第三章热力学第一定律

(3)热量和功量的相似之处 Similarities between heat and work （
热量和功量是系统与外界能量交换的机理。 Heat and work are energy transfer mechanisms between a system and its surroundings.
mc E ke 2
2
Potential energy is the energy a system possesses as a result of its elevation in a gravitational field.
E p mgz
3.系统的总能量 (Total energy）
m c2 E U Eke E p U m gz 2
(2) Heat is a directional quantity. (热量是有方向的量) Heat addition (加热） is the transfer of heat into a system. Heat rejection（放热） is the transfer of heat out of a system. Formal sign convention: heat addition is positive, „+‟. heat rejection is negative, „-‟. (3) “Adiabatic ” means no heat is transferred （“绝热”意味着没有热量传 递。）. (4) Heat transfer can change the state of the system.（传热可以引起系统状 态的变化。）
热力学能的微观组成
microscopic forms of internal energy
移动 translation 分子动能 转动 rotation 振动 vibration 分子位能 binding forces
热力学能
化学能 chemical energy
核能 nuclear energy
1909年，C. Caratheodory最后完善热一律
能量守恒定律
Conservation of energy principle states that energy can be neither created nor destroyed; it can only change from one form to another but the total amount of energy remains constant.
Both are path functions.（两者都是路径的函数） If the change in a function is dependent on the route taken, then the function is known as a path function.
E = internal energy + kinetic energy + potential energy 1.热力学能U Microscopic energy-----Internal energy U
热力学能指系统所有微观形式的能量之和. Internal energy is defined as the sum of all the microscopic forms of energy of a system.
“第一类永动机是不可能制成的” Perpetual –motion machine of the first kind can be created.
Perpetual –motion machine of the first kind
电 加 热 器 汽轮机
Q
锅 炉
发电机
凝 汽 器
Wnet
给水泵
Qout
On a unit mass basis
1 2 e u eke e p u c gz 2
§3.2 Energy transfer by Heat, Work and Mass (热量、功量及质量引起的能量传递------传递中的能量）
⒈传热和热量（Heat transfer and heat）
第三章 热力学第一定律 Chapter 3. The first law of thermodynamics
3.1系统的宏观和微观储存能 Macroscopic and microscopic energy of system 3.2热量、功量及质量引起的能量传递------传递中的能量 Energy transfer by Heat, Work and Mass 3.3热力学第一定律与闭口系统的能量平衡方程 The first law of thermodynamics and Energy balance equation of closed system 3.4开口系统的能量平衡方程 Energy balance equation of open system 3.5稳态稳定流动的能量平衡 Energy balance for steady-flow systems 3.6工程中的几种稳态稳定流动装置 Some steady-flow engineering devices
The change in energy of a system is equal to the difference between the heat added to the system and the work done by the system.
系统能量的变化量等于加给的热量与系统对外所作 功量之差。 ΔE = Q - W
Heat is energy interaction between a system and its surroundings if its driving force is temperature difference only. 热量是以温差为推动力时，系统与外界之间传递的能量 (1) Heat is energy in transition. （热量是传递中的能量 ） Eg. The baked potato contains energy, this energy is heat transfer only as it passes through the skin of potato to reach the air. Once in the surroundings, the transferred heat becomes part of the internal energy of the surroundings, or vise versa.
work done on a system is negative, ‘-’. That is, energy added to the system, （外界对系统 作功，功为负，即能量加入系统。）
(In defining work, we focus on the effects that the system (e.g. an engine) has on its surroundinห้องสมุดไป่ตู้s.
热力学第一定律的本质 Essence of the First Law of Thermodynamics
Essense：能量转换及守恒定律在热过程中的应用 18世纪初，工业革命，热效率只有1%
1842年，J.R. Mayer阐述热一律，但没有 引起重视 1840-1849年，Joule用多种实验的一致性 证明热一律，于1850年发表并得到公认
2. Macroscopic energy---kinetic energy and potential energy 宏观储存能：动能和势能
They are related to some outside reference frame。
Kinetic energy is the energy a system possesses as a result of its motion relative to some reference frame. It is denoted as Eke..
热力学能的说明
Thermodynamic energy is a state property
热力学能是状态量
U : extensive property 广延参数 [ kJ ]
u : specific properties 比参数

[kJ/kg]
热力学能总以变化量出现热力学能零点人为定义，

功量和热量都要穿越边界。 Both heat and work are boundary phenomena. 系统具有能量，但不是功量或热量 System possess energy, but not heat or work.

两者都是过程量，而不是状态量 Both are associated with a process, not a state.
2.功 ( Energy transfer by Work ）
Work is the energy transfer associated with a force acting through a distance. (1)功量也是传递中的能量 Work is also energy in transition. We can have push-pull work (e.g. in a piston-cylinder, lifting a weight), electric and magnetic work (e.g. an electric motor), chemical work, surface tension work, elastic work, and shaft work.
(2)理想气体热力学能的物理解释
u f (T )
理想气体u只与T有关
热力学能＝内动能＋内位能 T T, v
For ideal gases, there is no bond force between molecules.
理想气体无分子间作用力，热力学能只决定于内动能 ? 如何求理想气体的热力学能 u
能量守恒定律阐明能量既不能被创造，也不能消灭， 它只能从一种形式转换成另一种形式，或从一个系统 转移到另一个系统，而其总量保持恒定。
热力学第一定律
The first law of thermodynamics is viewed as the Conservation of energy principle which governs the energy transfer process from thermal energy to mechanical ones. 热力学第一定律主要说明热能与机械能在转换过 程中的能量守恒
(2) Work is also directional quantity 功量是有方向的量
It is stipulated: work done by a system is positive, ‘+’.
That is, energy leaves the system. ( 系统作功，功为 正，也即能量离开系统。
§3.1系统的宏观和微观储存能 Macroscopic and microscopic energy of system
Energy is a property of every system. It is denoted as E for a system, or e for a system with a unit mass.
（1）分子的动能和势能 Kinetic and potential energies of the molecules
热力学能＝内动能＋内位能 T
T, v
u is a function of the state of the system.
u = u (p, T), or u = u (p, v), or u = u(v,T).