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CDB2033 Chemical Engineering

Thermodynamics

By AP Dr. Lau Kok Keong

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INTRODUCTION

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Dr. Lau Kok KeongRoom 04-03-29

E-mail: laukokkeong@petronas.com.my

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Lecturers

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3 Credit Values:

3 hours of lecture/week

1 hours of tutorial/week

Project/Assignment/Quiz 10%

Test 30%

Final examination 60%

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Course Layout & Schedule

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4

Course Layout & Schedule

CDB2033 Chemical Engineering Thermodynamics

CDB2024 (Group 1) - Jan 2016

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Smith J. M., Van Ness H. C. and Abbott M. M.,

Introduction to Chemical Engineering

Thermodynamics, 7th Ed., McGraw-Hill, 2005.

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Reference

CDB2033 Chemical Engineering Thermodynamics

When I get a little money,I buy books;

and if anyis left,

I buy foodand clothes.- Desiderius Erasmus (1466-1536)

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By the end of this lecture, you are expected to:

Know the scope of thermodynamics

Understand fundamental for the intensive

and extensive properties

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Learning Outcome

CDB2033 Chemical Engineering Thermodynamics

Note: For easy reference, numbers assigned to equations are equivalent to Smith et al. 2005

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What is thermodynamics?

thermo means heat, dynamics means power

use the power of heat to produce work

Relate energy and works, state properties (P,V,T), and

equilibrium matter properties (composition, phases).

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Scope of Thermodynamics

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Thermodynamic systems

a system is a bounded entity which consists of an

arrangement of physical components

a system can be classified as open, closed or isolated

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Scope of Thermodynamics

CDB2033 Chemical Engineering Thermodynamics

SYSTEM

SURROUNDINGS

BOUNDARY

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Commonly used measures of amount or size: Mass, m

Number of moles, n

Total volume,

Total volume may be divided by mass or number of moles toyield:

Specific volume,

Molar volume,

Extensive properties depend on the size or amount ofmatter of a system (e.g.: mass, volume, kinetic energy)

Intensive propertiesdo not depend on the size or amount ofmatter of the system (e.g.: pressure, temperature,specific/molar volume, specific/molar density)

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Amount or Size

CDB2033 Chemical Engineering Thermodynamics

11 densityspecificmVV t

11 densitymolarnVV t

tV

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SI unit for force (F): Newton, N representing kg m s-2

Newtons second law

F= ma; where m = mass (kg), a = acceleration (m s-2

)

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Force

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Indicates degree ofhotness

Isothermal constant temperature ( = 0)

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Temperature

CDB2033 Chemical Engineering Thermodynamics

T (K) = t (oC) + 273.15

t(oF) = 1.8 t (oC) + 32

T(R) = t(oF) + 459.67

T(R) = 1.8 T (K)

Figure 1.1: Relations among temperature scales

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Fluid pressure exerted on a surface, =

=

=

=

Pabsolute= Pgauge+ Patmospheric

Isobaric constant pressure( = 0)

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Pressure

CDB2033 Chemical Engineering Thermodynamics

Figure 1.2: Dead-weight gauge

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The work done by a system in terms of observable force and displacementis: dW= F dl

(1.1)

Work can generally be classified as(a) flow work and (b) shaft work

Expansion or compression work can be written as

=

= (1.2)

= (1.3)

For compression, volume change is negative force and displacement are in the same direction work is positive

For expansion, work is negative volume change is positive force and displacement are in opposite directions work is negative

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Work

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Energy can bestoredin various macroscopic forms, can betransformed

from one form to another and can betransferredbetween systems.

Units of all forms of energy are joules or newton-meters (SI)

Forms ofmechanical energy which can be converted into work are:

Kinetic energy, 1

22 (1.5)

Potential energy, (1.7)

Work of accelerating a body, = =

2Work done on elevating a body, = =

Only changes of kinetic and potential energy are meaningful since object

speed and elevation must be defined relative to some reference frame and

position.

In a frictionless system,principle of energy conservationcan be used to

equate the change in potential energy to the change in kinetic energy.

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Energy

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When there is atemperature differenceacross a boundary, heat (Q) is the

net energy transferredacross the boundary.

Heat flows from a higher temperature to a lower temperature until

temperatures are equal. When there isno temperature difference, there

isno net transfer of heat.

By convention, heat transfer to a system is positive and heat transfer froma system is negative.

There are three basic mechanisms of heat transfer: conduction,

convection and radiation.

Heat is never stored within a body and exists only as energyin transit

between a system and its surroundings.

When energy in the form of heat is added to a system, it is stored as

kineticandpotential energyof atoms and molecules of a body; not as

heat.

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Heat

CDB2033 Chemical Engineering Thermodynamics