Heat store

Abstract

The invention relates to a heat store for storing thermal energy, wherein the heat store has a storage element arrangement with one or more combination heat store elements, wherein each combination heat store element has a solid-state heat store element which consists of a solid-state material and in which one or more cavities are formed which are filled with a phase change material.

Description

[0001] Heat storage

[0002] The invention relates to a heat accumulator for storing thermal energy.

[0003] Heat storage systems are storage devices for storing thermal energy and are also known as thermal energy storage systems. Heat storage systems can be used, in particular, to decouple the generation or provision of heat from its use. Heat storage systems can be charged, for example, using industrial waste heat. Heat storage systems can also be used, for example, to store surplus electrical energy. If there is a surplus of electrical energy, this is converted into thermal energy or heat using electrical heaters and the heat generated in this way is stored. If required, the stored thermal energy can be extracted and used, for example, directly in the form of heat, for example to heat buildings or to supply industrial applications with process heat. The extracted thermal energy can, however, also be converted into electrical energy using a thermal power process and fed into the electricity grid, for example.

[0004] Different types of heat storage are known, e.g. sensible heat storage and latent heat storage.

[0005] Sensible heat storage devices change their temperature during the charging process (i.e., heat input) and discharging process (i.e., heat removal). They heat up during charging and cool down during discharging. Sensible heat storage devices do not undergo a change of state (within the intended temperature range), but rather are based on the heat capacity of the storage material. Sensible heat storage devices can, in particular, be in the form of solid-state storage devices or solid-state heat storage devices, i.e., they consist of solid material in the solid state. Such solid materials can be, for example, (high-temperature) ceramics, flint, or (high-temperature) concrete.

[0006] Latent heat storage systems consist of a material that undergoes a phase change (within the specified temperature range) and changes its physical state. Such a material is referred to as a phase-change material, or PGM (where PGM stands for Phase Change Material). The heat storage function of latent heat storage systems is based primarily on the fact that the phase-change material changes its physical state at a material-specific phase-change temperature, absorbing heat in the form of latent heat during charging and releasing heat in the form of latent heat during discharging without any temperature change. The phase-change material can be charged or discharged beyond its latent heat level; only then does a temperature increase or decrease occur.As a rule, the phase transition between the solid and the liquid state is used for latent heat storage; in this case, the phase change temperature is given by the melting temperature of the phase change material.

[0007] In latent heat storage systems, the phase-change material is traditionally stored in specially designed containers to retain it in the designated locations even in the liquid state and to prevent the liquid phase-change material from leaking out. Heat exchangers (e.g., in the form of pipes) are also traditionally provided for loading and unloading the latent heat storage system using a dedicated heat transfer fluid, through which the heat transfer fluid is brought into thermal contact with the phase-change material. The design of heat storage systems with such containers and heat exchangers entails a correspondingly complex and cost-intensive structure.Furthermore, many phase-change materials used as latent heat storage devices exhibit a high tendency to corrosion compared to the materials conventionally used for the storage vessels and heat exchangers (usually metallic), which negatively impacts the service life of such heat storage devices. The storage vessels also reduce the heat transfer between the phase-change material and other components of the heat storage device (such as the heat transfer fluid or other heat storage material). Combined with the limited thermal contact area of ​​the phase-change material, this reduces the effectiveness of the heat storage device, particularly since the phase-change material always melts first at the heat-transferring wall when the storage device is loaded, thus leading to increased thermal resistance (since the phase-change material has a lower thermal conductivity in the liquid state than in the solid state).Since maintenance is usually carried out at lower temperatures and thus solidified phase change material, the material in contact with the solidified.

[0008] Since the walls of the storage tanks and heat exchangers made of phase-change materials are inaccessible or difficult to access, conventional latent heat storage systems require increased maintenance. Solid-state storage systems, on the other hand, often exhibit low thermal conductivity, which can result in, for example, undesirable inhomogeneous temperature distribution and corresponding limitations during charging and discharging. Since heat transport within solids can only occur through thermal conduction, and the thermal conductivity of typical materials for solid-state heat storage systems is low, the charging and discharging rates of solid-state heat storage systems are also correspondingly limited.

[0009] Heat storage systems that combine a sensible heat storage unit with a latent heat storage unit are known from the prior art. For example, WO 2014 / 089717 A1 describes a heat storage system with a sensible main heat storage unit and a latent heat storage unit connected in series. The limitations explained above apply essentially analogously to these combination heat storage systems known from the prior art.

[0010] The invention is intended to provide a heat storage device which can be realized with a simple and cost-effective design and requires little maintenance, enables a high energy storage density and a long service life, and enables effective loading with thermal energy and discharging of thermal energy.

[0011] According to one aspect of the invention, a heat accumulator for storing thermal energy is provided, wherein the heat accumulator functions as an arrangement or device for storing thermal energy and can also be referred to as such.

[0012] The heat storage device comprises a storage element arrangement with one or more heat storage elements designed to store thermal energy. The storage element arrangement comprises at least one heat storage element referred to as a combination heat storage element. The storage element arrangement can thus comprise a single combination heat storage element or multiple combination heat storage elements.

[0013] Such a combination heat storage element has a solid-state heat storage element consisting of a solid-state material, wherein at least one cavity filled with a phase change material is formed in the solid-state heat storage element. Such a solid-state heat storage element can also be referred to as a solid-state element for short. Each solid-state heat storage element of a respective combination heat storage element can thus have a single cavity or several cavities in which phase change material is accommodated. Such a cavity can also be referred to as a recess. Each combination heat storage element has a separate solid-state heat storage element. Each combination heat storage element thus has solid-state material and phase change material, wherein the solid-state material is in the form of a one-piece ormonolithic solid-state heat storage element, and wherein the phase-change material is accommodated in one or more cavities formed in the solid-state heat storage element. Each combination heat storage element thus has phase-change material in that phase-change material is accommodated in one or more cavities formed in the solid-state heat storage element of the respective combination heat storage element.

[0014] The phase change material is a material that undergoes a phase change at a material-specific phase change temperature and functions as a latent heat storage device. The phase change material is, in particular, a material that undergoes a phase change during the intended operation (in particular within the temperature range intended for operation) of the heat storage device. This is a phase change between the solid and the liquid state, whereby the phase change material changes from the solid to the liquid state when the temperature increases from a temperature below the phase change temperature to a temperature above the phase change temperature (e.g. when charging the heat storage device), and whereby the phase change material changes from the solid to the liquid state when the temperature decreases from a temperature above the phase change temperature to a temperature below the phase change temperature (e.g.when discharging the heat storage device) changes from the liquid to the solid state. In this case, the phase change temperature is therefore given by the melting temperature of the phase change material. The phase change material can in particular comprise or be a metallic material. For example, it can be provided that the phase change material comprises or consists of a metal (e.g. aluminum, lead, zinc, tin) or a metal alloy (e.g. an aluminum alloy, brass, bronze, steel). However, it can also be provided that the phase change material is a salt or a paraffin. The selected phase change temperature can depend on the intended application, e.g. depending on the source of the heat used to charge the heat storage device and / or the purpose for which the heat extracted when discharging the heat storage device is to be used.When loading the heat storage system with industrial waste heat from steel and aluminum production and / or when using the heat extracted from the heat storage system for steel and aluminum production, it can be provided, for example, that the phase change material is a material with a melting temperature in the range from 500 °C to 1600 °C. When loading the heat storage system with industrial waste heat from the cement industry and / or when using the heat extracted from the heat storage system for the cement industry, it can be provided, for example, that the phase change material is a material with a melting temperature in the range from 200 °C to 450 °C. When loading the heat storage system with industrial waste heat from the paper industry and / or when using the heat extracted from the heat storage system for the paper industry, it can be provided, for example, that the phase change material is a material with a melting temperature in the range from 60 °C to 210 °C.When loading the heat storage system with industrial waste heat from the ceramics and glass industry and / or when using the heat extracted from the heat storage system for the ceramics and glass industry, it can be provided, for example, that the phase change material is a material with a melting temperature in the range from 320 °C to 1300 °C. When loading the heat storage system with industrial waste heat from ethylene production and / or when using the heat extracted from the heat storage system for ethylene production, it can be provided, for example, that the phase change material is a material with a melting temperature in the range from 150 °C to 650 °C. When loading the heat storage system with industrial waste heat from ammonia production and / or when using the heat extracted from the heat storage system for ammonia production, it can be provided, for example, that the phase change material is a material with a melting temperature in the range from 300 °C to 1200 °C.When loading the heat storage device with industrial waste heat from drying plants and / or when using the heat extracted from the heat storage device for drying plants, it can be provided, for example, that the phase change material is a material with a melting temperature in the range from 40 °C to 150 °C. The phase change material is preferably a material with a phase change temperature or a melting temperature of at least 500 °C. It can be provided, for example, that the heat storage device is intended to operate a re-electrification process, and that the phase change material has a melting temperature that is optimal for the re-electrification process, i.e. a melting temperature that enables the highest possible thermodynamic efficiency in the re-electrification process.

