工程热力学与传热学(英文) 第1章 基本概念

• •
Single-valued function of the system state. Related with States but have nothing to do with the path from one state to another.
1-2-2 Equilibrium State
(2) Mechanical equilibrium（力平衡）
No motion of a fluid in the different part of the system.
Condition: no pressure differential
(3) Chemical equilibrium（化学平衡）
Ｑ＝０
adiabatic system
system
analysis
any non- isolated system
+
relative surrounding
=
Isolated system
环境
孤立系统
Most systems we discuss are:
The Universe
Simple compressible systems (简单可压缩系统).
Thermodynamics
--- Chapter 1 Basic Conceptions ---
Chapter 1 Basic Conceptions Contents：
Thermodynamic System and Its Classification State and Equilibrium Basic Properties: Pressure, Temperature, Specific volume Quasi-static Process and Reversible Process Work and Heat
4. Example: Simple steam power system
（简单蒸汽动力系统）
Superheater 6 boiler pump 4 3 2 condenser cooler water 1 turbine generator
Processes in heat engine（热机的工作过程）
Absorb heat from higher temperature source Convert some of the heat into work Transfer heat into lower temperature source
1-1-2 Thermodynamic System
1. Thermodynamic System (System )（热力系统）
• Chemical composition does not change with time. • No chemical reactions occur.
(4) Phase equilibrium（相平衡） If a system involves two phases, it is in phase equilibrium when the mass of each phase reaches an equilibrium level and stay there.
（1）Definition: The force exerted by a fluid per unit area，p （2）Units（单位）
SI: Pa (pascal ), kPa Times of the atmospheric pressure: atm, at Height of liquid column: mH2O, mmHg bar, 1kgf/cm2 (in Europe): psi(lbf/in2) ( in English)
思考题
分析下面的说法是否正确： 1.闭口系统具有恒定的质量,但具有恒定质量的系 统不一定就是闭口系统。 2.孤立系统一定是闭口的,反之则不然。 3.孤立系统一定是绝热系统，但绝热系统不一定都 是孤立的。 4.孤立系统的热力学状态不能发生变化。
1-2 Equilibrium State and Properties 1-2-1 Thermodynamic State
2. Conditions（平衡条件）
(1) Thermal equilibrium（热平衡）
• No heat flow in system. • The temperature is the same throughout the • • •
entire system. Condition: no temperature differential
Analysis：“equilibrium” and “uniform”(均匀)
1-2-3 Basis Properties（基本状态参数）
1. Temperature
（1）Thermodynamics definition of temperature（温度） It’s the property to describe if systems are in thermal equilibrium . （2）The zeroth law of thermodynamics（热力学第零定律） If two bodies are in thermal equilibrium with a third body , they are also in thermal equilibrium each other.
The lowest temperature is 0K.
Celsius scale (热力学摄氏温标)
t = T – 273.15 notes ℃
1K= 水的三相点温 度的1/273.16
0 ℃ = 273.15K . On triple point: t = 0.01 ℃.
2. Pressure（压力）
Thermodynamic temperature scale in SI（热力学温标）
Thermodynamic temperature: symbol: T，unit: K. Datum point: the triple point of water.
The value on triple point is 273.16 K.
An open system with one inlet and one exit
出口
（outlet）
The boundary can be real or imaginary, fixed or movable, has no thickness and volume , and does not contain any substance.
（3）Temperature scale （温标） Four temperature scales: • Kelvin scale (SI) • Celsius scale • Fahrenheit scale (English) • Rankine scale Three factors of temperature scale ： • Zero point • Two states point • Scale
1. Thermodynamic state (热力学状态)
Thermodynamic state of substance
state of system
2. Properties (状态参数)
A property is any observable characteristic of a system which is observable while the system is in any one state. notes
（2）Whether energy can cross the boundary a: Simple system (简单系统) A system has only heat and one form work transfer across its boundary. b: Adiabatic system (绝热系统) A system that no heat cross the boundary. c: Isolated system (孤立系统) A system that neither energy nor mass can cross the boundary.
3. Conclusions（结论）
When a system has no unbalanced potential difference within it and its surrounding, the state of the system is equilibrium state. Any non-equilibrium system will reach a state of thermodynamic equilibrium after it has been left to itself long enough.
2. Substance（工质）
In general, the working substances are fluids. Such as: air, steam.
3. Heat Source（热源） • Higher temperature source
• Lower temperature source
(control mass)
system
b: Open system（开口系统 )
boundry
• Both mass and energy can cross the boundary
(control volume )
inlet
closed system
system boundry open system outlet
2. Classifications of System（热力系统分类）
（1）Whether a mass can cross the boundary a：Closed system （闭口系统 )
• No mass can enter or leave a closed system • Energy (in the form of heat, work) can cross the boundary

1-1 Thermodynamic System
1-1-1 Processes that Heat Transfer into Work in Heat Engine（热机中热转化为功的过程） 1. Heat Engine（热机）
Heat engine is a device in which energy is supplied in the form of heat and some of this energy is transformed into work.
A quantity of matter or a region in space for study.
入口 热力系统
（system） （inlet）
热力系统
（system）
边界 （boundary）
环境（外界）
（surrቤተ መጻሕፍቲ ባይዱunding）
边界
（boundary）
A closed system with moving boundary
1. Equilibrium State（平衡状态）
If there are no changes occurred in the state of the system without the aid of an external stimulus, the system is said to be in an equilibrium state. notes a: No properties change with time. b: Only in equilibrium state , we can describe the state of a system with definite properties. c: Thermodynamics deals with equilibrium state.