DE102011085722B4 - Latent heat storage device with a phase change material and a method for generating a phase change in the phase change material - Google Patents

Abstract

Latent heat storage (10) with at least one dimensionally stable storage container (12), in which a phase change material (16, 18) is arranged below an expansion pad (22), and at least one tube (14) as a heat exchange device for inducing phase changes in the phase change material (16) , 18) through which a heat exchange fluid flows in order to bring about the phase change,
characterized in that
the heat exchange device (14) is configured and arranged in such a way that at any point in time of a phase change from a solid state to a liquid state, the contiguous region or regions of liquid phase (18) are in contact with the expansion cushion (22), and
the inlet of the heat exchange fluid into the phase change material (16, 18) is arranged on the side of the expansion cushion (22).

Description

The invention relates to a latent heat store with a phase change material (English: phase change material, hereinafter abbreviated to PCM) according to claim 1 and a method for generating a phase change or phase transition in the PCM according to claim 12.

A latent heat store is a heat store that can store thermal energy without a significant temperature increase in the PCM, with little loss and with many repetitive cycles. Latent heat storage systems function by utilizing the enthalpy of reversible thermodynamic changes in state of the first order (for example the phase transition liquid → solid) of a storage medium, the PCM mentioned above, whereby different materials are used for different temperature ranges. When “charging” commercial latent heat storage devices (for example “pocket warmers”), special salts, salt hydrates or paraffins used as PCMs are usually liquefied or melted, which absorb a great deal of thermal energy (heat of fusion). Since this process is reversible, the PCM gives off exactly the heat supplied during solidification. For technical applications as latent heat storage, crystallization just below the melting temperature is generally desired. For this purpose, a suitable nucleating agent is added to the PCM, which prevents the melt from undercooling.

For most materials, the density decreases on transition from the solid to the liquid state, i.e. H. they expand (exceptions are e.g. water (anomaly of the water) and potassium fluoride tetrahydrate), whereby an increase in volume of 10% to 15% is typical. In order to increase the melting point by 1 K, a pressure of several kbar must be exerted on the material. Conversely, this means that pressures in the kbar range can occur if the material is enclosed and heated 1 Kelvin above the melting point. Such pressures cannot be handled in known heat accumulators with a rigid storage container in which the PCM is accommodated and lead to its destruction.

From the synopsis of the EP 0 158 378 A1 and the JP 2001-317 886 A a latent heat storage device with a dimensionally stable storage container is known in which a phase change material is arranged below an expansion cushion, and a tube as a heat exchange device for inducing phase changes in the phase change material through which a heat exchange fluid flows in order to bring about phase changes.

The object of the present invention is to provide a latent heat storage device with a rigid storage container which is designed so that it is not damaged by the expansion of the PCM accommodated in the storage container during its transition from its solid to its liquid phase. It is also an object of the present invention to propose a method for inducing a phase change from the solid phase to the liquid phase in a phase change material of the latent heat accumulator.

This object is achieved by the features of claims 1 and 12, respectively.

According to the present invention (claim 1), a latent heat accumulator comprises at least one dimensionally stable storage container in which a phase change material is arranged adjacent to [al an expansion cushion], and [b | at least one tube as a heat exchange device] for inducing phase changes in the phase change material, the heat exchange device being configured and arranged in such a way that at each point in time of a phase change from a solid state to a liquid state [dl the connected region or regions] is more liquid Phase are in contact with the expansion cushion] and wherein the inlet of the heat exchange fluid into the phase change material is arranged on the side of the expansion cushion.

To [a]. The expansion pad resides within the storage canister and is mechanically coupled to the PCM; H. it is compressed solid → liquid by the expansion of the PCM during the phase change. According to advantageous embodiments of the present invention, the expansion cushion - anticipating the subject matter defined in claims 9 and 10 at this point - be either just a gas (claim 9), a gas in connection with a membrane (claim 10) or a gas balloon or the like . The expansion cushion is used to provide space within the storage container for the expansion of the phase change material during the phase change solid → liquid.

