DE102011085722A1 - Latent heat accumulator, has heat exchange device configured such that coherent regions of liquid phase of phase change material are in contact with expansion pad at each time point of phase change from solid state into fluid state - Google Patents

Abstract

The accumulator (10) has a form-stable storage vessel (12) i.e. straight circular cylinder, in which a solid phase change material (PCM) (16) bordering on an expansion pad is arranged. A heat exchange device induces phase changes in the PCM. The heat exchange device is configured and arranged such that coherent regions of a liquid phase of the PCM are in contact with the expansion pad at each time point of phase change of the PCM from a solid state into a fluid state. The heat exchange device has an axial pipe (14) through which heat exchange fluid flows to the storage vessels. An independent claim is also included for a method for generating a phase change from solid to a liquid phase of a phase change material of a latent heat accumulator.

Description

The invention relates to a latent heat storage with a phase change material (abbreviated in the following PCM) according to claim 1 and a method for generating a phase change or phase transition in the PCM according to claim 11.

A latent heat storage is a heat storage that can store thermal energy without significant temperature increase of the PCM, with low loss, with many repetition cycles. Latent heat stores function by utilizing the enthalpy of reversible thermodynamic state changes of the first order (for example, the liquid → solid phase transition) of a storage medium, the PCM already mentioned above, using different materials for different temperature ranges. When "charging" commercial latent heat storage (for example "pocket warmer"), special salts, salt hydrates or paraffins usually used as PCM are liquefied or melted, which absorb a great deal of heat 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 shortly below the melting temperature is generally desired. For this purpose, a suitable nucleating agent is added to the PCM, which prevents subcooling of the melt.

For most materials, the density decreases upon transition from the solid state to the liquid state of aggregation, ie. H. they expand (exceptions are, for example, water (anomaly of water) and potassium fluoride tetrahydrate), with a volume increase of 10% to 15% being typical. In order to achieve a melting point increase of 1 K, a pressure of several kbar must be exerted on the material. This in turn means that pressures in the kbar range can occur when the material is trapped and 1 Kelvin is heated above the melting point. Such pressures are in known heat storage with rigid storage container in which the PCM is included, not to handle and lead to its destruction.

It is an object of the present invention to provide a latent heat accumulator with a rigid storage container, which is designed so that it is not damaged by the expansion of the recorded in the storage container PCM in its transition from its solid to its liquid phase. It is a further 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 storage.

The solution of this problem is achieved by the features of claims 1 and 11, respectively.

According to the present invention (claim 1) comprises a latent heat storage at least one dimensionally stable storage container in which a phase change material adjacent to [a | an expansion pad], and [b | a heat exchange device] for inducing [c | Phase changes in the phase change material, wherein the heat exchange device is configured and arranged so that at any time of a phase change from a solid state to a liquid state [d | the contiguous areas] liquid phase are in contact with the expansion pad].

To [a]. The expansion pad is located within the storage container and is mechanically coupled to the PCM, i. H. it is solid → liquid compressed by the expansion of the PCM during the phase change. According to advantageous embodiments of the present invention, the expansion pad - anticipating the object defined in claims 10 and 11 at this point - may be either only a gas (claim 10), a gas in conjunction with a membrane (claim 11) or a gas balloon or the like , The expansion pad serves to provide space inside the storage container for the expansion of the phase change material during the phase change solid → liquid.

To [b]. According to advantageous embodiments of the present invention, the heat exchange device - the object defined in claims 2 and 9 anticipating at this point - (i) by a tube assembly, which is traversed by a heat exchange fluid (claim 2) or (ii) an electric heater (claim 9).

To [c]. The heat exchanger device according to the invention is suitable for either supplying heat to the PCM or dissipating heat from the PCM and thus firmly inducing a phase change in liquid form or a liquid phase change. Therefore, claim 1 speaks of the fact that the heat exchange device induces phase change (plural), but goes further from the phase change fixed → liquid.

To [d]. The feature [d] means that there is no "inclusion of a liquid PCM phase" during the phase change solid → liquid within the PCM, ie no region whose temperature is higher than that of it completely (apart from elements of the heat exchange device or regions of the Storage tank) surrounding solid PCM phase. Because this would have the consequence that the PCM in this inclusion / area earlier than that surrounding PCM and would not be able to expand into the expansion pad non-destructively. 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 "contiguous regions" to exclude the reading that two separate regions are interpreted as one region.

