WO2014086462A1

WO2014086462A1 - Latent heat store and method for the production thereof

Info

Publication number: WO2014086462A1
Application number: PCT/EP2013/003518
Authority: WO
Inventors: Bernhard Sixt
Original assignee: Bernhard Sixt
Priority date: 2012-12-03
Filing date: 2013-11-21
Publication date: 2014-06-12
Also published as: DE102012111707A1

Abstract

A latent heat store with an storage medium that can undergo phase changes between solid and liquid and which is encased by an encapsulation material is characterized in that a metal or a metal alloy is provided as a storage medium (5), in that the encapsulation material (9) is heat-resistant and stable with respect to the storage medium, and in that the encapsulation material (9) forms a matrix (3) with individual compartments (4) in which the storage medium (5), divided into separate storage particles (7), is sealingly enclosed.

Description

Latent heat store and method for its production The invention relates to a latent heat store with a

solid / liquid-phase storage medium, which is covered with the necessary expansion clearance of a capsule material.

Latent heat storage have a high storage capacity, because in addition to the specific heat of the storage medium in the liquefaction

absorbed heat of fusion is used. Accordingly, the melting temperature of the storage medium determines the operating range of the

Latent heat storage, which stores heat during liquefaction and during

Solidifying dissipates heat.

Latent heat storage are known in different versions. in the

In the simplest case, they consist of a closed container which contains the volume of storage medium required for the intended application. In addition, latent heat storage are known in which the

Storage medium is divided into encapsulated storage particles. This may be a macroencapsulation in plastic balls or a microencapsulation in which the small capsules with the enclosed storage medium are embedded in plaster or concrete. The known latent heat storage are used for hot water storage and in the encapsulated version as a heat storage in building, especially in the form of wall panels or floors. It is called as

Storage medium paraffin with one of the desired room temperature

used corresponding melting temperature. Here is the latent effect

Heat storage in the sense of keeping the room temperature constant, whereby cooling by solidification and superheating by liquefaction of the paraffin is counteracted.

The known encapsulation of the storage medium by means of plastic such as polyethylene or silicone and the storage media used allow the use of the known latent heat storage only in the low temperature range. Accordingly, the invention has the object, a

To provide latent heat storage with an extended scope and new uses.

This task is based on the above-described

Latent heat storage inventively achieved in that as a storage medium, a metal or a metal alloy is provided that the capsule material is heat resistant and stable to the storage medium and that the capsule material forms a matrix with individual compartments in which the divided into separate storage particles storage medium is tightly enclosed.

The different metals offer a wide range of different

Melting temperatures ranging from below 100 ° C to over 1000 ° C. In this case, in particular by alloys with different compositions almost any transformation temperatures (melting temperatures) in

Adaptation to the respective circumstances.

By way of example, suitable metals and alloys with the associated melting temperatures are mentioned in ascending order: Gallium 29.8 ° C, bismuth alloys 50 ° to 100 ° C, indium 157 ° C, tin 232 ° C, bismuth 271 ° C, lead 327 ° C, zinc 420 ° C, antimony 631 ° C, aluminum 660 ° C.

Preferred is a light metal or a storage medium

Light metal alloy, in particular aluminum or an aluminum alloy used. Zinc also comes as a particularly suitable storage medium in

Consideration.

The capsule matrix provided according to the invention can, regardless of its dimensions and its outer contour, contain compartments of a selectable size and corresponding number, the chambers for receiving the

Form memory particles and any necessary expansion volume. The capsule matrix can be given a more complex form corresponding to the particular application, whereby a high volume loading with storage medium can be achieved if many small compartments and accordingly storage particles are provided.

In a particularly advantageous embodiment of the latent heat accumulator, the capsule material is a ceramic material. Ceramic is highly resistant to heat and at the same time chemically stable to hot metal melts. In addition, ceramic material can be processed well and design during the manufacturing process advantageously both simple cuboid bricks and more complex forms, for example, too

Storage tiles for heating heat, as used in tiled stoves application.

Alternatively, however, other capsule materials such as refractory concrete or graphite may be provided, which are also characterized by heat resistance and stability. Also, a capsule material can be selected from metal, which has a higher melting point than the storage medium and with the

Storage material does not form an alloy.

Such a metallic capsule material is characterized by a high

mechanical strength (compressive strength) and tightness (freedom from pores) so that can be dispensed with separate measures to ensure the seal against the encapsulated storage medium.

In an advantageous embodiment, a double encapsulation of

Storage particles of an inner metal layer and an outer ceramic matrix provided.

