The most commonly used refrigeration system is the vapor compression cycle evaporative system. Here a circulating refrigerant such as Freon enters the compressor as a vapor, is compressed, condensed and transfers out heat, is run through an orifice where the pressure drops and expands into a gas and draws heat from its surroundings. Then the cycle repeats. Many different mediums have been used as the refrigerant including water. See the history timeline at the bottom of this page.
1) Compression: The vapors of refrigerant enter the compressor and are compressed to high pressure and high temperature. During this process the entropy (temperature*pressure) of the refrigerant ideally remains constant and it leaves in superheated state.
2) Condensation: The superheated refrigerant then enters the condenser where it is cooled either by air or water due to which its temperature reduces, but pressure remains constant and it gets converted into liquid state.
3) Expansion: The liquid refrigerant then enters the expansion valve or throttling valve where sudden expansion of the refrigerant occurs, due to which its temperature and pressure falls down. The refrigerant leaves expansion valve in partially liquid state and partially in gaseous state.
4) Evaporation or cooling: The partially liquid and partially gaseous refrigerant at very low temperature enters the evaporator where the substance to be cooled is kept. It is here where the refrigeration effect is produced. The refrigerant absorbs the heat from the substance to be cooled and gets converted into vapor state.
The most common compressors used in chillers are reciprocating, rotary screw, centrifugal, and scroll compressors. Some of the refrigerants that have been used in a compression vapor system are ethyl ether, ammonia, carbon dioxide, alcohols, dimethyl ether, sulphur dioxide, sio-butane, water, chlorofluorocarbons, hydrochlorofluorocarbons and hydrochlorofluorocarbons.
With an Air Cycle Machine (ACM) a gas is used as the working fluid. No condensation or evaporation of a liquid is involved. In aircraft the cooled air output from the process is sometimes used directly for cabin ventilation or for cooling electronic equipment. The air cycle machine is common on gas turbine-powered jet aircraft because compressed air is readily available from the engines' compressor sections. These jet aircraft's cooling and ventilation units also serve the purpose of pressurizing the aircraft. This is also called the Bell Coleman cycle.
The basic principle of the gas cycle is that, the temperature of a gas decreases when:
1. it expands adiabatically (without external heat transfer) and
2. does external work. The heat equivalent of the mechanical work performed on the piston (or turbine wheel) is abstracted from the air
In 1842 John Gorrie invented the first gas cycle or air cycle machine. In 1862 Alexander Kirk designed one that was steam driven. Bell and Coleman in 1875 invented the open type machine that still used in aircraft now. In 1881 J & E Hall Company, of Dartford, England was [[http://www.machine-history.com/Air%20Refrigerating%20Machine%201881|building air compression refrigerators for ships]] involved in the Australian meat trade.
Refrigerators that use heat usually by burning fuel to operate are based on the cycle invented in the 1920s by two Swedish students, Carl Munters and Balizar von Platen at the Royal Institute of Technology in Stockholm. The system they invented utilizes the fact that ammonia (NIL) is very soluble in cold water but much less soluble in hot water, while hydrogen is hardly soluble in either and balances the pressure throughout the system. After ammonia is dis¬solved in cold water, a portion of this water is heated to produce ammonia under high pressure and elevated temperature. This high-pressure ammonia is cooled off by normal room temperatures outside the refrigerator. The resulting cooled high-pressure ammonia is then expanded through a nozzle in a tubular assembly inside the refrigerator, and the temperature of the ammonia drops as it expands rapidly from a high to a low pressure. It is this cold, low-pressure ammonia that then absorbs heat, keeping the inside of the refrigerator cold. The low-pressure ammonia then dissolves into water once more, and the cycle starts over again, the hydrogen keeping the system pressure balanced. This cycle operates steadily in moving heat from the inside to the outside of the refrigerator.
