Transcript Uniqueness and Universality of Heat Transfer by M. Kostic

Heat Transfer, Thermal Energy
and Entropy - Demystified:
Challenges and Opportunities
for Improving Heat Transfer Processes The Quest and Nature
of Energy, Heat and Entropy
PLENARY LECTURE
The 6th WSEAS International Conference on HEAT and MASS TRANSFER
(WSEAS - HMT'09)
Ningbo, China, January 10-12, 2009
Prof. M. Kostic
Mechanical Engineering
NORTHERN ILLINOIS UNIVERSITY
© M. Kostic <www.kostic.niu.edu>
2009 January 10-12
Focus and Goal:
Focuses on
philosophical and practical aspects
of energy, heat and entropy,
with emphasis on
reversibility and irreversibility, and
goal to establish the concept of
“reversible heat transfer,”
regardless that heat transfer
is a typical irreversible process.
© M. Kostic <www.kostic.niu.edu>
2009 January 10-12
Heat transfer is Unique and Universal:
Heat transfer is a spontaneous irreversible process where
all organized (structural) energies are disorganized or
dissipated as thermal energy with irreversible loss of
energy potential (from high to low temperature) and
overall entropy increase.
Thus, heat transfer and thermal energy are
unique and universal manifestation of all
natural and artificial (man-made) processes,
… and thus … are vital for more efficient cooling and
heating in new and critical applications, including
energy production and utilization, environmental
control and cleanup, and bio-medical applications.
© M. Kostic <www.kostic.niu.edu>
2009 January 10-12
Objective:
… to emphasize known,
but not so well-recognized issues
about energy, heat and entropy,
irreversibility and reversibility,
as well as to put certain physical and
philosophical concepts in perspective,
and initiate discussion and arguments about the
paper theme.
© M. Kostic <www.kostic.niu.edu>
2009 January 10-12
The Grand Law of Nature
The universe consists of local material structures
in forced equilibrium and their interactions via forced
fields. The forces are balanced at any time
(including inertial - process rate forces) thus
conserving momentum, while charges/mass and
energy are transferred and conserved during
forced displacement in space all the times, but energy
is degraded as it is redistributed (transferred) from
higher to lower non-equilibrium potential towards
equilibrium
(equi-partition of energy). (by M. Kostic)
© M. Kostic <www.kostic.niu.edu>
2009 January 10-12
Energy and Entropy
•DEFINITION of ENERGY: "Energy is a fundamental property of a physical system
and refers to its potential to maintain a material system identity or structure (forced
field in space) and to influence changes (via forced-displacement interactions, i.e.
systems' re-structuring) with other systems by imparting work (forced directional
displacement) or heat (forced chaotic displacement/motion of a system molecular or
related structures). Energy exists in many forms: electromagnetic (including light),
electrical, magnetic, nuclear, chemical, thermal, and mechanical (including kinetic,
elastic, gravitational, and sound); where, for example, electro-mechanical energy may
be kinetic or potential, while thermal energy represents overall potential and chaotic
motion energy of molecules and/or related micro structure.
"... Energy is the ‘‘building block’’ and fundamental property of matter and space and,
thus, the fundamental property of existence. Energy exchanges or transfers are
associated with all processes (or changes) and, thus, are indivisible from time.“
DEFINITION of ENTROPY: "Entropy is an integral measure of (random) thermal
energy redistribution (due to heat transfer or irreversible heat generation) within a
system mass and/or space (during system expansion), per absolute temperature
level. Entropy is increasing from orderly crystalline structure at zero absolute
temperature (zero reference) during reversible heating (entropy transfer) and entropy
generation during irreversible energy conversion, i.e. energy degradation or random
equi-partition within system material structure and space." (by M. Kostic)
© M. Kostic <www.kostic.niu.edu>
2009 January 10-12
Energy: Property vs. Transfer
© M. Kostic <www.kostic.niu.edu>
2009 January 10-12
More Definitions …
© M. Kostic <www.kostic.niu.edu>
2009 January 10-12
Energy: Property vs. Transfer
© M. Kostic <www.kostic.niu.edu>
2009 January 10-12
Energy: Forms of Heat Transfer
© M. Kostic <www.kostic.niu.edu>
2009 January 10-12
Energy Interactions:
© M. Kostic <www.kostic.niu.edu>
Coupled, Adiabatic, and Caloric
2009 January 10-12
Energy & Entropy: Control Volume
© M. Kostic <www.kostic.niu.edu>
2009 January 10-12
Heat Transfer:
Heat transfer like any other energy transfer,
may be achieved
from any-to-any temperature level,
and in limit be reversible,
if temperature of an intermediary cyclic
substance is adjusted as needed, using
isentropic compression and expansion
© M. Kostic <www.kostic.niu.edu>
2009 January 10-12
This is practically demonstrated…
This is practically demonstrated
in refrigeration and heat pump devices,
and enables further increase in energy
efficiency.
A dual power-and-heat-pump cycle is
introduced and analyzed here,
to provide for reversible heat transfer.
It may be considered as a reversible
heat-transfer transformer,
from-any-to-any temperature levels.
© M. Kostic <www.kostic.niu.edu>
2009 January 10-12
Limits and Practical Potentials:
The reversible heat transfer limits
are the most efficient
and demonstrate limiting potentials
for practical heat transfer processes.
© M. Kostic <www.kostic.niu.edu>
2009 January 10-12
REVERSIBILITY AND
IRREVERSIBILITY:
ENERGY TRANSFER AND DISORGANIZATION,
RATE AND TIME, AND ENTROPY GENERATION
Net-energy transfer is in one direction
only, from higher to lower energy-potential,
and the process cannot be reversed.
Thus all real processes are irreversible in
the direction of decreasing energy-potential
(like pressure and temperature)
© M. Kostic <www.kostic.niu.edu>
2009 January 10-12
Quasi-equilibrium Process :
in limit, energy transfer process with infinitesimal
potential difference (still from higher to
infinitesimally lower potential, P).
Then, if infinitesimal change of potential difference
direction is reversed
P+dP → P-dP
with infinitesimally small external energy, since dP→0,
the process will be reversed too, which is
characterized with infinitesimal entropy generation,
and in limit, without energy degradation (no further
energy disorganization) and no entropy generation
thus achieving a limiting reversible process.
© M. Kostic <www.kostic.niu.edu>
2009 January 10-12
REVERSIBILITY –Relativity of Time:
Therefore, the changes are ‘fully reversible,’ and
along with their rate of change and time,
totally irrelevant, as if nothing is effectively
changing (no permanent-effect to the
surroundings or universe)
The time is irrelevant as if it does not exist,
since it could be reversed or forwarded at will
and at no ‘cost’ (no permanent change and,
thus, relativity of time).
© M. Kostic <www.kostic.niu.edu>
2009 January 10-12
REVERSIBILITY –Relativity of Time
(2):
Real time cannot be reversed,
it is a measure of permanent changes,
like irreversibility, which is in turn measured
by entropy generation.
In this regard the time and entropy
generation of the universe have to be
related.
© M. Kostic <www.kostic.niu.edu>
2009 January 10-12
(a)
T
2S
W12= Q12
SG=SS -SR=0
2S
1S
SS
S
For example:

reversible adiabatic expansion
(dW=-dU).

Work potential is lost during
unrestricted expansion (Fig. 1b)
SR
Q12>0
SS
R
(b)
T
Unrestricted
expansion


1R
1S
W12= 0
It is possible to obtain work
from the equal amount of disorganized
thermal energy
or heat, if such process is reversible.
Could be reversed
2R
2S

SG=SS>0
Could NOT be
reversed
1S
2S
1S
reversible expansion at
constant internal energy,
e.g. isothermal ideal-gas expansion,
(dW=dQ),
see Fig. 1a, and
S
S
Q12=0
SS
© M. Kostic <www.kostic.niu.edu>
2009 January 10-12
T
2R
(a)
1R
T > 0
Heat Transfer and
Irreversibility:
(b)
Multiple Heat
Reservoirs
with T 0
2S
ENTROPY TRANSFER and
GENERATION
1R
2S
1S
2R
SG =SS - SR > 0
Irreversible
SG =SS - SR = 0
Could be reversed
1S
S
S
SG
SR
SR
SS
SS
(c)
Variable T
Reservoir
with T 0
1R
2S
2R
SG =SS - SR = 0
Could be reversed
1S
S
SR
SS
© M. Kostic <www.kostic.niu.edu>
2009 January 10-12
Entropy …
… entropy of a system for a given state is
the same, regardless whether it is reached
by reversible heat transfer or irreversible heat
or irreversible work transfer.
However, the source entropy will decrease
to a smaller extent over higher potential, thus
resulting in overall entropy generation for
the two interacting systems.
© M. Kostic <www.kostic.niu.edu>
2009 January 10-12
Entropy …
We could consider a system internal thermal
energy and entropy, as being accumulated
from absolute zero level, by
disorganization of organized or higher level
energy potential with the corresponding
entropy generation.
Thus entropy as system property is
associated with its thermal energy
(but also space).
© M. Kostic <www.kostic.niu.edu>
2009 January 10-12
Entropy Primer:
entropy could be transferred in reversible
processes along with heat transfer, and
additionally generated if work or thermal
energy are disorganized at the lower thermal
potential during irreversible processes.
Once a process completes, any generated
entropy due to irreversibility becomes
(permanent) system property and cannot be
reversed by itself
(thus, a permanent change).
© M. Kostic <www.kostic.niu.edu>
2009 January 10-12
Entropy Primer (2):
Thus, entropy transfer is
due to reversible heat transfer and could be
ether positive or negative,
while entropy generation is always
positive and always due to irreversibility.
© M. Kostic <www.kostic.niu.edu>
2009 January 10-12
Entropy Primer (3):
If heat or work at higher potential (temperature or pressure) than necessary, is
transferred to a system, the energy at excess potential will dissipate spontaneously
to a lower potential (if left alone) before new equilibrium state is reached, with
entropy generation, i.e. increase of entropy displacement over a lower potential. A
system will ‘accept’ energy at minimum necessary (infinitesimally higher) or higher
potential. Furthermore, the higher potential energy will dissipate and entropy
increase will be the same as with minimum necessary potential, like in reversible
heating process, i.e.:
dS 
Q
T
or S  
Q
T
 S ref
However, the source entropy will decrease to a smaller extent over higher
potential, thus resulting in overall entropy generation for the two interacting
systems,
© M. Kostic <www.kostic.niu.edu>
2009 January 10-12
T
1H
2H
TH
PC
TL
CPC
2L
1L
HPC
QL=TLSL=THSH= QH
T0
Reversible Heat Transfer and
Practical Potentials:
Dual Power-Heat Pump
cycle
SG=SL-SH>0
Irreversible
SG
SH
(a)
S
SL
T
1H
2H
TH
TL
2L
2L′
1L
T
Heat Pump Cycle
C
T0
SH
QH  TH  S H
Eq. (2)
QL  TL  S L  TL (S H  S 0 )
Eq. (3)
Reversible
Heat Transfer
T
WPC =WHPC
Eq. (1)
SG=0
Power
Cycle
C
(TH  TL )S H  (TL  T0 )S 0
Saved Energy
COPPHP 
QL TL TH  T0 350 1050 300




