EP3430103A1

EP3430103A1 - Method for producing a latent heat accumulator and latent heat accumulator

Info

Publication number: EP3430103A1
Application number: EP17709427.3A
Authority: EP
Inventors: Günter Rinn; Klaus Reiser
Original assignee: Schunk Carbon Technology GmbH; Schunk Kohlenstofftechnik GmbH
Current assignee: Schunk Carbon Technology GmbH; Schunk Kohlenstofftechnik GmbH
Priority date: 2016-03-14
Filing date: 2017-03-07
Publication date: 2019-01-23
Also published as: KR20180129820A; US20190071594A1; DE102016104661A1; JP2019508662A; CN109072052B; DE102016104661B4; US10781350B2; WO2017157723A1; CN109072052A

Abstract

The invention relates to a method for producing a latent heat accumulator of expanded graphite by expanding a graphitic starting material. The invention is characterized in that the graphitic starting material is introduced into a mold which corresponds at least in sections to the negative mold of the latent heat accumulator, and that the graphitic starting material is subsequently expanded in the closed mold.

Description

description

Process for producing a latent heat accumulator and such

The invention relates to a method for producing a latent heat storage device, wherein a phase change material is introduced into a molded body produced by expansion of a graphitic starting material. Also, the invention relates to a latent heat storage.

Latent heat storage use thermodynamic changes in state of a storage medium, wherein predominantly the phase transition is used solid / liquid and vice versa.

EP 1 837 617 B1 discloses a latent heat accumulator which has a shaped body which is produced by isostatic pressing of a mixture of a phase change material and an expandable graphite material.

In order to achieve an optimum effect, a large number of mixtures of phases of exchange materials and expanded graphite are known, as is apparent from DE 102 50 249 A1 or EP 1 416 027 B1. For the production of a latent heat storage, a mixture of phase change material and particulate expanded graphite is used according to EP 1 416 027 Bl, which is pressed into a shaped body.

According to WO 2013/153067 Al, a pressed graphite plate is used to produce a latent heat storage, which is impregnated with a phase change material.

Expanded graphite is usually first pressed into a shaped body to be then infiltrated with the phase change material. However, it is also possible to first mix expanded graphite and phase change material and then to form the corresponding mixture under pressure into a shaped article (see for example EP 1 416 027 B1).

It often causes problems to produce complex geometries of corresponding expanded moldings.

By pressing the expanded graphite material, pore volumes and channel variations in the expanded graphite material change so that there may be a disadvantage that after molding, the phase change material infiltration does not occur to the required or desired extent.

The present invention has the object, a method of the type mentioned and a latent heat storage so educate that easily desired geometries of the molded body to be produced can be provided. In another aspect, the infiltration should not be adversely affected by the shaping.

To solve the problem, it is essentially suggested

Introducing the graphitic starting material into a mold,

- closing the mold,

- Expanding the graphitic starting material by

Applying heat, taking the mold before or after Incorporation of the graphitic starting material is heated

or the energy required for expansion is introduced directly into the graphitic starting material,

- After forming the molding inserting the

Phase change material.

Notwithstanding the prior art, the graphitic starting material to be expanded is expanded in a mold that already dictates the shape of the molding. Thus, it is not necessary that after the expansion of the graphitic starting material, in particular graphite salt, a pressure achieved shaping is carried out with the result that changes in the porosity and / or extending in the expanded material channels do not occur. This results in advantages in terms of the infiltration of the phase change material in the production of a latent heat storage.

Advantages arise in particular for components with significant cross-sectional changes, since compared to the prior art results in a more uniform compression and homogeneous pore structure.

In order to introduce the required heat into the graphitic starting material to be expanded, there is the possibility that the mold is heated prior to introduction of the graphitic starting material.

Another possibility is that the graphitic starting material is introduced into the mold and then the mold is heated to a temperature required for expanding the graphitic starting material.

Alternatively or additionally, the energy required for its expansion can be introduced directly into the graphitic starting material. In particular, it is possible to introduce the mold in an electrically, gas or oil-fired oven. Heating by means of an induction source is also possible.

If the energy required for expansion is to be introduced directly into the graphitic starting material, then heating by means of microwaves can take place.

In a further development of the invention it is provided that a porous form, in particular consisting of or containing silicon carbide, graphite, ceramic, sintered metal is used as the mold. Also, a mold having vents and / or of a porous or perforated material such as metal such. B. copper, can be used.

Thus, all materials are suitable which are resistant to the temperatures to which the graphitic starting material is to be heated. Temperatures up to 1,000 ° C are possible without further ado.

If closed-pore materials are used for the mold, passage openings are introduced in order to be able to discharge the gas produced during expansion. The cross-section of corresponding openings is smaller than the particle size of the particles of the starting material.

After forming the shaped body, the phase change material can then be introduced. In this case, a pressureless Kapillarinfiltration is preferably provided, which has the advantage over the prior art to be taken vacuum-pressure method that there is the possibility of a residue-free retraction of the phase change material in the molding. In contrast, it can be seen in the vacuum-pressure process that residues remain on the surface of a molded article which must be removed. In non-pressure infiltration (capillary filtration), adhesion and capillary forces are utilized whereby the liquid saturant flows by itself into the porous body.

