湿空气性质Word格式.docx
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湿空气性质Word格式.docx
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(3)通用气体常数Rm:
推导:
将理想气体状态方程两边都乘以分子量:
p1μ1v1=μ1R1T1p2μ2v2=μ2R2T2
根据阿佛伽德罗定律,在p1=p2,T1=Tp2时,μ1v1=μ2v2,因此有μ1R1=μ2R2
由此可知,对于任何气体μR都是一个不变量,称为通用气体常数,记Rm=μR
由此可以很容易计算任何气体的气体常数R=Rm/μ
4、道尔顿分压定律:
混合气体的总压力等于各组分气体的分压力之和,如干空气由78%氮气,21%氧气和1%的氩气组成,,那么干空气的压力P=PN+PO+PAr
二、湿空气的热力学性质
1、湿空气的组成:
组成空气的成分很多,但空调技术主要关心水蒸气和干空气,干空气的组成成分:
氮–78.084;
氧气–20.9476;
氩–0.934;
二氧化碳–0.0314;
氖–0.001818;
氦–0.000524;
甲烷–0.00015;
硫二氧化物–0到0.0001;
氢–0.00005;
和如氪、氙、和臭氧等较少的成份–0.0002。
这些组分在全部的空调处理过程中数量、相态都保持不变,可以当成一个整体来对待,其平均分子量为μa=28.9645。
水蒸气虽然在空气中占用的份额不大,但对空调技术来讲确是意义重大,其平均分子量为μw=18.01528。
因此,干空气的气体常数为Ra=8314.6594/28.9645=287.0638J/(kg.k),水蒸气的气体常数为Rw=8314.6594/18.01528=461.5337J/(kg.k)
2、湿空气的常见状态参数:
(1)压力:
空气压力随海拔,季节。
天气而变化。
大气压力和温度随海拔变化规律:
p=101.325(1-2.5577×
10-5Z)5.2559
t=15-0.0065×
Z
其中Z=高度,m
P=大气压力,kPa
t=温度,K
资料源自于国家航空暨太空总署(NASA)(1976),从-5000m到11000m是精确的。
(2)温度:
华氏温度和摄氏温度关系:
F=C*9/5+32
热力学温度和摄氏温度关系:
T=t+273.15
(3)含湿量d:
定义:
每公斤干空气中所包含的水蒸气的质量称为含湿量d。
公式:
即:
(4)绝对湿度Z:
每立方米所含的水蒸气的质量,kg/m3
实际上就是水蒸气的密度。
(5)相对湿度
:
空气中水蒸气量的最大限度:
一定温度下,当湿空气中所包含的水蒸气分压力达到该温度下水的饱和压力时,水蒸气量不可能在增加,否则水蒸气就是不稳定的,会有水滴凝结出来(结露)。
饱和水蒸气温度-压力关系类似于氟利昂,可通过下式计算,或查表:
溫度範圍由-100到0℃冰的飽和壓力:
ln(pws)=C1/T+C2+C3T+C4T2+C5T3+C6T4+C7ln(T)
其中
C1=-5.6745359×
103
C2=6.3925247
C3=-9.6778430×
10-3
C4=6.2215701×
10-7
C5=2.0747825×
10-9
C6=-9.4840240×
10-13
C7=4.1635019
溫度範圍由0到200℃液態水的飽和壓力:
ln(pws)=C8/T+C9+C10T+C11T2+C12T3+C13ln(T)
C8=-5.8002206×
C9=1.3914993
C10=-4.8640239×
10-2
C11=4.1764768×
10-5
C12=-1.4452093×
10-8
C13=6.5459673
在上述两个方程式中,
ln=自然對數
pws=飽和壓力,Pa
T=絕對溫度,K=℃+273.15
相对湿度是空气中水蒸气分压力和同温度下饱和水蒸气分压力之比,
相对湿度表示空气接近饱和的程度,但不表示水蒸气的含量,
越小,表示空气饱和程度小,吸收水汽的能力强;
越大,表示空气饱和程度大,吸收水汽的能力弱;
=100%时,表示空气已是饱和状态,不能再吸收水分了。
(6)焓h:
湿空气的焓由两部分组成:
干空气的焓:
hg=Cpgt,Cpg=1.005kJ/(kg.C)是干空气的定压比热,以0℃干空气作为干空气焓值零点;
水蒸气的焓:
hw=r+Cpwt,=1.84J/(kg.C)是水蒸气定压比热,r=2501kJ/kg是水在0℃的汽化潜热,以0℃液态水作为水的焓值零点;
考虑到干空气和水蒸汽的组分,得到湿空气的焓:
h=hg+d*hw=Cpgt+d(r+Cpwt)kJ/kg干空气
(7)密度ρ和比容v:
(8)湿球温度ts:
A、热力湿球温度:
如右图,经过足够长的时间,在整个系统平衡后,水温tw等于空气出口温度ts*,对空气来讲,下式成立:
h+(ds*-d)hw*=hs*
式中
hw*:
温度ts*的水的焓,即温度为ts*的水的焓hw*=Cpwt,Cpw=4.186KJ/kg.C,为水的比热
hs*:
空气出口状态的焓,即温度为ts*的饱和空气焓
ds*:
空气出口状态的含湿量,即温度为ts*的饱和空气的含湿量
h:
空气进口状态的焓
d:
空气进口状态的含湿量
由以上关系式决定的温度值ts*即为热力学湿球温度,它与测量方法无关。
B、湿球温度ts:
由于测试手段所限,用干湿球方法所测得的湿球温度不可能与热力湿球温度,要精确测定时,必须采用通风干湿球温度计,干湿球温度计测得的相对湿度可按下式计算:
式中
表示测定的湿球温度ts下的饱和水蒸汽压力,Pa,
表示干球温度t下的饱和水蒸汽压力,Pa,p是空气压力,Pa,A值按下式计算:
,v是空气流速,m/s,试验要求v≥2.5-4m/s。
(9)露点温度td:
维持非饱和的湿空气的压力和含湿量不变,给空气降温,在温度达到某一数值后,开始由凝结水出现,刚开始结露点的温度就成为露点温度td.
露点温度td只决定于空气的含湿量d,它对应于含湿量d相应的饱和空气温度,可按下式估算:
当露点温度范围在0到93℃时:
td=C14+C15α+C16α2+C17α3+C18(Pw)0.1984
露点温度低于0℃时:
td=6.09+12.608α+0.4959α2
td=露点温度,℃
α=ln(Pw),Pw=水蒸汽分压,kPa
C14=6.54
C15=14.526
C16=0.7389
C17=0.09486
C18=0.4569
