Patent Application
20200292213
The invention relates to a magnetocaloric device, in particular to a magnetocaloric heat pump, according to the preamble part of claim 1.
Magnetocaloric materials can be used for pumping heat since they change their temperature upon an application and removal of an external magnetic field.
The magnetocaloric effect occurs under application of an external magnetic field to a suitable magnetocaloric material and under an ambient temperature in the vicinity of its Curie temperature. The applied external magnetic field causes an alignment of the randomly aligned magnetic moments of the magnetocaloric material from a disordered paramagnetic phase to an ordered ferromagnetic phase and thus a magnetic phase transition, which can also be described as an induced increase of the Curie temperature of the material above the ambient temperature. This magnetic phase transition implies a decrease in magnetic entropy ΔSmag and in a nearly adiabatic process (thermal isolation from the ambient temperature) leads to an increase in the entropy contribution of the crystal lattice of the magnetocaloric material by phonon generation in order to conserve entropy under the adiabatic condition. As a result of applying the external magnetic field, therefore, a temperature rise (ΔT) of the magnetocaloric material occurs.
In technical cooling applications, this additional heat is removed from the material by heat transfer to an ambient heat sink. The heat is transported from the material to the ambient heat sink by a heat transfer medium. Water is an example of a heat transfer medium used for heat removal from the magnetocaloric material. For temperatures below 0° C., an antifreeze additive such as ethylene or propylene glycol, ethanol, or a salt may be added to the water.
Subsequently, removing the external magnetic field can be described as a decrease of the Curie temperature back below an initial temperature of the magnetocaloric material, and thus allows the magnetic moments reverting back to a random arrangement. The external magnetic field is removed under nearly adiabatic conditions, i.e., thermal isolation from the ambient temperature, which means that the overall entropy within the system stays unchanged. Since the magnetic entropy increases to its starting level without the external magnetic field, the entropy contribution of the crystal lattice of the magnetocaloric material itself is reduced, and under nearly adiabatic process conditions, thus, results in a cooling of the magnetocaloric material below the initial temperature.
The described process cycle including magnetization and demagnetization is typically performed periodically in device applications.
Document US 2012/0031107 A1 describes a thermal generator with at least one thermal module comprising at least two magnetocaloric elements. The thermal generator is characterized in that it comprises at least two magnetic assemblies in which one magnetic assembly subjects at least one magnetocaloric element of the thermal module to alternate magnetic phases. The thermal generator is further characterized in that it comprises a thermally insulating body insulating the magnetic assemblies from each other and forming thermally insulated cells comprising one magnetic assembly and its corresponding magnetocaloric elements.
The prior art designs can be improved. The object of the invention is to create an improved magnetocaloric device. In particular it is an object of the invention to reduce heat leaks caused by the temperature differences between the environment of the magnetocaloric material and the magnetocaloric material itself.
The object is achieved according to the invention with a magnetocaloric device as defined in claim 1.
The invention provides a magnetocaloric device, in particular to a magnetocaloric heat pump, comprising:
a field generator, preferably formed by a magnet assembly, arranged to provide a changing external magnetic field, preferably a periodically changing external magnetic field,
a magnetocaloric regenerator arrangement, comprising a magnetocaloric element, preferably a plurality of magnetocaloric elements, wherein the magnetocaloric element comprises magnetocaloric material, and wherein the magnetocaloric regenerator arrangement is arranged to be exposed to the changing external magnetic field of the field generator.
According to the invention the magnetocaloric device further comprises:
an insulating means, wherein the insulating means is arranged such that the magnetocaloric regenerator arrangement is hermetically surrounded by the insulating means.
The magnetocaloric device according to the invention advantageously provides an insulating means around the magnetocaloric element, which comprises the magnetocaloric material. In particular, the thermal conductivity between the magnetocaloric element and the magnet assembly and/or the ambient environment is reduced compared to magnetocaloric devices without an insulation means that surrounds the magnetocaloric element.
