CN109742971B - Heat energy collector based on magnetic phase change alloy-flexible piezoelectric material - Google Patents

Abstract

The invention relates to a thermal energy collector based on a magnetic phase change alloy/flexible piezoelectric material, belonging to the field of thermal energy collection. The thermal energy collector includes a fixed table, a flexible piezoelectric film, a magnetic phase change alloy sheet, a permanent magnet, a cantilever arm, and a heating table; the flexible piezoelectric film is bonded above the cantilever arm, and a fixed table is set under one end of the cantilever arm and fixed on the fixed table , a magnetic phase change alloy sheet is adhered to the lower surface of the other end of the cantilever arm, a heating table is placed under the magnetic phase change alloy sheet, and the permanent magnet is suspended above the magnetic phase change alloy sheet. The application uses antiferromagnetic-ferromagnetic phase change alloy sheets and permanent magnets, so that when the heating temperature of the alloy sheets increases, a magnetic phase transition from weak magnetic martensite to ferromagnetic austenite occurs, and the alloy sheets are attracted, so that the The permanent magnet does not need to be bonded to the heat source, which avoids the phenomenon that the permanent magnet is thermally demagnetized due to contact with the heat source, and also makes it unnecessary to use an additional radiator to ensure the operation of the device and save energy.

Description

Thermal energy harvester based on magnetic phase change alloy-flexible piezoelectric material

technical field

The invention belongs to the field of thermal energy collection, in particular to a thermal energy collector based on a magnetic phase change alloy-flexible piezoelectric material.

Background technique

The thermal energy collector can replace some traditional batteries to continuously supply power to the sensor, and has high application value in the fields of waste heat and natural heat collection. At present, the commonly used thermal energy collectors utilize the thermoelectricity, pyroelectricity, thermoelasticity and thermomagnetism of materials, and these types of thermal energy collectors have a series of problems such as complex process, high cost and limited application conditions. The problem is that the connection of thermal energy harvesters to magnetic materials has begun to receive wider attention.

At present, the existing technology of using magnetic materials to make thermal energy collectors is constantly improving. In 2011, RDJames et al. directly used coils to convert thermal energy into electrical energy by heating Ni ₄₅ Co ₅ Mn ₄₀ Sn ₁₀ alloy, using Faraday's law of electromagnetic induction, Its peak voltage can reach 0.6mV. However, the thermal energy collector has some problems. It can only convert thermal energy once, and cannot be converted repeatedly. It is also affected by the number of coil turns and the strength of the magnetic field. In 2015, Marcel Gueltig et al. used the cantilever arm structure, bonding Ni _50.4 Co _3.7 Mn _32.8 In _13.1 at the end of the cantilever arm and winding coils around it to achieve the continuous and repeated conversion of heat energy into electrical energy. However, the energy collection efficiency of small devices is limited by the speed of the cutting magnetic field line, the number of coil turns, and the size of the magnetic flux, and the conversion efficiency is low. In order to overcome these problems and make better use of magnetic materials, in 2017 Chun et al. used polyvinylidene fluoride (PVDF) cantilevers and gadolinium (Gd) alloys to convert thermal energy into electricity, when gadolinium is lower than its Curie temperature. , it becomes ferromagnetic and is attracted by the permanent magnet, and when it contacts the heat source, its temperature rises above the Curie temperature and becomes paramagnetic, then Gd is pulled back by the spring to contact the heat sink, and then It begins to regain its magnetic properties when its temperature falls below the Curie temperature. When the magnetic force is greater than the spring force, the permanent magnet pulls Gd towards the heat source, and the cycle continues. In the reciprocating motion, the cantilever arm is used to convert the mechanical energy into electrical energy, and the output power of the single bimorph cantilever reaches 158 μW under the temperature difference of 80 °C. The peak voltage can reach 2.8V. However, there are some problems with this technology. First of all, the Curie temperature of the Gd metal sheet is near room temperature, and the magnet sticking to the hot end will easily weaken the magnetism of the magnet and cause the device to fail. At the same time, a stable heat sink is also required to ensure that the temperature of the cold end is maintained. At -10°C, more energy needs to be consumed to maintain the normal operation of the device.

SUMMARY OF THE INVENTION

The technical problem solved by the present invention is to provide a thermal energy collector based on a magnetic phase change alloy/flexible piezoelectric material, so as to realize the continuous conversion of thermal energy into electrical energy.

