Journal of Modern Physics, 2013, 4, 52-58
http://dx.doi.org/10.4236/jmp.2013.47A2008 Published Online July 2013 (http://www.scirp.org/journal/jmp)
Proposal for Generalized Exergy and Entropy Properties
Based on Stable Equilibrium of Composite
System-Reservoir
Pierfrancesco Palazzo
Technip, Rome, Italy
Received April 20, 2013; revised May 25, 2013; accepted June 27, 2013
Copyright © 2013 Pierfrancesco Palazzo. This is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
ABSTRACT
The present theoretical study represents a proposal aimed at investigating about the possibility of generalizing the ca-
nonical entropy-exergy relationship and the reservoir concept. The method adopted assumes the equality of pressure
and chemical potential as necessary conditions of mutual stable equilibrium between a system and a reservoir in addi-
tion to the equality of temperature that constitutes the basis for defining entropy as deriving from energy and exergy
concepts. An attempt is made to define mechanical and chemical entropy as an additional and additive component of
generalized entropy formulated from generalized exergy property. The implications in exergy method and the possible
engineering applications of this appro ach are outlined as future developments among the domains involved.
Keywords: Adiabatic Availability; Available Energy; Generalized Exergy; Generalized Entropy; Reservoir; Stable
Equilibrium; Exergy Method
1. Introduction 2. Theoretical Model and Method
The formulation of the Seco nd Law is based on the exis-
tence and uniqueness of the state of stable equilibrium of
a system interacting with a reservoir “among all the
states of a system that have a given value of the energy
and are compatible with a given set of values of the
amounts of constituents and of the parameters” [1]. This
general statement requires compliance with the necessary
conditions of equ ality of (absolute) temperature, pressure
and chemical potential between system and reservoir.
The Second Law implies the definition of entropy prop-
erty in relation to temperature. The entrop y of system
The following assumptions are posited: 1) the analysis is
focused on “simple systems” according to the terminal-
ogy and definitions adopted by Gyftopoulos and Beretta
[1]; 2) the external reference system behaves as a reser-
voir as defined in the literature [1]; 3) the system may be
large or small, even at molecular level, and may experi-
ence states of equilibrium and nonequilibrium [1]; 4)
physical and chemical exergy are accounted for; 5) ki-
netic energy and the potential energy of the system as a
whole are neglected. These assumptions are posited in
order to constitute the requirements complying with the
fundamental framework to which the addressed literature
refers.
A
can also be derived as the difference of energy and
exergy associated with the generalized available
energy
E
EX
R
with respect to a reservoir at constant
temperature R
R
The method adopted assumes the equality of pressure
and chemical potential of the composite system-reservoir
T [1]. The Second Law, expressed as in-
dicated above, has to account for pressure and chemical
potential in add ition to temperature, hence the purpose of
this present study is to conceive a generalized formula-
tion of exergy, and consequently of entropy, based on
equality of pressure and chemical p oten tial, in additio n to
temperature, between a system
A
and a reservoir
at constant temperature
A
R as additional necessary conditions for mutual stable
equilibrium, other than equality of temperature. The for-
mulation of the entropy property is derived from exergy,
related to a reservoir at constant temperature, constant
pressure and constant chemical potential. This set of ge-
neralized potentials equality constitutes a necessary and
sufficient condition for the stable equilibrium of a com-
posite system-reservoir consistent with the Second Law
R
R
T, constant pressure
R
P and
constant chemical potential
R

.
C
opyright © 2013 SciRes. JMP

P. PALAZZO 53
statement.
3. Thermal Entropy Derived from Thermal
Exergy
The behaviour of the exergy property is characterized by
additivity because it is defined considering an external
reference system or an internal part of the system itself
that behaves as a reservoir [1,2]. Exergy is derived from
the generalized available energy that is a consequence of
the concept of adiabatic availability when the system
interacts with a reservoir [1]; the definitions of available
energy and exergy are based on the mutual stable equi-
librium of a system
A
with a reservoir at constant
temperature R
R
T

MAX
10
AR
W
and account for work interaction by
means of a weight process; this implies that, as defined in
these terms, (thermal) exergy expresses the maximum net
useful work connecting two states 0 and 1
obtained by means of a weight process resulting from the
available energy between variable temperatures Tof
system
A
and constant temperature
R
T
R of reservoir as expressed by the following equations adopting the
symbology used by Gyftopoulos and Beretta [1]:




MAX
0
10
R
RR
PVV


T
S


MAX
10 1
101 0
TAR R
TT
EX W
UUT SS


 (1)
The definition of entropy is derived from the differ-
ence between energy and available energy [1] and is here
defined as thermal entropy by virtue of the consid-
erations discussed above:

10 10
1
TT
R
SS EE
T
 


1 0
T
R R



(2)
These equations, reported in the addressed literature,
constitute the outset of the present study underpinned by
the consideration that equality of temperature is a neces-
sary condition that is not sufficient to prove that a system
is in stable equilibrium with the reservoir. Indeed, even
though two interacting systems are in thermal stable
equilibrium owing to equality of temperatures, the two
systems may experience nonequ ilibrium states due to the
non-null difference between pressures or chemical poten-
tials. The equality of total potential and pressure between
system and reservoir should therefore constitute the set
of additional necessary conditions to ensure the stable
equilibrium so that the equality of the complete set of
“generalized potentials” constitutes a necessary and suf-
ficient condition for mutual stable equilibrium in com-
pliance with the Second Law as worded by Gyftopoulos
and Beretta [1]. As a consequence of the procedure
adopted for its definition by the said Authors [1], entropy
is an additive property that can be generalized to include
the contribution of additional components fulfilling to the
conditions of equality of pressure and chemical potential
that guarantee the mutual stable equilibrium of the com-
posite system-reservoir.
An intuitive rationale of the pro cedure here adopted to
define entropy may be explained considering that internal
energy is characterized by a “hybridization” of ordered
and disordered (due to distribution of molecule’ position
and velocity of system’s particles) energy status. Entropy
may be regarded as the measure of the amount of disor-
dered energy – released to the reservoir – resulting from
the difference of hybrid energy – ordered and disordered
– and available energy – ordered energy – transferred, as
useful interaction, to th e external system.
4. Mechanical Entropy Derived from
Mechanical Exergy
The formulation of thermal exergy in Equation (1) ex-
presses the weight process as the result (and the measure)
of the maximum net useful work that can be extracted
from a system interacting with a thermal reservoir. The
weight process can also be regarded as the minimum net
useful work delivered to the system and hence can be as-
sociated with the maximum net useful heat according to
the concepts of equivalence and interconvertibility [3-5].
In this case, the weight process is calculated as the result
of the interaction of the system with a mechanical reser-
voir at constant pressure
R
P. The mechanical reservoir
is here assumed to possess the same properties as a ther-
mal reservoir [1,2,6] that is characterized and defined
without explicit reference to any specific form of gener-
alized potential.
The equality of pressu re between system and reservo ir
is assumed to be an additional necessary condition of
mutual stable equilibrium. This condition should there-
fore be complied with equality of temperature to ensure
that the status of composite system-reservoir is one of
stable equilibrium.
R
If the concept of generalized available energy

[1]
is now referred to, then the formulation of mechanical
exergy should be translated into the following expression
where the superscript “M” stands for “Mechanical reser-
voir” since the composite system-reservoir undergoes a
“work interaction” and the physical meaning becomes
the “maximum” net useful heat of the system:

MAX
101 0
M
MAR RR
EXQ  (3)
The definition of mechanical exergy is the basis for
deriving the expression of mechanical entropy using the
procedure adopted for thermal exergy and thermal en-
tropy:


1010 10
M
MM RR
RR
R
SS EE
PV


 (4)



P. PALAZZO 54
This expression of mechanical entropy can be demon-
strated considering that the procedure conceived by Gy-
ftopoulos and Beretta proving the formulation of (ther-
mal) entropy [1], does not impose any restriction with re-
spect to the form of energy and generalized available
energy that constitute the expression of entropy. There-
fore the same procedure can be considered valid regard-
less of the physical nature of the properties involved. Th e
minimum amount of weight process corresponds to the
maxim um amount of heat interact i on:


10 1
MIN
10
AR RR
EE
WP

 



0
1 0
ln ln
M
RR
VVV




(5)
which expresses the (minimum) amount of work interac-
tion absorbed from mechanical reservoir at constant pres-
sure
R
P and constant
R
V (total volume coincides with
specific volume in the particular case of a reservoir). Equ-
ation (5), substituted in the former relation, expresses the
mechanical entropy:

1 0
ln lnRVV
NET
WG
10
MM
SS (6)
5. Chemical Entropy Derived from Chemical
Exergy
The chemical potential generated by interaction among
the molecules of an open system constitutes a component
of internal energy and is defined as a form of “disordered
energy”, as thermal energy is [7].
The maximum work of a reversible (internally and ex-
ternally) chemical reaction is expressed by the Gibbs
function so that REV . The Van’t Hoff equilib-
rium open system at constant temperature and constant
pressure is a suitable device for reproducing a typical
chemical reaction where A, B are reactants and C, D are
products [7] :
0
0
PG
KRT


ln
AB CD
nA nBnCnD  (7)
is adopted to express maximum work tak ing into account
the internal mechanism of chemical reaction by means of
the expression depending on the equilibrium constant
P
K
of the reaction.
The Gibbs relation, obtained from mass and internal
energy balance, is as follows:
,,
dddd
dd
ii
i
i
Vn Sn
UTSPVn
UU
SV
SV
  

 

 

 


,,
d
i
iVSn
U
n
n






(8)
where
,,
iVSn
U
n





-ith


represents the chemical potential
of the constituent.
Chemical exergy is defined by Kotas [7] as “the ma-
ximum work obtainable from a substance when it is
brought from the environmental state to the dead state by
means of processes involving interaction only with the
environment”. The chemical reservoir can be character-
ized according to the definition proposed by Gyftopoulos
and Beretta [1] as a “reservoir with variable amounts of
constituents”. The whole chemical and physical process
is modelled by a schema subdivided in two typical steps
[7]: the initial molecular system form’s rearrangement
(molecular structure) and the final molecular system’s di-
mensional change (geometry-kinematics or pressure and
temperature). The two representative processes are: che-
mical reaction open system and physical operation open
system; the two processes in series provide an expression
of maximum net useful work withdrawn from the system
expressed by Equa t i o n [ 7]:
MAX 1
10 0
ln
CAR RP
EXWRT P


n

(9a)
Mass interaction is the characteristics of the chemical
energy transfer and is moved by the difference of chemi-
cal potential between the system and the reservoir.
In the more general case of a mixture of chemical
constituents:
MAX
10 ln
nn
CAR
R
ii
i
ii
EXWRTx x



 
MAX
101 0
C
CAR RR
EXW  

(9b)
The equality of total potentials is accounted for as an
additional necessary condition of mutual stable equilib-
rium between the system and the reservoir other than the
equality of temperature [1]. This implies a definition of
chemical entropy derived from chemical exergy and che-
mical energy in line with the methodology previously
adopted.
If the concept of generalized available energy is now
again considered, the formulation of chemical exergy
should be translated into the following expression:
(10)
where the superscript “C” stands for “Chemical reser-
voir” since the composite of system and reservoir under-
goes a “mass interaction”.
Now that chemical exergy is defined, and considering
that entropy is an additive property, the expression used
for entropy associated with heat interaction can be ex-
tended to chemical potential depending on mass interac-
tion:


101010
1C CRR
R
SS EE



 
(11)


This constitutes the expression of the chemical entrop y
derived from chemical exergy based on the equality of

P. PALAZZO 55
chemical potential which constitutes a necessary condi-
tion for mutual stable equilibrium between the system
and the chemical reservoir.
Since entropy is an inherent property of all systems
[8-11], chemical entropy would be characterized by the
chemical potential of all atoms and sub-molecules that
constitute all compounds and determine the supra-mo-
lecular architecture and configurations of all molecular
systems. The dimensions and shapes of molecular struc-
tures play, in this perspective, a fundamental role in de-
termining the minimum entropy level that ensures the
stability of matter and its capability to react with other
co-reactants, as well as to undergo endogenous or ex-
ogenous processes. Typical is organic chemistry and bio-
chemistry in which same chemical formula are incapable
of describing materials and compounds that display dif-
ferent physical and chemical characteristics and proper-
ties. The vibration degree of freedom is an additional
aspect correlated to molecular structure complexity.
6. Generalized Exergy and Entropy
The definition of a thermo-chemical-mechanical reser-
voir characterized by constant temperature, pressure and
chemical potential implies the additivity [1,2] of the com-
ponents constitu ting the generalized exergy:
GT
EX EX
MC
EX EX (12)
The internal energy balance of the composite system-
reservoir, adopting the symbology in [1], provides the
amount of weight process due to therm a l , mechanical and
chemical contributions:



TEM ,
AR
SYSTEM RESERVOIR
SYSTEM , SYS
SYSTEM ,
GARAR
R
Q
QW
RC
C
EX WQM
UU
UU
UU

 
 

 
RW
UU


,RQ
(13)
where:
R
UQ ,RC is the minimum heat interaction
with the thermal reservoir;
R
UM is the mini-
mum mass interaction with the chemical reservoir and
,RW
R
UW
IR
,
is the minimum work interaction with the
mechanical reservoir.
The isothermal process r ealizes energy conversion and
at the same time an entropy conversion from thermal en-
tropy to mechanical entropy that occurs due to simulta-
neous heat interaction and work interaction. Both con-
versions are accounted for in the physical exergy expres-
sion:

SYSTEM RESERVO
TOTAL
0
,,
G
R
R
R
R
P V
TOTAL,
R
TR C
RR
EX UU
UUTS
TS S 
 
 
 
(14)
where the term
R
R represents the contribu-
tion to entropy conversion only occurring inside the res-
ervoir and the terms
TS
,,
R
TR CR
PVTSS   
GTMC
SSSS 
ddd0STVPn
RR R
represent the contribution transferred from the system to
the reservoir. It is noteworthy that entropy conversion is
inherent in energy conversion and that entropy conver-
sion requires the additional term that contributes to ex-
ergy balance expressed in the above formulation which
therefore considers the effect of both energy and entropy
conversion processes. Considering that entropy is an ad-
ditive property constituted by components deduced from
the corresponding generalized exergy’s components, the
generalized entropy may be defined as the sum of ther-
mal, mechanical and chemical terms:
.
7. Remarks upon the Gibbs-Duhem Relation
The Gibbs-Duhem relation [1] constitutes a condition
among all intensive properties temperature—pressure and
chemical potential—that define the state of a heteroge-
neous system. If the system is homogeneous and consti-
tuted by one con stituent only, th ere are no phase changes
or chemical reaction mechanisms inside the system im-
plying the system itself is at chemical equilibrium and
the Gibbs-Duhem relation is:


 (15)
Chemical potential

is defined as the component of
internal energy ge nerated by the interactions of in ter-par-
ticle positions and relative distance, except for kinetic
potential (due to inter-particle relative velocity). Consid-
ering these assumptions, the system model characteristics
can be assimilated to those ado pted in the Kinetic Theory
of Gas [12] which, in p articular, considers molecules un-
dergoing elastic repulsive interaction forces (Lennard-
Jones) on collision with other molecules and with the
wall of the container but otherwise exert no attractive in-
teraction forces (Van der Waals) on each other or on the
container wall [13]. The container walls represent a geo-
metrical volume constraint con dition imposed on the sys-
tem.
In the special case of the system’s undergoing an iso-
thermal process, the pressure changes are due to the
change of volume that determines the frequency of parti-
cle collisions [12]; if the system is characterized as as-
sumed, then the differential of chemical potential among
all atoms or molecules is due to the temperature that is
the only inter-particle kin etic energy transformed into in-
ter-particle potential energ y due to repulsive collisio n in-
teractions (attractive interactions are negligible by as-
sumption). Considering that no chemical reactions occur
inside the system as assumed, then d0

, as reported
by Kotas [6] for systems with a fixed chemical composi-

P. PALAZZO 56
tion, and the Gibbs-Duhem relations becomes:
ddST VP
S
d0T
dP
d0
0
(16)
where and V are not null both being inherent pro-
perties of any system [8]. If the system undergoes an
isothermal reversible process, then the temperature re-
mains constant by definition, so that ; on the
other side, is not null in the same isothermal proc-
ess and therefore an inconsistency appears. The same in-
consistency is displayed if an isobaric process is ac-
counted for using the Gibbs-Duhem relation where pres-
sure remains constant, so that , and temperature
does not. This inconsistency involves the intensive prop-
erties temperature and pressure which determine the
thermo-mechanical conversions involved in the concept
of available energy and exergy. The alternative ap proach
set forth in the present study resolves this inco nsistency.
P
The chemical potential expressed by the Gibbs func-
tion reveals that entropy property is variable in the iso-
thermal process and consequently the chemical potential
is not constant, which is in contradiction with the as-
sumption set forth.
The chemical potential that appears in assumed system
model is due exclusively to the repulsive interactions on
collisions and depends solely on molecules’ velocity, so
that temperature constitutes the first contribution to pres-
sure. The second contribution is due to the (specific) vo-
lume determining the frequency of collisions between
molecules and the external system which, on the other
side, does not determine the chemical potential due to at-
tractive interactions among the molecules which does not
exist in the model assumed.
If d

