CN102706028A - Magnetic cold storage device for magnetic refrigerator - Google Patents

Abstract

The invention discloses a thermal switch magnetic cold storage device for a magnetic refrigerator, which is used to be arranged in a controllable magnetic field source. The device includes a magnetic cold storage and a heat transfer assembly constituting a heat transfer circuit. The heat transfer assembly includes at least A thermal switch unit, the magnetic regenerator is a container containing magnetic working fluid, and a part of the thermal switch unit is arranged inside the magnetic regenerator in contact with the magnetic working medium, so that the magnetic working medium can effectively transmit heat to the outside during the change of the magnetic field transport. Thermal switches are thermal diodes, superconducting switches, magnetothermal switches or other forms of heat transfer control devices, and magnetic working fluids are solid, liquid or other forms of magnetocaloric materials. Under the action of the controllable magnetic field, the magnetic working medium releases heat to the heat source in the magnetization stage and absorbs heat to the cold source in the demagnetization stage, so as to achieve the purpose of refrigeration. The device has excellent heat transport directionality and efficient magneto-thermal coupling mechanism, and has the advantages of high efficiency, compact structure, stable operation and good economy.

Description

A magnetic cold storage device for a magnetic refrigerator

technical field

The invention belongs to the application field of clean energy magnetic refrigeration technology, and specifically relates to a magnetic cold storage device for a magnetic refrigerator, which can improve the energy conversion efficiency, reliability, economy and practicability of electromagnetic energy and thermal energy.

Background technique

Magnetic refrigeration is based on the application of the magnetocaloric effect (MCE) of magnetic materials in the field of refrigeration. The magnetocaloric effect is an inherent characteristic of magnetic materials. When the magnetic material is magnetized by the external magnetic field, the magnetic order of the system is strengthened (the magnetic entropy decreases), and it releases heat to the outside world; when the external magnetic field is removed and demagnetized, the magnetic order decreases (the magnetic entropy increases), absorb heat from the outside. The processes of excitation, heat absorption, demagnetization, and heat release form a closed thermodynamic cycle. Through the change of the external magnetic field, the magnetic entropy is controlled, and the energy conversion based on the magnetocaloric effect can continuously release heat from one end and absorb heat from the other end. for refrigeration purposes.

Magnetic refrigeration technology is an efficient and green refrigeration technology. Compared with the existing general traditional refrigeration technology relying on gas compression and expansion, it has significant advantages:

1. The efficiency of the magnetic refrigeration cycle can reach 30% to 60% of the Carnot cycle, while the refrigeration cycle relying on the compression and expansion of gas can only reach 5% to 10%.

2. Magnetic refrigeration uses magnetic materials as the refrigerant, which has no pollution to the atmosphere and the ozone layer.

3. The entropy density of the magnetic working fluid material is much greater than that of the gas, so the refrigeration device can be made more compact.

4. Magnetic refrigeration can use electromagnets, superconducting magnets, and permanent magnets to provide the required external magnetic field, without a compressor, and without mechanical wear of moving parts. Therefore, it has the characteristics of low mechanical vibration and noise, high working reliability and long service life.

Although magnetic refrigerator technology has significant technical advantages, there are some key technical and technical difficulties in actual design and manufacture.

When the temperature is above 20K, especially near room temperature, the thermal motion of the magnetic ion system is greatly enhanced, and the lattice entropy of the magnetic material increases to a level that cannot be ignored, and part of the cooling capacity of the magnetic refrigeration system will be consumed for cooling the heat load of the lattice. As a result, the cooling capacity of the system is reduced.

Adding a magnetic regenerator in the system can store the heat released by the lattice system in a certain stage of the cycle, and return it to the lattice system in another stage, so that the part of the magnetic refrigeration system used to cool the heat load of the lattice Part of the refrigeration capacity will be used more effectively, the effective entropy change will increase, and the temperature span will increase.