The absorption cycle is similar to the compression cycle, except for the method of raising the pressure of the refrigerant vapor and that the refrigerant stage changing is helped through absorption and rejection with another secondary chemical. In the absorption system, the compressor is replaced by an absorber which dissolves the refrigerant in a suitable liquid, a liquid pump (or just gravity) which raises the pressure and a generator which, on heat addition, drives off the refrigerant vapor from the high-pressure liquid. Some work may be required by the liquid pump in some systems but, for a given quantity of refrigerant, it is much smaller than needed by the compressor in the vapor compression cycle. In an absorption refrigerator, a suitable combination of refrigerant and absorbent is used. The most common combinations are ammonia (refrigerant) and water (absorbent), and water (refrigerant) and lithium bromide (absorbent).
With lithium bromide absorption system the refrigerant used is actually water, as that is the working medium that experiences a phase change that causes the cooling affect. The second fluid that drives the process is a salt, generally lithium bromide. Heat is used to separate the two fluids; when they are brought back together in a near vacuum environment, the water experiences a phase change to remix with the salt at a very low temperature (at normal atmosphere pressure, water vaporizes at 212F; in an absorber, water vaporizes cold enough to produce 46F chilled water) .
Refrigerants used in absorption systems have included
• water and Sulfuric acid (H2SO4)
• ammonia and water
• ammonia, butane and water
• water and lithium bromide salt
• Fluorocarbons and organic compounds (like DMAC) or (NMP)
An evaporative cooler (called a swamp cooler, desert cooler or wet air cooler) Air washers and wet cooling towers use the same principles as evaporative coolers and may be used in conjunction with other mechanical refrigeration systems. For example, an evaporative cooler may be designed to cool coils of a large air conditioning vapor-compression system to increase its efficiency. Evaporative cooling is especially well suited for climates where the air is hot and humidity is low.
The steam-jet cycle uses water as the refrigerant. High-velocity steam jets provide a high vacuum in the evaporator, causing the water to boil at low temperature and at the same time compressing the flashed vapor up to the condenser pressure level. Its use is limited to air conditioning and other applications for temperatures above 32°F (0°C)(water freezing damage).
An ejector was invented by Sir Charles Parsons around 1901 for removing air from steam engine condensers. In about 1910, the ejector was used by Maurice Leblanc in the steam ejector refrigeration system. It experienced a wave of popularity during the early 1930s for air conditioning large buildings. Steam ejector refrigeration cycles were later supplanted by systems using mechanical compressors.
Steam jet refrigeration systems use steam ejectors to reduce the pressure in a tank containing the return water from a chilled water system. The steam jet ejector utilizes the energy of a fast-moving jet of steam to capture the flash tank vapor and compress it. Flashing a portion of the water in the tank reduces the liquid temperature. Figure 3.66 presents a schematic arrangement of a steam jet refrigeration system for water cooling. In the system shown, high-pressure steam expands while flowing through the nozzle 1. The expansion causes a drop in pressure and an enormous increase in velocity. Due to the high velocity, flash vapor from the tank 2 is drawn into the swiftly moving steam and the mixture enters the diffuser 3. The velocity is gradually reduced in the diffuser but the pressure of the steam at the condenser 4 is increased 5-10 times more than that at the entrance of the diffuser (e.g. from 0.01 bar to 0.07 bar).
This pressure value corresponds to the condensing temperature of 40°C. This means that the mixture of high-pressure steam and the flash vapor may be liquefied in the condenser. The latent heat of condensation is transferred to the condenser water, which may be at 25 °C. The condensate 5 is pumped back to the boiler, from which it may again be vaporized at a high pressure. The evaporation of a relatively small amount of water in the flash tank (or flash cooler) reduces the temperature of the main body of water. The cooled water is then pumped as the refrigeration carrier to the cooling-load heat exchanger.
Also called: solid-state refrigeration, thermoelectric cooling effect, electrocaloric effect
Jean Charles Athanase Peltier, discovered thermoelectric cooling effect, also known as Peltier cooling effect, in 1834. Peltier discovered that the passage of a current through a junction formed by two dissimilar conductors caused a temperature change. However, Peltier failed to understand this physics phenomenon, and his explanation was that the weak current doesn’t obey Ohm’s law. Peltier effect was made clear in 1838 by Emil Lenz, a member of the St. Petersburg Academy. Lenz demonstrated that water could be frozen when placed on a bismuth-antimony junction by passage of an electric current through the junction. He also observed that if the current was reversed the ice could be melted.
