Roots-type supercharger
The Roots type blower is a positive displacement lobe pump which operates by pumping a fluid with a pair of meshing lobes not unlike a set of stretched gears. Fluid is carried from the intake side to the exhaust; the most common application of the Roots type blower has been as the induction device on two-stroke Diesel engines, such as those produced by Detroit Diesel and Electro-Motive Diesel. Roots type blowers are used to supercharge Otto cycle engines, with the blower being driven from the engine's crankshaft via a toothed or V-belt, a roller chain or a gear train; the Roots type blower is named after the American inventors and brothers Philander and Francis Marion Roots, founders of the Roots Blower Company of Connersville, Indiana USA, who patented the basic design in 1860 as an air pump for use in blast furnaces and other industrial applications. In 1900, Gottlieb Daimler included a Roots-style blower in a patented engine design, making the Roots-type blower the oldest of the various designs now available.
Roots blowers are referred to as air blowers or PD blowers, can be called "huffers" when used with the gasoline-burning engines in hot rod customized cars. The Roots-type blower is simple and used, it can be more effective than alternative superchargers at developing positive intake manifold pressure at low engine speeds, making it a popular choice for passenger automobile applications. Peak torque can be achieved by about 2000 rpm. Unlike the basic illustration, most modern Roots-type superchargers incorporate three-lobe or four-lobe rotors. Accumulated heat is an important consideration in the operation of a compressor in an internal combustion engine. Of the three basic supercharger types, the Roots design possessed the worst thermal efficiency at high pressure ratios. In accordance with the ideal gas law, a compression operation will raise the temperature of the compressed output. Additionally, the operation of the compressor itself requires energy input, converted to heat and can be transferred to the gas through the compressor housing, heating it more.
Although intercoolers are more known for their use on turbochargers, superchargers may benefit from the use of an intercooler. Internal combustion is based upon a thermodynamic cycle, a cooler temperature of the intake charge results in a greater thermodynamic expansion and vice versa. A hot intake charge provokes detonation in a petrol engine, can melt the pistons in a diesel, while an intercooling stage adds complexity but can improve the power output by increasing the amount of the input charge as if the engine were of higher capacity. An intercooler reduces the thermodynamic efficiency by losing the heat introduced by compression, but increases the power available because of the increased working mass for each cycle. Above about 5 psi the intercooling improvement can become dramatic. With a Roots-type supercharger, one method employed is the addition of a thin heat exchanger placed between the blower and the engine. Water is circulated through it to a second unit placed near the front of the vehicle where a fan and the ambient air-stream can dissipate the collected heat.
The Roots design was used on two-stroke diesel engines, which require some form of forced induction, as there is no separate intake stroke. The Rootes Co. two-stroke diesel engine, used in Commer and Karrier vehicles, had a Roots-type blower. The superchargers used on top fuel engines, funny cars, other dragsters, as well as hot rods, are in fact derivatives of General Motors Coach Division blowers for their industrial diesel engines, which were adapted for automotive use in drag racing; the model name of these units delineates their size. Current competition dragsters use aftermarket GMC variants similar in design to the 71 series, but with the rotor and case length increased for added pumping capacity. Roots blowers are used in applications where a large volume of air must be moved across a small pressure differential; this includes low vacuum applications, with the Roots blower acting alone, or in combination with other pumps as part of a high vacuum system. One common industrial application is in pneumatic conveying systems, the blower delivering a high volume of air for the movement of bulk solids through pipes.
