Heat pipe, system and method for switching and / or programming heat transport

Abstract

The invention relates to a heat pipe 1 with at least one working chamber 2, comprising at least one evaporator section 3 operatively connected to a heat source and at least one condenser section 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. Crucially, the heat pipe is designed as a switchable and / or programmable thermal diode or as a switchable and / or programmable thermal switch by providing at least one activatable functional material, which is arranged and configured to, in a second operating state, keep the evaporator section free of the working fluid and / or prevent the working fluid from evaporating in order to reduce and / or prevent heat transfer and / or change the preferred direction of heat conduction.The invention further relates to a system and a method for switching and / or programming the heat transport in a heat pipe.

Description

[0001] 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. A heat pipe according to the preamble of claim 1 is known from Figure 16 of WO2005 / 050717A.

[0002] Heat pipes (also known as heat pipes) are known to enable high heat flux densities by transporting heat via latent heat of vaporization. Heat pipes typically have a hot side, the heat source, and a cold side, the heat sink. A working fluid is contained within the heat pipe, which evaporates near the heat source and condenses near the heat sink. Heat transfer occurs through the transport of the working fluid and the transfer of latent heat of condensation and vaporization.

[0003] Conventional heat pipes have a preferred direction for heat flow, meaning 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.

[0004] Such a thermal diode is described, for example, in Boreyko et al. (2011), Applied Physics Letter 99 (23) and in the publication US 8716689 B2. The use of superhydrophobic coatings in the heat sink area and superhydrophilic coatings in the heat source area creates a preferred direction for the heat in the described thermal diode: Due to the superhydrophobic coating, the surface in the heat sink area repels the working fluid, so that it is transported back to the superhydrophilic area of ​​the heat source, where it can evaporate again.

[0005] A disadvantage of the previously known thermal diodes from the state of the art is that the preferred direction for heat transport is predetermined and the diodecity is fixed by design, ie it cannot be changed or adjusted during operation.

[0006] 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 limitations of the methods and devices known from the prior art.

[0007] This object is achieved by a heat pipe according to claim 1 and by a method for switching and / or programming 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. Claims 12 to 14 contain embodiments 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 wording of all claims is hereby explicitly incorporated into the description by reference.

[0008] The heat pipe according to the invention comprises, as is known per se, at least one working chamber with at least one evaporator region and at least one condenser region. The evaporator region is operatively connected to a heat source, and the condenser region is connected to 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.

[0009] It is essential that the heat pipe is designed as a switchable and / or programmable thermal diode or thermal switch in which at least one activatable functional material is provided, which is arranged and designed to keep the evaporator region 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 transport and / or to change the preferred heat conduction direction of the heat transport.

[0010] The working fluid fills the working chamber and, depending on pressure and temperature, exists in both liquid and gaseous form. The phrase "keeping the evaporator region free of the working fluid" refers to the working fluid in the liquid phase being in direct contact and / or direct interaction with the surface of the evaporator region. It is also within the scope of the invention for the working fluid in the gaseous phase to be present in the evaporator region, since the working fluid in the gaseous phase fills the entire volume of the working chamber of a heat pipe.

[0011] The invention is based on the applicant's finding that heat transport can be controlled and even reversed by appropriately designing the conditions in the working chamber.

[0012] The heat pipe according to the invention thus differs from previously known heat pipes in essential aspects: 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 activatable functional material enables heat transport in the preferred heat 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 region free of the working fluid or prevents the working fluid from evaporating. Since heat transport in the heat pipe functions primarily via the evaporation of the working fluid in the evaporator region and the transport of the evaporated working fluid to the condenser region, this reduces or prevents 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 heat conduction direction is changed by the activatable functional material.

[0013] In a preferred embodiment of the invention, the heat pipe is designed as a switchable thermal diode or thermal switch, in which the at least one activatable functional material is configured to at least partially change its properties in an external field. Possible properties of the activatable functional material that can be changed by the external field include surface wetting properties, swelling capacity, fluid-binding properties, and volume.

[0014] In an alternative embodiment of the invention, the heat pipe is designed as a programmable thermal diode or thermal switch, in which the at least one activatable functional material is configured 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 include surface wetting properties, swelling capacity, fluid-binding properties, and volume.