To [b]. According to the advantageous embodiment of the present invention, the heat exchange device can be an electrical heating device.

To [c]. The heat exchange device according to the invention is suitable for either supplying heat to the PCM or removing heat from the PCM and thus inducing a phase change solid → liquid or a phase change liquid → solid. Therefore, claim 1 speaks of the fact that the heat exchange device phase change (plural) induced, but continues from the phase change solid → liquid.

To [d]. The feature [d] means that - during the phase change solid → liquid within the PCM there is no “inclusion of a liquid PCM phase”, i.e. no area whose temperature is higher than that of the whole (apart from elements of the heat exchange device or areas of the Storage container) surrounding solid PCM phase. The consequence of this would be that the PCM in this inclusion / area would melt earlier than the PCM surrounding it and could not expand non-destructively into the expansion cushion. Such a case would occur, for example, if the heat exchange device were completely below the surface of the PCM (cf. 2 ). Feature [d] also speaks of “connected areas” in order to exclude the reading according to which two separate areas are interpreted as one area.

In this case, the storage container can surround a tube or a plurality of tubes, so that the heat exchange fluid guided in the tube or tubes flows “through” the storage container (advantageous embodiment of the present invention according to claim 2).

Or, conversely, a pipe can enclose one or more storage containers so that the heat exchange fluid flows “around” the storage container or containers (advantageous embodiment of the present invention according to claim 3). Since the heat exchange fluid travels through the PCM for some time, continuously giving off heat to the PCM and cooling down, the storage material first melts at the inflow section of the pipe into the PCM, i. H. in the area of the interface, and only later at its outflow section, so that no PCM that has become liquid is enclosed and no high pressures build up in the PCM (cf. the wedge-shaped hatching in the figures).

According to an advantageous embodiment of the present invention (claim 4), the at least one pipe has an inflow section and an outflow section which penetrate the surface of the storage container on the same side, while according to a further advantageous embodiment of the present invention (claim 5) the inflow section and the outflow portion on different sides of the storage container penetrate its surface. Both configurations naturally relate to the variant in which a fluid, passed through a pipe or several pipes, flows “through” the PCM. The arrangement and shape of the at least one tube are basically arbitrary as long as - as described above - no inclusions are formed when the PCM is melted. As the preferred embodiments described below show, the bandwidth of possible constructions is very large, so that the latent heat storage device according to the present invention can be used flexibly.

According to an advantageous embodiment of the present invention (claim 6), the latent heat accumulator comprises a plurality of tubes, each of which has an inflow section which branches off from a collective inflow tube (distributor). This has the advantage that the storage container is only pierced by pipes at a few points. Another advantage is that the heat exchange takes place quickly through the tubes, which can be thinner than the common inflow tube.

According to an advantageous embodiment of the present invention (claim 7), the at least one pipe is a multi-chamber profile pipe, MPE pipe for short (English “multi port extruded aluminum pipe”). Such tubes enable a comparatively very efficient heat transfer and are therefore ideal for use in highly effective heat exchangers.

According to an advantageous embodiment of the present invention (claim 8), the heat exchange device is an electrical heating device. The electrical heating device can be provided as an alternative to the pipe arrangement described above with at least one pipe or in addition thereto. In contrast to a heat coupling with the help of the pipe arrangement with at least one pipe, although there is a temperature gradient of the heat exchange fluid along the at least one pipe, but the PCM is also warmed up a little at the end of the pipe, the PCM is heated with the help of the electrical heating device uniform, ie the temperature of a heat-emitting surface of the heating device - which can be designed as a heating rod or as a heating plate or equivalent heating elements - is essentially constant over this surface. It is conceivable, for example, that the heating device is designed as a plate and is arranged in a plane which extends parallel to an interface between the expansion cushion and the PCM, so that - if for example in the in 1 Such a plate would be used - each cutting plane through the PCM parallel to the plate would be a two-dimensional isotherm. The heating device variant has the advantages over the pipe variant, for example, that no heat exchange fluid has to circulate and therefore no related leakage problems need to be taken into account, that electrical power can be used instead of a pump and thus the heat exchange device can be designed spatially smaller and therefore for industrial or laboratory applications is more suitable. Of course, the heating device in the form of the plate is to be designed in such a way that the PCM can expand upwards 'past the plate'. This can be done, for example, in that said plate has openings of suitable size and at suitable intervals. Alternatively, the heating device can also be like that in 1 The tube shown extend vertically through the PCM, for example in the form of a rod, provided that it is ensured that the PCM melts simultaneously along the heating device.

