制冷技术英文版Ch1109064Word格式文档下载.docx

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Fig.11-2Classificationofcondensers[1]

11-2）Water-CooledCondensers

Typesofwater-cooledcondenserscanbeclassifiedaccordingtotheirconstruction（Fig.11-2）.Eachhasfeaturesthatmakeitsuitableforcertainapplication.

（1）Double-pipecondenser

Fig.11-3,Double-pipewater-cooledcondenser

Fig.11-4Circularandtrombonedouble-tubecondenser[11]

Fig.11-5Doublepipecondenserwithcleanabletubes

（2）Shell-and-coilcondenser壳盘管冷凝器

Fig.11-6Shell-and-coilcondenser（verticaltype）[1]

（3）Shell-and-tubecondenser壳管冷凝器

Theshell-and-tubecondenserconsistsofacylindricalmetalshellandanumberofstraighttubeswhicharearrangedinparallelandheldinplaceattheendsbytubesheets.Therearetwomaintypesofshell-and-tubecondensers:

horizontalandvertical.

a）Horizontalshell-and-tubecondenser

Fig.11-7Two-passshellandtubecondenser

b）Verticalshell-and-tubecondensers

Fig.11-10Verticalshell-and-tubecondenser

（4）Heattransferinwatercooledcondenser

Thefollowingequationisusedtocalculateheattransferinwatercooledcondenser.

（11-1）

where

:

Heattransferrate,kW.

overallheattransfercoefficient,kW/m2K

Heattransferarea,m2

meaneffectivetemperaturedifference（METD）,K

Theoverallheattransfercoefficient:

（11-2）

thermalresistanceinrefrigerantside

thermalresistanceoftubewall

thermalresistanceofwaterfouling

thermalresistanceinwaterside

ratioofoutsidetoinsidetubesurfacearea

Sincethetemperatureofcoolingmediaisconstantlychanginginacondenser,thetemperaturedifferencebetweenthetherefrigerantandthecoolingmediaisnotconstant,asseeninFig.11-11.AmeantemperaturedifferencebetweenthemmustbedeterminedforEquation11-1.IthasbeenfoundthattheMeanEffectiveTemperatureDifference（METD）isthebestwaytorepresentthismeantemperaturedifference,whichcanbeobtainedfromthefollowingequation:

（11-3）

temperaturedifferenceatoneendofthecondenser,K

temperaturedifferenceatotherendofthecondenser,K

Fig.11-11Temperatureprofileinacondenser

AswecanfindfromEquation11-1,increasing

i.e.,METD,isoneofthewaystoenhanceheattransferforthecondensers.Themeantemperature,

canbeincreasedbytheflowarrangementinthecondensers.Counterflowandparallelflowsaretwocommonarrangementsappliedtoshell-and-tubeheatexchangers.Foragivensetofrequiredconditions,thecounterflowarrangmentgivesagreaterMETDthantheparallelflowarrangementdoes.However,theMETDisaffectedbytheflowarrangementwhentherefrigerantiscondensedfromsaturatedvaportosaturatedliquidbecausethethetemperatureoftherefrigerantisconstantinthisprocess（Fig.11-11）.

Inordertoincreasetheheattransferperformanceofcondensers,theoverallthermalresistance,

shouldbeassmallaspossible.OfthefourelementsinvolvedinEquation11-2,thethermalresistanceofmetaltubewallresistanceRwistheleastsignificantandcanbeignored.usually.Thus,thekofacondenserisdeterminedprimarilybytheotherthreefactorsandusuallythefoulingresistanceandtheliquidfilmresistancearethemostsignificant.Table11-1comparesthethermalresistancesinawatercooledcondenserwiththeammoniaasrefrigerant.

Table11-1Thermalresistancesinawatercooledcondenser

Thermalresistancetype

Heattransfercoefficient（

）

Thermalresistance

（

Condensationofrefrigerant

10602

9.4×

10-5

Lubricationoilfilm*

2500~3333

3~4×

10-4

Thermalconduction（steeltube）

18182

5.5×

Foulingofwater

2674

3.74×

Convectionofwater

4759

2.10×

Total

923.5

10.83×

*:

Thisisspecialforammonia.Someoftherefrigerantsdonothavethistypeofresistancebecausethelubricationoilcandissolveintheserefrigerants.

11-3）CoolingTower冷却塔

（1）TypesofCoolingTowers

Fig.11-13MechanicalDraftCoolingTower[13]

（2）CoolingTowerPerformance

Fig.11-14Rangeandapproachofcoolingtowers

（11-4）

（3）Make-upwaterandpurging（补充水和排污）

Incoolingtowers,evaporationandwaterdropletscarriedawaybytheairflowarethetwocausesofwaterloss.Also,waterinthetowerbasinshouldberegularlyremovedtopreventtheaccumulationofthedissolvedsolids.Forthesereasons,itisessentialtosupplyenoughmake-upwatertothecoolingtower.

Theevaporatedwaterdoesnotcarryawaythesolids,sothattheconcentrationofthesolidswouldreachalevelatwhichtheywouldprecipitateoutofthewateronsurfacesasacoating,orscale.Thiswillreducetheeffectivenessofthecondenser.

Fig.11-15Make-upandpurgingofacoolingtower

（11-5）

Andthemake-upwaterhasthustobe:

（11-9）

11-4）Air-CooledCondensers

Fig11-16,Air-cooledcondenser（naturaldrafttypewithwirefins）[15]

Fig.11-17Typicalforceddraftaircondenserarrangement

11-5）EvaporativeCondensers蒸发式冷凝器

Fig.11-18Schematicdiagramofevaporativecondenser

References

1.DossatR.J.,PrinciplesofRefrigeration,ThirdEdition,Prentice-Hall,Inc.1991.

2.WangS.K.HandbookofAirconditioning&

Refrigeration,McGraw-Hill,1994.

3.GosneyM.W.,PrinciplesofRefrigeration,CambridgeUniversityPress,1982

4.Source:

Perry’sChemicalEngineersHandbook（Page:

12-17），McGraw-Hill,1997

5.BureauofEnergyEfficiency,MinistryofPower,India.CoolingTowers.In:

Energy

6.EfficiencyinElectricalUtilities.Chapter7,pg135-151.Edward,2004

7.ZhuP.G.Theprincipleandcalculationofheatexchangers.TsinghuaPub.Comp.,Beijing.1987.7

8.WuY.Z.Theprincipleandequipmentofrefrigeration.XianJiaotongPress.,Xian,1998.1

9.WuY.Z.Designofrefrigerationsystem.MechanicalPress.Beijing,1988

10.ZhengX.D.Theprincipleandequipmentofrefrigeration.MechanicalPress.Beijing,1988

11.

12.

13.http:

//www.geo4va.vt.edu/A2/A2.htm

14.