Note: Descriptions are shown in the official language in which they were submitted.
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05869P0179CA01
Geothermal Probe
The invention relates to a geothermal probe for using
geothermal heat, having a bundle comprising a number of closed
heat pipes that are filled for heat transport with a two-phase
working medium that can be evaporated by means of geothermal
heat and can be condensed in a heat output zone, the respective
heat pipes being subdivided over their length into at least a
heat absorbing zone, heat transport zone and heat output zone.
Geothermal heat for heating streets is proposed in
DE 35 32 542 Al. The planned application intended was an
automobile test track. In order to heat this large surface area
during a test program, very large heat absorbing spaces have to
be opened up in the ground for very long bores. In order to
limit this, the heat was collected and stored in storage
containers and output when required to the street to be heated
by a controller guided by climate sensors. Consequently, there
is provided in the case of this heating a suitably designed
system that outputs heat only upon overshooting or undershooting
of climate specific limit values such as atmospheric humidity,
air temperature, wind speed, surface temperature and surface
humidity, and thus spares the heat stored in the ground.
Publication DE 30 37721 Al describes a heat pipe for
utilizing the heat capacity of the ground and/or groundwater,
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for example in order to prevent points from freezing. The probe
pipe is introduced into the ground in the form of a drilling
core such that the surrounding ground acts as heat capacity. The
heat pipe is here a closed pipe having a liquid/gaseous working
medium and surface enlarging inserts for an improved transfer of
heat at the heat source of the heat in the ground to the working
medium. A heat absorbing surface enlarged by satellite pipes or
ribs is mentioned here as a particular feature. The aim of these
measures is to maximize the quantity of the heat flowing in. In
fact, the quantity of heat flowing in is limited largely by the
conductivity of the surrounding ground, and so an increase in
the quantity of heat that can be absorbed is chiefly achieved by
enlarging the diameter of the cylindrical absorbing surface. In
order to utilize the heat more rationally, switches are built
into the heat pipe to control the heat transport according to
requirements by interrupting the return of condensate or by
separating condensation and evaporation parts, or by means of a
switching liquid. A water/alcohol mixture, HCFC or HFC is used
here as working liquid.
Moreover, an implemented prototype system with propane
as working medium that uses a similar method is known.
Publication EP 1529880 and WO 002005045134 relates to a
geothermal probe that heats traffic installations directly and
whose heat flux is led via at least one heat pipe from the heat
source over the transport zone and is distributed over a number
of heat distribution pipes before the heat is output in the
region of a heat sink.
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Patent EP 1194723 Bl represents a design in which the
liquid medium flows downward in a spirally guided pipe that
winds around the pipe with the rising medium. A similar proposal
is made in US5816314.
Patent DE 4240082 Cl describes a probe in which the
advance of the gas is separated from the return of the
condensate of the working medium by perforated plates. This is
performed in order in the case of a capillary tube to separate
the gas bubbles from the liquid as early as on the transport
path, and to feed them to the gas flow.
DE29824676U1, DE20320409U1, DE20210841U1 are known as
publications concerning applications of CO2 as medium in
geothermal probes.
DE20210841U1 describes a probe whose condensate flow is
separated from the gas flow by virtue of the fact that the gas
flow rises in the middle in a separate, central, perforated
pipe, and the condensate flow flows downward along the pipe
outer wall.
DE 29824676U1 describes a probe that can be provided
with ribs in order to improve the heat transfer.
Publication DE20320409U1 describes a probe made from
stainless steel in the form of a corrugated pipe, which is
designed as a single pipe or double pipe. The aim of this is to
enable even relatively long pipes made from non stainless steel
of relatively large diameter to be introduced into the borehole
from a roll in one piece. A further goal in this case is for the
condensate film flowing down not to be impeded by the rising gas
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flow in the case of relatively large borehole depths, a large
pipe diameter and, therefore, a large moving volume of the
working medium. Given the pipe diameter or volume of the probe
pipe envisaged here, this component is subject to relatively
strict provisions of the GPSG (German equipment and product
safety act).
