《第七章湿空气》由会员分享，可在线阅读，更多相关《第七章湿空气（42页珍藏版）》请在金锄头文库上搜索。
1、Chapter 7. Moist Air (第章湿空气）第章湿空气）o7.1 Introduction (介绍介绍)o7.2 Properties of Moist Air （湿空气的参数）（湿空气的参数）o7.3 H-d Diagram of Moist Air （湿空气的（湿空气的H-d 图图)o7.4 Thermodynamic Process of Moist Air （湿空气的热力过程）（湿空气的热力过程）湿空气湿空气（干空气干空气水蒸气水蒸气） 空调、通风、烘干、空调、通风、烘干、冷却塔冷却塔、储存、储存 湿空气与一般理想混合气体的湿空气与一般理想混合气体的最大区别最大区别是：是：
2、水蒸气的成分可能变化水蒸气的成分可能变化。分压低分压低理想混合气体理想混合气体Dry airAtmospheric air7.1 Introduction (介绍介绍)Definition of Atmospheric Air（湿空气的定义）（湿空气的定义）Dry air + Water vapor (Moisture) =Atmospheric Air(含有水蒸汽的空气称为湿空气。含有水蒸汽的空气称为湿空气。)Air that contains no water vapor is called dry air.(完全不含水蒸汽的空气称为干空气。完全不含水蒸汽的空气称为干空气。)2. Char
3、acteristics of Moisture Air (湿空气的特点湿空气的特点) Atmospheric air contains a very small amount of water vapor. The partial pressure of water vapor is very low so that water vapor in the atmospheric air is always at superheated state. Thus, water vapor can be treated as ideal gas. (湿空气中水蒸汽含量很小，分压力很低，常处于过热状态
4、，可以湿空气中水蒸汽含量很小，分压力很低，常处于过热状态，可以当作理想气体来处理。当作理想气体来处理。) Atmospheric air can be treated as a binary mixture (二元混合物） of ideal gases, dry air and moisture Rda =8314.41/28.9645=287.055J/(kgK)Rw =8314.41/18.01528=461.520J/(kgK)Dry air:pdaV= mdaRdaTWater vapor:pwV= mdaRwT饱和蒸汽饱和蒸汽(1)未饱和湿空气未饱和湿空气(Unsaturated A
5、ir): Dry air+ Superheated water vapor过热蒸汽过热蒸汽水蒸气水蒸气干空气干空气过热过热水蒸气水蒸气pv ps(T)Tspvps加入水蒸气加入水蒸气，pv3. Saturated Air and Unsaturated Air (未饱和空气和饱和空气未饱和空气和饱和空气)未饱和湿空气未饱和湿空气(2)饱和湿空气饱和湿空气(Saturated air)干空气干空气饱和饱和水蒸气水蒸气pv ps(T)Tsps温度一定，不能再加温度一定，不能再加入水蒸气入水蒸气Saturated Air: Dry air+Saturated water vapor (饱和湿空气：干
6、空气和饱和水蒸汽的混合物。饱和湿空气：干空气和饱和水蒸汽的混合物。)饱和湿空气饱和湿空气(3)从未饱和到饱和的途径从未饱和到饱和的途径TspvpsA. T 加水蒸气加水蒸气, pvabC. pv 不变，不变，Ta ba ddcB. pv ，Ta cD. va ee结露结露Td 露点温度露点温度7.2 湿空气的参数湿空气的参数Properties of Moist Air The barometric pressure of atmospheric air vary considerably with altitude as well as with local geographic and w
7、eather conditions.1. Pressure of atmospheric air-500107.4780101.32550095.461100089.875150084.556200079.495250074.682300070.108400061.640500054.020600047.181700041.061800035.600900030.7421000026.4361200019.2841400013.786160009.632180006.556200004.328lThe partial pressure of water vapor is also called
8、 vapor pressure.2.干球温度干球温度 (Dry-bulb temperature) It is the temperature of moist air. The dry-bulb temperature of water vapor and dry air is the same. It is denoted as t.3.露点温度露点温度(Dew-point Temperature) It is defined as the temperature at which condensation begins when the air is cooled at constant
9、 pressure. In other words, it is the saturation temperature of water corresponding to the vapor pressure.结露结露:A点表示未饱和湿空气中水蒸汽的状态，若保持空气点表示未饱和湿空气中水蒸汽的状态，若保持空气中水蒸汽的含量（中水蒸汽的含量（pv）不变，降低温度，使之达到）不变，降低温度，使之达到pv对应的饱和温度对应的饱和温度ts，则湿空气成为饱和湿空气，为点，则湿空气成为饱和湿空气，为点B。若继续降温，水分析出，称为结露。若继续降温，水分析出，称为结露。 露点露点:B点所对应的点所对应的pv
10、下的饱和温度成为露点，用下的饱和温度成为露点，用td表示。表示。4.相对湿度相对湿度 (Relative Humidity of Air)定义：湿空气中实际包含的水蒸汽量与同温度下最多能定义：湿空气中实际包含的水蒸汽量与同温度下最多能包含的水蒸汽量的百分比。包含的水蒸汽量的百分比。The relative humidity is defined as the ratio of the amount of moisture in the air to the maximum amount of moisture the air can hold at the same temperature.