The main scientific issues of magnetic refrigeration technology are the coupling mechanism of electromagnetic energy and thermal energy and the effective heat transport mechanism. From the point of view of improving the thermal efficiency of the magnetic refrigerator, it is necessary to make the cold generated by the MCE take away as much as possible within the cycle of the refrigeration cycle. In this way, in addition to adopting an efficient heat transfer mechanism, it is necessary to reduce heat return and ensure the directionality of heat transfer. appears to be particularly important.

Compared with the existing magnetic refrigerators that use valves to control the direction of heat transfer, magnetic refrigerators that use thermal switches (such as thermal diodes) not only have simple structure and reliable operation, but also can more quickly, directly and effectively control the temperature of the magnetic storage device. Therefore, the magnetic refrigerator using the thermal switch magnetic cold storage device can greatly reduce the irreversible loss in the cycle, so that the actual magnetic refrigeration cycle is closer to the reverse Carnot cycle, so that the magnetic refrigerator can obtain higher thermal efficiency.

The Chinese patent document of CN 2610281Y published on April 7, 2004 "a heat transfer device for magneto-calorie" uses a heat pipe to transfer the heat generated by the magneto-caloric effect, and has the characteristics of simplicity and high efficiency. But the deficiency is that this patent document only serves as a kind of heat transfer device.

The Chinese invention patent publication CN 101115962A disclosed on January 30, 2008 discloses a method for manufacturing a magnetic regenerator for an active magnetic refrigerator. The magnetic material in the active magnetic regenerator is both a magnetic working fluid and a cold storage material. But some main problems of cold storage in the reverse thermodynamic cycle are not involved. Generally speaking, there are very few reports in this area at home and abroad.

Magnetic refrigeration technology is the conversion of electromagnetic energy and thermal energy. The study of magnetothermal coupling mechanism is the main theoretical basis and key technology for breakthroughs in the application of magnetic refrigeration technology. The coupling of electromagnetic transport and thermal transport in the lattice system has both transient timing and strict heat flow directionality. Directional studies addressing heat flow have not been reported.

Contents of the invention

The invention is based on the energy conversion mechanism of the magnetocaloric effect, and provides a magnetic cold storage device for a magnetic refrigerator. The magnetic cold storage device has the characteristics of high efficiency, compact structure, stable operation and good economy.

The invention provides a magnetic cold storage device for a magnetic refrigerator, which is used to be installed in a controllable magnetic field source. The assembly includes at least one thermal switch unit. The magnetic regenerator is a container containing a magnetic working medium. A part of the thermal switch unit is arranged inside the magnetic regenerator to contact the magnetic working medium. During the change of the magnetic field, the magnetic working medium is effectively separated from the outside world. heat transport.

As an improvement of the above technical solution, when only one thermal switch unit is included in the heat transfer assembly, the thermal switch unit is used for the heat release or heat absorption process of the magnetic regenerator, and the heat absorption or heat release process of the magnetic regenerator is controlled by the magnetic The cold storage is connected with valves, pumps, pipelines and heat exchangers to form a circulation circuit to complete.

As a further improvement of the above technical solution, the heat transfer assembly includes at least two thermal switch units, and when used in the same heat flow direction, each thermal switch unit maintains the consistency of the heat transfer direction.

The magnetocaloric effect is the conversion of electromagnetic energy and thermal energy. This is an energy conversion based on a complex magneto-thermal coupling mechanism. It quickly and efficiently converts energy between the spin system and the heat source. Under the action of magnetic field changes and electromagnetic effects , the heat transport characteristics in the magnetic cold storage device of the present invention have both transient time sequence and strict heat flow directionality.

In the magneto-thermal coupling process, the longer the magnetization/demagnetization time of the magnetic material (that is, the period of the magnetic refrigeration cycle), the greater the cooling capacity obtained, but this will lose the efficiency of the magnetic refrigeration device. The invention uses a thermal switch to control the heat transport in the magnetic regenerator under the change of the magnetic field, which can not only efficiently and stably control the direction of heat transport, but also realize the transmission of heat as much as possible within the limited refrigeration cycle time, and greatly reduce the heat The loss makes the refrigeration cycle process of the whole device closer to the reverse Carnot cycle, and the mechanism can be compact and efficient, thereby improving the conversion efficiency of the entire magnetic refrigerator.

