Chpt05 Mod03 Second Law-3(24)

7/29/2019 Chpt05 Mod03 Second Law-3(24)

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Chapter 5 Module3 Slide #

The Second Law of Thermodynamics -The Equivalence of theClausius and Kelvin-Planck Statements of the Second Law

Instructors Visual Aids

Heat, Work and Energy. A First Course in Thermodynamics 2001, F. A. Kulacki

THE SECOND LAW OF

TMERMODYNAMICS-3The Equivalence of the Clausius

and Kelvin-Planck Statements ofthe Second Law


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Clausius statement...


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Clausius statement

It is impossible for anysystem to operate in such a

way that the sole result

would be an energy transfer

by heat from a cooler to a

hotter body.


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Clausius Statement - foundations

Heat will generally flow froma hot region to a cold region,

i.e., in the direction ofdecreasing temperature.

Recall the development of theZeroth Law.


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Clausius Statement - foundations

If we put a cyclic heatpump between two thermal

reservoirs, then we can getheat to flow toward the

higher temperature.


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Wcycle

High Temperature reservoir

Low Temperature Reservoir

Q1

Q2

Schematic of heat pump/refrigeration cycle

to raise heat to the high temperature reservoir.

cyclecyclecycle

Cycle Cycle

WQQ

QW

,2,1


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Kelvin-Planck statement...


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Kelvin-Planck Statement

It is impossible for any system to

operate in a thermodynamic cycle

and deliver a net amount of workto its surroundings while

receiving energy by heat transferfrom a single thermal reservoir.


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Kelvin-Planck statement - foundations

Mass

Pulley

Thermal ReservoirQ1Q2

System

cycleW

cycle cycle

WQ But.these types of systemsare never practically possible.


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Equivalence...The internal self consistency of the

two statements of the Second Law


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The two statements of the

Second Law are internallyconsistent, or equivalent.

Assume a violation of one

form and prove the

violation of the other.


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Heat flow from a low toa higher temperature: A

violation of the Clausius

Statement

Cyclic heat engine, E, is

added to produce work.

TH

TC

Q

TH

TC

Q E

cycleW

Q


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Cyclic heat engine, E, violates the Kelvin-Planck form

of the Second Law.

The net effect is

the extraction

of heat from the

reservoir at

THand theperformance of an

equal amount of

work, Wcycle.

cycleW

E

TH

TC

cycleWQ

Q

Q


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Assume that a cyclic engine exists that withdraws heat

from a single reservoir and does and equivalent amountof work and thus violates the Kelvin-Planck form of the

Second Law.

Q

QWcycle

TH

E

CycleCycleCycle

Cycle Cycle

WQQ

WQ

,2,1


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cycleWQ cycleHC WQ

TC

cycleW

TH

E

HCQ

Cyclic heat engine, E, plus the refrigerator violates the

Clausius form of the Second Law. The net effective is

the transfer of heat QC-Hfrom a low to high

temperature without net work being done.


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Key concepts and terms

The Second Law - Clausius Statement

The Second Law - Kelvin-Planck

Statement

Chpt05 Mod03 Second Law-3(24)

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