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Патент USA US2407166

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Sept 3» 1946“
I ~ '
Filed Nov. 8, 1941
2 Sheets-Sheet 1
T2 '
Fig.1. '
Sepia 39 ‘1946,
Filed Nov. 8, 1941
ZSheets-Sheet 2
Patented Sept. 3, 1946 ,
‘Johann Kreitner, New York, and Frederick
Nettel, Manhasset, N. Y.
' Application November 8, 1941, Serial No. 418,288
5 Claims.
(01. 60—1)
The present invention‘deals with heat cycles’
for power production in heat engines‘of any type,
with preferred application to power sys‘temsof
the continuous combustion type. Its object is to
Brayton cycle by reducing the compression work
through inter-cooling, and/or by increasing the
_ that of any known heat cycle which is practi
It ‘is known in the art to improve upon the
improve the thermal overall e?iciency beyond"
cally realizable withlpresent'means.
ticularly in plants of the continuous combustion
expansion work through re-heating. Both inter- ,
cooling and reheating have been proposed either
Ever since the conception of the theoretical
uniformly distributed over the whole compres
reversible cycle by Carnot as the one yielding the
sion and expansion, or concentrated in a de?
highest possible thermal e?iciency, efforts have
10 nite number of individual points substantially»
been made to reproduce it in practical power
uniformly distributed over the whole compres
plants, or to approximate it.
sion and expansion, respectively. In both meth
For well known reasons power plants with
ods it was the declared purposes of these measures
to approach, as closely as practically possible,
water vapor as working medium can never achieve
this. Gaseous working ?uids are basically better
isothermic expansion and/or compression, thus
suited. But also there the Carnot cycle, repre
aiming at an ideal cycle which had been conceived
sented by a rectangle in the T~S diagram, ‘meets
already by Ericsson. This Ericsson cycle is rep
unsurmountable di?iculties if it is to utilize tem—
resented in a T-S diagram by a quadrilateral with
perature ranges as available today, for example
two isothermic and two isobaric ‘sides, thus in
between 15 deg. C. and 650deg‘: C. forlplant's of 20 volving the sequence of isothermic cooled com—
the continuous combustion type, and between 15
pression, isobaric heating, isothermic heated‘ ex-‘
deg. C, and about 1200 deg. C. for plants ‘of the
pansion, and isobaric rejection, or re-cooling in’
intermittent combustion type. To reach these
the case of a “closed cycle.” The Ericsson, or
temperatures, the‘ isentropic sides of the Carnot
“double-isothermal cycle,” offers considerable
rectangle lead to extremely high compression end 25 difficulties in practical execution due to the great
pressures and/or extremely. low expansion end
amount of intercooling and re-heating through
pressures, that is, into pressure ratios which can
out the compression and expansion, respectively,
not be managed with existing compressing means.
but it represents according to the teachings of
For example a Carnot cycle for the‘ ?rst men
the present art, the highest re?nement of the
tioned temperature ‘range would require a com 30 ‘fisobaric cycles.”
pression ratio well over 1:100, and for the second
It is also known in the art to combine isother
mentioned temperature r‘ange‘of well over 1:700.
mal compression with isentropic-expansion or
Thus the practical utilization of the techno
vice versa, which measures, however, do not lead
logically available temperature range requires
to improved e?iciencies.
cycles with isobaric heating, which‘ permits‘ to‘ 35 The present invention consists in the realiza
reach the top temperature without involving ex
tion that there exists a cycle, so to speak,‘ in
Amongst these “isobaric cycles” the simples in
application is the‘ Brayton cycle represented in
between the Braytonand ‘the Ericsson cycles,
which requires less inter-cooling and re-heating
than the latter, yet is superior in efficiency to
its ideal form,‘ for example in a T-S diagram, as a 40
either of them.
treme top pressures.
quadrilateral with two isentropic and two isobaric
sides. In other words the Brayton cycle consists
of isentropic compression, isobaric heating, isen
tropic expansion, and isobaric rejection; or in the
In the drawings, Fig. 1 represents a tempera
“ ture-entropy diagram of the Brayton cycle; Fig.
