The present invention relates to magnetocaloric devices for use in refrigeration, heat pump, or power generation applications.
Based on
It is thus an object of the present invention to provide an efficient magnetocaloric device.
According to a first aspect, a magnetocaloric device is provided, comprising at least one magnetocaloric material embedded between two heat transfer structures; and at least one electric source for generating a magnetic field. With the magnetocaloric material being embedded between the heat transfer structures, heat transfer from and to the magnetocaloric material can be achieved in an efficient manner without the need for any working fluid to flow through the porous structure of the magnetocaloric material. Thus, the device can be miniaturized, since there is no need to provide large pores or voids within the magnetocaloric material. The magnetocaloric device of the present invention further comprises at least one hydraulic circuit in which the working fluid flows in a constant direction and which comprises at least one propulsion means for the working fluid. Thus, the working fluid can constantly flow past the respective heat transfer structures and can thus provide an efficient transport of heat in the magnetocaloric device.
According to embodiments, the heat transfer structures may comprise at least one thermal switch which is adapted to vary transfer or transport of the heat from the magnetocaloric material to the hydraulic circuit or from the hydraulic circuit to the magnetocaloric material. Thus, the direction of the heat transfer to and from the magnetocaloric material can be efficiently controlled using the at least one thermal switch.
According to further embodiments, the heat transfer structures may comprise at least one multifunctional coating which is adapted to affect the wetting effect of the working fluid, or/and to affect the thermal or velocity boundary layer of the working fluid, or/and to affect the chemical protection of the magnetocaloric material, and/or to affect the mechanical properties of the magnetocaloric material, and/or to affect the effective thermal properties of the magnetocaloric material and the multifunctional layer.
According to further embodiments, the heat transfer structures may comprise at least one means for time varying fluctuation of the heat transfer from the hydraulic circuit to the magnetocaloric material or for time varying fluctuation of the heat transfer from the magnetocaloric material to the hydraulic circuit, wherein the time varying fluctuation of the heat transfer may be provided by a time dependent variable fluid flow above and/or below the magnetocaloric material. Thus, the heat transfer between the magnetocaloric material and the hydraulic circuit may be controlled by the heat transfer structures such that, during a first time period, heat is transferred substantially only from the hydraulic circuit to the magnetocaloric material and that, after changing the heat transfer properties of the heat transfer structures, during a second time period, heat is transferred substantially only from the magnetocaloric material to the hydraulic circuit.
According to embodiments, the electric source may comprise electric windings, a core for the manipulation of the magnetic flux direction, and an electric circuit which enables the regeneration of magnetic energy.
The electric source may be adapted to perform a time dependent variation of increasing or decreasing magnetic field intensity in the range between 0.0001 to 5 seconds. Alternatively or additionally, the electric source may be adapted to perform a variation of the magnetic field intensity in the range between 0 to 40 Tesla. Thus, the electric source can provide e.g. a magnetic field intensity at high frequencies, so that the individual thermodynamic cycles of the magnetocaloric device are repeated at high frequencies in the range of 0.2 Hz-1 kHz.
According to embodiments, the magnetocaloric device may perform refrigeration, heat pumping or power generation by one of a magnetic Brayton, magnetic Stirling, magnetic Carnot, or magnetic Ericsson cycle.
According to embodiments, the magnetocaloric device may perform refrigeration, heat pump or power generation by non-conventional thermodynamic cycles, comprising a combination of magnetic isofield process(es), and/or magnetic isothermal magnetization or demagnetization, and/or magnetic isentropic or polytropic magnetization or demagnetization, and/or isomagnetization process(es).
According to embodiments, the hydraulic circuit with the working fluid may be connected to at least one heat exchanger, such as a heat source or/and a heat sink heat exchanger.
According to embodiments, the working fluid propulsion may be created by ionic, or magnetohydrodynamic, or magnetocaloric, or magnetorheologic, or ferrofluidic, or electrocaloric, or electrowetting, or electrophoeretic, or electrokinetic, or electrohydrodynamic principles.
