absorbed heat is removed from the refrigeration system in the condenser as the refrigerant changes liquid to a gas in the evaporator. state from a gas back to. A refrigeration system is a combination of components and equipment systems are the most widely adopted refrigeration systems in both comfort and process. Using the same principle, refrigeration works by removing heat from a product and There are five basic components of a refrigeration system, these are.
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The contents of this book are intended to interest those who are not engaged every day with refrigeration plant but who wish to extend their knowledge on the. This lesson discusses the most commonly used refrigeration system, i.e. Vapour compression refrigeration system. The following things are emphasized in detail . Air cycle refrigeration systems, Air cycle refrigeration systems, PDF, kb Vapour Compression Refrigeration Systems:Performance Aspects And Cycle.
Heat transfer depends on the properties of the refrigerant. Different refrigerants will obviously have different enthalpy values for a given state. In dealing with one specific refrigerant, the enthalpy values depend on the temperatures and pressures in the warm and cold regions. The surrounding temperature affects how well the refrigeration system is able to cool the enclosed region. Clearly, if the outside temperature is very hot i. Moran, Michael J. Langley, Billy C. Reston Publishing Company, Inc.
Detail of Compressor Valve Function. The condenser removes heat given off during the liquefication of vaporized refrigerant. Heat is given off as the temperature drops to condensation temperature. Then, more heat specifically the latent heat of condensation is released as the refrigerant liquefies.
There are air-cooled and water-cooled condensers, named for their condensing medium. The more popular is the air-cooled condenser. The condensers consist of tubes with external fins. The refrigerant is forced through the condenser. One way of dealing with such situations is to perform the refrigeration process in stages, that is, to have two or more refrigeration cycles that operate in series.
Such refrigeration cycles are called cascade refrigeration 22 cycles. Cascade Refrigeration Systems A two-stage cascade refrigeration cycle is shown. The two cycles are connected through the heat exchanger in the middle, which serves as the evaporator for the topping cycle and the condenser for the bottoming cycle. A two stage compression refrigeration system with a flash chamber.
A two-stage cascade refrigeration system with the same refrigerant 23 in both stages. Cascade Refrigeration Systems Assuming the heat exchanger is well insulated and the kinetic and potential energies are negligible, the heat transfer from the fluid in the bottoming cycle should be equal to the heat transfer to the fluid in the topping cycle.
Thus, the ratio of mass flow rates through each cycle should be The coefficient of performance of the cascade system is 24 Problem Cascade Refrigeration Systems Consider a two-stage cascade refrigeration system operating between pressure limits of 0.
Each stage operates on the ideal vapor-compression refrigeration cycle with refrigeranta as the working fluid. Heat rejection from the lower cycle to the upper cycle takes place in an adiabatic counter-flow heat exchanger where both streams enter at about 0. If the mass flow rate of the refrigerant through the upper cycle is 0. In commerce and manufacturing, there are many uses for refrigeration. Refrigeration is used to liquify gases — oxygen , nitrogen , propane and methane , for example.
In compressed air purification, it is used to condense water vapor from compressed air to reduce its moisture content. In oil refineries , chemical plants , and petrochemical plants, refrigeration is used to maintain certain processes at their needed low temperatures for example, in alkylation of butenes and butane to produce a high octane gasoline component.
Metal workers use refrigeration to temper steel and cutlery. When transporting temperature-sensitive foodstuffs and other materials by trucks, trains, airplanes and seagoing vessels, refrigeration is a necessity.
Dairy products are constantly in need of refrigeration, and it was only discovered in the past few decades that eggs needed to be refrigerated during shipment rather than waiting to be refrigerated after arrival at the grocery store. Meats, poultry and fish all must be kept in climate-controlled environments before being sold. Refrigeration also helps keep fruits and vegetables edible longer.
Before the discovery of refrigeration, many sushi connoisseurs were at risk of contracting diseases. The dangers of unrefrigerated sashimi were not brought to light for decades due to the lack of research and healthcare distribution across rural Japan. Around mid-century, the Zojirushi corporation, based in Kyoto, made breakthroughs in refrigerator designs, making refrigerators cheaper and more accessible for restaurant proprietors and the general public.
Methods of refrigeration can be classified as non-cyclic , cyclic , thermoelectric and magnetic. This refrigeration method cools a contained area by melting ice, or by sublimating dry ice. Regular ice can maintain temperatures near, but not below the freezing point, unless salt is used to cool the ice down further as in a traditional ice-cream maker. Dry ice can reliably bring the temperature well below freezing.
This consists of a refrigeration cycle, where heat is removed from a low-temperature space or source and rejected to a high-temperature sink with the help of external work, and its inverse, the thermodynamic power cycle. In the power cycle, heat is supplied from a high-temperature source to the engine, part of the heat being used to produce work and the rest being rejected to a low-temperature sink. This satisfies the second law of thermodynamics.
A refrigeration cycle describes the changes that take place in the refrigerant as it alternately absorbs and rejects heat as it circulates through a refrigerator. It is also applied to heating, ventilation, and air conditioning HVACR work, when describing the "process" of refrigerant flow through an HVACR unit, whether it is a packaged or split system. Heat naturally flows from hot to cold. Work is applied to cool a living space or storage volume by pumping heat from a lower temperature heat source into a higher temperature heat sink.
