DE102020001380B4 - latent heat storage - Google Patents

Abstract

Latent heat storage device with at least one phase change material accommodated in at least one storage device, which has a crystallization temperature (Tswitching PCM) at which the phase change material changes exothermically from a fluid state to a crystalline state, and- a melting temperature above the crystallization temperature (Tswitching PCM). (Tmelting PCM), in which the phase change material changes from the crystalline state to the fluid state, and having at least one triggering mechanism for triggering the crystallization of the phase change material, the triggering mechanism comprising a crystallization nucleating agent which is connected to a mechanical actuating element (1) in Active connection is, characterized in that the actuating element (1) of the triggering mechanism contains at least one two-way shape memory polymer or is formed entirely from it, which is programmed such that the actuating element (1) between a a first mode in which the actuating element (1) brings the nucleating agent into contact with the phase change material to initiate its crystallization, and- a second mode in which the actuating element (1) brings the nucleating agent out of contact with the phase change material, reversibly to and fro is switchable, wherein the at least one two-way shape memory polymer of the actuating element (1) has at least- a first switching temperature (Tswitching-1), in which it is converted from its second form into the first form, and- one compared to the first switching temperature (Tswitching- 1) higher, second switching temperature (TSwitch-2), in which it is converted from its first form into the second form.

Description

• - eine Kristallisationstemperatur, bei welcher das Phasenwechselmaterial exotherm von einem fluiden Zustand in einen kristallinen Zustand übergeht, und
• - eine oberhalb der Kristallisationstemperatur gelegene Schmelztemperatur, bei welcher das Phasenwechselmaterial aus dem kristallinen Zustand in den fluiden Zustand übergeht,

aufweist, und mit wenigstens einem Auslösemechanismus zum Auslösen der Kristallisation des Phasenwechselmaterials, wobei der Auslösemechanismus einen Kristallisationskeimbildner umfasst, welcher mit einem mechanischen Betätigungselement in Wirkverbindung steht.The invention relates to a latent heat storage device with at least one phase change material accommodated in at least one storage device

• - a crystallization temperature at which the phase change material exothermically transitions from a fluid state to a crystalline state, and
• - a melting temperature above the crystallization temperature at which the phase change material changes from the crystalline state to the fluid state,

having, and having at least one triggering mechanism for triggering the crystallization of the phase change material, wherein the triggering mechanism comprises a crystallization nucleating agent, which is operatively connected to a mechanical actuating element.

Latent heat accumulators of the type mentioned above are known in various configurations, their heat storage capacity being based on a phase change material accommodated in a memory which uses the enthalpy of reversible thermodynamic changes of state. Examples of such phase change materials, also referred to as “PCM” (phase change materials), primarily, although not exclusively, include various salt hydrates. The phase change materials have a relatively high enthalpy of fusion, with the phase change material changing from a solid, usually crystalline, state to a fluid, especially liquid state when the latent heat store is “charged” when it reaches its melting temperature, in which heat can be stored over a long period of time . During cooling, the phase change material then remains in the liquid phase in the form of a supercooled melt in a metastable state over a relatively wide temperature range until it reaches its crystallization temperature. As soon as crystallization is triggered in the supercooled melt, the phase change material heats up as a result of the heat of crystallization released in the process, ie it changes exothermically from its fluid, in particular liquid, state to the crystalline state. Examples of phase change materials (PCM) based on salt hydrates in the form of calcium chloride hexahydrate (CaCl ₂ • 6H ₂ O), sodium acetate trihydrate (CH ₃ COONa • 3H ₂ O), sodium thiosulfate pentahydrate (Na ₂ S ₂ O ₃ • 5 H ₂ O) and sodium sulfate decahydrate (Na ₂ SO ₄ • 10 H ₂ O) together with their melting temperature (T _{melting PCM} ), their melting enthalpy (ΔH _{melting PCM} ) and their between the melting and The supercooling temperature range (ΔT _U-PCM ) extending beyond the crystallization temperature, in which they remain in their metastable, liquid state during cooling, is given as an example: PCM T _{Enamel PCM} ΔT _U-PCM ΔH _{melting PCM} (CaCl ₂ 6H ₂ O) 30°C 20°C 190 J/g ( _{CH3COONa.3H2O )} 58°C 70°C 230 J/g ( _{Na2SO4 10H2O )} 48°C 25°C 206 y/g ( _{Na2SO4 10H2O )} 32°C 25°C 254 J/g

Further examples of such phase change materials based on salt hydrates, to which additives including chelating agents can also be added, include potassium fluoride tetrahydrate (KF • 4 H ₂ O) with a melting point of 19° C. and lithium nitrate trihydrate (LiNO ₃ • 3 H ₂ O) with a melting temperature of 29°C.

In the course of anthropogenic climate change, latent heat storage systems based on such phase change materials are becoming increasingly important, for example in solar thermal systems for storing solar energy, for heat-storing floor and wall heating elements, for energy self-sufficient temperature control of transport and storage containers through to hand or pocket warmers can find application.

In order to convert the supercooled melt, which is in a metastable state, into the crystalline state so that the heat of crystallization released can be used, generic latent heat storage devices require a triggering mechanism by means of which the crystallization of the phase change material can be initiated reliably and, in particular, repeatedly. This is done in particular by adding a nucleating agent, such as by adding foreign nuclei or autologous nuclei in the form of a portion of the phase change material in the crystalline state the local formation of intrinsic nuclei of the phase change material can be achieved, for example, by a local mechanical shock load (cf. e.g DE 601 07 382 T2 , DE 10 2010 046 243 A1 , EP 0 350 460 A2 or U.S. 5,378,337 A ) . Other ways of initiating nucleation in the supercooled phase change material are, for example, local cooling of the supercooled melt to the crystallization temperature of the phase change material (cf., for example, EP 3 056 868 A1 ) or in the electrochemical activation by means of electrodes arranged in the memory.

the U.S.A. 4,817,704 describes a latent heat accumulator with phase change materials based on salt hydrates, which comprises a plurality of chambers for accommodating the phase change materials, which are connected to one another by means of a capillary. Since the chambers communicate with one another in this way, if the phase change material in one of the chambers crystallizes, crystallization nuclei pass through the capillary into the supercooled melt of the phase change material in an adjacent chamber, so that this can also crystallize. A capillary section protruding from at least one of the chambers serves as the triggering mechanism for initiating an exothermic crystallization of the phase change material that is in a supercooled molten state can be contacted.

A particular disadvantage of the known latent heat storage devices is that their triggering mechanism requires the supply of energy—be it mechanical or electrical—in order to initiate crystallization of the supercooled melt of the phase change material and to be able to use the heat released in the process.

The invention is based on the object of proposing a simple and cost-effective triggering mechanism for a latent heat storage device of the type mentioned at the outset, while at least largely avoiding the aforementioned disadvantages, which makes it possible to initiate the crystallization of the supercooled melt of the phase change material both in a reproducible and, in particular, in an energy self-sufficient manner .

• - einer ersten Form, in welcher das Betätigungselement den Kristallisationskeimbildner mit dem Phasenwechselmaterial in Kontakt bringt, um dessen Kristallisation auszulösen, und
• - einer zweiten Form, in welcher das Betätigungselement den Kristallisationskeimbildner mit dem Phasenwechselmaterial außer Kontakt bringt,

reversibel hin und her schaltbar ist, wobei das wenigstens eine Zweiwege-Formgedächtnispolymer des Betätigungselementes zumindest

• - eine erste Schalttemperatur, in welcher es aus seiner zweiten Form in die erste Form überführt wird, und
• - eine gegenüber der ersten Schalttemperatur höhere, zweite Schalttemperatur, in welcher es aus seiner ersten Form in die zweite Form überführt wird,

aufweist.According to the invention this object is achieved in a latent heat storage device of the type mentioned in that the actuating element of the triggering mechanism 'contains at least one two-way shape memory polymer or is formed entirely from it, which is programmed in such a way that the actuating element between

• - a first form in which the actuator brings the nucleating agent into contact with the phase change material to induce crystallization thereof, and
• - a second form in which the actuator brings the nucleating agent out of contact with the phase change material,

is reversibly switchable back and forth, wherein the at least one two-way shape memory polymer of the actuating element at least

• - a first switching temperature at which it is transformed from its second form into the first form, and
• - a second switching temperature, which is higher than the first switching temperature, in which it is converted from its first form into the second form,

having.

