Note: Descriptions are shown in the official language in which they were submitted.
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P.7791/St/Li
Allied Heat Exchange Technology AG, A-1120 Vienna (Austria)
Heat exchanger arrangement and method for the operation of same
The invention relates to a heat exchanger arrangement in accordance with the
preamble of claim 1 and to a method for the operation of same in accordance
with the preamble of claim 13.
Heat exchangers are used in a variety of technical applications for example in
refrigeration systems and refrigeration apparatus for cooling rooms or
domestic refrigerators, in heating systems and air conditioning systems for
buildings or means of transportation such as automobiles, buses, ships and
aircraft or as coolers in power stations, combustion engines, computers or
other heat producing devices. In practical use, the heat exchangers are
frequently connected to a circuit which contains a heat transfer medium such
as a coolant, with the heat exchanger being able to absorb heat directly, i.e.
without any phase conversion from the liquid or gaseous heat transfer
medium, or being able to output it to the same or with it also being able to
act
as a condenser or as an evaporator for the heat transfer medium.
A widespread embodiment is the finned heat exchanger which is known, for
example, from domestic refrigerators. In the simplest case, a finned heat
exchanger is made up of a pipe for the conducting of a heat transfer medium
and of a plurality of fins which are connected to the pipe and are in
so communication with a second medium in operation. This design is
particularly
expedient when the second medium is gaseous and consists, for example, of
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ambient air since it has a comparatively low heat transfer coefficient which
can be compensated by a correspondingly large surface of the fins. The
finned heat exchanger can naturally also include a plurality of pipes for more
than one heat transfer medium or the pipes can be connected to one another
in parallel and/or in series as required.
The efficiency is essentially determined by the temperature difference
between the fins, on the one hand, and the pipe or pipes, on the other hand.
The temperature difference is the smaller, i.e. the heat transfer the more
effective, the greater the conductivity and the thickness of the fins and the
smaller the mutual spacing of the pipes. It is thus advantageous with respect
to the efficiency if a plurality of pipes are used. A plurality of pipes,
however,
also means higher material and processing costs so that a higher efficiency is
normally associated with higher costs.
So-called microchannel heat transfer elements have therefore been used in
heat exchangers for some years. They can, for example, be made as an
extruded section which is manufactured from a material having good thermal
conductivity, such as aluminum. The microchannel heat transfer elements, i.e.
the extruded sections in the present case, include a plurality of channels
having a diameter of typically 1 mm for the heat transfer medium. Other
diameters are naturally also possible which can be, for example, in the range
from 0.5 mm to 3 mm or 0.5 mm to 2 mm.
A condensation plant for use in a cooling system is described in the document
EP 1 557 622 A2 to condense refrigerant evaporated for refrigerating .
purposes. The condensation plant described there includes a plurality of
microchannel cooling coils which are each made as heat exchanger modules
and one or more fans to generate an airflow through the heat exchanger
modules. Each heat exchanger module includes a plurality of microchannel
heat transfer elements, which are made as flat pipes and which are arranged
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parallel to and spaced apart from one other, as well as cooling ribs which are
arranged between the flat pipes and are connected to same. The cooling ribs
each form a zig-zag pattern between two adjacent pipes. The heat exchanger
modules furthermore each include an inlet manifold and an outlet manifold
which are connected to the microchannel heat transfer elements of the
respective heat exchanger module. The condensation plant described in EP 1
557 622 A2 admittedly actually does have a compact design, but the base
surface required for the installation of the plant is still considerable.
The object of the present invention is to provide a heat exchanger
arrangement which allows the base surface required for the installation or the
material effort or the energy effort for the ventilation to be reduced with
respect to the prior art described above. A further object is to provide a
method for a comparatively economic operation of the heat exchanger
arrangement.
This object is satisfied in accordance with the invention by the heat
exchanger
arrangement defined in claim 1 and by the method defined in claim 13.