[0015] It can be provided that the storage element arrangement comprises only a single phase-change material. Accordingly, it can be provided that all cavities of the combination heat storage elements filled with a phase-change material are filled with the same phase-change material. However, it can also be provided that the storage element arrangement comprises two or more different phase-change materials. Accordingly, it can be provided that the storage element arrangement or its combination heat storage elements comprises two or more groups of cavities filled with different phase-change materials (where all cavities of a group are filled with the same phase-change material).

[0016] The solid-state material is a material that is in the solid state and functions as a sensible heat storage device. Each solid-state heat storage element of a respective combination heat storage element can thus function as a sensible heat storage device. The solid-state material is, in particular, a material that is always in the solid state during intended operation (in particular within the temperature range intended for operation) of the heat storage device and does not change its state. The solid-state material is, in particular, a material that is in the solid state up to and above the phase change temperature or the melting temperature of the phase change material contained in the combination heat storage elements. It can be provided, for example, that the solid-state material is a material that can withstand temperatures up to at least 100 Kelvin, e.g.of at least 200 Kelvin, preferably at least 300 Kelvin, above the melting temperature of the phase change material. Alternatively or additionally, the solid material can be a material that is or remains in the solid state up to a temperature of at least 120%, e.g., at least 140%, preferably at least 160%, of the melting temperature of the phase change material.

[0017] If several different phase change materials with different melting temperatures are present, it can be provided that the solid material is a material that exists or remains in the solid state up to a temperature of at least 100 Kelvin, e.g., at least 200 Kelvin, preferably at least 300 Kelvin, above the highest melting temperature of all phase change materials present.Alternatively or additionally, if several different phase change materials with different melting temperatures are present, it can be provided that the solid material is a material that is or remains in the solid state up to a temperature of at least 120%, e.g. of at least 140%, preferably of at least 160% of the highest melting temperature of all phase change materials present.

[0018] The solid material can be any solid heat storage material. The solid material can, in particular, be a non-metallic material. For example, the solid material can comprise or consist of ceramic (e.g., a high-temperature ceramic), concrete (e.g., high-temperature concrete), flint, vitrified ash, and / or fireclay ash.

[0019] The phase-change material is preferably selected such that the amount of heat or fusion enthalpy required for the phase transition makes a significant contribution to the thermal storage capacity of the storage element arrangement. For example, it can be provided that each phase-change material incorporated in the combination heat storage elements is selected such that the fusion enthalpy required to melt a given volume of the phase-change material (present in the solid state) is at least as large as the amount of heat required for a temperature change of the same volume of the solid material by 200 Kelvin (more preferably by 350 Kelvin).

[0020] The storage element arrangement has one or more combination heat storage elements which have sensible heat storage material in the form of the solid material and latent heat storage material in the form of the phase change material and thus combine them with one another, wherein the phase change material is accommodated in cavities in the solid material or in the solid heat storage elements consisting of it. The solid material is cost-effective and enables thermal energy to be stored at high temperatures. The phase change material enables the storage density of the heat storage device to be increased by means of the enthalpy of fusion and enables the heat storage device to be charged and discharged at a high and constant temperature level during the phase change, which supports, for example, the effective charging and discharging of the heat storage device. For example, the transfer of thermal energy to a downstream power generation process is possible at a high and constant orenables a more constant temperature level, thereby enabling higher power generation efficiency than, for example, with pure solid-state thermal storage systems. Because the phase change material is contained in cavities within the solid-state heat storage elements, the solid-state heat storage elements act as receptacles for the phase change material. Therefore, no additional or separate receptacles are required to hold the phase change material. Furthermore, no separate heat exchanger is required for thermally charging and / or discharging the phase change material, particularly since the thermal charging and discharging of the phase change material can occur via thermal contact between the solid-state heat storage element and the phase change material contained therein.Since neither separate receiving vessels for the phase-change material nor a separate heat exchanger for thermal loading and unloading of the phase-change material are required, the heat storage system can be realized with a simple and relatively cost-effective design. Furthermore, corrosion effects on such separate receiving vessels and heat exchangers caused by the phase-change material can be avoided, which contributes to a long service life. Since conventional solid-state heat storage materials are generally corrosion-resistant compared to conventional phase-change heat storage materials, or the solid-state material and the phase-change material can be selected or matched in such a way that the solid-state material is corrosion-resistant compared to the phase-change material, corrosion effects between the solid-state material and the phase-change material can be avoided or minimized.By incorporating the phase-change material into the solid-state heat storage elements, uncomplicated maintenance of the heat storage is possible at temperatures below the melting temperature of the phase-change material, thus solidifying the phase-change material. By having the phase-change material in physical and thermal contact with the solid-state material, the thermal conductivity within the combination storage elements can be increased, enabling a more homogeneous temperature distribution within the combination heat storage elements and also within the storage element arrangement, as well as additionally supporting effective thermal charging and discharging. By having the phase-change material in direct physical and thermal contact with the solid-state material, effective heat transfer between the phase-change material and the solid-state material is enabled.By means of an appropriate number and design of the cavities, a large thermal contact area between the phase change material and the solid material is made possible, which can further support the effectiveness and temperature homogenization and, in particular, compensate for the increased thermal resistance during melting of the phase change material.

[0021] The storage element arrangement comprises one or more combination heat storage elements with solid-state material and phase-change material, as explained above. In particular, it can be provided that the heat storage device or the heat storage arrangement comprises exclusively such combination heat storage elements, so that each heat storage element comprises both solid-state material and phase-change material; in this case, the advantages explained above are particularly evident. According to another embodiment, it is provided that at least 50%, preferably at least 75%, of the heat storage elements are such combination heat storage elements.

[0022] According to one embodiment, the heat storage device comprises a container for accommodating the storage element arrangement, wherein the container is also referred to as a storage container. Accordingly, the heat storage elements of the storage element arrangement, in particular the combination heat storage elements of the storage element arrangement, are arranged in the storage container. The storage container can be thermally insulated in a known manner, e.g., by providing the wall of the storage container with thermal insulation to minimize heat losses due to heat quantities released via the container wall.

[0023] It can be provided that the storage element arrangement is designed such that all phase-change material of the heat storage device is accommodated in the solid-state elements of the combination heat storage elements, and (within the storage container) no phase-change material is located outside the solid-state elements. Accordingly, it can thus be provided that, within the storage container, phase-change material is arranged exclusively in the cavities of the solid-state elements, and in particular that no phase-change material is arranged between different solid-state elements or between different combination heat storage elements. This enables reliable storage of the phase-change material within the storage container without additional receiving containers and additionally supports effective temperature homogenization.

[0024] According to one embodiment, the heat storage device has a passage device designed to pass a fluid through the storage container, wherein the fluid functions as a heat transfer fluid and is also referred to as such. The heat transfer fluid is preferably a gas. The heat transfer fluid can be provided for thermally charging and / or discharging the heat storage elements of the storage element arrangement, i.e., for introducing thermal energy into the heat storage elements and / or for discharging thermal energy from the heat storage elements. In this regard, the heat storage elements of the storage element arrangement can in particular be designed and arranged in the storage container in such a way that the heat transfer fluid can flow through the storage container while flowing around the heat storage elements. For example,It should be provided that all heat storage elements of the storage element arrangement are designed and arranged in such a way that a free flow area remains between two adjacent heat storage elements. This further supports effective heat exchange between the heat transfer fluid and the heat storage elements.

