WO2021255176A1

WO2021255176A1 - Heat pipe, system and method for switching and/or programming a transport of heat

Info

Publication number: WO2021255176A1
Application number: PCT/EP2021/066424
Authority: WO
Inventors: Martin Kluge; Jürgen CLADE; Christoph EBERL; Markus Winkler; Erik Wischerhoff; Kilian Bartholomé; Olaf SCHÄFER-WELSEN; Murat TUTUS; Martin Krus
Original assignee: Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e. V.
Priority date: 2020-06-18
Filing date: 2021-06-17
Publication date: 2021-12-23
Also published as: CN115968437A; US20230417492A1; EP3926285A1; JP2023531430A; KR20230037570A

Abstract

The invention relates to a heat pipe (1) having at least one working chamber (2) having at least one evaporator region (3) operatively connected to a heat source and at least one condenser region (4) operatively connected to a heat sink, wherein a working fluid (5) is provided in the working chamber (2) and in a first operating state heat is transported from the heat source to the heat sink by means of the working fluid (5). It is essential to the invention that the heat pipe is designed as a switchable and/or programmable thermal diode or as a switchable and/or programmable heat switch by providing at least one activatable functional material, which is arranged and designed, in a second operating state, to keep the condenser region free of working fluid and/or to prevent the working fluid from evaporating, in order to reduce and/or prevent the transport of heat and/or to change the preferred direction of heat conduction. The invention also relates to a system and a method for switching and/or programming the transport of heat in a heat pipe.

Description

Heat pipe, system and method for switching and / or programming one

Heat transfer

description

The invention relates to a heat pipe according to the preamble of claim 1, a system with a heat pipe according to claim 12 and a method for switching and / or programming the heat transport in a heat pipe according to the preamble of claim 15.

As is known, heat pipes (also known as heat pipes) enable a high heat flux density to be achieved through the heat transport via evaporation heat. Heat pipes usually have a hot side, the heat source, and a cold side, the heat sink. A working fluid is provided in the heat pipe, which is evaporated in the area of the heat source and condensed in the area of the heat sink. The heat transport takes place via the transport of the working fluid and the transfer by means of latent heat of condensation and evaporation.

Known heat pipes have a preferred direction for the heat flow, that is, they are designed as thermal diodes. This means that the diode conducts heat very well in one direction and very poorly in the opposite direction.

Such a thermal diode is for example in Boreyko et al. 2011, Applied Physics Letter 99 (23) and in the document US 8716689 B2. The use of superhydrophobic coatings in the area of the heat sink and superhydrophilic coatings in the area of the heat source results in a preferred direction of the thermal diode described for the heat: Due to the superhydrophobic coating, the surface in the area of the heat sink repels the working fluid so that it is returned to the superhydrophilic area of the heat source is transported and can evaporate there again. The disadvantage of the known thermal diodes from the prior art is that the preferred direction for the heat transport is predetermined and the diode is fixed due to the design, ie cannot be changed or adapted during operation.

The invention is therefore based on the object of proposing a heat pipe or a method for heat transport that is more variable and overcomes the limits of the methods and devices known from the prior art.

This object is achieved by a heat pipe according to claim 1 and by a method for switching and / or programming the heat transport in a heat pipe according to claim 15. Preferred embodiments of the heat pipe according to the invention can be found in claims 2 to 11. In claims 12 to 14 there are configurations of a system with a heat pipe according to the invention. Preferred embodiments of the method according to the invention can be found in claims 16 and 17. The word according to all claims is hereby explicitly included in the description by reference.

As is known per se, the heat pipe according to the invention comprises at least one working chamber with at least one evaporator area and at least one condenser area. The evaporator area is in operative connection with a heat source and the condenser area in connection with a heat sink. A working fluid is provided in the working chamber. In a first operating state, heat is transported from the heat source to the heat sink by means of the working fluid.

It is essential that the heat pipe is designed as a switchable and / or programmable thermal diode or heat switch in which at least one activatable functional material is provided, which is arranged and designed to keep the evaporator area free of the working fluid in a second operating state and / or to prevent the working fluid from evaporating in order to reduce and / or prevent the heat transfer and / or to change the preferred direction of heat transfer. The working fluid fills the working chamber and, depending on the pressure and temperature, is both liquid and gaseous. The phrase “to keep the evaporator area free of the working fluid” refers to the working fluid in the liquid phase in direct contact and / or direct interaction with the surface of the evaporator area. It is also within the scope of the invention that working fluid is present in the gaseous phase in the evaporator area, since the working fluid in the gaseous phase fills the entire volume of the working chamber of a heat pipe.