By providing a reduced thermal conductivity, the magnetocaloric device according to the invention enables a reduced amount of heat leaks and therefore more heat can be pumped for a given work input, which results in an improved efficiency of the magnetocaloric device. Besides the low thermal conductivity, a low heat transfer of parts of the magnetocaloric device can advantageously reduce the overall heat transfer coefficient of the magnetocaloric device. In particular, the insulating means can prevent or decrease water condensation, freezing or heat transfer to the ambient or between components in the system at different temperatures, which are thermally connected by the ambient environment. The heat transfer coefficient for natural convection is typically less than 10 W/m2/K. In contrast, the heat transfer due to condensation typically leads to a heat transfer coefficient larger than 100000 W/m2/K, and the convection forced by a rotating field generator can lead to a heat transfer coefficient of more than 100 W/m2/K. Therefore it is particularly advantageous to provide a magnetocaloric device, wherein the insulating means can reduce the heat transfer due to condensation and/or the convection forced by a rotating field generator.
The highest temperature gradients of the magnetocaloric device are usually in a surrounding of the magnetocaloric element, according to a heating and cooling of the magnetocaloric material during the magnetization and demagnetization phases triggered by the periodically changing external magnetic field. Therefore it is particularly advantageous to provide the insulating means in the surrounding of the magnetocaloric element.
A further advantage of the insulating means is that the magnetocaloric regenerator arrangement is protected against influences of the environment, such as water, dust or dirt. This is particularly advantageous for allowing an outdoor use of the magnetocaloric device or for using the magnetocaloric device in rooms with a high humidity.
The magnetocaloric device according to the invention can be a magnetocaloric heat pump that is arranged to be used as a cooling device or as a heating device. More particularly, the magnetocaloric device can be a wine cooler, a refrigerator, a freezer or an air-conditioner.
In the following, developments of the magnetocaloric device according to claim 1 of the invention will be described.
In a preferred development the magnetocaloric device further comprises a fluid directing system, comprising at least a first and a second channel, arranged to direct a fluid through the first channel to the magnetocaloric regenerator arrangement and to direct the fluid through the second channel away from the magnetocaloric regenerator arrangement, and wherein the insulating means further comprise a flow-through for a passing of the fluid through the at least first and second channel. The at least first and second channels are typically arranged for providing a fluid flow of the fluid directing system through the flow-through to a heat exchanger outside of the insulating means. In order to not disturb a heat exchange of the heat exchanger by the insulating means, an arranging of the heat exchanger outside of the insulating means is particularly advantageous.
In a preferred development, the insulating means is an insulating casing. The insulating casing of a preferred variant is at least partly not in contact with the magnetocaloric regenerator arrangement. Furthermore, the insulating casing is filled or adapted to be filled with an insulation. The insulator casing might be an enclosure or a shield and it can be made of different materials, such as for instance glass, a metal or plastic. It can also be provided as a foam, filled with air or a further fluid as insulation. It is advantageous to provide an insulating casing since this casing can be easily arranged such that the magnetocaloric regenerator arrangement is hermetically surrounded by the insulating casing. The magnetocaloric device according to the invention can therefore lead to cheap and simple additional production steps compared to prior art magnetocaloric devices.
In a preferred variant of the previous development, the insulation has a lower thermal conductivity than atmospheric air. This is particularly advantageous for providing a thermal insulation of the magnetocaloric regenerator arrangement. In another variant, the insulation has a higher thermal conductivity, as it is the case for an example for an insulation casing that is filled with a foam.
In an alternative development, the insulating means is an insulating coating, which is completely in contact with the magnetocaloric regenerator arrangement. The insulating coating might be for instance a foam, a varnish, a paint or a foil. The insulating coating can advantageously protect the magnetocaloric element against influences of the environment, such as rain, dust or dirt. It is particularly simple to provide an insulating coating that hermetically surrounds the magnetocaloric arrangement by automated production steps.
In a preferred development of the magnetocaloric device the flow-trough is arranged to leave a gap between insulating casing and the at least first and second channel and a sealing member is arranged to seal the gap. In a variant of this development, the at least first and second channel are configured to be rotated with respect to the casing and the sealing member is formed as a rotational seal or as a sealing bearing allowing a rotation of the at least first and second channel while sealing the gap to the insulating casing. This can be particularly advantageous for the magnetocaloric device, wherein the first and the second channel are integrated into a crankshaft that rotates the field generator with respect to the magnetocaloric regenerator arrangement.