2 of theEricsson cycle; Fig. 3 of the new cycle.
Fig. 4 is a similar diagram of the new cycle in
case of the so-called “closed cycles,” which use 45 cluding the internal losses in compressors and
the same working ?uid over again, isobaric cool
turbines; Fig. 5 of a cycle approximating the iso
ing before re-c‘ompression.
The Brayton cycle, however, ‘is limited to low
thermic parts of the new cycle by two individual
intercoolings and two individual reheatings. Fig.
compression ratios and furnishes ‘therefore a
6 shOWS a power system operating on the new
comparatively small output per weight unit of 50 cycle.
working ?uid, and is accordingly sensitive to the
In the Fig. 1 the Brayton cycle, in Fig. 2 the
internal losses of the practical compression and
Ericsson cycle, and in Fig. 3 the new cycle are
expansion means and in conduits.
shown in the usual T-S diagrams, each'within
the same temperature rangeTi .‘ . . T2 and the“
This results in compartively low‘practical ther
mal overall e?lciencies for the Brayton‘ cycle, par
same pressure range ‘m . . . p2‘.
In Fig. 1, the quadrilateral l l--l2—l3-—|4 rep
resents the Brayton cycle, in Fig. 2, the quadri
lateral 2I—22_23—-24 represents the Ericsson
cycle; in Fig. 3, the hexagon 3l—32—-33-—34-—
35-35 represents the fundamental theoretical (11
45-46, are not strictly isentropic any more, but
somewhat inclined due to the 15 per cent internal
losses in the compression and expansion means.
The Figures 3 and 4 represent, so to speak,
form of the new cycle, which for the purposes
ners. These are, however, not essential for the
present invention. In practical execution some
of the corners may be rounded off or disappear
of this speci?cation may be referred to hereafter
as “Hexagon cycle.” It consists of an isothermic
schematic forms of the new cycle, with six cor
altogether; in Fig. 4 this isshown by dotted lines
32——33, an isobaric heating 33—34‘, an isothermic 10 42' and 45’ for the corners 42 and 45, indicating
that there must not necessarily exist a de?nite
expansion 34—35, an isentropic expansion 35—36,
demarcation between an isothermal and an isen
and isobaric rejection, or re-cooling in the case
tropic, or near-isentropic, part of the compres
of a closed cycle, 36—3l. Dotted lines in Fig. 3
sion and expansion, respectively. It is only es
show the corresponding Brayton cycle 3l-32’-—
sential for this invention that the compression as
34—35', and the corresponding Ericsson cycle
a whole leads from a starting point 4| to an end
point 43 which has both a substantially higher
The isobaric heating 33-44 of the Hexagon
temperature and a substantially smaller entropy,
cycle may be carried out solely by direct or in
and that the expansion as a whole leads from a
direct transfer of fuel combustion heat to the
starting point 44 to an end point 46 which has
compressed working ?uid, or partly by regenera
both a substantially lower temperature and a
tion of waste heat from the exhaust gases past
substantially larger entropy.
point 36, as in the case of other cycles. The
With “substantially larger entropy” we do not
“ef?ciency” of such regenerative heat transfer is
mean an increase in entropy due to internal
determined by the ratio of the transferred heat
to the enthalpy difference between points 38
losses, but an increase corresponding to an in
crease in useful expansion work; and with “sub
and 33.
