Vapor Compression Refrigeration Cycle Engineering Essay

Vapor Compression infrigidation motorbike Engineering striveA ironor is a mechanical device that utilize increases the insistence of a compressible fluid. The inlet wardrobe level can be each value from a deep vacuum to a high haughty compel. The discharge pressure can range from sub-atmospheric levels to high values in tens of thousands of pounds per squargon inch. The inlet and outlet pressure atomic number 18 related, corresponding with the fiber of compressor ant its configuration. Compressors argon similar to pumps both increase the pressure on a fluid and both can transport the fluid d unity a pipe. The fluid can be any compressible fluid, either spoil pedal or dehydration, and can reach a wide molecular(a) weight range, that are from 2 for hydrogen to 352 for uranium hexafluoride. As natural hitmanes are compressible, the compressor also reduces the volume of a tout. Liquids are relatively incompressible, so the principal(prenominal) action of a pump is t o pressurize and transport crystallines. Applications of sozzled gas vary from consumer products, such as the home refrigerator, to whopping complex petrochemical seed installations.A vaporization capsule refrigeration system uses a cold sealed in an airtight and leak proof mechanism. The cold is circulated d single the system and it undergoes a no of changes in its differentiate while go through and through various components of the system. Each such change in the province of evaporation is called a exactlyt against. The process of repetition of a similar lay out of operation is called a cycle. The condensing cycle is given this name because it is the coalescency of the refrigerating by the compressor which permits transfer of come alive energy. The refrigerant absorbs that from one grade and releases it to an early(a) place. In other words the compressor is employ to put the heat laden refrigerant vapor in such a anatomy that it may dispute the heat it in different at small(a) pressure from the refrige roamd lieu, to an easily available cooling medium. Oil refineries, petrochemical and chemical touch plants, and natural gas processing plants are among the many types of industrial plants that often utilize immense vapor-compression refrigeration systems.2.1 Description of Vapor Compression constitutionMost of the modern refrigerators spend a penny on this cycle. In its simplest form on that localize are four fundamental operations require to complete one cycle.Compressor The low pressure vapor in dry enounce is emaciated from the evaporator during the suction stroke of the compressor. During compression stroke the pressure and temperature increase until vapor temperature is greater than the temperature of capacitance cooling medium.Condenser When the high pressure refrigerant vapor enters the capacitance heat flows from condenser to cooling medium hence allowing the vaporized refrigerant to re moot to liquid state.Expa nsion Valve After condenser the liquid refrigerant is insertd in the liquid receiver until needed. From the receiver it passes through an expansion valve where the pressure is reduced sufficiently to allow the vaporization of liquid a low temperature of about -10C.Evaporator The low pressure refrigerant vapor after expansion in the expansion valve enters the evaporator or refrigerated space where a considerable amount of heat is absorbed by it and refrigeration is furnished.The schematic diagram of the arrangement is as shown in propose 2.1 below. The low temperature, low pressure vapor at state B is compressed by a compressor to high temperature and pressure vapor at state C. This vapor is condensed into high pressure vapor at state D in the condenser and then passes through the expansion valve. Here, the vapor is throttled defeat to a low pressure liquid and passed on to an evaporator, where it absorbs heat from the milieu from the circulating fluid (being refrigerated) and vaporizes into low pressure vapor at state B. The cycle then repeats.BDCAFigure 2.1 simple-minded Vapor Compression System.The exchange of energy is as followsCompressor requires work, w. The work is supplied to the system from the surroundingsDuring densification, heat Q1 the equivalent of latent heat of condensation etc, is lost from the refrigerator.During evaporation, heat Q2 equivalent to latent heat of vaporization is absorbed by the refrigerant.There is no exchange of heat during throttling process through the expansion valve as this process occurs at constant enthalpy.2.2 Simple Vapor Compression CycleFigure 2.2 below shows the simple vapor compression cycleFigure 2.2 Simple Vapor Compression CycleProcess 1-2 The refrigerant as a mixture of liquid and vapour corresponding to state point 1 enters the compressor where isentropic compression takes place. The compression process increases the temperature of refrigerant from lower limit T2 to the upper limit Tl. campaign is s upplied to the system and after compression, the vapour is wet or saturated but not superheated.Process 2-3 The refrigerant in the form of vapour enters the condenser at state 2 and heat is rejected at constant pressure and temperature. At exit from the