7/30/2019 my nn

1/8

Cu to v nguyn l hot ng my nn kh, Cc chng loi my nn kh

Nguyn lKh nn c to ra t my nn kh, nng lng c hc ca ng c in hoc cang c t trong c chuyn i thnh nng lng kh nn v nhit nng. My nn khc hot ng theo hai nguyn l sao:

- Nguyn l thay i th tch : Khng kh c dn vo bung cha, th tch cabung cha s nh li. Nh vy theo nh lut Boyle-Matiotte p sut trong bung chas tng ln. My nn kh hot ng theo nguyn l ny nh kiu my nn kh piston,bnh rng, cnh gt

- Nguyn l ng nng : khng kh c dn trong bung cha v gia tc bi mt bphn quay vi tc cao, p sut kh nn dc to ra nh s chnh lch vn tc,nguyn tc ny to ra lu lng v cng sut rt ln. My nn kh hot ng theo nguynl ny nh my nn kh ly tm.

- C nhiu loi my nn kh khc nhau ang c s dng trong cng nghip, t n gindng trong vic bm xe v dng vo mt s vic khc, n cc nh my trung bnh v lndng trong cong nghip hm m v cc xng sn xut. Do ty theo cch phn loimy nn kh:

My nn kh p sut thp P 15barMy nn kh p sut cao P > 300barMy nn kh trc vt p sut 8barMy nn kh trc vt khng du p sut 8barMy nn kh trc vt hi du 8barMy nn kh piston thp p 8-15bar

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My nn kh piston cao p khng du 15-35barMy nn kh piston cao p c du 15- 35bar

Cc chng loi my nn kh

My nn kh kiu piston:

My nn kh piston mt cp k np, chn khng c to lp pha trn piston, do khng kh c y vo bung nn khng qua van np. Van ny m t ng do s chnhlch p sut gy ra bi chn khng trn b mt piston. Khi piston i xung ti imchch di v bc u i ln., khng kh i vo bung nn do s mt cn bng p sutpha trn v di nn van np ng li v qu trnh nn kh bt u xy ra. Khi p sut

trong bung nn tng ti mt mc no s lm cho van thot m ra, kh nn s thotqua van thot i vo h thng kh nn.

* C hai van np v thot thng c l xo v cac2 van ng m t ng do s thongkh s chnh lch p sut pha ca mi van.

* Sao khi piston ln n im cht trn v bt u i xung tr li, van thot ng vmt chu trnh nn kh mi bt u.

* My nn kh kiu piston mt cp c th ht c lng n 10m/phc v p sut nn

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3/8

c 6 bar, c th trong mt s trng hp p sut nn n 10 bar. My nn kh kiupiston 2 cp c th nn n p sut 15 bar. Loi my nn kh kiu piston 3,4 cp c thnn p sut n 250 bar.

* Loi my nn kh mt cp v hai cp thch hp h thng iu khin bng kh nntrong cng nghip. My nn kh piston c phn loi theo s cp nn, loi truyn ng

v phng thc lm ngui kh nn.My nn kh kiu trc vt:

* My nn khi trc vt hot ng theo nguyn l thay i th tch. My nn kh trc vtgm c hai trc. Trc chnh v trc ph.

* My nn kh trc vt c khong nm 1950 v chim lnh mt th trng ln tronglnh vt kh nn, Loi my nn kh ny c mt v t bit bao boc quanh hai trc vtquay, 1 li mt lm. Cc rng ca hai trc vt n khp vi nhau v s rng trc vt li thn trc vt lm 1 n 2 rng. Hai trc vt phi quay ng b vi nhau, gia cc trc vtv v bc c khe h rt nh.

* Khi cc trc vt quay nhanh, khng kh c ht vo bn trong v thng qua ca npv i vo bung kh gia cc trc vt v khng kh c nn gia cc rng khibun kh nh li, sao kh nn i ti ca thot. C ca np v ca thot s c ng

hot c m t ng khi cc trc vt quay hoc khng che cc ca, ca thot ca mynen kh c lp mt van mt chiu ngn cc trc vt t quay khi qu trnh nn d ngng.* My nn kh trc vt c nhiu tnh cht ging vi my nn kh cnh gt, chng hn

nh s n nh v khng dao ng trong kh thot, t rung ng v ting n nh. t hiusut cao nht khi hot ng gn y ti.