In the known designs of geothermal probes, copper pipes,
protected against corrosion by PE film coating, are also used
with the maximum possible diameter that still permits a slight
deformability such that the pipes can be unwound from a roll,
shaped to be straight and lowered into the borehole. The
greatest possible pipe diameter is prescribed by the minimum
deformability required for installation. Use is made here of a
number of identical-length pipes in a bore. These designs have
already been installed in the case of numerous building heating
systems that use geothermal heat. It is likewise prior art to
use a press material in the borehole with additives that improve
the thermal conduction. In all known cases, the heat absorption
takes place uniformly over the entire borehole depth, at least
from below the neutral zone - a depth where there are no
temperature fluctuations over the course of the year.
In a predominant proportion of the known probes, the
heat is collected either in pipes of the largest possible
diameter and fed to just one use, or it is collected in a number
of pipes of smaller diameter and fed to just one use, for
example a heat exchanger with a downstream heat pump.
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It is the object of the invention to develop a device
for collecting geothermal heat that is adapted to the specific
requirements of an intended use and in this case constitutes a
more efficient and more economic solution.
The invention is reflected in the features of claim 1.
The further back-referred claims relate to advantageous
refinements and developments of the invention.
The invention includes the technical teaching with
reference to a geothermal probe for using geothermal heat,
having a bundle comprising a number of closed heat pipes that
are filled for heat transport with a two-phase working medium
that can be evaporated by means of geothermal heat and can be
condensed in a heat output zone. In this case, the respective
heat pipes are subdivided over their length into at least a heat
absorbing zone, heat transport zone and heat output zone, at
least two heat pipes having different lengths in the heat
absorbing zone and/or in the heat transport zone.
The invention proceeds in this case from the
consideration that, in order to collect geothermal heat by means
of heat pipes, in the case of thermal probes a liquid/gaseous
working medium is used whose condensation temperature is
somewhat below the temperature of the heat source used. The
latter preferably serves as a heat source for keeping traffic
routes and transportation facilities such as railroad facilities
free from frost. This is chiefly done by using a slight
temperature gradient between thermal heat and/or the heat
contained in the groundwater and/or waste water by comparison
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with the temperatures required for the buildings or facilities
to be heated, at least by comparison with the freezing point of
water. There is no need in this case for any additional pumps
driven by extraneous energy, or for other moving parts. In this
context, geothermal heat is to be understood as any low
temperature heat source available below the Earth's surface, for
example including waste heat from sewers.
The invention proposed here operates on the basis of
what are known technically as heat pipes. A heat pipe is a pipe
that is closed in a gastight fashion and installed in a way
largely vertical or greatly sloping and in which the working
medium evaporates at the heat source, rises in the heat sink,
condenses there and flows down again to the heat source in the
same pipe.
The mass flow is the essential influencing variable for
transmissible power. The maximum transmissible power results
from the chain composed of the productiveness of the ground in
the heat absorbing region, the thermal conductivity of the
ground in the surroundings of the bore and of the press material
around the bore, the thermal conductivity of the pipe material
and the type, alignment and size of the heat absorbing surface.
In this case, the productiveness and conductivity as well as the
size and alignment of the absorbing surface are the main
criteria. This shows that the thermal conduction of the probe
material is of lesser significance.
Since there is a requirement for the possibility of
transmitting a number of small, in parts identical powers to in
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each case exactly the same number of heat sinks, and not of
guiding as great as possible a power from one or more pipes onto
a heat exchanger, it is proposed not to feed a number of heat
sinks from a probe pipe, but to assign each heat sink exactly
one heat pipe from a pipe bundle of a probe. In this case, there
is extracted from the ground over the extent of the respective
heat absorbing surface of a heat pipe only as much heat as is
required for the respective heat sink.
It is also possible in this way to fulfil the
requirement for various temperatures for the respective heat
sinks. Since the ground also becomes warmer at greater depth,
the individual pipes can be designed in various lengths and can
then supply different temperatures for their limited heat
absorbing zone from the respective layers. The heat absorbing
surface is limited in that the pipe is thermally insulated
thereabove, and so a heat absorbing region that is precisely
defined in terms of temperature and area is present.
In cases where the absorbing zone of a probe reaches
through a number of geologic layers each having a different heat
capacity, the quantity of heat required at the heat sink is
supplied by adapting the length of the respective heat absorbing
zone.
