DE20210841U1 - heat pipe - Google Patents

Description

The invention relates to a heat pipe according to the preamble of claim

Recently, heating systems with heat pumps have increasingly become competitors of heating systems that run on fossil fuels. This increasing use of renewable energies can counteract the problems of fossil energy supplies. The use of renewable energy sources requires the use of heat pumps of different designs.

The principle of heat pumps is that heat is absorbed from the environment and transformed to a higher temperature level. The coefficient of performance or the heating coefficient of a heat pump depends crucially on the temperature difference between the heat source and the heat sink. Since the temperature of the heat sink is usually predetermined, the quality of the heat source determines the possible applications and the economic efficiency of the heat pump.

Since the use of air as a heat source still presents considerable difficulties due to significant disadvantages, such as large equipment volumes, acoustic problems, strongly fluctuating outside temperatures and the pronounced divergence between the heat pump's heating output and the building's heating energy requirements, some applications are already known in which the ground is used as a heat source due to its temperature stability and high heat capacity. The heat is extracted from the ground using heat exchangers, whereby two systems are basically distinguished.
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In direct systems, the heat exchangers of an evaporator are laid directly in the ground and are flowed through by the coolant of the heat pump circuit.

In indirect systems, the energy is transported from the ground to the heat pump's evaporator via a heat transfer medium that flows in pipes laid in the ground. These pipes are thermodynamically coupled to the heat pump's evaporator, so that the amount of heat required to evaporate the coolant can be extracted from the heat transfer medium.

A distinction is made between ground collectors and ground probes in heat exchangers. The ground collectors are laid over a large area in the ground at a relatively shallow depth (between one and two meters). Geothermal probes, also called heat pipes, are installed vertically or diagonally in the ground and therefore require a much smaller footprint than ground collectors. Such geothermal probes are used, for example, in the

[File:ANM\FK0108K1.DOC] Description^ 09.07.02

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DE 42 11 576 Al. In this known solution, the geothermal probe is filled with a coolant as a heat transfer medium, which is evaporated in the lower part due to the earth's heat. The coolant vapor rises and condenses in the upper, cold part of the probe. The condensation heat released is used to evaporate the coolant in the heat pump circuit. The condensed coolant in the probe then flows back into the lower part and is evaporated there again - the internal circuit of the geothermal probe is closed.

DE 298 24 676 describes a heat pipe in which CO2 is used as the heat transfer medium for the heat pipe instead of CFCs, ammonia or hydrocarbons. The main advantage of CO2 is its good environmental compatibility, so that there is no risk of environmental damage if the heat pipe leaks. Furthermore, CO2 is non-flammable, non-toxic and has a lower thermal conductivity than conventional refrigerants.

negligible greenhouse potential under certain fundamental

performance limits.

In contrast, the object of the invention is to create a heat pipe that can be operated with a satisfactory coefficient of performance.
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This object is achieved by a heat pipe having the features of claim 1.

According to the invention, the heat pipe has an inner pipe which is surrounded by an outer pipe. The annular casing between the inner and outer pipes forms a flow space for the condensed partial flow of the heat transfer medium, which flows downwards on the peripheral walls as a liquid film due to the effect of gravity. In the opposite direction, the gaseous partial flow evaporated by the earth's heat rises upwards in the inner pipe, so that the flowing gas flow is separated from the condensate flow in terms of flow. In this way, the liquid film can build up essentially unhindered to the lower end of the heat pipe, so that the risk of a reduction in the coefficient of performance due to an obstruction of the liquid flow is minimal.

In a particularly preferred variant, the inner tube is provided with openings at least in sections, which are designed, for example, as a perforated grid or as a slot formation. The gaseous phase can enter the inner tube from the annular space via these openings, so that the liquid film can build up unhindered even at high gas velocities.

To improve the heat exchange performance, fins can be formed on the outer peripheral surface of the outer tube so that the heat exchange area is increased.

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The heat pipe according to the invention is preferably operated with CO2 as a heat carrier, but also with other vaporizable substances.

The double-walled heat pipe according to the invention can be assigned a heat exchanger, the inlet of which is connected to the inner pipe carrying the vaporous phase and the outlet of which is connected to the annular space of the heat pipe which receives the condensate. This heat exchanger is then in turn operatively connected to an evaporator of a refrigerant circuit.
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In principle, it is also possible to connect the heat pipe directly to a refrigerant circuit, i.e. without the aforementioned heat exchanger. In this case, suitable measures must be taken to maintain the oil balance of the refrigeration system, such as sucking out the oil that accumulates in the lower area, for example using a mechanical or a steam or liquid jet pump.

The heat exchanger is preferably designed as a plate, tube bundle, coaxial or tube coil heat exchanger.
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Other advantageous further developments are the subject of the further subclaims.

A preferred embodiment of the invention is explained in more detail below using schematic drawings. They show:

Figure 1 is a schematic representation of a heat pump system with a heat pipe according to the invention and

Figure 2 shows a schematic representation of the heat pipe from Figure 1.

Figure 1 shows a schematic of a heat pump system 1, such as can be used for a heating system in a residential building, for example. In such a heat pump system, a coolant is isentropically compressed by a compressor 2 and fed to a heat exchanger 4. In this heat exchanger 4, the compressed coolant is condensed, and the condensation heat is used in the heat exchange with the environment to heat up a medium or the environment. The condensed coolant is expanded in a throttle 6 or an expansion machine and evaporated in an evaporator 8, so that the initial state of the coolant is again present at the outlet of the evaporator 8. The evaporation heat required for the evaporation of the coolant must be supplied externally to the evaporator 8. In the embodiment shown in Figure 1, this takes place via a heat pipe 10.