According to an advantageous embodiment of the present invention (claim 2), the heat exchange device comprises at least one tube, which, in order to effect the phase changes, is flowed through by a heat exchange fluid. 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 3). Or it can - vice versa - a tube enclosing one or more storage containers, so that the heat exchange fluid or the storage container "flows around" (advantageous embodiment of the present invention according to claim 4). As the heat exchange fluid travels through the PCM for some time while continuously releasing and cooling heat to the PCM, the storage material melts first at the inflow portion of the tube into the PCM, i. H. in the area of the interface, and only later on its outflow section, so that no liquid PCM is trapped and build up high pressures in the PCM (see the wedge-shaped hatching in the figures).

According to an advantageous embodiment of the present invention (Claim 5), the at least one tube has an inflow portion and an outflow portion which penetrate the surface of the same on the same side of the storage container, while according to a further advantageous embodiment of the present invention (claim 6) of the inflow and the outflow portion on different sides of the storage container penetrate the surface thereof. Of course, both embodiments relate to the variant in which a fluid, passed through a pipe or a plurality of 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 during melting of the PCM. As the preferred embodiments described below show, the bandwidth of possible designs is very large, so that the latent heat storage according to the present invention can be used flexibly.

According to an advantageous embodiment of the present invention (claim 7), the latent heat accumulator comprises a plurality of tubes, each having an inflow portion, which branches off from a Sammeleinströmrohr (distributor). This has the advantage that the storage tank is pierced only in a few places by pipes. Another advantage is that the heat exchange through the thinner than the Sammeleinströmrohr dimensionable tubes is done quickly.

According to an advantageous embodiment of the present invention (claim 8), the at least one tube is a multi-chamber profile tube, short MPE tube (English "multi port extruded aluminum pipe"). Such pipes allow 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 9), the heat exchange device is an electric heater. The electric heating device can be provided as an alternative to the pipe arrangement described above with at least one tube or in addition thereto. In contrast to a heat input by means of the tube assembly with at least one tube, although there is a temperature gradient of the heat exchange fluid along the at least one tube, but the PCM is also warmed up a little at the end of the tube, the heating of the PCM takes place by means of the electric heater uniform, ie the temperature of a heat-emitting surface of the heater - which may be formed as a heating element or as a heating plate or equivalent heating elements - is substantially constant over this surface. It is conceivable, for example, that the heating device is designed as a plate and arranged in a plane which extends parallel to an interface between the expansion pad and the PCM, so that - if, for example, in the in 1 shown latent heat storage such a plate would be used - each plane parallel to the plate cutting plane through the PCM would be a two-dimensional isotherm. The Heizvorrichungsvariante has compared to the tube variant, for example, the advantages that no heat exchange fluid must circulate and thus no relevant leakage problems are taken into account that electric power can be used instead of a pump and thus the heat exchange device can be designed spatially smaller and therefore more suitable for industrial or laboratory applications , Of course, the heating device in the form of the plate is to be designed so that the PCM can 'extend past the plate' upwards. This can be done, for example, by having said plate opening of suitable size and at suitable intervals. Alternatively, the heater may also be like that in 1 shown extending pipe vertically through the PCM, for example in the form of a rod, if provided ensuring that the PCM melts simultaneously along the heater.

According to an advantageous embodiment of the present invention (claim 10), the expansion pad (only) is formed from a gas. The gas occupies the space limited by the PCM, the heat exchange device and the storage tank. In this variant, for the design of the heat exchange device whose orientation - more precisely their "range of possible orientations" - must be determined in the space of the latent heat storage during operation to ensure the defined in claim 1 of the present invention, inclusions avoiding spatial relationship between the PCM and the heat exchange device , The term "range of possible orientations" means that the heat exchange device can be designed such that the spatial relationship defined in claim 1 of the present invention is given in a range of angles which characterize the orientation, which could be termed "orientation tolerance" ,

According to an advantageous embodiment of the present invention (claim 11), the expansion pad comprises (a) a gas and (b) a membrane which rests on the phase change material, the gas is spatially separated 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 storage, as z. In 1 is shown can be selected without having to consider the subsequent installation position substantially, since the relative position of the heat exchange device with respect to the PCM does not change greatly due to the elastic membrane. The "orientation tolerance" to pick up on the concept introduced above is therefore higher here. For example, in a latent heat storage, which includes a single storage tank with a single tube, as in 1 is shown, the phase change material in the in 1 shown, upright position of the latent heat storage solidifies (crystallized) and then melted the phase change material in a rotated by 90 ° to the left position of the latent heat storage or the storage container (a phase transition between the solid and the liquid state of matter performed), the phase change material will expand and arch the membrane resting on it to the left and - due to gravity - down into the gas space. This process is however u. U. not completely reversible, insofar as it u when solidifying the phase change material. U. not completely reversed, since the membrane usually hardly returns to exactly their original flat shape. With appropriate design and choice of material of the membrane is assumed their assumed liquid state of the phase change material curved shape well defined, and defined in claim 1 of the present invention, inclusions avoiding spatial relationship between the PCM and the heat exchange device can be ensured.