Insulation is used to reduce the work and energy needed to achieve and maintain a lower temperature in the cooled space. The operating principle of the refrigeration cycle was described mathematically by Sadi Carnot in as a heat engine.
The most common types of refrigeration systems use the reverse-Rankine vapor-compression refrigeration cycle, although absorption heat pumps are used in a minority of applications. The vapor-compression cycle is used in most household refrigerators as well as in many large commercial and industrial refrigeration systems.
Figure 1 provides a schematic diagram of the components of a typical vapor-compression refrigeration system. The thermodynamics of the cycle can be analyzed on a diagram  as shown in Figure 2.
In this cycle, a circulating refrigerant such as Freon enters the compressor as a vapor. From point 1 to point 2, the vapor is compressed at constant entropy and exits the compressor as a vapor at a higher temperature, but still below the vapor pressure at that temperature.
From point 2 to point 3 and on to point 4, the vapor travels through the condenser which cools the vapor until it starts condensing, and then condenses the vapor into a liquid by removing additional heat at constant pressure and temperature.
Between points 4 and 5, the liquid refrigerant goes through the expansion valve also called a throttle valve where its pressure abruptly decreases, causing flash evaporation and auto-refrigeration of, typically, less than half of the liquid. That results in a mixture of liquid and vapor at a lower temperature and pressure as shown at point 5. The cold liquid-vapor mixture then travels through the evaporator coil or tubes and is completely vaporized by cooling the warm air from the space being refrigerated being blown by a fan across the evaporator coil or tubes.
The resulting refrigerant vapor returns to the compressor inlet at point 1 to complete the thermodynamic cycle. The above discussion is based on the ideal vapor-compression refrigeration cycle, and does not take into account real-world effects like frictional pressure drop in the system, slight thermodynamic irreversibility during the compression of the refrigerant vapor, or non-ideal gas behavior, if any. More information about the design and performance of vapor-compression refrigeration systems is available in the classic Perry's Chemical Engineers' Handbook.
In the early years of the twentieth century, the vapor absorption cycle using water-ammonia systems was popular and widely used. After the development of the vapor compression cycle, the vapor absorption cycle lost much of its importance because of its low coefficient of performance about one fifth of that of the vapor compression cycle.
Today, the vapor absorption cycle is used mainly where fuel for heating is available but electricity is not, such as in recreational vehicles that carry LP gas. It is also used in industrial environments where plentiful waste heat overcomes its inefficiency. The absorption cycle is similar to the compression cycle, except for the method of raising the pressure of the refrigerant vapor. In the absorption system, the compressor is replaced by an absorber which dissolves the refrigerant in a suitable liquid, a liquid pump which raises the pressure and a generator which, on heat addition, drives off the refrigerant vapor from the high-pressure liquid.
Some work is needed by the liquid pump 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 with water absorbent , and water refrigerant with lithium bromide absorbent. When the working fluid is a gas that is compressed and expanded but doesn't change phase, the refrigeration cycle is called a gas cycle.
Air is most often this working fluid.
As there is no condensation and evaporation intended in a gas cycle, components corresponding to the condenser and evaporator in a vapor compression cycle are the hot and cold gas-to-gas heat exchangers in gas cycles. The gas cycle is less efficient than the vapor compression cycle because the gas cycle works on the reverse Brayton cycle instead of the reverse Rankine cycle.
As such the working fluid does not receive and reject heat at constant temperature. In the gas cycle, the refrigeration effect is equal to the product of the specific heat of the gas and the rise in temperature of the gas in the low temperature side.
Therefore, for the same cooling load, a gas refrigeration cycle needs a large mass flow rate and is bulky. Because of their lower efficiency and larger bulk, air cycle coolers are not often used nowadays in terrestrial cooling devices.
However, the air cycle machine is very common on gas turbine -powered jet aircraft as cooling and ventilation units, because compressed air is readily available from the engines' compressor sections. Such units also serve the purpose of pressurizing the aircraft.
Thermoelectric cooling uses the Peltier effect to create a heat flux between the junction of two types of material. This effect is commonly used in camping and portable coolers and for cooling electronic components and small instruments.
Magnetic refrigeration, or adiabatic demagnetization , is a cooling technology based on the magnetocaloric effect, an intrinsic property of magnetic solids.
The refrigerant is often a paramagnetic salt , such as cerium magnesium nitrate. The active magnetic dipoles in this case are those of the electron shells of the paramagnetic atoms.
A strong magnetic field is applied to the refrigerant, forcing its various magnetic dipoles to align and putting these degrees of freedom of the refrigerant into a state of lowered entropy.
A heat sink then absorbs the heat released by the refrigerant due to its loss of entropy. Thermal contact with the heat sink is then broken so that the system is insulated, and the magnetic field is switched off. This increases the heat capacity of the refrigerant, thus decreasing its temperature below the temperature of the heat sink. Because few materials exhibit the needed properties at room temperature, applications have so far been limited to cryogenics and research.
