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3. Vapour Compression Refrigeration Cycle
Vapor-compression refrigeration is one of the many refrigeration cycles available for use. It has been and is the most widely used method for air-conditioning of large public buildings, offices, private residences, hotels, hospitals, theaters, restaurants and automobiles. It is also used in domestic and commercial refrigerators, large-scale warehouses for chilled or frozen storage of foods and meats, refrigerated trucks and railroad cars, and a host of other commercial and industrial services. Oil refineries, petrochemical and chemical processing plants, and natural gas processing plants are among the many types of industrial plants that often 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 also be called a heat pump.
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 typical, single-stage vapor-compression system. All such systems have four components: a compressor, a condenser, a Thermal expansion valve (also called a throttle valve), and 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 then in the thermodynamic state known as a superheated vapor and it is at a temperature and pressure at which it can be condensed with typically available cooling water or cooling air. That hot vapor is routed through a condenser where it is cooled and condensed into a liquid by flowing through a coil or tubes with cool water or cool 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 (whichever may be the case).
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 then 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 which is 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.
Refrigeration Process
Process Description
1-2s: A reversible, adiabatic (isentropic) compression of the refrigerant.
The saturated vapour at state 1 is superheated to state 2.
⇒ wc = h2s− h1
2s-3: An internally, reversible, constant pressure heat rejection
in which the working substance is desuperheated and then condensed
to a saturated liquid at 3. During his process, the working substance
rejects most of its energy to the condenser cooling water.
⇒ qH = h2s− h3
3-4 An irreversible throttling process in which the temperature and
pressure decrease at constant enthalpy.
⇒ h3 = h4
4-1 An internally, reversible, constant pressure heat interaction
in which the working fluid is evaporated to a saturated vapour
at state point 1. The latent enthalpy necessary for evaporation
is supplied by the refrigerated space surrounding the evaporator.
The amount of heat transferred to the working fluid in the evaporator
is called the refrigeration load.
⇒ qL = h1− h4
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Why coefficient of performance of absorption cycle is less than compression cycle?
In case of vapour compression cycle (VCC) the COP is given by (desired effect / work input). in the other words it can be defines as what we want and what we are paying for that... so in VCC the paying amount is very less as due to low temperature difference that why its value is more than 1. but in case of vapour absorption system the COP is given by (heat taken by evaporator/ heat given to generator). the heat input taken by evaporator is less as compared to heat given to generator.. that why its COP is less than 1......
Bell Coleman Cycle it is the air refregeration cycle?
The Bell-Coleman Cycle is also known as the Air-Standard Refrigeration Cycle or Reverse Brayton Cycle. This 4-process refrigeration cycle involves isentropic compression, followed by isobarric heat rejection, then isentropic expansion (usually by a turboexpander), and finally isobarric heat intake.This cycle is commonly used in jet aircraft, using engine bleed air for compression and venting to the atmosphere. It is also commonly used in commercial air liquification plants.
What is the difference between gas power cycles and vapour power cycles?
Vapor-compression cycle(See Heat pump and refrigeration cycle and Vapor-compression refrigeration for more details)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.Figure 1: Vapor compression refrigerationThe thermodynamics of the cycle can be analyzed on a diagram[11][12] 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.Figure 2: Temperature-Entropy diagramThat 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.[13]Vapor absorption cycleMain article: Absorption refrigerator 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) and water (absorbent), and water (refrigerant) and lithium bromide[absorbent].
How does the thermal efficiency of an ideal Otto Cycle change with the compression ratio of the engine and the specific heat ratio of the working fluid?
The answer is 38.
What is carnot engine in thermodynamics?
A Carnot cycle representes a gas undergoing a theoretical - means it cannot be implemented realistically - thermodynamic cycle composed of 4 reversible steps (meaning you can go back and everything will be back to the state it was, or scientifically speaking, the entropy of the universe will remain constant): 1- isothermal expansion of the gas (working fluid) - heat is added from the surroundings to the working fuild and it expands at constant temperature; 2- isentropic expansion of the gas - the gas is allowed to expand and produce work; 3- isothermal compression of the gas - the gas rejects heat to the surroundings at constant temperature; 4- isentropic compression of the gas - the gas is compressed and work is need for that compression.
Why actual cop of vapour compression refrigeration is less than theoretical cop?
Mahit Nahi
Why coefficient of performance of absorption cycle is less than compression cycle?
In case of vapour compression cycle (VCC) the COP is given by (desired effect / work input). in the other words it can be defines as what we want and what we are paying for that... so in VCC the paying amount is very less as due to low temperature difference that why its value is more than 1. but in case of vapour absorption system the COP is given by (heat taken by evaporator/ heat given to generator). the heat input taken by evaporator is less as compared to heat given to generator.. that why its COP is less than 1......
How water flow rate affect performance of vapour compression cycle?
the sun heat up the water
How subcooling increase the COP of vapour compression refrigeration?
The sub-cooling or under-cooling in the saturated liquid line increases the refrigeration effect or cooling effect, thus the COP of VCR system increases.
What has the author Brian Mongey written?
Brian Mongey has written: 'The experimental evaluation of a ternary mixture as an alternative to R22 in the vapour compression refrigeration cycle'
How does vapour compression work?
See my answer to~How does air conditiong work~ on this site.
What is the compression cycle?
the vapor compression cycle is the cycle used in the process of the refrigerator. for more info go to www.wikipedia.com . thanx for asking ur questions!!!!! ~tammie
What is the vapor compression cycle?
the vapor compression cycle is the cycle used in the process of the refrigerator. for more info go to www.wikipedia.com . thanx for asking ur questions!!!!! ~tammie
What does a combination of a compression and a rarefraction create?
it creates a cycle
What is Vapour absorption machine?
It is a refrigeration unit based on Vapour Absorption Refrigeration Cycle (typically refrigerants used are Water or Ammonia).
What does vapor mean in the water cycle?
The clouds seen in the sky is formed from water vapour. It is water that has changed from a liquid into a gas (vapour).
Water vapour forms clouds and returns to earth?
The water cycle.
