西建工程熱力學(xué)雙語課件07濕空氣

Chapter7.MoistAir

第七章濕空氣

7.1Introduction(介紹)7.2PropertiesofMoistAir（濕空氣的參數(shù)）7.3H-dDiagramofMoistAir（濕空氣的H-d圖)7.4ThermodynamicProcessofMoistAir

（濕空氣的熱力過程）濕空氣＝（干空氣＋水蒸氣）

空調(diào)、通風(fēng)、烘干、冷卻塔、儲存濕空氣與一般理想混合氣體的最大區(qū)別是：水蒸氣的成分可能變化。分壓低理想混合氣體DryairAtmosphericair7.1Introduction(介紹)1.DefinitionofAtmosphericAir（濕空氣的定義）Dryair+Watervapor(Moisture)=AtmosphericAir(含有水蒸汽的空氣稱為濕空氣。)Airthatcontainsnowatervaporiscalleddryair.(完全不含水蒸汽的空氣稱為干空氣。)2.CharacteristicsofMoistureAir(濕空氣的特點(diǎn))Atmosphericaircontainsaverysmallamountofwatervapor.Thepartialpressureofwatervaporisverylowsothatwatervaporintheatmosphericairisalwaysatsuperheatedstate.Thus,watervaporcanbetreatedasidealgas.(濕空氣中水蒸汽含量很小，分壓力很低，常處于過熱狀態(tài)，可以當(dāng)作理想氣體來處理。)Atmosphericaircanbetreatedasabinarymixture(二元混合物）ofidealgases,

dryairandmoisture

Rda

=8314.41/28.9645=287.055J/(kg·K)Rw

=8314.41/18.01528=461.520J/(kg·K)Dryair:

pdaV=mdaRdaTWatervapor:

pwV=mdaRwTSaturatedvapor

飽和蒸汽

(1)未飽和濕空氣(UnsaturatedAir):Dryair+SuperheatedwatervaporSuperheatedvapor過熱蒸汽Watervapor干空氣＋過熱水蒸氣pv

<ps(T)

Tspvps加入水蒸氣，pv3.SaturatedAirandUnsaturatedAir(未飽和空氣和飽和空氣)Unsaturatedair未飽和濕空氣(2)飽和濕空氣(Saturatedair)干空氣＋飽和水蒸氣pv

＝ps(T)

Tsps溫度一定，不能再加入水蒸氣Ifthetemperatureisfixed,nomorewatervaporitcanabsorb.SaturatedAir:Dryair+Saturatedwatervapor(飽和濕空氣：干空氣和飽和水蒸汽的混合物。)Saturatedair飽和濕空氣(3)從未飽和到飽和的途徑TspvpsA.

T

加水蒸氣,pvabC.

pv

不變，TabaddcB.

pv

，TacD.

vaee結(jié)露Td露點(diǎn)溫度B.

pv

，TB.

pv

，TB.

pv

，TA.

T

加水蒸氣,pvA.

T

加水蒸氣,pvA.

T

加水蒸氣,pvA.

T

加水蒸氣,pvA.

T

加水蒸氣,pvA.

T

加水蒸氣,pvA.

T

加水蒸氣,pv7.2濕空氣的參數(shù)PropertiesofMoistAir

Thebarometricpressureofatmosphericairvaryconsiderablywithaltitudeaswellaswithlocalgeographicandweatherconditions.1.Pressureofatmosphericair-500107.4780101.32550095.461100089.875150084.556200079.495250074.682300070.108400061.640500054.020600047.181700041.061800035.600900030.7421000026.4361200019.2841400013.786160009.632180006.556200004.328Thepartialpressureofwatervaporisalsocalledvaporpressure.2.干球溫度(Dry-bulbtemperature)Itisthetemperatureofmoistair.Thedry-bulbtemperatureofwatervaporanddryairisthesame.Itisdenotedas‘t’.3.露點(diǎn)溫度(Dew-pointTemperature)Itisdefinedasthetemperatureatwhichcondensationbeginswhentheairiscooledatconstantpressure.Inotherwords,itisthesaturationtemperatureofwatercorrespondingtothevaporpressure.結(jié)露:A點(diǎn)表示未飽和濕空氣中水蒸汽的狀態(tài)，若保持空氣中水蒸汽的含量（pv）不變，降低溫度，使之達(dá)到pv對應(yīng)的飽和溫度ts，則濕空氣成為飽和濕空氣，為點(diǎn)B。若繼續(xù)降溫，水分析出，稱為結(jié)露。

露點(diǎn):B點(diǎn)所對應(yīng)的pv下的飽和溫度成為露點(diǎn)，用td表示。4.相對濕度φ(RelativeHumidityofAir)定義：濕空氣中實(shí)際包含的水蒸汽量與同溫度下最多能包含的水蒸汽量的百分比。Therelativehumidityisdefinedastheratiooftheamountofmoistureintheairtothemaximumamountofmoisturetheaircanholdatthesametemperature.Ifweuse“a”、“v”、“s”denotingdryair,watervaporandsaturatedwatervaporrespectively,then(若用下標(biāo)“a”、“v”、“s”表示干空氣、水蒸汽和飽和水蒸汽的參數(shù)，則有：)＝1

飽和濕空氣

(

SaturatedMoistAir)在相同的溫度下：＝0

干空氣

(dryair)0<<1

未飽和濕空氣

表明濕空氣與同溫下飽和濕空氣的偏離程度

Thelowerthevalueofφ,themorewatervaporitcanabsorb,andthedrieritis.(φ越小，空氣吸濕的能力越強(qiáng)，越干燥。)Thehigherthevalueofφ,thelesswatervaporitcanabsorb,andtheneareritapproachessaturatedmoistair.(Φ越大，空氣吸濕的能力越弱，越潮濕。)反映所含水蒸氣的飽和程度

5.濕空氣的含濕量(Humidityratio)ThemassofwatervaporpresentinaunitmassofdryairiscalledhumidityRatio.