Shape memory polymers are polymers which usually consist of at least two polymer components or, in particular, of one polymer component with different segments. On the one hand, these are "hard" segments that also function as network points. On the other hand, there are "soft" segments that connect the network points with each other and act as switching segments and are also referred to as such. The switching segments are amorphous or elastic at elevated temperatures, while rigid at lower temperatures (they are in semi-crystalline or vitrified form in this case). Such polymers can be programmed in terms of their shape by being heated to a temperature which corresponds at least to the so-called switching temperature at which the phase transition (glass transition or melting transition) of the soft or switching segments takes place. At such a temperature, the polymer can then under Einwir effect of a deformation force, after which it can be cooled to its so-called shape-fixing temperature while maintaining the deformation, which corresponds to the crystallization temperature or glass transition temperature of the soft or switching segments and can be in the range of the switching temperature of the shape memory polymers, but is usually at least slightly lower in comparison . The soft or switching segments are then again in a partially crystalline or vitrified form, so that the shape is retained. However, this shaping is only temporary insofar as when a shape memory polymer that is “programmed” in this way, i.e. mechanically deformed, is heated to a certain temperature, namely to its switching temperature, the soft segments (switching segments) are converted back into their amorphous or flexible form , so that they can no longer counteract the entropy-elastic restoring force induced by the hard component (network points) and the shape-memory polymer resumes its original shape, i.e. the mechanical deformation is "reversed" without the need for a new force to be applied. Furthermore, there is often also the possibility of programming by cold deformation, in that the shape memory polymers can be deformed at a temperature below their switching temperature, eg at ambient temperature, and optionally, if the shape-fixing temperature is lower than this, can be cooled to their shape-fixing temperature. In this case, too, only temporary deformation takes place insofar as repeated heating at least to the switching temperature in order to convert the soft segments (switching segments) into the amorphous or flexible phase and thereby relax the mechanical stresses induced during the cold deformation, recovery takes place without having to apply a deformation force again.

In addition to such a shape memory, thermoresponsive polymers usually also have a temperature memory. This is understood to mean that when the shape memory effect is triggered, the shape recovery begins at about the temperature at which the mechanical deformation was previously introduced into the material. Such material behavior is exhibited, for example, by shape memory polymers with semi-crystalline network structures, such as thermoplastic polyurethane elastomers (N. Fritzsche, T. Pretsch in Macromolecules 47, 2014, 5952-5959; N. Mirtschin, T. Pretsch in RSC Advances _5, 2015, 46307- 46315).

In addition, shape-memory polymers are known which have two-way shape-memory properties and can therefore be switched thermoreversibly, with the switching segments of such two-way shape-memory polymers undergoing a change in shape during the transition between their primarily partially crystalline state and their primarily amorphous or flexible state such that on the one hand they can be changed by cooling of the polymer below the crystallization temperature, which is referred to as the "first switching temperature" in the context of the present disclosure, on the other hand, by heating the polymer in the switching temperature range, which is referred to as the "second switching temperature" in the context of the present disclosure, reversibly between its permanent shape and its temporary shape can be switched back and forth, ie the correspondingly programmed two-way shape memory polymer automatically deforms back and forth with the appropriate temperature control. Such two-way shape memory polymers are, for example, from T. Pretsch, M. Bothe: "Bidirectional actuation of a thermoplastic polyurethane elastomer", Journal of Materials Chemistry A, 46 (2013), 14.491-14.497, or from M. Bothe, T. Pretsch: "Two-way shape changes of a shape-memory poly(ester urethane)", Macromol. Chem. Phys. 213 (2012), 2378-2385).

The back and forth deformation of such two-way shape memory polymers can, on the one hand, take place more or less purely temperature-induced, without deformation forces having to be applied for this purpose. As explained in more detail below, two-way shape-memory polymers are also known which develop their two-way shape-memory properties in particular under the influence of a permanent mechanical preload, such as as a result of permanent pressure, so that they are under permanent tension in order to crystallize the soft segments to favor during cooling, as for example from the article by M. Bothe, T. Pretsch: "Two-Way Shape Changes of a Shape Memory Poly(ester urethane)" in Macromol. Chem. Phys. 213 (2012), 213, 2378-2385.

• - einer ersten Form, in welcher das Betätigungselement den Kristallisationskeimbildner mit dem Phasenwechselmaterial in Kontakt bringt, um dessen Kristallisation auszulösen, und
• - einer zweiten Form, in welcher das Betätigungselement den Kristallisationskeimbildner mit dem Phasenwechselmaterial außer Kontakt bringt,

reversibel und insbesondere ohne Aufbringen äußerer Kräfte hin und her schaltbar ist. Das wenigstens eine Zweiwege-Formgedächtnispolymer des Betätigungselementes besitzt hierbei zumindest

• - eine erste Schalttemperatur, in welcher es aus seiner zweiten Form, in welcher das Betätigungselement den Kristallisationskeimbildner mit dem Phasenwechselmaterial außer Kontakt bringt, in die erste Form überführt wird, und
• - eine gegenüber der ersten Schalttemperatur höhere, zweite Schalttemperatur, in welcher es aus seiner ersten Form, in welcher das Betätigungselement den Kristallisationskeimbildner mit dem Phasenwechselmaterial in Kontakt bringt, um dessen Kristallisation auszulösen, in die zweite Form überführt wird.

The invention now provides that the mechanical actuating element of the triggering mechanism' of the latent heat storage device contains such a two-way shape memory polymer or is essentially formed entirely from it, the two-way shape memory polymer of the mechanical actuating element being programmed in such a way that it is at least between

• - a first form in which the actuator brings the nucleating agent into contact with the phase change material to induce crystallization thereof, and
• - a second form in which the actuator brings the nucleating agent out of contact with the phase change material,

is reversible and in particular can be switched back and forth without the application of external forces. The at least one two-way shape memory polymer of the actuating element in this case has at least

• - a first switching temperature in which it is transformed from its second form, in which the actuator displaces the nucleating agent out of contact with the phase change material, into the first form, and
• - a second switching temperature, higher than the first switching temperature, in which it is converted from its first form, in which the actuating element brings the nucleating agent into contact with the phase change material in order to trigger its crystallization, into the second form.

In this way, a purely temperature-dependent and energy-autonomous, reversible change in shape between its first form and its second form is programmed into the at least one two-way shape-memory polymer of the actuating element of the triggering mechanism in such a way that, on the one hand, at low temperatures (e.g. at night), as soon as the two-way Shape memory polymer below its first switching temperature, at which the two-way shape memory polymer is in its first form, as a result of contact of the crystallization nucleating agent with the phase change material accommodated in the reservoir when the latter is in the form of a supercooled melt in a metastable liquid phase state, the exothermic crystallization of the phase change material can be triggered reproducibly. On the other hand, at higher temperatures (e.g. during the day) above the second switching temperature, at which the two-way shape memory polymer is in its second form, the crystallization nucleating agent is brought out of contact with the now molten phase change material present in the liquid phase, so that the latter during its subsequent Cooling is converted back into a metastable, supercooled state in which it can be crystallized again when the first switching temperature of the two-way shape memory polymer is reached due to the concomitant conversion from its second to its first form in order to release the heat of crystallization.

As already indicated, the at least one two-way shape-memory polymer of the actuating element of the triggering mechanism of the latent heat storage device according to the invention can essentially not be mechanically preloaded, with a purely temperature-dependent and reversible shape change taking place without the action of external forces in the at least one two-way shape-memory polymer of the actuating element programmed between its first form and its second form. Such a configuration is particularly suitable for portable applications of the latent heat storage device with the lowest possible intrinsic weight. Instead, depending on the type of two-way shape memory polymer used for the actuating element of the triggering mechanism, it can also be provided that the at least one two-way shape memory polymer of the actuating element of the triggering mechanism is mechanically under permanent tension, with gravity in particular being used to generate such a permanent tension a surface load acting on the actuating element, springs or the like, so that the permanent mechanical preloading to promote the two-way shape memory effect also requires no external energy supply.

In addition to known applications of generic latent heat storage, such as in the construction industry, the inventive design of the energy self-sufficient triggering mechanism opens up new, environmentally friendly areas of application for the latent heat storage device, such as for temperature-controlled transport and storage containers, etc., with the switching temperatures of the two-way shape memory polymer of the actuating element of the triggering mechanism' can be specifically adapted both to the melting and crystallization temperature and in particular to the supercooling temperature range of the phase change material and to the target temperatures of the latent heat storage device, within which heating is to be triggered or heat is to be stored.

According to one embodiment, it can be provided, for example, that the crystallization nucleating agent is applied to the surface of the actuating element of the triggering mechanism and/or dispersed into it, so that as a result of the crystallization nucleating agent immobilized on the actuating element itself being brought into contact with the phase change material when the actuating element is in its first Shape is (the two-way shape memory polymer of the actuator is below its first switching temperature), which was in the metastable liquid supercooled state lowing phase change material can be transferred or crystallized into the solid phase. Alternatively or additionally, it can be provided, for example, that the crystallization nucleating agent is applied at least to the surface of a stationary or displaceable element and/or dispersed into it, the stationary or displaceable element being able to be brought into and out of contact with the phase change material by means of the actuating element. In this case, the actuating element is able, if it is converted from its second (or first) shape into its first (or second) shape, for example by being cooled to its first switching temperature (or heated to its second switching temperature), with the Bringing nucleating agent provided, stationary or displaceable element, e.g. as part of the reservoir or the actuating element itself, into contact (or out of contact) with the phase change material, e.g. by covering or exposing the nucleating agent applied to the stationary or displaceable element, or by it places the displaceable element in a first and second position, respectively, in which the nucleation agent is in contact and not in contact with the phase change material.