[0025] The heat storage device can therefore be charged with thermal energy, for example, by the heat transfer fluid being introduced into the storage container by means of the flow-through device at a high temperature (e.g. a temperature above the phase change temperature of the phase change material), flowing around the heat storage elements of the storage element arrangement and charging them with thermal energy, and exiting the storage container at a lower temperature. However, it can also be provided that the thermal charging of the heat storage device takes place in another way. During the charging process, the combination heat storage elements are first heated until the melting temperature of the phase change material is reached, then energy is introduced at a constant temperature until the phase transition is completely completed (i.e. until the phase change material has completely melted), and then the temperature is further increased.

[0026] The discharging of the heat storage device (i.e. the removal of thermal energy from the heat storage device) can, for example, be carried out by introducing the heat transfer fluid into the storage container by means of the feed-through device at a low temperature (e.g. a temperature below the phase change temperature of the phase change material), flowing around the heat storage elements of the storage element arrangement and thereby being charged with thermal energy, and then exiting the storage container at a higher temperature. However, it can also be provided that the discharging of the heat storage device takes place in another way. During the discharging process, the temperature of the combination heat storage elements initially drops until the melting or solidification temperature of the phase change material is reached, then energy is discharged at a constant temperature until the phase transition is completely completed (i.e.until the phase change material has completely solidified), and then the temperature continues to drop.

[0027] The passage device is designed to pass the heat transfer fluid through the storage container. The passage device can, for example, have a first passage device for passing the heat transfer fluid between the interior and the exterior of the storage container and a second passage device for passing the heat transfer fluid between the interior and the exterior of the storage container. The first passage device can, for example, be designed in the form of a first passage opening formed in the storage container, and the second passage device can, for example, be designed in the form of a second passage opening formed in the storage container. It can be provided that one of the two passage devices serves to admit the heat transfer fluid into the storage container and the other of the two passage devices serves to discharge the heat transfer fluid from the storage container.It can also be provided that the two passage devices exchange their respective functionalities during thermal loading and unloading, ie that during thermal loading the first passage device serves to admit the heat transfer fluid into the storage container and the second passage device serves to discharge the heat transfer fluid from the storage container, and that during thermal unloading the second passage device serves to admit the heat transfer fluid into the storage container and the first passage device serves to discharge the heat transfer fluid from the storage container.

[0028] The passage device can be designed, in particular, to pass the heat transfer fluid through the storage container along a predetermined main flow axis. Accordingly, the passage device for passing the heat transfer fluid through the storage container can be designed such that the heat transfer fluid flows through the storage container along a predetermined main flow axis, so that the heat transfer fluid flows through the storage container along a main flow direction running parallel to the main flow axis. In this regard, the passage device can be designed such that the main flow direction during thermal charging of the heat storage device is opposite to the main flow direction during thermal discharging of the heat storage device. The main flow axis can, for example, run through the first and second passage devices, i.e.be defined by a straight line running through the first and second passage devices. The main flow axis can thus be defined, for example, by a straight connection which connects the first passage device to the second passage device. The storage container and the passage device can, for example, be designed such that the storage container has a longitudinal axis, which is also referred to as the container longitudinal axis, and that the main flow axis runs along the container longitudinal axis, wherein the main flow axis can, for example, be parallel to the container longitudinal axis and / or coincide with the container longitudinal axis. The container longitudinal axis corresponds to the direction of the greatest extent of the storage container. The container longitudinal axis can, for example, correspond to an axis of symmetry of the storage container or approximately correspond to an axis of symmetry of the storage container.Such an arrangement of the main flow axis along the longitudinal axis of the container can contribute to a more effective heat exchange between the heat transfer fluid flowing through the container and the heat storage elements arranged in the storage container.

[0029] The passage device can be designed, in particular, to pass the heat transfer fluid through the storage container such that the heat transfer fluid flows into the storage container on one side of the storage element arrangement and flows out of the storage container on the opposite side of the storage element arrangement. This can be achieved, for example, by arranging the first passage device on one side of the storage element arrangement and the second passage device on the opposite side of the storage element arrangement. Accordingly, the heat transfer fluid flows into the storage container on a first side of the storage element arrangement, flows around the heat storage elements of the storage element arrangement, and flows out of the storage container on a second side of the storage element arrangement opposite the first side.

[0030] In particular, it can be provided that the main flow axis and thus also the main flow direction run vertically, i.e., parallel to the vertical direction. Accordingly, the passage device can be designed such (e.g., by appropriately arranging the first and second passage devices) that, when the heat accumulator is used as intended, the main flow axis runs vertically and thus the heat transfer fluid flows essentially vertically through the storage container. This can be achieved, for example, by arranging the first passage device and the second passage device vertically one above the other.

[0031] The passage device can, for example, be designed such that the main flow direction during thermal charging runs vertically from bottom to top, and thus the heat transfer fluid flows through the storage tank essentially from bottom to top during thermal charging, and such that the main flow direction during thermal discharging runs vertically from top to bottom, and thus the heat transfer fluid flows through the storage tank essentially from top to bottom during thermal discharging. Such a vertical flow can be advantageous both in terms of fluid dynamics and with regard to heat exchange, particularly due to the temperature gradient within the storage tank, which also runs primarily vertically.

[0032] Alternatively or additionally, the longitudinal axis of the container can be provided to run vertically. Accordingly, the storage container can be designed and arranged such that, when the heat storage device is used as intended, the longitudinal axis of the container runs vertically. Particularly in combination with a vertical main flow axis, a design with a vertical longitudinal axis of the container can be advantageous both in terms of flow and heat exchange, particularly due to the temperature gradient within the storage container, which also runs primarily vertically.

[0033] According to one embodiment, the ratio between the volume of the phase change material and the volume of the solid material for the storage element arrangement is in the range from 1:4 to 4:1, i.e. the volume of the phase change material is at least a quarter and at most four times the volume of the solid material. Preferably, it can be provided that the ratio between the volume of the phase change material and the volume of the solid material for the storage element arrangement is in the range from 1:2 to 2:1, e.g. 1:1. Alternatively or additionally, it can be provided that the ratio between the volume of the phase change material and the volume of the solid material for all combination heat storage elements of the storage element arrangement is in the range from 1:4 to 4:1, i.e. has a value in the range from 1:4 to 4:1.It can preferably be provided that the ratio between the volume of the phase change material and the volume of the solid material for all combination heat storage elements of the storage element arrangement is in the range from 1:2 to 2:1, e.g. 1:1. It can particularly be provided that the ratio between the volume of the phase change material and the volume of the solid material for each combination heat storage element of the storage element arrangement is in the range from 1:4 to 4:1. It can preferably be provided that the ratio between the volume of the phase change material and the volume of the solid material for each combination heat storage element of the storage element arrangement is in the range from 1:2 to 2:1, e.g. 1:1.Such a volume ratio between phase change material and solid material enables, in particular, an effective improvement of the thermal conductivity within the combination heat storage elements while simultaneously ensuring their mechanical stability.

[0034] Alternatively or additionally, it can be provided that the ratio between the heat capacity of the phase-change material for sensible heat (i.e., the heat capacity based on temperature change without taking into account the enthalpy of fusion) and the heat capacity of the solid-state material for sensible heat for the storage element arrangement lies in the range from 1:3 to 3:1, i.e., the sensible heat capacity of the phase-change material of the storage element arrangement is at least one-third and at most three times the sensible heat capacity of the solid-state material of the storage element arrangement. The heat capacity for sensible heat or sensible heat capacity C of a body or material volume indicates the ratio between the heat Q supplied to it and the resulting temperature increase AT: C = Q / AT.Preferably, it can be provided that the ratio between the heat capacity of the phase change material for sensible heat and the heat capacity of the solid material for sensible heat for the storage element arrangement is in the range of 2:3 to 3:2. Alternatively or additionally, it can be provided that the ratio between the heat capacity of the phase change material for sensible heat and the heat capacity of the solid material for sensible heat for all combination heat storage elements of the storage element arrangement is in the range of 1:3 to 3:1, preferably in the range of 2:3 to 3:2. In particular, it can be provided that the ratio between the heat capacity of the phase change material for sensible heat and the heat capacity of the solid material for sensible heat for each combination heat storage element of the storage element arrangement is in the range of 1:3 to 3:1, preferably in the range of 2:3 to 3:2.In this regard, the heat capacity of the phase-change material can refer to the heat capacity of the phase-change material in the solid and / or liquid state, preferably to the heat capacity of the phase-change material in the solid state. If several different phase-change materials are present in the storage element arrangement, the quantity of all combination heat storage elements, or a respective combination heat storage element, the heat capacity of the phase-change material refers to the summed heat capacity of all phase-change materials present. Such a ratio between the heat capacity of the phase-change material for sensible heat and the heat capacity of the solid-state material for sensible heat enables, in particular, an effective contribution of the solid-state elements to heat storage and an effective buffering effect of the solid-state material during thermal loading and unloading.In addition, such a ratio is advantageous in terms of temperature homogenization and mechanical integrity, ie in terms of strength, stability and toughness.