It is clear from the discussion that a high gas
throughput in a pipe leads to high flow rates. The pipe diameter
limits the mass throughput given a prescribed maximum speed of
the medium. This means that the uniform flow of the condensate
film at the pipe wall downward to the probe foot is prevented by
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the rising gas flow as soon as the flow rate and/or the mass
flow exceed(s) the critical magnitude. This is prevented here by
virtue of the fact that the heat absorbing surface, the quantity
of the fluid in the pipe, and thus the maximum power throughput
are limited. The heat absorbing surface is delimited by virtue
of the fact that the pipe is thermally insulated thereabove and
a heat absorbing region precisely defined in terms of
temperature and area is therefore present.
The particular advantage persists in that the inventive
geothermal probe has an efficiency with reference to heat use,
material use and economy that exceeds the current level. The
efficiency with reference to heat use results from the optimized
absorption of the heat led under control from the ground and
flowing in via a temperature gradient.
It follows that in the case of a probe there is an
application specific subdivision of the heat available in the
ground over the working medium in the framework of a number of
small heat sinks having precisely defined quantities of heat.
Subdivision of the heat flux into a pipe bundle with a number of
heat exchangers improves the operational reliability and
functionality via a multiplicity of subsystems operating
independently of one another. Consequently, a source of error in
the adaptation of the heat fluxes that supply the quantity of
heat to the heat exchangers is just as much avoided as a
potential source of damage, specifically leakiness of the probe
pipe at at least three additional connecting points per
subdivision.
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Different performance requirements of a number of heat
exchangers can be fulfilled in terms of the concept by means of
a single probe. In this case, the material outlay can likewise
be minimized, particularly through the.different lengths of the
probe pipes.
Such geothermal probes with novel components for
obtaining heat are suitable for heating buildings and facilities
and particularly for transportation facilities, for example in
railroad engineering for keeping points free from snow and ice,
platforms and grade crossings and other traffic areas including
outside railroad engineering.
The heat requirement referred to the application can be
fulfilled with heat pipes of smaller diameter than previously
customary. The use of a relatively small pipe diameter permits
substantially thinner walls in conjunction with the same
bursting strength. The following further advantages result
therefrom: material savings, better workability and handling,
and greater flexibility in selection of material. Moreover, a
further material saving of up to 45% can be realized owing to
the different lengths of probe pipes.
At least two heat pipes in the heat absorbing zone
and/or in the heat transport zone can advantageously be of
different diameter. Alternatively, or in combination with this,
different gas pressures can prevail in at least two heat pipes.
Furthermore, different working media can be introduced into at
least two heat pipes. All these embodiments open up the
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possibility of designing individual heat pipes with different
thermal performances, in accordance with requirement.
In a preferred refinement of the invention, the heat
pipes in the heat transport zone can be thermally insulated. In
order further to improve the obtaining of heat, each pipe can be
thermally insulated in the section above the heat absorbing
zone, specifically also against the parallel running probe pipes
with heat absorbing zones lying further below. As a result, only
a negligibly small uncontrolled heat exchange with the
surroundings takes place in the heat transport zone of each
pipe.
In a preferred embodiment, the heat absorbirig zone is
located at the lower end of the respective heat pipe in the pipe
bundle, in order to ensure in each case that no liquid working
medium that would be withdrawn from the thermal circulation can
collect at the pipe end. In order to achieve a more effective
use of the heat source, the various heat absorbing zones of a
pipe bundle are thus arranged at various depths.
A number of heat absorbing zones and heat transport
zones can advantageously be arranged on a heat pipe.
In a preferred refinement of the invention, the heat
absorbing zones of the individual heat pipes can be arranged in
a multistage fashion. Consequently, a number of heat pipes with
heat absorbing zones can be arranged at each stage around the
circumference of the pipe bundle. The number is governed by the
fact that every point at which heat is extracted in the ground
is not substantially influenced by the adjacent heat extraction
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zones. For example, approximately six heat pipes with heat
absorbing zones are thus arranged in each stage around the
circumference.