The heat exchanger arrangement in accordance with the invention is
equipped with at least one heat exchanger module, which includes a plurality
of microchannel heat transfer elements and a plurality of heat exchange ribs
which are connected to the microchannel heat transfer elements in a thermally
conductive manner and which form air channels, and with at least one
ventilation apparatus to generate an airflow in the air channels. The heat
exchanger arrangement additionally includes a wetting apparatus to wet the
microchannel heat transfer elements and/or the heat exchange ribs with liquid,
for example with water, and is furthermore characterized in that the heat
exchanger module or modules is/are arranged at an angle with respect to the
vertical.
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The angle is advantageously determined in that the gravity and/or the inertia
forces which act on drops of the liquid on or in a heat exchanger module in
operation are in balance with the buoyancy forces of the airflow.
In an advantageous embodiment, the angle with respect to the vertical is
between 100 and 40 or between 15 and 30 . In a further advantageous
embodiment variant, the heat exchanger module or modules are each
arranged horizontally.
In an advantageous embodiment, the microchannel heat transfer elements
have a longitudinal direction and are each arranged at an angle to the
vertical
in the longitudinal direction. The microchannel heat transfer elements can in
this respect be arranged at the same angle to the vertical as the respective
heat exchanger module in which they are contained. On a case by case basis,
the microchannel heat transfer elements can be arranged horizontally in the
longitudinal direction.
In a further advantageous embodiment, the heat exchanger modules have a
lower side and an upper side, in particular based on the arrangement at an
angle to the vertical, with the ventilation apparatus being configured to
generate an airflow from the lower side to the upper side in the air channels
and with the wetting apparatus being configured to wet the microchannel heat
transfer elements and/or the heat exchange ribs from the upper side or the
lower side. The wetting apparatus is advantageously configured to wet the
microchannel heat transfer elements and/or the heat exchange ribs both from
the lower side and from the upper side.
In addition, the ventilation apparatus can be configured to generate an
airflow
from the upper side to the lower side in the air channels and the wetting
apparatus can be configured to wet the microchannel heat transfer elements
and/or the heat exchange ribs from the upper side.
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In a further advantageous embodiment, openings and/or louvers are formed in
the heat exchange ribs. In an advantageous embodiment variant, the
openings or louvers are made as flow channels which, for example, have an
5 attack angle with respect to the direction of the airflow or which have side
walls, for example, with the side walls being able to be made to project with
respect to the respective heat exchange rib and/or being able to have an
attack angle with respect to the direction of the airflow. Thanks to the
louvers
or openings, in particular when they are made up of a plurality of small
and/or
narrow openings, the wetting liquid amount in the air channels can be
increased.
Independently of the above-mentioned embodiments and embodiment
variants, the angle (a) is advantageously adapted for a maximum cooling
capacity with a given installation area of the heat exchanger arrangement
and/or with a given total area of the heat exchanger modules.
In a further advantageous embodiment, the heat exchanger arrangement
additionally optionally includes a humidification device arranged at the inlet
side in the airflow for the cooling of the air and/or includes a drop catcher
arranged at the outlet side in the airflow.
In the method in accordance with the invention for the operation of a heat
exchanger arrangement in accordance with one or more of the above-
described embodiments and embodiment variants, the quantity of the liquid
supplied for the purpose of wetting the microchannel heat transfer elements
and/or the heat exchange ribs and the speed of the airflow are regulated so
that no drops or at most a fixed amount of drops of liquid present on or in a
heat exchange module is/are taken along by the airflow.
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In an advantageous embodiment variant of the method, the quantity of the
liquid supplied for the purpose of wetting the microchannel heat transfer
elements and/or the heat exchange ribs and the speed of the airflow are
regulated such that the gravity and/or the inertia forces which act on drops
of
the liquid on or in a heat exchanger module are in balance with the buoyancy
forces of the airflow.