[0035] According to one embodiment, the phase-change material incorporated in the solid-state heat storage elements of the combination heat storage elements has a higher thermal conductivity than the solid-state material from which the solid-state heat storage elements are made. For example, it can be provided that the phase-change material, in its solid state and / or in its liquid state, has a higher thermal conductivity than the solid-state material of the solid-state heat storage elements. This enables more effective temperature homogenization within the combination heat storage elements and also within the storage element arrangement, which, for example, supports more effective thermal charging and discharging.If several different phase change materials with different thermal conductivities are present, it can be provided that each of the phase change materials has a higher thermal conductivity than the solid material of the solid-state heat storage elements.

[0036] According to a further embodiment, each of the cavities filled with phase change material has a longitudinal axis, which is also referred to as the cavity longitudinal axis. Accordingly, each cavity is formed with an elongated shape, wherein the longitudinal extent of the cavity is greater than the (maximum) transverse extent of the cavity, and wherein the cavity longitudinal axis corresponds to the direction of the greatest extent of the respective cavity. The cavity longitudinal axis of a respective cavity can, for example, correspond to an axis of symmetry of this cavity or approximately correspond to an axis of symmetry of this cavity. The longitudinal extent of a respective cavity refers to the (maximum) extent of this cavity along the associated cavity longitudinal axis, while the transverse extent refers to the extent of the cavity transversely or perpendicularly to its cavity longitudinal axis. The transverse extent can also be referred to as the cross-sectional extent.In this regard, it can be provided in particular that the longitudinal extent of each cavity is at least twice as large as the (maximum) transverse extent of the cavity, preferably at least three times as large, e.g. at least five times as large.

[0037] For example, it can be provided that a respective cavity is designed as a recess in the form of a blind hole with a circular cross-section whose depth is greater than its diameter; in this case, the longitudinal axis of the cavity is given by the central axis or axis of rotation of the blind hole. As another example, it can be provided that a respective cavity is designed as a recess in the form of an elongated cuboid, i.e. a cuboid whose extent in one of the three dimensions is greater than its extent in the other two dimensions; in this case, the longitudinal axis of the cavity is given by the central axis or (e.g. two-fold) axis of rotation of the cuboid running parallel to the longest edge or longitudinal direction of the cuboid.

[0038] An elongated cavity geometry (especially with a vertical cavity longitudinal axis) can help minimize the thermal stresses that occur during the phase change (especially during solidification) of the phase-change material. By designing the cavities formed in the solid-state heat storage elements and filled with the phase-change material in an elongated shape, effective heat exchange between the respective solid-state heat storage element and the phase-change material contained therein is also possible for each cavity volume.

[0039] According to one embodiment, the longitudinal extent of each cavity filled with phase-change material of a respective solid-state heat storage element is at least 50% of the extent of the solid-state heat storage element along the associated cavity longitudinal axis. Accordingly, the solid-state heat storage element of each combination heat storage element is designed such that the longitudinal extent of each cavity formed in the solid-state heat storage element and filled with phase-change material along its cavity longitudinal axis is at least 50%, preferably at least 75%, e.g., at least 90%, of the extent of the solid-state heat storage element along this cavity longitudinal axis.

[0040] By extending the cavities formed in the solid-state elements and filled with phase-change material so far within the respective solid-state element, the heat exchange between the solid-state material and the phase-change material, as well as the temperature homogenization within the combination heat storage elements, can be further improved. Furthermore, it can be provided that the longitudinal extent of each cavity filled with phase-change material of a respective solid-state heat storage element amounts to a maximum of 95% of the extent of the solid-state heat storage element along the associated cavity longitudinal axis, for example, to ensure the mechanical stability of the solid-state heat storage elements.

[0041] According to one embodiment, the longitudinal axes of all cavities filled with phase-change material run parallel to one another. Accordingly, the solid-state heat storage elements of all combination heat storage elements are designed and arranged such that the longitudinal axes of all cavities filled with phase-change material are parallel to one another. Such a parallel alignment of all cavities can contribute to a homogenization of the heat exchange and thus also of the temperature distribution within the storage element arrangement.

[0042] In particular, it can be provided that the longitudinal axes of the cavities of all cavities filled with phase change material run vertically, i.e., parallel to the vertical direction. Accordingly, it can also be provided that the solid-state heat storage elements of all combination heat storage elements are designed and arranged such that the longitudinal axes of the cavities filled with phase change material are parallel to one another and, when the heat storage element is used as intended, run vertically. By arranging the cavities with their longitudinal axes and thus their longitudinal orientation running vertically, an additional attenuation of the mainly vertical temperature gradients is possible, thus further supporting temperature homogenization within individual combination heat storage elements and within the storage element arrangement.

[0043] According to one embodiment, it is provided that the solid-state elements of all combination heat storage elements are designed and arranged such that (when the heat storage device is used as intended) all cavities filled with phase-change material are open at the top and extend downwards into the respective solid-state heat storage element with a vertically extending cavity longitudinal axis. In this regard, it can also be provided that the longitudinal extent along the vertical direction of each cavity filled with phase-change material of a respective solid-state heat storage element amounts to at least 50% (preferably at least 75%, e.g., at least 90%) of the extent along the vertical direction of the solid-state heat storage element and thus covers a correspondingly large part of the height of the solid-state heat storage element.Accordingly, it can be provided that the depth of the cavities filled with phase change material in each solid-state heat storage element is at least 50% (preferably at least 75%, e.g., at least 90%) of the height of the respective solid-state heat storage element. Furthermore, it can be provided that the longitudinal extent along the vertical direction of each cavity filled with phase change material in a respective solid-state heat storage element is a maximum of 95% of the extent of the solid-state heat storage element along the associated cavity longitudinal axis, e.g., that the depth of the cavities filled with phase change material in each solid-state heat storage element is a maximum of 95% of the height of the respective solid-state heat storage element.

[0044] The cavities filled with phase-change material are preferably filled with the phase-change material in such a way that the phase-change material in the solid state occupies a maximum of 95% of the volume of the respective cavity. Accordingly, each cavity filled with phase-change material can contain sufficient phase-change material so that the volume of the phase-change material in the solid state is a maximum of 95% of the volume of the respective cavity. This allows for the thermal expansion of the phase-change material during the transition from the solid to the liquid state to be easily accounted for.

[0045] According to one embodiment, the heat accumulator is designed such that (when used as intended) the longitudinal axes of all cavities filled with phase-change material run parallel to the main flow axis, whereby the main flow axis can run, for example, along the container's longitudinal axis or parallel to it. Accordingly, the passage device and the solid-state heat storage elements of all combination heat storage elements can be designed and arranged such that (when used as intended), the longitudinal axes of all cavities filled with phase-change material are parallel to one another and parallel to the main flow axis (and thus also parallel to the main flow direction).Such an arrangement of the cavity longitudinal axes parallel to the main flow axis can contribute to a more effective heat exchange between the heat transfer fluid flowing in the container and the heat storage elements arranged in the storage container.

[0046] According to this embodiment, it can be provided, in particular, that the heat storage device is designed such that (when used as intended) the longitudinal axes of all cavities filled with phase-change material run vertically, and the main flow axis also runs vertically. In addition, it can be provided that the container's longitudinal axis also runs vertically, and thus the longitudinal axes of the cavities, the main flow axis, and the container's longitudinal axis all run parallel to one another along the vertical direction. These configurations enable effective temperature homogenization within individual combination heat storage elements and within the storage element arrangement and are advantageous both in terms of fluid dynamics and heat exchange.

[0047] According to one embodiment, the heat storage device comprises two or more different phase change materials, each with different melting temperatures.

