第三章 热力学第一定律Chapter 3. The first law of .
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热力学能总以变化量出现，热力学能零点人为定义
2.宏观储存能：动能和势能
Macroscopic energy---kinetic energy and potential energy
They are related to some outside reference frame。
Kinetic energy is the energy a system possesses as a
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.
热力学第一定律的本质 Essence of the First Law of Thermodynamics
本质：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
E p mgz
3.系统的总能量 (Total energy）
E
U
Eke
Ep
U
mc 2 2
mgz
On a unit mass basis
e
u
eke
ep
u
1 c2 2
gz
§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）
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.
⒈传热和热量（Heat transfer and heat）
热量是以温差为推动力时，系统与外界之间传递的能量 Heat is energy interaction between a system and its surroundings if its driving force is temperature difference only.
热力学第一定律
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 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.
result of its motion relative to some reference frame. It
wenku.baidu.com
is denoted as Eke...
mc 2 Eke 2
Potential energy is the energy a system possesses as a result of its elevation in a gravitational field.
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。
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.
Energy is a property of every system. It is denoted as E for a system, or e for a system with a unit mass.
E = internal energy + kinetic energy + potential energy
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 surroundings.
(1) 热量是传递中的能量（Heat is energy in transition. ）
Eg. The baked potato contains energy, this energy is heat transfer only as it passes through the skin of potato to reach the air.
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
分子动能
移动 translation 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
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.
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, a rotating shaft.
（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).
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.
Example. Work vs. heat transfer -- which is which?
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
Can have one, the other, or both? It depends on what crosses the system boundary. For example consider a resistor that is heating a
(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.
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, ‘+’.
(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
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
热力学能的说明
热力学能是状态量 state property
U : 广延参数 [ kJ ] u : 比参数 [kJ/kg]
Once in the surroundings, the transferred heat becomes part of the internal energy of the surroundings, or vise versa.
(2)热量是有方向的量(Heat is directional quantity. )
ΔE = Q - W
“第一类永动机是不可能制成的” Perpetual –motion machine of the first kind
Perpetual –motion machine of the first kind
Q
电
锅
加
炉
热
器
汽轮机
发电机 凝 汽 器
给水泵
Wnet Qout
§3.1系统的宏观和微观储存能 Macroscopic and microscopic energy of system
(2)功量是有方向的量 Work is also directional quantity. (
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。
证明热一律，于1850年发表并得到公认
1909年，C. Caratheodory最后完善热一律
能量守恒定律
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。
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.
2.宏观储存能：动能和势能
Macroscopic energy---kinetic energy and potential energy
They are related to some outside reference frame。
Kinetic energy is the energy a system possesses as a
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.
热力学第一定律的本质 Essence of the First Law of Thermodynamics
本质：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
E p mgz
3.系统的总能量 (Total energy）
E
U
Eke
Ep
U
mc 2 2
mgz
On a unit mass basis
e
u
eke
ep
u
1 c2 2
gz
§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）
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.
⒈传热和热量（Heat transfer and heat）
热量是以温差为推动力时，系统与外界之间传递的能量 Heat is energy interaction between a system and its surroundings if its driving force is temperature difference only.
热力学第一定律
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 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.
result of its motion relative to some reference frame. It
wenku.baidu.com
is denoted as Eke...
mc 2 Eke 2
Potential energy is the energy a system possesses as a result of its elevation in a gravitational field.
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。
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.
Energy is a property of every system. It is denoted as E for a system, or e for a system with a unit mass.
E = internal energy + kinetic energy + potential energy
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 surroundings.
(1) 热量是传递中的能量（Heat is energy in transition. ）
Eg. The baked potato contains energy, this energy is heat transfer only as it passes through the skin of potato to reach the air.
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
分子动能
移动 translation 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
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.
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, a rotating shaft.
（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).
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.
Example. Work vs. heat transfer -- which is which?
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
Can have one, the other, or both? It depends on what crosses the system boundary. For example consider a resistor that is heating a
(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.
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, ‘+’.
(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
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
热力学能的说明
热力学能是状态量 state property
U : 广延参数 [ kJ ] u : 比参数 [kJ/kg]
Once in the surroundings, the transferred heat becomes part of the internal energy of the surroundings, or vise versa.
(2)热量是有方向的量(Heat is directional quantity. )
ΔE = Q - W
“第一类永动机是不可能制成的” Perpetual –motion machine of the first kind
Perpetual –motion machine of the first kind
Q
电
锅
加
炉
热
器
汽轮机
发电机 凝 汽 器
给水泵
Wnet Qout
§3.1系统的宏观和微观储存能 Macroscopic and microscopic energy of system
(2)功量是有方向的量 Work is also directional quantity. (
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。
证明热一律，于1850年发表并得到公认
1909年，C. Caratheodory最后完善热一律
能量守恒定律
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。
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.