Note: Descriptions are shown in the official language in which they were submitted.
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System and method for cooling at least one heat-producing device in an
aircraft
TECHNICAL FIELD
The invention relates to a system for cooling at least one heat producing
device in an
aircraft, to a method for cooling at least one heat producing device, to the
use of a
system for cooling at least one heat producing device in an aircraft, and to
an aircraft
comprising at least one heat producing device and at least one system for
cooling the
heat producing device.
BACKGROUND TO THE INVENTION
In larger aircraft of a modern design, increasingly a multitude of devices are
integrated
which during normal operation of the aircraft produce a considerable amount of
heat
which must safely and reliably be removed from the aircraft and dissipated,
for
example to the environment. For example, modern commercial aircraft comprise a
multitude of different arithmetic units or other (power) electronics units,
which are
generally referred to as "avionics" and which are accommodated in an avionics
compartment. In the state of the art avionics compartments in aircraft are
cooled by
means of various systems. Systems are known in which a coolant by way of a
coolant
circuit absorbs heat from the avionics compartment and dissipates said heat to
the
environment by means of a skin-section heat exchanger. However, in this
arrangement
the situation when the aircraft is located on the ground on hot days is
critical, because
the temperature difference between the skin-section heat exchanger and the
environment may be insufficient to carry out adequate heat dissipation.
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Furthermore, it is known, at least in flight, to cool components in the
avionics
compartment by blowing in air from the aircraft cabin, wherein air from the so-
called
"triangular region" underneath the cabin floor and near the fuselage wall
could be
removed and, after absorbing heat from the avionics devices, leaves the
avionics
compartment in a heated state. However, this requires that the air
conditioning system
of the aircraft is already operative and, in particular during stops on the
ground on hot
days, the cabin has been cooled down to a predetermined temperature level.
Accordingly, it may be required, during operation of an aircraft on a hot day,
to first
operate the air conditioning system before the avionics devices can be
switched on.
Furthermore, it is known for outside air to be used in order to dissipate heat
from the
interior of an aircraft to its environment. To this effect, by way of a so-
called ram air
duct, air that flows past the aircraft in flight is guided into the interior
of the aircraft, is
fed by way of a heat exchanger that thermally communicates with the coolant to
be
cooled, and is discharged to the aircraft environment by way of an outlet
opening. In
this process the air flowing through the ram air duct absorbs heat to be
dissipated. This
principle is, for example, already used in aircraft air conditioning systems
in order to
cool hot compressed air that is later to flow into the aircraft cabin.
Furthermore, this
principle is used in cooling systems, as described for example in DE 4340317.
The air
flowing through the ram air duct could, however, noticeably increase the
aerodynamic
resistance of the aircraft in flight. On the ground the ram air can be
conveyed through
the ram air duct by means of a fan.
SUMMARY OF THE INVENTION
It could thus be considered to be an object of the invention to propose a
cooling
system for cooling heat producing devices in an aircraft, which cooling system
independently of an ambient temperature and independently of an air
conditioning
system makes possible reliable cooling of the heat producing devices.
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Likewise it could be considered an object of the invention to propose such a
cooling
system that is associated with as little complexity as possible, with the
lowest possible
energy requirement, the lightest possible weight, which cooling system in
particular
does not generate any additional aerodynamic resistance.
This object is met by a system for cooling at least one heat producing device
in an
aircraft, comprising at least one coolant circuit through which coolant flows
in order
to absorb heat from the heat producing device, wherein the coolant circuit
comprises a
feed line arranged upstream of the heat producing device, and a return line
arranged
downstream of the heat producing device. The system according to the invention
is
characterized in that a heat dissipation device that thermally communicates
with the
return line of the coolant circuit for dissipating heat from the coolant
circuit is
provided, in that a temperature spreading device reduces the temperature of
the
coolant in the feed line of the coolant circuit and increases a heat
dissipation
temperature of the heat dissipation device relative to the temperature of the
coolant in
the return line of the coolant circuit.
The type of heat dissipation device does not limit the invention. Instead,
numerous
types of heat dissipation devices are to be considered as being suitable, by
means of
which heat can be dissipated to an environment. The use of heat transfer
devices
suggests itself, which heat transfer devices implement direct, indirect
(recuperative),
and/or semi-direct heat transfer.