According to an advantageous embodiment of the present invention (claim 12), the expansion pad for limiting a pressure increase in the latent heat storage during the phase change from the solid state to the liquid state through an opening in the storage container in the region of the expansion pad is connected to an environment of the latent heat storage. The said "orifice" is to be understood as meaning that it may either be simply a hole or the like, or a valve which allows a regulation of the pressure rise. In this sense, the expression "limitation of a pressure rise" is to be understood: In a hole-like opening, a complete pressure equalization with the environment of the latent heat storage, so that the phase change no pressure change takes place, so no pressure increase at a phase change liquid → solid. By a suitable valve, in turn, for example, a maximum pressure in the space occupied by the expansion pad can be adjusted.

According to the present invention (claim 13), in a process for generating a phase change from a solid phase to a liquid phase of the PCM of the above-described latent heat storage, the liquid phase (s) in contact with the expansion pad are at any point in the phase change. By this method, the phase change of the PCM is performed so that no liquid phase inclusions are formed therein, and thus the PCM to be melted does not apply pressures to the receiving tank accommodating it.

Further details, features and advantages of the invention will become apparent 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 accumulator, which is the same structure as in 1 however, the flow direction of the fluid flowing in the pipe is shown vice versa (counter example 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;

4 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;

6 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;

7 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 accumulator with a plurality of dimensionally stable storage containers, each having 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 tanks that the respective latent heat storage tank comprises, (b) the number of pipes per storage tank and (c) the shape and arrangement of the pipe or pipes. All arrangements shown may also comprise the membrane described above, although not shown in the figures and not described in detail.

1 shows a schematic sectional view of a latent heat storage 10 in a vertical arrangement, with a single, dimensionally stable storage container 12 and a single tube 14 according to a first preferred embodiment of the present invention. The storage tank 12 formed in the form of a straight circular cylinder with a height of 50 cm and a diameter of 10 cm. Through the storage tank 12 extends axially a pipe 14 (DN15) as a heat exchange device, by means of the heat from outside the storage tank 12 into a PCM included in it 16 . 18 coupled and can be discharged from this again to the outside. The storage tank 12 is from a ground 20 of the storage container 12 up to a height h with the PCM 16 . 18 filled. About the PCM 16 . 18 there is a gas room 22 as an expansion pad, in which a gas is absorbed. The storage tank 12 stands upright and the heat transfer fluid flows to melt the PCM from above into the storage tank 12 one, leaving it through the gas space 22 through into the area of the storage container 12 in which the PCM to be melted is located. As a result, the liquefying PCM in the gas space 12 expand. In 1 is by a Rechtsschraffur still firm PCM 16 and by a left hatching wedge-shaped the already melted PCM 18 shown. As it is in 1 you can see that is the pipe 14 surrounding area of the molten PCM 18 with the gas space 22 directly connected, so no pressure on the storage tank 12 be exercised. The in the sectional view of 1 shown boundary line between the not yet melted PCM 16 and the already melted PCM 18 wanders in 1 steadily down during the phase change and right until the entire PCM is in liquid form. Since in the reverse phase change liquid → solid the PCM 18 , which is performed by heat dissipation, contracts, is the flow direction (by an arrow from top to bottom in the upper area in 1 shown) for this phase change irrelevant.

2 shows an embodiment which is not an embodiment according to the present invention. The structure corresponds to that of the first embodiment in FIG 1 , with the difference that the hot heat transfer fluid for melting the storage material is fed from below into the store (by an arrow from bottom to top in the lower part of 1 shown). Consequently, the heat exchange fluid does not first pass through the headspace 12 before passing through the PCM 16 . 18 is passed so that the melting memory material 18 between the storage tank 12 and still firm PCM 16 is included. This creates a high pressure in this area, on the wall of the storage tank 12 and the heat exchange device 14 is transmitted. This can damage the storage container 12 or the heat exchange device 14 to lead.