According to embodiments, the working fluid propulsion may be created by at least one piston, or by at least one turbine, or at least one membrane, or at least one peristaltic mechanism, or at least one ejector principle, or at least one magnetohydrodynamic principle, or at least one electrohydrodynamic or electrokinetic principle, or at least one electrophoretic principle, or at least one electrowetting principle, or at least one ferrohydrodynamic principles, or at least one magnetorheologic principle.
The magnetocaloric material may be any material which exhibits the magnetocaloric effect in the range of temperature between 0 to 3000 K.
According to embodiments, a plurality of magnetocaloric materials may be used, each of which having a Curie temperature in the range between 0 to 3000 K.
According to embodiments, at least one or several magnetic field sources and several magnetocaloric materials may be present in order to provide an upgrade from the micro-scale to the macroscopic device for refrigeration or heat pumping, or power generation.
According to embodiments, the device may comprise at least one magnetic field source and a plurality of magnetocaloric materials, wherein each magnetocaloric material is embedded between two heat transfer structures, and wherein a common hydraulic circuit is provided such that the heat transfer structures are adapted to control the transfer or transport of heat between each magnetocaloric material and the working fluid. Thus, a macro-scale magnetocaloric device can be provided by using a minimum of one, but rather a plurality of micro-scale assemblies comprising respective magnetocaloric material and heat transfer structures. Therein, the micro-scale assemblies may be combined with a common magnetic field source, such as e.g. a multi-pole magnetic field source, or may be provided with a plurality of magnetic field sources.
Moreover, in a special case, the magnetic field source can represent a combination of the electric coil, combined with permanent magnets.
According to embodiments, a plurality of magnetocaloric devices as described above may be combined to form a cascade system. A cascade system comprises a plurality of magnetocaloric devices, where in the case of refrigeration or heat pumping, the heat sink of the first device with lowest temperature represents heat source of the second stage, etc.
According to embodiments, a heat transfer structure comprising at least one thermal switch may be based on anisotropy of the thermal conductivity of the thermal switch material. Alternatively, the thermal switch may comprise at least one thermal switch composite material which exhibits anisotropy of the effective thermal conductivity. In this particular case, the anisotropy of the thermal conductivity of the thermal switch changes with external influences (e.g. temperature change, magnetic or electric means or others). The aim of such principle is that a thermal switch material or composite allows heat to flow in desired direction at the certain temperature, and prevents or decreases the rate of heat to flow in that direction at another temperature.
Alternatively, the thermal switch may be based on mechanical contact by elastomer materials, or liquid crystals, or on ferrofluids, or magnetorheologic principles, or liquid metals, or electrorheologic principles or magnetohydrodynamic principles or electrowetting, or electrophoeretic or electrokinetic or electrohydrodynamic principles. In this particular case, the thermal switch, being in the state of solid, suspension, or liquid, represents a thermal contact, which can be manipulated by electricity, magnetism, or thermal effects. When heat need to be removed from the magnetocaloric material, this kind of thermal switch absorbs heat from the magnetocaloric material (when this is in magnetized state), and by manipulation of in this paragraph mentioned mechanisms, changes its shape or position in order to perform a mechanical contact heat to the heat sink (vie e.g. the extended surface). When the magnetocaloric material is demagnetized (e.g. cold), the same thermal switch prevents heat to flow from the heat sink (e.g. via extended surface) to the magnetocaloric material. However, another thermal switch at this time provides a mechanical contact between the heat source (via another extended surface) and the magnetocaloric material.
As a further alternative, the thermal switch principle may be based on thermoelectric (Peltier or Seebeck), or thermionic, or spincaloritronic (spin Peltier or spin Seebeck). Also in this case, as an example, the magnetocaloric material may be embedded between two thermal switches or e.g. its upper and lower surface. The thermal switch in this case may act as a heat pump which is on one side attached to the magnetocaloric material and on the other side attached to the extended surface. When the magnetocaloric material is magnetized, then the e.g. upper thermal switch is set on (e.g. by setting the electric current flow). Heat is ballistically transported from the magnetized magnetocaloric material to the extended surface. At the same time, the lower thermal switch is set off, thus preventing heat flow from the magnetocaloric material to the heat source (via the lower extended surface). When the magnetocaloric material is demagnetized, then the upper thermal switch is set off, and the lower thermal switch is set on, thus heat is pumped from the heat source (via the lower extended surface), to the magnetocaloric material.
