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From Wikipedia

Absorption refrigerator

An absorption refrigerator is a refrigerator that uses a heat source (e.g., solar, kerosene-fueled flame) to provide the energy needed to drive the cooling system. Absorption refrigerators are a popular alternative to regular compressor refrigerators 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). For example, absorption refrigerators powered by heat from the combustion of liquefied petroleum gas are often used for food storage in recreational vehicles.

Both absorption and compressor refrigerators use a refrigerant with a very low boiling point (less than 0|°F|°C|abbr=on|disp=/). 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. In comparison, a compressor refrigerator uses an electrically-powered compressor to increase the pressure on the gas, and then condenses the hot high pressure gas back to a liquid by heat exchange with a coolant (usually air). Once the high pressure gas has cooled, it passes through an expansion device which drops the refrigerant temperature to below freezing. The other difference between the two types is the refrigerant used. Compressor refrigerators typically use an HCFC or HFC, while absorption refrigerators typically use ammonia.

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

Principles

Absorptive refrigeration uses a source of heat to provide the energy needed to drive the cooling process. The most common use is in commercial climate control and cooling of machinery. Absorptive refrigeration is also used to air-condition buildings using the waste heat from a gas turbine or water heater. This use is very efficient, since the gas turbine produces electricity, hot water and air-conditioning (called Trigeneration).

The absorption cooling cycle can be described in three phases:

1)Evaporation: Low partial pressure of gaseous refrigerant causes the remaining liquid refrigerant to evaporate, thus extracting heat from its surroundings – the refrigerator

2)Absorption: Gaseous refrigerant is absorbed – reducing its partial pressure in the evaporator

3)Regeneration: The absorbent is heated to evaporate out the refrigerant which is then condensed 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 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, hydrogen gas, and water. 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 of the hydrogen is used to regulate the total pressure, which in turn regulates the vapour pressure and thus the boiling point 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 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 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, 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 in 1858. The original design used water and sulfuric acid.



From Encyclopedia

absorption

absorption [Lat.,=sucking from], taking of molecules of one substance directly into another substance. It is contrasted with adsorption , in which the molecules adhere only to the surface of the second substance. Absorption may be either a physical or a chemical process, physical absorption involving such factors as solubility and vapor-pressure relationships and chemical absorption involving chemical reactions between the absorbed substance and the absorbing medium.

Absorption

The process by which substances are taken into the tissues of organisms is called absorption. It is essential to functions such as digestion, circulation, and respiration. During digestion, valuable nutrients are absorbed across the epithelial lining of the digestive tract. Absorption occurs largely in the small intestine, which has developed a large surface area for this purpose. The walls of the small intestine contain numerous finger-like projections called villi, which are in turn covered by countless microvilli. Different nutrients are absorbed across the gut epithelium in different ways. The methods of absorption include active transport , facilitated diffusion , and passive diffusion . Active transport requires energy in the form of adenosine triphosphate (ATP ), as well as special carrier molecules that ferry nutrients, (their substrates), across the gut lining. Active transport is involved in the absorption of proteins, which have usually been processed into amino acids or other small peptides. Most ions are also absorbed through active transport, as are most carbohydrates. Some carbohydrates, however, are absorbed in a process known as facilitated diffusion. Facilitated diffusion describes a situation in which special carrier molecules are necessary, but energy (ATP) is not. Fructose is an example of a carbohydrate that is absorbed through facilitated diffusion. Other nutrients, such as lipids , are absorbed through passive diffusion. In passive diffusion, neither energy expenditure nor a special carrier molecule is required. Lipids interact with bile salts from the liver, combining with them to form structures known as micelles. Micelles are able to diffuse freely through cell membranes and so can pass directly across the gut lining. Water is another substance that diffuses passively across the gut walls. The circulatory system transfers nutrients and other products throughout the body. Tissues absorb the products they need from tiny blood vessels called capillaries. Capillaries are characterized by very high surface areas and very low blood-flow rates, both of which facilitate absorption. The walls of capillaries are also very thin, consisting of only one or a few layers of flattened endothelial cells. Capillaries also possess small pores through which transport and absorption can occur. The absorption of materials from the capillaries occurs in one of several ways. Lipid-soluble substances are able to diffuse directly across the cell membranes of capillary cells into the tissues. Water diffuses directly as well, although it makes use of special pores in the cell membranes of capillary cells. Exchange via diffusion is comparatively rapid. The absorption of other nutrients from the blood requires transportation through the capillary walls inside special vesicles. This process is called transcytosis. The vesicles are membrane-bound and are believed to be constructed by a cellular organelle known as the Golgi apparatus. Vesicles shuttle products repeatedly between the inner and outer walls of capillary cells. Because capillary beds in the brain are characterized by fewer transport vesicles, many substances cannot be absorbed into brain tissue, and the absorption of those that can be is slowed. This is often referred to as the blood-brain barrier. In the process of respiration, oxygen is absorbed by the integument , lungs , gills , or trachea from the air or water. As with the circulatory and digestive systems, large respiratory surface areas allow for efficient absorption. Oxygen is absorbed from the environment by the red blood cells, or erythrocytes . Erythrocytes contain respiratory pigments , which bind oxygen and works to transport it to tissues. These specialized oxygen-binding molecules are called pigments because they are often brightly colored when carrying bound oxygen. Respiratory pigments have a high affinity for oxygen and are also able to dramatically increase the oxygen-carrying capacity of blood. Hemoglobin is the respiratory pigment in vertebrate erythrocytes and is also common throughout the animal kingdom. Hemoglobin is a large molecule consisting of four polypeptide chains, each of which is capable of binding an oxygen molecule. The oxygen-binding part of the chain is called the heme group and includes an iron atom. Hemoglobin binds oxygen cooperatively, meaning that once it has bound a single oxygen molecule, it is more likely to bind additional oxygen molecules. Hemoglobin's oxygen affinity, or the degree to which oxygen binds to it, varies according to such external factors as pH. This plasticity (flexibility) of oxygen affinity allows hemoglobin simultaneously to bind oxygen in the oxygen-rich environment of the lungs and to release it in the oxygen-poor environments of the tissues. Another respiratory pigment, myoglobin, is present in the muscles and is responsible for pulling oxygen molecules from the blood into the tissues. Myoglobin resembles hemoglobin but consists of only a single polypeptide chain. see also Digestion; Transport. Jennifer Yeh Gould, James L., and William T. Keeton. Biological Science, 6th ed. New York: W. W. Norton, 1996. Withers, Philip C. Comparative Animal Physiology. Fort Worth, TX: Saunders College Publishing, 1992.