11、If we use “a”、“v”、“s” denoting dry air, water vapor and saturated water vapor respectively, then (若用下标若用下标“a”、“v”、“s”表表示干空气、水蒸汽和饱和水蒸汽的参数，则有：示干空气、水蒸汽和饱和水蒸汽的参数，则有：) 1 饱和湿空气饱和湿空气 ( Saturated Moist Air)在相同的温度下在相同的温度下： 0 干空气干空气 (dry air)0 tw tdDry-bulb, Wet-bulb and Dew Point temperature7.3 湿空气的焓湿图湿空气的焓湿
12、图The Psychrometric Chart (h-d图图)Saturation Line (饱和湿空气线）饱和湿空气线）In addition, there are other lines(还有下列曲线：）还有下列曲线：）1. Lines of constant enthalpy (定焓线，与定焓线，与y轴成轴成45oC角向下角向下)2. Lines of constant humidity ratio (定含湿量线，垂直直线定含湿量线，垂直直线)3.Lines of constant temperature (定温线定温线)4. Lines of constant volume ( 定
13、容线定容线)5. Lines of constant relative humidity line( 定相对湿度线。定相对湿度线。)6. Lines of constant pv和和d. (水蒸汽分压力水蒸汽分压力pv和和d关系曲线关系曲线 )1.1.焓湿图焓湿图的的结构结构d=0 干空气干空气dh(2) h 线线(1) d 线线 人为将人为将 h 旋转旋转135度度 h135度度1.1.焓湿图焓湿图的的结构结构dh(3) t 线线 正斜率的直线正斜率的直线 h等干球温度线等干球温度线t1.1.焓湿图焓湿图的的结构结构dhht(4) 线线ts=99.63oCd1.1.焓湿图焓湿图的的结构结构d
14、hht(5) 线线d1.1.焓湿图焓湿图的的结构结构dhht(6)露点露点 tdpv下饱和湿空气下饱和湿空气td1.1.焓湿图焓湿图的的结构结构dhht(7) 湿球温度湿球温度tw绝热饱和温度绝热饱和温度tdtwt(8) 等热湿比线等热湿比线Process Line for Air Conditioned SpaceThe room process line, known also as room ratio line (RRL) is defined by the condition of supplied air and the desired air condition in the s
15、pace.The RRL is dependent on both sensible and latent heat load.1.焓湿图焓湿图的的结构结构dhht热湿比热湿比h-d图上为直线图上为直线: : : :角系数：过程方向与特角系数：过程方向与特征征dhht12已知初态已知初态1过程斜率已知过程斜率已知可确定终态可确定终态twtd不同的不同的B不同的不同的h-d图图7.4 湿空气的热力过程湿空气的热力过程（Thermodynamic Process of Moist Air ）1. Sensible Heating Process (单纯加热过程加热过程)SensibleHeatin
16、gProcessisaprocessduringwhichthedry-bulbtemperatureofairisincreased.Theprocessoccursatconstantmoisturecontent.Theairpassesoverahotanddrysurfacewhichmightbepipecoilusingsteamorhotwater,electricalresistanceoranair-to-airheatrecoveryunit.Theloadontheheateris:BA 加热过程加热过程2. Sensible Cooling Process at Co
17、nstant Moisture Content (单纯冷却过程单纯冷却过程)Sensible cooling process at constant moisture content is aprocess during which the dry-bulb temperature of air is decreased. If the temperature of the cooling medium is still above its dew point temperature, then(若冷却介质温度没有降到露点以下，则过程前后若冷却介质温度没有降到露点以下，则过程前后)：AB冷却过
18、程冷却过程The air passes over a cooling coil which uses chilled water or direct expansion of some refrigerant into the pipe coil. If the air is continuously cooled to a temperature which below its dew-point temperature, then water vapor will condense.(温度下降到露点以后，继续降温，析出水分，减小含湿量。)CAB3. Sensible Cooling wit
19、h Dehumidification (冷却去湿冷却去湿)4. Humidification Process (加湿过程加湿过程)由于水的由于水的焓值很小，可以忽略不很小，可以忽略不计，所以可以看作加湿之后，所以可以看作加湿之后焓不不变，在，在h-dh-d图上是沿着定上是沿着定焓线向向d d增大的方向增大的方向进行（行（过程程1-21-2）。）。 (1) Adiabatic Humidification Process (绝热加湿过程绝热加湿过程)(2) Isothermal Humidification Process (等温加湿等温加湿)5. Mixing of Two Air Strea
20、ms (混合过程混合过程)例题例题(Example)dh12已知空气的已知空气的t1=20oC， p1=0.1MPa将其加热至将其加热至t2=50oC，后送入干燥后送入干燥室，从干燥室排出时室，从干燥室排出时t3=30oC，求：求：1）2）从干燥室每吸收）从干燥室每吸收1kg水分所需空水分所需空气量和加热量气量和加热量h2h13Solution:dh12h2h13根据根据t1=20oC，p1=0.1MPa，查图查图d1=8.9g水蒸气水蒸气/kg(d.a.)h1=42.8kJ/kg(d.a.)根据根据d2=d1, t2=50oC查图查图h2=73.5kJ/kg(d.a.)根据根据h3=h2, t3=30oC查图查图d3=17.0g水蒸气水蒸气/kg(d.a.)dh12h2h13含含1kg干空气的湿空气所吸收水分干空气的湿空气所吸收水分每吸收每吸收1kg水分所需干空气水分所需干空气每吸收每吸收1kg水分所需湿空气水分所需湿空气每吸收每吸收1kg水分所需加热量水分所需加热量
