Chemical Engineering ?· 1.ABOUT Chemical Engineering Thermodynamics 1.1 Chemical technology (C.T) Interdisciplinary…

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  • Chemical Engineering

    Thermodynamics

    zhengycg@163.com

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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 couldnt live better than ever before, Chemical engineering

    is closely linked to our daily life:Soap/ detergent, vegetable oil, drug, wine, beverage drinking

    WE couldnt 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

    i

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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 ..

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    3 About content / text3.1

    3.2 J.M.Smith .Chemical engineering thermodynamics

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    (Thermo-dynamics )

    4

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    (1)(2)(3).

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    p, V, T,

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    1V=V(T,P) MM(T,P)

    TP

    2

    3

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    Some terms about thermodynamics

    Extensive property

    Intensive property

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    Closed system Open system isolated system

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    PT

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    Foundation Relationship

    UHSAFGCpCv

    PVT State E.---Virial Equation,Cubic Equation

    ApplicationCalculation 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-

    PVTCpig

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    5

    1.MTP VM=M(T,P)

    2. PVTCigP

    M=MT2P2-MT1P1=M(T2,P2)-Mig(T2,P0) -M(T1,P1)-Mig (T1,P0) +Mig (T2,P0)-Mig (T1,P0)

    #:T1,P1,T2,P2

    T

    (T1,P1)

    (T2,P2)P

    (T1,P0)(T2,P0)

    P0

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    3

    (TP)

    :Virral, van der Waals, Soave

    Cpiga+bT2+cT3+dT4

    4

  • Reference

    1,2001

    2 Introduction to Chemical Engineering ThermodynamicsSmith,J.M

    3.,,

    4. Phase Equalibrium in Chemical Engineering, Stanlney M.Walas