In 1909 and 1911 another scientist Altenkirch derived the basic theory of thermoelectrics. His
work pointed out that thermoelectric cooling materials needed to have high Seebeck coefficients,
good electrical conductivity to minimize Joule heating, and low thermal conductivity to reduce
heat transfer from junctions to junctions. Shortly after the development of practical
semiconductors in 1950’s, bismuth telluride began to be the primary material used in the thermoelectric cooling.
Thermoelectric cooler (TEC), or Peltier Cooler is a solid-state heat pump that uses the Peltier
effect to move heat. The modern commercial TEC consists of a number of p- and n- type
semiconductor couples connected electrically in series and thermally in parallel. These couples
are sandwiched between two thermally conductive and electrically insulated substrates. The heat
pumping direction can be altered by altering the polarity of the charging DC current.
The electrocaloric effect (ECE) in dielectric materials has great potential in realizing solid-state cooling devices with compact size and high efficiency, which are highly desirable for a broad range of applications. The electrocaloric effect is the change in the entropy and temperature in a dielectric material induced by an applied voltage. Dr. Q. M. Zhang observed that certain polymer dielectrics exhibit giant ECE. The results of these experiments were published in Science magazine in August 2008. Since that time, research teams have made further development to the ECE materials that exhibit giant ECE at room temperature.
Solid state cooling systems use a thermoelectric device, consisting of a semiconductor based bi-metal junction, a heat sink, and DC power. A typical solid state cooling system is a semiconductor–based component, soldered between two ceramic plates, with a sandwich-type structure filled with bismuth telluride particles and doped to obtain N-P junctions. When current is passed through the junction of the two different conductors, a temperature change is achieved. There are no moving parts and no refrigerants.
Common uses for thermoelectric coolers are, cooling electronic components, small instruments, biological tests, experiments and spacecraft.
The Free-Piston Stirling Cooler (FPSC) has a high energy efficiency and uses earth friendly cooling substances. It has long life through the use of non-contact running surfaces, high efficiency over a wide temperature range, is light weight and uses environmentally safe helium as the working fluid. Free-piston Stirling cryocoolers are available commercially and are employed in wireless, pharmaceutical, sensor, bio-preservation and medical applications. Such machines are currently flying in space and are slated for further space missions in the future. The FPSC makes use of the stirling cycle and a moving magnet linear motor for cooling applications. The stirling cycle belongs to a class of thermodynamic cycles that yield the highest conversion efficiency between mechanical and thermal energy. The stirling cycle is a reversible cycle which means that heat can be put into the machine and electric power will be produced or as with the FPSC, electric power can be put in and heat will be removed.
Thermoacoustic (TA) uses high-amplitude sound waves in a mixture of harmless gases to create oscillations in pressure, temperature and displacement, which are used to pump heat. Although the temperature oscillations are small, research has shown that this "thermoacoustic" effect can be harnessed to produce efficient heat engines. Thus, these engines with no moving parts have the potential to be both simple and reliable. A thermoacoustic unit is comprised of a regenerator, consisting of a stack of fine-mesh window screening material, much like a sieve; two heat exchangers; and a loudspeaker to supply acoustic energy. The loudspeaker is modified to generate extremely highly amplified sound in a contained environment of helium, an environmentally sound inert gas that is converted into cooling energy. The sound wave levels are so high, around 170 decibels, they can barely be heard by humans; this level is many times louder than an average rock concert. These sound levels can only be attained in an atmosphere of contained, pressurized gas.
Thermoacoustics has been relatively obscure within the commercial engineering community, due to its initial specialized use in space for military applications. Recent interest in thermoacoustics as an alternative heat transfer process underpins the timing of investing and developing this technology to replace applications relying on environmentally hazardous refrigeration gases.
[[http://www.machine-history.com/Vortex%20Tube|The Vortex Tube]] is a mechanical device that separates a compressed gas into hot and cold streams. It has no moving parts.