Futhermore, the sealing member may be chosen in order to thermally disconnect the component from the insulating casing. In a variant of this development, this is realized by using a material with low thermal conductivity compared to the materials that the insulating materials and the shaft are made from. This can be ceramic materials, polymeric materials, metals or metal alloys with comparatively low thermal conductivity, or a combination thereof. Furthermore, the shape can be such that advantageously little cross section exists for thermal conduction from the component to the insulating casing, or a porous or hollow structure can decrease the thermal connection between the at least first and second channel and the insulating casing.
In a further preferred development, the magnetocaloric device further comprises a filling valve arranged at the insulating casing and configured to allow a filling of the insulating casing with the insulation. The filling valve can provide a comfortable way for the filling of the magnetocaloric device with the insulation. In a variant, the filling valve is further configured to allow an emptying of the insulating casing, in particular an emptying into an appropriate insulation storage box. This can be advantageous in order to change the insulation or for a repairing of parts of the magnetocaloric device. During an operation of the magnetocaloric device, the filling valve of this development is arranged to seal a valve opening of the insulating casing, which is provided by the sealing valve. In a preferred variant, the insulating casing can just be filled via the filling valve by using a respective filling device, which is configured with respect to a design of the filling valve.
In a further development the insulation is a dry gas. In a variant of this development, the dry gas comprises dry air and/or an inert gas such as nitrogen, helium, neon, argon, krypton, or xenon. Compared to atmospheric air, which has a thermal conductivity of about 0.024 W/(mK) at a temperature of 25° C., argon has a thermal conductivity of about 0.016 W/(mK) and krypton of about 0.009 W/(mK) at a temperature of 25° C. Thus, the insulation of this variant can advantageously reduce the thermal conductivity in a surrounding of the magnetocaloric element.
In a further development the insulation comprises a foam, preferably a foam combined with a gas. In a variant of this development, the foam is combined with solids, as for example milled graphite, which can lead to an advantageously low thermal conductivity of the insulation.
In a further development of the magnetocaloric device a drying agent is provided in the insulating means, preferably in a carrier that is arranged within the insulating means. The drying agent can additionally support a drying of the insulation. Thus the drying agent can reduce the thermal conductivity of the surrounding of the magnetocaloric element and therefore advantageously improve the efficiency of the magnetocaloric device. The drying agent is preferably formed by an inert substance which can be advantageously arranged in the carrier within the insulation means, in a preferred variant of this development. Thereby, the drying agent that is arranged in the carrier is also in contact with the insulation in order to support the drying of the insulation. Furthermore, another advantage of the drying agent is that it can in case of leakage and therefore gradual penetration of humidity into the insulating means a drying of this humidity during operation and after days and years of operation without having to perform maintenance on the system. Non-limiting examples for the drying agent are silica, silica gel, calcium chloride, metal organic framework materials, a molecular sieve arranged within the insulating means, aluminium oxide, calcium, calcium oxide, calcium hydroxid, calcium sulphate, potassium carbonate, potassium hydroxide, copper sulphate, lithium aluminium hydride, sodium hydroxid, sodium sulphate, magnesium sulphate, zeolites and superabsorbent.
In a further preferred development, the field generator and the magnetocaloric regenerator arrangement are both located in the insulating means. In a preferred variant of this development, the field generator comprises a first and a second magnetic body and the magnetocaloric regenerator arrangement is arranged in a magnetic gap formed by the first and second magnetic body. The magnetic gap can be small in this development, since the magnetic gap is located in the insulating means so that consequently the insulating means is not located in the magnetic gap. A decreasing magnetic gap increases the external magnetic field. Therefore, a small magnetic gap can improve the efficiency of the magnetocaloric device and thereby reduces costs arising during an operation of the magnetocaloric device. Particularly, the field generator of this development can be provided in small sizes if the magnetic gap is small. Thereby the material and production costs of the field generator might be reduced. The insulating means of this development is preferably formed by the insulating casing. The insulating casing allows an insulator to be provided even within a small magnetic gap of the magnetocaloric device.