According to a further embodiment, provision can be made, for example, for the crystallization nucleating agent to be immobilized in a separate chamber which can be connected to and separated from the reservoir accommodating the phase change material by means of the actuating element. The actuating element can consequently, when it is converted from its second (or first) shape to its first (or second) shape, for example by having been cooled to its first switching temperature (or heated to its second switching temperature), the chamber containing the nucleating agent to the reservoir holding the phase change material (or to separate the chamber holding the nucleating agent from the reservoir holding the phase change material).

• - in seiner ersten Form, in welcher es den Kristallisationskeimbildner mit dem Phasenwechselmaterial in Kontakt bringt, um dessen Kristallisation auszulösen, wenigstens einen Durchlasskanal aufweisen, so dass beispielsweise das in dem Speicher aufgenommene Phasenwechselmaterial über den Durchlasskanal mit dem in der Kammer aufgenommenen Kristallisationskeimbildner in Kontakt steht), und
• - in seiner zweiten Form, in welcher es den Kristallisationskeimbildner mit dem Phasenwechselmaterial außer Kontakt bringt, keinen Durchlasskanal aufweist, so dass beispielsweise das in dem Speicher aufgenommene Phasenwechselmaterial durch das Betätigungselement selbst oder durch ein von diesem betätigtes, verlagerbares Element von dem in der Kammer aufgenommenen Kristallisationskeimbildner getrennt ist.

For this purpose, the actuator z

• - in its first form, in which it brings the nucleating agent into contact with the phase change material in order to trigger its crystallization, have at least one through-channel, so that, for example, the phase-change material received in the reservoir is in contact with the nucleating agent received in the chamber via the through-channel ), and
• - in its second form, in which it brings the crystallization nucleating agent out of contact with the phase change material, has no passage channel, so that, for example, the phase change material accommodated in the reservoir can be separated from that accommodated in the chamber by the actuating element itself or by a displaceable element actuated by it Crystal nucleating agent is separated.

• - in seiner ersten Form, in welcher es den Kristallisationskeimbildner mit dem Phasenwechselmaterial in Kontakt bringt, um dessen Kristallisation auszulösen, andere Außenabmessungen und/oder wenigstens eine andere Erstreckungsebene aufweist als
• - in seiner zweiten Form, in welcher es den Kristallisationskeimbildner mit dem Phasenwechselmaterial außer Kontakt bringt.

Alternatively or additionally, it can be provided for this purpose, for example, that the actuating element

• - in its first form, in which it brings the nucleating agent into contact with the phase change material to induce crystallization thereof, has different external dimensions and/or at least one different plane of extent than
• - in its second form, in which it takes the nucleating agent out of contact with the phase change material.

In this case, for example, it is conceivable that the actuating element has "shrunk" in its first form, i.e. has smaller external dimensions than in its second form, in which it is "stretched" to z. B. to bring the phase change material accommodated in the reservoir into contact with or separate from the nucleating agent accommodated in the chamber.

The actuating element of the triggering mechanism can have any configuration so that it can fulfill its intended function. In the case of a very simple and cost-effective configuration in terms of production technology, it is essentially foil-shaped or plate-shaped or essentially designed like a stamp can be.

As a crystallization nucleating agent, which - as mentioned above - can be applied, for example, at least to the surface of the actuating element of the triggering mechanism and/or dispersed into it or can also be arranged in a separate chamber assigned to the reservoir accommodating the phase change material, any material, in particular powder or particulate solids into consideration, which are suitable for initiating crystallization of the melt of the phase change material in the metastable, supercooled state, the crystallization nucleating agent, for example by foreign germs or by a portion of the phase change material which is permanently associated with foreign germs.

With regard to the cooling of the at least one two-way shape memory polymer of the actuating element of the triggering mechanism of the latent heat storage device to its first switching temperature in order to convert it from its second form to the first form, in which it brings the crystallization nucleating agent into contact with the phase change material, on the one hand It can be provided that the at least one two-way shape memory polymer of the actuating element can be brought passively to its first switching temperature due to the ambient temperature, i.e. the actuating element is converted from its second shape into the first shape solely as a result of passive cooling of at least the actuating element or the entire latent heat accumulator at least to the first switching temperature of its at least one two-way shape memory polymer in order to trigger the crystallization of the phase change material present in the metastable, supercooled state and the exothermic crystal to use heat of insulation. Alternatively or additionally, it can be provided that the at least one two-way shape memory polymer of the actuating element can be actively brought to its first switching temperature, in which it is converted from its second shape into the first shape, by means of a cooling device assigned to it. In the latter case, there is also the possibility of crystallization, if required, of the phase change material, which is also already in the metastable, supercooled state, at ambient temperatures above the first switching temperature of the two-way shape memory polymer of the actuating element, in that this is actively cooled to the first switching temperature of the two-way shape memory polymer by means of the cooling device, to induce crystallization of the phase change material present in the metastable, supercooled state and to utilize the exothermic heat of crystallization. In principle, the cooling device can be designed in any known manner, which can be, for example, an electrical cooling device.

While the heating of the at least one two-way shape memory polymer of the actuating element to its second switching temperature and also the heating of the phase change material accommodated in the reservoir at least to its melting temperature or also to a regeneration temperature of the phase change material that is at least slightly higher than this, at which it is ensured that the phase change material is completely has been transferred to the molten phase and there are no longer any crystals, can in principle also take place purely due to the ambient temperatures of the latent heat storage device, according to a further development it can also be provided that the storage device accommodating the phase change material is assigned a heating device in order to heat up the phase change material for regeneration purposes to heat a regeneration temperature above its melting temperature. The heating device can be any known heating device, such as an electric, high-frequency heating device or the like, with the heating device in particular being self-sufficient in terms of energy and being operated by thermal solar energy, for example, if the latent heat storage device is used to heat a building or the like .

The switching temperatures of the at least one two-way shape memory polymer of the actuating element of the triggering mechanism of the latent heat store should expediently be adjusted to the melting temperature of the phase change material on the one hand and to its crystallization temperature on the other hand - or more precisely: to its supercooling temperature range between the melting and the crystallization temperature, in which it is supercooled in the form of a supercooled melt is present in a metastable state in the liquid phase - be adjusted. The at least one two-way shape memory polymer of the actuating element preferably has a first (“cold”) switching temperature at which it is converted from its second form, in which the actuating element brings the crystallization nucleating agent out of contact with the phase change material, into the first form or is switched, in which the actuating element brings the crystallization nucleating agent into contact with the phase change material in order to trigger its crystallization, this first switching temperature being between the melting temperature and the crystallization temperature, i.e. in the metastable supercooling range of the phase change material. The temperature at which the latent heat accumulator releases the heat stored in the phase change material can be preset in a reproducible manner in a targeted manner by appropriately setting the first switching temperature of the at least one two-way shape memory polymer of the actuating element of the triggering mechanism, the first switching temperature of the two-way shape memory polymer can be chosen freely, in particular over the entire supercooling temperature range of the respective phase change material.

On the other hand, the at least one two-way shape memory polymer of the actuating element preferably has a second ("warm") switching temperature which is higher than the first ("cold") switching temperature, at which it moves out of its first form, in which the actuating element forms the crystallization nucleus with the phase change material brings into contact in order to initiate its crystallization, is converted or switched back to the second form, in which the actuating element brings the crystallization nucleating agent out of contact with the phase change material, this second switching temperature being below the regeneration temperature, in particular below the melting temperature, but closer to the Melting temperature than the crystallization temperature of the phase change material. If no heating device for regenerating the phase change material is assigned to the accumulator of the latent heat accumulator accommodating the phase change material and the at least one two-way shape memory polymer of the actuating element is consequently heated to its second switching temperature purely due to the ambient temperature or the temperature of the phase change material, then the ("warm" ) second switching temperature of the two-way shape memory polymer of the actuating element is advantageously in the range of or slightly below the melting temperature of the phase change material, so that it is ensured that the actuating element is switched back to its second form when the second switching temperature is reached, in which it the crystallization nucleating agent with the Brings phase change material out of contact. If the storage device of the latent heat storage device that accommodates the phase change material is assigned a heating device for regenerating the phase change material and the at least one two-way shape memory polymer of the actuating element can consequently be heated by means of the heating device to a regeneration temperature of the phase change material above its melting point, the ("warm") second Switching temperature of the two-way shape memory polymer of the actuating element can also lie between the melting temperature and the regeneration temperature of the phase change material, for example, so that it is also ensured that the actuating element is switched back to its second form when the second switching temperature is reached, in which it separates the crystallization nucleus with the phase change material contact.

In this context, it should be noted that a return of the actuating element from its first shape to the second shape in the range of the second switching temperature of the at least one two-way shape memory polymer can also take place with a time delay, if, for example, the (not yet) fully melted, (partly) crystalline Phase change material (still) prevents the deformation of the actuating element. However, if a sufficient proportion of the phase change material has been converted into the molten phase, the actuator can perform its thermoresponsive recovery, which is why its second (“warm”) switching temperature should in any case not be above the regeneration temperature of the phase change material.

