080125© m. kostic prof. m. kostic mechanical engineering northern illinois university uniqueness...

080125© M. Kostic <www.kostic.niu.edu>

Prof. Prof. M. KosticM. Kostic Mechanical EngineeringMechanical Engineering

NORTHERN ILLINOIS UNIVERSITYNORTHERN ILLINOIS UNIVERSITY

Uniqueness and Universality Uniqueness and Universality of Heat Transfer:of Heat Transfer:

Challenges and OpportunitiesChallenges and Opportunitiesfor Improving Heat Transfer Processesfor Improving Heat Transfer Processes - -

The Quest and Nature The Quest and Nature of Energy, Heat and Entropyof Energy, Heat and Entropy

PLENARY LECTUREPLENARY LECTURE

The 5th WSEAS International Conference on HEAT and MASS TRANSFER The 5th WSEAS International Conference on HEAT and MASS TRANSFER ((WSEAS - HMT'08WSEAS - HMT'08))

Acapulco, Mexico, January 25-27, 2009Acapulco, Mexico, January 25-27, 2009


Focus and GoalFocus and Goal::

Focuses on Focuses on philosophical and practicalphilosophical and practical aspects aspects of energy and entropy, of energy and entropy, with emphasis on with emphasis on reversibility and irreversibility, and reversibility and irreversibility, and

goal to establish the concept of goal to establish the concept of ““reversible heat transferreversible heat transfer,” ,” regardless that heat transfer regardless that heat transfer is a typical irreversible process. is a typical irreversible process.


Heat transfer isHeat transfer is Unique and Unique and UniversalUniversal::

Heat transferHeat transfer is a is a spontaneous irreversible processspontaneous irreversible process where all organized (structural) energies are where all organized (structural) energies are disorganized or dissipated as disorganized or dissipated as thermal energythermal energy with with irreversible loss of energy potential (from high to irreversible loss of energy potential (from high to low temperature) and overall entropy increase.low temperature) and overall entropy increase.

Thus, heat transfer and thermal energy are Thus, heat transfer and thermal energy are unique and universal manifestation of all unique and universal manifestation of all natural and artificial (man-made) processes, natural and artificial (man-made) processes,

… … and thus … are vital for and thus … are vital for more efficientmore efficient cooling and cooling and heating heating in new and critical applicationsin new and critical applications, including , including energy production and utilization, environmental energy production and utilization, environmental control and cleanup, and bio-medical applications. control and cleanup, and bio-medical applications.


ObjectiveObjective::

… … to emphasize to emphasize knownknown, , but but not so well-recognizednot so well-recognized issues issues about entropy, irreversibility and about entropy, irreversibility and reversibility,reversibility,

as well as to put certain physical and as well as to put certain physical and philosophical concepts philosophical concepts in perspectivein perspective, ,

and initiate discussion and arguments and initiate discussion and arguments about the paper theme. about the paper theme.


Heat TransferHeat Transfer::

Heat transfer like any other energy Heat transfer like any other energy transfer, may be achieved transfer, may be achieved from any-to-any temperature levelfrom any-to-any temperature level, , and and in limit be reversiblein limit be reversible, ,

if temperature of an intermediary cyclic if temperature of an intermediary cyclic substance is adjusted as needed, using substance is adjusted as needed, using isentropic compression and expansion isentropic compression and expansion


This is practically This is practically demonstrated…demonstrated…

This is practically This is practically demonstrateddemonstrated in in refrigerationrefrigeration and and heat pumpheat pump devices, devices, and enables further increase in energy and enables further increase in energy efficiency. efficiency.

A A dual power-and-heat-pumpdual power-and-heat-pump cycle is cycle is introducedintroduced and analyzed and analyzed herehere, , to provide for reversible heat transfer. to provide for reversible heat transfer.

It may be considered as a It may be considered as a reversiblereversible heat-transfer transformerheat-transfer transformer, , from-any-to-any temperature levels.from-any-to-any temperature levels.


Limits and Practical Limits and Practical PotentialsPotentials::

The reversible heat transfer limits The reversible heat transfer limits are the most efficient are the most efficient

and demonstrate and demonstrate limiting potentialslimiting potentials for for practicalpractical heat transfer heat transfer processesprocesses..