三、湿空气的焓湿图与换热器处理中的空气处理过程:
1、焓湿图:
焓湿图中反映的参数:
p,t,d,ρ,φ,h,pw
坐标轴:
横坐标d,纵坐标h,坐标轴夹角大于等于135度
等温线
等相对湿度线
水蒸汽分压力
热湿比线ε=Δh/Δd
2、换热器处理中的空气处理过程:
a、干式加热(冷凝工况) b、干式冷却(蒸发工况:
蒸发/水度高)
c、冷却结露(蒸发/水温度适中)d、冷却结霜(蒸发温度过低):
表冷器的热交换效率:
,t0是进口冷媒温度
表冷器的接触系数:
水在饱和状态之热力性质
绝对比容,m3/kg焓,kJ/kg熵,kJ/(kg.K)
温度压力,
t,kPaSat.LiquidEvap.Sat.VaporSat.LiquidEvap.Sat.VaporSat.LiquidEvap.Sat.VaporTemp.,
℃pvf/vfvfg/vfgvghf/hfhfg/hfghgsf/sfsfg/sfgsg℃
-600.001080.00108290942.0090942.00-446.402836.272389.87-1.685413.306511.6211-60
-590.001240.00108279858.6979858.69-444.742836.462391.72-1.766713.245211.5677-59
-580.001410.00108270212.3770212.37-443.062836.642393.57-1.669813.814511.5147-58
-570.001610.00108261805.3561805.35-441.382836.812395.43-1.662013.124311.4623-57
-560.001840.00108254469.3954469.39-439.692836.972397.28-1.654213.064611.4104-56
-550.002090.00108248061.0548061.05-438.002837.132399.12-1.646413.005411.3590-55
-540.002380.00108242455.5742455.57-436.292837.272400.98-1.638612.946811.3082-54
-530.002710.00108337546.0937546.09-434.592837.422402.83-1.630812.888611.2578-53
-520.003070.00108333242.1433242.14-432.872837.552404.68-1.623012.830911.2079-52
-510.003480.00108329464.6729464.67-431.142837.682406.53-1.615312.773811.1585-51
-500.003940.00108326145.0126145.01-429.412837.802408.39-1.607512.717011.1096-50
-490.004450.00108323223.6923223.70-427.672837.912410.24-1.599712.660811.0611-49
-480.005030.00108320651.6820651.69-425.932838.022412.09-1.591912.605111.0131-48
-470.005680.00108318383.5018383.51-424.272838.122413.94-1.584212.549810.9656-47
-460.006400.00108316381.3516381.36-422.412838.212415.79-1.576412.494910.9185-46
-450.007210.00198414612.3514512.36-420.652838.292417.65-1.568612.440510.8719-45
-440.008110.00108413047.6513047.66-418.872838.372419.50-1.560912.386610.8257-44
-430.009110.00108411661.8511661.85-417.092838.442421.35-1.553112.333010.7799-43
-420.010220.00108410433.8510433.85-415.302838.502423.20-1.545312.279910.7346-42
-410.011470.0010849344.259344.25-413.502838.552425.05-1.537612.227310.6897-41
-400.012850.0010848376.338376.33-411.702838.602426.90-1.529812.175010.6452-40
-390.014380.0010857515.867515.87-409.882838.642428.76-1.522112.123210.6011-39
-380.016080.0010856750.366750.36-508.072838.671430.61-1.514312.071810.5575-38
-370.017960.0010856068.166068.17-406.242838.702432.46-1.506612.020810.5142-37
-360.020040.0010855459.825459.82-404.402838.712434.31-1.498811.970210.4713-36
-350.022350.0010854917.094917.10-402.562838.732436.16-1.491111.919910.4289-35
-340.024900.0010854432.364432.37-400.722838.732438.01-1.483311.870110.3868-34
-330.027710.0010853998.713998.71-398.862838.722439.86-1.475611.820710.3451-33
-320.030820.0010863610.713610.71-397.002838.712441.72-1.467811.771610.3037-32
-310.034240.0010863263.203263.20-395.122838.692443.57-1.460111.722910.2628-31
