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1.ABOUT Chemical Engineering Thermodynamics
1.1 Chemical technology (C.T)Interdisciplinary science, which apply pure science to applied science.
• Importance :WE couldn’t live better than ever before, Chemical engineering
is closely linked to our daily life:Soap/ detergent, vegetable oil, drug, wine, beverage drinking
WE couldn’t imagine modern life without…
antibiotics, fertilizers, agricultural chemicalsagriculture.ppt, special materials, electric power
CH1 INTRODUCTION
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How can we become chemical engineers?
(1) multicomponent thermodynamics and kinetics
(2) transport phenomena
(3) unit operationsunit operation.ppt
(4) reaction engineering
(5) process design and control
(6) plant design and systems engineering
Training developmentThe core curriculum , C.T. include following contents:
1.2 Contents of C.T
Here, I will give a question to you: what do you think of being a C.E. ? terrible, It need master a lot of chemical knowledge.
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2.The scope of Thermodynamics
Born in the 19th century of the need to describe the operation of steam engines and to set forth the limits of what they can accomplish .
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James Watt
James Watt was a Scottish inventor and mechanical engineerwhose improvements to the steam engine were fundamental to the changes brought by the Industrial Revolution in both the Kingdom of Great Britain and the world.
(19 January 1736 – 25 August 1819)
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Subsequent developments using pressurized steam and conversion to rotary motion enabled the powering of a wide range of manufacturing machinery could be obtained. Significantly, this power source would later be applied to mobile devices such as steam tractors and railway locomotives.
Modern steam turbines generate about half of the electric power in the world using a variety of heat sources.
Work is done by steam / gas
spout
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A scale model traction engine– an example of a self-propelled steam engine
A steam engine is a heat engine that performs mechanical work using steam as its working fluid . Steam engines have a long history, going back at least 2000 years.
heat engines using boiling water to produce mechanical motion
prime mover
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Thermodynamics:
1) means heat power ,or power developed from heat. However, such a restriction on its-meaning has long since disappeared .
2)In its broader sense , thermodynamics is the science which deals with transformations of energy of all kinds from one form to another .
3)The general restrictions :fluids meet the first and second laws of thermodynamics.These laws cannot be proved in the mathematical sense. Rather,their validity rests upon experience.
concerned with energy
2.1 characteristic
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• The first law of thermodynamics is simply an expression of the conservation of energy :
Although energy assumes many forms, the total quantity of energy is constant, and when energy disappears in one form it appears simultaneously in other form.
• The 2nd law of thermodynamics asserts that energy has quality as well as quantity; and actual process occurs in the direction of decreasing quality of energy:
(1) No apparatus can operate in such a way that its only effect (in system and surroundings) is to convert heat absorbed by a system completely into work.
(2) Any process which consists solely in the transfer of heat from one temperature to higher one is impossible.
---------2 statements
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The value of thermodynamics lies in
these laws and certain accompanying definitions have been given mathematical expression .This has led to the development of a consistent network of equations from which a wide range of practical results and conclusions may be deduced .
dWdQdU -=1st law
2nd law TdSdQrev =
PVUH += TSUA -= TSHG -=
VdPTdSdH += SdTPdVdA --= SdTVdPdG -=
PdVTdSdU -=
Enthalpy H
Helmholtz A
Gibbs G
Differential energy equations Entropy S
(a) (b) (c)
(2) (3) (4)
(1)
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In each case the basic principles are the same ,but the applications differ. The chemical engineers : to cope with a particularly wide variety of problems:
(1) the determination of heat and work requirements for many physical and chemical processes ,
(2) the determination of equilibrium conditions for (a) chemical reactions (b) the transfer of chemical species between phases .
2.2 Application:
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2.3.Limitations on the thermodynamics method
Thermodynamics considerations
1) are not sufficient to allow calculation of the rates of chemical or physical processes .Because Rates depend on both driving force and resistance. Although driving force are thermodynamic variables, resistance are not .
do not establish
2) offers no clue to the mechanisms of either physical or chemical processes.-------- cannot reveal the microscopic (molecular) mechanisms of physical or chemical processes
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Cause of limitationand training
Results from the lack of sufficient data to allow effective use of thermodynamics.
(1)Numerical results of thermodynamics analysis are accurate only to the extent that required data are accurate.
(2)The chemical engineer must work with a large number of chemical substances, frequently in mixtures, and adequate data are known for only a relatively few. Thus he must learn to estimate result when only meager data are available.
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In spite of these limitations, the science of thermodynamics is
remarkable in the number and variety of conclusions ,that are based on two fundamental laws. All the rest is either definition or deduction.
Thus , in order to apply the thermodynamics method ,one must
★ develop the ability to proceed logically from one deduction to the next ,always making use of precisely defined terms
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2.4.Concluding Remark
• If everything is so simple, why does thermodynamics have the reputation of being hard?
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Concluding Remark
• It is full of hard words and signs and numbers, not very entertaining or understandable looking ...