In a further development of the magnetocaloric device all further parts of the magnetocaloric device are located in the insulating means. Further parts can be a motor that rotates the magnetocaloric regenerator arrangement with respect to the field generator and a crankshaft that connects the motor with the magnetocaloric regenerator arrangement or with the field generator. No further part according to this development is a heat exchanger which is connected to the fluid directing system of the magnetocaloric device. In order to not disturb a heat exchange of the heat exchanger by the insulating material, the heat exchanger is arranged outside of the insulating means. Preferably, the insulating means of the magnetocaloric device of this development is configured to provide an access for electrical connectors, in order to provide the motor inside the insulating means with electrical power from outside of the insulating means.
In a further development the insulating casing is formed as an evacuable vacuum chamber. The thermal conductivity of a gas in the insulating casing just depends on, i.e. is proportional to a level of pressure, if the mean free path of a particle within the gas is larger than a distance between walls of the insulating casing or the distance between other components in the insulating casing preferably such parts that are at different relative temperatures more preferably the distance especially the shortest distance between magnetocaloric regenerator and magnet assembly. Thus, the smaller the magnetic gap, the larger can be the level of pressure without loosing a proportional dependence between thermal conductivity and level of pressure. The mean free path of particles in a medium vacuum can be larger than several meters. Thus, by reducing the amount of gas particles in the insulating casing, the thermal conductivity can by decreased, depending on a level of pressure, which is below atmospheric pressure. The mean free path of a particle in a fluid further depends on the mass of the particle. Therefore, it can be advantageous to use heavy gases as insulation in order to reduce the mean free path and therefore reduce the thermal conductivity of the insulation.
In a preferred development, the magnetocaloric device comprises a crankshaft, which is arranged and configured to move the magnetocaloric regenerator arrangement and the field generator with respect to each other during an operation of the magnetocaloric device, and wherein the insulating means allows an access to the crankshaft from an outer side of the insulating means. The access is preferably provided by a further opening of the insulating means, wherein the opening is arranged to leave a shaft gap between insulating means and the crankshaft and wherein a shaft sealing member is arranged to seal the shaft gap. In a variant, the shaft sealing member is formed as a rotational seal or as a sealing bearing allowing a rotation of the crankshaft while sealing the gap to the insulating means.
Futhermore, the shaft sealing may be formed in order to thermally disconnect the shaft from the insulating means. In a variant, this is realized by using a material with a low thermal conductivity compared to the materials that the insulating materials and the shaft are made from. This can be ceramic materials, polymeric materials, metals or metal alloys with low thermal conductivity, or a combination thereof. Furthermore, the shape can be such that advantageously little cross section exists for thermal conduction from the shaft to the insulating means, or a porous or hollow structure can decrease the thermal connection between the crankshaft and the insulating means.
In a further development, the magnetocaloric device further comprises a support structure, which is arranged to support the field generator and the magnetocaloric regenerator arrangement, and wherein the insulating means allows an access to the support structure from the outer side of the insulating means to allow an attaching of the magnetocaloric device to an external object. The support structure can improve a robustness of the magnetocaloric device. The access according to this development can be provided by screw holes that are provided to attach the support structure at the external object via screws. In a variant, the support structure is further arranged to provide a constant distance between insulating means and magnetocaloric regenerator arrangement over time.
In a further development, the magnetocaloric device comprises at least one further magnetocaloric regenerator arrangement comprising a further magnetocaloric element, wherein the magnetocaloric element comprises magnetocaloric material, and wherein the further magnetocaloric regenerator arrangement is arranged to be exposed to the changing external magnetic field, and wherein a further insulating means is provided such that the further magnetocaloric regenerator arrangement is located in the insulating means. The further magnetocaloric regenerator arrangement can increase a total amount of magnetocaloric material exposed to the external magnetic field and therefore increase the efficiency of the magnetocaloric device. Alternatively, one insulating means can be provided for both the first and any further magnetocaloric regenerator arrangement. This could reduce the costs of such a combined system.