The coolant can be of a liquid or gaseous nature. Any type of commonly used
coolant
or special coolant can be used. The invention is not limited to the type of
coolant.
Thus by means of the temperature spreading device the coolant is cooled down
to a
suitable temperature so that a distinct and adequate temperature difference to
corresponding heat transfer means (cooling elements, heat exchangers and the
like) on
the heat producing devices is produced in order to in an efficient manner
absorb heat
from the heat producing devices. At the same time, by means of the temperature
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spreading device, the heat dissipation temperature of a heat dissipation
device is
significantly increased relative to the temperature of the coolant in the
return line,
which means that even when the aircraft is situated on the ground on hot days
in the
sun an adequate temperature difference between the heat dissipation device and
the
environment of the aircraft can be ensured.
This provides a further technical effect in that it is not necessary to have
already
started up an air conditioning system of the aircraft in order to be able to
provide
adequately cool air for cooling the heat producing devices. Instead, it is
imaginable to
start up the temperature spreading device already shortly before starting up
the heat
producing devices so that in a relatively timely manner adequate cooling of
the heat
producing devices can be ensured even in the case of extreme temperatures
within the
aircraft. By means of the significant increase in temperature relative to the
temperature of the coolant in the return line of the coolant circuit any type
of heat
dissipation device, for example a heat exchanger or the like, can dissipate
the heat
absorbed by the coolant to the environment even in the case of extreme ambient
temperatures.
The invention is not limited to the use of a single design of a temperature
spreading
device; instead, any equipment, devices and systems can be used that are able
to
spread a temperature level between two coolant lines. Accordingly, compression
cooling machines, absorption cooling machines, diffusion absorption cooling
machines, adsorption cooling machines, cooling machines based on the Joule-
Thomson effect, thermo-electrical cooling generators (Peltier elements) and
the like
are imaginable. In addition, pure heat sinks or heat sources are imaginable in
order to
increase or decrease the temperature in a coolant line.
The design of the system according to the invention is not complex, involves
low-cost
technically mature components, and can be operated without active blowing of
cooling air or the like from the aircraft to the outside.
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According to an advantageous improvement of the system according to the
invention,
the heat dissipation device is designed as a skin-section heat exchanger. The
skin-
section heat exchanger can in particular in flight ensure adequate heat
transport to the
environment.
In order to improve the cooling performance with the aircraft situated on the
ground,
the skin-section heat exchanger can extend into an air duct pointing towards
the
aircraft interior, which air duct comprises at least one conveying device for
conveying
air from the environment or for conveying ram air. The extension of the skin-
section
heat exchanger into the air duct means that the skin-section heat exchanger
can not
only dissipate heat on the outside of the aircraft, but also comprises
lamellae, ribs or
other air-permeable structures towards the interior of the aircraft, which
structures
make it possible to dissipate heat to the ambient air. With the aircraft
stationary on the
ground, an air flow through the air duct can be enforced by operating the
conveying
device.
In an advantageous improvement of the system according to the invention, on
openings that are directed towards the surroundings the air duct comprises
closing
elements which during adequate flight speed of the aircraft can be closed in
order to
eliminate the additional aerodynamic resistance. The closing elements could,
for
example, be designed in the form of flaps or rotary-closure screens, wherein
the drive
is to be implemented by electric, pneumatic, or hydraulic actuators that are
customary
in this special field.
In an advantageous improvement of the system according to the invention the
coolant
circuit is an open circulation system. This provides an advantage in that air
can be
used as a coolant. Since a certain air volume flow needs to be removed anyway
from
the cabin of the aircraft to the environment, at least part of this can be
used as coolant
for the system according to the invention.
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Furthermore, in a favorable embodiment the temperature spreading device
comprises
a first coolant medium circuit with a condenser and an evaporator. In this
way, by
means of mature technology, in a mechanically simple manner and economical
manner adequate temperature spreading and consequently particularly efficient
cooling can be achieved by means of the system according to the invention.