The invention solves the problems of common cold storage devices, such as flow dead volume affecting heat transfer, and pipeline fluid backflow loss of cooling capacity when valves are switched on and off, avoiding complex structures of pipelines and valves, difficulty in miniaturization, and low economic efficiency. At the same time, it also solves the problem that the single use of heat pipes as heat transfer devices cannot effectively utilize the magneto-caloric effect of magnetic materials, and establishes a mechanism for high-efficiency magnetic refrigerators to achieve the purpose of using MCE for high-efficiency refrigeration in magnetic refrigerators with thermal switches and magnetic regenerators. The essence is that the actual efficiency of the entire magnetic refrigeration system mainly depends on two aspects, one is the scientific coupling and conversion mechanism of electromagnetic transport and heat transport, and the other is the improvement and optimization of the cold storage and heat transport performance and as far as possible Reduce heat loss during transmission. The magnetic cold storage device has the advantages of high efficiency, compact structure, stable operation and good economy.

Description of drawings

Fig. 1 is the schematic diagram of principle of the present invention;

Fig. 2 is a structural schematic diagram of a magnetic cold storage device using multiple thermal switch structures, wherein (a) is a schematic diagram of the overall structure, and (b) is a top sectional view;

Fig. 3 is the schematic diagram of embodiment 1 of the present invention;

Fig. 4 is the schematic diagram of embodiment 2 of the present invention;

Fig. 5 is a schematic diagram of a thermal switch used in the present invention.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.

As shown in Figure 1 and Figure 2, the thermal switch magnetic cold storage device of the magnetic refrigerator provided by the present invention is set in a controllable magnetic field source, including a magnetic cold storage and at least one thermal switch unit, to complete the magnetic cold storage during the change of the magnetic field The magnetic working medium in the device conducts heat transport with the outside world. The magnetic regenerator is a container containing magnetic working fluid, and a part of the thermal switch unit is arranged inside the magnetic regenerator to be in contact with the working fluid.

The magnetic working medium can be solid (such as metal Gd), liquid (such as liquid magnetic nanocomposite) or other forms of magnetocaloric materials. The cold storage working fluid can be the magnetic working fluid itself, or it can be combined with other heat transfer working fluids. When the magnetic working medium is solid, the magnetic cold storage can be filled with liquid or gaseous heat exchange medium.

When the thermal switch magnetic cold storage device of the magnetic refrigerator is used in combination with flow components such as pipes and valves, the heat exchange medium used may be liquid, gas or other forms of fluid. The thermal switch unit may be a thermal diode, a superconducting switch, a magnetothermal switch or other forms of heat transfer control devices. When a net and a seal are arranged between the cavity of the magnetic cold accumulator and the nozzle, the leakage of the magnetic working medium and the cold storage working medium can be prevented. A thermal insulation structure is provided outside the outer wall of the magnetic cold storage, the outer wall of the thermal switch unit, the outer wall of the pipeline and other components to reduce the loss of heat leakage.

When only one thermal switch unit is included in the heat transfer component, the thermal switch unit is used for the heat release or heat absorption process of the magnetic regenerator. The heat exchangers are connected to form a circulation loop to complete.

When the heat transfer component includes multiple thermal switch units, the number of thermal switch units located at both ends of the magnetic regenerator can be equal or different, and multiple thermal switch units are used to maintain the consistency of the heat transfer direction when used in the same heat flow direction .

In the thermal switch magnetic cold storage device of the magnetic refrigerator, the thermal switch unit includes an enhanced heat transfer component added thereon, and the enhanced heat transfer component can adopt structures such as fins.

Example 1

One of the embodiments of the thermal switch magnetic cold storage device of the magnetic refrigerator of the present invention is that a thermal diode is used as the thermal switch unit, as shown in FIG. 3 . It is placed in the periodic magnetic field provided by the controllable magnetic field source 5 by the magnetic regenerator 3. The upper and lower ends of the magnetic regenerator 3 are respectively connected to a thermal diode 4a, 4b, wherein the evaporation section of the thermal diode 4a is placed in the magnetic regenerator. 3, the condensation section is set at the upper part of the magnetic cold storage 3 and contacts the heat source 7; the condensation section of the thermal diode 4b is placed inside the magnetic cold storage 3, and the evaporation section is set at the lower part of the magnetic cold storage 3 and is in contact with the cold source 6. At the same time, the magnetic cold storage The outer wall of the device 3 and the outer wall of the thermal insulation section of the thermal diode 4 are provided with an insulating structure to reduce heat loss.