It is advantageously possible that the heat pipes have
at least sectionally axially running protuberances, or there are
arranged in the interior guide plates whose influence targets
the transport of the returning condensate. In this case, the
returning condensate is fed into the probe pipe, into a region
partially separated from the gas by uninterrupted protuberances,
and also flows therein down to the transport zone as far as into
the heat absorbing zone. This raises the effectiveness, because
the rising gas makes scarcely any contact with the returning
condensate, and so the flow losses and pressure losses in the
pipes are minimized.
Alternatively, the heat pipe can advantageously have
within its walls a spirally running embossment. As a pipe turned
in on itself and having a spiral embossment, the heat pipe
improves the flow conditions, and thus the efficiency. The
effect of this is that a swirl is imparted to the rising gas,
and likewise to the condensate flowing down. Owing to the
different densities of the two aggregate states of the working
medium, and to the different centrifugal forces resulting
therefrom, the gas is very largely separated from the
condensate, the condensate flowing down at the outer wall.
It is advantageously possible that the heat absorbing
surfaces of the heat pipes are enlarged by spiral guidance of
the heat pipes in the heat absorbing zone around the borehole
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axis and/or by additional outer ribs. The smaller diameter of
the probe pipes, correspondingly decreases the circumference,
and thus the absorbing surface, by comparison with a pipe of
large diameter. In order, nevertheless, to utilize optimally
thermal capacity of the ground surrounding the heat absorbing
zone, the pipe can, for example, be guided in a spiral fashion
around the pipe bundle in the zone respectively absorbing heat,
the result being to multiply the absorbing surface.
In a preferred refinement of the invention, it is
possible that in the heat absorbing zone the heat pipes are
designed at least sectionally as a panel heat exchanger that
wholly or partly grips the inwardly lying heat pipes of the
bundle. Relatively large proportions of geothermal heat are
thereby efficiently collected in a simple way over the entire
circumference, or else only a portion of the pipe bundle and
are, for example, made available to selected heat pipes.
It is advantageously possible that the inner wall of the
heat pipes is rough at least in the region of the heat absorbing
zone. Consequently, alongside the increased heat transferring
surface it is additionally possible also to distribute the
returning fluid over the entire surface in the pipe interior.
It is likewise possible that at least one heat pipe is
widened at its pipe end in the region of the heat absorbing
zone. Consequently, there is an increased heat input, in
particular, at the lowermost collecting point of the returning
liquid working medium.
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It is possible in a preferred refinement of the
invention that the heat pipes are twisted about their own axis
in the region of the respective heat absorbing zones. An
improvement in the principle of the heat absorption is achieved
by arranging the pipes in such a way that only the outer ones
absorb heat, and it can additionally be improved by virtue of
the fact that the heat absorbing surface is enlarged in the
absorbing zone by being spirally guided around the insulated
heat pipes, which here form a type of insulated core. This can
also be performed in such a way that a number of pipes are
guided in a quasi-parallel fashion like a multistart thread with
a relatively large pitch. If this results in a flat pitch of the
spiral of the heat absorbing pipe section, and the condensate
flows only at the pipe bottom and is not distributed uniformly
on the pipe wall, it is proposed that the pipe be rotated into
itself in the heat absorbing region. As a result, the condensate
is thrown back again onto the pipe inner wall at least partially
with each rotation of the pipe.
The heat pipe can advantageously be made from aluminum
or steel.
Exemplary embodiments of the invention are explained in
more detail with the aid of schematics, in which:
figure 1 shows a heat probe with heat pipes of different
lengths of the heat absorbing zone H below the Earth's
surface,
figure 2 shows a heat probe with heat pipes of different
lengths of the heat transport zone N through an
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insulation below the Earth's surface and heat
absorbing zones H arranged in multistage fashion,
figure 3 shows a heat probe in which the heat pipe is guided in
a multistage spiral fashion in the heat absorbing zone
H around the borehole axis,
figure 4 shows a heat probe with spiral guidance of two heat
pipes in the heat absorbing zone H around the borehole
axis,
figure 5 shows a heat probe with heat pipes that are designed
in the heat absorbing zone H as a panel heat
exchanger, which grips the inwardly lying heat pipes
of the bundle,
figures 6A to H show a cross section of various designs of panel
heat exchangers at different stages of a heat probe
that at least partly grip the inwardly lying heat
pipes of the bundle,
figure 7 shows a heat pipe of a heat probe with a protuberance
on the wall side,
figure 8 shows a cross section of a heat pipe according to
figure 7,
figure 9 shows a heat pipe of a heat probe with internal guide
plates, and
figure 10 shows a cross section of a heat pipe according to
figure 9.