[0015] The activatable functional material is therefore preferably switchable or programmable by external or internal influences. "Switchable" in this context means that the operating state can be changed by actively applying an external field. "Programmable" in this context means that the heat pipe changes its state independently through material-inherent internal factors when environmental conditions, especially those in the working chamber, change.

[0016] This results in the advantage that the heat transport in the heat pipe according to the invention can be controlled in a targeted manner.

[0017] In a preferred embodiment of the invention, the heat pipe is designed as a programmable thermal diode or thermal switch, in which the at least one activatable functional material is configured to change its properties depending on conditions within the working chamber, in particular temperature, pH of the working fluid, and / or ionic strength of the working fluid. Advantageously, no external fields are required; instead, the heat transport in the heat pipe can be controlled solely via the working fluid or direct properties of the heat pipe.

[0018] The working chamber is preferably designed as a closed volume, in particular such that heat is transported by convection of the evaporated fluid and the condensed fluid is transported back from the condenser region to the evaporator region. 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, are removed from the pressure-tight system. Various designs are possible for this purpose, which differ in the way the working fluid is transported back. Known designs include a heat pipe or a two-phase thermosyphon.

[0019] Preferably, the activatable functional material is provided within the working chamber. It is also possible for the activatable functional material to be provided as part of the working chamber, for example, the floor and ceiling of the working chamber.

[0020] In a preferred embodiment of the invention, the heat pipe is designed with a fluid circuit for the working fluid. The fluid circuit preferably includes a fluid return line for transporting the condensed working fluid from the condenser region to the evaporator region. This allows the working fluid to be fed back to the evaporator region in a targeted and metered manner, thus preventing the evaporator region from drying out.

[0021] In a preferred embodiment of the invention, the enclosed volume in the evaporator region has a fluid-phobic coating and / or in the condenser region a fluid-philic coating. It is also within the scope of the invention for the enclosed volume, i.e., the working chamber, to have additional structuring in both the evaporator region and / or the condenser region. This can, for example, optimize the wetting properties of the surfaces.

[0022] Preferably, the at least one activatable functional material is designed in the form of a switchable coating of the evaporator region and / or the condenser region of the working chamber, in which at least the surface properties of the coating of the evaporator region can be changed from fluid-philic to fluid-phobic. Preferably, both the coating of the evaporator region and the condenser region are designed such that the surface property of the coating of the evaporator region can be changed from fluid-philic to fluid-phobic, while the surface property of the coating of the condenser region can be changed from fluid-phobic to fluid-philic. 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 operating state to the second operating state.

[0023] If the hot side, i.e., the evaporator region, 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 region evaporates, enabling heat transfer from the evaporator region to the condenser region. Here, the working fluid condenses on the fluid-phobic coating of the condenser region. Due to the fluid-phobic surface properties in the condenser region, droplets of the working fluid form. With a highly fluid-phobic surface design, the working fluid "jumps" back into the evaporator region. Alternatively, fluid recirculation of the droplets can be provided via capillary forces, for example, in the form of a hydrophilic wick structure, as known from the prior art for heat pipes. In this state, the thermal diode is thermally conductive.

[0024] If, in the second operating state (hereinafter also referred to as the off-state), the surface properties of the coating in the evaporator and / or condenser regions are changed, for example, by applying an external electric field, the hot side, i.e., the evaporator region, at the heat source now exhibits hydrophobic properties. Insufficient working fluid collects on this coating, and the working fluid that does collect there quickly evaporates and condenses on the fluid-philic coating of the condenser region. The working fluid remains there and is not transported back to the evaporator region, as the aforementioned return mechanisms are not effective. Thus, the hot side of the working chamber dries out, and no heat transfer via the working fluid takes place. The thermal diode is blocked.

[0025] The switchable coating is preferably formed as ORMOCER® and / or with ORMOCER®. ORMOCER®s are inorganic-organic hybrid polymers that can advantageously influence the surface properties of many substrates, see, for example, Sanchez et al., Chem. Soc. Rev. 40, 2011, 696-753. ORMOCER®s can also be formed as switchable coatings from hydrophilic to hydrophobic and back again using mechanisms known from the specialist literature, see B. Xin, J. Hao, Chem. Soc. Rev. 39, 2010, 769-782. ORMOCER®s according to the invention therefore contain, for example, imidazolium alkyl end groups for electrically switchable surface properties or fluoroalkylazobenzene or spiropyran end groups for photochemically switchable surface properties.