* Lu lng t 1,4m/phuc v c th len ti 60m/phuc,

My nn kh li tm:

7/30/2019 my nn

4/8

- Trong my nn kh li tm, mi cp gm mt ngn, mt cnh qut, mt b khuch tnv mt ng khuch tn t hp. Khi cnh quat quay c nhiu cnh vi tc cao, khngkh c ht vo gia cnh qut vi vn tc ln v p sut cao sao khng kh i vovng khuch tn tnh, khng kh gin n v vy vn tc ca n gim nhng p suttng mt cch ng k. T b khuch tn t hp, khng kh gin n them v p sut

tng ri i n cp k tip hoc trc tip n ng ra. Khng ging nh loi my nn khhng trc, vic chia cp ca my nn khi ny rt n gin.

Theo maydien.com; nh Thanh Sn

c thm bi vit ting anh:

Types of compressors

The main types of gas compressors are illustrated and discussed below:

Centrifugal Compressors Centrifugal compressors use the rotating action of an impeller wheel toexert centrifugal force on refrigerant inside a round chamber (volute). Refrigerantis sucked into the impeller wheel through a large circular intake and flowsbetween the impellers. The impellers force the refrigerant outward, exertingcentrifugal force on the refrigerant. The refrigerant is pressurized as it is forcedagainst the sides of the volute. Centrifugal compressors are well suited tocompressing large volumes of refrigerant to relatively low pressures. Thecompressive force generated by an impeller wheel is small, so chillers that use

centrifugal compressors usually employ more than one impeller wheel, arrangedin series. Centrifugal compressors are desirable for their simple design and fewmoving parts.

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Diagonal or mixed-flow compressors Diagonal or mixed-flow compressors are similar to centrifugalcompressors, but have a radial and axial velocity component at the exit from therotor. The diffuser is often used to turn diagonal flow to the axial direction. Thediagonal compressor has a lower diameter diffuser than the equivalentcentrifugal compressor.

Axial-flow compressors Axial-flow compressors are dynamic rotating compressors that usearrays of fan-like aerofoils to progressively compress the working fluid. They areused where there is a requirement for a high flows or a compact design.Thearrays of aerofoils are set in rows, usually as pairs: one rotating and onestationary. The rotating aerofoils, also known as blades or rotors, decelerate andpressurise the fluid. The stationary aerofoils, also known as a statorsor vanes,turn and decelerate the fluid; preparing and redirecting the flow for the rotorblades of the next stage. Axial compressors are almost always multi-staged, withthe cross-sectional area of the gas passage diminishing along the compressor to

maintain an optimum axial Mach number. Beyond about 5 stages or a 4:1 designpressure ratio, variable geometry is normally used to improve operation. Axialcompressors can have high efficiencies; around 90% polytropic at their designconditions. However, they are relatively expensive, requiring a large number ofcomponents, tight tolerances and high quality materials. Axial-flow compressorscan be found in medium to large gas turbineengines, in natural gas pumpingstations, and within certain chemical plants.

Reciprocating Compressors A reciprocating compressor uses the reciprocating action of a piston

http://en.wikipedia.org/w/index.php?title=Aerofoils&action=edit&redlink=1http://en.wikipedia.org/w/index.php?title=Stators&action=edit&redlink=1http://en.wikipedia.org/w/index.php?title=Stators&action=edit&redlink=1http://en.wikipedia.org/wiki/Mach_numberhttp://en.wikipedia.org/wiki/Mach_numberhttp://en.wikipedia.org/wiki/Variable_geometryhttp://en.wikipedia.org/wiki/Polytropichttp://en.wikipedia.org/wiki/Gas_turbinehttp://en.wikipedia.org/wiki/Gas_turbinehttp://en.wikipedia.org/w/index.php?title=Aerofoils&action=edit&redlink=1http://en.wikipedia.org/w/index.php?title=Stators&action=edit&redlink=1http://en.wikipedia.org/wiki/Mach_numberhttp://en.wikipedia.org/wiki/Variable_geometryhttp://en.wikipedia.org/wiki/Polytropichttp://en.wikipedia.org/wiki/Gas_turbine

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inside a cylinder to compress refrigerant. As the piston moves downward, avacuum is created inside the cylinder. Because the pressure above the intakevalve is greater than the pressure below it, the intake valve is forced open andrefrigerant is sucked into the cylinder. After the piston reaches its bottom positionit begins to move upward. The intake valve closes, trapping the refrigerant inside

the cylinder. As the piston continues to move upward it compresses therefrigerant, increasing its pressure. At a certain point the pressure exerted by therefrigerant forces the exhaust valve to open and the compressed refrigerant flowsout of the cylinder. Once the piston reaches it top-most position, it starts movingdownward again and the cycle is repeated.