However, it should be explicitly mentioned at this point that the second (“warm”) switching temperature of the at least one two-way shape memory polymer of the actuating element can also be above the melting temperature of the phase change material and above any regeneration temperature of the same, with the actuating element being provided with a heating device, such as a resistance heating device, for example , Induction heating device or the like, can be assigned to heat the two-way shape memory polymer to the second switching temperature as required, thereby switching it from its first form to the second form.

In order to be able to vary the desired temperature at which the latent heat accumulator is to release the heat stored there as a result of the crystallization of the phase change material induced by the actuating element of the triggering mechanism (i.e. the second switching temperature of the at least one two-way shape memory polymer of the actuating element), within the broadest possible limits, the metastable supercooling range of the phase change material extends between its melting temperature and its crystallization temperature preferably over the widest possible temperature interval of expediently at least about 10°C, in particular at least about 15°C, preferably at least about 20°C, for example at least about 25°C . Furthermore, the phase change material should be selected in such a way that its metastable supercooling range, within which the first switching temperature of the at least one two-way shape memory polymer of the actuating element expediently lies for the reasons mentioned above, includes the temperature at which the latent heat accumulator releases the (crystallization) stored in the phase change material to release heat.

In principle, any known phase change materials, such as waxes with a chain with at least 10 carbon atoms, in particular paraffins, with melting and crystallization temperatures suitable for the respective purpose of the latent heat storage device and in particular supercooling temperature ranges, can be considered as phase change material, with phases Swap materials that contain at least one salt hydrate or are essentially entirely formed from it have proven to be advantageous. Examples of such salt hydrates include the aforementioned calcium chloride hexahydrate (CaCl ₂ • 6 H ₂ O), sodium acetate trihydrate (CH ₃ COONa • 3 H ₂ O), sodium thiosulfate pentahydrate (Na ₂ S ₂ O ₃ • 5 H ₂ O) , sodium sulfate decahydrate (Na ₂ SO ₄ • 10 H ₂ O), potassium fluoride tetrahydrate (KF • 4 H ₂ O) and lithium nitrate trihydrate (LiNO3 3 H ₂ O), but also, for example, magnesium sulfate heptahydrate (MgSO ₄ • 7 H ₂ O), copper sulfate pentahydrate (CuSO ₄ • 5 H ₂ O), copper sulfate monohydrate (CuSO ₄ • H ₂ O), and the like including mixtures of salt hydrates.

While in principle any known two-way shape memory polymer can be used for the actuating element of the triggering mechanism, the switching temperatures of which are in a range that is suitable for the respective application of the latent heat storage device according to the invention, the at least one two-way shape memory polymer of the actuating element can be, for example, preferably a polyurethane elastomer , in particular a polyester or polyether urethane elastomer, whereby of course polymer mixtures or blends or compounds made of or with two-way shape memory polymers can also be used. Examples of such two-way shape memory polymers are known, for example, from the article by T. Pretsch, M. Bothe: "Bidirectional actuation of a thermoplastic polyurethane elastomer", Journal of Materials Chemistry A, 20 (2013), 14.491-14.497, with a thermoplastic polyurethane elastomer being used as an example with hard segments or network points based on methylenediphenyl isocyanate (MDI) and 1,4-butanediol (semi-crystalline/amorphous) and with switching or soft segments based on polybutylene-1,4-adipate, which is obtained by reacting 1,4 -Butanediol can be obtained with adipic acid, should be mentioned. If this polymer is first heated to a deformation temperature of about 60°C, it can be deformed for the purpose of its two-way shape memory programming, preferably with a slow deformation rate of, for example, about 1%/s, e.g. with a total elongation of up to about 1000%. whereupon it is cooled to about 0°C to achieve elongation of the material. If the polymer is then heated up to the switching temperature range ("second switching temperature") of around 30°C to 55°C, the switching segments are melted and converted from their primarily semi-crystalline state into their primarily amorphous or flexible state, so that the polymer is switched back again or contracts without a deformation force having to be applied again for this purpose. If it is then cooled back to its crystallization temperature (“first switching temperature”) in the range below about 20°C, the switching segments crystallize again and the polymer is switched or deformed again, etc. Examples of two-way shape memory polymers, their two-way shape memory properties can be favored in particular by the action of a permanent compressive force, so that the two-way shape memory polymer is under permanent mechanical stress, for example from the article by M. Bothe, T. Pretsch: "Two-way shape changes of a shape memory poly (ester urethane) ‟ in Macromol. Chem. Phys. 213 (2012), 213, 2378-2385, with a polyester urethane having soft segments made of crystallizable poly(1,4-butylene adipate) (PBA) being mentioned as an example, which has two-way shape memory properties in the correspondingly programmed state in order to change under the crystallization temperature (“first switching temperature”) to expand and to contract when heated above the switching temperature range (“second switching temperature”). In order in particular to favor the transition between an amorphous state of the PBA at high temperatures into a semi-crystalline state of the PBA at low temperatures and to achieve a very high proportion of crystallinity of the PBA - accompanied by a very strong deformation - such a two-way shape memory polymer can with a mechanical stress, for example in the range of about 1.5 MPa, applied. In addition, it should be pointed out at this point that by varying such a mechanical stress, in particular the crystallization temperature (“first switching temperature”) of the soft segments of the two-way shape memory polymer and, as a result, their melting temperature (“second switching temperature”), can also be adjusted specifically to the respective intended use of the device according to the invention Latent heat storage or can be adapted to the local conditions of its location. Furthermore, the at least one two-way shape memory polymer of the actuating element can, for example, only be under permanent mechanical stress in certain areas, for example as a result of the gravitational pull of a surface load acting on the actuating element only in certain areas.

In addition, the at least one two-way shape memory polymer of the actuating element can advantageously be a plasticizable, thermoplastic polymer, which makes it easy to manufacture using practically any thermoplastic processing method and makes it more environmentally friendly than thermosets in terms of easy recycling. While such thermoplastic two-way shape-memory polymers, as stated, are largely processed into the actuating element by means of conventional thermoplastic processing methods such as, for example, extrusion, injection molding, hot pressing, calendering, blow molding, rotational molding, etc which can then be programmed to its first and second form in the manner described above, the actuating element can in particular also be produced by means of a rapid prototyping method, such as in particular by a fused layer method, as is primarily used in 3D printers . The melt layer process, also known as "fused deposition modeling" (FDM) or "fused filament fabrication" (FFF), is a manufacturing process in which a thermoplastic polymer or a polymer blend made of thermoplastic polymers is plasticized and using a process that is usually installed in the print head of the 3D Printer provided nozzle is deposited in layers to produce the polymer molding ultimately formed from a plurality of such layers in its permanent form. On the one hand, this enables the layered production of relatively complex molded parts, which is also suitable for small series and cannot be produced or can only be produced with difficulty, for example by conventional thermoplastic processing methods such as injection molding, extrusion, etc., with the melt layer process also being suitable for the series production of polymer molded parts with relatively complex Geometry and / or surface structures can be used. In 3D printing, also referred to as “additive manufacturing”, a three-dimensional model of the polymer molding to be produced is usually created digitally, which can be done in particular using the well-known methods of computer-aided design (CAD). In addition, using suitable software, such as a so-called slicer program (e.g. Cura™ or similar), the three-dimensional model of the molded part to be produced is broken down into a number of thin layers, whereupon the plasticized polymer is cut layer by layer using the nozzle of the correspondingly moved print head is deposited to build up the molded part layer by layer. The hardening process - or more precisely: the solidification process - begins immediately after the discharge of the more or less strand-like or droplet-shaped polymer plasticate from the nozzle of the print head, whereby the separated plasticate solidifies, for example at ambient temperature or with active cooling. If a molded part produced in this way from a thermoresponsive two-way shape memory polymer is heated or cooled to the respective switching temperature after it has been previously programmed in the manner described above, it can also be switched back and forth reversibly between its first shape and its second shape in the case of an actuating element produced in several layers by means of the melt layer process, it is also possible in a relatively simple manner to disperse the crystal nucleating agent in one or more layers of the deposited plasticate, be it in essentially constant or different proportions, and/or it primarily applied to the surface of the confirmation element.

the CN 105 936 747 A describes, for example, such a filament made of a polymer blend of thermoplastic polyurethanes on the one hand and acrylonitrile-butadiene-styrene (ABS) on the other hand, which can be processed using the melt layer process using 3D printers and has two-way shape memory properties. In addition, in the context of the present invention is also preferred polymer blend with such two-way shape memory properties based on thermoplastic polyurethanes and polyolefins, such as in particular high density polyethylene (HDPE), from the DE 10 2018 003 274 A1 known, which is hereby made the subject of the present disclosure.