According to an advantageous embodiment of the present invention (claim 9), the expansion cushion is (only) formed from a gas. The gas takes up the space limited by the PCM, the heat exchange device and the storage container. In this variant, in order to design the heat exchange device, its orientation - more precisely its "area of possible orientations" - must be determined in the space of the latent heat storage device during operation in order to ensure the spatial relationship between the PCM and the heat exchange device that avoids inclusions as defined in claim 1 of the present invention . The expression “range of possible orientations” means that the heat exchange device can be designed in such a way that the spatial relationship defined in claim 1 of the present invention is given in a range of angles that characterize the orientation, which could be referred to as “orientation tolerance” .

According to an advantageous embodiment of the present invention (claim 10), the expansion cushion comprises (a) a gas and (b) a membrane that rests on the phase change material, spatially separates the gas from the phase change material and is firmly connected to the storage container. This has the advantage that a functionally optimally designed construction of the latent heat accumulator, as it z. B. in 1 is shown, can be selected without having to consider the later installation position significantly, since the relative position of the heat exchange device with respect to the PCM does not change significantly due to the elastic membrane. The “orientation tolerance”, to use the term introduced above, is therefore higher here. For example, it is used in a latent heat storage device that comprises a single storage container with a single tube, as shown in FIG 1 is shown, the phase change material in the in 1 shown, upright position of the latent heat storage solidifies (crystallizes) and the phase change material is then melted in a position of the latent heat storage or the storage container rotated 90 ° to the left (a phase transition between the solid and the liquid state of aggregation is carried out), the phase change material will expand and the membrane resting on it to the left and - due to gravity - arch down into the gas space. However, this process is u. U. not completely reversible, insofar as it is u during the solidification of the phase change material. U. not completely reversed, since the membrane usually hardly takes on its original flat shape again. With an appropriate design and choice of material for the membrane, its arched shape assumed in the liquid state of aggregation of the phase change material is well defined, and the spatial relationship between the PCM and the heat exchange device, which avoids inclusions, can be ensured, as defined in claim 1 of the present invention.

According to an advantageous embodiment of the present invention (claim 11), the expansion cushion for limiting a pressure increase in the latent heat storage device during the phase change from the solid state to the liquid state is connected to the surroundings of the latent heat storage device through an opening in the storage container in the area of the expansion cushion. The aforementioned “opening” is to be understood in general as it can either simply be a hole or the like or else a valve that enables the pressure increase to be regulated. The expression "limitation of a pressure increase" is to be understood in this sense: In the case of a hole-like opening, there is complete pressure equalization with the surroundings of the latent heat accumulator, so that there is no pressure change during a phase change, i.e. no pressure increase during a phase change liquid → solid. By means of a suitable valve, for example, a maximum pressure can in turn be set in the space occupied by the expansion cushion.

According to the present invention (claim 12) in a method for generating a phase change from a solid to a liquid phase of the PCM of the latent heat storage device described above, the continuous region or regions of the liquid phase is in contact with the expansion cushion at any point in time of the phase change. With this method, the phase change of the PCM is carried out in such a way that no inclusions of liquid phase occur therein and thus the PCM to be melted does not exert any pressure on the storage container receiving it.