condenser, the refrigerant becomes saturated liquid at state point 3.Process 3-4 The refrigerant at state point 3 enters the expansion cylinder expands isentropic ally and its temperature drops to lower temperature T2 at the end of the expansion process. Work is obtained during the expansion process.Process 4-1 The liquid refrigerant at point 4 enters the evaporator and extracts heat at constant pressure and temperature from the space or substance being cooled and thus produces refrigerating effect.2.3 RefrigerationRefrigeration may be defined as lowering the temperature of an enclose space by removing heat from that space and transferring it elsewhere. A device that performs this exercise may also be called a heat pump. Freon is a backing name for a family of haloalkane refrigerants make by DuPont and other companies. These refrigerants were commonly utilize due to their superior stability and safety properties they were not flammable nor obviously toxic as were the fluids they replaced, such as sulfur dioxide.Newer refrigerants that have reduced ozone depletion effect include HCFCs (R-22, utilize in most homes today) and hydrofluorocarbons (R-134a, use in most cars) have replaced most CFC use. HCFCs in turn are being phased out under the Montreal Protocol and replaced by hydrofluoro hundreds (HFCs), such as R-410A, which lack chlorine. However, CFCs, HCFCs, and HFCs all have large global thawing potential.Newer refrigerants are currently the subject of research, such as supercritical carbon dioxide, known as R-744.4 These have similar efficiencies compared to existing CFC and HFC based compounds, and have many orders of magnitude lower global melting potential.3.0 TYPES OF COMPRESSORS3.1 Centrifugal CompressorCentrifugal compressors use a rotating disk or impeller in a shaped housing to force the gas to the rim of the impeller, increase the velocity of the gas. A diffuser (divergent duct) section converts the velocity energy to pressure energy. They are primarily used for continuous, stationary service in industries such as oil refineries, chemical and petrochemical plants and natural gas processing plants.Their covering can be from 100horse military unit (75kW) to thousands of horsepower. With multiple staging, they can make extremely high output pressures greater than 10,000psi (69MPa). Many large snowmaking operations (like ski resorts) use this type of compressor. They are also used in internal combustion engines as superchargers and turbochargers. Centrifugal compressors are used in small gas turbine engines or as the final compression stage of medium sized gas turbines.3.2 Axial Flow CompressorAxial-flow compressors are dynamic rotating compressors that use arrays of f an-like airfoils to progressively compress the working fluid. They are used where there is a requirement for a high flow rate or a compact design. The arrays of airfoils are set in rows, unremarkably as pairs one rotating and one stationary.The rotating airfoils, also known as blades or rotors, accelerate the fluid. The stationary airfoils, also known as stators or vanes, decelerate and redirect the flow direction of the fluid, preparing it for the rotor blades of the next stage. Axial compressors are almost always multi-staged, with the cross-sectional area of the gas passage change magnitude along the compressor to maintain an optimum axial Mach number. Beyond about 5 stages or a 41 design pressure ratio, protean geometry is normally used to improve operation.Axial compressors can have high efficiencies nigh 90% polytropic at their design conditions. However, they are relatively expensive, requiring a large number of components, tight tolerances and high quality materials. Ax ial-flow compressors can be effectuate in medium to large gas turbine engines, in natural gas pumping stations, and within certain chemical plants.4.0 APPLICATION OF COMPRESSORSGas compressors are used in various occupations where either higher pressures or lower volumes of gas are neededPipeline transport of purified natural gas To spark off the gas from the production site to the consumer, or the transportation of goods through a pipe. Most commonly, liquid and gases are sent, but pneumatic tubes that transport steadfast capsules using compressed air have also been used. Often, the compressor in this application is driven by a gas turbine which is fueled by gas bled from the pipeline. Thus, no external power source is necessary.Plants and refineries Petroleum refineries, natural gas processing plants, petrochemical and chemical plants, and similar large industrial plants for compressing medium and end product gases.Refrigeration and air conditioner equipment To move heat fr om one place to another in refrigerant cycles see Vapor-compression refrigeration.Gas turbine systems To compress the intake combustion airCommercial industry Storing purified or manufactured gases in a small volume, high pressure cylinders for medical, welding and other uses.Cylinder SCUBA diving, hyperbaric oxygen therapy and other life support devices to store breathing gas in a small volume such as in diving cylinders.Many various industrial, manufacturing and building processes to power all types of pneumatic tools.