Rotary CompressorsIn a rotary compressor the refrigerant is compressed by the rotating

action of a roller inside a cylinder. The roller rotates eccentrically (off-centre)around a shaft so that part of the roller is always in contact with the inside wall ofthe cylinder. A spring-mounted blade is always rubbing against the roller. Thetwo points of contact create two sealed areas of continuously variable volumeinside the cylinder. At a certain point in the rotation of the roller, the intake port isexposed and a quantity of refrigerant is sucked into the cylinder, filling one of thesealed areas. As the roller continues to rotate the volume of the area therefrigerant occupies is reduced and the refrigerant is compressed. When theexhaust valve is exposed, the high-pressure refrigerant forces the exhaust valveto open and the refrigerant is released. Rotary compressors are very efficientbecause the actions of taking in refrigerant and compressing refrigerant occur

simultaneously.

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Diaphragm compressor A diaphragm compressor (also known as a membrane compressor) is avariant of the conventional reciprocating compressor. The compression of gasoccurs by the movement of a flexible membrane, instead of an intake element.The back and forth movement of the membrane is driven by a rod and acrankshaft mechanism. Only the membrane and the compressor box come intouch with the gas being compressed. Diaphragm compressors are used for

hydrogen and compressed natural gas (CNG) as well as in a number of otherapplications.

A three-stage diaphragm compressorRotary Scroll Compressors

In a scroll compressor refrigerant is compressed by two offset spiraldisks that are nested together. The upper disk is stationary while the lower diskmoves in orbital fashion. The orbiting action of the lower disk inside the stationary

disk creates sealed spaces of varying volume.Refrigerant is sucked in throughinlet ports at the perimeter of the scroll. A quantity of refrigerant becomes trappedin one of the sealed spaces. As the disk orbits the enclosed space containing therefrigerant is transferred toward the centre of the disk and its volume decreases.

As the volume decreases, the refrigerant is compressed. The compressedrefrigerant is discharged through a port at the centre of the upper disk. Scrollcompressors are quiet, smooth-operating units with the highest efficiency ratio of

http://en.wikipedia.org/wiki/Compressed_natural_gashttp://en.wikipedia.org/wiki/Compressed_natural_gas

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all compressor types. They are commonly used in automobile air conditioningsystems and commercial chillers.

Rotary Screw CompressorsScrew compressors use a pair of helical rotorsAs the rotors rotate they

intermesh, alternately exposing and closing off interlobe spaces at the ends ofthe rotors. When an interlobe space at the intake end opens up, refrigerant issucked into it. As the rotors continue to rotate the refrigerant becomes trappedinside the interlobe space and is forced along the length of the rotors. Thevolume of the interlobe space decreases and the refrigerant is compressed. Thecompressed refrigerant exists when the interlobe space reaches the other end.(male and female) inside a sealed chamber.

Rotary vane compressorsRotary 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 housingwhich can be circular or a more complex shape. As the rotor turns, blades slidein and out of the slots keeping contact with the outer wall of the housing.Thus, aseries of decreasing volumes is created by the rotating blades. Rotary Vanecompressors are, with piston compressors one of the oldest of compressortechnologies. With suitable port connections, the devices may be either a

compressor or a vacuum pump. They can be either stationary or portable, can besingle or multi-staged, and can be driven by electric motors or internalcombustion engines. Dry vane machines are used at relatively low pressures(e.g., 2 bar) for bulk material movement whilst oil-injected machines have thenecessary volumetric efficiency to achieve pressures up to about 13 bar in asingle stage. A rotary vane compressor is well suited to electric motor drive andis significantly quieter in operation than the equivalent piston compressor.