[0026] In a particularly preferred embodiment, the ORMOCER ®< coatings have a micro-, meso- or nanostructuring that enhances their fluidphilic / fluidphobic properties by utilizing the capillary or lotus effect.

[0027] In a preferred embodiment of the invention, the activatable functional material is designed such that the evaporator region and condenser region exchange properties in the second operating state. The second operating state is therefore not a blocking state, but rather enables heat transport in the opposite direction to the first operating state. In this case, in the second operating state, the working fluid in the original condenser region, which now acts as the evaporator region, can evaporate and absorb heat from a heat source and transport it to the original evaporator region, which now acts as the condenser region. In the new condenser region, the working fluid condenses and releases the heat to a heat sink. This reverses the preferred heat conduction direction of the thermal diode.

[0028] Preferably, the activatable functional material is formed as an ORMOCER® coating in both the evaporator and condenser regions. The coatings are selected such that the surface wetting properties of the evaporator and condenser regions are swapped by applying an external field, preferably an electric field or a radiation field, i.e., (UV) light radiation.

[0029] To realize the inventive electrical switchability of fluidphilic / fluidphobic properties, ORMOCER®s are used, for example, whose functional end groups consist of an ionic group (trialkylammonium, imidazolium, sulfonate, etc.) covalently bonded to the ORMOCER® network via a "spacer," i.e., a linear alkyl chain with 2-20 C atoms, preferably 3-12 C atoms. By applying an electric field (cf. Langer et al., Science 299, 2003, 371-374), the ionic end groups are repelled from a substrate with the same electrical charge and protrude into the interior of the thermal diode, resulting in a hydrophilic property of the surface. On the other hand, the ionic groups are attracted to an electrically oppositely charged substrate, so that the non-polar "spacer" chains protrude into the interior of the thermal diode, resulting in a hydrophobic property of the surface.If both opposing surfaces of the thermal diode are coated with the same functional ORMOCER®, applying an electric field creates a hydrophilic and a hydrophobic side, with the properties also being reversed by reversing the field direction. The electrical voltage applied to the thermal diode is preferably < 50 V, particularly preferably < 5 V.

[0030] 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. The reservoir controls the absorption and release of the working fluid required for heat transport. This means that the available quantity of working fluid can be varied. 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 blocked 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.

[0031] In this description, the phrase "the heat pipe no longer conducts heat" refers to the diode's off state. This means that heat transfer is significantly reduced compared to the other switching states. Nevertheless, a small amount of heat can still flow, for example, through thermal conduction of components.

[0032] Preferably, the reservoir for the working fluid is designed as a gel, in particular as a polymer gel, as an adsorbent or as a mesoscopically structured surface.

[0033] Particularly preferably, the reservoir is formed as a chemically cross-linked polymer gel. The cross-linked polymer gel is designed such that it swells when exposed to the working fluid and then exhibits a volume phase transition, preferably between a swollen and a collapsed state of the hydrogel.

[0034] Particularly in the case where 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, i.e., 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 the LCST type (Lower Critical Solution Temperature). In a volume phase transition of the UCST type, the cross-linked polymer gel is only swollen by the working fluid when the critical temperature (limit temperature) is exceeded.In a volume phase transition of the LCST type, the working fluid is displaced from the cross-linked polymer gel when the critical temperature (limit temperature) is exceeded. Consequently, the heat pipe shuts off above the critical temperature during a UCST transition. In an LCST transition, the heat pipe shuts off below the critical temperature. The limit temperature can thus be used to define a switching temperature for the transition from the first operating state to the heat pipe's shut-off state.

[0035] Known polymers exhibiting a UCST volume phase transition are described, for example, in Macromol. Rapid Commun. 33, 1898–1920, 2012. Known polymers exhibiting a LCST volume phase transition are described, for example, in Adv. Polym. Sci. 242, 29–89, 2011. The polymer gels mentioned interact with water and are therefore particularly suitable for a heat pipe in which water is used as the working fluid. However, there are also a number of polymers that exhibit the described properties and behavior with organic fluids, such as mineral oils, for example, J. Polym. Sci. A46, 5724–5733, 2008. In this case, a fluid other than water can also be used as the working fluid.