REVERSIBILITY AND REVERSIBILITY AND IRREVERSIBILITY:IRREVERSIBILITY:

ENERGY TRANSFER AND DISORGANIZATION, ENERGY TRANSFER AND DISORGANIZATION, RATE AND TIME, AND ENTROPY GENERATIONRATE AND TIME, AND ENTROPY GENERATION

Net-energy transfer is in one Net-energy transfer is in one direction onlydirection only, from higher to lower , from higher to lower energy-potential, and the process energy-potential, and the process cannot be reversed. cannot be reversed.

Thus Thus all real processes are all real processes are irreversibleirreversible in the direction of in the direction of decreasing energy-potential decreasing energy-potential (like pressure and temperature) (like pressure and temperature)


Quasi-equilibrium Process Quasi-equilibrium Process ::in limit, energy transfer process with in limit, energy transfer process with infinitesimal infinitesimal

potential differencepotential difference (still from higher to (still from higher to infinitesimally lower potential, P). infinitesimally lower potential, P).

Then, if infinitesimal change of potential difference Then, if infinitesimal change of potential difference direction is direction is reversedreversed

P+dP → P-dPP+dP → P-dP

with infinitesimally small external energy, since with infinitesimally small external energy, since dP→0dP→0, ,

the the process will be reversed tooprocess will be reversed too, which is , which is characterized with characterized with infinitesimal entropy generationinfinitesimal entropy generation, ,

and and in limitin limit, without energy degradation (no further , without energy degradation (no further energy disorganization) and no entropy generationenergy disorganization) and no entropy generation

thus thus achieving a limiting reversible processachieving a limiting reversible process. .


REVERSIBILITY –Relativity of REVERSIBILITY –Relativity of Time:Time:

Therefore, the changes are ‘fully Therefore, the changes are ‘fully reversible,’ and along with their rate of reversible,’ and along with their rate of change and time, totally irrelevant, as if change and time, totally irrelevant, as if nothing is effectively changing (nothing is effectively changing (no no permanent-effectpermanent-effect to the surroundings to the surroundings or universe) or universe)

The The time is irrelevanttime is irrelevant as if it does not as if it does not exist, since it could be reversed or exist, since it could be reversed or forwarded at will and at no ‘cost’ (no forwarded at will and at no ‘cost’ (no permanent change and, thus, relativity permanent change and, thus, relativity of time). of time).


REVERSIBILITY –Relativity of REVERSIBILITY –Relativity of Time (2):Time (2):

Real time cannot be reversedReal time cannot be reversed, , it is a it is a measure of permanent measure of permanent changeschanges, like irreversibility, which is in , like irreversibility, which is in turn measured by entropy generation. turn measured by entropy generation.

In this regard the In this regard the time and entropytime and entropy generationgeneration of the universe have to be of the universe have to be relatedrelated..


Entropy …Entropy …

… … entropy of a system for a given state is entropy of a system for a given state is

the same, regardlessthe same, regardless whether it is whether it is reached by reversible heat transfer or reached by reversible heat transfer or irreversible heat or irreversible work irreversible heat or irreversible work transfer. transfer.

However, the However, the source entropy will source entropy will decreasedecrease to a smaller extent over to a smaller extent over higher potential, thus resulting in higher potential, thus resulting in overall entropy generationoverall entropy generation for the for the two interacting systems. two interacting systems.


S

W12= 0 Unrestricted expansion

T

S

1S

2S

Q12=0

1S 2S

SS

SG=SS>0 Could NOT be

reversed

S

R

T

S

1S

2S

Q12>0

1S 2S

2R 1R

SR

SS

SG=SS -SR=0 Could be reversed

(a)

(b)

S

T

S

1S

1S 2S

S

R

W12= Q12

2R

It is possibleIt is possible to obtain work to obtain work from the equal amount of from the equal amount of disorganized thermal energy disorganized thermal energy or heat, if such process is or heat, if such process is reversible. reversible.

For example:For example:

reversible expansion at reversible expansion at constant internal energyconstant internal energy, , e.g. isothermal ideal-gas e.g. isothermal ideal-gas expansion, (expansion, (dW=dQdW=dQ), ), see Fig. 1a, andsee Fig. 1a, and

reversible adiabatic reversible adiabatic expansionexpansion ( (dW=-dUdW=-dU).).