In addition, the thermoplastic two-way shape memory polymer of the actuating element can also be produced, for example, by means of selective laser sintering (SLS), as described, for example, in the technical article "Characterization of creeping and shape memory effect in laser sintered thermoplastic polyurethane" by S. Yuan et al., Journal of Computing and Information Science in Engineering, 16 (2016), Issue 4, pages 041007-041007-5, it also being possible to impart very complex geometries and/or surface finishes.

Two exemplary embodiments of two-way shape-memory polymers suitable for the actuating element of the triggering mechanism' of a latent heat storage device according to the invention in the form of thermoplastic polyester urethanes (TPU) based on poly(1,6-hexylene adipate)diol (PHA) or poly(1), 4-butylene adipate)diol (PBA) as the polyol component and 4,4'-methylenediphenyl isocyanate (MDI) as the diisocyanate component with 1,4-butanediol (BD) as the chain extender, which have been synthesized from the starting materials listed in the table.

Example 1:

Two-way shape memory polymer "TPU-PHA 3000/15":

• - Crystallization temperature range of the switching or soft segments based on PHA (“first switching temperature”):
  • approx. 0°C to approx. 20°C,
• - Melting temperature range of the switching and soft segments based on PHA (“second switching temperature”):
  • approx. 30°C to approx. 50°C,
• - Hard segment content (MDI/BD): approx. 15%,
• - NCO index: 1.005.

component substance proportion of molar mass polyol PHA 100 3000 diisocyanate MDI 15.5 250.25 chain extender BD 2.5 90.12 catalyst Titanium (IV) Cat. 0.0005 - - - additive 1 antioxidant 0.1 - - - additive 2 processing additive 0.7 - - - additive 3 hydrolysis stabilizer 0.6

Example 2:

Two-way shape memory polymer "TPU-PBA 4000/15":

• - Crystallization temperature range of the switching and soft segments based on PBA (“first switching temperature”):
  • approx. -10°C to approx. 10°C,
• - Melting temperature range of the switching and soft segments based on PBA (“second switching temperature”):
  • approx. 30°C to approx. 50°C,
• - Hard segment content (MDI/BD): approx. 15%,
• - NCO index: 1.005.

component substance proportion of molar mass polyol PBA 100 4000 diisocyanate MDI 14.8 250.25 chain extender BD 3.0 90.12 catalyst Titanium (IV) Cat. 0.0005 - - - additive 1 antioxidant 0.1 - - - additive 2 processing additive 0.7 - - - additive 3 hydrolysis stabilizer 0.6

However, it should be pointed out at this point that the at least one two-way shape memory polymer of the actuating element does not necessarily have to be a thermoplastic polymer, but in principle primarily elastomeric or duroplastic polymers can also be considered. Suitable representatives of such thermoset two-way shape memory polymers are for example in the technical paper "Catalyst-free thermoset polyurethane with permanent shape reconfigurability and highly tunable triple-shape memory performance" by N. Zheng et al. in ACS Macro Letters 6, 4 (2017), pages 326-330.

• - der elektromagnetische Strahlung, wie z.B. im Mikrowellenspektrum oder im infraroten bis hin zum ultravioletten Spektrum einschließlich des sichtbaren Spektrums, absorbierenden Stoffe, insbesondere auf der Basis von Kohlenstoff, z.B. in Form von (expandiertem) Graphit, Graphen, Kohlenstoff-Nanoröhren (carbon nano tubes, CNT) und dergleichen, Metallen, Metalloxiden und Metallclustern, wie z.B. (oligomeren) Silsesquioxanen und dergleichen,
• - der magnetischen und/oder ferromagnetischen Stoffe, insbesondere aus der Gruppe Eisen, Eisenoxid bzw. Magnetit, Nickel, Zink und deren Metallclustern, wie z.B. (oligomeren) Silsesquioxanen und dergleichen,
• - der Nanoclays, insbesondere auf der Basis der Carbide, Nitride und Oxide von Silicium, Zirkonium und Aluminium, z.B. in Form von Siliciumnitrid, Siliciumcarbid, Siliciumoxid, Zirkonoxid, Aluminiumoxid und dergleichen, und
• - der Verstärkungsfasern, z.B. in Form von natürlichen und/oder synthetischen Fasern, wie Kohlenstoff-, Glas-, Aramidfasern und dergleichen,

ausgewählt ist.In addition, according to a development of the latent heat storage device according to the invention, it can be provided that the at least one two-way shape memory polymer of the actuating element contains at least one filler and/or reinforcing material, which in particular is from the group

• - Materials that absorb electromagnetic radiation, such as in the microwave spectrum or in the infrared to ultraviolet spectrum including the visible spectrum, in particular based on carbon, e.g. in the form of (expanded) graphite, graphene, carbon nanotubes , CNT) and the like, metals, metal oxides and metal clusters, such as (oligomeric) silsesquioxanes and the like,
• - Magnetic and/or ferromagnetic substances, in particular from the group of iron, iron oxide or magnetite, nickel, zinc and their metal clusters, such as (oligomeric) silsesquioxanes and the like,
• - nanoclays, in particular based on carbides, nitrides and oxides of silicon, zirconium and aluminum, for example in the form of silicon nitride, silicon carbide, silicon oxide, zirconium oxide, aluminum oxide and the like, and
• - the reinforcing fibers, for example in the form of natural and/or synthetic fibers such as carbon, glass, aramid fibers and the like,

is selected.

By means of such fillers and/or reinforcing materials, the at least one two-way shape memory polymer of the actuating element can be given additional properties in order to adapt it—if desired—to the respective intended use of the latent heat accumulator. For example, magnetoresponsive and/or electroactive additives, such as electromagnetic radiation-absorbing and/or (ferro)magnetic fillers, preferably in finely particulate form, make it possible, if necessary, to inductively heat the actuating element, for example to heat it specifically to the second switching temperature and thereby to be able to switch from its first form to the second form, in which case this second switching temperature--as mentioned above--can also be above the melting temperature and above any regeneration temperature of the phase change material, for example. Fillers that absorb electromagnetic radiation in the infrared and/or ultraviolet spectrum, with which the at least one two-way shape memory polymer of the actuating element can be added and/or coated, for example, also allow the actuating element to heat up more rapidly when the outside temperature rises and/or under solar radiation , in order to be able to reliably switch the actuating element from its first form into its second form as a result of the second switching temperature of the two-way shape memory polymer being exceeded. of course, combinations of several different filler materials can also be used, such as magnetoresponsive and/or electroactive additives in combination with reinforcing fibers and optionally other fillers. In addition, the at least one two-way shape memory polymer of the actuating element can, in principle, also have other additives that are largely known from the prior art and are preferably physiologically harmless, such as lubricants and other processing aids, plasticizers, antioxidants, UV stabilizers, reinforcing materials, flame retardants , antistatic agents, hydrolysis stabilizers, impact modifiers, biostatic agents, etc.

Finally, depending on the intended use of the latent heat storage device, it can prove to be advantageous if the phase change material is mixed with at least one additive, in which case, in addition to any additives known as such, in particular those from the group of gel formers can be advantageous in order to keep the phase change material in its molten phase to gel and in this way to prevent large amounts of phase change material from being released in the event of a leak in the accumulator. Examples of suitable gelling agents include silicon oxide, especially in finely particulate form, gelatin, thermoplastic elastomers (TPE), especially based on polyurethane (TPU), cellulose acetate, e.g., in the form of carboxymethylcellulose sodium salt (CMC), and the like. In this context, it should be explicitly pointed out that the term “liquid” or “molten” in relation to the phase change material within the scope of the present disclosure also includes a gel-like viscous state of the phase change material, as can be achieved by adding a gelling agent.

Alternatively or additionally, at least the phase change material can be provided with an antimicrobial finish in order to avoid unwanted germ or fungus formation. The antimicrobial finish should be harmless to health, and it can include, for example, fillers, fibers or threads based on silver and its sparingly or insoluble salts.