The technical solution that realizes the purpose of the present invention is:

A thermal energy collector based on magnetic phase change alloy-flexible piezoelectric material, the thermal energy collector comprises a fixed table, a flexible piezoelectric film, a magnetic phase change alloy sheet, a permanent magnet, a cantilever arm, and a heating table;

A flexible piezoelectric film is bonded above the cantilever arm, a fixing table is arranged under one end of the cantilever arm and is fixed on the fixing table, a magnetic phase change alloy sheet is stuck on the lower surface of the other end of the cantilever arm, and a heating table is placed under the magnetic phase change alloy sheet, The permanent magnet is suspended above the magnetic phase change alloy sheet.

The magnetic phase transition alloy sheet is an antiferromagnetic-ferromagnetic phase transition alloy, which undergoes a magnetic phase transition from weak magnetic martensite to ferromagnetic austenite when the temperature increases, and the phase transition temperature of the alloy is between 40°C and 40°C. between 200°C.

The antiferromagnetic-ferromagnetic phase change alloy is a NiMnInCo alloy.

The flexible piezoelectric film is a PVDF film, and the thickness of the film is 20-40 μm.

The material of the cantilever arm is a flexible polymer.

The flexible polymer is a polyimide with a lower elastic modulus.

The permanent magnet is 5-20mm away from the upper surface of the cantilever arm, the size of the permanent magnet is 50-1000mm×20-50mm×5-10mm, and the magnetic field intensity around the permanent magnet is above 1000Oe.

The permanent magnet is suspended by a bracket, and the position of the permanent magnet on the bracket can be adjusted, so that the height of the permanent magnet can be adjusted.

A method for collecting thermal energy using the above-mentioned thermal energy collector, when the magnetic phase alloy sheet contacts the heat source of the heating table, the temperature rises, and the magnetic phase alloy sheet undergoes a magnetic phase transition from weak magnetic martensite to ferromagnetic austenite ;

Due to the attraction of the permanent magnet to the ferromagnetic material, the magnetic phase alloy sheet is attracted, which in turn makes the cantilever arm and the flexible piezoelectric film bend;

A voltage is generated between the upper and lower surfaces of the flexible piezoelectric film, which realizes the conversion of thermal energy to electric energy;

Since the magnetic phase alloy sheet that is attracted is far away from the heat source, the temperature decreases, and it changes back to a weak magnetic state, the attractive force disappears, the cantilever arm straightens, and the magnetic phase alloy sheet returns to the initial position to continue heat exchange;

The above cycle is repeated continuously, and thermal energy is continuously converted into electrical energy.

Compared with the prior art, the present invention has the following significant advantages:

(1) The application adopts an antiferromagnetic-ferromagnetic phase transition alloy sheet and a permanent magnet, so that when the heating temperature of the alloy sheet increases, a magnetic phase transition from weak magnetic martensite to ferromagnetic austenite occurs, and the alloy sheet is attracted In this way, the permanent magnet does not need to be bonded to the heat source, which avoids the phenomenon that the permanent magnet is thermally demagnetized due to contact with the heat source, and also makes it unnecessary to use an additional radiator to ensure the operation of the device and save energy.

(2) The thermal energy collector of the present application can better convert the deformation into electric energy by bonding the PVDF film on the cantilever arm, and can have a higher output voltage.

(3) The present invention has higher conversion efficiency, controllable working temperature range, is not limited by factors such as the number of coil turns, magnetic field strength, etc., and does not require temperature gradients, and the thermal energy collector of the present invention can be continuously realized The conversion of thermal energy to electric energy meets practical application, and has the characteristics of simple structure, convenient preparation and energy saving and high efficiency.

The present invention will be described in further detail below with reference to the accompanying drawings.

Description of drawings

Figure 1 is a schematic diagram of a thermal energy harvester based on a magnetic phase change alloy-flexible piezoelectric material.

Figure 2 is a schematic diagram of the working principle of a thermal energy harvester based on a magnetic phase change alloy/flexible piezoelectric material.

FIG. 3 is a physical view of a thermal energy harvester based on magnetic phase change alloy/flexible piezoelectric material in an embodiment.

FIG. 4 is a thermomagnetic curve diagram of Ni ₄₅ Mn _36.91 In _13.09 Co ₅ alloy in an example under a 0.1T external magnetic field.

FIG. 5 is a voltage-time graph of a magnetic phase change alloy/flexible piezoelectric material based thermal energy harvester in an embodiment.

Description of reference numbers:

1-Fixed stage, 2-Flexible piezoelectric film, 3-Magnetic phase change alloy sheet, 4-Permanent magnet, 5-Cantilever arm, 6-Heating stage.