The insulating casing can be made from metal preferably thin metal such as sheet metal, preferably stainless steel. Alternatively, plastic preferably engineering plastics such as PVC, ABS, Ultrason, etc. can be used. The insulating casing can furthermore be part of another component of the magnetocaloric heat pump or of the device, the magnetocaloric heat pump is part of. This may for example be the housing or the insulation or the support structure of a refrigeration, air-conditioner, or a heat pump in general.
The invention will be apparent and elucidated with reference to the embodiments described hereinafter.
In the following, the drawing shows in:
The magnetocaloric device 100 of this first embodiment is a magnetocaloric heat pump, which comprises the field generator 120, comprising the magnetic gap 125 between a first magnet assembly 126 and a second magnet assembly 128, and a magnetocaloric regenerator arrangement 130, arranged in the magnetic gap 125. The magnetocaloric regenerator arrangement 130 comprises a plurality of magnetocaloric elements 132, wherein each of the magnetocaloric elements 132 comprises magnetocaloric material 135, and wherein the magnetocaloric regenerator arrangement 130 is arranged to be exposed to a periodically changing external magnetic field 122, which is provided by the field generator 120.
The magnetocaloric device 100 further comprises a fluid directing system 140, comprising a first 141, a second 142, a third 143 and a fourth 144 channel, arranged to direct a cold fluid through the first channel 141 to the magnetocaloric regenerator arrangement 130 and to direct the cold fluid through the second channel 142 away from the magnetocaloric regenerator arrangement 130, and to direct a hot fluid through the third channel 143 to the magnetocaloric regenerator arrangement 130 and to direct the hot fluid through the fourth channel 144 away from the magnetocaloric regenerator arrangement 130. The fluid is thereby directed according to magnetization and demagnetization phases of a process cycle of the magnetcaloric heat pump 100, wherein the process cycle is well known by prior art. The cold fluid, which is directed through the second channel 142 away from the magnetocaloric regenerator arrangement 130 is directed to a first heat exchanger 146 before it is again directed through the first channel 141 to the magnetocaloric regenerator arrangement 130. The hot fluid, which is directed through the fourth channel 144 away from the magnetocaloric regenerator arrangement 130 is directed via a pump 147 to a second heat exchanger 148 before it is again directed through the third channel 143 to the magnetocaloric regenerator arrangement 130.
According to the invention, the magnetocaloric device 100 further comprises the insulating casing 110, wherein the magnetocaloric regenerator arrangement 130 is located in the insulating casing 110 and the insulating casing 110 is arranged such that the magnetocaloric regenerator arrangement 130 is hermetically surrounded by the insulating casing 110 with a flow-through 150 for a passing of the fluid through the first 141, second 142, third 143 and fourth 144 channel. The flow-trough 150 is arranged to leave a gap between insulating casing 110 and the channels 141, 142, 143, 144 and a flow sealing member 155 is arranged to seal the gap. Furthermore, the insulating casing 110 is filled with an insulation 160 that has a lower thermal conductivity than atmospheric air.
In the depicted embodiment, the insulation 160 is dry air and a drying agent 165 is additionally provided in a carrier 168 that is arranged within the insulating casing 110. The drying agent 165 additionally reduces a humidity of the dry air, in order to reduce the thermal conductivity of the insulation 160. In an embodiment not shown, the insulating casing is formed as an evacuable vacuum chamber.
The insulating casing 110 is arranged in the magnetic gap 125 of the field generator 120. A motor 170 of the magnetocaloric device 100 is connected to a power supply (not shown) via electrical connectors 175 and is arranged to rotate the first and second magnet assembly 126, 128 of the field generator 120 during an operation of the magnetocaloric device by rotating a crankshaft 180 that is attached to the first and second magnet assembly 126, 128. The insulating casing 110 allows an access to the crankshaft 180 from an outer side of the insulating casing 110. The access is provided by a first and a second opening 182, 184 of the insulating casing 130, wherein the first and second opening 182, 184 is arranged to leave a shaft gap between insulating casing 110 and the crankshaft 180 and wherein a respective shaft sealing member 185 is arranged to seal the respective shaft gap. The shaft sealing member 185 is formed as a rotational seal allowing a rotation of the crankshaft 180 while sealing the shaft gap to the insulating casing 110. In an embodiment not shown, the sealing member is formed as a sealing bearing.