The heat exchanger arrangement in accordance with the invention and the
method in accordance with the invention have the advantage that, thanks to
the wetting, the cooling capacity can be increased with respect to the
initially
described prior art with a given total area of the heat exchanger modules and
a given speed of the airflow. On the other hand, the total area of the heat
exchanger modules and/or the speed of the airflow can be reduced for a
preset cooling capacity so that the efficiency of the heat exchanger
arrangement is increased accordingly. Thanks to the circumstance that no
drops or at most a fixed quantity of drops of liquid present on or in a heat
exchanger module is/are taken along by the airflow, the energy expenditure
for the generation of the airflow can be minimized. In addition, thanks to the
openings or louvers formed in the heat exchange ribs, the wetting liquid
amount and thus the cooling capacity at a given size of the heat exchanger
arrangement can be increased or the material effort can be minimized with a
preset cooling capacity.
The above description of embodiments and embodiment variants only serves
as an example. Further advantageous embodiments can be seen from the
dependent claims and from the drawing. Furthermore, individual features from
the embodiments and variants described or shown can also be combined with
one another within the framework of the present invention to form new
embodiments.
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The invention will be explained in more detail in the following with reference
to
the embodiments and to the drawing. There are shown:
Fig. 1 a schematic representation of an embodiment of a heat
exchanger arrangement in accordance with the present
invention;
Fig.2 a schematic representation of an embodiment of a heat
exchanger module for use in a heat exchanger arrangement
in accordance with the present invention;
Figs. 3A-3E embodiment variants for the direction of the airflow and the
direction of the wetting in a heat exchanger arrangement in
accordance with the present invention;
Figs. 4A, 4B two embodiment variants for the arrangement of the
microchannel heat transfer elements in a heat exchanger
arrangement in accordance with the present invention;
Fig. 5A an embodiment for the configuration of the heat exchange
ribs in a heat exchanger arrangement in accordance with the
present invention; and
Fig. 5B a section through a heat exchange rib of the embodiment in
accordance with Fig. 5A.
Fig. 1 shows a schematic representation of an embodiment of a heat
exchanger arrangement in accordance with the present invention. The heat
exchanger arrangement 1 is equipped with at least one heat exchanger
module 2.1, 22, which includes a plurality of microchannel heat transfer
elements and a plurality of heat exchange ribs which are connected to the
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microchannel heat transfer elements in a thermally conductive manner and
which form air channels, and with at least one ventilation apparatus 4 to
generate an airflow in the air channels. The heat exchanger arrangement 1
additionally includes a wetting apparatus 5 which can, for example, include
one or more spray heads 5.1 - 5.4 to wet the microchannel heat transfer
elements and/or the heat exchange ribs with liquid 10, for example with water,
and is furthermore characterized in that the heat exchanger module or
modules 2.1, 2.2 is/are arranged at an angle with respect to the vertical.
The wetting apparatus 5 can be arranged, for example, such that the heat
exchanger modules 2.1, 2.2 are wetted from the interior of the heat exchanger
arrangement, for example by means of spray heads 5.1, 5.2 and/or from the
outside, for example by means of spray heads 5.3, 5.4, and/or the wetting
apparatus can include a liquid distribution system 5.5, 5.6 which is
integrated
into the respective heat exchanger module 2.1, 2.2 and which is equipped, as
shown in document DE 198 04 636 Al, for example, with outlet openings
which are arranged in or at the respective heat exchanger module.
The angle is advantageously determined in that the gravity and/or the inertia
forces which act on drops of the liquid on or in a heat exchanger module in
operation are in balance with the buoyancy forces of the airflow. In an
advantageous embodiment, the angle with respect to the vertical is between
10 and 40 or between 15 and 30 . In a further advantageous embodiment
variant, the heat exchanger module or modules are each arranged
horizontally. The size and number of the heat exchanger modules 2.1, 2.2 can
be fixed in accordance with the required cooling capacity.
Fig. 2 shows a schematic representation of an embodiment of a heat
exchanger module 2 for use in a heat exchanger arrangement in accordance
with the present invention. The heat exchanger module shown includes a
plurality of microchannel heat transfer elements 6.1, 6.2 which can, for
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example, be made as flat pipes and which are usually arranged parallel to and
spaced apart from one another as well as a plurality of heat exchange ribs
7.1, 7.2 which are arranged between the microchannel heat transfer elements
and are connected to the same in a thermally conductive manner, for example
by means of a solder connection. The heat exchange ribs 7.1, 7.2 form air
channels which extend perpendicular to the plane of the diagram in the heat
exchanger module shown in Fig. 2. The heat exchanger ribs are typically
made from a folded strip of sheet metal which can have a zig-zag pattern, for
example.