 and and considering attractive in-
teractions as negligible, repulsive interaction potential is
equal to kinetic poten tial (transformation during collision
only). The Gibbs rel at i on:
d0T
dVQ WddUTSP

   (17)
can be reformulated in different terms adopting thermal
entropy and mechanical entropy as defined in Equation
(6):
 
dQ Wdd
TM
PV
UT SS
R

   (18)
and transformed, by using the state equation PV RT
 

d
TM
T S
QW
valid in this special case, and consistent with the Kinetic
Theory of Gases [12], in the following form:

dd
dd
TM
UTS
TSS



 
0U
TOTAL 0 TM
SSS

  (19)
This, associated with the temperature, takes into ac-
count either heat or work interactions contributing to va-
riations in internal energy.
It is noteworthy that, in the case of work interaction,
the work put into the system, which is considered posi-
tive, corresponds to a decrease of mechanical entropy as
per Equation (6). This is the opposite of heat interaction
that is positive if thermal entropy increases. In other
terms, heat inpu t causes thermal entropy to increas e, work
input causes mechanical entropy to decrease, therefore
work depends on pressure in the opposite manner that
heat depends on temperature. If the system releases work,
it increases mechanical entropy because mechanical en-
ergy, distributed among the particles that constitute the
system, progressively becomes similar to thermal energy
i.e. energy distributed by the velocity of the same parti-
cles. Increasing volume means that pressure is progres-
sively determined by particles’ kinetic energy (tempera-
ture) with respect to the contribution of the frequency of
collisions among particles and with the external system
surface determined by the volume. Pressure is thus pro-
gressively the more like temperature as volume in-
creases.
The balance of entropy, along the isothermal expan-
sion reversible process d, is deduced from the
equation

 T S where is the ther-
mal entropy input due to heat flowing into the system
and
M
S
TOTAL
S
TOTAL 0 TM
SSS
is the mechanical entropy output from the
system which is the opposite of the mechanical entropy
input flow inherent in the expansion work output from
the system itself. The physical meaning is that conver-
sion from a kinetic form into a geometric form, required
to convert heat into work, necessitates an increase in me-
chanical entropy.
Due to the fact that mechanical entropy must enter the
system because of work output, then the mechanical en-
tropy direction is inverted compared to the thermal en-
tropy direction in the system’s entropy balance. Total en-
tropy is consequently constant if either thermal and me-
chanical entropy enter into the system. The rationale of
this statement is that these two entrop y components have
an opposite origin and elide each other.
If the term is expressed by means of

, the total entropy, resulting from
the addition of thermal and mechanical components of
entropy, implies that thermal entropy would be constant
in an isothermal reversible process that requires heat in-
teraction by means of thermal entropy exchange.
On the other side, pressure does not derive from in-
ter-particle chemical potential and is just the mechanical
effect produced by the temperature itself (apparent po-
tential).
The Gibbs relation, expressed in terms of the Equation
(19), resolves the apparent inconsistency highlighted in
the Gibbs-Duhem relation. In fact, this can be reformu-
lated as follows:

P. PALAZZO 57

d
d
TM
dS n
n




T M
TS n
dd
dd
TM
UTS
TS TS

 (20)
The Euler relation is obtained from the Gibbs relation
by integration at constant temperature and constant
chemical potential [1], so that:

TOTAL
TM
UTS
TSSn TS

  
S nP

  (21)
If compared with the classical expression of the Gibbs
relation UT V

 PV, the term corre-
sponds to the term
M
TS
n
. Moreover, in the case of an
isothermal process (and absence of chemical reactions so
that chemical potential is constant) it requires that total
entropy is constant also implying that thermal entropy
variation is equal to mechanical entropy variation.
It is noteworthy that, in the case of an ideal system as
assumed, internal energy U is associated with the kinetic
energy of the molecules, and thus to temperature only;
however, internal energy components depend on the
terms

 and which both depend on volume
as well. This dependence ensures that real systems in
which thermodynamic cond itions are affected by interac-
tions among molecules that determine the potential en-
ergy, are characterized by volume. In differential terms,
the Euler relations are:
PV
dd
d d
dd
nn
n n