Detailed ways

The present invention discloses a thermal energy collector based on a magnetic phase change alloy/flexible piezoelectric material. The thermal energy collector includes a flexible piezoelectric film 2 , a cantilever arm 5 , a permanent magnet 4 and a magnetic phase change alloy sheet 3 .

The preparation process of the thermal energy collector of the present invention is as follows: firstly, the flexible piezoelectric film 2 is bonded to the cantilever arm 5 with epoxy resin, and then the antiferromagnetic-ferromagnetic phase change alloy sheet is bonded to the end of the cantilever arm 5 and the One end of the unbonded alloy sheet is fixed on the fixing table 1 (or any object that can fix the cantilever), and finally a permanent magnet 4 is fixed above the alloy sheet.

The present invention relates to the working principle of the heat energy collector: when the antiferromagnetic-ferromagnetic phase change alloy contacts the heat source, the temperature rises, and the magnetic phase transition from weak magnetic martensite to ferromagnetic austenite occurs; due to the permanent magnet 4 Attraction to the ferromagnetic material, the alloy sheet 3 is sucked up, thereby causing the bending of the cantilever and the flexible piezoelectric material; since the flexible piezoelectric material is a piezoelectric material, a voltage is generated between its upper and lower surfaces at this time, which is achieved. The conversion of thermal energy to electrical energy; after that, since the sucked alloy sheet is far away from the heat source, the temperature decreases, and it changes back to a weak magnetic state, the attractive force of the magnet disappears, the cantilever is straightened, and the alloy sheet returns to the initial position to continue heat exchange. The above cycle is repeated continuously, and thermal energy is continuously converted into electrical energy.

Further, the magnetic phase transition alloy is an antiferromagnetic-ferromagnetic phase transition alloy, which will undergo a magnetic phase transition from weak magnetic martensite to ferromagnetic austenite when the temperature increases, and the phase transition of the alloy will occur simultaneously. The temperature is between 40°C and 200°C.

Further, the flexible piezoelectric material is preferably a PVDF film with a thickness of 28 μm. The PVDF film has a mature preparation process, can be easily obtained, and has stable piezoelectric properties.

Further, the material used for the cantilever arm is a flexible polymer, preferably polyimide, which has a lower elastic modulus and can better deform the flexible piezoelectric material.

Further, the permanent magnet is fixed by a bracket, and the bracket is a commonly used iron bracket, and the height of the permanent magnet can be freely controlled by adjusting the position of the nut (the size of the permanent magnet is 50-1000mm × 20-50mm × 5-10mm, the magnetic field around the permanent magnet is The intensity is above 1000Oe).

Example 1:

In a specific embodiment, the present invention relates to the antiferromagnetic-ferromagnetic phase change alloy used in the thermal energy collector is a Heusler type NiMnInCo alloy with a composition of Ni ₄₅ Mn _36.91 In _13.09 Co ₅ . The antiferromagnetic-ferromagnetic phase change alloy uses high-purity metal elements Ni, Co, Mn and In as raw materials, and accurately proportions each metal element according to the alloy expression, and is prepared by an arc melting method; smelting in high-purity argon gas. carried out under the protection of atmosphere; the smelted alloy was annealed at 850 °C for 72 hours, then quenched and sized by wire cutting; finally, the energy harvester was built according to the design drawing. The prepared thermal energy collector can realize thermal energy harvesting at 80°C for a constant heat source.

As shown in Figure 1, it is a theoretical model diagram of a thermal energy harvester based on a magnetic phase change alloy/flexible piezoelectric material. As shown in Figure 2, it is the working principle diagram of the thermal energy harvester based on the magnetic phase change alloy/flexible piezoelectric material. Its working principle is: when the alloy contacts the heat source, the temperature rises, and the magnetic transition from weak magnetism to ferromagnetism occurs; due to the attraction of the permanent magnet to the ferromagnetic material, the alloy sheet is attracted, which in turn causes the cantilever and flexible piezoelectric material. Since the PVDF film is a flexible piezoelectric material, a voltage is generated between its upper and lower surfaces at this time, that is, the conversion of thermal energy to electric energy is realized; after that, since the sucked alloy sheet is far away from the heat source, the temperature decreases, and the transition back to weak In the magnetic state, the attractive force of the magnet disappears, the cantilever is straightened, and the alloy sheet returns to the initial position to continue heat exchange. The above cycle is repeated continuously, and thermal energy is continuously converted into electrical energy.

