An absorption refrigerator is a refrigerator that uses a heat source (for example, solar energy, a fossil fuel fire, a waste heat from a factory, or a district heating system) to provide the energy needed to drive the cooling process.
Absorption of refrigerators is often used for food storage in recreational vehicles. This principle can also be used to build air conditioning using waste heat from gas turbines or water heaters. Using waste heat from the gas turbine makes the turbine very efficient because it first generates electricity, then hot water, and finally, AC (called cogeneration/trigeneration).
The American National Standards Institute standard for absorption refrigerators is provided by ANSI/AHRI standard 560-2000.
Video Absorption refrigerator
History
In the early years of the twentieth century, the steam absorption cycle used the popular and widely used water-ammonia system, but after the development of the vapor compression cycle it lost much of its importance because its coefficient of performance was low (about one-fifth of that of the vapor-compression cycle). Currently, the steam absorption cycle is only used where heat waste is available or where heat comes from solar collectors. Absorption of refrigerators is a popular alternative to regular compressor refrigerators where electricity is unreliable, expensive, or unavailable, where noise from the compressor is problematic, or where excess heat is available (eg, from turbine exhaust or industrial process, or from solar power plant).
The cooling absorption was created by the French scientist Ferdinand Carrà ©  © in 1858. The original design uses water and sulfuric acid.
In 1922, Baltzar von Platen and Carl Munters, while they were still students at the Royal Institute of Technology in Stockholm, Sweden, upgraded the principle with a 3-fluid configuration. This "Platen-Munters" design can operate without a pump.
Commercial production began in 1923 by the newly formed company AB Arctic purchased by Electrolux in 1925. In the 1960s, absorption cooling saw a revival due to substantial demand for refrigerators for caravans (trailers travel). AB Electrolux established a subsidiary in the United States, named Dometic Sales Corporation. The company markets refrigerators for RVs under the Dometic brand. In 2001, Electrolux sold most of its spare products to the EQT venture capital company that created Dometic as a stand-alone company.
In 1926, Albert Einstein and his former student LeÃÆ'³ SzilÃÆ'¡rd proposed an alternative design known as the Einstein refrigerator.
At the 2007 TED Conference, Adam Grosser presented his research on the new and very small "intermittent absorption" vacuum cooling unit for use in third world countries. The refrigerator is a small unit placed over a campfire, which can then be used to cool 15 liters of water just above freezing for 24 hours in an environment of 30 ° C.
Maps Absorption refrigerator
Principles
Refrigerator absorption and compressors use very low boiling refrigerants (less than -18 ° C (0 ° F)). In both of these types, when this refrigerant evaporates (boils), it takes some heat with it, giving a cooling effect. The main difference between the two systems is the way the refrigerant is converted from the gas back into liquid so that the cycle can be repeated. The absorption refrigerator converts the gas back into liquid using a method that requires only heat, and has no moving parts other than the refrigerant itself.
The absorption absorption cycle can be explained in three phases:
- Evaporation : Liquid refrigerant evaporates in a low partial pressure environment, thus extracting heat from the surrounding (eg refrigerator compartment). Due to the low partial pressure, the temperature required for evaporation is also low.
- Absorption : The gas refrigerant is now absorbed by other liquids (eg salt solution).
- Regeneration : The heatsink-saturated liquid is heated, causing the refrigerant to evaporate outward. The hot gas refrigerant passes through the heat exchanger, transfers heat outside the system (such as to ambient air surrounding temperature), and condenses. The condensed refrigerant (liquid) supplies the evaporation phase.
For comparison, refrigerator compressors use a compressor, usually powered by an electric or electric combustion motor, to increase the pressure on the gas refrigerant. The resulting high pressure hot gas is condensed into a liquid form by cooling in a heat exchanger ("condenser") exposed to the external environment (usually indoor air). The condensed refrigerant, now at a temperature close to the external environment, then passes the orifice or throttle valve to the evaporator section. Orifice or throttle valves create pressure drops between high pressure condenser parts and low pressure evaporator parts. The lower pressure in the evaporator section allows the liquid refrigerant to evaporate, which absorbs heat from the refrigerator food compartment. The refrigerant is now evaporated and then returned to the compressor to repeat the cycle.
Another difference between the two types is the refrigerant used. Refrigerator compressors usually use HCFC or HFC, while absorption refrigerators usually use ammonia or water.