stantially smaller entropy at the end point of
The means for the practical execution of the
compression” we mean a decrease in entropy cor
Hexagon cycle are basically the same as for the
responding to a saving in mechanical compres
Ericsson cycle; the difference consists in re
stricting the inter-cooling to the ?rst part of 30 sion work. In other words, a straight line con
necting, for example in Fig. 4, the starting point
the compression, and the re-heating to the ?rst
4| and the end point 43 of the compression, shall
part of the expansion. The uncooled part of the
have a substantial inclination both against the
compression shall, according to this invention,
cover at least forty per cent of the pressure diiier
horizontal and the vertical, forming a very rough
ence between the highest and lowest pressure in 35 ly approximated perpendicular to the isobars
43--44 and 46—4l. This distinguishes the new
the system. Thus the practical execution be
comes simpler. Yet the e?iciency is superior to
cycle from those known in the art, which aim at
both the Brayton and the Ericsson cycles~
ideal compression lines either throughout hori
In a comparative numerical example, calcu
zontal (isothermal) or throughout vertical (isen
tropic), deviating therefrom only to the extent
lated for identical conditions, the thermal e?i
ciency of the three cycles is as follows:
due to the imperfection of the practical means of
Brayton Ericsson Hexagon
It is within the scope of this invention to real
ize, compression in a way as may be represented
by curves of various forms between the points 4!
and 43 thus characterized. The same holds good
Without waste heat regeneratiom. _ l
21. l
21. 5
25. 6
for curves representing the expansion between
Vi’1th‘5?% Waste heat regeneration. . _
24. 3
31. 2
34. 0
points. 44 and 46. While the cycle. with the fun
dammital isothermic-isentropic angle (3l-—32-_
All ?gures of the above table are calculated for
33, and. 34-—35-36 in Fig; 3), gives the highest
temperature limits 15 deg. C. and 650 deg. 0.,
theoretical e?iciency, deviations therefrom may
pressure limits 1 and 6 at absolute, and 85 per
be resorted to for practical considerations. For
cent internal efficiency for compression and ex
example the isothermic. part of the compression
pansion. The accuracy of the computation can
and/or expansion may be approximated by inter
be easily veri?ed by anyone skilled in the art.
cooling and/or re-heating in a de?nite number
The above ?gures, which represent. practical
of individual points between stages of compres
working conditions, clearly demonstrate that the
sion or expansion, respectively; 'Ilhe intercool
Hexagon cycle combines simpli?cation in ‘prac
ing and/or re-heating may lead back to the start
tical execution with a marked improvement in
ing temperature or to a different temperature.
e?iciency over what the art has so far known.
In actual execution the e?iciency difference 60 Fig. 5 shows such a cycle with intercooling and
reheating in two individual points each. The
between the Hexagon cycle and the Ericsson cycle
corresponding schematic Hexagon cycle is indi
will be still larger than that shown in the above
cated in dotted. lines. In its form of execution
table, in which the pressure losses in the sys
by intercooling and reheating in individual
tems have not been taken into account. Near
compression 31-32., an isentropic compression
isothermic compression and expansion, however,
if practically carried out, involve pressure losses
in the corresponding cooling and heating means,
which lower the ef?ciency. Since the Hexagon
cycle needs materially less cooling and heating
that the Ericsson cycle, the detrimental in?uence
of these pressure losses is correspondingly smaller
in the Hexagon cycle.
Fig. 4 shows a Hexagon cycle such as assumed
for the mentionedcomputation. The second part
of the compression, 42—43, and of the expansion,
points, the Hexagon cycle falls partly within the
scope of ‘our co-pending applications Serial No.
399,242 of June 21, 1941, and Serial No. 401,702
?led July 10, 1941, the latter now abandoned.
It hasalready been realized that too late re
heating may adversely affect the e?iciency and
it has been proposed to restrict reheating to the
?rst part of the expansion. It has, however,
never before been recognized that such. consid
eration is only a part of a basic general, law which
applies equally to. the compression as well as to.
the expansion, and that the combined applica
grade, higher than the highest temperature in
tion of corresponding new rules to cooled com
pression and heated expansion leads to a new
superior cycle as described hereinbefore.
Fig. 6 shows by way of a non-limiting example
the ?rst half of the compression range, that is
at any pressure under 1/2.(p1+p2). In Fig. 5,
for example, the point 53 shall be more than 40
degrees oentigrade higher in temperature than
a combustion turbine power system of the con
the point 52';
tinuous combustion type operating on the cycle
This rule leads to a compression
with a predominantly isotherrnic‘?rst part, and
a predominantly isentropic second part, irrespec
Ambient air is taken in at 60 into multistage
tive of the special character of the curve in the
compressor means 6|, compressed, and cooled 10 T-S diagram representing the practical perform
during compression in coolers 62a, 62b, 62c, and
62d. The cooling takes place only during the
?rst part of the compression, the second part
ance of the compressing and cooling means.
