrigerators for caravan
Travel trailer
A travel trailer or caravan is towed behind a road vehicle to provide a place to sleep which is more comfortable and protected than a tent . It provides the means for people to have their own home on a journey or a vacation, without relying on a motel or hotel, and enables them to stay in places...

s. AB Electrolux established a subsidiary in the U.S, named Dometic Sales Corporation. The company marketed refrigerators for caravans under the Dometic brand. In 2001 Electrolux sold most of its Leisure Products line to the venture-capital company EQT which created Dometic
Dometic
Dometic is a product brand by Dometic Group. Dometic was established as a brand in the US in 1968 by Electrolux Leisure Appliances, by that time a part of the Electrolux Group...

 as stand alone company.

In 1926 Albert Einstein
Albert Einstein
Albert Einstein was a German-born theoretical physicist who developed the theory of general relativity, effecting a revolution in physics. For this achievement, Einstein is often regarded as the father of modern physics and one of the most prolific intellects in human history...

 and his former student Leó Szilárd
Leó Szilárd
Leó Szilárd was an Austro-Hungarian physicist and inventor who conceived the nuclear chain reaction in 1933, patented the idea of a nuclear reactor with Enrico Fermi, and in late 1939 wrote the letter for Albert Einstein's signature that resulted in the Manhattan Project that built the atomic bomb...

 proposed an alternative design known as Einstein refrigerator
Einstein refrigerator
The Einstein-Szilard or Einstein refrigerator is an absorption refrigerator which has no moving parts, operates at constant pressure, and requires only a heat source to operate...

.

At the 2007 TED Conference, Adam Grosser presented his research of a new, very small, "intermittent absorption" vaccine refrigeration unit for use in third world countries. The refrigerator is a small unit placed over a campfire, that can later be used to cool 3 gallons of water to just above freezing for 24 hours in a 30 degree Celsius environment.

See also

  • Absorption heat pump
    Absorption heat pump
    Absorption heat pump is essentially an air-source heat pump driven not by electricity, but by a heat source such as solar-heated water, or geothermal-heated water...

  • Einstein refrigerator
    Einstein refrigerator
    The Einstein-Szilard or Einstein refrigerator is an absorption refrigerator which has no moving parts, operates at constant pressure, and requires only a heat source to operate...

  • Icyball
  • Solar thermal cooling
  • Timeline of low-temperature technology
    Timeline of low-temperature technology
    The following is a timeline of low-temperature technology and cryogenic technology .-16th century BCE – 17th century CE :...


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