Some civil defense sirens used. The most well known are the Federal Signal Thunderbolt Series, ACA Hurricane; these sirens are known as "supercharged sirens". Roots blowers are used in reverse to measure the flow of gases or liquids, for example, in gas meters; the simplest form of a Roots blower has cycloidal rotors, constructed of alternating tangential sections of hypocycloidal and epicycloidal curves. For a two-lobed rotor, the smaller generating circles are one-quarter the diameter of the larger. Real Roots blowers may have more complex profiles for increased efficiency; the lobes on one rotor will not drive the other rotor with minimal free play in all positions, so that a separate pair of gears provide the phasing of the lobes. Because rotary lobe pumps need to
Jackhammer
A jackhammer is a pneumatic or electro-mechanical tool that combines a hammer directly with a chisel. It was invented by William Mcreavy, who sold the patent to Charles Brady King. Hand-held jackhammers are powered by compressed air, but some are powered by electric motors. Larger jackhammers, such as rig mounted hammers used on construction machinery, are hydraulically powered, they are used to break up rock and concrete. A jackhammer operates by driving an internal hammer down; the hammer is first driven down to strike the back and back up to return the hammer to the original position to repeat the cycle. The effectiveness of the jackhammer is dependent on, it is used like a hammer to break the hard surface or rock in construction works and it is not considered under earth moving equipment, along with its accessories. In British English, electromechanical versions are colloquially known as "Kangos"; the first steam-powered drill was patented by Samuel Miller in 1806. This drill used steam only for raising the drill.
Pneumatic drills were developed in response to the needs of mining, quarrying and tunneling. A pneumatic drill was proposed by a C. Brunton in 1844. In 1846 a percussion drill that could be worked by steam or atmospheric pressure obtained from a vacuum was patented in Britain by Thomas Clarke, Mark Freeman and John Varley; the first American "percussion drill" was made in 1848 and patented in 1849 by Jonathan J. Couch of Philadelphia, Pennsylvania. In this drill, the drill bit passed through the piston of a steam engine; the piston hurled it against the rock face. It was an experimental model. In 1849, Couch's assistant, Joseph W. Fowle, filed a patent caveat for a percussion drill of his own design. In Fowle’s drill, the drill bit was connected directly to the piston in the steam cylinder; the drill had a mechanism for turning the drill bit around its axis between strokes and for advancing the drill as the hole deepened. By 1850 or 1851, Fowle was using compressed air to drive his drill, making it the first true pneumatic drill.
The demand for pneumatic drills was driven by miners and tunnelers, because steam engines needed fires to operate and the ventilation in mines and tunnels was inadequate to vent the fires' fumes. By contrast, compressed air could be conveyed over long distances without loss of its energy, after the compressed air had been used to power equipment, it could ventilate a mine or tunnel. In Europe since the late 1840s, the king of Sardinia, Carlo Alberto, had been contemplating the excavation of a 12-kilometer tunnel through Mount Fréjus to create a rail link between Italy and France, which would cross his realm; the need for a mechanical rock drill was obvious and this sparked research on pneumatic rock drills in Europe. A Frenchman, Cavé, in 1851 patented, a rock drill that used compressed air. In 1854, in England, Thomas Bartlett made and patented a rock drill whose drill bit was connected directly to the piston of a steam engine. In 1855 Bartlett demonstrated his drill, powered by compressed air, to officials of the Mount Fréjus tunnel project.
Bartlett’s drill was refined by the Savoy-born engineer Germain Sommeiller and his colleagues and Grattoni, by 1861. Thereafter, many inventors refined the pneumatic drill. Sommeiller took his drill to the lengthy Gotthard Pass Tunnel being built to link railways between Switzerland and Italy under the Alps. Atlas Copco and Ingersoll Rand were two important drill companies in Europe and America each holding patents and dominating the industry. From this mining and railway tunnelling expanded; the word "jackhammer" is used in North American English and Australia, while "pneumatic drill" is used colloquially elsewhere in the English speaking world, although speaking a "pneumatic drill" refers to a pneumatically driven jackhammer. In Britain, electromechanical versions are colloquially known as "Kangos"; the term comes from the former British brand name now owned by Milwaukee tools. A full-sized portable jackhammer is impractical for use against walls and steep slopes, except by a strong person, as the user would have to both support the weight of the tool, push the tool back against the work after each blow.