[0036] 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 loading. With increasing temperature (and the associated increase in the vapor pressure of the bound fluid), the loading of an adsorbent decreases, and the fluid is released again.

[0037] Preferably, the adsorbent has a threshold temperature such that when this threshold temperature, or a certain vapor pressure of the fluid, is exceeded, the fluid is released quite abruptly from the adsorbent. The threshold temperature can thus be used to define a switching temperature for the transition from the blocking state to the first operating state of the heat pipe.

[0038] An example of an adsorbent material with a defined limit temperature or the associated vapor pressure of the fluid is the adsorbent AQSOA ™< -Z05 from Mitsubishi ™< .

[0039] It is also within the scope of the invention that the properties of the liquid storage device are influenced not by temperature, but by another physical or chemical stimulus. Examples of these include UV light or microwave radiation, as well as pH value, ionic strength, or the presence of certain organic molecules. Examples of these are described in Angew. Chem. Int. Ed. 55, 6641-6644, 2015. The switching of the thermal diode is thus possible through a variety of factors and can be adapted accordingly to the application area and the ambient conditions.

[0040] The object of the invention is also achieved by a system comprising a heat pipe having the properties described above according to the invention and means for applying a field in order to change the properties of the activatable functional material.

[0041] Preferably, 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 provided as means for applying the field. Either just one of the mentioned field generators or a combination of several of the mentioned field generators can be provided. Examples of these are a capacitor, a coil, an eccentric, a (UV) light source, or a heating and cooling device. This allows the control options to be individually adapted to the working fluid used and the activatable functional material used.

[0042] 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.

[0043] The system is preferably designed to be flexible with respect to the hot side and cold side. If the heat pipe is designed as a heat pipe with a reversible preferred heat conduction direction, means are preferably provided to assign their functions to the evaporator region and condenser region through contact with a hot side or, correspondingly, a cold side. Good thermal contact is preferably provided between the evaporator region and condenser region and the hot side or cold side, respectively. Good thermal contact between the heat sink and heat source and the heat pipe is provided.

[0044] In a preferred embodiment, the system is designed with a heat pipe comprising a combination of two functional materials, one of which is designed as a liquid reservoir as described above, particularly in the form of a polymer gel. The other functional material is preferably designed as an ORMOCER® whose fluidphilic / fluidphobic properties can be modified, preferably under the influence of light, particularly UV light.

[0045] The object of the invention is also achieved by a method having the features of claim 15. As is known per se, the method for switching and / or programming heat transfer is carried out using a heat pipe with at least one working chamber, at least one evaporator region, at least one condenser region, and a working fluid. It comprises the following method steps: A Evaporation of the working fluid in the evaporator region, wherein heat is transported with the gaseous working fluid from the evaporator region to the condenser region, B Condensation of the working fluid in the condenser region, wherein the heat is dissipated to a heat sink.

[0046] It is essential that the heat pipe is operated as a thermal diode or thermal switch by changing the thermal conductivity by applying an external field and / or depending on conditions within the working chamber.

[0047] The method according to the invention is preferably designed for implementation using 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 for implementation of the method according to the invention and / or a preferred embodiment of the method according to the invention.

[0048] The method according to the invention also shows the above-described advantages and features of the heat pipe according to the invention and / or the system according to the invention.

[0049] Preferably, the thermal conductivity of the heat pipe is changed by keeping the evaporator region free of the working fluid and / or preventing the working fluid from evaporating.

[0050] 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 in the evaporator region to a cold side (heat sink) arranged in the condenser region. By applying an external field in a method 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 heat and / or cold using light, in particular UV light. In the second operating state, no working fluid, or at least insufficient working fluid, is available in the evaporator region. The evaporator region dries out, and the heat pipe no longer conducts heat in the preferred heat conduction direction of the first operating state.

[0051] Alternatively, the working fluid can switch from the first operating state to the second operating state depending on conditions within the working chamber. Parameters that can initiate a switch from the first operating state to the second operating state include temperature, pH of the working fluid, and / or ionic strength of the working fluid. This offers the advantage that the heat pipe can be "programmed" to change operating states under certain conditions without the need for external influence.