The magnetic working medium 1 contained in the magnetic cold storage is Gd, which is a granular filler, and the heat exchange medium 2 is a fluid such as an aqueous solution. The present invention can also use other magnetic materials with magnetocaloric effect and corresponding heat exchange media. The outer wall of the magnetic regenerator 3 is made of stainless steel or other materials, and the magnetic regenerator 3 and the thermal diode 4 are connected by welding or other methods. The tube wall material of thermal diode 4 is made of stainless steel, and the working fluid in the tube is liquid ammonia, and other tube wall materials and compatible working fluids can also be selected. The outer walls at both ends of the thermal diode are fin structures to enhance heat transfer. The controllable magnetic field source 5 can be an electromagnet, a superconducting magnet or a permanent magnet, and provides a periodic magnetic field for the magnetic regenerator 4 through static magnetization/demagnetization of the magnet or relative movement between the magnet and the magnetic regenerator 4 .

Its working principle is that through the action of the controllable magnetic field source 5 and the process of adding a magnetic field, when the magnetic working medium 1 in the magnetic regenerator 4 is magnetized, due to the magnetocaloric effect, the temperature of the magnetic working medium 1 rises and transfers heat to heat exchange The medium 2 makes the internal temperature of the magnetic regenerator 3 higher than that of the heat source 7, and the heat is transferred to the heat source 7 through the thermal diode 4a; in the process of removing the magnetic field, the temperature of the magnetic working medium 1 in the magnetic regenerator 4 decreases due to demagnetization, and Absorb heat to the heat exchange medium 2, so that the internal temperature of the magnetic regenerator 3 is lower than the temperature of the cold source 6, and the heat is transferred from the cold source 6 to the magnetic regenerator 3 through the thermal diode 4b, so that the temperature of the cold source 6 is reduced, and the cooling effect is achieved . The refrigeration process can be completed by repeating the above cycle.

The invention realizes the reverse thermodynamic cycle based on perfecting the exothermic process of magnetization and the heat absorption process of demagnetization, and efficiently uses the magnetic working medium to undergo magnetic field excitation/demagnetization process to change the magnetic entropy and generate temperature change for heat release/absorption Heat, the thermal switch that strictly controls the heat transfer direction, and the heat transfer mechanism with high heat transfer efficiency, realize the efficient and compact use of the magnetocaloric effect of the magnetic working medium for refrigeration.

Example 2

Embodiment 2 of the thermal switch magnetic cold accumulator of the magnetic refrigerator of the present invention is shown in Figure 4. One end of the magnetic cold accumulator adopts a thermal diode type thermal switch, and the other end is connected with pipelines, valves, pumps and heat exchangers to form a circulation circuit. It is placed in the periodic magnetic field provided by the controllable magnetic field source 5 by the magnetic regenerator 3. The lower end of the magnetic regenerator 3 is connected to the thermal diode 4, wherein the condensation section of the thermal diode 4 is located inside the magnetic regenerator 3, and its evaporation section is located in the magnetic regenerator. The lower part of the regenerator 3 is in contact with the cold source 6; the upper end of the magnetic regenerator 3 is connected to the pipeline 11, and forms a circulation circuit with the valve 10, the pump 9 and the heat exchanger 8, wherein the heat exchanger 8 is the regenerator to dissipate heat to the outside of the system.

The above circulation circuit can be a fully closed structure as shown in FIG. 4 , or a hybrid connection can be used. In the hybrid connection, the heat exchange medium 2 flows into the magnetic regenerator 3 through the pipeline, and the heat exchange medium 2 and the magnetic working medium 1 directly contact and exchange heat, and then flow out of the magnetic regenerator through the corresponding pipeline.