Pressurized gas is injected tangentially into a swirl chamber and accelerates to a high rate of rotation. Due to the conical nozzle at the end of the tube, only the outer shell of the compressed gas is allowed to escape at that end. The remainder of the gas is forced to return in an inner vortex of reduced diameter within the outer vortex. The Ranque effect was discovered in 1931 by George Ranque. They are commonly used when compressed air is available for spot cooling and for miners or workers in hot environments who need fresh air and have available compressed air anyhow.
Magnetic Refrigeration relies on the magnetocaloric effect (MCE) using materials called magnetocalorics.
Cycles of MCE Refrigeration
1. heats up when exposed to a powerful magnetic field
2. cooled off by radiating this heat away, heat exchanger
3. turn cold when the magnetic field is removed, dramatically, to near absolute zero.
4. another heat exchanger removes heat from the refrigerator.
The structure of crystals (microstructure) in different metals directly affects how dramatically they heat up and cool down when a magnetic field is applied and removed. Two different temperature change processes simultaneously occur at the molecular level, known as first order and second order changes. Until now, magnetocalorics haven’t been very useful to the refrigeration technology because the materials they were made of were the prohibitively expensive and rare, metal gadolinium and a deadly substance, arsenic. National Institute of Standards and Technology (NIST)’s Center for Neutron Research (NCNR) researchers discovered a metallic alloy made of manganese, iron, phosphorus and germanium, which works as a near-room-temperature magnetocaloric.
Karl Gschneidner of Ames Laboratory has claimed “ Magnetic cooling and refrigeration is 20 to 30 percent more energy efficient than conventional vapor-compression refrigeration.”
Thermoelastic Cooling (TC) is where a “thermally elastic” smart metal alloy, when strained or stretched results in a solid phase change of the material. This phase change is accompanied by a nearly reversible temperature rise in the material. The material in its strained state rejects heat to its surroundings. When said material is relaxed from its strained state, a solid phase change occurs back to its initial phase. This phase change is accompanied by a nearly reversible temperature drop, in the material. In the relaxed state said material absorbs heat from a low temperature source.
The thermoelestic effect refers to a phenomenon where when a solid is heated or cooled a volume change occurs. Conversely, if a solid’s volume is changed (by straining it) a temperature change occurs.
Some devices patented include stretching of metals to produce heat which is removed through some heat transfer method and release and contraction of the metal to produce cold metal and heat transfer to utilize the heat removal capacity.
Passive cooling is mechanically done in many ways. Using evaporation trickling water in buildings down screen walls exposed to the prevailing breeze. Forming a pool of water on the roof then a movable insulating cover over the pool is added. For summer, the pool is covered in the day-time to avoid solar heating and to allow the water to absorb heat from the room below. At night, the uncovered pool loses heat by evaporation to prepare it for the next day. Some other ways include high thermal mass cooling by pumping water from a cold body of water, or pipes buried deep in the earth drawing transferred cooler air or by pumping a liquid through the underground pipes .
During the ice house days a Ton of Refrigeration was defined as the energy removal rate that will freeze one short ton of water at 0 °C (32 °F) in one day. One ton is approximately 11,958 BTU/hr. British thermal unit (BTU or Btu)(now rounded to 12,000). A BTU is a unit of energy equal to the amount of energy needed to heat 1 pound (0.454 kg) of water 1 °F. One ton of refrigeration is also equivalent to 3.5 kWH. The Coefficient of Performance (COP) is an important measurement of how well a machine cools. The COP is the ratio of the heat removed from the cold reservoir to input work. For example a refrigeration machine with a COP of 3 removes 3 units of heat for each unit of energy consumed. So 1 KWH of electrical energy will remove 3 KWH of heat.
The Roman’s used a solar power air conditioner. The Romans, used a natural structure for air conditioning or ventilation. They would dig a 100–200 yards trench that went in a straight line away from the house. A pipe and chimney were fitted in and over the trench so that the heated air in the chimney(black) would rise, drawing air through the cool pipe. The pipe, which was underground, cooled the air to the temperature of the earth. This cool air was allowed to circulate through the house to keep the temperature lower than outside.