The invention is based on the applicant's knowledge that the heat transport can be controlled and even reversed by appropriately designing the conditions in the working chamber.

The heat pipe according to the invention thus differs in essential aspects from previously known heat pipes:

An activatable functional material is provided in the heat pipe, which can change from a first state (first operating state of the heat pipe) to a second state (second operating state of the heat pipe). In the first state, the functional material that can be activated enables heat to be transported in the preferred thermal conduction direction of the first operating state or has no influence on the function of the heat pipe. In the second state, the activatable functional material keeps the evaporator area free of the working fluid or prevents the working fluid from evaporating. Since the heat transport in the heat pipe works mainly via the evaporation of the working fluid in the evaporator area and the transport of the evaporated working fluid in the condenser area, this reduces or prevents the heat transport in the heat pipe. It is also within the scope of the invention that the activatable functional material is designed in such a way that, in the second operating state, the preferred thermal conduction direction is changed by the activatable functional material.

In a preferred embodiment of the invention, the heat pipe is designed as a switchable thermal diode or heat switch in which the at least one functional material that can be activated is designed, in an outer one Field to at least partially change its properties. Possible properties of the activatable functional material, which can be changed by the external field, are surface wetting properties, swelling properties, fluid-binding properties and volume.

In an alternative embodiment of the invention, the heat pipe is designed as a programmable thermal diode or heat switch in which the at least one activatable functional material is designed to at least partially change its properties depending on conditions within the working chamber. Possible properties of the activatable functional material that can be changed by the external field are surface wetting properties, swelling capacity, fluid-binding properties and volume.

The functional material that can be activated is thus preferably switchable or programmable by external or internal influences. In this context, "switchable" means that the operating state can be changed by actively applying an outer field. In this context, "programmable" means that the heat pipe changes its state automatically through material-inherent factors when environmental conditions, in particular the conditions in the working chamber, change.

This has the advantage that the heat transport in the heat pipe according to the invention can be controlled in a targeted manner.

In a preferred embodiment of the invention, the heat pipe is designed as a programmable thermal diode or heat switch, in which the at least one activatable functional material is designed, depending on conditions within the working chamber, in particular temperature, pH of the working fluid and / or ionic strength of the Working fluids to change its properties. So there are advantageously no external fields necessary, but the control of the heat transport in the heat pipe can take place solely via the working fluid or direct properties of the heat pipe.

The working chamber is preferably designed as a closed volume, in particular in such a way that a heat transport by means of convection of the evaporated fluid and a return transport of the condensed fluid from the Condenser area takes place in the evaporator area. In particular, the closed volume of the working chamber is designed as a pressure-tight system. In particular, essentially all foreign gases with the exception of the working fluid have been removed from the pressure-tight system. Various designs are possible for this, which differ in the return transport of the working fluid. The design as a heat pipe or as a 2-phase thermosyphon is known here.

The functional material that can be activated is preferably provided within the working chamber. It is also possible that the functional material that can be activated is provided as part of the working chamber, for example of the floor and ceiling of the working chamber.

In a preferred embodiment of the invention, the heat pipe is designed with a fluid circuit for the working fluid. The fluid circuit preferably comprises a fluid return for a return transport of the condensed working fluid from the condenser area to the evaporator area. This allows the working fluid to be directed back into the evaporator area in a targeted and metered manner, thus preventing the evaporator area from drying out.

In a preferred embodiment of the invention, the enclosed volume has a fluid-phobic coating in the evaporator area and / or a fluid-phobic coating in the condenser area. It is also within the scope of the invention that the closed volume, that is to say the working chamber, has an additional structure both in the evaporator area and / or in the condenser area. In this way, for example, the wetting properties of the surfaces can be optimized.

The at least one activatable functional material is preferably designed in the form of a switchable coating of the evaporator area and / or the condenser area of the working chamber, in that at least the surface properties of the coating of the evaporator area can be changed from fluid-philic to fluid-phobic. Preferably, both the coating of the evaporator area and the condenser area are designed in such a way that the surface property of the coating of the evaporator area is fluid-philic fluid-phobic is changeable, while the surface property of the coating of the capacitor area can be changed from fluid-phobic to fluid-phobic. In this case, the heat pipe is designed as a switchable thermal diode: by applying an external field, the heat pipe can be changed from the first operational state to the second operational state.