Simple salt and water system
Simple absorption refrigeration systems common to large commercial plants use lithium bromide and lithium chloride and water salts. The water under low pressure is evaporated from the cooled coil. Water is absorbed by lithium bromide/water solution. This system moves water from a solution of lithium bromide with heat.
Cooling water spray absorption
Another variant, pictured on the right, uses air, water, and brine. Warm intake, moist air is passed through a sprayed brine solution. The spray lowers the moisture but does not significantly change the temperature. Less humid and warm air is then passed through an evaporative cooler, which consists of fresh water spray, which cools and moisturizes the air. Humidity is removed from the air cooled by a spray of another salt solution, providing a cool and dry air outlet.
Salt solution is regenerated by heating it under low pressure, causing the water to evaporate. The water evaporated from the salt solution is condensed back, and flowed back to the evaporative coolant.
Single pressure absorber cooling
A single pressure absorption refrigerant takes advantage of the fact that the boiling point of a substance depends on the pressure of the partial vapor above the liquid and descends with a lower partial pressure. Despite having the same total pressure throughout the system, the refrigerator maintains a low partial pressure of the refrigerant (hence the low boiling point) in the part of the system that draws heat out of the refrigerator's low temperature interior, but maintains the refrigerant at high partial pressure (due to the point high boiling) in the system part that releases heat to ambient air outside the refrigerator.
The refrigerator uses three substances: ammonia, hydrogen gas, and water. The cycle is closed, with all hydrogen, water and ammonia collected and reused non-stop. The system is pressed down to the pressure at which the ammonia boiling point is higher than the temperature of the condenser coil (the coil that transfers heat into the air outside the refrigerator, becoming hotter than the outside air.) This pressure is usually 14-16 atm where the dew point of ammonia will to about 35 Ã, Â ° C (95Ã, Â ° F).
The cooling cycle begins with liquid ammonia at room temperature entering the evaporator. The evaporator volume is greater than the volume of liquid, with excess space occupied by ammonia and hydrogen gas mixtures. The presence of hydrogen lowers the partial pressure of the ammonia gas, thereby lowering the boiling point of the liquid below the refrigerator's interior temperature. Ammonia evaporates, taking a small amount of heat from the liquid and lowering the liquid temperature until it reaches its boiling point. Then continue to evaporate, no liquid falling below the boiling point, whereas the large enthalpy of evaporation (heat) flows from the refrigerator's warmer interior to cooler ammonia and then to more ammonia gas.
In the next two steps, the ammonia gas is separated from the hydrogen so it can be reused.
- The mixture of ammonia (gas) and hydrogen (gas) flows through the pipe from the evaporator to the absorber. In the absorber, this gas mixture is water contact (technically, a weak ammonia solution in water). Ammonia gas is soluble in water, whereas hydrogen, which does not, collects at the top of the absorber, leaving the ammonia-and-water solution now at the bottom. Hydrogen is now separated while ammonia is now dissolved in water.
- The next step separates ammonia and water. Ammonia/water solutions flow into the generator (boiler), where heat is applied to boil the ammonia, leaving most of the water (which has a higher boiling point) behind. Some moisture and bubbles remain mixed with ammonia; the water is removed at the last separation step, passing it through the separator, a series of rising bent pipes with small obstacles to blow bubbles, allowing moisture to condense and flow back to the generator.
The pure ammonia gas then enters the condenser. In this heat exchanger, hot ammonia gas transfers its heat to the outside air, which is below the boiling point of full pressure ammonia, and therefore condenses. Liquid (liquid) ammonia flows down to mix with the hydrogen gas released from the adsorption step, repeating the cycle.
See also
- Quantum absorption refrigerator
- RV Refrigerator
- Icyball
References
Further reading
-
Levy, A.; Kosloff, R. (2012). "Quantum Absorption Refrigerator". Phys. Pastor Lett . 108 : 070604. arXiv: 1109.0728 . Bibcode: 2012PhRvL.108g0604L. doi: 10.1103/PhysRevLett.108.070604.
External links
- Ingestion Heat Pump (Office of Energy Efficiency and Renewable Energy).
- Arizona Energy Explanation with diagram
- Analysis of Einstein's Cooling Cycle Design, Andrew Delano (1998). Retrieved 13 September 2005.
- Air Conditioning Thermodynamics, published by California EPA, Air Resources Board
- Lithium-Bromide/Water Cycle - Absorption Cooling for Campus Cooling at BYU.
Source of the article : Wikipedia
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