06第六章 水和水蒸气的性质解析

The rate of condensation depends upon the density of vapor in the space above the liquid. (凝结的速率取决于液面上方气相空间气体分子的密度,即蒸气压力)
wc g( ) f ( pv )
Liquid molecule has to overcome the surface tension to become vapor, therefore vaporization consumes energy. ( 液相分子必须克服表面张力才能进入气相空间而气化,因此气化是要耗 能的)
The sublimation line separates the solid and vapor regions;
The vaporization line separates the liquid and vapor it ends at the critical point.
The melting line
regions;
separates the solid and liquid regions;
The three lines meet at the triple point. Triple point(三相点）：all three phases coexist in equilibrium. (三种相态以平衡共存) Critical point (临界点): The point at which the saturated liquid and saturated vapor states are identical. No distinction can be made between liquid and vapor phases above the critical point. (临界点就是气相与液相一致的状态点,温度高于临界 点之上,气相与液相没有明显的区别)
过热器
汽轮机
因固相不流动， 更关心汽液两相锅Leabharlann 炉发电机 凝 汽 器 给水泵
冰蓄冷
§6-2 汽化与饱和
6.2.1 汽化与凝结
气化(Vaporization): 由液态变成气态的物理过程 (不涉及化学变化) The Process of Changing from liquid into gas/vapor is called vaporization. 凝结(Condensation)： 由气态变成液态的物理过程 The process of changing from gas/vapor into liquid is called Condensation
思考题
1. 溜冰冰刀 2. 北方冬天晾在外边的衣服，是否经过液相
3. 有没有500º C的水？
4. 有没有-3 ℃ 的蒸汽？ 5. 一密闭容器内有水的汽液混合物，对其 加热，是否一定能变成蒸汽？
饱和线、三相线和临界点
饱和液线
临界点
饱和气线
p
三相线
饱和固线
v
T
Vapor and Liquid (汽相和液相)
水和水蒸气是实际气体的代表
在空气中含量极小，当作理想气体 一般情况下，为实际气体，使用图表 18世纪，蒸气机的发明，是唯一工质 直到内燃机发明，才有燃气工质 目前仍是火力发电、核电、供暖、化工的工质 优点: 便宜，易得，无毒， 膨胀性能好，传热性能好 是其它实际气体的代表
水蒸气
§ 6-1 纯物质的热力学面及相图 Pure substance
饱和状态：汽化与凝结的动态平衡
At the equilibrium state, the pressure corresponding to only one temperature. That is, . Saturation temperature 饱和温度Ts 饱和压力ps Saturation pressure
Chapter 6. The property of Water and Vapor (第6章. 水和水蒸气的性质)
6.1 Basic conceptions (基本概念)
6.2 Phase change Process of Pure Substance (纯质的 相变过程)
6.3 Property Tables (水蒸气性质表) 6.4 h-s diagrams for Water Vapor (水蒸气的h-s图) 6.5 Thermodynamic Processes of Water Vapor (水蒸气的热力过程)
物质三种聚集状态：
Solid Liquid Gas
固态、 液态、 气态
水的三态： 冰、
Ice
Water Steam
水、
蒸汽
Phase changes (相变): 任何一种物质都可以经历下列所述的相变. Any kind of substance may undergo various types of phase changes as following : 溶解(Fusion/melting) = solid to liquid 凝固(Freezing) = liquid to solid 气化(Vaporization)= liquid to gas 凝结(Condensation)= gas to liquid 升华(Sublimation) = solid to gas
The equilibrium is called Saturation State.(饱和状态） The properties at this state is called Saturation Properties. (饱和 参数）
Ts
ps
6.2.2 饱和状态Saturation state
wv g1 (T )
The rate of Vaporization depends on the liquid temperature.(气化的速率取决于液相的温度)
wv wc
wv wc
vapori zation(气化）
condensati on (凝结）
wv wc
equilibrium (平衡状态）