含濕量d：以干空氣為基準(zhǔn)，包含1千克干空氣的濕空氣中中所含有的水蒸汽的質(zhì)量。

Ｄistheratiooftheairhumidityratiodtothehumidityratiods

ofsaturatedmoistairatthesametemperatureandpressure．

(飽和度是濕空氣的含濕量與同溫度下的飽和濕空氣的含濕量之比）6.Degreeofsaturation(飽和度）

Thedensityofamoistairmixtureistheratioofthetotal

mass

tothetotalvolume:

７.Density(密度)Thedensityofmoistairisalwayslessthanthatofdryair.（濕空氣的密度總比干空氣的密度?。〢ndthehigherthetemperature,thelessthedensity.（而且溫度越高，密度越?。?濕空氣的焓(EnthalpyofAtmosphericAir)

Theenthalpyofatmosphericairisexpressedperunitmassofdryair.

含有1kg干空氣的濕空氣的焓

Itisthesumoftheenthalpiesofdryairandwatervapor.Theatmosphericairisat℃.（１）Ifisrelativehumidityisequalto60%,thencalculatesuchpropertiesas（２）If℃,thencalculatesuchpropertiesas

Discussion:Todeterminethestateofmoistair,itneedsthreestatepropertiesatleast.(為了確定濕空氣的狀態(tài)，至少需要３個狀態(tài)參數(shù)）Example:

９．熱力學(xué)濕球溫度(Thermodynamicwet-bulbtemperaturet*)t*isthetemperatureatwhichwater(liquidorsolid),byevaporatingintomoistairata

givendry-bulbtemperaturetandhumidityratiod,canbringairtosaturationadiabaticallyatthesametemperaturet*whilethetotalpressurepismaintainedconstant.濕球溫度Wet-bulbTemp.(2)干、濕球溫度法圖5-9干濕球溫度計t-twt-twt=tw=ts(pv)球面上蒸發(fā)熱=對流熱t(yī)w絕熱飽和溫度T2干球溫度,濕球溫度與露點(diǎn)溫度圖5-9干濕球溫度計t=tw=tdTstwtdtt>tw>tdDry-bulb,Wet-bulbandDewPointtemperature7.3濕空氣的焓濕圖ThePsychrometricChart(h-d圖)SaturationLine(飽和濕空氣線）Inaddition,thereareotherlines(還有下列曲線：）1.Linesofconstantenthalpy(定焓線，與y軸成45oC角向下)2.Linesofconstanthumidityratio(定含濕量線，垂直直線)3.Linesofconstanttemperature(定溫線)4.Linesofconstantvolume(定容線)5.Linesofconstantrelativehumidityline(定相對濕度線。)6.Linesofconstantpv和d.(水蒸汽分壓力pv和d關(guān)系曲線)1.焓濕圖的結(jié)構(gòu)d=0干空氣dh(2)

h線(1)d

線

人為將

h

旋轉(zhuǎn)135度

h135度1.焓濕圖的結(jié)構(gòu)dh(3)t

線

正斜率的直線

h等干球溫度線t1.焓濕圖的結(jié)構(gòu)dhht(4)

線ts=99.63oCd1.焓濕圖的結(jié)構(gòu)dhht(5)

線d1.焓濕圖的結(jié)構(gòu)dhht(6)露點(diǎn)tdpv下飽和濕空氣td1.焓濕圖的結(jié)構(gòu)dhht(7)濕球溫度tw絕熱飽和溫度tdtwt(8)等熱濕比線

ProcessLineforAirConditionedSpace

Theroomprocessline,knownalsoasroomratioline(RRL)isdefinedbytheconditionofsuppliedairandthedesiredairconditioninthespace.TheRRLisdependentonbothsensibleandlatentheatload.

1.焓濕圖的結(jié)構(gòu)dhht熱濕比h-d圖上為直線ⅣⅠⅡⅢⅠ:Ⅱ:Ⅲ:Ⅳ:角系數(shù)：過程方向與特征dhht12已知初態(tài)1過程斜率已知可確定終態(tài)twtd不同的B不同的h-d圖7.4濕空氣的熱力過程（ThermodynamicProcessofMoistAir）1.SensibleHeatingProcess(單純加熱過程)

SensibleHeatingProcessisaprocessduringwhichthedry-bulbtemperatureofairisincreased.Theprocessoccursatconstantmoisturecontent.Theairpassesoverahotanddrysurfacewhichmightbepipecoilusingsteamorhotwater,electricalresistanceoranair-to-airheatrecoveryunit.Theloadontheheateris:

BA

加熱過程2.SensibleCoolingProcessatConstantMoistureContent(單純冷卻過程)Sensiblecoolingprocessatconstantmoisturecontentisaprocessduringwhichthedry-bulbtemperatureofairisdecreased.Ifthetemperatureofthecoolingmediumisstillaboveitsdewpointtemperature,then(若冷卻介質(zhì)溫度沒有降到露點(diǎn)以下，則過程前后)：AB冷卻過程Theairpassesoveracoolingcoilwhichuseschilledwaterordirectexpansionofsomerefrigerantintothepipecoil.Iftheairiscontinuouslycooledt