[0052] Preferably, the working fluid is displaced from the evaporator area of ​​the working chamber by means of a switchable surface coating, as already described above.

[0053] 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. The reservoir controls the absorption and release of the working fluid required for heat transport. This means that the available quantity of 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 blocked 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.

[0054] In a preferred embodiment of the invention, the preferred heat conduction direction of the thermal diode is reversed by swapping the surface properties of the evaporator region and the condenser region through the application of an external field and / or depending on conditions within the working chamber. In this case, in a second operating state, the working fluid in the original condenser region, which now acts as the evaporator region, can evaporate and absorb heat from a heat source and transport it to the original evaporator region, which now acts as the condenser region. In the new condenser region, the working fluid condenses and releases the heat to a heat sink. As a result, the preferred heat conduction direction is reversed compared to operating state 1.

[0055] 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 for controlling or regulating them. 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 transfer in the conductive state, have very low thermal resistance. Furthermore, they can be realized in very compact designs and are therefore easy to integrate. Depending on the design, the heat pipes are simple in construction, consist of few individual components, and do not need to contain any moving parts.

[0056] Further preferred features and embodiments of the heat pipe according to the invention and the method according to the invention are explained below with reference to exemplary embodiments and the figures. Figure 1 shows a schematic representation of a first embodiment of a heat pipe according to the invention, Figure 2 shows a schematic representation of a second embodiment of a heat pipe according to the invention.

[0057] 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 region and the condenser region with the partial images a) in the conducting state and b) in the blocking state.

[0058] The heat pipe 1 has a working chamber 2 with at least one evaporator region 3 and at least one condenser region 4. The evaporator region 3 is in operative connection with a heat source (not shown), in this case with the temperature T 1 = 100° C, and the condenser region 4 is in connection with a heat sink (not shown) with the temperature T 2 = 10° C. A working fluid 5 is provided in the working chamber 2.

[0059] The working chamber 2 is in the present case designed as a closed, pressure-tight volume which is designed in such a way that heat transport takes place by means of convection of the evaporated working fluid 5 and a return transport of the condensed working fluid 5 takes place.

[0060] The working fluid 5 is water in this case.

[0061] The evaporator region 3 and the condenser region 4 are formed with a coating 6 made of activatable functional material. Both the coating 6 of the evaporator region 3 and the condenser region 4 are designed such that the surface property of the coating 6a of the evaporator region 3 can be changed from hydrophilic to hydrophobic and back again, while the surface property of the coating 6b of the condenser region 4 can be changed from hydrophobic to hydrophilic and back again. The coatings 6 are designed such that the evaporator region 3 and the condenser region 4 have precisely opposite surface wetting properties.

[0062] In the present case, the coating 6 made of activatable functional material is formed as a switchable coating 6 made of ORMOCER® and / or with ORMOCER®. ORMOCER® are, as already described, inorganic-organic hybrid polymers that can advantageously influence the surface properties of many substrates. ORMOCER® can also be formed as switchable coatings 6 from hydrophilic to hydrophobic and back again using mechanisms known from the specialist literature, see B. Xin, J. Hao, Chem. Soc. Rev. 39, 2010, 769-782.

[0063] In the present case, the coatings 6a in the evaporator region 3 and 6b in the condenser region 4 are formed 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 from a substrate with the same electrical charge and protrude into the interior of the thermal diode by "stretching" the dodecyl chain. In the present case, the substrate in the evaporator region is designed with the same electrical charge. This leads to a hydrophilic property of the surface 6a in the evaporator region 3. An electrically oppositely charged substrate is provided in the condenser region 4.This, in turn, attracts the ionic groups, so that the non-polar dodecyl chains protrude into the interior of the thermal diode, which leads to a hydrophobic property of the surface 6b in the capacitor region.

[0064] By applying an electric field, a hydrophilic and a hydrophobic side are created, with the properties also being reversed by reversing the field direction.