According to an advantageous improvement of the system according to the
invention,
the condenser can be cooled with air from an additional air source, wherein
the air
source is situated in the interior of the aircraft and/or is implemented with
the use of
ambient air and/or bleed air. In this manner still further improved
temperature
spreading is achieved. This suggests itself in those cases where air is used
as a
coolant, and in particular where the coolant circuit is open.
It is equally advantageous if the condenser is arranged at the return line of
the coolant
circuit. In this manner at the same time the temperature reduction that can be
achieved
by the evaporator is improved, and consequently the overall efficiency of the
system
according to the invention is improved.
At the same the evaporator too can be arranged at the return line of the
coolant circuit,
wherein in this case, however, the condenser is not to be arranged at the feed
line of
the coolant circuit, but instead could, for example, be directly connected to
the heat
dissipation device or to some other heat dissipating element.
According to an advantageous improvement of the system according to the
invention,
the condenser can be connected to a heat exchanger that is subjected to air
from an air
source, wherein the air source is located in the interior of the aircraft,
and/or is
implemented by ambient air. Consequently, in this embodiment, too, the heat of
the
condenser can be dissipated by means of the heat exchanger to the through-
flowing air
from the air source.
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Furthermore, in an advantageous improvement of the system according to the
invention, the temperature spreading device could comprise a first heat
exchanger for
cooling coolant from the return line of the coolant circuit with air from an
air source,
wherein the air source is situated in the interior of the aircraft, and/or is
implemented
by ambient air. In this manner, at least in the case where the air
conditioning system of
the aircraft is already in operation, or in the case of adequately low ambient
temperatures, reliable operation of the system according to the invention can
be
achieved, wherein the temperature spreading device should then in addition
comprise
further measures at least for cooling the coolant in the feed line.
The object is furthermore met by a method for cooling at least one heat
producing
device, by the use of a system according to the invention for cooling at least
one heat
producing device in an aircraft, and by an aircraft comprising at least one
heat
producing device and at least one system for cooling a heat producing device
in an
aircraft.
BRIEF DESCRIPTION OF THE DRAWINGS
Further characteristics, advantages and application options of the present
invention are
disclosed in the following description of the exemplary embodiments and of the
figures. All the described and/or illustrated characteristics per se and in
any
combination form the subject of the invention, even irrespective of their
composition
in the individual claims or their interrelationships. Furthermore, identical
or similar
components in the figures have the same reference characters.
Fig. 1 shows a diagrammatic view of a first exemplary embodiment of the system
according to the invention.
Fig. 2 shows a diagrammatic view of a second exemplary embodiment of the
system
according to the invention.
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Fig. 3 shows a diagrammatic view of a third exemplary embodiment of the system
according to the invention.
Fig. 4 shows a diagrammatic view of a fourth exemplary embodiment of the
system
according to the invention.
Fig. 5 shows a diagrammatic view of a fifth exemplary embodiment of the system
according to the invention.
Fig. 6 shows a diagrammatic view of a sixth exemplary embodiment of the system
according to the invention.
Fig. 7 shows a diagrammatic view of a skin-section heat exchanger according to
the
invention.
Fig. 8 shows a diagrammatic view of a method according to the invention.
Fig. 9 shows an aircraft comprising at least one system according to the
invention.
DETAILED PRESENTATION OF EXEMPLARY EMBODIMENTS
In Fig. 1 a first exemplary embodiment of a system 2 according to the
invention for
cooling at least one heat producing device 4 in an aircraft is presented. As
an example
a space 6 is shown in which the heat producing devices 4 are accommodated. The
design of this space 6, which can, for example, be an avionics compartment,
does not
form part of the invention and accordingly is not described in detail.
However, it
should be pointed out that the heat producing devices 4 comprise suitable
means with
which heat can be dissipated to a coolant. These means can be of any design,
for
example heat exchangers, cooling elements or cooling fins around which air or
the
like flows.
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The system 2 according to the invention further comprises a heat dissipation
device 8
which with a feed line 10 and a return line 12 of the space 6 or the heat
producing
device 4 forms a closed circulation system. In this circulation system a
coolant
circulates that flows from the feed line 10 to the heat producing devices 4
where it
absorbs heat, subsequently flows into the return line 12 to the heat
dissipation device 8
where it dissipates heat to the environment of the aircraft, and subsequently
again
flows to the feed line 10 where it is again available for heat absorption.