If the hot side, ie the evaporator area, is heated by the heat source in the first operating state, the working fluid that has collected on the fluid-philic coating of the evaporator area evaporates and enables heat to be transported from the evaporator area to the condenser area. Here the working fluid condenses on the fluid-phobic coating of the capacitor area. Due to the fluid-phobic surface property in the capacitor area, drops form in the working fluid. In the case of a strongly fluid-phobic configuration of the surface, the working fluid "jumps" back into the evaporator area. Alternatively, a fluid return of the droplets via capillary forces can also be provided, for example in the form of a hydrophilic wick structure, as is known from the prior art for heat pipes. In this state, the thermal diode is thermally conductive.

If the surface properties of the coating in the evaporator area and / o the condenser area are changed in the second operating state (hereinafter also called the blocking state), for example by applying an external electrical field, the hot side, i.e. the evaporator area, now has hydrophobic properties at the heat source. Not enough working fluid collects on this coating and the working fluid that collects there evaporates quickly and condenses on the fluid-philic coating of the condenser area. The working fluid remains there and is not transported back into the Ver evaporator area, since the above-mentioned recirculating mechanisms do not work. Thus, the hot side of the working chamber dries out and there is no heat transfer via the working fluid. The thermal diode blocks.

Preferably, the switchable coating as ORMOCER ^® and / or with ORMOCER ^® is formed. ORMOCER ^® e are inorganic-organic hybrid polymers that can advantageously influence the surface properties of many substrates, cf. B. Sanchez et al. , Chem. Soc. Rev. 40, 2011, 696-753. ORMOCER ^® s may also act as switchable coatings are formed from hydrophilic back utilizing multiple Lite of temperature from the known mechanisms, see B. Xin, J. Hao, Chem. Soc hyd to rophob and. Rev. 39, 2010, 769-782. ^{ORMOCER ®} e according to the invention therefore contain z. B. imidazolium alkyl end groups for electrically switchable surface properties or fluoralkylazobenzene or spiropyran end groups for photochemically switchable surface properties.

In a particularly preferred embodiment, the ORMOCER ^® coatings have a micro-, meso- or nano-structuring that strengthens their fluidphil / fluidphobic properties by utilizing the capillary or lotus effect.

In a preferred embodiment of the invention, the functional material that can be activated is configured in such a way that the evaporator area and capacitor area swap properties in the second operating state. The second operating state is therefore not a blocking state, but enables heat to be transported in the opposite direction as the first operating state. In this case, in the second operating state, the working fluid in the original condenser area, which now acts as the evaporator area, evaporates and absorbs heat from a heat source and transports it to the original evaporator area, which now acts as the condenser area. In the new condenser area the working fluid condenses and transfers the heat to a heat sink. This reverses the preferred thermal conduction direction of the thermal diode.

Preferably, the activatable material is det function both in Verdampferbe rich and in the capacitor region as ORMOCER ^® coating ausgebil. The coatings are chosen so that by applying an external field, preferably an electric field or a radiation field, ie (UV) light radiation, the surface wetting properties of the evaporator area and condenser area are exchanged.

^{ORMOCER ®} s, for example, are used to realize electrical switchability of the fluidphilic / fluidphobic properties, whose functional end groups consist of an ionic group (trialkylammonium, imidazolium, sulfonate, etc.), which is connected via a “spacer”. , ie one linear alkyl chain with 2-20 carbon atoms, preferably 3-12 carbon atoms, are covalently bound to the ORMOCER ^® network. By applying an electric field (cf. Langer et al., Science 299, 2003, 371-374) the ionic end groups are repelled from an electrically charged substrate of the same name and protrude into the interior of the thermal diode, which leads to a hydrophilic property of the surface . On the other hand, the ionic groups are attracted by an electrically oppositely charged substrate, so that the non-polar “spacer” chains protrude into the interior of the thermal diode, which leads to a hydrophobic property of the surface. If both opposing surfaces of the thermal diode are ^{coated with the same functional ORMOCER ®} , a hydrophilic and a hydrophobic side are created by applying an electrical field, whereby the properties are also reversed by reversing the field direction. The electrical voltage to be applied to the thermal diode is preferably <50 V, particularly preferably <5 V.