-300.038020.0010862951.642951.64-393.252838.662445.42-1.452411.674610.2222-30
-290.042170.0010862672.032672.03-391.362838.632447.27-1.444611.626610.1820-29
-280.046730.0010862420.892420.89-389.472838.592449.12-1.436911.479010.1421-28
-270.051740.0010862195.232195.23-387.572838.532450.97-1.429111.531810.1026-27
-260.057250.0010871992.151992.15-385.662838.482452.82-1.421411.484910.0634-26
-250.063290.0010871809.351809.35-383.742838.412454.67-1.413711.438310.0246-25
-240.069910.0010871644.591644.59-381.342838.342456.52-1.405911.39219.9862-24
-230.077160.0010871495.981495.98-379.892838.262458.37-1.398211.34629.9480-23
-220.085100.0010871361.941361.94-377.952838.172460.22-1.390511.30079.9102-22
-210.093780.0010871240.771240.77-376.012838.072462.06-1.382811.25559.8728-21
-200.103260.0010871131.271131.27-374.062837.972463.91-1.375011.21069.8356-20
-190.113620.0010881032.181032.18-372.102837.862465.76-1.367311.16619.7988-19
-180.124920.001088942.46942.47-370.132837.742467.61-1.359611.12189.7623-18
水在饱和状态之热力性质
-170.137250.001088861.17861.18-368.152837.612469.46-1.351811.07799.7261-17
-160.150680.001088787.48787.49-366.172837.472471.30-1.344111.03439.6902-16
-150.165300.001088720.59720.59-364.182837.332473.15-1.336410.99109.6546-15
-140.181220.001088659.86659.86-362.182837.182474.99-1.328710.94809.6193-14
-130.198520.001089604.65604.65-360.182837.022476.84-1.321010.90539.5844-13
-120.217320.001089554.45554.45-358.172836.852478.68-1.323210.86299.5497-12
-110.237740.001089508.75508.75-356.152836.682480.53-1.305510.82089.5153-11
-100.259900.001089467.14467.14-354.122836.492482.37-1.297810.77909.4812-10
-90.283930.001089429.21429.21-352.082836.302484.22-1.290110.73759.4474-9
-80.309980.001090394.64394.64-350.042836.102486.06-1.282410.69629.4139-8
-70.338190.001090363.07363.07-347.992835.892487.90-1.274610.65529.3806-7
-60.368740.001090334.25334.25-345.932835.682489.74-1.266910.61459.3476-6
-50.401760.001090307.91307.91-343.872835.452491.58-2.259210.47419.3149-5
-40.437470.001090283.83283.83-341.802835.222493.42-1.251510.53409.2825-4
-30.476060.001090261.79261.79-339.722834.982495.26-1.243810.49419.2503-3
-20.517720.001091241.60241.60-337.632834.722497.10-1.236110.45449.2184-2
-10.562670.001091223.11223.11-335.532834.472498.93-1.228410.41519.1867-1
00.611150.001091206.16206.16-333.432834.202500.77-1.220610.37609.15530
00.61120.001000206.141206.143-0.042500.812500.77-0.00029.15559.15530
10.65710.001000192.455192.4564.182498.432502.610.01539.11349.12861
20.70600.001000179.769179.7708.392496.052504.450.03069.07169.10222
30.75800.001000168.026168.02712.602493.682506.280.04599.03029.07613
40.81350.001000157.137157.13816.812491.312508.120.06118.98909.05014
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