In a preferred embodiment, the matrix has an open-pored structure. In this variant, in which the matrix between the capsule material receiving compartments are open-pored, a gaseous or liquid heat transfer fluid can flow through the open-pore structure, whereby the heat exchange is significantly improved because the heat exchange takes place not only on the edge surfaces of the latent heat storage, but also in its interior can be done.

It is advantageous if at least a portion of the open pores of the

open-pore matrix is interconnected and forms channels which are formed for the passage of a heat transfer fluid and between the

Compartments run. Such a dedicated channel structure in the matrix allows a targeted heat exchange inside the

Latent heat storage.

It is furthermore advantageous if at least a part of the open pores of the open-pore matrix is connected to one another and forms at least one collecting channel which is designed to pass through a heat transport fluid, if the channels open into the at least one collecting channel and if

Collector opens to at least one surface of the latent heat storage. By providing such a collecting duct or several of them, heat transfer fluid can be selectively introduced into or out of the latent heat storage, thus allowing the latent heat storage to be easily integrated into an existing heating or cooling circuit. Also advantageous is a variant of the latent heat accumulator according to the invention, in which the channels open to at least one surface of the latent heat accumulator. Such a latent heat storage has a plurality of channel openings in its outer surfaces and can be placed for heat exchange in a space to be cooled or heated where the atmosphere present in the room, for example air, can penetrate into the channels from the outside and there particularly effective heat can take or leave.

The inventively provided subdivision of the storage medium into individual storage particles, which are embedded in a matrix, allows flexible

Formations of the matrix while maintaining homogeneity. At the same time this serves

Measure of safety. Should during operation of the memory through

Material failure a crack in the matrix arise, so only the molten storage medium from the affected compartments escape. A large number of small compartments is therefore desirable.

Basically, the size of the storage particles and according to the

Compartments are freely chosen. The memory effect is not affected by this choice. As an approximation, you can opt for optimal assembly of the

Heat storage with compartments and storage particles as the densest possible ball packing consider. The total volume of the balls is independent of their size and accounts for two-thirds of the total volume of the enclosing matrix and the embedded balls. An idealized heat storage comparison between a conventional brick and a latent heat storage according to the invention from a corresponding brick matrix with embedded in a compact arrangement spherical

Aluminum particles as storage medium are as follows: Brick: Specific heat [kJ dm ³ K ^"1 ] = 1.7

Aluminum: Specific heat [kJ dm ³ K ^" ] = 2.7

Enthalpy of fusion [kJ dm ³ ] = 2889

Melting temperature [K] = 933 The pure brick stores in the operating range of for example 300 K and 1 100 K about 1360 kJ of sensitive heat. For the brick according to the invention with embedded aluminum particles applies with the volume distribution of one third brick to two thirds aluminum in the same temperature range a memory value of 3819 kJ, resulting from the sensitive heat of the brick portion of 453 (= 1360 x 1/3) kJ, the sensitive heat of aluminum 1440

(= 1360 x 2.7: 1, 7 x 2/3) kJ and the latent heat of the

Aluminum melting process of 1926 (= 2889 x 2/3) kJ composed. Thus, the tile according to the invention has a 2.8 times (= 3819: 1360) increased storage capacity compared to the normal tile. Accordingly, with the same thickness, a significantly higher storage capacity or, for the same storage capacity, a significantly smaller thickness can be achieved. The invention also relates to a method for producing the

Latent heat accumulator in its execution with a ceramic matrix.

This method is characterized in that granules, so small particles of the storage medium with ceramic capsule material is completely coated, that the granules thus obtained capsules are compacted into blanks, and that then the blanks are fired or sintered to the stable end product.

This process leads to a mechanically and thermally stable end product. It allows a largely free shaping of the latent heat storage, which can thus be optimally adapted to the intended use. It is possible to support the exact formation by applying additional ceramic material at critical points, for example in the area of corners and edges. It is advantageous if the granules thus obtained to

closed-pore encapsulated blanks are compacted and shaped. This compression of the matrix material forming ceramic capsule material the coating of the storage medium at the same time provides for a sealing medium tightly enclosing the storage medium of the individual compartments.

Alternatively, the resulting granule capsules can be compacted and shaped into open-pore encapsulated blanks. This variant, which is used in particular when the storage medium is encapsulated sealed by a material other than the matrix material, and when the matrix material located between the capsules is open-pored, is particularly suitable for cases in which the heat exchange in the interior of the Latent heat storage is to be made, as has already been described above.