FIG. 3 is a physical view of a thermal energy harvester based on magnetic phase change alloy/flexible piezoelectric material in an embodiment. In the embodiment, the cantilever arm is selected from polyimide, and the size is 7mm×5mm. The PVDF film thickness is 28 μm and the size is 5 mm × 4 mm. The magnetic alloy composition is Ni ₄₅ Mn _36.91 In _13.09 Co ₅ , and the size is 5 mm×5 mm×1 mm. The heat source was kept at 80°C.

FIG. 4 is a thermomagnetic curve diagram of Ni ₄₅ Mn _36.91 In _13.09 Co ₅ alloy in an example under a 0.1T external magnetic field. The data were obtained by a comprehensive physical property measurement system (Physical Property Measurement System: PPMS). The martensitic transformation temperature of the alloy is 338K, and the austenite transformation temperature is 355K. When the martensitic transformation occurs, the alloy changes from high-temperature ferromagnetic to low-temperature weak magnetic, on the contrary, when the austenite transformation occurs, the alloy changes from low-temperature weak magnetic to high-temperature ferromagnetic. This magnetic change combined with the attractive force of the permanent magnet causes the cantilever to bend/recover periodically.

Figure 5 is a voltage-time curve of a magnetic phase change alloy/flexible piezoelectric material based thermal energy harvester in an example. Before the test, both sides of the PVDF film are connected with wires, and the voltage signal caused by PVDF bending will be collected by the charge amplifier and oscilloscope through the wires. As shown, the measured peak voltage can reach 29V.

Claims (8)

1. A thermal energy collector based on a magnetic phase change alloy-flexible piezoelectric material, characterized in that the thermal energy collector comprises a fixed table (1), a flexible piezoelectric film (2), a magnetic phase change alloy sheet (3), permanent magnet (4), cantilever arm (5), heating table (6); A flexible piezoelectric film (2) is bonded above the cantilever arm (5), a fixing table (1) is arranged under one end of the cantilever arm (5) and is fixed on the fixing table (1), and the lower surface of the other end of the cantilever arm (5) is A magnetic phase change alloy sheet (3) is adhered, a heating table (6) is placed under the magnetic phase change alloy sheet (3), and the permanent magnet (4) is suspended above the magnetic phase change alloy sheet (3); The magnetic phase transition alloy sheet (3) is an antiferromagnetic-ferromagnetic phase transition alloy, and a magnetic phase transition from weak magnetic martensite to ferromagnetic austenite occurs when the temperature increases, and the phase transition temperature of the alloy is Between 40°C and 200°C. 2 . The thermal energy collector of claim 1 , wherein the antiferromagnetic-ferromagnetic phase change alloy is a NiMnInCo alloy. 3 . 3 . The thermal energy collector according to claim 1 , wherein the flexible piezoelectric film ( 2 ) is a PVDF film, and the thickness of the film is 20-40 μm. 4 . 4. The thermal energy collector according to claim 1, characterized in that, the material of the cantilever arm (5) is a flexible polymer. 5. The thermal energy collector of claim 4, wherein the flexible polymer is a polyimide having a lower elastic modulus. 6 . The thermal energy collector according to claim 1 , wherein the permanent magnet ( 4 ) is 5-20 mm away from the upper surface of the cantilever arm ( 5 ), and the size of the permanent magnet ( 4 ) is 50-1000 mm×20- 50mm×5～10mm, and the magnetic field strength around the permanent magnet (4) is above 1000Oe. 7. The thermal energy collector according to claim 1, wherein the permanent magnet (4) is suspended by a bracket, and the position of the permanent magnet (4) on the bracket is adjustable, thereby realizing the height of the permanent magnet (4) Adjustable. 8. A method for collecting thermal energy using the thermal energy collector according to any one of claims 1-7, characterized in that when the magnetic phase alloy sheet (3) contacts the heat source of the heating table (6), the temperature rises , the magnetic phase alloy sheet (3) undergoes a magnetic phase transition from weak magnetic martensite to ferromagnetic austenite; Due to the attractive force of the permanent magnet (4) to the ferromagnetic material, the magnetic phase alloy sheet (3) is pulled up, thereby causing the cantilever arm (5) and the flexible piezoelectric film (2) to bend; A voltage is generated between the upper and lower surfaces of the flexible piezoelectric film (2) to realize the conversion of thermal energy into electrical energy; Since the attracted magnetic phase alloy sheet (3) is far away from the heat source, the temperature decreases, and it changes back to a weak magnetic state, the attractive force disappears, the cantilever arm (5) is straightened, and the magnetic phase alloy sheet (3) returns to the initial position to continue the replacement. hot; The above cycle is repeated continuously, and thermal energy is continuously converted into electrical energy.

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