A technique developed by experienced workers is a two-man team to overcome this obstacle of gravity: one operates the hammer and the second assists by holding the hammer either on his shoulders or cradled in his arms. Both use their combined weight to push the bit into the workface; this method is referred to as horizontal jackhammering. Another method is overhead jackhammering, requiring strength conditioning and endurance to hold a smaller jackhammer, called a rivet buster, over one's head. To make overhead work safer a platform can be used. One such platform is a P. A. M.. This unit takes all vibration from the user. A pneumatic jackhammer known as a pneumatic drill or pneumatic hammer, is a jackhammer that uses compressed air as the power source; the air supply comes from a portable air compressor driven by a diesel engine. R
Pump
A pump is a device that moves fluids, or sometimes slurries, by mechanical action. Pumps can be classified into three major groups according to the method they use to move the fluid: direct lift and gravity pumps. Pumps operate by some mechanism, consume energy to perform mechanical work moving the fluid. Pumps operate via many energy sources, including manual operation, engines, or wind power, come in many sizes, from microscopic for use in medical applications to large industrial pumps. Mechanical pumps serve in a wide range of applications such as pumping water from wells, aquarium filtering, pond filtering and aeration, in the car industry for water-cooling and fuel injection, in the energy industry for pumping oil and natural gas or for operating cooling towers. In the medical industry, pumps are used for biochemical processes in developing and manufacturing medicine, as artificial replacements for body parts, in particular the artificial heart and penile prosthesis; when a casing contains only one revolving impeller, it is called a single-stage pump.
When a casing contains two or more revolving impellers, it is called a double- or multi-stage pump. In biology, many different types of chemical and biomechanical pumps have evolved. Mechanical pumps may be placed external to the fluid. Pumps can be classified by their method of displacement into positive displacement pumps, impulse pumps, velocity pumps, gravity pumps, steam pumps and valveless pumps. There are two basic types of pumps: centrifugal. Although axial-flow pumps are classified as a separate type, they have the same operating principles as centrifugal pumps. A positive displacement pump makes a fluid move by trapping a fixed amount and forcing that trapped volume into the discharge pipe; some positive displacement pumps use an expanding cavity on the suction side and a decreasing cavity on the discharge side. Liquid flows into the pump as the cavity on the suction side expands and the liquid flows out of the discharge as the cavity collapses; the volume is constant through each cycle of operation.
Positive displacement pumps, unlike centrifugal or roto-dynamic pumps, theoretically can produce the same flow at a given speed no matter what the discharge pressure. Thus, positive displacement pumps are constant flow machines. However, a slight increase in internal leakage as the pressure increases prevents a constant flow rate. A positive displacement pump must not operate against a closed valve on the discharge side of the pump, because it has no shutoff head like centrifugal pumps. A positive displacement pump operating against a closed discharge valve continues to produce flow and the pressure in the discharge line increases until the line bursts, the pump is damaged, or both. A relief or safety valve on the discharge side of the positive displacement pump is therefore necessary; the relief valve can be external. The pump manufacturer has the option to supply internal relief or safety valves; the internal valve is used only as a safety precaution. An external relief valve in the discharge line, with a return line back to the suction line or supply tank provides increased safety.
A positive displacement pump can be further classified according to the mechanism used to move the fluid: Rotary-type positive displacement: internal gear, shuttle block, flexible vane or sliding vane, circumferential piston, flexible impeller, helical twisted roots or liquid-ring pumps Reciprocating-type positive displacement: piston pumps, plunger pumps or diaphragm pumps Linear-type positive displacement: rope pumps and chain pumps These pumps move fluid using a rotating mechanism that creates a vacuum that captures and draws in the liquid. Advantages: Rotary pumps are efficient because they can handle viscous fluids with higher flow rates as viscosity increases. Drawbacks: The nature of the pump requires close clearances between the rotating pump and the outer edge, making it rotate at a slow, steady speed. If rotary pumps are operated at high speeds, the fluids cause erosion, which causes enlarged clearances that liquid can pass through, which reduces efficiency. Rotary positive displacement pumps fall into three main types: Gear pumps – a simple type of rotary pump where the liquid is pushed between two gears Screw pumps – the shape of the internals of this pump is two screws turning against each other to pump the liquid Rotary vane pumps – similar to scroll compressors, these have a cylindrical rotor encased in a shaped housing.