However, many and especially low cost ceramic masses significantly shrink when fired or sintered with the aid of heat. In a typical firing operation at 1200 ° C, depending on the moisture of the ceramic material, a fade is observed, which can reach up to the double-digit percentage range (e.g., 15%). It should also be noted that the

Components of the latent heat storage when heating different

can expand and that a volume change of the storage medium can take place during the phase transition. Therefore, it is necessary at least for the ceramic latent heat storage normally

Provide shrinking play and / or expansion play to harmful

To avoid compressive stresses in the final product.

For this reason, a useful development of the method is characterized in that the granules before encapsulation, an organic substance is added to create an expansion volume, which burns during firing or sintering and leaves the expansion volume.

Conveniently, this organic substance can be introduced by either coating the granules before encapsulation with the organic substance or by starting from a mixed granulate of powdered storage material and the organic substance becomes. In both cases, the respective capsule volume is greater than the volume of the enclosed pure storage medium.

As an organic substance, for example, wax, sugar, cellulose or a polymer can be used. During thermal firing / sintering, these substances gas and volatilize in the desired manner.

Another expedient possibility for creating a volume expansion is that a porous or foamed granules is used. In this case, the expansion volume is already contained in finely divided form in the granules to be coated and no longer needs to be generated by the firing process. However, this leads to a melting of the metal foam, in which the metal is compressed to a smaller volume and thereby expelled gas forms a now separate expansion volume.

In a further expedient development of the method, the granules are first tightly coated with a metal layer before the ceramic

Capsule material is applied, wherein the metal layer has a melting temperature above the operating temperature of the latent heat storage and does not undergo alloy with the storage medium. This method leads to a tight encapsulation of the storage particles already through the inner metal layer. Therefore, it is not absolutely necessary to compress the outer capsule (matrix) to a closed-pore state. One of many possible applications of the invention

Latent heat storage is the furnace. Become by the energy revolution

Heaters based on domestic renewable resources such as wood again very attractive. The increase in price for heating purposes is usually decentralized in room ovens, which directly heat the surrounding air and only small

Have heat storage capacity. Widely used is the tiled stove, which uses a large mass as a sensitive energy storage. Disadvantages are the enormous space required, the large weight and the high production costs, which often do not allow retrofitting into existing living space. Therefore often becomes resorted to compact and therefore easy to retrofit stoves, which are offered inexpensively in every hardware store. These consist of a metal combustion chamber, usually clad with eg ceramic or soapstone as a sensitive heat storage. However, the memory effect is low due to the comparatively very low mass of the sensitive heat storage material compared to a tiled stove. By using bricks or tiles, which are formed according to the invention as latent heat storage, the heat storage capacity can be significantly increased in the same space requirements in wood-burning stoves. Also, the coupling of a latent heat storage with existing

Central heating makes energy sense, since they have in most cases no buffer for heating and only relatively small hot water tank. This leads to many short heating intervals. By coupling with a heat storage tank less but longer heating intervals are achieved, which can increase the effectiveness of the existing heating by up to 30%.

Another application is the safe (i.e., no groundwater hazard, such as by oil) and non-hazardous long-term storage of thermal energy, e.g. is centrally produced in a cogeneration plant, and can be used locally as needed as electrical and / or heating energy. For this purpose, a super-insulated container (e.g., a container with substance-based vacuum insulation) is fitted with specially shaped latent heat accumulators to create channels for heat exchange. Heat can be loaded or unloaded with a suitable liquid or gaseous medium.

The temperature gradient achievable by the latent heat storage is also suitable for being a decentralized, environmentally friendly, emission-free energy source

To serve cogeneration plant, in addition to the thermal energy, for. With the help of a Stirling engine electrical energy can be obtained.

Latent heat storage tanks with a working temperature below 100 ° C are predestined for solar applications. Embodiments of the invention are described below with reference to a

Schematic drawing explained in more detail. Show it:

Fig. 1 a cuboid latent heat storage (brick) in

longitudinal section perspective partial view with an enlarged detail view; the process steps 2a to 2d with the basic steps of the inventive method for producing a ceramic latent heat storage;

Fig. 3, the process steps 3a to 3e for the preparation of

Latent heat storage with consideration of a

Expansion volume; the process steps 4a to 4d with an alternative Vorgeh to achieve the expansion volume; the method steps 5a to 5d with a third alternative to

Achieving the expansion volume;

6 shows the method steps 6a to 6e for the production of a

Latent heat storage with a double encapsulation of the storage medium; and

Fig. 7 shows a variant of the latent heat accumulator according to the invention with

open-pored matrix material and channels as well as collecting channels for a heat transfer fluid. According to Figure 1, the latent heat storage L ais cuboid brick 2 is formed. This has a matrix 3 of a suitable capsule material, which is stable in the working range of the latent heat storage. The matrix 3 encloses compartments 4, which are preferably at least approximately spherical Chambers are formed and present in a compact arrangement within the matrix 3.