Other methods of refrigeration include the air cycle machine used in aircraft; the vortex tube used for spot cooling, when compressed air is available; and thermoacoustic refrigeration using sound waves in a pressurized gas to drive heat transfer and heat exchange; steam jet cooling popular in the early s for air conditioning large buildings; thermoelastic cooling using a smart metal alloy stretching and relaxing.
Many Stirling cycle heat engines can be run backwards to act as a refrigerator, and therefore these engines have a niche use in cryogenics. In addition there are other types of cryocoolers such as Gifford-McMahon coolers, Joule-Thomson coolers, pulse-tube refrigerators and, for temperatures between 2 mK and mK, dilution refrigerators. Another potential solid-state refrigeration technique and a relatively new area of study comes from a special property of super elastic materials.
These materials undergo a temperature change when experiencing an applied mechanical stress called the elastocaloric effect. Since super elastic materials deform reversibly at high strains , the material experiences a flattened elastic region in its stress-strain curve caused by a resulting phase transformation from an austenitic to a martensitic crystal phase. When a super elastic material experiences a stress in the austenitic phase, it undergoes an exothermic phase transformation to the martensitic phase, which causes the material to heat up.
Removing the stress reverses the process, restores the material to its austenitic phase, and absorbs heat from the surroundings cooling down the material. The most appealing part of this research is how potentially energy efficient and environmentally friendly this cooling technology is.
The different materials used, commonly shape-memory alloys , provide a non-toxic source of emission free refrigeration. The most commonly studied materials studied are shape-memory alloys, like nitinol and Cu-Zn-Al. The main challenge however comes from potential energy losses in the form of hysteresis , often associated with this process. Since most of these losses comes from incompatibilities between the two phases, proper alloy tuning is necessary to reduce losses and increase reversibility and efficiency.
Balancing the transformation strain of the material with the energy losses enables a large elastocaloric effect to occur and potentially a new alternative for refrigeration. The Fridge Gate method is a theoretical application of using a single logic gate to drive a refrigerator in the most energy efficient way possible without violating the laws of thermodynamics.
It operates on the fact that there are two energy states in which a particle can exist: The excited state carries a little more energy than the ground state, small enough so that the transition occurs with high probability.
There are three components or particle types associated with the fridge gate. The first is on the interior of the fridge, the second on the outside and the third is connected to a power supply which heats up every so often that it can reach the E state and replenish the source.
In the cooling step on the inside of the fridge, the g state particle absorbs energy from ambient particles, cooling them, and itself jumping to the e state. In the second step, on the outside of the fridge where the particles are also at an e state, the particle falls to the g state, releasing energy and heating the outside particles.
Determination of COP of a Refrigeration System.pdf
In the third and final step, the power supply moves a particle at the e state, and when it falls to the g state it induces an energy-neutral swap where the interior e particle is replaced by a new g particle, restarting the cycle. MIT researchers have devised a new way of providing cooling on a hot sunny day, using inexpensive materials and requiring no fossil fuel-generated power. The passive system, which could be used to supplement other cooling systems to preserve food and medications in hot, off-grid locations, is essentially a high-tech version of a parasol.
The measured capacity of refrigeration is always dimensioned in units of power. A refrigeration system's coefficient of performance CoP is very important in determining a system's overall efficiency. It is defined as refrigeration capacity in kW divided by the energy input in kW.
While CoP is a very simple measure of performance, it is typically not used for industrial refrigeration in North America. Owners and manufacturers of these systems typically use performance factor PF. A system's PF is defined as a system's energy input in horsepower divided by its refrigeration capacity in TR.
Both CoP and PF can be applied to either the entire system or to system components. For example, an individual compressor can be rated by comparing the energy needed to run the compressor versus the expected refrigeration capacity based on inlet volume flow rate. It is important to note that both CoP and PF for a refrigeration system are only defined at specific operating conditions, including temperatures and thermal loads.
Moving away from the specified operating conditions can dramatically change a system's performance. From Wikipedia, the free encyclopedia. Process of moving heat from one location to another in controlled conditions. Main article: Timeline of low-temperature technology. See also: Ice cutting and Ice trade. Ice trade.
Heat pump and refrigeration cycle. Vapor-compression refrigeration. Figure 1: Vapor compression refrigeration. Figure 2: Temperature—Entropy diagram. Absorption refrigerator. Magnetic refrigeration.From point 2 to point 3, the vapor travels through part of the condenser which removes the superheat by cooling the vapor. The first to achieve this breakthrough was an entrepreneur who had emigrated to New Zealand.
The introduction of refrigeration allowed for the hygienic handling and storage of perishables, and as such, promoted output growth, consumption, and the availability of nutrition. Work is applied to cool a living space or storage volume by pumping heat from a lower temperature heat source into a higher temperature heat sink.
Determination of COP of a Refrigeration System.pdf
The evaporator consists of finned tubes, which absorbs heat from the air blown through a coil by a fan. Namespaces Article Talk.
In fact, consumers that used the icebox in faced the same challenge of a moldy and stinky icebox that consumers had in the early s.
Franklin wrote, "From this experiment, one may see the possibility of freezing a man to death on a warm summer's day".
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