• 1 ein Schaubild der Temperatur über die Zeit zur Veranschaulichung der Funktionsweise einer ersten Ausführungsform eines erfindungsgemäßen Latentwärmespeichers mit passiver Schaltung des Betätigungselementes seines Auslösemechanismus' aus Zweiwege-Formgedächtnispolymer rein aufgrund der Umgebungstemperatur;
• 2 ein im Wesentlichen der 1 entsprechendes Schaubild der Temperatur über die Zeit zur Veranschaulichung der Funktionsweise einer zweiten Ausführungsform eines erfindungsgemäßen Latentwärmespeichers mit aktiver Schaltung des Betätigungselementes seines Auslösemechanismus' aus Zweiwege-Formgedächtnispolymer mittels bedarfsweiser Abkühlung des Zweiwege-Formgedächtnispolymers;
• 3 bis 5 stark schematisierte Ansichten verschiedener Ausführungsformen eines Betätigungselementes aus Zweiwege-Formgedächtnispolymer einerseits in einer ersten Form (jeweils unten), in welcher es einen in einer Kammer immobisierten Kristallisationskeimbildner mit einem nicht zeichnerisch wiedergegebenen Phasenwechselmaterial in Kontakt bringt, um die Kristallisation des Phasenwechselmaterials auszulösen, andererseits in einer zweiten Form (jeweils oben), in welcher es die den Kristallisationskeimbildner aufnehmende Kammer verschließt, um den Kristallisationskeimbildner mit dem Phasenwechselmaterial außer Kontakt zu bringen;
• 6 bis 9 stark schematisierte Ansichten verschiedener Ausführungsformen eines im Wesentlichen platten- oder folienförmigen Betätigungselementes aus Zweiwege-Formgedächtnispolymer, welches mit einem bereichsweise zumindest oberflächig auf diesen aufgebrachten Kristallisationskeimbildner versehen ist;
• 10 bis 12 stark schematisierte Ansichten verschiedener Ausführungsformen eines im Wesentlichen nach Art eines Stempels ausgebildeten Betätigungselementes aus Zweiwege-Formgedächtnispolymer einerseits in einer ersten Form (jeweils oben), in welcher es einen an der Oberfläche eines verlagerbaren oder stationären Elementes immobilisierten Kristallisationskeimbildner mit einem nicht zeichnerisch wiedergegebenen Phasenwechselmaterial in Kontakt bringt, um die Kristallisation des Phasenwechselmaterials auszulösen, andererseits in einer zweiten Form (jeweils unten), in welcher es den Kristallisationskeimbildner abdeckt, um ihn mit dem Phasenwechselmaterial außer Kontakt zu bringen;
• 13 bis 16 stark schematisierte Ansichten verschiedener Möglichkeiten des zumindest oberflächigen bereichsweisen Aufbringens eines Kristallisationskeimbildners auf ein Betätigungselement aus Zweiwege-Formgedächtnispolymer, z.B. gemäß den 6 bis 9, oder auf eine Oberfläche, z.B. gemäß 10 bis 12; und
• 17 bis 19 stark schematisierte Ansichten verschiedener Ausführungsformen eines im Wesentlichen nach Art eines Stempels ausgebildeten Betätigungselementes aus Zweiwege-Formgedächtnispolymer einerseits in einer ersten Form (jeweils oben), in welcher es einen an der Oberfläche des Betätigungselementes immobilisierten Kristallisationskeimbildner mit einem nicht zeichnerisch wiedergegebenen Phasenwechselmaterial in Kontakt bringt, um die Kristallisation des Phasenwechselmaterials auszulösen, andererseits in einer zweiten Form (jeweils unten), in welcher es den Kristallisationskeimbildner abdeckt, um ihn mit dem Phasenwechselmaterial außer Kontakt zu bringen.

Further features and advantages of the invention result from the following description of exemplary embodiments with reference to the drawings. show:

• 1 a diagram of the temperature over time to illustrate the functioning of a first embodiment of a latent heat accumulator according to the invention with passive switching of the actuating element of its triggering mechanism 'made of two-way shape memory polymer purely due to the ambient temperature;
• 2 an essentially the 1 Corresponding diagram of the temperature over time to illustrate the functioning of a second embodiment of a latent heat storage device according to the invention with active switching of the actuating element of its triggering mechanism made of two-way shape memory polymer by means of cooling the two-way shape memory polymer as required;
• 3 until 5 highly schematized views of various embodiments of an actuating element made of two-way shape memory polymer on the one hand in a first form (each below), in which it brings a crystallization nucleating agent immobilized in a chamber into contact with a phase change material, not shown in the drawing, in order to trigger the crystallization of the phase change material, on the other hand in a second form (each above) in which it closes the nucleating agent-receiving chamber to bring the nucleating agent out of contact with the phase change material;
• 6 until 9 highly schematized views of various embodiments of an essentially plate-shaped or foil-shaped actuating element made of two-way shape memory polymer, which is provided with a crystallization nucleating agent applied to it at least on the surface in some areas;
• 10 until 12 highly schematized views of various embodiments of an actuating element made of two-way shape-memory polymer, designed essentially in the manner of a stamp, on the one hand in a first form (each above), in which it contacts a crystallization nucleating agent immobilized on the surface of a movable or stationary element with a phase change material not shown in the drawing to induce crystallization of the phase change material, on the other hand in a second form (each below) in which it covers the nucleating agent to bring it out of contact with the phase change material;
• 13 until 16 highly schematized views of various possibilities of applying a crystallization nucleating agent to an actuating element made of two-way shape memory polymer, at least on the surface in certain areas, for example according to 6 until 9 , or on a surface, e.g. according to 10 until 12 ; and
• 17 until 19 highly schematized views of various embodiments of an actuating element made of two-way shape-memory polymer, designed essentially in the manner of a stamp, on the one hand in a first form (each above), in which it brings a crystallization nucleating agent immobilized on the surface of the actuating element into contact with a phase change material, not shown in the drawing, in order to to trigger the crystallization of the phase change material, on the other hand in a second form (each below) in which it covers the nucleating agent in order to bring it out of contact with the phase change material.

In the 1 12 is a graph of temperature versus time to illustrate the operation of a first embodiment of a latent heat accumulator according to the invention with passive switching of the actuating element of its triggering mechanism made of two-way shape memory polymer purely based on the ambient temperature. The temperatures entered on the y-axis are, on the one hand, the melting temperature T _{melting PCM} of a phase change material (PCM) contained in a store of the latent heat storage device, e.g. in the form of one or more salt hydrates, and on the other hand its crystallization temperature T _{switching PCM} and the between these extending supercooling temperature range ΔT _U-PCM , in which the phase change material is in a metastable, liquid state during cooling. In addition, a regeneration temperature T _Reg-PCM of the phase change material which is above the melting temperature T _{melt PCM} of the phase change material is indicated on the y-axis, at which the latter, for example by means a heater of the type described above, to completely convert the phase change material to the molten phase. On the other hand, on the y-axis are both the first ("cold") switching temperature T _switching-1 of the two-way shape memory polymer of the actuator, which lies in the supercooling temperature range ΔT _U-PCM of the phase change material, in which the latter has a first form in which it contains a crystallization nucleating agent with contacting the phase change material to induce crystallization thereof, as well as the second (“warm”) switching temperature T _switch-2 of the two-way shape memory polymer of the actuator at which the latter brings the nucleating agent out of contact with the phase change material. In the present case, the second switching temperature T _switch-2 of the two-way shape memory polymer is between the melting temperature T _{melting PCM} of the phase change material and its regeneration temperature T _Reg-PCM , but can also below the melting temperature T _melt-PCM of the phase change material, but preferably in the upper part of its supercooling temperature range ΔT _U-PCM (not shown). Finally, on the y-axis, the target temperatures T _{target low} and T _{target high} , depending on the respective application of the latent heat storage device, are plotted at which the latent heat storage device should emit heat as a result of crystallization of the phase change material or the phase change material should be “charged” with heat .

If the phase change material is based on calcium chloride hexahydrate (CaCl ₂ .6H ₂ O), for example, its melting temperature T _{melting PCM} is about 30° C. and its crystallization temperature T _{switching PCM} is about 10° C , ie the metastable subcooling temperature range ΔT _U-PCM extends over approx. 20°C. If the two-way shape memory polymer is, for example, based on “TPU-PHA 3000/15” according to Example 1 above, its first (“cold”) switching temperature T _switch-1 is optionally about 15° C., for example (corresponding to the crystallization temperature range of the switching or soft segments based on PHA and its second (“warm”) switching temperature T _switch-2 eg about 40°C (corresponding to the melting temperature range of the switching or soft segments).

If the phase change material is, for example, based on sodium acetate trihydrate (CH ₃ COONa.3H ₂ O), its melting temperature T _{melting PCM} is about 58° C. and its crystallization temperature T _{switching PCM} is about −12 °C, ie the metastable subcooling temperature range ΔT _U-PCM extends over approx. 70°C. If the two-way shape memory polymer is, for example, based on “TPU-PBA 4000/15” according to example 2 above, its first (“cold”) switching temperature T _switching-1 is between about -10, for example °C and about 10 °C (corresponding to the crystallization temperature range of the switching or soft segments based on PBA and its second (“warm”) switching temperature T _switching-2 e.g. about 45°C (corresponding to the melting temperature range of the switching or soft segments) .

How now from the 1 As can be seen, the temperature T _IST-PCM of the phase change material of the latent heat storage device, which corresponds to the ambient temperature, for example, lies at the beginning of the time axis initially between the target temperatures T _{target low} and T _{target high} , here for example slightly below the melting temperature T _{melting PCM} in the metastable supercooling range ΔT _U-PCM of the phase change material (PCM) . If the environment cools down as time goes on and the temperature T _IST-PCM of the phase change material of the latent heat storage device thus also falls until the first ("cold") switching temperature T _switching-1 of the two-way shape memory polymer of the actuating element is reached, then the The "internal switching" point in time due to this drop in ambient temperature alone causes the actuator to switch from its second form to its first form, such that the nucleating agent contacts the phase change material and the latter exothermically crystallizes. The phase change material then heats up at least approximately to its melting temperature T _{melting PCM} . Depending on the ambient temperature, the phase change material can now cool down again, in which case it is in the form of a supercooled melt, or it is regenerated immediately or later, for example if sufficient heat is available (e.g. from a thermal solar system) and - if its crystallization temperature T _{switching -PCM} has now fallen below - completely melted by being heated to its regeneration temperature T _Reg-PCM . In the course of regeneration, the second switching temperature T _switch-2 of the two-way shape memory polymer of the actuating element is also exceeded, so that the latter switches back from its first shape to the second shape and contact of the crystallization nucleating agent with the phase change material is prevented. This thermoreversible process can then be repeated practically any number of times.