An analysis of the above formulae shows that
both the Brayton and the Ericsson cycles are spe
being uncooled.
cial border cases of the general Hexagon cycle
Thus the compressed air leaves the compressor 15 for following reasons: If the assumed pressure
means at 62 at a substantially increased tem
range is so small that the corresponding tem
perature, is further preheated in recuperator
perature rise for isentropic compression equals
means 63, and ?nally heated to the metallurgi
the value derived from the ?rst formula, the
cally admissible temperature by internal combus
Hexagon cycle loses its isothermal parts and
tion of fuel in heater 64. Thereafter it is ex~
deteriorates into a Brayton cycle. If, at the
panded in multistage turbine‘ means 65, and re
other hand, the e?iciency of waste heat regen
heated during expansion in reheaters 66a, 68b,
and 66c. The heating takes place only during
the ?rst part of the expansion, the second part
being unheated. Thus the working fluid leaves
eration is assumed as one hundred per cent,
(70:1), the Hexagon cycle loses its isentropic
parts and deteriorates into an Ericsson cycle.
Though these considerations have predomi
nantly ‘theoretical importance, they are deemed
necessary for the ready comprehension of the
essence and bearing of the new Hexagon cycle.
In practical applications such border cases will
the expansion means at 61 at a substantially re
duced temperature, and is further cooled by re
generative heat exchange in recuperator 63 be
fore being exhausted to the atmosphere at 68.
The turbine means drive the compressor means, ‘
never occur: It takes a prescribed total pressure
ratio of under 1:3 to make the Brayton cycle the
and the excess power serves to drive an electric
generator 69.‘
best and such limitation will hardly ever be met
in practice; and hundred per cent efiiciency of
waste heat regeneration is an unattainable theo
retical assumption, as is hundred per cent in
ternal efliciency for a turbine.
The means described are basically the same as
for an Ericsson cycle; the difference consists in
the arrangement of both the coolers and heaters
exclusively in the ?rst part of the compression
and expansion, respectively, the‘ second part of
‘ It is further necessary for the complete com
both processes being near-isentropi‘c.
prehension of the bearing of the new Hexagon
cycle to realize that also'the Carnot cycle‘ ap
‘ The present invention further comprises “rules
for the proper selection of the relative position
of the starting point and end point of compres
sion and expansion respectively. For the theo
retical Hexagon cycle with exact isothermic-isen
tropic compression and expansion, and for cycles
pears as one border case of the universal solu
tion represented in the above equations. If we
assume no waste heat regeneration, (lc=0),
but ideal compression and expansion without
losses, and a pressure range su?iciently wide to
closely approximating this fundamental form,
applicants have found that highest efliciency is
permit approach to the “ideal Carnot e?iciency”
reached if the temperature rise during compres
sion is
per cent of the absolute temperature at the start
of compression, and the temperature drop dur
ing expansion is
the introduction of these values for k and 6
results in a temperature rise during compression
equal “T2——T1,” and an identical value for the
temperature drop during expansion. Thus the
equations directly prescribe the entire tempera
ture range between the lowest temperature T1
and the highest temperature T2 to be bridged by
isentropic compression and expansion, thereby
representing the ideal Carnot cycle as another
per cent of the absolute temperature at the start
special solution of the general relations herein dis
of the expansion, where “e” is the thermal over
closed. The Carnot cycle thus emerges from the
all eiiiciency of the practical cycle, and “It” is the
above equations as the best cycle for its condi
efficiency of the waste heat regeneration.