• 1 eine schematische Schnittansicht eines Latentwärmespeichers mit einem einzigen, formstabilen Speicherbehälter und einem einzigen Rohr gemäß einer ersten bevorzugten Ausführungsform der vorliegenden Erfindung;
• 2 eine schematische Schnittansicht eines Latentwärmespeichers, der gleich aufgebaut ist, wie der in 1 dargestellte, wobei jedoch die Strömungsrichtung des in dem Rohr strömenden Fluids umgekehrt ist (Gegenbeispiel und somit nicht Teil der vorliegenden Erfindung);
• 3 eine schematische Schnittansicht eines Latentwärmespeichers mit einem einzigen, formstabilen Speicherbehälter und einem einzigen Rohr gemäß einer zweiten bevorzugten Ausführungsform der vorliegenden Erfindung;
• 4 eine schematische Schnittansicht eines Latentwärmespeichers mit einem einzigen, formstabilen Speicherbehälter und einer Mehrzahl von Rohren gemäß einer dritten bevorzugten Ausführungsform der vorliegenden Erfindung;
• 5 eine schematische Schnittansicht eines Latentwärmespeichers mit einem einzigen, formstabilen Speicherbehälter und einem einzigen Rohr gemäß einer vierten bevorzugten Ausführungsform der vorliegenden Erfindung;
• 6 eine schematische Schnittansicht eines Latentwärmespeichers mit einer Mehrzahl formstabiler Speicherbehälter und einem einzigen Rohr gemäß einer fünften bevorzugten Ausführungsform der vorliegenden Erfindung;
• 7 eine schematische Schnittansicht eines Latentwärmespeichers mit einem einzigen, formstabilen Speicherbehälter und einer Mehrzahl von Rohren gemäß einer sechsten bevorzugten Ausführungsform der vorliegenden Erfindung; und
• 8 eine schematische Schnittansicht eines Latentwärmespeichers mit einer Mehrzahl von formstabilen Speicherbehältern mit jeweils einem einzigen Rohr gemäß einer siebten bevorzugten Ausführungsform der vorliegenden Erfindung.

Further details, features and advantages of the invention emerge from the following description of preferred embodiments with reference to the accompanying drawings. In the drawings are:

• 1 a schematic sectional view of a latent heat accumulator with a single, dimensionally stable storage container and a single tube according to a first preferred embodiment of the present invention;
• 2 a schematic sectional view of a latent heat storage, which is constructed the same as that in 1 shown, but the direction of flow of the fluid flowing in the tube is reversed (counterexample and thus not part of the present invention);
• 3 a schematic sectional view of a latent heat accumulator with a single, dimensionally stable storage container and a single tube according to a second preferred embodiment of the present invention;
• 4th a schematic sectional view of a latent heat accumulator with a single, dimensionally stable storage container and a plurality of tubes according to a third preferred embodiment of the present invention;
• 5 a schematic sectional view of a latent heat accumulator with a single, dimensionally stable storage container and a single tube according to a fourth preferred embodiment of the present invention;
• 6th a schematic sectional view of a latent heat accumulator with a plurality of dimensionally stable storage containers and a single tube according to a fifth preferred embodiment of the present invention;
• 7th a schematic sectional view of a latent heat accumulator with a single, dimensionally stable storage container and a plurality of tubes according to a sixth preferred embodiment of the present invention; and
• 8th a schematic sectional view of a latent heat storage device with a plurality of dimensionally stable storage containers, each with a single tube according to a seventh preferred embodiment of the present invention.

The preferred embodiments of the present invention described below differ in (a) the number of storage containers that the respective latent heat storage comprises, (b) the number of tubes per storage container and (c) in the shape and arrangement of the tube or tubes. All of the arrangements shown can also include the membrane described above, although this is not shown in the figures and is not described in detail.