In the 2 is a diagram of the temperature over time to illustrate the functioning of a second embodiment of a latent heat store according to the invention with active switching of the actuating element of its triggering mechanism 'made of two-way shape memory polymer by cooling the two-way shape memory polymer as required. This second embodiment differs from the first according to FIG 1 primarily in that the switching of the two-way shape memory polymer from its second form to its first form can also be actively triggered when the phase change material has a temperature above the first switching temperature T _Switch-1 of the two-way shape memory polymer. In the present case, this happens at the time of "external switching", in that the actuating element is cooled, for example by means of a cooling device, to a temperature at or below the first switching temperature T _switching-1 of its two-way shape memory polymer, so that the crystallization nucleating agent in turn comes into contact with the phase change material can occur and the latter can crystallize exothermically.

In the 3 until 19 Various embodiments of the actuating element made of two-way shape-memory polymer, provided overall with the reference number 1, of the triggering mechanism of a latent heat storage device according to the invention are shown in a schematic form, wherein the storage device serving to accommodate the phase change material as such can be designed essentially according to the prior art and is therefore not illustrated is shown. Of course, the actuating element 1 can also be designed in any other way in terms of construction, provided that it is able to fulfill its intended function, which consists in programming the two-way shape memory polymer in its first (“cold”) form nucleating agent symbolized by an asterisk (*) contacts the phase change material to induce its exothermic crystallization, whereas in its second (“warm”) form it brings the nucleating agent out of contact with the phase change material.

In the configurations of 3 until 5 the crystallization nucleating agent symbolized by an asterisk (*) is immobilized in a chamber 2, whereby the crystallization nucleating agent can be, for example, foreign nuclei or a portion of the phase change material itself, which is in constant contact with foreign nuclei in chamber 2, for example, so that at the first (“cold”) switching temperature of the two-way shape memory polymer of the actuating element 1 it is in the solid or semi-crystalline state. The chamber 2 communicates via one or more openings 3 with the reservoir (not shown) which receives the phase change material. The essentially plate-shaped or foil-shaped actuating element 1 is due to appropriate programming of its two-way shape memory polymer in the 3 until 5 each below in its first form, in which it uncovers the opening 3 and in this way brings the crystallization nucleating agent contained in the chamber 2 into contact with the phase change material in order to trigger its crystallization when it is in its metastable subcooling temperature range ΔT _U-PCM ( cf. the 1 and 2 ). In the 3 until 5 In each case, the two-way shape memory polymer of the actuating element 1 is at the top by exceeding its second ("warm") switching temperature T _switching-2 (cf. again the 1 and 2 ) has been switched to its second form, in which it closes the opening 3 and in this way brings the crystallization nucleating agent received in the chamber 2 out of contact with the phase change material, so that the latter during a subsequent cooling to a temperature between its crystallization temperature T _{switching PCM} and its melting temperature T _melting-PCM , i.e. to a temperature within its metastable supercooling temperature range ΔT _U-PCM (cf. again the 1 and 2 ), can be converted into a supercooled, (still) liquid state.

The actuator 1 made of two-way shape memory polymer can according to 3 e.g. unilaterally fixed to the chamber 2 at a distance from the opening 3 and reversible between its first shape (bottom), in which it is bent upwards from the chamber 2 and uncovers the opening 3, and its second shape (top), in which it extends approximately parallel to the chamber (here: for example approximately in one plane) and closes the opening 3, be switchable back and forth. In addition, according to the 3 at the end of the actuating element 1 facing the opening 3, for example, a plug 4 approximately complementary to the opening 3 may be formed in order to ensure an improved sealing effect when the actuating element 1 is in its second form.

The actuator 1 made of two-way shape memory polymer can according to 4 for example, also fixed at a distance on both sides of the opening on the chamber 2 and reversible between its first shape (bottom), in which it curves upwards from the opening 3 of the chamber 2 and releases the opening 3, and its second shape (top) , in which it extends approximately parallel to the chamber (here: for example again approximately in one plane) and closes the opening 3, can be switched back and forth. From management form of 5 differs from that of 4 in particular by the fact that - to this extent largely in accordance with the 3 - on the approximately central portion of the actuating element 1 contacting the opening 3, a plug 4 approximately complementary to the opening 3 is molded in order to provide an improved sealing effect when the actuating element 1 is in its second form.

In the 6 until 9 Various embodiments of an - here: again essentially plate-shaped or foil-shaped - actuating element 1 made of two-way shape memory polymer are shown schematically, which are provided with a crystallization nucleating agent applied to them at least on the surface, e.g. in the form of immobilized foreign nuclei, as is shown in 6 until 9 is indicated with an asterisk. In this case, the actuating element 1, which in the 6 until 9 is reproduced only in its first (or second) form, e.g. be arranged at an opening of the reservoir (not shown) for receiving the phase change material and in its first form bring the crystal nucleating agent applied thereto into contact with the phase change material via the opening while being with in its second form, the portion provided with the nucleating agent is spaced from the opening so that there is no contact of the nucleating agent with the phase change material. While the nucleating agent in the case of 6 e.g .B. is applied directly to an approximately central portion of the actuator 1, it is in the case of 7 for example, on a projection 5 formed on the actuating element 1. The actuating element 8 is designed in two layers, for example, with the crystallization nucleating agent on the in FIG 8th upper layer is applied in areas. In case of 9 can the nucleating agent, for example, largely according to the 1 be applied to a portion of the actuator 1, which it in the situation according to 9 e.g. against a stationary element 6a, e.g. in the form of an inside projection of the reservoir accommodating the phase change material (the crystallization nucleating agent can consequently not come into contact with the phase change material; the actuating element 1 is in its second form), while the actuating element 1 is in its second form (not shown) can be curved downwards, for example by the stationary element 6a, which is configured as a projection, for example, so that the crystallization nucleating agent can come into contact with the phase change material. Alternatively or additionally, the crystallization nucleating agent can also be applied in this case, for example, to the side of the stationary element 6a facing the actuating element 1 .

the 10 until 12 show exemplary embodiments of an actuating element 1 made of two-way shape memory polymer, designed essentially in the manner of a stamp, on the one hand in a first form (each above), in which there is a crystallization nucleating agent immobilized on the surface of a stationary element 6a or a displaceable element 6b, which in turn has a Star is symbolized, brings it into contact with a phase change material, not shown in the drawing, in order to trigger the crystallization of the phase change material, on the other hand in a second form (each below), in which it covers the crystallization nucleating agent in order to bring it out of contact with the phase change material. In the design of 10 the stationary element 6a carrying the crystallization nucleating agent is, for example, a section of the inner wall of the reservoir (not shown) for accommodating the phase change material, the two-way shape memory polymer of the essentially stamp-shaped actuating element 1 being programmed in such a way that it either does not covers to bring it into contact with the phase change material (cf. the 10 above; actuator 1 is in its first form, the length of the "stamp" is sufficiently short to expose the nucleating agent immobilized on the stationary element 6a to the phase change material), or the actuating element 1 covers the nucleating agent to keep it out of contact with the To bring phase change material (cf. the 10 below; the actuator 1 is in its second form, the length of the “stamp” is long enough for the nucleating agent immobilized on the stationary element 6a to be covered by the actuator 1). Alternatively or additionally, the crystallization nucleating agent can also be applied, for example, to the end face of the actuating element 1 facing the stationary element 6a.

In case of 11 the crystallization nucleating agent is immobilized, for example, on an element 6b that can be displaced together with the actuating element 1—here: essentially in the form of a carrier plate—which is fastened to the end face of the approximately stamp-shaped actuating element 1 made of two-way shape memory polymer. The latter is programmed in such a way that the crystal nucleus is either exposed in order to bring it into contact with the phase change material (cf. the 11 above; the actuating element 1 is in its first form, the length of the “stamp” is sufficiently short so that the crystallization immobilized on the element 6b carried and thereby displaceable by it nucleating agent at a distance from a stationary element 6a, e.g. in the form of a projection arranged inside the reservoir containing the phase change material and to which the phase change material is exposed), or the actuating element 1 presses the displaceable element 6b provided with the crystallization nucleating agent against the stationary element 6a in order to to cover the crystallization nucleating agent and thus to bring it out of contact with the phase change material (cf 11 below; the actuating element 1 is in its second form, the length of the "stamp" is sufficiently long so that the crystallization nucleating agent immobilized on the element 6b carried thereby and thereby displaceable can be separated from the stationary element 6a, e.g arranged projection, is covered). Alternatively or additionally, the crystallization nucleating agent can also be applied here, for example, to the side of the stationary element 6a facing the actuating element 1 .