From Yahoo Answers

Question:difference between adsorption and absorption

Answers:Absorption is when something gets sucked in, like a sponge. Adsorption is when molecules go to the surface of something (surface tension).

Question:

Answers:Adsorption is a surface phenomenon, but absorption is not a boundary layer effect. In adsorption, molecules, gases and dissolved substances are adhered to the surface of a material. In absorption, the molecules, gases and dissolved substances enter the interior of the material.

Question:

Answers:absorption. molecules are "taken up" by a bulk phase adsorption...molecules are physically or chemically attached to a surface. examples. absorption.. CO2 being absorbed into water in a packed column adsorption.. N2 gas condensing on a surface during BET surface area measurement.

Question:and what is the main applications for each of them?? Thaaaaaaaaaaaaanks

Answers:Main Entry: ad sorp tion Pronunciation: ad-'sorp-sh&n, -'zorp- Function: noun Etymology: ad- + absorption : the adhesion in an extremely thin layer of molecules (as of gases, solutes, or liquids) to the surfaces of solid bodies or liquids with which they are in contact Main Entry: ab sorp tion Pronunciation: &b-'sorp-sh&n, -'zorp- Function: noun Etymology: French & Latin; French, from Latin absorption-, absorptio, from absorbEre a : the process of absorbing or of being absorbed -- compare ADSORPTION b : interception of radiant energy or sound waves I am not sure of their applications, but the definitions look pretty clear to me. Hope it helps.

From Youtube

Absorption And Adsorption :Check us out at www.tutorvista.com Adsorption is the adhesion of molecules of gas, liquid, or dissolved solids to a surface. This process creates a film of the adsorbate (the molecules or atoms being accumulated) on the surface of the adsorbent. It differs from absorption, in which a fluid permeates or is dissolved by a liquid or solid. The term sorption encompasses both processes, while desorption is the reverse of adsorption. Similar to surface tension, adsorption is a consequence of surface energy. In a bulk material, all the bonding requirements (be they ionic, covalent, or metallic) of the constituent atoms of the material are filled by other atoms in the material. However, atoms on the surface of the adsorbent are not wholly surrounded by other adsorbent atoms and therefore can attract adsorbates. The exact nature of the bonding depends on the details of the species involved, but the adsorption process is generally classified as physisorption (characteristic of weak van der Waals forces) or chemisorption (characteristic of covalent bonding). Adsorption is present in many natural physical, biological, and chemical systems, and is widely used in industrial applications such as activated charcoal, capturing and using waste heat to provide cold water for air conditioning and other process requirements (adsorption chillers), synthetic resins, increase storage capacity of carbide-derived carbons for tunable nanoporous carbon, and water purification. Adsorption, ion ...