1 shows a schematic sectional view of a latent heat store 10 in a vertical arrangement, with a single, dimensionally stable storage container 12 and a single pipe 14th according to a first preferred embodiment of the present invention. The storage container 12 is designed in the form of a straight circular cylinder with a height of 50 cm and a diameter of 10 cm. Through the storage container 12 axially extends the tube 14th (DN15) as a heat exchange device, using the heat from outside the storage tank 12 into a PCM incorporated therein 16 , 18th can be coupled in and discharged from this again to the outside. The storage container 12 is from a bottom 20th of the storage tank 12 up to a height h with the PCM 16 , 18th filled. Above the PCM 16 , 18th there is a gas compartment 22nd as an expansion cushion in which a gas is absorbed. The storage container 12 stands upright and the heat transfer fluid flows into the storage tank from above to melt the PCM 12 one so that it is through the gas space 22nd through into the area of the storage container 12 where the PCM to be melted is located. This allows the liquid PCM to enter the gas space 12 expand. In 1 is the still fixed PCM through right hatching 16 and the already melted PCM in a wedge shape through left hatching 18th shown. As in 1 you can see it is the pipe 14th surrounding area of the molten PCM 18th with the gas compartment 22nd directly connected, so that no pressure on the storage tank 12 be exercised. In the sectional view of 1 Boundary line shown between the not yet melted PCM 16 and the already melted PCM 18th migrates in 1 steadily downwards and to the right during the phase change until all of the PCM is in liquid form. Since the reverse phase change is liquid → solid, the PCM 18th , which is carried out by heat removal, is the direction of flow (indicated by an arrow from top to bottom in the upper area in 1 shown) is irrelevant for this phase change.

2 Fig. 10 shows an embodiment that is not an embodiment according to the present invention. The structure corresponds to that of the first exemplary embodiment in FIG 1 , with the difference that the hot heat transfer fluid to melt the storage material is fed into the storage tank from below (by an arrow from bottom to top in the lower area of 1 shown). Consequently, the heat exchange fluid does not flow through the gas space first 12 before it goes through the PCM 16 , 18th is directed so that the melting storage material 18th between the storage tank 12 and still firm PCM 16 is included. This creates a high pressure in this area, which is applied to the wall of the storage tank 12 and the heat exchange device 14th is transmitted. This can damage the storage container 12 or the heat exchange device 14th to lead.

3 FIG. 11 shows a schematic sectional view of a latent heat storage device according to a second preferred embodiment of the present invention, which differs from the embodiment of FIG 1 differs in that the pipe 14th through an upper container wall 24 into the storage enclosure 12 enters, is diverted within the PCM and exits the PCM upwards again before it enters the storage container 12 through the upper container wall 24 leaves again. In this embodiment, the direction of flow of the heat transfer medium can be reversed.

4th FIG. 11 shows a schematic sectional view of a latent heat storage device according to a third preferred embodiment of the present invention, which differs from the embodiment of FIG 1 differs in that several pipes 14th used to run the PCM 16 to transfer to the liquid state. These pipes 14th branches from one inside the storage tank 12 located collecting inflow pipe 26th from. This collecting inflow pipe 26th is above the PCM 16 , 18th in the gas compartment 22nd arranged, and each of the tubes 14th leads through the gas space 22nd before going into the PCM 16 , 18th immersed. This is important because manifolds like the manifold inflow pipe 26th usually a higher wall thickness than the pipes 14th and therefore the heat transfer into the PCM is worse here and the PCM on the pipe 14th can melt earlier than at the collecting inlet pipe 26th .

5 FIG. 11 shows a schematic sectional view of a latent heat storage device according to a fourth preferred embodiment of the present invention, which differs from the embodiment of FIG 1 differs in that the pipe 14th does not have a section which is completely covered by the gas in the gas space 22nd is enclosed. Rather, the pipe is 14th from a side face 26th of the storage tank 12 introduced and extends in a horizontal section along the surface of the PCM, whereupon it dips into the PCM. In this embodiment too, every PCM area that is melting is at all times with the gas space 22nd in connection and can expand there, although this in 5 is not immediately apparent. But the horizontal section of the pipe 14th heats the area of the PCM surrounding it up to or from its surface.