TOTAL TOTAL
d
dd
dd d
dddd
TM TM
TMTM
U
TSSTn n
TS SSST
TSTSST ST





 

d0VP n


 
(22)
On combining the Gibbs relation and Euler relation
expressed in the terms set forth, the Gibbs-Duhem rela-
tion ddST



d
dd
dd0
Tn
Tn
STn

assumes the form:
TOTAL
dd
TM
TM
STS
SS





TPV


(23)
where: constitutes the inter-particle kinetic potential
component of internal energy resulting in the
macroscopic work interaction transferred by means of a
weight process;

constitutes the inter-particle chemi-
cal potential component of internal energy resulting in
the macroscopic work interaction transferred by
means of a weight process. The kinetic and chemical
constitute the two fundamental potentials at microscopic
inter-particle level interacting at macroscopic level that
constitute the hierarch ical geometric and kinematic struc-
ture.
PV
The dualism of kinetic potential and chemical potential
constitutes the inh erent structure of potentials even in the
special case of an ideal system for which inter-particle
potential energy in null. In this case, in fact, potential
energy still exist in the form of repulsive reaction poten-
tial energy that is due to kinetic energy transformed on
collision only, without macroscopic effects on the entire
system.
This different form of the Gibbs-Duhem relation re-
solves the apparent inconsistency in the special case of
the isothermal ideal process. In fact, d0n


d0T
dP
d0T
because
the system model is ideal and remains the only
condition to be satisfied since no longer appears in
the Gibbs-Duhem relatio n as expressed in Equ ation (23).
The rationale of these statements can also be found in the
behaviour of elements, molecules and atoms, constituting
the system as a whole. In fact, in the isothermal process,
the temperature and subsequent intermolecular repulsive
interactions on each collision are constant and the varia-
tions of kinetic potential and chemical potential (due to
intermolecular repulsive interactions) are therefore null:

and consequently d0


0T
d0
. In the case of the
isobaric process, temperature and pressure are variable or
kinetic potential and chemical po tential (due to repulsive
interactions at each inter-particle collision) both change
along the isobaric process: d and consequently


. Even in the case of an ideal system, there is du-
alism and symmetry of kinetic energy and potential en-
ergy among the molecules so that and d0d0T

.
Pressure is the mechanical effect of the contribution
related to kinetic interaction and related potential and
chemical interaction and related potential. In this per-
spective, pressure can viewed as the outcome of the
temperature and chemical potential of a complex mul-
ti-particle system, converted into work interaction with
the external reservoir and with the external weight proc-
ess.
Finally, notwithstanding the restrictions assumed for
the model adopted, the behaviour of the system is coher-
ent with expectations in terms of phenomena and ten-
dency of the properties in the general case of real sys-
tems and processes where each particle experiences at-
tractive interaction with all others, and does not contra-
dict the fundamentals reported in the literature.
8. Conclusion
The three additive components of exergy discussed in
this study constitute the components of generalized ex-
ergy that depends on temperature, pressure and chemical
potential and, at microscopic level, on the kinetic energy
and potential energy generated by interactions among the
molecules of the system. Moreover, three components of
entropy property have been inferred from the corre-
sponding exergy components. In particular, chemical
exergy and entropy are correlated to the molecular struc-
ture of matter due to the composite of molecules geome-

P. PALAZZO 58
try and chemical bonds characteristics. The aim of seek-
ing a property related to molecular or supra-molecular
architecture is to obtain a method able to pred ict a-priori
stability as well as capability in self-assembling proc-
esses and the related intermediate phases of chemical
compounds that are not available in the environment and
which could undergo a building process by means of na-
no-sciences technologies. Such a method would make it
possible to design materials characterized by properties
that could be evaluated prior to being realized and to
confirm predictions by means of experiments and labo-
ratory tests. Finally, the method of Entropy Generation
Minimization (EGM) [14-16] associated with the Ex-
tended Exergy Accounting (EEA) [17,18] could be fur-
ther generalized to provide an overarching paradigm for
analysing the whole process.
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