The microchannel heat transfer elements 6.1, 6.2 can, for example, be made
as an extruded section which is manufactured from a material having good
thermal conductivity such as aluminum or an aluminum alloy. The
microchannel heat transfer elements, i.e. the extruded sections in the present
case, include a plurality of channels having a diameter of typically 1 mm for
the heat transfer medium 3. Other diameters are naturally also possible which
can be, for example, in the range from 0.5 mm to 3 mm or 0.5 mm to 2 mm.
If required, the heat exchanger module 2 can have an inlet manifold and an
outlet manifold 8, 9, which are connected to the microchannel heat transfer
elements 6.1, 6.2 in a liquid conductive manner, as well as an inlet 8a and an
outlet 9a.
The individual parts of the heat exchanger module such as microchannel heat
transfer elements 6.1, 6.2, heat exchange ribs 7.1, 7.2, inlet and outlet
manifolds 8, 9 and inlet and outlet 8a, 9a can be made wholly or partly from
aluminum or from an aluminum alloy and the assembled parts can be
completely soldered in a soldering furnace.
Figs. 3A-3E show embodiment variants for the direction of the airflow and the
direction of the wetting in a heat exchanger arrangement in accordance with
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the present invention. In Figures 3A to 3E, the heat exchanger modules 2 are
each arranged at an angle with respect to the vertical. In Figures 3A and 3E,
the angle shown is <90 , whereas it amounts to 900 in the Figures 3B, 3C and
3D, i.e. the heat exchanger modules are arranged horizontally in Figures 3B,
5 3C and 3D. The heat exchanger modules 2 have a lower side and an upper
side due to the arrangement at an angle to the vertical. In an advantageous
embodiment, the ventilation apparatus is configured to generate an airflow
from the lower side to the upper side in the air channels of the heat
exchanger
module 2 and the wetting apparatus is configured to wet the microchannel
10 heat transfer elements and/or the heat exchange ribs of the heat exchanger
modules from the upper side, as shown in Fig. 3D. This embodiment allows a
high degree of wetting at low air speeds. It is, however, also possible to wet
the microchannel heat transfer elements and/or the heat exchange ribs of the
heat exchanger module from the lower side, as shown in Figures 3A and 3B.
In the embodiment shown in Fig. 3A, the cooling capacity maximum is at an
angle a of 100 to 40 . The embodiment shown in Fig 3B with a horizontally
arranged heat exchanger module requires a comparatively high air speed,
with a power regulation only being possible with limitations by varying the
air
speed. The wetting apparatus is advantageously configured to wet the
microchannel heat transfer elements and/or the heat exchange ribs both from
the lower side and from the upper side, as shown in Fig. 3E. This embodiment
allows a high degree of wetting with a low air quantity.
In addition, as shown in Fig. 3C, the ventilation apparatus can be configured
to generate an airflow from the upper side to the lower side in the air
channels
and the wetting apparatus can be configured to wet the microchannel heat
transfer elements and/or the heat exchange ribs from the upper side. In this
embodiment, the excess water exiting on the lower side can be captured by
baffles and recirculated.
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Independently of the direction of the airflow and of the direction of the
wetting,
the cooling capacity can be regulated by varying the air speed or the liquid
quantity for the wetting. In some embodiments, such as with an airflow from
below and a wetting from above, the range in which the cooling capacity can
be regulated by varying the air speed can be limited.