Efficient heat dissipation by the heat dissipation device 8 to the
environment, and
particularly efficient heat absorption from a heat producing device 4 by the
coolant
from the feed line 10 can be achieved only in those cases where there is a
corresponding temperature gradient to the environment or to the coolant. In
particular
at high temperatures it can be difficult or entirely impossible to achieve a
correspondingly high heat dissipation temperature in the heat dissipation
device 8,
which makes possible a heat flow to the environment in the first place.
Likewise
without further equipment the temperature of the coolant in the feed line 10
would be
so high that there is no adequate temperature difference for cooling the heat
producing
devices 4, and in turn as a result of this a very high volume flow of the
coolant
becomes necessary. If the temperature of the environment is too high, even the
highest
coolant flow may not be sufficient to dissipate the heat.
For this reason the system 2 according to the invention comprises a
temperature
spreading device 14 which as an example is designed as a cooling medium
circuit with
a condenser 16, a flow control valve 18, an evaporator 20, and a compressor
22. This
cooling medium circuit, which is also referred to as a cold-vapor cooling
machine, is
able to increase the temperature of the coolant from the return line 12 by
means of the
condenser 16, and to lower said temperature by means of the evaporator 20.
This
means that the coolant from the return line 12, which has already absorbed
heat, is
heated still further so that the heat dissipation temperature in the heat
dissipation
device 8 is clearly increased. This has the effect that the temperature
gradient to the
environment is adequate even on hot days, thus allowing efficient dissipation
of heat.
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Likewise, the coolant flowing to the feed line 10 is cooled to a significantly
lower
temperature by the evaporator 20 so that, as a result of this, efficient
absorption of
heat from the heat producing device 4 can take place.
If it were to become necessary, for example due to a low ambient temperature,
to
increase to a lesser extent the temperature of the coolant flowing into the
return line
12, in order to reduce heating of the coolant a bypass 24 can be arranged on
the
condenser 16 so that at least part of the coolant flowing into the return line
12 can
flow directly to the heat dissipation device 8.
Fig. 2 shows a modification in the form of a system 26 according to the
invention,
wherein here again the temperature spreading device 14 is designed as a
cooling
medium circuit; however, in this embodiment the overarching coolant circuit is
not
closed. This implicitly means that in particular air is used as a coolant,
which air is
taken from an air source and is again dissipated to the environment of the
aircraft.
In addition, the system 26 according to the invention comprises an optional
further air
source 28, which introduces air into the return line 12 of the coolant
circuit. As a
result of this the temperature of the coolant from the return line 12 is
reduced before
said coolant reaches the condenser 16. An optional bypass 24, shown in a
dashed line
in the illustration, serves to maintain the volume flow balance, and possibly
for the
exclusive use of air from the air source 28 for cooling the condenser 16,
should this air
be cooler than the temperature in the return line 12 of the coolant circuit.
If the aircraft is stationed on the ground on a hot day, it is not expected
that ambient
air automatically enters the aircraft in order to be used in the system 26
according to
the invention. The system 26 according to the invention thus comprises, for
example,
two conveying devices 30 and 32 by means of which fresh air from the
surroundings
of the aircraft is channeled to the evaporator 20 in the direction of the feed
line 10 and
is then conveyed from the aircraft to the outside. In this arrangement the
conveying
devices 30 and 32 are located on suitable air openings 34 and 36, which, for
example,
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in flight can be closed by means of closing elements 38 and 40, and on the
ground can
be opened again.
Fig. 3 shows a further embodiment of the system 42 according to the invention,
in
which system 42 a liquid coolant, conveyed by means of a conveying device 62,
could
be used in a closed circulation system, wherein the closed circulation system
comprises a heat dissipation device 44 which is, for example, implemented by
combining a heat exchanger 46 and a fan 48 in a ram air duct 50.