[0065] The heat pipe 1 is thus designed as a switchable thermal diode: In a first operating state, heat is transported from the heat source to the heat sink by evaporating the working fluid 5, which transports heat with the gaseous working fluid 5 from the evaporator region 3 to the condenser region 4. The evaporator region 3 is heated by the heat source, and the working fluid 5, which has collected on the hydrophilic coating 6a of the evaporator region 3, evaporates, enabling heat to be transported from the evaporator region 3 to the condenser region 4. In the condenser region 4, the working fluid 5 condenses on the hydrophobic coating 6b of the condenser region 4, and the heat is dissipated to a heat sink. Due to the hydrophobic surface properties in the condenser region 4, droplets of the working fluid 5 form.Due to the highly hydrophobic design of the surface, the working fluid 5 "jumps back" into the evaporator area 3.

[0066] By applying an external field, in this case with a voltage of 5 V, the heat pipe 1 can be switched from the first heat-conducting operating state to the second non-heat-conducting operating state.

[0067] By applying the external field, the surface properties of the coating 6 in the evaporator region 3 and in the condenser region 4 change, as described. The evaporator region 3 at the heat source now exhibits hydrophobic properties. Insufficient working fluid 5 collects on the coating 6a of the evaporator region 3, and the working fluid 5 that collects there quickly evaporates and condenses on the hydrophilic coating 6b of the condenser region 4. The working fluid 5 remains there and is not transported back to the evaporator region 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 no heat transfer via the working fluid 5 takes place. The thermal diode blocks.

[0068] Figure 2shows 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 conducting state and b) in the blocking state.

[0069] To avoid repetition, only the differences to Figure 1 be addressed.

[0070] 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: Put together 9 Monomer 1 Mol -% Monomer 2 Mol -% Networker Mol -% 1 50 - 80 0 - 30 2 - 20 2 50 - 85 2 - 30 2 - 20 3 50 - 85 2 - 30 2 - 20 4 30 - 80 10 - 45 2 - 25 5 30 - 80 10 - 45 2 - 25 6 30 - 80 10 - 45 2 - 25 7 80 - 98 - 2 - 20 8 20 - 80 10 - 50 2-20 9 30 - 90 10 - 40 2 - 20 9 20 - 80 10 - 50 2 - 20

[0071] Hydrogels with a UCST-type volume phase transition can be produced, for example, by radical polymerization using the following monomers. The compositions mentioned are not to be understood as exclusive: Composition Monomer 1 Mol -% Monomer 2 Mol -% Networker Mol -% 1 80 - 98 - 2 - 20 2 80 - 98 - 2 - 20 3 60 - 90 10 - 30 2 - 20 4 60 - 90 10 - 30 2 - 20

[0072] Furthermore, it is also possible to produce suitable hydrogels exhibiting a volume phase transition by subsequent crosslinking of soluble polymers. To obtain a hydrogel with a volume phase transition of the LCST type, 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.

[0073] The water-binding hydrogel 7 makes the available quantity of the working fluid 5 variable. The water-binding hydrogel 7 has a water-binding state and a significantly less water-binding state. In this case, 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 this case in a temperature range from room temperature to approximately 150°C. This heating occurs by heating the hot side on the evaporator side, i.e., without an external field.

[0074] In the first operating state of the heat pipe 1, the working fluid 5 is available for heat conduction. 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. In this bound form, the working fluid 5 is no longer available for heat transport. The heat pipe 1 no longer conducts heat.

[0075] In contrast to Figure 1 No coating is provided to ensure the return transport of the working fluid 5 from the condenser region 4 to the evaporator region 3. The heat pipe 1 is therefore designed with a fluid return in the form of a wick structure (not shown).

Claims

1. Heat pipe (1) with at least one working chamber (2) with 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), wherein the working chamber (2) is configured as a closed volume which is configured such that heat is transported by means of convection of the evaporated working fluid (5) and the condensed working fluid (5) is transported back, wherein the closed volume is configured as a pressure-tight system and essentially all foreign gases, except for the working fluid (5), are removed from the pressure-tight system, and the heat pipe (1) is designed as a switchable and / or programmable thermal diode or as a switchable and / or programmable heat switch, in that at least one activatable functional material is provided, which is arranged and designed to keep the evaporator region (3) free of the working fluid (5) in a second operating state and / or to prevent the working fluid (5) from evaporating in order to reduce and / or prevent the heat transfer and / or change the preferred direction of heat conduction, the heat pipe is characterized in that the at least one functional material is configured in the form of a switchable coating of the evaporator region (3) and / or the condenser region (4), in that at least the surface property of the coating of the evaporator region (3) can be changed from fluid-philic to fluid-phobic and / or in that the at least one functional material is configured in the form of a reservoir for the working fluid (5).