As the rotor orbits, the vanes trap fluid between the rotor and the casing, drawing the fluid through the pump. Reciprocating pumps move the fluid using one or more oscillating pistons, plungers, or membranes, while valves restrict fluid motion to the desired direction. In order for suction to take place, the pump must first pull the plunger in an outward motion to decrease pressure in the chamber. Once the plunger pushes back, it will increase the pressure chamber and the inward pressure of the plunger will open the discharge valve and release the fluid into the delivery pipe at a high velocity. Pumps in this category range from simplex, with one cylinder, to in some cases quad cylinders, or more. Many reciprocating-type pumps are triplex cylinder, they can be either single-acting with suction during one direction of piston motion and discharge on the other, or double-acting with suction and discharge in both directions. The pumps can be powered manually, by air or steam
Shock mount
In a variety of applications, a shock mount or isolation mount is a mechanical fastener that connects two parts elastically. They are used for vibration isolation. Isolation mounts allow a piece of equipment to be securely mounted to a foundation and/or frame and, at the same time, allow it to float independently from the substrate. Shock mounts can be used to isolate the foundation or substrate from the dynamics of the mounted equipment; this is vital on submarines. Another common example of this are the motor and transmission mounts that are used in every automobile manufactured today. Without isolation mounts, the interior noise and comfort level in today’s vehicles would be different than what we have grown accustomed to. In this case and vibration isolation mounts are chosen by the nature of the dynamics produced by the equipment and the weight of the equipment. Shock mounts can be used to isolate sensitive equipment from undesirable dynamics of the foundation or substrate. Sensitive laboratory equipment needs to be isolated from handling shocks and ambient vibration.
Military equipment and ships need to be able to withstand nearby explosions. Shock mounts are found in some disc drives and compact disc players, in which soft bushings are all that mechanically hold the disk and reading assembly, thereby isolating it from outside vibrations and from other outside loads such as torsion. In this case, isolation mounts are chosen by the sensitivity of the equipment to shock and vibration and the weight of the equipment; this and nature of the input shock and vibration must be matched. A shock pulse is characterised by its peak acceleration, the duration, the shape of the shock pulse; the Shock response spectrum is a method for further evaluating a mechanical shock. Maxwell and Kelvin–Voigt models of viscoelasticity use springs and dashpots in series and parallel circuits respectively. Hydraulic and pneumatic components can be included, depending on the use. One common type of isolation mounts is laminated pads; these pads consist of a cork or polymeric foam core, laminated between two pieces of ribbed neoprene sheet.
Molded rubber isolation mounts are manufactured for specific applications. The best example of this is automotive transmission mounts. Rubber bushings compress synthetic rubber rings on bolts to provide some isolation:operating temperature is sometimes a factor. Other shock mounts have mechanical springs or an elastomer engineered to isolate an item from specified mechanical shock and vibration; some form of dashpot is used with a spring to provide viscous damping. Viscoelastic materials are common. Temperature is a factor in the dynamic response of rubber. A molded rubber mount is best suited for heavy loads producing higher frequency vibrations. Cable mounts are based around a coil of wire rope fixed to an lower mounting bar; when properly matched to the load, these mounts provide isolation over a broad frequency range. They are applied to high performance applications, such as mounting sensitive instrumentation into off-road vehicles and shipboard. Coil spring isolation mounts provide the greatest degree of movement and the best low frequency performance.