[0048] For example, it can be provided that the storage element arrangement or its combination heat storage elements have at least two groups of cavities filled with different phase-change materials with different melting temperatures. Such a group of cavities is also referred to as a cavity group, with each cavity group having at least one cavity. Each cavity of such a group is formed in a solid-state heat storage element of a combination heat storage element of the storage element arrangement. All cavities of a respective cavity group are filled with the same phase-change material.In particular, it can be provided that all cavities of the storage element arrangement filled with the same phase change material form a common group and thus the cavities of different groups are filled with different phase change materials, each with different melting temperatures.

[0049] In this regard, it can be provided that all cavities filled with a phase change material of a respective combination heat storage element are filled with the same phase change material (and can, for example, belong to the same group). It can, for example, be provided that each combination heat storage element is designed such that all cavities filled with a phase change material of the respective combination heat storage element are filled with the same phase change material. In this case, it can, for example, be provided that a respective cavity group is formed by a corresponding group of combination heat storage elements. Such a group of combination storage elements is also referred to as a storage element group, wherein each storage element group has at least one combination heat storage element.All cavities of a storage element group filled with phase-change material are filled with the same phase-change material. The cavities of a respective storage element group can, for example, form a common cavity group. Accordingly, it can be provided that the storage element arrangement has two or more storage element groups that have different phase-change materials with different melting temperatures. In particular, it can be provided that all combination storage elements of the storage element arrangement filled with the same phase-change material form a common storage element group, and thus the cavities of different storage element groups are filled with different phase-change materials, each with different melting temperatures.

[0050] However, it can also be provided that a respective combination heat storage element has cavities that are filled with different phase change materials (and thus belong to different groups).

[0051] By having the heat storage device or its combination heat storage elements comprise two or more phase change materials with different melting temperatures, each phase change material enabling a constant temperature level at the respective melting temperature during the phase change, it is possible, for example, to load and unload the heat storage device with a temperature profile with two or more essentially constant temperature levels, which can be advantageous.the reaching of a correspondingly low temperature level acts as a sign that a predetermined minimum filling level of the heat storage is about to be reached and / or the reaching of a correspondingly high temperature level acts as a sign that a predetermined maximum filling level of the heat storage is about to be reached, whereby due to the essentially constant temperature during the phase change, appropriate measures can be initiated with sufficient lead time.

[0052] Furthermore, the use of different phase change materials with different melting temperatures can contribute to compensating temperature gradients and thus to temperature homogenization within the storage container or the storage element arrangement.

[0053] According to one embodiment, the storage element arrangement can comprise a first cavity group and a second cavity group, wherein the cavities of the first cavity group are filled with a first phase-change material and the cavities of the second cavity group are filled with a second phase-change material, and wherein the first phase-change material has a different melting temperature than the second phase-change material. In this regard, it can be provided, in particular, that the first phase-change material has a higher melting temperature than the second phase-change material, and that (when the heat storage device is aligned and used as intended) the second cavity group is arranged above the first cavity group.Accordingly, the cavities of the second cavity group containing the second phase change material with the lower melting temperature are arranged above the cavities of the first cavity group containing the first phase change material with the higher melting temperature.

[0054] In general, it can be provided that the combination heat storage elements are designed and arranged in such a way that the storage element arrangement has a plurality of groups of cavities in such a way that the cavity groups are arranged one above the other when the heat storage device is arranged and used as intended, wherein all cavities of a respective group are filled with the same phase change material and the plurality of groups each have different phase change materials with different melting temperatures in such a way that the phase change materials of the different groups have decreasing melting temperatures in a direction from bottom to top.Accordingly, the lowest cavity group contains the phase-change material with the highest melting temperature, and the topmost group contains the phase-change material with the lowest melting temperature, with the melting temperature of the respective phase material of the intermediate group(s) decreasing from bottom to top. This can be achieved, for example, by constituting a respective cavity group with a corresponding group of combination heat storage elements.Accordingly, the storage element arrangement can have a plurality of groups of combination heat storage elements such that the storage element groups are arranged one above the other when the heat storage device is arranged and used as intended, wherein all combination storage elements of a respective storage element group have the same phase change material and the plurality of storage element groups each have different phase change materials with different melting temperatures such that the phase change materials of the different storage element groups have decreasing melting temperatures in a direction from bottom to top.Accordingly, the lowest storage element group comprises the phase change material with the highest melting temperature, and the topmost storage element group comprises the phase change material with the lowest melting temperature, with the melting temperature of the respective phase material of the storage element group(s) arranged between them decreasing from bottom to top. In this regard, it can be provided, for example, that the storage element arrangement comprises combination heat storage elements arranged in several superimposed levels, with all combination heat storage elements arranged in the same level belonging to the same storage element group, and with the combination storage elements of one level or several consecutive levels forming a common storage element group.

[0055] By having the heat storage device or storage element arrangement comprise different phase-change materials with decreasing melting temperatures from bottom to top, the predominantly vertical temperature gradient can be reduced, thus further supporting temperature homogenization within the storage element arrangement or within the storage container. In particular, this effectively homogenizes the temperature distribution within the storage container during loading and / or unloading, thereby improving heat transfer and reducing loading and unloading times. In this regard, it can be provided, in particular, that the melting temperatures of the different phase-change materials differ by at least 10% of the lowest melting temperature of all phase-change materials present, preferably by at least 20% of the lowest melting temperature.The lowest melting temperature is the melting temperature of the phase change material that has the lowest melting temperature of all phase change materials included in the combination heat storage elements or in the storage element arrangement. In this regard, it can be provided that the melting temperatures of the different phase change materials differ such that for each phase change material with a predetermined melting temperature, the melting temperature of the phase change material with the next highest melting temperature is at least 10% (preferably at least 20%) higher than the predetermined melting temperature.that for each phase change material with a predetermined melting temperature, the melting temperature of the phase change material with the next lowest melting temperature is at least 10% (preferably at least 20%) lower than the predetermined melting temperature. Accordingly, it can be provided in particular that the heat accumulator has a first phase change material with a first melting temperature and a second phase change material with a second melting temperature such that the second melting temperature is lower than the first melting temperature, and that the temperature difference between the first melting temperature and the second melting temperature is at least 10% (preferably at least 20%) of the second melting temperature. Temperature differences dimensioned in this way enable particularly effective homogenization of the temperature distribution, in particular during thermal loading and unloading of the heat accumulator.

[0056] The heat storage device is designed for operation in an operating temperature range that extends from a temperature below the melting temperature of the phase-change material accommodated in the cavities of the combination heat storage elements to a temperature above the melting temperature of the phase-change material. If several different phase-change materials are present, the heat storage device can be designed for operation in an operating temperature range that extends from a temperature below the lowest melting temperature of all phase-change materials present to a temperature above the highest melting temperature of all phase-change materials present. The solid-state material is a material that is in the solid state throughout the entire operating temperature range of the heat storage device.

[0057] According to one embodiment, the heat storage device comprises a heating device designed to heat the storage element arrangement. The heating device is thus designed to heat or thermally charge the heat storage elements (in particular the combination heat storage elements) of the storage element arrangement. The heating device is designed, in particular, to heat the storage element arrangement to a temperature that is at least as high as or higher than the melting temperature of the phase-change material contained in the combination heat storage elements.If several different phase-change materials with different melting temperatures are present, it can be provided that the heating device is designed to heat the storage element arrangement to a temperature that is at least as high as or higher than the highest melting temperature of all phase-change materials contained in the combination heat storage elements. The heating device can thus be designed to heat the storage element arrangement or the heat storage elements to a temperature equal to or above the (highest) phase-change material melting temperature, so that the phase-change material contained in the combination heat storage elements can be melted by means of the heating device during thermal charging of the heat storage device with the corresponding energy input.

[0058] The heating device can, for example, be designed to indirectly heat the storage element arrangement using the heat transfer fluid. For example, it can be provided that the heating device is implemented by a supply device designed to supply a fluid acting as a heat transfer fluid to the passage device at a temperature that is at least as high as or higher than the melting temperature of the phase change material accommodated in the combination heat storage elements. If several different phase change materials with different melting temperatures are present, it can accordingly be provided that the supply device is designed to supply a heat transfer fluid to the passage device, the heat transfer fluid having a temperature that is at least as high as or higher than the highest melting temperature of all phase change materials accommodated in the combination heat storage elements.The heat transfer fluid supplied by the supply device to the passage device thus has a temperature equal to or greater than the (highest) phase change material melting temperature. By means of the passage device, the heat transfer fluid can then be passed through the storage container, flowing around the heat storage elements of the storage element arrangement, and thereby transferring thermal energy to the heat storage elements.