3 shows a schematic sectional view of a latent heat accumulator according to a second preferred embodiment of the present invention, which differs from the embodiment of the 1 this distinguishes that the tube 14 through an upper container wall 24 in the storage enclosure 12 enters, is redirected within the PCM and exits back up from the PCM before it enters the storage container 12 through the upper container wall 24 leaves again. In this embodiment, the flow direction of the heat transfer medium can be reversed.

4 shows a schematic sectional view of a latent heat accumulator according to a third preferred embodiment of the present invention, which differs from the embodiment of the 1 this distinguishes that several tubes 14 used to the PCM 16 to convert into the liquid state. These pipes 14 branch from one inside the storage tank 12 located thereon Sammeleinströmrohr 26 from. This collective inflow pipe 26 is above the PCM 16 . 18 in the gas space 22 arranged, and each of the tubes 14 leads through the gas space 22 before it enters the PCM 16 . 18 dips. This is important because manifolds like the manifold inlet 26 usually a higher wall thickness than the pipes 14 and therefore here the heat transfer into the PCM is worse and the PCM on the pipe 14 can melt earlier than at the Sammeleinströmrohr 26 ,

5 shows a schematic sectional view of a latent heat accumulator according to a fourth preferred embodiment of the present invention, which differs from the embodiment of 1 this distinguishes that the tube 14 has no portion completely of the gas in the gas space 22 is enclosed. Rather, the tube 14 from a side surface 26 of the storage container 12 and extends in a horizontal section along the surface of the PCM, dipping into the PCM on that section. Also in this embodiment, each melted PCM area is at the same time with the gas space 22 and can expand there, although in 5 not immediately apparent. But the horizontal section of the pipe 14 heats the surrounding area of the PCM up to or from its surface.

6 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 container 12 in a single tube 14 are arranged, all of which in the pipe 14 flowing heat exchange fluid "to" flows. For example, according to this preferred embodiment, the storage containers may be 2 cm thick and about 50 cm long.

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

8th shows a schematic sectional view of a latent heat accumulator according to a sixth preferred embodiment of the present invention. In the latent heat storage according to this preferred embodiment, a plurality of latent heat storage according to the 1 connected in parallel and thus combined to form a larger unit.

LIST OF REFERENCE NUMBERS

10

Latent heat storage

12

storage container

14

Tube)

16

solid PCM

18

melted PCM

20

Ground of 12

22

headspace

24

Container wall (wall of 12 )

26

Sammeleinströmrohr

Claims (13)

A latent heat storage device comprising at least one dimensionally stable storage container in which a phase change material is disposed adjacent to an expansion pad, and a heat exchange device for inducing phase changes in the phase change material, wherein the heat exchange device is configured and arranged so that at any time of a phase change from a fixed Condition in a liquid state or the contiguous areas of liquid phase are in contact with the expansion pad. Latent heat store according to claim 1, characterized in that the heat exchange device comprises at least one tube which, in order to effect the phase change, is flowed through by a heat exchange fluid. Latent heat store according to claim 2, characterized in that the at least one tube is formed so that the heat exchange fluid flows through the at least one storage container. Latent heat store according to claim 2, characterized in that the at least one tube is formed so that the heat exchange fluid flows around the at least one storage container. Latent heat store according to claim 3, characterized in that the at least one tube has an inflow portion and an outflow portion which on the same side of the storage tank penetrate its surface. Latent heat store according to claim 3, characterized in that the at least one tube has an inflow section and an outflow section, which penetrate its surface on different sides of the storage container. Latent heat store according to claim 4, characterized in that it comprises a plurality of tubes, each having an inflow portion which branches off from a Sammeleinströmrohr. Latent heat store according to one of claims 2 to 7, characterized in that the at least one tube is a multi-chamber profile tube. Latent heat store according to claim 1, characterized in that the heat exchange device is an electric heater. Latent heat store according to one of claims 1 to 9, characterized in that the expansion pad is formed from a gas. Latent heat store according to one of claims 1 to 9, characterized in that the expansion pad (a) comprises a gas and (b) a membrane which rests on the phase change material, the gas spatially separated from the phase change material and is fixedly connected to the storage container comprises. Latent heat store according to one of claims 1 to 11, characterized in that the expansion pad is connected to limit a pressure increase in the latent heat storage during the phase change from the solid state into the liquid through an opening in the storage container in the region of the expansion pad with an environment of the latent heat storage. A method of producing a phase change from a solid phase to a liquid phase of the phase change material of the latent heat accumulator of any one of claims 1 to 12, wherein at any point in time of the phase change the continuous liquid phase (s) are in contact with the expansion pad.

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