There is e.g. the ability to place impregnating agent in solid form on the body to be impregnated and to heat. The impregnating agent melts and runs into the body.

In hervorzuhebender development is provided that the shaped body is produced with a recess is introduced into the phase change material so that it then penetrates into the moldings.

There is also the possibility that, for introducing the phase change material, the shaped body is embedded in liquid phase change material and / or is contacted in a floating manner with the phase change material.

In particular, when the phase change material, such as wax, is filled in a recess of the shaped body, a precise metering can take place.

Furthermore, it is possible to carry out the infiltration or impregnation of the molding in a continuous furnace, so that a high throughput can be achieved.

In the continuous process, so when using a continuous furnace, molded bodies can be produced.

Filtration takes place after removal of the molding from the mold.

Preferably, as graphitic starting material in the form of graphite salt, one having a bulk density of between 0.1 g / ml to 0.9 g / ml, in particular 0.3 g / ml to 0.8 g / ml, wherein a bulk density in the range of 0.7 g / ml is preferable. The grain size of the starting material may, for. B. have the following distribution: D10 = 130 μπι, D50 = 240 μπι, D90 = 360 μπι.

Good results can also be obtained if 80% of the grains have dimensions smaller than 150 μm.

In particular, it is provided that the particle size of the graphite salt is D50 = 50 μιη to 400 μιη.

Due to the teachings of the invention, a molded body of desired geometry can be produced without difficulty, without fundamentally requiring machining after expansion, since the mold itself predetermines the desired geometry of the molded article. Thus, geometrically complex moldings can be made, a possibility that does not offer the prior art.

Self-inventing is also - and thus independent of the production of the molded article - the pressureless infiltration (Kapillarinfiltration) of the molding, in particular the metered introduction into a recess of the molding or the floating contact with the phase change material are emphasized.

The invention further relates to a latent heat storage consisting of a molded body which is infiltrated with phase change material, and in particular has been prepared by method steps, which have been previously explained. In particular, the shaping by the form in which the graphitic starting material is expanded, and the pressureless Kapillarinfiltrieren are emphasized.

In particular, it is provided that the shaped body without phase change material has a porosity between 64% and 99.4%. Further, the molded article should have a bulk density between 0.014 g / cm 3 and 0.79 g / cm 3.

The volume fraction of the expanded graphitic starting material to the volume fraction of the phase change material in the molding should be between 1: 2 and 1:10.

For more details, advantages and features of the invention will become apparent not only from the claims, the features to be taken these features - alone and / or in combination - but also from the following description of the drawing to be taken preferred embodiments.

Show it:

Fig. 1 is a schematic representation of a mold for producing a

Molding and

Fig. 2 is a schematic representation of another form for producing a

Molding.

FIG. 1 shows a schematic representation of a mold 10 by means of which a shaped body of expanded graphite salt is to be produced for a latent heat store, the interior 12 of the mold 10 specifying the outer geometry of the shaped body.

The mold 12 is in the embodiment of a bottom part 14, a cover part 16 and between them extending peripheral wall 18, in which it is z. B. may be a hollow cylinder section. Regardless thereof, bottom part 14, cover part 16 and peripheral wall 18 may have desired inner geometries, which are designed for the shape of the molded part to be produced.

In the interior 12 a graphite salt of defined amount is introduced. For the production of graphite salt usually a well-ordered, highly crystalline, flaky natural graphite is used. This is converted with a storage medium into a graphite salt. This is expanded or blown by a thermal shock treatment. The storage medium escapes. The graphite flakes increase their volume up to a factor of 400.

The treatment is carried out with acids, so that acid residues such as sulphates or nitrates are interposed between the graphite layers.

After closing the interior 12, the mold 10 z. B. positioned in a furnace to introduce the required heat in the graphite salt so that it can expand, wherein the expanded graphite salt fills the entire interior space 12 of the mold 10.

FIG. 2 shows a further basic illustration of a mold 100, which consists of a cup-shaped bottom part 102 and a top part 104. As the sectional representation illustrates, the bottom part 102 and the upper part 104 define a sectionally U-shaped interior 112, which predetermines the shape of the produced expanded graphite. Notwithstanding the fact that the molded part in the upper edge region compared to the bottom portion has a significant reduction in cross-section, a uniform compression and homogeneous pore structure of the expanded molded body is achieved due to the teaching of the invention, according to the shaping takes place during the expansion of the graphite salt to be entered into the mold 100 and not - as in the prior art - after expanding by pressure the shape is achieved.

The expanded molded body remains dimensionally stable, since the expanded particles adhere to one another by adhesion forces and mechanical anchoring (clawing). If, according to the prior art, a mold is to be produced which corresponds to FIG. 2, disadvantages would arise in the upper region due to the reduction in cross section compared to the bottom region and the resulting different pressure effects with regard to the pore structure and channel cross sections Infiltrate the molding with a phase change material adversely affect.