In further preferred embodiments, any kind of insulation means is arranged in the magnetic gap instead of an insulating casing. In particular, an insulating coating is provided in a preferred embodiment not shown, wherein the insulating coating is completely in contact with the magnetocaloric regenerator arrangement. The insulating coating can be for instance a foam, a varnish, a paint or a foil.
In a further embodiment not shown, the crankshaft is arranged to rotate the magnetocaloric regenerator arrangement while the field generator is fixed. The channels of the fluid directing system of this further embodiment are arranged in the crankshaft and connected to the magnetocaloric regenerator arrangement via rotary valves.
The insulating casing 110 further comprises a filling valve 188 arranged at the insulating casing 110 and configured to allow a filling of the insulating casing 110 with the insulation 160. The filling valve 188 is further configured to allow an emptying of the insulating casing 110, in particular an emptying into an appropriate insulation storage box.
The magnetocaloric device 100 according to the embodiment shown in
In an embodiment not shown, the magnetocaloric device comprises at least one further magnetocaloric regenerator arrangement comprising a further plurality of magnetocaloric elements, wherein each of the magnetocaloric elements comprises magnetocaloric material, and wherein the further magnetocaloric regenerator arrangement is arranged to be exposed to the periodically changing external magnetic field, and wherein a further insulating casing is provided such that the further magnetocaloric regenerator arrangement is located in the insulating casing. In this embodiment, the magnetocaloric regenerator arrangement and the further magnetocaloric regenerator arrangement are both arranged in the magnetic gap of the field generator. In a further embodiment not shown, the magnetocaloric device is provided such that the first magnetic assembly, the magnetocaloric regenerator arrangement, the second magnetic assembly, the further magnetocaloric regenerator arrangement and a third magnetic assembly are arranged in this order along the crankshaft. In an alternative embodiment not shown, an insulating casing is provided such that the magnetocaloric regenerator and the further magnetocaloric regenerator are located in the insulating casing.
The magnetocaloric device 200 is arranged as the magnetocaloric device 100 shown in
For embodiments, wherein the magnetocaloric regenerator arrangement and the field generator are located inside the insulating means, the use of an insulating casing as insulating means, as shown in
The support structure 190 is arranged as shown in
In contrast to the magnetocaloric device 100 shown in
Furthermore, the support structure 340 is arranged in the insulating casing 310 in contrast to the support structure 190, illustrated in
In an embodiment not shown, the motor is further insulated by an additional insulating casing, which guides heat from the motor to an outside of the insulating casing, preferably with cooling fins that connect the additional insulating casing with the insulating casing. Thus, the device of this embodiment advantageously reduces a heat production inside the insulating casing, compared to the embodiment shown in
100 magnetocaloric device
105 insulating means
110 insulating casing
120 field generator
122 external magnetic field
125 magnetic gap
126 first magnet assembly
128 second magnet assembly
130 magnetocaloric regenerator arrangement
132 magnetocaloric element
135 magnetocaloric material
140 fluid directing system
141 first channel
142 second channel
143 third channel
144 fourth channel
146 first heat exchanger
147 pump
148 second heat exchanger
150 flow-trough
155 flow sealing member
160 insulation
165 drying agent
168 carrier
170 motor
175 electrical connector
180 crankshaft
182 first opening
184 second opening
185 shaft sealing member
188 filling valve
190 support structure
195 external object
200 second embodiment of the magnetocaloric device
205 insulating means of the second embodiment
210 insulating casing of the second embodiment
220 bearing of the crankshaft
300 third embodiment of the magnetocaloric device
305 insulating means of the third embodiment
310 insulating casing of the third embodiment
320 bearing of the crankshaft of the third embodiment
330 connection opening
340 support structure of the third embodiment
| Number | Date | Country | Kind |
|---|---|---|---|
| 16162288.1 | Mar 2016 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2017/056869 | 3/22/2017 | WO | 00 |