• The difficulty comes from making precise descriptions of phenomena and in developing a mathematical framework that allows us to cultivate an understanding of the Laws
If you stick to it , you ‘ll get too much
Example:She believed that the springs of action, as Lowes Dickinson once said, lie deep in ignorance and madness. She wished to cultivateher understanding and to be sane ……..她希望养成自己的判断力，保持清醒的头脑
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3 About content / text3.1 陈新志 化工热力学
3.2 J.M.Smith .Chemical engineering thermodynamics
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热力学(Thermo-dynamics )的原始含义：是讨论热与功的转化规律。经典热力学建筑在热力学的三个基本定律之上，运用数学方法，得到热力学性质之间的依赖关系，简单地讲，这种依赖关系就是经典热力学的原理。经典热力学原理在解决工程实际问题中有重要价值。
4 化工热力学的内容及安排
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学习目的是运用经典热力学原理来解决实际问题。具体地讲，所解决的实际问题可以归纳为三类：
(1)过程进行的可行性分析和能量有效利用；(2)平衡问题，特别是相平衡；(3)平衡状态下的热力学性质计算. 特别是流体的性
质随着温度、压力、相态、组成等的变化。
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化工过程经常要与物性打交道，从混合物获得纯组分必须由一定的分离过程来完成，如蒸馏、萃取、结晶等过程的基础就是相平衡及其相平衡状态下的各相的性质。研究流体相平衡、p, V, T,焓、熵等热力学性质及其它们之间的相互关系，是分离过程设计、优化和操作中不可缺少的基础工作。化学反应过程也是同样如此。
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• （1）将热力学参数相互关联起来：V=V(T,P) ，M＝M(T,P) ，从已知的推算未知的。
T和P是最容易获得的性质，从能直接测量的性质推算难以直接测量的性质是我们重要目标之一。
• （2）对实验数据进行补充（完整）：通过热力学性质之间的依赖关系推算其它条件下的数据。例如，从局部的实验数据推算系统完整的信息；从常温、常压下的物性数据来推算苛刻条件下的性质，从容易获得的物性数据来推算较难测定的数据；从纯物质的性质的信息求取混合物的信息等等。
• （3） 校正实验数据。经典热力学提供的各种性质之间的普遍化关系式还是一种检验实验数据质量的手段，从而对实验数据作出评价和筛选。
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经典热力学原理，必须结合反映系统特征的模型，才能应用于解决化工过程的实际问题
Some terms about thermodynamics
★Extensive property
★ Intensive property
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系统与环境：热力学研究的对象总是选择宇宙空间中的一部分，这一部分选定的空间即称为系统，其余部分则是环境。封闭系统Closed system ：与环境之间无物质传递的系统敞开系统 Open system ：与环境之间有物质传递的系统孤立系统isolated system ：与环境之间既无物质又无能量传递的系统
封闭系统是我们最有兴趣的系统之一，它又可以分
为均相封闭系统和非均相封闭系统。均相封闭系统中只有一个相，且与环境之间没有物质传递，它代表了实际中的纯物质及均相定组成混合物。
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封闭系统
非均相封闭：与实际中的相平衡系统相对应。含有多个相，每个相都可以视为均相敞开系统。平衡时，各敞开系统之间通过边界传递物质的速率达到动态平衡，各相的组成、P、T不再发生变化。此时任何一个均相敞开系统都可以视为均相封闭系统
均相封闭：代表了实际中的纯物质．及均相定组成混合物。由均相封闭系统热力学原理和模型的结合来计算
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在本课程的学习中，我们应该强调：热力学原理上的
均相封闭系统——均相纯物质和均相定组成混合物；
非均相封闭系统——多相平衡
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Foundation Relationship
U、H、S、A（F）、G、Cp、Cv
PVT State E.---Virial Equation,Cubic Equation
Application：Calculation of properties of H-H C-O
systems
Activity Coefficient.E－－(1)S-H equation(2)Wilson equation
(3)NRTL equation
(4)UNIQUAC equation
(5) UNIFAC
Th
ermo
dan
amics
Models
Principle
Homogenerious closed/open systems
Hetero-
P、V、T、Cpig
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5 热力学性质计算的一般方法
1.变量分析：M与TP V的关系，M=M(T,P)。
• 2. 原理应用：将热力学性质与能直接测量的PVT性质和理想气体热容Cig
P联系起来。
ΔM=M（T2，P2）-M（T1，P1）=［M(T2,P2)-Mig(T2,P0) ］-［M(T1,P1)-Mig (T1,P0) ］+［Mig (T2,P0)-Mig (T1,P0)］
#例：计算始末态的性质变化:（T1,P1）,（T2,P2）
T
(T1,P1)
(T2,P2)P
(T1,P0)(T2,P0)
P0
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• 3．模型引入
经典热力学原理能给出热力学性质随强度性质(如T，P)
变化的关系式，但这是一般化的关系式，并非是从属变量与独立交量之间的具体公式，具体公式因系统而异，必须引入能表达系统特性的模型方程确定。
如状态方程:Virral, van der Waals, Soave
Cpig＝a+bT2+cT3+dT4
• 4．数学求解
Reference
1．化工热力学,陈新志等，化学工业出版社2001
2． Introduction to Chemical Engineering Thermodynamics，Smith,J.M
3.化工热力学,童景山主编, 清华大学出版社
4. Phase Equalibrium in Chemical Engineering, Stanlney M.Walas
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