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Such heat pipes 10 are in principle already known from the prior art, so that with regard to the function and structure, reference is made to the existing literature, for example to the DE 42 11 576 mentioned at the beginning and the literature cited therein.
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Figure 2 shows a schematic sectional view of a heat pipe 10, as can be used in the heat pump system described above. Such a heat pipe 10 is inserted vertically or at an angle into the ground 12, whereby the effective length can be between 5 and 25 meters. Particularly good results were achieved with heat pipes with a length of 18 meters. In the event that particularly high performance is required, several heat pipes can be connected in parallel.

According to Figure 2, the heat pipe 10 is designed as a double pipe and has an outer pipe 14 which surrounds an inner pipe 16 arranged coaxially thereto. The latter is provided with openings over at least a partial section, whereby in the embodiment shown in Figure 2 the openings are radial bores or differently shaped openings 18 which form a perforated grid. The outer and inner pipes 14, 16 delimit an annular space 20 in which the condensate 22 flows downwards as a film. The inner pipe 16 delimits a flow space 24 for the evaporated heat transfer medium (vaporous phase 26).

The annular space 20 is connected to the outlet of an intermediate heat exchanger 30 via a condensate line 28, while the flow space 24 is connected to the inlet of the intermediate heat exchanger 30 via a steam line 32. In the intermediate heat exchanger 30, the gaseous phase of the heat transfer medium is condensed and the released evaporation enthalpy is used in the evaporator 8 of the refrigerant circuit to evaporate the refrigerant.

In principle, it is also possible to connect the heat pipe directly to the refrigerant circuit without an intermediate heat exchanger, but suitable measures must be taken to maintain the oil balance of the refrigeration system.

The intermediate heat exchanger can be of conventional design, for example as a plate, tube bundle or coaxial heat exchanger; built-in tube coils can also be used as heat exchangers.

To increase the heat exchange surface, 14 fins or lamellae can be formed on the outer circumference of the outer tube.

In the embodiment shown in Figure 2, CO2 is used as the heat carrier, which is contained in the heat pipe 10 at a pressure of about 40 bar. Due to the geothermal energy, the liquid CO2 in the base 34 is evaporated by heat transfer with the surrounding soil. The steam 26 rises at a comparatively high speed in the flow space 24 delimited by the inner pipe 16 to the head 36 and exits via the

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Steam line 32 into the intermediate heat exchanger 30. The steam is condensed by heat exchange with the coolant and the condensate is introduced into the annular space 20 via the condensate line 28. The condensate flows as a liquid film along the peripheral walls of the annular space downwards to the base 34 and is evaporated in the process - the heat transfer circuit inside the heat pipe is closed. In this design, the inner peripheral surface of the outer tube 14 acts as a heat exchange surface for film evaporation, with the film evaporation distance being predetermined by the length of the heat pipe. The steam can enter the inner tube 16 through the radial bores 18 so that the build-up of the liquid film is not hindered by the steam flowing in the opposite direction. This means that the condensate film can build up unhindered up to the base of the heat pipe without the gas velocity restricting the length of the film due to the steam flow. This makes it possible to design the heat pipe 10 with a greater length than, for example, in designs such as in DE 298 24 676 or the German utility model DE 201 20 401.

[File:ANM\FK0108K1.DOC] Description, 09.07.02

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Reference list

1 Heat pump system 2 compressor 5 3 Heat exchanger 6 throttle 8th Evaporator 10 Heat pipe 12 soil 10 14 Outer tube 16 Inner tube 18 Radial bore 20 Annular space 22 condensate 15 24 Flow space 26 vaporous phase 28 Condensate line 30 Intermediate heat exchanger 32 Steam line 20 34 Foot 36 Head

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Claims (9)

1. Heat pipe with a receiving space for a heat transfer medium which can be evaporated by geothermal energy and can be condensed by heat exchange with a heat sink, characterized by an inner pipe ( 16 ) and an outer pipe ( 14 ) enclosing the inner pipe, wherein the condensed partial flow ( 22 ) of the heat transfer medium is guided essentially in the annular space ( 20 ) between the outer and inner pipes ( 14 , 16 ) and the vaporous partial flow is guided essentially in the inner pipe ( 16 ). 2. Heat pipe according to claim 1, wherein the inner tube ( 16 ) is provided entirely or at least partially with openings ( 18 ). 3. Heat pipe according to claim 2, wherein the openings (I8) form a perforated grid. 4. Heat pipe according to claim 2, wherein the openings are slots. 5. Heat pipe according to one of the preceding claims, wherein ribs are formed on the peripheral surface of the outer tube ( 14 ), which preferably run in the longitudinal direction of the tube. 6. Heat pipe according to one of the preceding claims, wherein the heat transfer medium is CO ₂ or contains another vaporizable substance. 7. Heat pipe according to one of the preceding claims, with an intermediate heat exchanger ( 30 ) whose inlet is connected to the inner pipe ( 16 ) and whose outlet is connected to the annular space ( 20 ). 8. Heat pipe according to claim 7, wherein the intermediate heat exchanger ( 30 ) is a plate, tube bundle, coaxial or tube coil heat exchanger. 9. Heat pipe according to one of the preceding claims, wherein several heat pipes with inner and outer tubes ( 16 , 14 ) are connected in parallel.