[0059] Phase change material can be melted with appropriate energy absorption.

[0060] The supply device may, for example, comprise a heating device designed to (e.g. electrically) heat a provided heat transfer fluid to the required temperature (ie to a temperature that is equal to or greater than the (highest) phase change material melting temperature of the phase change material accommodated in the combination heat storage elements of the storage element arrangement).

[0061] The invention is explained below using exemplary embodiments with reference to the accompanying figures, in which identical or similar features are provided with the same reference numerals; schematically show:

[0062] Figure 1 is a sectional view of a heat storage unit;

[0063] Figure 2A is a plan view of a combination heat storage element;

[0064] Figure 2B is a sectional view of the combination heat storage element according to Figure 2A;

[0065] Figure 3A is a plan view of another combination heat storage element;

[0066] Figure 3B is a sectional view of the combination heat storage element according to Figure 3A; and

[0067] Figure 4 shows a sectional view of another heat storage unit.

[0068] Figure 1 shows a sectional view of a heat storage device 1 according to one embodiment. The heat storage device 1 has a storage element arrangement 3 with a plurality of heat storage elements 5. Figure 1 shows nine heat storage elements 5 of the storage element arrangement 3. Each of the heat storage elements 5 of the storage element arrangement 3 is a combination heat storage element 5, which has a solid-state heat storage element 7 made of a solid material, in which one or more cavities 11 filled with a phase-change material 9 are formed. Figure 1 shows, by way of example, three combination heat storage elements 5 and three cavities 11. In the embodiment according to Figure 1, all cavities of all combination heat storage elements 5 are filled with the same phase-change material 9, so that all combination heat storage elements 5 of the storage element arrangement 3 have the same phase-change material 9.Each combination heat storage element 5 thus comprises a separate, one-piece or monolithic solid-state heat storage element 7 with one or more cavities 11 formed therein, wherein a phase-change material 9 is accommodated in the cavity or cavities. Phase-change material 9 is thus accommodated in each of the solid-state heat storage elements 5 or in each of the solid-state heat storage elements 7 of the storage element arrangement 3.

[0069] The phase change material 9 is a material that, during intended operation of the heat storage device 1, undergoes a phase change between the solid and the liquid state at a material-specific melting temperature. The heat storage device 1 is designed or used in such a way that, upon thermal charging of the heat storage device, the storage element arrangement 3 is heated to a temperature above the phase change material melting temperature, so that the phase change material acts as a latent heat storage device and its enthalpy of fusion contributes to heat storage. The heat storage device 1 can also be designed or used in such a way that, upon thermal discharging of the heat storage device 1, the storage element arrangement 3 is cooled to a temperature below the phase change material melting temperature. The phase change material 9 preferably comprises or consists of a metallic material.The phase change material 9 can be, for example, aluminum with a melting temperature of approximately 660 °C or an aluminum alloy (e.g. AlMgSiO,5) with a melting temperature of approximately between 550 °C and 650 °C.

[0070] The solid-state material is a material that is always in the solid state during intended operation of the heat storage device 1 and functions as a sensible heat storage device. Each solid-state heat storage element 7 of a respective combination heat storage element 5 thus functions as a sensible heat storage device. The solid-state material is, in particular, a material that remains in the solid state until above the melting temperature of the phase-change material accommodated in the cavities of the solid-state heat storage elements 7. The solid-state material is preferably a non-metallic material. The solid-state material can be, for example, a high-temperature ceramic or a high-temperature concrete.

[0071] The phase change material 9 incorporated in the solid-state heat storage elements 7 has a higher thermal conductivity, both in its solid state and in its liquid state, than the solid material from which the solid-state heat storage elements 7 are made. As an example, in the temperature range between 20 °C and 700 °C, aluminum has a thermal conductivity between 200 W / (m K) and 90 W / (m K) and a typical aluminum alloy (AlMgSiO,5) has a thermal conductivity between 210 W / (m K) and 90 W / (m K) (with the thermal conductivity increasing again at even higher temperatures), whereas in this temperature range high-temperature ceramics only have thermal conductivities in the range between approximately 1.6 W / (m K) and approximately 1.2 W / (m K) and high-temperature concrete only have thermal conductivities in the range between approximately 1.35 W / (m K) and approximately 0.75 W / (m K).

[0072] The ratio between the volume of the phase change material 9 accommodated in the cavities 11 of the solid-state heat storage elements 7 and the volume of the solid-state material of the solid-state heat storage elements 7 for the storage element arrangement 3 is in the range of 1:4 to 4:1, preferably in the range of 1:2 to 2:1. In the present case, the ratio between the volume of the phase change material 9 and the volume of the solid-state material for the storage element arrangement 3 is 1:1 as an example. This is achieved here in that the ratio between the volume of the phase change material 9 and the volume of the solid-state material for each combination heat storage element 5 of the storage element arrangement 3 has a value in the range of 1:4 to 4:1, preferably in the range of 1:2 to 2:1.In the present case, the ratio between the volume of the phase change material 9 and the volume of the solid material for each combination heat storage element 5 of the storage element arrangement 3 is 1:1 as an example.

[0073] Alternatively or in addition to the volume ratio explained above, it can be provided that the ratio between the heat capacity of the phase change material for sensible heat and the heat capacity of the solid material for sensible heat for the storage element arrangement is in the range of 1:3 to 3:1, preferably in the range of 2:3 to 3:2. This can be realized as an example in that the ratio between the heat capacity of the phase change material for sensible heat and the heat capacity of the solid material for sensible heat for each combination heat storage element 5 of the storage element arrangement 3 is in the range of 1:3 to 3:1, preferably in the range of 2:3 to 3:2.

[0074] The heat storage device 1 has a storage container 13. The storage element arrangement 3 and its heat storage elements 5 are accommodated in the storage container 13.

[0075] The heat accumulator 1 has a passage device designed to pass a gaseous heat transfer fluid through the storage container 13 (in Figure 1, the passage device or the heat transfer fluid flowing through the storage container 13 is indicated by arrows 15, wherein the arrows 15 indicate the flow direction of the heat transfer fluid). The passage device 15 has a first passage device 15.1 in the form of a first passage opening 15.1 formed in the storage container 13 and a second passage device 15.2 in the form of a second passage opening 15.2 formed in the storage container 13. Figure 1 shows the heat accumulator 1 during thermal loading, wherein the first passage opening 15.1 acts as an inlet opening for admitting the heat transfer fluid into the storage container 13 and the second passage opening 15.2 acts as an outlet opening for discharging the heat transfer fluid from the storage container 13.

[0076] The first passage device 15.1 and the second passage device 15.2 are arranged on opposite sides of the storage element arrangement 3, so that the heat transfer fluid enters the storage container 13 on one side of the storage element arrangement 3, flows around the combination heat storage elements 5 of the storage element arrangement 3, and exits the storage container 13 on the opposite side of the storage element arrangement 3. The combination heat storage elements 5 are arranged such that free flow areas remain between the combination heat storage elements, through which the heat transfer fluid can flow and, in the case of loading, can supply heat to the combination heat storage elements 5 or, in the case of discharging, can dissipate heat from the combination heat storage elements.

[0077] The storage tank 13 has a longitudinal axis 17, which is also referred to as the tank's longitudinal axis 17. The heat storage tank 1 is designed such that, when arranged and used as intended, the tank's longitudinal axis 17 runs vertically, i.e., parallel to the z-axis of the Cartesian xyz coordinate system shown in Figure 1. The z-axis of the xyz coordinate system shown in the figures runs vertically, i.e., parallel to the vertical direction, with the z-axis pointing vertically upwards. The x-axis and the y-axis of the xyz coordinate system shown in the figures run horizontally, i.e., perpendicular to the vertical direction.