To introduce the heat into the mold 10 or 100, an electrically, gas or oil-fired oven can be used. An induction furnace is also suitable. Another possibility is that the graphite salt is heated by means of microwaves.

The amount of graphite salt to be introduced into the interior 12, 112 depends, on the one hand, on the desired porosity to be achieved and, on the other, on the temperature at which foaming, also called puffing, takes place.

The material of the mold 10, 100 is to be chosen such that a permeability is ensured for the leaking when blowing propellant gas. Suitable materials are for. As per se porous materials such as silicon carbide, graphite, ceramic or sintered metal. But also a perforated metal comes into question. It is essential that the passage openings are smaller than the graphite salt grain size.

As graphite salt can be used such that z. B. has a bulk density in the range between 0.1 g / ml and 0.9 g / ml. The particle size distribution of the graphite salt may, for. Example: D10 = 130 μιη, D50 = 240 μιη and D90 = 360 μιη. However, these values are not meant to be limiting.

In particular, in industrial manufacturing moldings should be produced in a continuous process. For this purpose, appropriate forms can be passed through a continuous furnace. After expanding the graphite salt and cooling the mold 10, 100, the shaped body is removed, which, as mentioned, has a defined geometry, which is predetermined by the internal geometry of the interior 12, 112. Subsequently, the shaped body is preferably impregnated or infiltrated by pressureless capillary filtration with a phase change material (PCM). It can either be applied to the molding solid phase change material, which is then melted, z. In the temperature range up to 150 ° C to allow infiltration. However, there is also the possibility of immersing the shaped body in a liquid phase change material bath or floating in such a store, so that the pressureless Kapillarinfiltration is made possible.

Suitable phase change materials are, in particular, those which enable a phase change in the temperature range between 60 ° C. and 300 ° C., in particular in the range between 80 ° C. and 150 ° C. Preferred materials are waxes such as paraffin, sugar, alcohol, inorganic salt or salt hydrate.

The ratio of phase change material to expanded graphite should be in the ratio 10: 1 to 2: 1.

The bulk density of the expanded graphite should be between 0.014 g / cm 3 and 0.79 g / cm 3. The density is temperature-dependent. So z. B. at a temperature of 600 ° C, the grains or flakes of graphite salt increase their volume by a factor of up to 100 and at a temperature of 1,000 ° C by a factor of up to 400.

Due to the exiting gases, a mass loss of the graphite material between 20% and 22% occur, although lower values such. B. 10% come into question.

It will be explained below by way of examples how the final porosity of the shaped body depends on the amount of graphite salt. In a mold with an internal volume of 50 ml, 5 g of graphite salt are filled. This is kept at a temperature of 600 ° C for 15 min and then removed from the mold after cooling. Measurements have shown that the body has a density of 0.08 g / cm ^J and a porosity of 96.5%.

In a second experiment, 12 g of graphite salt are introduced into a similar mold with an internal volume of 50 ml. This is also heated at 600 ° C for 15 minutes. After cooling and demolding, a body results in a density of 0.19 g / cm and a porosity of 91.5%. On a corresponding molding the compressive strength was tested. This gives a value of 0.97 N / mm.

Claims

Claims The invention relates to a method for producing a latent heat accumulator and to a method for producing it

1. A method for producing a latent heat store, wherein a phase change material is introduced into a molded body produced by expansion of a graphitic starting material,

characterized by the method steps,

Introducing the graphitic starting material into a mold,

- closing the mold,

- Expanding the graphitic starting material by

Introduction of heat, wherein the mold is heated before or after introduction of the graphitic starting material or in the graphitic starting material immediately the energy required for expansion is introduced,

- After forming the molding inserting the

Phase change material.

2. The method according to claim 1,

characterized,

in that a porous form, in particular consisting of or containing silicon carbide, graphite, ceramic, sintered metal, is used as the mold.

3. The method according to claim 1 or 2,

characterized,

in that a mold is used which has vents and / or consists of a porous or perforated material such as perforated metal such as copper.

4. The method according to at least one of the preceding claims,

characterized,

a mold is used whose graphitic starting material accommodating the closed interior corresponds to the negative mold of the shaped body to be produced.

5. The method according to at least one of the preceding claims,

characterized,

that the phase change material is introduced into the shaped body by pressureless infiltration, in particular capillary filtration.

6. The method according to at least one of the preceding claims,

characterized,

that the shaped body is produced with a depression into which phase change material is introduced.

7. The method according to at least one of the preceding claims,

characterized,

in that, for introduction of the phase change material, the shaped body is stored in liquid phase change material and / or is contacted in a floating manner with the phase change material.

8. The method according to at least one of the preceding claims, characterized in that

graphite salt having a bulk density between 0.1 g / ml and 0.9 g / ml, in particular between 0.3 g / ml and 0.8 g / ml, is introduced into the mold as the graphitic starting powder.

9. latent heat storage consisting of a shaped body which is infiltrated with phase change material, in particular produced according to at least one of the preceding claims, wherein the shaped body without phase change material has a porosity between 64% and 99.4%, and the volume fraction of the expanded graphitic starting material to the volume fraction of Phase change material in the molded article is as 1: 2 to 1:10.