6th shows a schematic sectional view of a latent heat accumulator according to a fifth preferred embodiment of the present invention, wherein a plurality of storage containers 12 in a single tube 14th are arranged, all of which is in the tube 14th flowing heat exchange fluid "around". According to this preferred embodiment, the storage containers can for example be plates with a thickness of 2 cm and a length or width of approximately 50 cm.

7th shows a schematic sectional view of a latent heat store according to a sixth preferred embodiment of the present invention. The latent heat storage according to this preferred embodiment is with that of 1 identical, except that instead of just one tube 14th four tubes 14th inside the storage enclosure 12 are arranged.

8th shows a schematic sectional view of a latent heat store according to a sixth preferred embodiment of the present invention. In the latent heat store according to this preferred embodiment, several latent heat stores according to FIG 1 connected in parallel with each other and thus combined into a larger unit.

List of reference symbols

10

Latent heat storage

12

Storage tank

14th

Tube)

16

solid PCM

18th

molten PCM

20th

Bottom of 12

22nd

Gas space / expansion pad

24

Container wall (wall of 12 )

26th

Collecting inlet pipe

Claims (12)

Latent heat storage (10) with at least one dimensionally stable storage container (12), in which a phase change material (16, 18) is arranged below an expansion pad (22), and at least one tube (14) as a heat exchange device for inducing phase changes in the phase change material (16) , 18), through which a heat exchange fluid flows in order to bring about the phase change, characterized in that the heat exchange device (14) is configured and arranged in such a way that at any point in time of a phase change from a solid state to a liquid state the or the contiguous areas of liquid phase (18) are in contact with the expansion cushion (22), and the inlet of the heat exchange fluid into the phase change material (16, 18) is arranged on the side of the expansion cushion (22). Latent heat storage (10) after Claim 1 , characterized in that the at least one tube (14) is designed such that the heat exchange fluid flows through the at least one storage container (12). Latent heat storage (10) after Claim 1 , characterized in that the at least one tube (14) is designed so that the heat exchange fluid flows around the at least one storage container (12). Latent heat storage (10) after Claim 3 , characterized in that the at least one tube (14) has an inflow section and an outflow section which penetrate the surface (24) of the storage container (12) on the same side. Latent heat storage (10) after Claim 3 , characterized in that the at least one tube (14) has an inflow section and an outflow section which penetrate the surface (24) of the storage container (12) on different sides. Latent heat storage (10) after Claim 3 , characterized in that it comprises a plurality of tubes (14) each having an inflow section which branches off from a common inflow tube (26). Latent heat storage (10) according to one of the Claims 1 to 6th , characterized in that the at least one tube (14) is a multi-chamber profile tube. Latent heat storage (10) after Claim 1 , characterized in that the heat exchange device is an electrical heating device. Latent heat storage (10) according to one of the Claims 1 to 8th , characterized in that the expansion cushion (22) is formed from a gas. Latent heat storage (10) according to one of the Claims 1 to 9 , characterized in that the expansion cushion (22) (a) a gas and (b) a membrane which rests on the phase change material and spatially separates the gas from the phase change material (16, 18) and is firmly connected to the storage container (12) , includes. Latent heat storage (10) according to one of the Claims 1 to 10 , characterized in that the expansion cushion (22) to limit a pressure increase in the latent heat storage (10) during the phase change from the solid state (16) to the liquid (18) through an opening in the storage container (12) in the area of the expansion cushion (22 ) is connected to the surroundings of the latent heat accumulator (12). Method for generating a phase change from a solid (16) to a liquid phase (18) of the phase change material of the latent heat storage device (10) according to one of the Claims 1 to 11 wherein, at each point in time of the phase change, the continuous region or regions of the liquid phase (18) are in contact with the expansion cushion (22).

Images