They are popular for mounting equipment in buildings such as air handlers, filtration units, air conditioning and refrigeration systems and large pipes. Their degree of movement makes them ideal for applications where high flexure and/or expansion and contraction are a consideration. Shock mounts for microphones can provide basic protection from damage, but their prime use is to isolate microphones from mechanically transmitted noise; this can originate as floor vibrations transmitted through a floor stand, or as "finger" and other handling noise on boom poles. All microphones behave to some extent as accelerometers, with the most sensitive axis being perpendicular to the diaphragm. Additionally, some microphones contain internal elements such as vacuum tubes and transformers which can be inherently microphonic; these are cushioned by resilient internal methods, in addition to the employment of external isolation mounts. Traditionally the large side-address studio microphone has been strung in a "cat's cradle" mount, using fabric-wound rubber elastic elements to provide isolation.
These designs still find some favour, although the elements tend to deteriorate, sag with time. Newer designs, such as Rycote's "USM" lyre, use plastic elastomers, patented spring shapes to reduce this problem. For end-fire microphones, most employed for location work, similar elastic stringing was once used. More designs moved to o-ring elements, before the Rycote Lyre and Cinela Osix suspensions were introduced; these use spring element designs that give far greater displacement along the microphone's prime axis, while limiting it on the other two. This enables excellent isolation while retaining good control of the microphone. Shock mounts can be found in a wide variety of applications. A similar idea known as a shock mount, is found in furniture design, introduced by Charles and Ray Eames; this serves as a living hinge, allowing the seat back to pivot. Shock mounts are used in bicycle seats. Bushing Vibration isolation Shock absorber MIL-S-901 Microphonism Cushioning DeSilva, C. W. "Vibration and Shock Handbook", CRC, 2005, ISBN 0-8493-1580-8 Harris, C. M. and Peirsol, A. G. "Shock and Vibration Handbook", 2001, McGraw Hill, ISBN 0-07-137081-1 Shock and vibration testing of shock mounts
Rigger (industry)
A rigger is a person who specializes in the lifting and moving of large or heavy objects with the assistance of a crane or derrick or chain hoists. The term comes from the days of sailing ships, when a rigger was a person who worked with rigging, that is, ropes for hoisting the sails. Sailors could put their rope skills to work in hauling. In an era before mechanical haulage and cranes, ropes and muscle power were all, available to move heavy objects. A specialized subset are entertainment industry riggers. In time, rigging became a trade in itself, giving rise to modern usages with some original terminology remaining, with its roots all but forgotten. Riggers attach loads of equipment to cranes or structures using shackles, chains, clamps or straps, employing pulleys, lifts or chain hoists. Quick load calculations are necessary for each load and engineering principles are always in play. Riggers use various suspension techniques to get their load around obstacles on a construction site or loading dock or event site to the desired location and height.
World's Toughest Fixes, an American reality-TV series with a focus on industrial rigging Specialized Carriers and Riggers Association What is a Rigger? - Rigger.com, by Toolwell Subpart CC – Cranes and Derricks in Construction: Qualified Rigger - OSHA - 2010
Compressor
A compressor is a mechanical device that increases the pressure of a gas by reducing its volume. An air compressor is a specific type of gas compressor. Compressors are similar to pumps: both increase the pressure on a fluid and both can transport the fluid through a pipe; as gases are compressible, the compressor reduces the volume of a gas. Liquids are incompressible; the main and important types of gas compressors are illustrated and discussed below: A positive displacement compressor is a system which compresses the air by the displacement of a mechanical linkage reducing the volume. Reciprocating compressors use pistons driven by a crankshaft, they can be either stationary or portable, can be single or multi-staged, can be driven by electric motors or internal combustion engines. Small reciprocating compressors from 5 to 30 horsepower are seen in automotive applications and are for intermittent duty. Larger reciprocating compressors well over 1,000 hp are found in large industrial and petroleum applications.