In the embodiment variants for the arrangement of the microchannel heat
transfer elements in a heat exchanger arrangement in accordance with the
present invention shown in Figures 4A and 4B, the heat exchanger modules 2
are each arranged at an angle a, a' to the vertical which can, as shown there,
be < 90 . This angle can be of different magnitude for the optimization of the
cooling object in dependence on the orientation of the microchannel heat
transfer elements shown in Figures 4A and 4B. The heat exchanger modules
shown each include a plurality of microchannel heat transfer elements 6.1,
6.2, which are usually arranged parallel to and spaced apart from one
another, as well as a plurality of heat exchange ribs 7.1, 7.2, which are
arranged between the microchannel heat transfer elements, are connected to
same in a thermally conductive manner and form the air channels. The heat
exchange ribs are typically made from a folded or bent sheet metal strip which
can, for example, be soldered to the microchannel heat transfer elements in a
soldering furnace.
In an advantageous embodiment, the microchannel heat transfer elements
6.1, 6.2 have a longitudinal direction and are each arranged at an angle to
the
vertical in the longitudinal direction. The microchannel heat transfer
elements
can in this respect, as shown in Fig. 4B, be arranged at the same angle a to
the vertical as the respective heat exchange module 2 in which they are
included, but can also be arranged at a further optimized angle a' or the
microchannel heat transfer elements can be arranged horizontally in the
longitudinal direction, as shown in Fig. 4A. The running off of the wetting
liquid
can be facilitated by louvers which are formed in the heat exchange ribs 7.1.
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7.2 with microchannel heat transfer elements not arranged horizontally in the
longitudinal direction. In contrast, a larger angle a tends to result with
microchannel heat exchange elements 6.1, 6.2 arranged horizontally in the
longitudinal direction.
Fig. 5A shows an embodiment for the design of the heat exchange ribs in a
heat exchanger arrangement in accordance with the present invention. The
individual heat exchange ribs 7' 7" can be manufactured, for example, as
shown in Fig. 5A, from a folded or bent sheet metal strip 7. In an
1o advantageous embodiment, openings and/or louvers 11.1 are formed in the
heat exchange ribs. Thank to the louvers or openings, in particular when they
are made from a plurality of small and/or narrow openings, the wetting liquid
quantity in the air channels can be increased and the propagation of a liquid
film can be promoted in dependence on the arrangement. Fig. 5B shows a
section through the embodiment in accordance with Fig. 5A. As shown in
section, a plurality of louvers 11.1, 11.2 can be arranged next to one another
or behind one another in the direction of the airflow 12. A possible wetting
direction 10 is additionally drawn in Fig. 5B. All the directions of the
airflow
and wetting explained within the framework of the description of Figures 3A to
3E are naturally possible.
Independently of the above-mentioned embodiments and embodiment
variants, the angle (a) is advantageously adapted for a maximum cooling
capacity with a given installation area of the heat exchanger arrangement
and/or with a given total area of the heat exchanger modules.
In a further advantageous embodiment, the heat exchanger arrangement
additionally optionally includes a humidification device arranged at the inlet
side in the airflow for the cooling of the air and/or includes a drop catcher
3o arranged at the outlet side in the airflow.
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The method in accordance with the invention for the operation of a heat
exchanger arrangement in accordance with one or more of the embodiments
and embodiment variants described above will be described with reference to
Figures 1 and 2 in the following. In this method, the quantity of the liquid
10
which is supplied for the purpose of wetting the microchannel heat transfer
elements 6.1, 6.2 and/or the heat exchange ribs 7.1, 7.2 and the speed of the
airflow are regulated such that no drops or at most a fixed quantity of drops
of
liquid present on or in a heat exchanger module 2 is/are taken along by the
airflow.
In an advantageous embodiment variant of the method, the quantity of the
liquid 10 supplied for the purpose of wetting the microchannel heat transfer
elements 6.1, 6.2 and/or the heat exchange ribs 7.1, 72 and the speed of the
airflow are regulated such that the gravity and/or the inertia forces which
act
on drops of the liquid on or in a heat exchanger module 12 are in balance with
the buoyancy forces of the airflow.
Thanks to the wetting with liquid, the performance capability of a heat
exchanger arrangement with microchannel heat transfer elements and folded
heat exchange ribs can be noticeably increased. In this respect, the cooling
capacity increases by the evaporation heat of the evaporating liquid released
per time unit, with the evaporation rate and thus the cooling capacity being
able to be regulated via the degree of wetting and the air speed.