In an alternative embodiment of the invention, the at least one activatable functional material is designed in the form of a reservoir for the working fluid, in particular in the form of a liquid reservoir. Through the reservoir, the intake or release of the Ar beitsfluids necessary for the transport of heat is controlled. This means that the available amount of the working fluid can be made variable. In the first operating state of the heat pipe, the working fluid is available for heat conduction. The heat pipe conducts heat. In the second operating state, the blocking state, the working fluid is bound in the reservoir, in particular in the form of a liquid reservoir. In this bound form, the working fluid is no longer available for heat transport. The heat pipe no longer conducts heat.

In the context of this description, the phrase “the heat pipe no longer conducts heat” means the blocking state of the diode. This means that the heat transport is considerably reduced compared to the other switching state. Nevertheless, a small heat flow can take place, for example via the thermal conduction of components. The reservoir for the working fluid is preferably designed as a gel, in particular as a polymer gel, as an adsorbent or as a mesoscopically structured surface.

The reservoir is particularly preferably designed as a chemically crosslinked polymer gel. The crosslinked polymer gel is designed in such a way that it swells up due to the working fluid and then has a volume phase transition, preferably between a swollen and a collapsed state of the hydrogel.

In particular in the event that the working fluid is water, the reservoir is preferably designed as a water-binding hydrogel. The polymer gel has a water-binding and a non-water-binding state. The transition from the first operating state to the blocking state of the heat pipe, that is to say from a non-fluid-binding state of the polymer gel to the fluid-binding state of the polymer gel, is preferably induced by a temperature transition. The polymer gel can be designed as a polymer gel with a volume phase transition of the UCST type (Upper Critical Solution Temperature) or of the LCST type (Lower Critical Solution Temperature). In the case of a volume phase transition of the UCST type, the crosslinked polymer gel is only swollen when the working fluid exceeds the critical temperature (limit temperature). In the case of a volume phase transition of the LCST type, the working fluid is displaced from the crosslinked polymer gel when the critical temperature (limit temperature) is exceeded. As a result, the heat pipe locks in the event of a UCST transition above the critical temperature. In the case of an LCST transition, the heat pipe blocks below the critical temperature. With the limit temperature, a switching temperature for the transition from the first operating state to the blocking state of the heat pipe can thus be defined.

Known polymers that have a UCST volume phase transition are, for example, in Macromol. Rapid Commun. 33, 1898 - 1920, 2012. Known polymers that have an LCST volume phase transition are, for example, in Adv. Polym. May be. 242, 29-89, 2011. The named polymer gels interact with water and are therefore particularly suitable for a heat pipe in which water is used as the working fluid. It however, there are also a number of polymers which have the properties described and the behavior described with organic fluids, such as mineral oils, for example J. Polym. May be. A46, 5724 - 5733, 2008.

In this case, a fluid other than water can also be used as the working fluid.

In a preferred embodiment of the invention, the reservoir is designed as an adsorbent. An adsorbent binds fluid. The amount of fluid bound in the adsorbent is also referred to as the load. With increasing temperature (and the associated increasing vapor pressure of the bound fluid) the loading of an adsorbent decreases and the fluid is released again.

The adsorbent preferably has a limit temperature so that when this limit temperature or a specific vapor pressure of the fluid is exceeded, the fluid is released again quite abruptly by the adsorbent. With the limit temperature, a switching temperature for the transition from the blocking state to the first operating state of the heat pipe can thus be defined.

A material example for an adsorbent with a defined limit temperature or the associated vapor pressure of the fluid is the adsorbent AQSOA ™ -Z05 from Mitsubishi ™.

It is also within the scope of the invention that the properties of the liquid storage device are not influenced by temperature, but by another physical or chemical stimulus. Examples of this are UV light or microwave radiation as well as pH value, ionic strength or the presence of certain organic molecules. Examples of this are given in Angew. Chem.

Int. Ed. 55, 6641 - 6644, 2015. The switching of the thermal diode is therefore possible due to a wide variety of factors and can be adapted accordingly to the area of application and the ambient conditions.