The compartments 4 contain a storage medium 5 made of metal or a metal alloy as well as in the illustrated embodiment

Expansion volume 6. The matrix 3 is mechanically and thermally stable and at the same time impermeable to the liquefied storage medium 5. This is subdivided by the compartmentalization into separate storage particles 7. According to FIG. 2, a finely dimensioned granulate 8 of the metallic storage medium 5 is used to produce a ceramic latent heat accumulator 1. This is coated according to Figure 2b with ceramic capsule material 9. The subsequent process step 2c illustrates a

Pressing with a compression in which the capsule material 9 a

closed-cell matrix 3 forms, which encloses the formed by the granules 8 metallic storage particles 7 firmly and sealingly. This shaped blank 10 is then fired or sintered according to process step 2d to the ceramic end product 11. This simple method according to FIG. 2 is suitable for the special case that the ceramic mass 9 does not shrink during firing or sintering, so that the blank 10 and end product 11 have the same size, the matrix and the storage material have no different thermal expansion behavior and the phase transition of the storage medium 5 leads to no change in volume. Otherwise, there would be tensions in the final product 11.

In many cases, however, a shrinkage of the ceramic capsule material 9 can be expected. For this, the illustrated in Figures 3 to 5 are

Variations of the method provided in accordance with Figure 2.

According to FIG. 3, the modification consists in that before the application of the capsule material 9 (FIG. 3 c) the intermediate step according to FIG. 3 b is switched on, in which the granules 8 are first coated with an organic substance 12 which serves as a placeholder for a later expansion volume. At the

Burning, that burns in the transition from Figure 3d to Figure 3e and

volatilizes the organic substance and shrinks the compacted

Capsule material 9, which is why here the final product 1 1 smaller dimensions than the blank 10 has.

The modification according to FIG. 4 consists in starting from a mixed granulate 13, which was obtained from a mixture of metal powder and the organic substance. Accordingly, an intermediate step

corresponding figure 3b omitted.

In the third alternative according to FIG. 5, a porous granulate 14 is assumed which has a lower density than the pure metal. The porous granules 14 may for example consist of a metal foam. Therefore, the firing process not only leads to shrinkage of the ceramic

Capsule material 9 but also to a corresponding compression of the porous granules 14, as Figure 5d shows in comparison to Figure 5c. The granules melt into pure storage medium. Although it can be dispensed with a separate encapsulation of the metallic storage medium 5 according to the methods described above, since the matrix 3 already causes a stable permanent encapsulation. However, it is also possible, according to FIG. 6, to provide an additional separate encapsulation of the individual storage particles 7. For this purpose, in the intermediate step 6b, the granules 8 with a

Metal layer 15 tightly coated. This metal will be chosen to be that

Melting point is higher than the operating temperature of the latent heat accumulator 1 and that it does not form an alloy with the metallic storage medium. Again, after the application of the capsule material 9, a molded blank 16 is pressed, which is then burned or sintered to the mechanically and thermally stable product 17. This product is characterized by a particularly high cycle stability in heat storage operation. Because of the double encapsulation, it is no longer absolutely necessary, the capsule material 9 to a blank 16th to compact with a matrix with fully closed pores. The matrix 3 'of a variant of this embodiment is therefore porous.

Such a variant with open-pored matrix material 3 'is shown in FIG. 7. The storage medium 5 containing compartments 4 have a dense

Capsule wall 9 ', which surrounds the storage medium and from a

Capsule material 9 is formed, which is different than the matrix material 3 'between the compartments 4 and, for example, made of metal, graphite or refractory concrete or from pre-compacted matrix material.

The matrix material 3 'surrounding the individual capsules or compartments 4 and enveloping the entirety of the capsules or compartments 4 is compacted only to the extent that it is sufficiently solidified to hold the capsules together but still maintains an open-pored structure. A portion of the open pores of this structure communicate with each other and form channels 18 or channel-like cavities between the individual compartments and in their external environment, either in the surface 1 'of the

Open latent heat storage (not shown) or open into collection channels 19, which are also formed in the matrix material 3 '. These collecting channels 19 are located, for example, in a more compacted outer area of the

Matrix material 3 ', where the pores are not in fluid communication with each other, so that the collecting channels - with the exception of the mouths of the channels 18 in an associated collecting channel 19 - sealed in the matrix material 3' extend. Where the collecting channels 19 open into the surface of the latent heat accumulator 1, suitable fluid connections, for example, for hoses or pipes, may be provided to connect to a

Heat transport fluid supply system to produce.

