B蒸汽初温对朗肯循环热效率的影响优点

q cvdT pdv
理想气体，任何过程
6. Corollaries of the First Law （热力学第一定律的推论） (1) Work done in any adiabatic (Q=0) process is path independent.
(2) For a cyclic process heat and work transfers are numerically equal
or
7. 稳态稳定流动系统能量方程
1 2 q h2 h1 (c2 c12 ) g ( z2 z1 ) ws 2
As shown in the following figure，it is known that pb=101325Pa, the height difference is H=300mm for mercury liquid. The gauge pressure of B is 0.2543MPa, Then what is the pressure for side A, and what is the value of Pg,A? 已知大气压pb=101325Pa，U型管内 汞柱高度差H=300mm，气体表B读数为 0.2543MPa，求：A室压力pA及气压表A的读数pgA
自发过程(Spontaneous Process)
不需要任何外界作用而自动进行的过程。 A process which can happy naturally without the interference from the surroundings.
5.稳态稳定流动(Steady-flow process)
7.比热容（Specific Heat)
将单位物量的物质温度升高1K所需加入的热量。
The energy required to raise the temperature of a unit quantity of a substance by one degree
8.分容积 ( component volume ) 假定混合气体中组成气体具有与混合气体相 同的温度及压力时，单独存在所占有的容积。 9.分压力（Component pressure） 假定混合气体中组成气体单独存在，并具有 与混合气体相同的温度及容积时的压力
解：
pB pb peB 101325Pa 0.2543 106 Pa 355600Pa
p A H pB (133.32 300) Pa 355600Pa 0.3956MPa
pA pb peA p eA pA pb 0.3956MPa 0.101325MPa 0.2943MPa
A process during which a fluid flows through a control volume steadily. That is, the properties remain the same at a fixed point during the entire process.
3.平均比热 Mean specific heat
c q 求O c 2在100-500℃平均定压热容 (cp ,cv) dt
c=f (t)
ct
t2
1
0.979 500 0.923 100 c 0 t2 cdt 500 100 t2 t t1 ct cdt t 1 t2 t1 c0 0 t t2 t1 c 0 t2 c 0 t1 t2 ct 1 t2 t1
绝对压力与相对压力
absolute pressure
relative pressure
当 p > pb
当 p < pb
表压力 pe Gage pressure 真空度 pv Vacuum pressure
p pe pb p pb pv
pe
p
pb
pv p
Exercise.1 (练习1）---压力的测量
It is the ratio of the flow speed, c, to the velocity of sound in the same fluid at the same state. It is denoted as M. (流体在某一点的运动速度和该点当地声速之比, 以M表示)
20.滞止参数(Stagnation Properties)
4.可逆过程(Reversible process)
系统经历某一过程后，如果能使系统与外界同时恢 复到初始状态，而不留下任何痕迹，则此过程为可 逆过程。 A process that can reversed without leaving any trace on the surroundings. That is, both the system and the surroundings are returned to their initial states at the end of the reverse process.
Point function---Exact differentials--d 一般式 Path function---Inexact differentials--- W Q Q = dU + W Q = U + W
q = du + w q = u + w 单位工质
气体速度为零时的状态称为滞止状态,该状态的参数称为滞止参数.
Stagnation properties represent the enthalpy of a fluid when it is brought to rest adiabatically
21.Critical Pressure Ratio(临界压力比)
6.循环 (Cycle)
If a system returns to its initial state at the end of the process, it is said a system have undergone a cycle. 系统经历了一系列状态变化过程，又回到了原来状态， 称为热力循环。
对开口系统而言，焓指流动工质所携带能量的一部 分，这部分能量取决于热力状态
11.饱和状态 Saturation state
饱和状态：汽化与凝结的动态平衡 12.蒸发（Evaporize）和沸腾（Boiling) 13.干度（Dryness) 14.汽化潜热（Latent heat)
15. 未饱和湿空气(Unsaturated Air) Dry air+ Superheated water vapor 干空气和过热水蒸汽的混合物。 饱和湿空气(Saturated Air) Dry air+ Saturated water vapor 干空气和饱和水蒸汽的混合物。
cp ,O2 100 q cdt = c t (t2 t1 )
t1
1
t2
500
t2
c0
t2 t1
t1
t2
t
4.理想气体u、 h和s的计算
h cp T
理想气体，任何过程
u cv T
T2 v2 s cv ln R ln T1 v1 T2 p2 s cp ln R ln T1 p1 v2 p2 s cp ln cv ln v1 p1
16.露点温度(Dew-point Temperature) It is defined as the temperature at which condensation begins when the air is cooled at constant pressure.
17.相对湿度φ (Relative Humidity of Air) It 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. 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。
5.闭口系统能量方程
适用条件： 1）任何工质 2) 任何过程
可逆闭口系能量方程
w = pdv q = du + pdv
q = u + pdv
简单可压缩系可逆过程
任何工质、可逆过程
q = Tds Tds = du + pdv
热力学恒等式
Tds = u + pdv
理想气体、可逆过程
Emphasis (强调)： pb is the pressure of environment in which the gauge is located (是测压仪表所在环境压力)
2. Equation of State for Ideal Gas （理想气体的状态方程 的应用）
Pv=RT Example. Determine the mass of air in a room whose dimensions are 4m× 5m× 6m at 100kPa and 25℃
22. 绝热节流 (Adiabatically Throttling) 流速为 的气流,由于局部阻力使流体降压膨 胀的现象称为节流, 因流速高,时间短,与外 界换热少,可视作绝热,故称绝热节流.
Critical Point(关键点）:
1. Pressure (压力）
Absolute pressure （绝对压力） Relative pressure （相对压力） Gage pressure （表压力） Vacuum pressure （真空度）
在无限小势差推动下的由连续平衡态组成的过 程，就是准静态过程。 When a process proceeds in such a manner that the system remains infinitesimally close to an equilibrium state at all times, it is called a quasistatic or quasi-equilibrium process.
总复习 (Overall Review)
Basic Concept
1. 系统 (Thermodynamic System): A quantity of matter or a region in space chosen for study. （系统就是指被选做研究对象的物体或空间。） 2. 平衡状态(Equilibrium State)
18.含湿量(Humidity ratio)
含湿量d：以干空气为基准，包含1千克干空气 的湿空气中中所含有的水蒸汽的质量。 The mass of water vapor present in a un Ratio.
19.马赫数：（The Mach number） M,
A system in equilibrium experiences no changes with time when it is isolated from its surroundings. 所谓平衡状态就是指在没有外界影响的情况下，系统 的状态不随时间而发生变化。
3.准静态过程(Quasi-static Process )
10.焓（Enthalpy） Enthalpy, a state function, is defined as follows, h= u + pv This energy is composed of two parts: the internal energy of the fluid (u) and the flow work (pv) associated with pushing the mass of fluid across the system boundary.