In order to achieve an efficient spread of the temperature level between the
heat
dissipation device 44 and the feed line 10 a temperature spreading device 52
in the
form of a cooling medium circuit is used, with the latter comprising an
evaporator 54,
a compressor 56, a condenser 58, and a flow control valve 60. However, in the
figure,
as an example the evaporator 54 is arranged between the feed line 10 and the
return
line 12 so that consequently the temperature of the coolant flowing from the
return
line 12 to the feed line 10 is reduced. Since already upstream of the
evaporator 54 a
heat dissipation device 44 can dissipate heat from the return line 12, with
the use of
the cooling medium circuit 52 the temperature in the feed line 10 can be
further
reduced to a significant extent.
Furthermore, the condenser 58 is cooled in a ram air duct or from an
additional air
source 28, for example with the use of extraction air that also, for example,
originates
from the avionics compartment, from the cockpit, or from the cabin. As an
alternative,
the alternative air source 28 can be implemented by means of an inlet valve
for
ambient air on the aircraft fuselage, or by means of bleed air from one or
several
engines 130.
Fig. 4 shows a further embodiment of the system 64 according to the invention,
wherein in the aforesaid the coolant circuit can be constructed so as to be
either closed
or open. A conveying device 66 conveys the coolant from the return line 12 to
the
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feed line 10, where the coolant flows through an evaporator 68 of a
temperature
spreading device 70 that is implemented as a cooling medium circuit that also
comprises a compressor 72, a condenser 74, and a flow control valve 76. As a
result of
this the temperature of the coolant in the feed line 10 is significantly
reduced, which
results in improved heat absorption of the heat from the heat producing
devices 4.
The condenser 74 of the cooling medium circuit 70 is cooled by means of a
secondary
cooling device 78, wherein the latter could, for example, comprise a conveying
device
80, a heat exchanger 82, and a fan 84 in a ram air duct 86.
Such an arrangement is associated with a particular advantage in that the
temperature
spreading device 70 can be accommodated and operated in a pressurized region
of the
aircraft fuselage. In theory a temperature spreading device, for example the
temperature spreading device 52 of Fig. 3, could partially or completely be
accommodated in a non-pressurized region of the aircraft, which could simplify
the
installation when compared to integration of the temperature spreading device
52 in
the non-pressurized region. However, this could be unfavorable for maintenance
purposes, because the cooling medium circuit would have to be interrupted for
maintenance purposes.
If the system 64 according to the invention is operated as an open circuit,
then the two
conveying devices 30 and 32 shown in Fig. 2 could be arranged upstream of the
feed
line 10 and downstream of the return line 12. In this case it would also be
possible to
use air from the environment or from the interior of the aircraft as a
coolant. If the
coolant circuit is designed so as to be closed, any suitable coolant can be
used.
It is of course possible to use not only one single system 2, 26, 42 or 64
according to
the invention in an aircraft; for reasons associated with redundancy,
multiplication is
also imaginable. For this reason Fig. 5 as an example shows a combination of
two
systems 42 according to the invention according to Fig. 3, albeit without the
ram air
duct 50, the heat exchanger 46 arranged therein, and the fan 48. This
embodiment of a
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system 88 according to the invention thus comprises two coolant circuits, each
being
cooled by a temperature spreading device 90 implemented as a cooling medium
circuit. The two coolant circuits are thermally interconnected by valves 92
and 94 as
well as / or by a heat exchanger 96.
It should be pointed out that the illustration is symmetrical, i.e. the upper
coolant
circuit in the drawing plane is shown in a mirror-inverted manner relative to
the lower
coolant circuit.
If, for example, one of the two temperature spreading devices 90 were to fail,
the
return lines 12 of the two coolant circuits could be pneumatically
interconnected by
means of the valve 92, and the feed lines 10 of the two coolant circuits could
be
pneumatically interconnected by means of a valve 94. As an alternative or in
addition
to this, it is also possible for heat to be transferred by way of the heat
exchanger 96
from one coolant circuit to the other coolant circuit. This ensures that, for
example,
two spaces 6 with several heat producing devices 4 in an aircraft, which
spaces are
positioned at locations that are situated apart from each other, can be cooled
adequately, also on the ground, also if one of the temperature spreading
devices 90
were to fail.