According to a further aspect, a magnetocaloric device is provided, comprising at least one magnetocaloric material embedded between two heat transfer structures. The device further comprises at least one electric source for generating a magnetic field, wherein the electric source enables regeneration of the magnetic energy, and at least one hydraulic circuit which comprises at least one propulsion means for the working fluid, wherein the heat transfer structures are adapted to control the transfer or transport of heat between the magnetocaloric material and the working fluid. Thus, during each cycle of the magnetocaloric device according to the further aspect, at least some of the magnetic energy produced by the electric source can be regenerated, so that the overall energy efficiency of the device can be increased.
According to embodiments, the electric source may comprise an electromagnet and an energy collector device. The energy collector device may be used for storing at least some of the energy of the magnetic field of the electromagnet, and may further be used to supply the stored energy to the electromagnet for generating a magnetic field in a subsequent operation cycle or operation phase of the device. Therein, the electric source may be adapted to charge the energy collector device when the magnetic field of the electromagnet is turned off, and use the charged energy collector device for generation of a magnetic field in the electromagnet when the magnetic field is turned on.
According to embodiments, the electric source may further comprise a first switching device for connecting the electromagnet to the energy collector device for charging the energy colletor device and a second switching device for connecting the energy collector device to the electromagnet for turning on the magnetic field in the electromagnet by releasing the energy stored in the energy collector device to start the current flow through the electromagnet.
According to embodiments, the energy collector device may comprise a battery or a capacitor.
According to embodiments, the magnetic field may be generated by at least one electric source and at least one permanent magnet material. Thus, a permanent magnet may be used for generation of the magnetic field for magnetizing the magnetocaloric material. Additionally, the electric circuit may enable regeneration of the magnetic energy in order to ensure a high energy efficiency of the magnetocaloric device.
Embodiments of the invention will now be described with reference to the drawings, in which like reference numerals denote the same or corresponding elements, and in which:
In the following description of various embodiments, reference will be made to the drawings, in which like reference numerals denote the same or corresponding elements. The drawings are not necessarily to scale. Instead, certain features may be shown exaggerated in scale or in a somewhat simplified or schematic manner, wherein certain conventional elements may have been left out in the interest of exemplifying the principles of the invention rather than cluttering the drawings with details that do not contribute to the understanding of these principles.
It should be noted that, unless otherwise stated, different features or elements may be combined with each other whether or not they have been described together as part of the same embodiment below. The combination of features or elements in the exemplary embodiments are done in order to facilitate understanding of the invention rather than limit its scope to a limited set of embodiments, and to the extent that alternative elements with substantially the same functionality are shown in respective embodiments, they are intended to be interchangeable, but for the sake of brevity, no attempt has been made to disclose a complete description of all possible permutations of features.
Furthermore, those with skill in the art will understand that the invention may be practiced without many of the details included in this detailed description. Conversely, some well-known structures or functions may not be shown or described in detail, in order to avoid unnecessarily obscuring the relevant description of the various implementations. The terminology used in the description presented below is intended to be interpreted in its broadest reasonable manner, even though it is being used in conjunction with a detailed description of certain specific implementations of the invention.