QH TH TL  T0 1050 350 300
 5  500%
S
S0
(b)Kostic <www.kostic.niu.edu>
S′′L
S′L
© M.
2009 January 10-12
Eq.(5)
Coefficients of Performance for Three
Typical Cases of Reversible Heat Transfer
TABLE I:
COEFFICIENTS OF PERFORMANCE FOR THREE TYPICAL CASES OF
REVERSIBLE HEAT TRANSFER
REVERSIBLE HEAT
TRANSFER TYPE
Heating from higher
temperature source:
Dual Power-Heat Pump
Cycle (introduced here)
COEFFICIENT OF PERFORMANCE
for TH> TL> T0> TR
COPPHP 
QL TL TH  T0


QH TH TL  T0
Eq. (4)
Cooling:
Refrigeration or AirConditioning
COPR 
Heating from lower
temperature source:
Heat Pump
COPHP 
© M. Kostic <www.kostic.niu.edu>
QR
TR

W T0  TR
Eq. (6)
QH
TH
Eq. (7)

W TH  T0
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)
2009 January 10-12
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.
© M. Kostic <www.kostic.niu.edu>
2009 January 10-12
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 energypotential 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).
© M. Kostic <www.kostic.niu.edu>
2009 January 10-12
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.
© M. Kostic <www.kostic.niu.edu>
2009 January 10-12
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.
© M. Kostic <www.kostic.niu.edu>
2009 January 10-12
Heat Transfer Potentials:
Minimize Irreversibilities and Entropy generation
Enhanced
Heat-Transfer Transformer
Power-Heat Pump cycle
Key Words:
T
1H
2H
TH
T
PC
TL
CPC
2L
1L
Conservation with Optimization
(to increase efficiency)
2R
(a)
1R
T > 0
(b)
Multiple Heat
Reservoirs
with T 0
2S
1R
2S
HPC
QL=TLSL=THSH= QH
T0
SG=SL-SH>0
Irreversible
SH
(a)
S
SG
Insulation (to minimize losses)
Regeneration (to recover losses)
T
1H
TH
TL
Reversible
Heat Transfer
T
C
Enabled by
SG=0
Power
Cycle
2L
2L′
1L
T
Heat Pump Cycle
1S
2R
SG =SS - SR > 0
Irreversible
SG =SS - SR = 0
Could be reversed
1S
S
SL
2H
Cogeneration
(to minimize irreversibility)
C
T0
Sophistication of
NEW Knowledge and Technology
S
SG
SR
SR
SS
SS
(c)
Variable T
Reservoir
with T 0
1R
2S
2R
SG =SS - SR = 0
Could be reversed
WPC =WHPC
SH
(b)
S′L
1S
Saved Energy
S
S
S0
SR
S′′L
SS
© M. Kostic <www.kostic.niu.edu>
2009 January 10-12
For further Info
you may contact Prof. Kostic at:
[email protected]
or on the Web:
www.kostic.niu.edu
Prof. M. Kostic
Mechanical Engineering
NORTHERN ILLINOIS UNIVERSITY
© M. Kostic <www.kostic.niu.edu>
2009 January 10-12