Fig. 6 diagrammatically shows a generalized advantageous embodiment of the
system
98 according to the invention, which embodiment can relate to all the above-
described
embodiments. A temperature spreading device 100, which can be implemented in
any
desired manner, is integrated in a coolant circuit that is connected to a
special form of
a heat dissipation device 8 in the form of a skin-section heat exchanger 102.
The skin-
section heat exchanger 102 comprises not only flow ducts 103 that for
convective heat
dissipation to the environment are thermally connected to an outer skin area
104,
through which flow ducts 103 coolant or cooling media flow, but also a ram air
duct
108 as illustrated in Fig. 7. The ram air duct 108, which comprises a first
opening 110
and a second opening 112, is located between the outer skin 104 of the skin-
section
heat exchanger 102 and the aircraft interior, which in the diagram is
designated by
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reference character 106. Through the first opening 110 air can flow into the
ram air
duct 108, and through the opening 112 said air can leave said ram air duct 108
again.
Heat dissipation elements 114, which as an example are designed as cooling
ribs,
extend from the skin-section heat exchanger 102 to the ram air duct 108,
around
which heat dissipation elements 114 air flowing through the flow duct 108
flows. In
this manner the efficiency of heat transfer to the environment can be
improved.
To achieve an adequate airflow for absorbing the heat of the skin-section heat
exchanger 102 when the aircraft is situated on the ground, in addition a fan
116 is
arranged in the ram air duct 108. Accordingly, the skin-section heat exchanger
102 is
not limited to heat transfer by convection on the outer skin 104.
In order to reduce the aerodynamic resistance during flight phases with
adequately
high flight speed and adequately good heat transfer through the outer skin
104, the
openings 110 and 112 can be closed by mechanically driven closing elements
118.
In a method according to the invention according to Fig. 8 at first heat from
heat
producing devices is absorbed 120 by means of a coolant flowing into a return
line of
a coolant circuit, and subsequently the temperature of the coolant in the
return line is
increased 122. By means of a heat dissipation device heat from the coolant
whose
temperature has been increased is dissipated 124, and subsequently the
temperature of
the coolant flowing into a feed line of the coolant circuit is reduced 126.
Finally, Fig. 9 shows an aircraft 128 that is equipped with at least one
system
according to the invention for cooling at least one heat producing device.
In addition, it should be pointed out that "comprising" does not exclude other
elements or steps, and "a" or "one" does not exclude a plural number.
Furthermore, it
should be pointed out that characteristics or steps which have been described
with
reference to one of the above exemplary embodiments can also be used in
combination with other characteristics or steps of other exemplary embodiments
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described above. Reference characters in the claims are not to be interpreted
as
limitations.
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LIST OF REFERENCE CHARACTERS
2 System according to the invention
4 Heat producing device
6 Space
8 Heat dissipation device
Feed line
12 Return line
14 Temperature spreading device
10 16 Condenser
18 Flow control valve
Evaporator
22 Compressor
24 Bypass
15 26 System according to the invention
28 Additional air source
Conveying device
32 Conveying device
34 Opening
20 36 Opening
38 Closing element
Closing element
42 System according to the invention
44 Heat dissipation device
25 46 Heat exchanger
48 Fan
Ram air duct
52 Temperature spreading device
54 Evaporator
30 56 Compressor
58 Condenser
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60 Flow control valve
62 Conveying device
64 System according to the invention
66 Conveying device
68 Evaporator
70 Temperature spreading device
72 Compressor
74 Condenser
76 Flow control valve
78 Secondary cooling device
80 Conveying device
82 Heat exchanger
84 Fan
86 Ram air duct
88 System according to the invention
90 Temperature spreading device
92 Valve
94 Valve
96 Heat exchanger
98 System according to the invention
100 Temperature spreading device
102 Skin-section heat exchanger
103 Flow ducts
104 Outer skin
106 Aircraft interior
108 Ram air duct
110 Opening
112 Opening
114 Cooling fins
116 Fan
118 Closing element
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120 Heat absorption
122 Increase in the temperature of the coolant
124 Heat dissipation
126 Decrease in the temperature of the coolant
128 Aircraft
130 Engine