In a first embodiment, as shown in
The basic operation is the following. When the magnetic field source 2 is switched on, the thermal switch TDhot is in operation, thus representing a means for thermal transport from the magnetocaloric material 5 to the extended surface EShot. Through the extended surface EShot, the working fluid flows in a direction from the heat source heat exchanger CHEX to the heat sink heat exchanger HHEX, wherein the propulsion of the working fluid is provided by the pumping means 6 or by any other working fluid propulsion system. In this manner, the working fluid absorbs heat from the extended surface EShot and rejects it in the HHEX. Before the magnetic field source 2 is switched off, operation of the thermal switch mechanism TDhot is deactivated. Thus, thermal transport between the magnetocaloric material and the extended surface EShot can be prevented, wherein the deactivated thermal switch may represent an adiabatic barrier. When the magnetic field source 2 is switched off, the thermal switch mechanism TDcold is activated, thus representing a means for thermal transport to the magnetocaloric material 5 via the thermal switch from the extended surface EScold. Through the extended surface EScold, the working fluid flows in a direction from the heat sink heat exchanger HHEX to the heat source heat exchanger CHEX, wherein the propulsion of the working fluid is provided by the pumping means 6 or by any other working fluid propulsion system. In this manner, the working fluid transfers heat from the extended surface EScold via the thermal switch TDcold to the magnetocaloric material. 5 This cycle is then repeated. The working fluid may flow continuously or discontinuously, depending on desired thermodynamic cycle. Furthermore, the working fluid flow, the operation of thermal switch mechanisms and the operation of the magnetic field source can be tuned in a manner that the micro-magnetocaloric device operates with different thermodynamic cycles.
In a third embodiment of this invention, the micro-magnetocaloric device 1 as shown in
The basic operation of the micro-magnetocaloric device 1 according to the third embodiment is the following. The magnetic field source 2 may comprise at least one iron or soft ferromagnetic material core 3, at least one coil winding 4 or other means for electric current flow, and at least one electric circuit for the control, regulation of operation and regeneration of the magnetic energy. When the magnetic field source 2 is switched on, the coating comprising the multifunctional surface MShot is in operation, thus representing a means to influence the thermal or velocity boundary layer, or wetting of the fluid flow. By this, the heat transfer between the magnetocaloric material 5 and the working fluid is enhanced. The coating comprising the multifunctional surface MShot thus represents a means for influencing the thermal transport from the magnetocaloric material 5 to the working fluid in the extended surface EShot. Through the extended surface Shot, the working fluid flows in a direction from the heat source heat exchanger CHEX to the heat sink heat exchanger HHEX, wherein the propulsion of the working fluid is provided by the pumping means 6 or by any other working fluid propulsion system. The working fluid absorbs heat from the extended surface EShot and the multifunctional surface MShot and rejects it in the HHEX. Before the magnetic field source 2 is switched off, the multifunctional surface MShot is deactivated, thus representing a means to prevent the thermal transport between the magnetocaloric material 5 and the working fluid in the extended surface EShot. The deactivated multifunctional surface MShot may represent an adiabatic barrier by influencing the thermal and velocity boundary layer or wetting of the working fluid. When the magnetic field source 2 is switched off, the multifunctional surface MScold is activated, thus representing a means for thermal transport from the working fluid in the extended surface EScold to the magnetocaloric material 5, by influencing the thermal and velocity boundary layer or wetting of the working fluid. Through the extended surface EScold, the working fluid flows in a direction from the heat sink heat exchanger HHEX to the heat source heat exchanger CHEX, wherein the propulsion of the working fluid is provided by the pumping means 6 or by any other working fluid propulsion system. In this manner, the working fluid transfers heat from the extended surface EScold and the multifunctional surface MScold to the magnetocaloric material 5. This cycle is then repeated. The working fluid may flow continuously or discontinuously, depending on desired thermodynamic cycle. Furthermore, the working fluid flow, the operation of multifunctional coatings and the operation of the magnetic field source 2 can be tuned in a manner that the micro-magnetocaloric device operates with different thermodynamic cycles.
