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3CHAPTERCHAPTER

The First Law ofThermodynamics:

Closed Systems

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Chapter SummaryChapter Summary

The first law of thermodynamics is essentially

an expression of the conservation of energy

principle. Energy can cross the boundaries of

a closed system in the form of heat or work.

If the energy transfer across the boundaries of

a closed system is due

to a temperature difference, it is heat;

otherwise, it is work.

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Chapter SummaryChapter Summary

Heat is transferred in three ways: conduction,convection, and radiation.

Conduction is the transfer of energy from the more

energetic particles of a substance to the adjacent less

energetic ones as a result of interactions between theparticles.

Convection is the mode of energy transfer between a

solid surface and the adjacent liquid or gas that is in

motion, and it involves the combined effects of

conduction and fluid motion. Radiation is the energy emitted by matter in the form of

electromagnetic waves (or photons) as a result of the

changes in the electronic configurations of the atoms

or molecules.

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Chapter SummaryChapter Summary

The three modes of heat transfer are expressed

as:

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Various forms of work are expressed as follows:

Electricalwork: (kJ)

Boundarywork: (kJ)

Gravitationalwork(=DPE): (kJ)

Accelerationwork(=DKE): (kJ)

Shaftwork: (kJ)

Spring work: (kJ)

Chapter SummaryChapter Summary3-25

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Chapter SummaryChapter Summary

For the ploytropicprocess (Pvn = constant) of real

gases, the boundary work can be expressed as:

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Chapter SummaryChapter Summary

The energy balance foranysystemundergoing

anyprocesscan be expressed as:

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Chapter SummaryChapter Summary

The energy balances foranysystemundergoing

anyprocesscan be expressed in the rateformas:

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Chapter SummaryChapter Summary

For a constant-pressureprocess, .

Thus

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Chapter SummaryChapter Summary

The amount of energy needed to raise the

temperature of a unit of mass of a substance by

one degree is called the specificheatatconstant

volume Cv for a constant-volume process and thespecificheatatconstantpressure Cp for a

constant pressure process. They are defined as:

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Chapter SummaryChapter Summary

For ideal gases u, h, Cv, and Cp are functions of

temperature alone. The #uand #h of ideal gases

can be expressed as:

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Chapter SummaryChapter Summary

For ideal gases Cv, and Cp are related by:

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Chapter SummaryChapter Summary

The specificheatratiok is defined as:

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Chapter SummaryChapter Summary

Forincompressiblesubstances(liquids and

solids), both the constant-pressure and constant-

volume specific heats are identical and denoted by

C:

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Chapter SummaryChapter Summary

The uand h of incompressible substances are

given by

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Chapter SummaryChapter Summary

The refrigeration and freezing of foods is a major

application area of thermodynamics.

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Heat TransferHeat Transfer3-1

(Fig. 3-3)

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Adiabatic ProcessAdiabatic Process

(Fig. 3-4)

3-2

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Convection: Heat TransferConvection: Heat Transfer

(Fig. 3-8)

3-3

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Convection: CoolingConvection: Cooling

(Fig. 3-9)

3-4

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RadiationRadiation

(Fig. 3-10)

3-5

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Heat and WorkHeat and Work

(Fig. 3-15)

3-6

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Path FunctionsPath Functions

(Fig. 3-16)

3-7

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Boundary WorkBoundary Work

(Fig. 3-27)

3-8

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Net Work per CycleNet Work per Cycle

(Fig. 3-29)

3-9

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Schematic/Diagram for Ex. 3-8Schematic/Diagram for Ex. 3-8

(Fig. 3-31)

3-10

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Schematic/Diagram for Ex. 3-9Schematic/Diagram for Ex. 3-9

(Fig. 3-32)

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Schematic/Diagram for thePolytropic ProcessSchematic/Diagram for thePolytropic Process

(Fig. 3-33)

3-12

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Schematic/Diagram for Ex. 3-13Schematic/Diagram for Ex. 3-13

(Fig. 3-43)

3-13

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Stretching a Liquid FilmStretching a Liquid Film

(Fig. 3-45)

3-14

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System Energy ChangeSystem Energy Change

(Fig. 3-52)

3-15

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Energy Change for a CycleEnergy Change for a Cycle

(Fig. 3-54)

3-16

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Closed-Systems, First-LawClosed-Systems, First-Law

(Fig. 3-55)

3-17

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Formal Definitions ofCv and CpFormal Definitions ofCv and Cp

(Fig. 3-72)

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Specific Heats for Some GasesSpecific Heats for Some Gases

(Fig. 3-76)

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Three Ways to Calculate uThree Ways to Calculate u3-20

(Fig. 3-80)

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Typical Freezing Curve (food)Typical Freezing Curve (food)

(Fig. 3-91)

3-21