Mutually corresponding parts are provided in all the
figures with the same reference symbols.
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Figure 1 shows a heat probe 1 with heat pipes 2 of
different lengths of the heat absorbing zone H below the Earth's
surface 0. The bundle is formed from a multiplicity of heat
pipes 2 running parallel in the ground and which are filled with
a two-phase working medium for the purpose of heat transport.
Owing to the geothermal heat, the working medium evaporates in
the region of the heat absorbing zone H and is transported into
a heat output zone K via the heat transport zone N. In the
region of the heat transport zone N, the temperature of the
vaporous working medium corresponds approximately to that of the
surrounding earth layer so that no heat is exchanged here. In
the heat output zone K, the working medium condenses after
outputting heat and flows deep again in the heat pipe 2 owing to
gravity. The heat transferred in the respective heat pipe 2 is a
function of the different pipe lengths in the heat absorbing
zone H.
Figure 2 also shows a heat probe 1 with heat pipes 2 of
different length in the case of the heat transport zone N. The
length of the heat transport zone N is fixed by an insulation 3
below the Earth's surface 0. The heat is transferred to the
working medium via the exposed pipe ends of the heat pipes 2.
The exposed pipe ends form heat absorbing zone H, arranged in
multistage fashion, for the respective heat pipe 2.
Figure 3 shows a heat probe 1 with multistage spiral
guidance of the heat pipes 2 in the heat absorbing zone H around
the borehole axis. A further embodiment is illustrated in figure
4. There, a heat probe 1 is shown with spiral guidance of two
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heat pipes 2 in the heat absorbing zone H, around the borehole
axis. Common to both solutions are enormously enlarged heat
absorbing surfaces owing to a spiral guidance of the heat pipes
2 in the heat absorbing zone H.
Figure 5 shows a heat probe 1 with heat pipes 2 that are
designed in the heat absorbing zone H as panel heat exchangers 7
that grip the inwardly lying heat pipes 2 of the bundle. The
pipe end 8 of the lowest heat pipe 2 is conically widened in the
region of the heat absorbing zone H.
Figures 6A to H show a cross section of different
designs of panel heat exchangers 7 at different stages of a heat
probe 1 that at least partly grip the inwardly lying heat pipes
2 of the bundle. In this case, there is formed at the lowest
lying stage (figure 6A) an annular panel heat exchanger 7 that
opens into the heat pipe 2, which leads centrally upward. On the
first stage (figure 6B), three further panel heat exchangers 7
are respectively arranged around one third of the circumference
about the central heat pipe 2. The heat pipes 2 opening from the
panel heat exchangers 7 are, in turn, guided upward in a fashion
as close as possible to the centrally running heat pipe 2 and
parallel to the latter. The further stages are illustrated
similarly in figures 6C to 6G. Figure 6H shows a cross section
through the pipe bundle as it is to be encountered, for example,
in the heat transport zone N. The inwardly running pipe lengths
are screened with thermal insulation in each stage.
Figure 7 shows a heat pipe 2 of a heat probe 1 with a
protuberance 4 on the wall side. Through these axially running
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protuberances, the returning condensate is fed into the probe
pipe in a region partly separated from the gas by continuous
protuberances or plates, and also flows therein through the
transport zone N downward as far as into the heat absorbing zone
H. The return channel 6 leads the liquid working medium directly
into the protuberance 4. Figure 8 shows the cross section of a
heat pipe according to figure 7.
Alternatively, figure 9 shows a heat pipe 2 of a heat
probe 1 with inner guide plates whose influence causes the
returning condensate likewise to be transported in a targeted
fashion. These solutions raise the effectiveness by virtue of
the fact that the rising gas scarcely makes contact with the
returning condensate, and so the flow losses and pressure losses
in the pipes are minimized. Figure 10 shows a cross section of a
heat pipe according to figure 9.
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