The object according to the invention is also achieved by a system with a heat pipe with the properties according to the invention described above and means for applying a field in order to change the properties of the functional material that can be activated. Field generators for an E-field, a B-field, a stress-strain field, for generating light, in particular UV light, for generating heat and / or for generating cold are preferably provided as the means for applying the field. Only one of the named field generators or a combination of several of the named field generators can be provided. Examples of this are a capacitor, a coil, an eccentric, a (UV) light source or a heating and cooling device. As a result, the control options can be individually adapted to the working fluid used and to the functional material that can be activated.

The system according to the invention also has the above-described advantages and properties of the heat pipe according to the invention and / or a preferred embodiment thereof.

The system is preferably designed to be flexible with regard to the hot side and cold side. If the heat pipe is designed as a heat pipe with a reversible heat conduction preferential direction, means are preferably provided that the evaporator area and condenser area are assigned their function by contact with a hot side or, accordingly, a cold side. A good thermal contact between the evaporator area and the condenser area and the hot side or cold side is preferably provided. There is good thermal contact between the heat sink and the heat source and the heat pipe.

In a preferred embodiment, the system is designed with a heat pipe with a combination of two functional materials, one of the two functional materials being designed as a liquid storage device as described above, in particular in the form of a polymer gel. The other functional material is preferably designed as an ORMOCER® that can be changed in its fluid-philic / fluid-phobic properties, preferably under the influence of light, in particular UV light.

The object according to the invention is also achieved by a method with the features of claim 15. As is known per se, the method for switching and / or programming the heat transport with a heat tube with at least one working chamber with at least one Verdampferbe rich and at least one condenser area and a working fluid Runaway leads. It includes the following procedural steps:

A evaporation of the working fluid in the evaporator area, heat being transported with the gaseous working fluid from the evaporator area to the condenser area,

B condensing the working fluid in the condenser area, the heat being dissipated to a heat sink.

It is essential that the heat pipe is operated as a thermal diode or thermal switch in that the thermal conductivity is changed by applying an external field and / or as a function of conditions within the working chamber.

The method according to the invention is preferably designed to be carried out by means of the heat pipe according to the invention and / or a preferred embodiment of the heat pipe according to the invention. The heat pipe according to the invention, on the other hand, is preferably designed to carry out the method according to the invention and / or a preferred embodiment of the method according to the invention.

The inventive method also shows the above-described parts and features of the heat pipe according to the invention and / or the system according to the invention.

The thermal conductivity of the heat pipe is preferably changed by keeping the evaporator area free of the working fluid and / or preventing the working fluid from evaporating.

In a preferred embodiment of the invention, in a first operating state, heat is transported in the heat pipe from a hot side (heat source) arranged on the evaporator area to a cold side (heat sink) arranged on the condenser area. By creating a External field in a process step C, the heat pipe is transferred to a second operating state. For this purpose, an E field, a B field, a stress-strain field is preferably generated or the activatable functional material is exposed to light, in particular UV light, with heat and / or cold. In the second operating state, no or at least insufficient working fluid is available in the evaporator area. The evaporator area dries out and the heat pipe no longer conducts heat in the direction of the preferred thermal conduction direction of the first operating state.

Alternatively, the working fluid can change from the first operating state to the second operating state as a function of conditions within the working chamber. Parameters that can initiate a change from the first operating state to the second operating state are temperature, pH value of the working fluid and / or ionic strength of the working fluid. This has the advantage that the heat pipe can be “programmed” to change the operating state under certain conditions without any external influence being necessary.

The working fluid is preferably displaced from the evaporator area of the working chamber by means of a switchable surface coating, as already described above.

Alternatively, the working fluid can be bound by means of an activatable functional material. For this purpose, the at least one activatable functional material is preferably designed in the form of a reservoir for the working fluid, in particular in the form of a liquid reservoir. Through the reservoir, the acquisition or release of the working fluid required for heat transport is controlled. This means that the available amount of the working fluid can be changed. In the first operating state of the heat pipe, the working fluid is available for heat conduction. The heat pipe conducts heat. In the second operating state, the blocking state, the working fluid in the reservoir, in particular special in the form of a liquid reservoir, is bound. In this bound form, the working fluid is no longer available for heat transport. The heat pipe no longer conducts heat. In a preferred embodiment of the invention, the preferred heat conduction direction of the thermal diode is reversed by changing the surface properties of the evaporator area and condenser area by applying an external field and / or depending on conditions within the working chamber. In this case, in a second operating state, the working fluid can evaporate in the original condenser area, which now acts as the evaporator area, and absorb heat from a heat source and transport it to the original evaporator area, which now acts as the condenser area. The working fluid condenses in the new condenser area and transfers the heat to a heat sink. As a result, the preferred direction of thermal conduction is reversed compared to Betriebszu stand 1.