The embodiment of 12 differs from that of 10 primarily in that the actuating element 1 - here: for example by means of coil springs - mechanically in the direction of its first form (cf 12 , above) which - as mentioned above - can promote the shape memory effect of some two-way shape memory polymers and/or protect the two-way shape memory polymer from overheating, for example.

Exemplary possibilities for regional, surface application of the phase change material, again indicated by an asterisk, to the actuating element 1 (cf. in particular 3 until 9 ) or on the surface of a stationary 6a or movable element 6b (cf 10 until 12 ) can be found in a schematic form in the 13 until 16 , wherein the nucleating agent is, for example, on the substantially planar surface ( 13 ), on a shape projection ( 14 ), inside a molded torus ( 15 ), inside a separate sealing ring ( 16 ) or the like can be immobilized more.

In the 17 until 19 Finally, there are various embodiments of actuating elements 1 made of two-way shape memory polymer, again designed essentially in the manner of a stamp, on the one hand in a first form (each above), in which there is a crystallization nucleating agent immobilized on the surface of the actuating element, again symbolized by a star, with a not shown in the drawing recited phase change material to induce crystallization of the phase change material, on the other hand in a second form (each below) in which it covers the nucleating agent to bring it out of contact with the phase change material. The actuators 1 of 17 until 19 have a more complex structure than the actuating elements 1 described above, as well as higher strength and rigidity, and they can be produced in one piece, for example from one or more thermoplastic two-way shape memory polymer(s) by means of the melt layer process using a 3D printer.

The actuating element 1 of 17 comprises, for example, a frame with a base plate 1a, on the central portion of which the crystallization nucleating agent is immobilized, two opposite side parts 1b and an upper part 1c connecting the latter essentially parallel to the base plate 1a. Extending from the upper part 1c above the section of the base plate 1a provided with the crystallization nucleating agent is a stamping section 1e, which is programmed in such a way that in its first form (cf 17 , above) is of short length such that the nucleating agent is exposed to the phase change material while in its second form (cf. the 17 , below) has a long length so that the stamping portion 1e covers the nucleating agent to keep it out of contact with the phase change material.

The one in the 18 illustrated embodiment of the actuating element 1, in which identical and functionally identical components are provided with the same reference numerals, differs from that of 17 mainly in that the stamping section 1e has an approximately constant length, while the side parts 1b of the frame are programmed in such a way that in their first form (cf 18 , above) have a short length such that the nucleating agent is exposed to the phase change material while in their second form (cf. the 18 , below) have a large length such that the stamping portion 1e covers the nucleating agent to keep it out of contact with the phase change material. Of course, the embodiments of 17 and 18 can also be combined in such a way that, for example, both the stamp section 1e and the side parts 1b are programmed in such a way that they experience a change in length when the two-way shape memory polymer is switched back and forth between the first and second shape.

The one in the 18 illustrated embodiment of the actuating element 1, in which identical and functionally identical components are again provided with the same reference numerals, differs from that of 18 finally notably in that the side parts 1b of the frame are not programmed to have different lengths but to have different bends when the two-way shape memory polymer is switched back and forth between the first and second shape.

Claims (15)

Latent heat accumulator with at least one phase change material accommodated in at least one accumulator, which has - a crystallization temperature (T _{switching PCM} ) at which the phase change material changes exothermically from a fluid state to a crystalline state, and - a temperature above the crystallization temperature (T _{switching PCM} ) located melting temperature (T _{melting PCM} ) at which the phase change material changes from the crystalline state to the fluid state, and having at least one triggering mechanism for triggering the crystallization of the phase change material, wherein the triggering mechanism comprises a crystallization nucleating agent which is connected to a mechanical actuating element ( 1) is operatively connected, characterized in that the actuating element (1) of the trigger mechanism contains at least one two-way shape memory polymer or is formed entirely from it, which is programmed such that the actuating element (1) between n - a first mode in which the actuating element (1) brings the nucleating agent into contact with the phase change material in order to initiate its crystallization, and - a second mode in which the actuating element (1) brings the nucleating agent out of contact with the phase change material, reversibly can be switched back and forth, the at least one two-way shape memory polymer of the actuating element (1) having at least - a first switching temperature (T _switch-1 ), in which it is converted from its second shape into the first shape, and - one opposite to the first Switching temperature (T _switch-1 ) higher, second switching temperature (T _switch-2 ), in which it is converted from its first form into the second form, has. latent heat accumulator claim 1 , characterized in that the crystallization nucleating agent - is applied to the surface of the actuating element (1) and/or dispersed into it; and/or - applied to the surface of a stationary or displaceable element (6a, 6b) and/or dispersed into it, the stationary or displaceable element (6a, 6b) being in contact with and out of contact with the phase change material by means of the actuating element (1). is bringable. latent heat accumulator claim 1 or 2 , characterized in that the crystallization nucleating agent is immobilized in a separate chamber (2) which can be connected to and separated from the reservoir accommodating the phase change material by means of the actuating element (1). Latent heat accumulator according to one of Claims 1 until 3 , characterized in that the actuating element (1) - in its first form, in which it brings the crystallization nucleating agent into contact with the phase change material in order to trigger its crystallization, has at least one passage channel, and - in its second form, in which it contains the crystallization nucleating agent brings out of contact with the phase change material, has no passage channel. Latent heat accumulator according to one of Claims 1 until 4 , characterized in that the actuating element (1) - in its first form, in which it brings the crystallization nucleating agent into contact with the phase change material in order to trigger its crystallization, has different external dimensions and/or at least one different extension plane than - in its second form, in which it takes the nucleating agent out of contact with the phase change material. Latent heat accumulator according to one of Claims 1 until 5 , characterized in that the actuating element (1) is formed essentially in the form of a film or plate or essentially in the manner of a stamp. Latent heat accumulator according to one of Claims 1 until 6 , characterized in that the crystallization nucleating agent is formed by foreign nuclei or by a portion of the phase change material which is permanently connected to foreign nuclei. Latent heat accumulator according to one of Claims 1 until 7 , characterized in that the at least one two-way shape memory polymer of the actuating element (1) - passive due to the ambient temperature; and/or - can be actively brought to its first switching temperature (T _switching-1 ) by means of a cooling device assigned to it, in which it is transferred from its second form into the first form. Latent heat accumulator according to one of Claims 1 until 8th , characterized in that the phase change material accommodating memory is assigned a heating device to heat the phase change material for regeneration purposes to a regeneration temperature (T _Reg-PCM ) above its melting point (T _Switch-PCM ). Latent heat accumulator according to one of Claims 1 until 9 , characterized in that the at least one two-way shape memory polymer of the actuating element (1) - has a first switching temperature (T _switching-1 ) at which it is converted from its second form into the first form, which is between the melting temperature (T _{melting PCM} ) and the crystallization temperature (T _switch-PCM ) is in the metastable undercooling range (ΔT _U-PCM ) of the phase change material; and/or - has a second switching temperature (T _Switch-2 ) that is higher than the first switching temperature (T _Switch-1 ), at which it is converted from its first form into the second form, which is below the regeneration temperature (T _Reg-PCM ), in particular below the melting temperature (T _{melting_PCM} ), but closer to the melting temperature (T _{melting PCM} ) than to the crystallization temperature (T _{switching PCM} ), of the phase change material. Latent heat accumulator according to one of Claims 1 until 10 , characterized in that the metastable undercooling range of the phase change material between its melting temperature (T _{melting PCM} ) and its crystallization temperature (T _{switching PCM} ) over a temperature interval of at least 10°C, in particular at least 15°C, preferably at least 20° C, extends. Latent heat accumulator according to one of Claims 1 until 11 , characterized in that the phase change material contains at least one salt hydrate or is essentially entirely formed therefrom. Latent heat accumulator according to one of Claims 1 until 12 , characterized in that the at least one two-way shape memory polymer of the actuating element (1) is an elastomer, in particular a thermoplastic, polyester or polyether urethane elastomer. Latent heat accumulator according to one of Claims 1 until 13 , characterized in that the at least one two-way shape memory polymer of the actuating element (1) contains at least one filler and/or reinforcing material, which is selected in particular from the group of materials which absorb electromagnetic radiation, in particular based on carbon, metals, metal oxides and metal clusters - Magnetic and/or ferromagnetic materials, in particular from the group of iron, iron oxide, nickel, zinc and their metal clusters, - Nanoclays, in particular based on carbides, nitrides and oxides of silicon, zirconium and aluminum, and - Reinforcement fibers is selected. Latent heat accumulator according to one of Claims 1 until 14 , characterized in that the phase change material - is mixed with at least one additive, in particular from the group of gel formers; and/or - is provided with an antimicrobial finish.

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