[0078] The heat accumulator 1 and the passage device 15 are designed such that, when the heat accumulator 1 is arranged and used as intended, the second passage opening 15.2 is arranged vertically above the first passage opening 15.1, so that the heat transfer fluid flows through the storage container 13 along a vertically extending main flow axis. The vertically extending main flow axis is defined by a vertical straight line extending from the first passage device 15.1 to the second passage device 15.2. In the present case, the main flow axis runs parallel to the container's longitudinal axis 17 and, in particular, coincides with the container's longitudinal axis 17. The heat transfer fluid flows through the storage container 13 along a main flow direction parallel to the main flow axis.The passage device 15 is designed such that the main flow direction during thermal charging of the heat accumulator 1 is opposite to the main flow direction during thermal discharging of the heat accumulator 1. The passage device 15 is designed in particular such that during thermal charging of the heat accumulator 1, the heat transfer fluid flows through the storage container 13 from bottom to top, and thus the main flow direction during thermal charging runs vertically from bottom to top, and that during thermal discharging of the heat accumulator 1, the heat transfer fluid flows through the storage container 13 from top to bottom, and thus the main flow direction during thermal discharging runs vertically from top to bottom. Figure 1 shows the heat accumulator 1 during thermal charging, with the heat transfer fluid 15 flowing through the storage container from bottom to top.

[0079] Each of the cavities 11 filled with the phase-change material 9 has an elongated shape with a longitudinal extension running along a respective longitudinal axis 19 and a comparatively smaller transverse extension. The longitudinal axis of a respective cavity is also referred to as its cavity longitudinal axis 19. Figure 1 shows the cavity longitudinal axes 19 of two cavities 11 as examples.

[0080] As an example, it can be provided that each of the cavities 11 is designed as a recess in the form of a blind hole with a circular cross-section, the depth of which is greater than its diameter, as shown in Figures 2A and 2B. In this case, the cavity longitudinal axis 19 of a respective cavity 11 is defined by the central axis or axis of rotation of the blind hole. Figure 2A shows a plan view of a combination heat storage element 5 with eight cavities 11 filled with phase change material 9 in the form of such blind holes. Figure 2B shows a section through this combination heat storage element running parallel to the yz plane. The combination heat storage element shown can be, for example, one of the combination heat storage elements arranged centrally on the container longitudinal axis 17 according to Figure 1.As another example, it can be provided that each of the cavities 11 is designed as a recess in the form of an elongated cuboid, i.e. a cuboid whose extension in one of the three dimensions is greater than its extension in the other two dimensions, as shown in Figures 3A and 3B. In this case, the cavity longitudinal axis 19 of a respective cavity 11 is given by the central axis or rotation axis of the cuboid, which runs parallel to the longest edge or longitudinal direction of the cuboid. Figure 3A shows a plan view of a combination heat storage element 5 with eight cavities 11 filled with phase change material 9 in the form of such elongated cuboids. Figure 3B shows a section running parallel to the yz plane through this combination heat storage element, wherein the combination heat storage element 5 shown, for example,can be one of the combination heat storage elements 5 arranged centrally on the container's longitudinal axis 17 according to Figure 1.

[0081] In the present case, each of the cavities 11 filled with phase-change material 9 is open at the top and extends with a vertically extending cavity longitudinal axis 19 into the respective solid-state heat storage element 7. Thus, the cavity longitudinal axes 19 of all cavities 11 filled with the phase-change material 9 are parallel to each other as well as to the main flow axis and to the container longitudinal axis 17.

[0082] In particular, it can be provided that the longitudinal extent of each cavity 11 (ie, in this case, its extent along the z-direction) is at least twice as large as its maximum transverse extent, preferably at least three times as large. In this example, the longitudinal extent of each cavity 11 is more than five times as large as its maximum transverse extent.

[0083] In addition, the longitudinal extent of each cavity 11 of a respective solid-state heat storage element 7 is at least 50% (preferably at least 75%, e.g. at least 90%) and at most 95% of the extent of the solid-state heat storage element 7 along the associated cavity longitudinal axis 19. In the present case, the longitudinal extent of each cavity 11 of a respective solid-state heat storage element 7 is, as an example, 95% of the extent of the solid-state heat storage element 7 along the associated cavity longitudinal axis 19. The longitudinal extent of a respective cavity 11 along the associated cavity longitudinal axis 19 corresponds in the embodiment according to Figure 1 to the depth of the respective cavity along the vertical direction. The extent of a respective solid-state heat storage element 7 along the longitudinal axis 19 of the cavity corresponds in the embodiment according to Figure 1 to the height of the solid-state heat storage element 7 along the vertical direction.

[0084] Heat storage element 7. In the embodiment according to Figure 1, the depth of each cavity 11 is at least 50% (in this example 95%) of the height of the associated solid-state heat storage element 7.

[0085] Each of the cavities 1 is filled with phase-change material 9 such that the phase-change material in the solid state occupies a maximum of 95% of the volume of the respective cavity 11. In the present example, the volume of the phase-change material in the solid state accommodated in a respective cavity 11 corresponds to 95% of the volume of the respective cavity 11.

[0086] The heat storage device 1 is designed for operation in an operating temperature range that extends from a temperature below the melting temperature of the phase change material 9 to a temperature above the melting temperature of the phase change material 9. The solid material is a material that is present in the solid state throughout the entire operating temperature range of the heat storage device 1.

[0087] The heat storage device 1 has a heating device 21 designed to heat the storage element arrangement 3 or to introduce thermal energy into the storage element arrangement 3. The heating device 21 can thus thermally charge the heat storage elements 5 of the storage element arrangement 3. The heating device 21 is designed to heat the storage element arrangement 3 to a temperature above the melting temperature of the phase-change material 9.

[0088] In the embodiment according to Figure 1, the heating device 21 is designed as a supply device 21, which is designed to supply appropriately tempered heat transfer fluid to the passage device 15. The supply device 21 is designed to supply the heat transfer fluid at a temperature above the melting temperature of the phase change material 9 accommodated in the combination heat storage elements 5 to the first passage device 15.1. During thermal charging, the supply device 21 thus provides the heat transfer fluid at a temperature such that its temperature is greater than the melting temperature of the phase change material 9, and the heat transfer fluid, tempered in this way, is supplied to the first passage device 15.1 and introduced into the storage container 13 via the first passage device 15.1.The heat transfer fluid then flows around the heat storage elements 5 of the storage element arrangement 3 and charges them with thermal energy, whereby the phase change material 9 is melted due to the temperature of the heat transfer fluid being above the phase change material melting temperature. After flowing around the heat storage elements 5, the heat transfer fluid flows out of the storage container 13 via the second passage device 15.2. In the embodiment according to Figure 1, the heating device 21 is thus designed to heat the storage element arrangement 3 or the combination heat storage elements 5 using a correspondingly tempered heat transfer fluid.

[0089] Figure 4 shows a sectional view of a heat accumulator T according to a further embodiment. Unlike the heat accumulator 1 according to Figure 1, the heat accumulator T according to Figure 4 has several (namely three) different phase change materials. Otherwise, the structure and operation of the heat accumulator T according to Figure 4 correspond to those of the heat accumulator 1 explained with reference to Figures 1, 2A / B, and 3A / B, so that in this regard, reference is made to the explanations with reference to Figures 1, 2A / B, and 3A / B.

[0090] The heat storage device T according to Figure 4 has a first phase change material 9.1, a second phase change material 9.2 and a third phase change material 9.3.

[0091] The heat accumulator T has three groups of combination heat storage elements 5, wherein all combination heat storage elements 5 of the heat accumulator T arranged at a common height each form a common group. Such a group of combination heat storage elements 5 is also referred to as a storage element group. The heat accumulator T has, in particular, a first group 23.1 of combination heat storage elements 5, a second group 23.2 of combination heat storage elements 5, and a third group 23.3 of combination heat storage elements 5. The second group 23.2 is arranged above the first group 23.1, and the third group 23.3 is arranged above the second group 23.2. Therefore, the first group 23.1 is also referred to as the lower group 23.1, the second group 23.2 is also referred to as the middle group 23.2, and the third group 23.3 is also referred to as the upper group 23.3.

[0092] All cavities 11 of the combination heat storage elements 5 of the first group 23.1 are filled with the first phase-change material 9.1, all cavities 11 of the combination heat storage elements 5 of the second group 23.2 are filled with the second phase-change material 9.2, and all cavities 11 of the combination heat storage elements 5 of the third group 23.3 are filled with the third phase-change material 9.3. All combination heat storage elements 5 of a respective storage element group thus have the same phase-change material, whereas combination heat storage elements 5 of different storage element groups have different phase-change materials.