The heat pipe according to the invention, the system according to the invention and the method according to the invention are particularly suitable for effectively switching heat flows on and off or being able to control or regulate. Heat switches or thermal diodes based on heat pipes are particularly suitable because they can achieve high switching factors and, due to the high heat transport, have only a very low thermal resistance in the conductive state. In addition, they can be implemented as very compact designs and are therefore easy to integrate. Depending on the design, the heat pipes are simple, consist of a few individual parts and do not have to contain any moving parts.

Further preferred features and embodiments of the heat pipe according to the invention and the method according to the invention are explained below using exemplary embodiments and the figures. It shows:

Figure 1 is a schematic representation of a first embodiment of a heat pipe according to the invention,

Figure 2 is a schematic representation of a second embodiment of a heat pipe according to the invention.

Figure 1 shows a schematic representation of a thermal diode with an activatable functional material in the form of a switchable coating in the Evaporator area and the condenser area with the partial images a) in the conductive state and b) in the blocked state.

The heat pipe 1 has a working chamber 2 with at least one evaporator area 3 and at least one condenser area 4. The evaporator area 3 is in operative connection with a heat source (not shown), with the temperature Ti = 100 ° C and the condenser area 4 in the connection to a heat sink (not shown) with the temperature T2 =

10 ° C. A working fluid 5 is provided in the working chamber 2.

In the present case, the working chamber 2 is designed as a closed, pressure-tight volume, which is designed in such a way that heat is transported by means of convection of the evaporated working fluid 5 and the condensed working fluid 5 is transported back.

In the present case, the working fluid 5 is water.

The evaporator area 3 and the condenser area 4 are formed with a coating 6 made of functional material that can be activated. Both the coating 6 of the evaporator area 3 and the condenser area 4 are designed in such a way that the surface property of the coating 6a of the evaporator area 3 can be changed from hydrophilic to hydrophobic and back again, while the surface property of the coating 6b of the condenser area 4 can be changed from hydrophobic to hydrophilic and can be changed back again. The coatings 6 are designed in such a way that the evaporator area 3 and the condenser area 4 have the opposite surface wetting properties.

In the present case, the coating is det 6 ausgebil of activatable function as a switchable material coating 6 of ORMOCER ^® and / or with ORMOCER®. As already described, ORMOCERE ^® are inorganic-organic hybrid polymers that can advantageously influence the surface properties of many substrates. ORMOCERE ^® can also function as switchable coatings 6 of hydrophilic to hydrophobic and back are formed by utilizing technical literature from the known mechanisms, see B. Xin, J. Hao, Chem. Soc. Rev. 39, 2010, 769-782. In the present case, the coatings are formed in the evaporator 6a and 6b region 3 in the condenser section 4 out with an electrically switchable ORMOCER ^®, as described above. In the present case, the coatings consist of an ORMOCER ^® with functional end groups in the form of methylimidazolium dodecylsilyl groups. By applying an electric field (cf. Langer et al., Science 299, 2003, 371-374) these ionic end groups are repelled by an electrically charged substrate of the same name and protrude into the interior of the thermal by “stretching” the dodecyl chain Diode. In the present case, the substrate is formed from electrically charged with the same name in the evaporator area. This leads to a hydrophilic property of the surface 6a in the evaporator region 3. In the condenser region 4, a substrate with an electrically oppositely charged charge is provided. As a result, however, the ionic groups are attracted, so that the non-polar dodecyl chains protrude into the interior of the thermal diode, which leads to a hydrophobic property of the upper surface 6b in the capacitor area.

By applying an electric field, a hydrophilic and a hydrophobic side are created, the properties also being reversed by reversing the field direction.