Discharge pressures can range from low pressure to high pressure. In certain applications, such as air compression, multi-stage double-acting compressors are said to be the most efficient compressors available, are larger, more costly than comparable rotary units. Another type of reciprocating compressor employed in automotive cabin air conditioning systems, is the swash plate or wobble plate compressor, which uses pistons moved by a swash plate mounted on a shaft. Household, home workshop, smaller job site compressors are reciprocating compressors 1½ hp or less with an attached receiver tank. A linear compressor is a reciprocating compressor with the piston being the rotor of a linear motor. An ionic liquid piston compressor, ionic compressor or ionic liquid piston pump is a hydrogen compressor based on an ionic liquid piston instead of a metal piston as in a piston-metal diaphragm compressor. Rotary screw compressors use two meshed rotating positive-displacement helical screws to force the gas into a smaller space.
These are used for continuous operation in commercial and industrial applications and may be either stationary or portable. Their application can be from 3 horsepower to over 1,200 horsepower and from low pressure to moderately high pressure; the classifications of rotary screw compressors vary based on stages, cooling methods, drive types among others. Rotary screw compressors are commercially produced in Water Flooded and Dry type; the efficiency of rotary compressors depends on the air drier, the selection of air drier is always 1.5 times volumetric delivery of the compressor. Designs with a single screw or three screws instead of two exist. Rotary vane compressors consist of a rotor with a number of blades inserted in radial slots in the rotor; the rotor is mounted offset in a larger housing, either circular or a more complex shape. As the rotor turns, blades slide in and out of the slots keeping contact with the outer wall of the housing. Thus, a series of increasing and decreasing volumes is created by the rotating blades.
Rotary Vane compressors are, with piston compressors one of the oldest of compressor technologies. With suitable port connections, the devices may be either a vacuum pump, they can be either stationary or portable, can be single or multi-staged, can be driven by electric motors or internal combustion engines. Dry vane machines are used at low pressures for bulk material movement while oil-injected machines have the necessary volumetric efficiency to achieve pressures up to about 13 bar in a single stage. A rotary vane compressor is well suited to electric motor drive and is quieter in operation than the equivalent piston compressor. Rotary vane compressors can have mechanical efficiencies of about 90%; the Rolling piston in a rolling piston style compressor plays the part of a partition between the vane and the rotor. Rolling piston forces gas against a stationary vane. 2 of these compressors can be mounted on the same shaft to increase capacity and reduce vibration and noise. A design without a spring is known as a swing compressor.
In refrigeration and air conditioning, this type of compressor is known as a rotary compressor, with rotary screw compressors being known as screw compressors. A scroll compressor known as scroll pump and scroll vacuum pump, uses two interleaved spiral-like vanes to pump or compress fluids such as liquids and gases; the vane geometry may be archimedean spiral, or hybrid curves. They operate more smoothly and reliably than other types of compressors in the lower volume range. One of the scrolls is fixed, while the other orbits eccentrically without rotating, thereby trapping and pumping or compressing pockets of fluid between the scrolls. Due to minimum clearance volume between the fixed scroll and the orbiting scroll, these compressors have a high volumetric efficiency; these compressors are extensively used in air conditioning and refrigeration because they are lighter and have fewer moving parts than reciprocating compressors and they are more reliable. They are more expensive though, so peltier coolers or rotary and reciprocating compressors may be used in applications where cost is the most important or one of the most important factors to consider when designing a refrigeration or air conditioining
Vapor-compression refrigeration
Vapor-compression refrigeration or vapor-compression refrigeration system, in which the refrigerant undergoes phase changes, is one of the many refrigeration cycles and is the most used method for air-conditioning of buildings and automobiles. It is used in domestic and commercial refrigerators, large-scale warehouses for chilled or frozen storage of foods and meats, refrigerated trucks and railroad cars, a host of other commercial and industrial services. Oil refineries and chemical processing plants, natural gas processing plants are among the many types of industrial plants that utilize large vapor-compression refrigeration systems. Refrigeration may be defined as lowering the temperature of an enclosed space by removing heat from that space and transferring it elsewhere. A device that performs this function may be called an air conditioner, air source heat pump, geothermal heat pump or chiller; the vapor-compression uses a circulating liquid refrigerant as the medium which absorbs and removes heat from the space to be cooled and subsequently rejects that heat elsewhere.