In the fourth embodiment of this invention, as shown in
Each of these coatings are attached to or represent a part of the fluid flow channels provided by extended surfaces, denoted by extended surface EScold and extended surface EShot, respectively. The basic operation of the micro-magnetocaloric device 1 according to the fourth embodiment is the following. The magnetic field source 2 comprises at least one iron or soft ferromagnetic material core 3, at least one coil winding 4 or other means for electric current flow, and at least one electric circuit for the control, regulation of operation and regeneration of the magnetic energy. When the magnetic field source 2 is switched on, the coating comprising the multifunctional surface MShot is in operation, thus representing a means to influence the thermal or velocity boundary layer, or wetting of the fluid flow. By this, the heat transfer between the magnetocaloric material 5 and the working fluid is enhanced. The multifunctional surface MShot thus represents a means for thermal transport from the working fluid to the magnetocaloric material 5. Through the extended surface EShot, the working fluid flows in a direction from the heat source heat exchanger HHEX to the heat sink heat exchanger CHEX, wherein the propulsion of the working fluid is provided by the pumping means 6 or by any other working fluid propulsion system. In this manner, the working fluid transfers heat to the extended surface EShot and the multifunctional surface MShot. In the heat sink heat exchanger CHEX, the working fluid rejects heat out of the system. Before the magnetic field source 2 is switched off, the multifunctional surface MShot is deactivated, thus representing a means to prevent the thermal transport between the magnetocaloric material and the working fluid in the extended surface EShot by influencing the thermal and velocity boundary layer or wetting of the working fluid. Therein, the deactivated multifunctional surface MShot may represent an adiabatic barrier. When the magnetic field source 2 is switched off, the multifunctional surface MScold is activated, thus representing a means for thermal transport from the magnetocaloric material 5 via the extended surface EScold and the multifunctional surface MScold to the working fluid, by influencing the thermal and velocity boundary layer or wetting of the working fluid. Through the extended surface EScold, the working fluid flows in a direction from the heat sink heat exchanger CHEX to the heat source heat exchanger HHEX, wherein the propulsion of the working fluid is provided by the pumping means 6 or by any other working fluid propulsion system. In this manner, the magnetocaloric material 5 transfers heat to the working fluid via the extended surface EScold and the multifunctional surface MScold. This cycle is then repeated. The working fluid may flow continuously or discontinuously, depending on desired thermodynamic cycle. Furthermore, the working fluid flow, the operation of multifunctional coatings and the operation of the magnetic field source 2 can be tuned in a manner that the micro-magnetocaloric device operates with different thermodynamic cycles.
In the ninth embodiment as shown in
A tenth embodiment, as shown in
The various embodiments illustrated in
Further alternative embodiments are illustrated in
According to the first alternative embodiment as shown in
In the third alternative embodiment, as shown in
In all of the embodiments of the present invention, an electric circuit, as a part of the magnetic field source, may enable the regeneration of the magnetic energy. Embodiments of electric circuits are shown in
The energy of the magnetic field of the electromagnet can be equivalently expressed as
Emagn=½LI2,
where L is the inductance of the electromagnet and I is the current that flows through the coil of the electromagnet. As shown in
To turn on the magnetic field in the electromagnet, the switch S2 is used to release the energy stored in the energy collector to start the current flow through the electromagnet.
Due to resistive losses and losses of the energy collector device, a voltage source V is required, which maintains the current, once the current flow is established.
The circuit primarily acts as an efficient switching and energy storage device. The operation, combined with magnetocaloric material, is the following. In the case of refrigeration or heat pumping, the following steps are performed. When the magnetic field turns on (S2 turns on), the magnetocaloric material heats up, then heat transfer between the magnetocaloric material and working fluid is established (via advanced heat transfer solutions presented in this invention) so the magnetocaloric material dissipates heat into the working fluid. When the magnetic field is turned off (S1 turns on), the magnetocaloric material cools and when brought in contact with the working fluid (via advanced heat transfer solutions presented in this invention), it absorbs heat from the working fluid.
When the magnetocaloric device 1 operates as a heat engine (power generator), the procedure is reversed. The operation for the Carnot thermodynamic cycle will be described, however one should note that also other thermodynamic cycles can be developed. In the first stage (
When the steps 1., 2., 3., 4. are carried out, the current in the electromagnet changes in time as depicted in
For all embodiments of the invention, the magnetic field source 2 with the regeneration of magnetic energy, as described above, may also represent a structure in which the magnetocaloric material 5 is embedded. Some embodiments thereof are shown in
The effects of applying the alternative embodiments shown in
As an alternative to any of given solutions in this invention, the magnetic field source, besides of an electric coil, may comprise an additional permanent magnet material.
Number | Date | Country | Kind |
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15172694.0 | Jun 2015 | SI | national |
Filing Document | Filing Date | Country | Kind |
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PCT/EP2016/064053 | 6/17/2016 | WO | 00 |