The outer wall of the magnetic regenerator 3 , the outer wall of the thermal insulation section of the thermal diode 4 and the outer wall of the pipeline 11 are all provided with an insulating structure to reduce heat leakage loss.

The magnetic working medium 1 contained in the magnetic cold storage is Gd, which is a granular filler, and the heat exchange medium 2 is a fluid such as an aqueous solution. The present invention can also use other magnetic materials with magneto-caloric effects and corresponding heat exchange media, and the heat exchange media can be liquid, gas and media in other states.

The outer wall of the magnetic regenerator 3 is made of stainless steel or other materials, and the magnetic regenerator 3 and the thermal diode 4 are connected by welding or other methods. The thermal diode 4 uses a heat pipe with one-way heat conduction, and the tube wall material is made of a metal material such as stainless steel, and a working fluid compatible with the tube wall material is used in the tube, such as liquid ammonia.

The outer walls at both ends of the thermal diode are fin structures that enhance heat transfer. The controllable magnetic field source 5 can be an electromagnet, a superconducting magnet or a permanent magnet, and provides a periodic magnetic field for the magnetic regenerator 4 through static magnetization/demagnetization of the magnet or relative movement between the magnet and the magnetic regenerator 4 .

The working principle is that, through the action of the controllable magnetic field source 5, when the magnetic field is applied, when the magnetic working medium 1 in the magnetic regenerator 4 is magnetized, due to the magnetocaloric effect, the temperature of the magnetic working medium 1 rises and transfers heat to the heat exchange medium 2. Make the internal temperature of the magnetic regenerator 3 higher than the temperature of the heat source 7, and open the valve 10 at the same time, through the action of the pump 9, the heat transfer fluid flows from the regenerator 3 to the heat exchanger 8, and transfers the heat in the regenerator 3 to the heat source 7 Then remove the magnetic field, and close the valve 10 simultaneously, the magnetic working medium 1 in the magnetic regenerator 4 decreases in temperature due to demagnetization, and absorbs heat to the heat exchange medium 2, so that the internal temperature of the magnetic regenerator 3 is lower than the cold source 6 temperature, Heat is transferred from the cold source 6 to the magnetic regenerator 3 via the thermal diode 4b, so that the temperature of the cold source 6 decreases. The purpose of refrigeration is achieved by repeating the above cycle process.

Example 3

The structure of a thermal switch unit used in the device of the present invention is illustrated below with an example, as shown in FIG. 5 . It is a slender and hollow closed metal tube with a working fluid inside. The inner wall of the thermal diode tube in Figure 5 is a light tube structure, and the upper and lower ends of the outer wall are fin structures to enhance heat transfer. A capillary wick structure can also be arranged inside the heat pipe.

The tube wall of the heat pipe is made of metal materials such as stainless steel or copper, and the working medium in the tube can be fluids such as water, acetone, ammonia, and liquid nitrogen. The choice of working fluid should be based on the temperature range used by the heat pipe. On this premise, the compatibility between the working fluid and the tube wall and capillary core of the heat pipe should be stable, and it should have good thermal stability, high latent heat and thermal conductivity, and relatively low viscosity. To ensure high capillary force, the surface tension of the working fluid should be sufficiently high. Capillary cores are usually made of copper, nickel, stainless steel, titanium, etc., and there are ribbed tubes, as well as porous media materials such as powder, wire mesh, and fiber felt.

The working principle of the thermal diode is that the working fluid 2 is heated and vaporized in the evaporation section 1, and the evaporated gas gathers in the hollow tube of the evaporation section and flows to the condensation section 3 of the heat pipe at the same time. When the gas reaches the condensation section with a lower temperature, it starts to condense, and at the same time, the condensation section 3 releases heat to the outside. These condensed liquids flow back to the evaporating part due to capillary action or gravity, and such circulation makes the heat transfer from the evaporating section 1 to the condensing section 3.