Figure 1 depicts a single-stage vapor-compression system. All such systems have four components: a compressor, a condenser, a thermal expansion valve, an evaporator. Circulating refrigerant enters the compressor in the thermodynamic state known as a saturated vapor and is compressed to a higher pressure, resulting in a higher temperature as well; the hot, compressed vapor is in the thermodynamic state known as a superheated vapor and it is at a temperature and pressure at which it can be condensed with either cooling water or cooling air flowing across the coil or tubes. This is where the circulating refrigerant rejects heat from the system and the rejected heat is carried away by either the water or the air; the condensed liquid refrigerant, in the thermodynamic state known as a saturated liquid, is next routed through an expansion valve where it undergoes an abrupt reduction in pressure. That pressure reduction results in the adiabatic flash evaporation of a part of the liquid refrigerant.
The auto-refrigeration effect of the adiabatic flash evaporation lowers the temperature of the liquid and vapor refrigerant mixture to where it is colder than the temperature of the enclosed space to be refrigerated. The cold mixture is routed through the coil or tubes in the evaporator. A fan circulates the warm air in the enclosed space across the coil or tubes carrying the cold refrigerant liquid and vapor mixture; that warm air evaporates the liquid part of the cold refrigerant mixture. At the same time, the circulating air is cooled and thus lowers the temperature of the enclosed space to the desired temperature; the evaporator is where the circulating refrigerant absorbs and removes heat, subsequently rejected in the condenser and transferred elsewhere by the water or air used in the condenser. To complete the refrigeration cycle, the refrigerant vapor from the evaporator is again a saturated vapor and is routed back into the compressor; the selection of working fluids has a significant impact on the performance of the refrigeration cycles and as such it plays a key role when it comes to designing or choosing an ideal machine for a certain task.
One of the most widespread refrigerant is "Freon". Freon is a trade name for a family of haloalkane refrigerants manufactured by DuPont and other companies; these refrigerants were used due to their superior stability and safety properties: they were not flammable at room temperature and atmospheric pressure, nor toxic as were the fluids they replaced, such as sulfur dioxide. Haloalkanes are an order of magnitude more expensive than petroleum derived flammable alkanes of similar or better cooling performance. Chlorine- and fluorine-bearing refrigerants reach the upper atmosphere when they escape. In the stratosphere, CFCs break up due to UV radiation free radicals; these chlorine free radicals act as catalysts in the breakdown of ozone through chain reactions. One CFC molecule can cause thousands of ozone molecules to break down; this causes severe damage to the ozone layer that shields the Earth's surface from the Sun's strong UV radiation, has been shown to lead to increased rates of skin cancer.
The chlorine will remain active as a catalyst until and unless it binds with another particle, forming a stable molecule. CFC refrigerants in common but receding usage include R-11 and R-12. Newer refrigerants with reduced ozone depletion effect such as HCFCs and HFCs have replaced most CFC use. HCFCs in turn are being phased out under the Montreal Protocol and replaced by hydrofluorocarbons, such as R-410A, which lack chlorine. However, CFCs, HCFCs, HFCs all have large global warming potential. More benign refrigerants are the subject of research, such as supercritical carbon dioxide, known as R-744; these have similar efficiencies compared to existing CFC and HFC based compounds, have many orders of magnitude lower global warming potential. The thermodynamics of the vapor compression cycle can be analyzed on a temperature versus entropy diagram as depicted in Figure 2. At point 1 in the diagram, the circulating refrigerant enters the compressor as a saturated vapor. From point 1 to point 2, the vapor is isentropically compressed and exits the compressor as a superheated vapor.
From point 2 to point 3, the vapor travels through part of the condenser which removes the superheat by cooling the vapor. Between point 3 and point 4, the vapor travels through the remainder of the condenser and is condensed