Work potential is lostWork potential is lost during during unrestricted expansion (Fig. 1b)unrestricted expansion (Fig. 1b)


Heat Transfer and Heat Transfer and Irreversibility:Irreversibility:ENTROPY TRANSFER ENTROPY TRANSFER and GENERATIONand GENERATION

SG =SS - SR = 0 Could be reversed

S

1S

2S

2R

1R

SR

SS

Multiple Heat Reservoirs with T 0


S

1S

2S

2R

1R

SR

SS

Variable T Reservoir

with T 0

T

S

1S

2S

2R 1R

SR

SS

SG

T > 0

SG =SS - SR > 0 Irreversible

(a) (b)

(c)


Entropy …Entropy …

We could consider a system internal We could consider a system internal thermal energy and entropy, as being thermal energy and entropy, as being accumulated from absolute zeroaccumulated from absolute zero level, by disorganization of organized or level, by disorganization of organized or higher level energy potential with the higher level energy potential with the corresponding entropy generation.corresponding entropy generation.

Thus Thus entropyentropy as system property is as system property is associated with its thermal energyassociated with its thermal energy(but also space). (but also space).


Entropy Primer:Entropy Primer:

entropy could be entropy could be transferred in transferred in reversiblereversible processes processes along with heat along with heat transfertransfer, and additionally , and additionally generatedgenerated if if work or thermal energy are work or thermal energy are disorganized at the lower thermal disorganized at the lower thermal potential during potential during irreversible irreversible processesprocesses..

Once a process completes, any generated Once a process completes, any generated entropy due to irreversibility becomes entropy due to irreversibility becomes ((permanentpermanent) system property and ) system property and cannot be reversed by itself cannot be reversed by itself (thus, a permanent change). (thus, a permanent change).


Entropy Primer (2):Entropy Primer (2):

Thus, entropy transfer is Thus, entropy transfer is

due to reversible heat transfer and could due to reversible heat transfer and could be ether be ether positive or negativepositive or negative, ,

while while entropy generation is always entropy generation is always positivepositive and always and always due to due to irreversibilityirreversibility..


Reversible Heat Transfer and Reversible Heat Transfer and Practical Potentials:Practical Potentials:Dual Power-Heat Pump Dual Power-Heat Pump cyclecycle

)3(.)(

)2(.

)1(.)()(

0

00

EqSSTSTQ

EqSTQ

EqSTTSTT

HLLLL

HHH

LHLH

QL=TLSL=THSH= QH

SG=SL-SH>0

Irreversible

TH

TL

T0

S

S′′L

T

1L 2L

2H 1H

SH

SG=0 Reversible

Heat Transfer

2L′

S′L

S0

T C

T C

Power Cycle

Heat Pump Cycle

Saved Energy

SL

TH

TL

T0

T

S

1L 2L

2H 1H

SH SG

PC CPC

HPC

WPC =WHPC

(a)

(b)

)5.(%5005

300350

3001050

1050

350

0

0

Eq

TT

TT

T

T

Q

QCOP

L

H

H

L

H

LPHP


Coefficients of Performance for Three Coefficients of Performance for Three Typical Cases of Reversible Heat Typical Cases of Reversible Heat TransferTransfer

TABLE I: COEFFICIENTS OF PERFORMANCE FOR THREE TYPICAL CASES OF

REVERSIBLE HEAT TRANSFER

REVERSIBLE HEAT

TRANSFER TYPE COEFFICIENT OF PERFORMANCE

for TH> TL> T0> TR

Heating from higher temperature source:

Dual Power-Heat Pump Cycle (introduced here)

0

0

TT

TT

T

T

Q

QCOP

L

H

H

L

H

LPHP

Eq. (4)

Cooling: Refrigeration or Air-

Conditioning R

RRR TT

T

W

QCOP

0

Eq. (6)

Heating from lower temperature source:

Heat Pump 0TT

T

W

QCOP

H

HHHP

Eq. (7)

the most efficient reversible heat transfer

from system H at higher temperature TH

to system L at lower temperature TL

as presented on Fig. 3b may be obtained (as limiting case)

by using a dual power-and-heat-pump

cycle (PHP), which is governed

by the following conditions (WPC = WHPC)


Conclusion …Conclusion … Energy is a fundamental concept indivisible from

matter and space, and energy exchanges or transfers are associated with all processes (or changes), thus indivisible from time.