60 tions, that is, for ideal compression and expan
These formulae determine, as it were, the spot
sion without internal losses. But for actual com
“between” the Brayton and the Ericsson cycle
pression and expansion means with internal e?i
where efficiency is highest, sloping down towards
ciences small than one hundred per cent, the
either side. But since ‘the point thus determined
equations furnish values for the temperature
is the apex of a continuous efficiency curve of 65 differences during compression and expansion
parabolic character, a margin in the temperatures
much smaller than the entire temperature range,
derived from the formulae up to :- six to eight
thereby designating a six-cornered Hexagon
per cent of the absolute temperatures involved
cycle as the best possible cycle for the assumed
does not yet materially reduce the ef?ciency.
conditions. In other words, if the huge pres
For cycles with‘ a compression represented in a
sure ranges necessary for the realization of the
T-S diagram by a more irregular curve, or broken
Carnot cycle were available, as they might con
line, it has been found that the favorable effect
ceivably be in future, but practical compressors
of the new cycle is achieved if the compression
and turbines are to be reckoned with, the prac
end temperature is by the value derived from the
tical Hexagon cycle is superior to any practical
above formula, or at least by forty degrees centi
' Carnot cycle for identical conditions.
The difference is very considerable: For a cal
culated example in which the internal losses
bring the Carnot cycle down from 69 per cent
ideal e?iciency to thirty per cent practical ef?~
ciency, the corresponding Hexagon cycle still re
working fluid, the sequence of near-isothermic
compression approximated by intercooling in a
plurality of individual points between stages of
compression, uncooled compression, near-isobaric
heating, near isothermic expansion approximat
tains ?fty per cent practical e?ciency under
ed by reheating in a plurality of individual
sion, unheated expansion to a pressure near the
thermic expansion approximated by reheating in
points between stages of expansion, and unheated
identical assumptions.
expansion to a pressure near the starting pres
From the foregoing description it will be evi
sure of compression, the uncooled compression
dent that the invention may be embodied in
many speci?c forms and arrangements of appa 10 covering a pressure range of at least forty per
cent of the total difference between the highest
ratus, and that certain features of the invention
and the lowest pressure in the system.
may be employed to the exclusion of others. Ac
4. In the method of producing power in heat
cordingly, it is to be understood that the inven
engines through cyclic changes of a gaseous
tion includes all forms of apparatus that may fall
within the scope of the appended claims.
15 Working ?uid, the sequence of near-isothermic
cooled compression, uncooled compression, near
What we claim is:
isobaric heating, near-isothermic heated expan
1. In the method of producing power in heat
sion, unheated expansion to a pressure near the
engines through cyclic changes of a gaseous
starting pressure of compression, the end tem
Working fluid, the sequence of compression from
a starting point of given pressure and tempera 20 perature of said uncooled compression being more
than forty degrees centigrade higher than the
ture to a compression end point of substantially
highest temperature during that part of the
smaller entropy and a temperature more than
compression where the pressure is lower than
forty degrees centigrade higher than the tem
the arithmetical mean of the lowest and the
perature at any point within the ?rst half of
the compression range, heating to a still higher 25 highest pressure in the system.
5. In the method of producing power in heat
temperature at substantially constant pressure,
engines through cyclic changes of a gaseous
expansion therefrom to a point of substantially
working fluid, the sequence of near-isothermic
larger entropy, substantially lower temperature,
compression approximated by intercooling in a
and a pressure substantially equal to that of the
compression starting point.
30 de?nite number of individual points between
stages of compression, uncooled compression to a
2. In the method of producing power in heat
compression end temperature more than forty
engines through cyclic changes of a gaseous
degrees centigrade higher than the temperature
working fluid, the sequence of near-isothermic
at any point within the ?rst half of the com
cooled compression, uncooled compression, near
pression range, near-isobaric heating, near-iso
isobaric heating, near-isothermic heated expan
a de?nite number of individual points between
stages of expansion, unheated expansion to a
compression covering a pressure range at least
pressure near the starting pressure of compres
forty per cent of the total difference between
the highest and the lowest pressure in the sys 40 s1on.'
3.. In the method of producing power in heat
starting pressure of compression, the uncooled
engines through cyclic changes of a gaseous
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