When the temperature of the evaporating section 1 of the thermal diode is higher than the temperature of the condensing section 3, the thermal diode works normally, which is equivalent to the closure of the thermal switch; when the temperature of the evaporating section 1 is lower than the temperature of the condensing section 3 At this time, the vapor evaporated in the tube cannot be condensed into liquid, and the thermal diode cannot transfer heat at this time, that is, the thermal switch is turned off, and the heat flow is broken.

When the inner wall of the heat pipe tube is a light pipe structure, when the condensate returns from the condensation section to the evaporation section, it is realized by gravity, and the evaporation section of the gravity type thermal diode must be placed under the condensation section.

The present invention can adopt thermal diodes of other structures, such as horizontal thermal diodes, and the present invention can also adopt other forms of thermal switches, such as superconducting thermal switches, electromagnetic thermal switches, gas thermal switches, mechanical thermal switches, etc. wait.

When the required refrigeration power is large, a large-capacity magnetic cold storage device can be used, and the number of thermal switches can be increased; multiple sets of magnetic refrigerator thermal switch magnetic cold storage devices can also be arranged side by side in the controllable magnetic field source; controllable magnetic cold storage devices can also be provided. The strength of the magnetic field source.

It is easy for those skilled in the art to understand that the above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention, All should be included within the protection scope of the present invention.

Claims (10)

1. magnetic cold-storing device that is used for magnetic refrigerator; Be used for being arranged on a controllable magnetic field source, it is characterized in that, this device comprises magnetic regenerator and the heat-transferring assembly that constitutes heat transfer loop; This heat-transferring assembly comprises at least one thermal switch unit; Magnetic regenerator is the container that magnetic working medium is housed, and the part of thermal switch unit is arranged at magnetic regenerator inside and contacts with magnetic working medium, in the changes of magnetic field process, makes the magnetic working medium and the external world carry out thermotransport effectively.

2. the magnetic cold-storing device that is used for magnetic refrigerator according to claim 1; It is characterized in that; When including only a thermal switch unit in the said heat-transferring assembly; This thermal switch unit is used for the heat release or the endothermic process of magnetic regenerator, and the neither endothermic nor exothermic process of magnetic regenerator connects and composes flow cycle by magnetic regenerator and valve, pump, pipeline and heat exchanger and accomplishes.

3. the magnetic cold-storing device that is used for magnetic refrigerator according to claim 1 is characterized in that heat-transferring assembly comprises at least two thermal switch unit, and when being used for same direction of heat flow, each thermal switch unit keeps the uniformity of heat transfer direction.

4. according to claim 1, the 2 or 3 described magnetic cold-storing devices that are used for magnetic refrigerator, it is characterized in that said magnetic working medium is the magneto-caloric material of solid, liquid or other form.

5. the magnetic cold-storing device that is used for magnetic refrigerator according to claim 4 is characterized in that, when magnetic working medium is solid, and the heat exchange medium of filling liquid state or gaseous state in magnetic regenerator.

6. according to claim 1, the 2 or 3 described magnetic cold-storing devices that are used for magnetic refrigerator, it is characterized in that the thermal switch unit is that the heat of thermal diode, superconducting switch, magnetic thermal switch or other form transmits control device.

7. according to claim 1, the 2 or 3 described magnetic cold-storing devices that are used for magnetic refrigerator, it is characterized in that the thermal switch one or both ends are provided with the augmentation of heat transfer assembly, the augmentation of heat transfer assembly comprises fin structure.

8. according to claim 1, the 2 or 3 described magnetic cold-storing devices that are used for magnetic refrigerator, it is characterized in that, net and seal are set between the magnetic regenerator and the mouth of pipe, prevent the leakage of magnetic working medium and cold-storage working substance.

9. according to claim 1, the 2 or 3 described magnetic cold-storing devices that are used for magnetic refrigerator, it is characterized in that, heat insulating construction is set outside magnetic regenerator outer wall, thermal switch outer wall, pipeline outer wall and other assembly leaks heat loss to reduce.

10. the magnetic cold-storing device that is used for magnetic refrigerator according to claim 2; It is characterized in that; Said flow cycle is full-enclosed structure or hybrid combination, and in hybrid combination, the heat exchange medium in the flow cycle directly contacts with magnetic working medium in the magnetic regenerator.

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