Claims

claims

1. Latent heat storage with a fixed / liquid-phase variable

Storage medium, which is enveloped by a capsule material,

characterized,

in that a metal or a metal alloy is provided as the storage medium (5),

that the capsule material (9) is heat resistant and stable with respect to the storage medium, and

in that the capsule material (9) has a matrix (3) with individual ones

Forms compartments (4) in which the storage medium (5) subdivided into separate storage particles (7) is enclosed tightly.

2. Latent heat store according to claim 1,

characterized,

that the storage medium (5) is a light metal or a

Alloy is light alloy.

3. Latent heat store according to claim 2,

characterized,

the storage medium (5) is aluminum or an aluminum alloy.

4. latent heat store according to claim 1,

characterized,

the storage medium (5) is zinc.

5. Latent heat store according to one of claims 1 to 4,

characterized, the capsule material (9) is a ceramic material.

6. Latent heat store according to claim 5,

characterized,

that it is shaped as a ceramic tile (2).

7. Latent heat store according to claim 5 or 6,

characterized,

that it is shaped as a storage tile for heating heat.

8. latent heat store according to one of claims 1 to 4,

characterized,

that the capsule material (9) is a refractory concrete.

9. latent heat store according to one of claims 1 to 4,

characterized in that the capsule material (9) is graphite.

10. Latent heat store according to one of claims 1 to 4,

characterized,

in that the capsule material (9) is a metal which has a higher melting point than the storage medium (5) and does not alloy with the storage material (5).

11. Latent heat store according to claims 5 and 10,

characterized by a double encapsulation of the storage particles (7) of an inner metal layer (15) and an outer ceramic matrix (3).

12. Latent heat store according to one of the preceding claims,

characterized,

the matrix (3 ') has an open-pored structure.

13. Latent heat store according to claim 12,

characterized, in that at least a part of the open pores of the open - pore matrix (3 ') is connected to one another and forms channels (18) which are designed to pass through a heat transfer fluid and which are located between the two

Compartments (4) run.

Latent heat store according to claim 13,

characterized,

at least a part of the open pores of the open-pore matrix (3 ') is connected to one another and forms at least one collecting channel (19) which is designed to pass through a heat transport fluid,

the channels (18) open into the at least one collecting channel (19) and that the collecting channel extends to at least one surface of the

Latent heat accumulator (1) opens.

Latent heat store according to claim 13,

characterized,

that the channels () to at least one surface of the

Open latent heat accumulator (1).

Method for producing the latent heat accumulator according to one of

Claims 5 to 7,

characterized,

that a granulate (8) of the storage medium (5) with ceramic

Capsule material (9) is completely coated so that the obtained

Granules capsules are compacted and formed into blanks (10) and then that the blanks (10) are burned or sintered to the stable end product (11).

Method according to claim 16,

characterized,

the granules capsules thus obtained are compacted and shaped into blanks (10) sealed in a closed-cell manner.

18. The method according to claim 16,

characterized,

the granules capsules thus obtained are compacted and shaped into open-pored encapsulated blanks (16).

19. The method according to any one of claims 16 to 18,

characterized,

in that an organic substance (12) is added to the granules (8) prior to encapsulation in order to create an expansion volume

Burning or sintering burns and leaves the expansion volume.

20. The method according to claim 19,

characterized,

the granules (8) are coated with the organic substance (12) before they are encapsulated.

21. The method according to claim 19,

characterized,

that the granules a mixed granules (13) of powdered

Storage material (5) and the organic substance is.

22. The method according to any one of claims 19 to 21,

characterized,

that as organic substance (12) wax, sugar, cellulose or a

Polymer is used.

23. The method according to claim 16,

characterized,

that a porous granules (14) is used, the pores of a

Form expansion volume.

24. The method according to claim 16,

characterized, in that a foamed granulate is used to create an expansion volume.

25. The method according to any one of claims 16 to 24,

characterized,

in that the granules (8) are first densely covered with a metal layer (15) before the ceramic capsule material (9) is applied, wherein the metal layer (15) has a melting temperature above the operating temperature of the latent heat accumulator and no alloy with the

Storage medium (5) forms.