The heat pipe 1 is thus in the present case as a switchable thermal diode: In a first operating state, heat is transported from the heat source to the heat sink by evaporation of the working fluid 5 by transporting heat with the gaseous working fluid 5 from the evaporator area 3 to the condenser area 4 . The evaporator area 3 is heated by the heat source and the working fluid 5, which has collected on the hydrophilic coating 6a of the evaporator area 3, evaporates and allows light to transport heat from the evaporator area 3 to the condenser area 4. In the condenser area 4, the working fluid condenses 5 on the hydrophobic coating 6b of the capacitor area 4 and the heat is dissipated to a heat sink. Due to the hydrophobic surface property in the condenser area 4, drops form in the working fluid 5. Due to the highly hydrophobic design of the surface, the working fluid 5 "jumps" back into the evaporator area 3. By applying an external field, in the present case with a voltage of 5 V, the heat pipe 1 can be switched from the first thermally conductive operating state to the second non-thermally conductive operating state.

As described, the application of the external field changes the surface properties of the coating 6 in the evaporator area 3 and in the condenser area 4. The evaporator area 3 at the heat source now has hydrophobic properties. Not enough working fluid 5 collects on the coating 6a of the evaporator area 3 and the working fluid 5 that collects there evaporates quickly and condenses on the hydrophilic coating 6b of the condenser area 4. The working fluid 5 remains there and is not transported back into the evaporator area 3 , since the working fluid 5 is not repelled by the now hydrophilic surface. Thus, the hot side of the working chamber 2 dries out and there is no heat transport via the working fluid 5. The thermal diode blocks.

FIG. 2 shows a schematic representation of a thermal switch with an activatable functional material in the form of a liquid reservoir with the partial images a) in the conductive state and b) in the blocked state.

To avoid repetition, only the differences from FIG. 1 will be discussed below.

In the present case, the at least one activatable functional material is designed in the form of a reservoir for the working fluid 5, namely in the form of a water-binding hydrogel 7. The water-binding hydrogel 7 is designed as follows:

Hydrogels with a volume phase transition of the LCST type can be produced, for example, by radical polymerization using the following monomers. The compositions mentioned are not to be understood as exclusive:

Hydrogels with a volume phase transition of the UCST type can be produced, for example, by radical polymerization using the following monomers. The compositions mentioned are not to be understood as exclusive:

Furthermore, there is also the possibility of subsequently crosslinking soluble polymers to produce suitable hydrogels that have a volume phase transition. In order to obtain a hydrogel with a volume phase transition of the LCST type in this way, for example partially hydrolyzed poly (vinyl acetate) can be crosslinked with 1,4-butanediol diglycidyl ether, poly (ethylene glycol) diglycidyl ether or other di- or multifunctional epoxides .

The available amount of the working fluid 5 is made variable by the water-binding hydrogel 7. The water-binding hydrogel 7 has a what-binding and a significantly less water-binding state. The transition from the first operating state to the blocking state of the heat pipe 1, i.e. from a significantly less water-binding state of the hydrogel 7 to the water-binding state of the hydrogel 7, is induced by a temperature transition, in the present case in a temperature range from room temperature to approx. 150 ° C. This heating takes place by heating the hot side on the evaporator side, i. H. without an outside field.

In the first operating state of the heat pipe 1, the working fluid 5 is available for conduction of heat. The heat pipe 1 conducts heat. In the second operating state, the blocking state, the working fluid 5 is bound in the water-binding hydrogel 7. The working fluid 5 is not in this bound form more available for heat transport. The heat pipe 1 no longer conducts heat.

In contrast to FIG. 1, no coating is provided which ensures that the working fluid 5 is transported back from the condenser area 4 to the evaporator area 3. The heat pipe 1 is therefore embodied in the present case with a fluid return in the form of a wick structure (not shown).

Claims

Expectations

1. Heat pipe (1) with at least one working chamber (2) with at least one evaporator area (3) in operative connection with a heat source and at least one condenser area (4) in operative connection with a heat sink, with a working fluid (2) in the working chamber (2) 5) is provided, and in a first operating state by means of the working fluid (5) heat is transported from the heat source to the heat sink, characterized in that the heat pipe (1) as a switchable and / or programmable thermal diode or as a switchable and / or programmable heat switch is designed in that at least one activatable functional material is provided, which is arranged and designed to keep the evaporator area (3) free of the working fluid (5) and / or the working fluid (5) in a second operating state To prevent evaporation to reduce the heat metransport and / or prevent and / or to change the preferred direction of heat conduction.

2. Heat pipe according to claim 1, characterized in that the heat pipe (1) is designed as a switchable thermal diode or heat switch by the at least one activatable functional material is designed to at least partially change its own properties in an external field.