Energy is “the building block” and fundamental property of matter and space, thus fundamental property of existence. For a given matter (system) and space (volume) energy defines the system equilibrium state, and vice versa.

For a given system state (structure and phase) addition of energy will tend (spontaneously) to randomly distribute (disorganize) over the system microstructure and space it occupies, called internal thermal energy, increasing energy-potential (temperature) and/or energy-displacement (entropy), and vice versa.


Conclusion (2):Conclusion (2): Energy and mass are conserved within interacting systems

(all of which may be considered as a combined isolated system not interacting with its surrounding systems), and energy transfer (in time) is irreversible (in one direction) from higher to lower potential only, which then results in continuous generation (increase) of energy-displacement, called entropy generation, which is fundamental measure of irreversibility, or permanent changes, the latter also measured with the passing time.

Reversible energy transfer is only possible as limiting case of irreversible energy transfer at infinitesimally small energy-potential differences, thus in quasiequilibrium processes, with conservation of entropy. Since such changes are reversible, they are not permanent (could be reversed without leaving any relevant or effect on the surroundings) and, along with time, irrelevant (NOT permanent).


Conclusion (3):Conclusion (3): Entropy may be transferred from system to

system by reversible heat transfer and also generated due to irreversibility of heat and work transfer.

Heat transfer, like any other energy transfer, may be achieved from any-to-any temperature level (performed in real power and refrigeration cycles), and in limit be reversible, if temperature of an intermediary cyclic substance is adjusted as needed, using isentropic compression and expansion. The reversible heat transfer limits are the most efficient and demonstrate limiting potentials for practical heat transfer processes.


Conclusion (4):Conclusion (4): The “Dual Power-Heat Pump Cycle,” introduced

here, may be considered as a reversible heat-transfer transformer, from-any-to-any temperature levels.

The simple analysis of this dual, combined cycle (Eq. 4. and Fig. 3b), to achieve reversible heat transfer only (from higher to lower temperature system) and without any net-work produced or utilized,

Presented emphasis (with analysis) of underlying physical phenomena, including several hypothesis, is intended contribution of this paper.


Heat Transfer PotentialsHeat Transfer Potentials::Minimize Irreversibilities and Entropy Minimize Irreversibilities and Entropy

generationgeneration


S

1S

2S

2R

1R

SR

SS

Multiple Heat Reservoirs with T 0


S

1S

2S

2R

1R

SR

SS

Variable T Reservoir

with T 0

T

S

1S

2S

2R 1R

SR

SS

SG

T > 0

SG =SS - SR > 0 Irreversible

(a) (b)

(c)

QL=TLSL=THSH= QH

SG=SL-SH>0

Irreversible

TH

TL

T0

S

S′′L

T

1L 2L

2H 1H

SH

SG=0 Reversible

Heat Transfer

2L′

S′L

S0

T C

T C

Power Cycle

Heat Pump Cycle

Saved Energy

SL

TH

TL

T0

T

S

1L 2L

2H 1H

SH SG

PC CPC

HPC

WPC =WHPC

(a)

(b)

Enhanced Enhanced Heat-TransferHeat-Transfer TransformerTransformer

Power-Heat Pump cycle Power-Heat Pump cycle

Key WordsKey Words::

Conservation Conservation withwith Optimization Optimization(to increase efficiency) (to increase efficiency)

CogenerationCogeneration(to minimize irreversibility)(to minimize irreversibility)

Insulation Insulation (to minimize losses)(to minimize losses)

Regeneration Regeneration (to recover losses)(to recover losses)Enabled byEnabled by

Sophistication of Sophistication of NEW Knowledge and TechnologyNEW Knowledge and Technology


For further Info For further Info you may contact Prof. Kostic you may contact Prof. Kostic at:at:

[email protected] [email protected]

or on the Web:or on the Web:www.kostic.niu.eduwww.kostic.niu.edu

Prof. Prof. M. KosticM. Kostic Mechanical EngineeringMechanical Engineering

NORTHERN ILLINOIS UNIVERSITYNORTHERN ILLINOIS UNIVERSITY

080125© m. kostic prof. m. kostic mechanical engineering northern illinois university uniqueness...

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