[0093] All cavities 11 of the combination heat storage elements 5 of a respective storage element group form a common cavity group. Accordingly, the cavities of the combination heat storage elements 5 of the first storage element group 23.1 form a first cavity group 23.1, the cavities of the combination heat storage elements 5 of the second storage element group 23.2 form a second cavity group 23.2, and the cavities of the combination heat storage elements 5 of the third storage element group 23.3 form a third cavity group 23.3. Thus, the second cavity group 23.2 is arranged above the first cavity group 23.1, and the third cavity group 23.3 is arranged above the second cavity group 23.2. Furthermore, all cavities 11 of a respective cavity group are filled with the same phase-change material, whereas cavities of different cavity groups are filled with different phase-change materials.

[0094] The phase change materials 9.1, 9.2 and 9.3 each have different melting temperatures. In the embodiment according to Figure 4, the first phase change material 9.1 has a higher melting temperature than the second phase change material 9.2. Furthermore, the second phase change material 9.2 has a higher melting temperature than the third phase change material 9.3. Thus, the heat accumulator T according to Figure 4 has three groups 23.1, 23.2, 23.3 of combination heat storage elements 5 or cavities 11 such that different groups have different phase change materials with different melting temperatures such that the phase change materials of the different groups have decreasing melting temperatures in a direction from bottom to top.

[0095] As an example, it can be provided that the first phase change material 9.1 is aluminum (melting temperature approx. 660 °C), the second phase change material 9.2 is zinc (melting temperature approx. 420 °C), and the third phase change material 9.3 is lead (melting temperature approx. 327 °C). Thus, the melting temperatures of the different phase change materials 9.1, 9.2, and 9.3 each differ by at least 10% (in this case even by more than 20% each) of the lowest melting temperature of all phase change materials present, which in this case is given by the melting temperature of the third phase change material 9.3. This enables, in particular, effective homogenization of the temperature distribution during thermal charging and discharging of the heat storage device.

[0096] In the heat storage device T according to Figure 4, the solid material from which the solid-state heat storage elements 7 are made is a material that exists in the solid state up to and including the highest melting temperature of all phase change materials present. In the embodiment according to Figure 4, the solid material is thus a material that remains in the solid state up to and including the melting temperature of the first phase change material 9.1. The heat storage device T according to Figure 4 is also designed for operation in an operating temperature range that extends from a temperature below the lowest melting temperature of all phase change materials present to a temperature above the highest melting temperature of all phase change materials present. The heat storage device 1' according to Figure 4 is thus designed for operation in an operating temperature range that extends from a temperature below the melting temperature of the third phase change material 9.3 extends to a temperature above the melting temperature of the first phase-change material 9.1. Also according to the embodiment of Figure 4, the solid-state material is a material that is present in the solid state throughout the entire operating temperature range of the heat storage device T.

[0097] In the embodiment according to Figure 4, the heating device 21 is also designed to heat the storage element arrangement 3 to a temperature that is greater than the highest melting temperature of all phase change materials present. In the embodiment according to Figure 4, this is achieved by the heating device 21 being designed as a supply device 21 for supplying appropriately tempered heat transfer fluid to the feedthrough device 15 or the first passage device 15.1. In the embodiment according to Figure 4, the heating device 21 is designed, for example, to heat the storage element arrangement 3 to a temperature above the melting temperature of the first phase change material 9.1, in that the heating device 21 is designed as a supply device 21 which is designed to supply the heat transfer fluid at a temperature above the melting temperature of the first phase change material 9.1 to the first passage device 15.1.List of reference symbols used.

[0098] 1, T heat storage / heat storage arrangement

[0099] 3 Storage element arrangement

[0100] 5 Heat storage element / combination heat storage element

[0101] 7 Solid-state heat storage element

[0102] 9 Phase change material of the heat storage according to Figure 1

[0103] 9.1 first phase change material of the heat storage according to Figure 4

[0104] 9.2 second phase change material of the heat storage according to Figure 4

[0105] 9.3 third phase change material of the heat storage according to Figure 4

[0106] 11 Cavity

[0107] 13 containers / storage containers

[0108] 15 Pass-through device / flowing heat transfer fluid

[0109] 15.1 first passage device

[0110] 15.2 second passage device

[0111] 17 Tank longitudinal axis / main flow axis

[0112] 19 Longitudinal axis of a respective cavity / cavity longitudinal axis

[0113] 21 Heating device / feeding device

[0114] 23.1 first group of combination heat storage elements / cavities

[0115] 23.2 second group of combination heat storage elements / cavities

[0116] 23.3 third group of combination heat storage elements / cavities

Claims

Patent claims 1. Heat storage unit (1, T), comprising: - a storage element arrangement (3) with one or more combination heat storage elements (5), wherein each of the combination heat storage elements (5) has a solid heat storage element (7) made of a solid material in which one or more cavities (11) filled with a phase change material (9, 9.1, 9.2, 9.3) are formed.

2. Heat storage device according to claim 1, wherein the ratio between the volume of the phase change material (9, 9.1, 9.2, 9.3) and the volume of the solid material for the storage element arrangement (3) is in the range of 1:4 to 4:

1.

3. Heat storage device according to claim 1 or 2, wherein the ratio between the heat capacity of the phase change material (9, 9.1, 9.2, 9.3) for sensible heat and the heat capacity of the solid material for sensible heat for the storage element arrangement (3) is in the range of 1 :3 to 3:

1.

4. Heat storage device according to one of claims 1 to 3, wherein the phase change material (9, 9.1, 9.2, 9.3) has a higher thermal conductivity than the solid material.

5. Heat storage device according to one of claims 1 to 4, wherein the storage element arrangement (3) comprises at least two different phase change materials (9.1, 9.2, 9.3).

6. Heat storage device according to claim 5, wherein the storage element arrangement (3) comprises at least a first group (23.1) of cavities and a second group (23.2) of cavities such that the first group (23.1) comprises one or more cavities (11) filled with a first phase change material (9.1) and the second group (23.2) comprises one or more cavities (11) filled with a second phase change material (9.2), wherein the first phase change material (9.1) has a higher melting temperature than the second phase change material (9.2), and wherein the second group (23.2) is arranged above the first group (23.1).

7. Heat storage device according to one of claims 1 to 6, comprising a heating device (21) designed to heat the combination heat storage elements (5) to a temperature that is at least as high as or higher than the melting temperature of the element therein recorded phase change material (9, 9.1, 9.2, 9.3).

8. Heat storage device according to one of claims 1 to 7, comprising: - a container (13) wherein the storage element arrangement (3) is arranged in the container, and - a conveying device (15, 15.1, 15.2) designed to convey a fluid through the container (13).

9. Heat storage device according to claim 8, comprising a supply device (21) designed to supply a fluid with a temperature at least as high as or higher than the melting temperature of the phase change material (9.1, 9.2, 9.3) incorporated in the combination heat storage elements (5) to the flow device (15, 15.1 , 15.2).

10. Heat storage device according to claim 8 or 9, wherein the flow device (15, 15.1, 15.2) for passing the fluid through the container (13) along a main flow axis (17), wherein each cavity (11) filled with phase change material (9, 9.1, 9.2, 9.3) has a shape with a longitudinal extent extending along a cavity longitudinal axis (19), and wherein, during intended use of the heat storage device, the cavity longitudinal axes (19) of all cavities (11) filled with phase change material are parallel to the main flow axis (17).

11. Heat storage device according to any one of claims 1 to 10, wherein each cavity (11) filled with phase change material (9, 9.1 , 9.2, 9.3) has a shape with a longitudinal extension extending along a cavity longitudinal axis (19).

12. Heat storage device according to claim 11, wherein the longitudinal extent of each cavity (11) filled with phase change material of a respective solid heat storage element (7) corresponds to at least 50% of the extent of the solid heat storage element (7) along the associated cavity longitudinal axis (19).

13. Heat storage device according to claim 11 or 12, wherein each solid heat storage element (7) is designed and arranged such that, during intended use of the heat storage device, the longitudinal axes (19) of all cavities (11) filled with phase change material (9, 9.1, 9.2, 9.3) are parallel run towards each other.

14. Heat storage device according to claim 13, wherein each solid heat storage element (7) is designed and arranged such that, during intended use of the heat storage device, the cavity longitudinal axes (19) of all with phase change material (9, 9.1 , 9.2, 9.3) filled cavities (11) run vertically.

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