2. Heat pipe according to claim 1, characterized in that the heat pipe (1) is designed as a switchable thermal diode or heat switch, in that the at least one activatable functional material is designed to at least partially change its 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, in that the at least one activatable functional material is designed to change its properties as a function of conditions inside the working chamber (2), in particular the temperature, pH of the working fluid (5) and / or ionic strength of the working fluid (5).

4. Heat pipe according to any one of the preceding claims, characterized in that the heat pipe (1) is configured with a fluid circuit for the working fluid (5), preferably in that the fluid circuit comprises a fluid return for transporting the condensed working fluid (5) from the condenser region (4) back to the evaporator region (3).

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

6. Heat pipe according to any one of the preceding claims, characterized in that the at least one functional material is configured in the form of a switchable coating of the evaporator region (3) and / or the condenser region (4), in that at least the surface property of the coating of the evaporator region (3) can be changed from fluid-philic to fluid-phobic.

7. Heat pipe according to any one of the preceding claims, characterized in that the switchable coating (6) is configured as an inorganic-organic hybrid polymer whose surface properties can be changed from hydrophilic to hydrophobic and back again.

8. Heat pipe according to any of claims 1 to 6, characterized in that the at least one functional material is configured in the form of a liquid reservoir for the working fluid (5).

9. Heat pipe according to claim 8, characterized in that the reservoir for the working fluid (5) is configured as a gel, in particular a polymer gel, an adsorbent or a mesoscopically structured surface.

10. Heat pipe according to any one of claims 8 or 9, characterized in that the reservoir for the working fluid (5) is configured as a polymer gel which has a temperature-induced volume phase transition, in particular a polymer with a volume phase transition of the UCST type or a polymer with a volume phase transition of the LCST type.

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

12. System according to claim 11, characterized in that field generators are provided as a means of applying fields for an electric field, a magnetic field, a stress-strain field, for generating light, in particular UV light, for generating heat and / or for generating cold.

13. System according to any one of claims 11 or 12, characterized in that the system is configured with a combination of two functional materials, wherein one of the two functional materials is configured as a liquid reservoir according to any one of claims 8 to 10, and the other functional material is configured as an inorganic-organic hybrid polymer whose fluid-philic / fluid-phobic properties can be changed, preferably under the influence of light, in particular UV light.

14. 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 region (3) and at least one condenser region (4) and a working fluid (5) having the following method steps: A evaporating the working fluid (5) in the evaporator region (3), wherein heat is transported by the gaseous working fluid (5) from the evaporator region (3) to the condenser region (4), B condensing the working fluid (5) in the condenser region (4), wherein the heat is removed to a heat sink, wherein a heat transport takes place by means of convection of the evaporated working fluid (5) and a return transport of the condensed working fluid (5) takes place in that the closed volume is configured as a pressure-tight system and essentially all foreign gases, with the exception of the working fluid (5), are removed from the pressure-tight system, and the heat pipe (1) is operated as a thermal diode or heat switch in that the thermal conductivity is changed by applying an external field and / or as a function of conditions inside the working chamber (2), in that in the case of a functional material in the form of a switchable coating in the evaporator region (3) and / or the condenser region (4) at least the surface property of the coating of the evaporator region (3) is changed from fluid-philic to fluid-phobic and / or in that by having at least one functional material in the form of a reservoir for the working fluid (5) the working fluid in the evaporator region is at least reduced.

15. Method according to claim 14, characterized in that the thermal conductivity of the thermal diode or the heat switch is changed in that the evaporator region (3) is kept free of working fluid (5) and / or the working fluid (5) is prevented from evaporating.

16. Method according to claim 14 or 15, characterized in that the preferred direction of heat conduction of the thermal diode is reversed in that by applying an external field and / or depending on conditions inside the working chamber (2) the surface properties of the evaporator region (3) and the condenser region (4) are swapped.

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