3. Heat pipe according to claim 1, characterized in that the heat pipe (1) is designed as a programmable thermal diode or heat switch by the at least one activatable functi onsmaterial is designed, depending on conditions within the working chamber (2), in particular temperature to change the pH of the working fluid (5) and / or ionic strength of the working fluid (5).

4. Heat pipe according to one of the preceding claims, characterized in that that the working chamber (2) is designed as a closed volume, which is designed in such a way that heat is transported by means of convection of the evaporated working fluid (5) and the condensed working fluid (5) is transported back, in particular that the closed volume is pressure-tight System is designed, preferably that essentially all foreign gases with the exception of the working fluid (5) are removed from the pressure-tight system.

5. Heat pipe according to one of the preceding claims, characterized in that the heat pipe (1) is formed with a fluid circuit for the working fluid (5), preferably that the fluid circuit has a fluid return for a return transport of the condensed working fluid (5) from the condensator area (4) to the evaporator area (3).

6. Heat pipe according to one of the preceding claims, characterized in that the closed volume in the evaporator area (3) has a fluid-phobic coating (6) and / or structuring and / or in the condenser area (4) a fluid-philic coating (6) and / or structuring, in particular that the closed volume in the evaporator area (3) has a hydrophilic coating (6) and / or structuring and / or in the condenser area (4) a hydrophobic coating (6) and / or structuring or that the closed Volume in the evaporator area (3) has an oleophilic coating (6) and / or structuring and / or in the condenser area (4) an oleophobic coating (6) and / or structuring.

7. Heat pipe according to one of the preceding claims, characterized in that the at least one functional material is designed in the form of a switchable coating of the evaporator area (3) and / or the condenser area (4) by at least the surface property of the coating of the evaporator area (3 ) can be changed from fluidphil to fluidphob.

8. Heat pipe according to one of the preceding claims, characterized in that the switchable coating (6) is designed as ORMOCER ^® and / or with ORMOCER ^® .

9. Heat pipe according to one of claims 1 to 8, characterized in that the at least one functional material is designed in the form of a reservoir for the working fluid (5), in particular in the form of a liquid storage device.

10. Heat pipe according to claim 9, characterized in that the reservoir for the working fluid (5) is formed as a gel, in particular as a poly mergel, as an adsorbent or as a mesoscopically structured surface.

11th Heat pipe according to one of claims 9 or 10, characterized in that the reservoir for the working fluid (5) is designed as a polymer gel which has a temperature-induced volume phase transition, in particular as a polymer with a volume phase transition of the UCST type or as a polymer with a volume phase transition of the LCST type.

12. System comprising a heat pipe according to one of the preceding claims, characterized in that means are provided for applying the field in order to change the properties of the functional material that can be activated.

13. System according to claim 12, characterized in that the means for applying the field to a field generator for an electric field, a magnetic field, a stress-strain field, for generating of light, in particular UV light, are provided for generating heat and / or for generating cold.

14. System according to one of claims 12 or 13, characterized in that the system is formed with a combination of two functional materials, one of the two functional materials being formed as a liquid keitsspeicher according to one of claims 9 to 11, and the other functional material properties as a fluidphoben in its fluid hydrophilic / own changeable ORMOCER ^® is formed, preferably under a flow of light, in particular UV light.

15. A method for switching and / or programming the heat transport in a heat pipe with at least one working chamber (2) with at least one evaporator area (3) and at least one condenser area (4) and a working fluid (5) with the following process steps:

A evaporation of the working fluid (5) in the evaporator area (3), heat being transported with the gaseous working fluid (5) from the evaporator area (3) to the condenser area (4),

B condensing of the working fluid (5) in the condenser area (4), the heat being dissipated to a heat sink, characterized in that the heat pipe (1) is operated as a thermal diode or heat switch by increasing the thermal conductivity by applying an external field and / or is changed depending on conditions within the working chamber (2).

16. The method according to claim 15, characterized in that the thermal conductivity of the thermal diode or the heat switch is changed by leaving the evaporator area (3) free of the Working fluid (5) is held and / or the working fluid (5) is prevented from evaporating.

17. The method according to claim 15 or 16, characterized in that the preferred thermal conduction direction of the thermal diode is reversed by the surface properties of the evaporator area (3 ) and capacitor area (4) can be exchanged.