1755: Scottish professor William Cullen made the first refrigerating machine, which could produce a small quantity of ice in the laboratory.
1758: Benjamin Franklin and John Hadley, a chemistry professor at Cambridge University, conducted an experiment to explore the principle of evaporation as a means to rapidly cool an object.
1780: U.F. Clouet and G. Monge liquefied SO2 and learned the process of condensation requires heat rejection
1805: Oliver Evans described a closed refrigeration cycle to produce ice by ether under vacuum.
1806: Frederic Tudor, (“ice king”) began the trade in ice by cutting it from the Hudson River and ponds of Massachusetts and exporting it to various countries including India. In India Tudor’s ice was cheaper than the locally manufactured ice by nocturnal radiational cooling.
1810: John Leslie demonstrates the principle of absorption refrigeration that concentrated sulfuric acid, which absorbs water, could accelerate the evaporation of water in a dish to such a degree as to freeze the remaining water.
1820: British scientist and inventor Michael Faraday discovered that compressing and liquefying ammonia could chill air when the liquefied ammonia was allowed to evaporate.
1835: Jakob Perkins patented the closed evaporative cycle using ethyl ether.
1838: Emil Lenz uses thermoelectric refrigeration to freeze a drop of water using the Peltier effect (voltage creates a temperature difference).
1842: Florida physician John Gorrie used compressor technology and gas cycle refrigeration to create ice, which he used to cool air for his patients in his hospital in Apalachicola, Florida. He was granted the first U.S. patent for mechanical refrigeration in 1851.
1850: Alexander Twining patented evaporative cycle using ether, ammonia and carbon dioxide.
1856: James Harrison patented systems using ether, alcohols or ammonia. This maybe the first successful, practical system.
1858: Ferdinand Carré improved absorption refrigeration using ammonia as the evaporating fluid and water as the absorbing fluid.
1864: Charles Tellier of France patented an evaporative cycle using dimethyl ether.
1870: S. Liebmann’s Sons Brewing Company in Brooklyn, New York was one of the first companies equipped with a refrigerating machine (absorption). By 1891 nearly every brewery was equipped with mechanical refrigeration.
1881: [[http://www.machine-history.com/Air%20Refrigerating%20Machine%201881|J & E Hall Company, of Dartford, England built air compression refrigerators for ships involved in the Australian meat trade.]]
1891: Eastman Kodak installed the first air conditioning system in Rochester, New York for the storage of photographic films.
1902: The first modern electric motored air conditioning unit was invented by Willis Haviland Carrier.
1907: The Vapor Jet (steam jet) by Maurice Leblanc utilized the energy of a fast-moving jet of steam to capture the flash tank vapor and compress it.
1911: General Electric began selling the first domestic refrigeration machine.
1922: Absorption cycle refrigeration without need for a pump was invented by two Swedish students, Carl Munters and Balizar von Platen at the Royal Institute of Technology in Stockholm. The machine they invented utilizes the fact that ammonia (NIL) is very soluble in cold water but much less soluble in hot water, while hydrogen is hardly soluble in either and balances the pressure throughout the system.
1926: General Electric Company introduced the first refrigerator with a hermetic compressor.
1930: Frigidaire’s Thomas Midgley, made the world's first chlorofluorocarbon (Freon) refrigeration machine which solved the problem of toxic, flammable refrigerants.
1931: George Ranque discovers the Ranque effect or Vortex Tube.
1939: First automobile air conditioning offered as an option in a Packard.
1955: 80% of American homes now have refrigerators
1987: The Montreal Protocol findings say that chlorofluorocarbons damage the Earth's protective ozone layer.
1993: R 11, R12, R22 chlorofluorocarbons (CFCs) used in vapor compression systems began to be phased towards newer hydrochlorofluorocarbons (HCFCs) refrigerants like R134A (developed in 1936), R-410A and R-407C.
2020: Hydrofluorocarbons (HFCs) are to replace Hydrochlorofluorocarbons(HCFCs).