A sensitive coil of a high-temperature liquid metal liquid level sensor and a preparation method thereof

Abstract

The application discloses a sensitive coil of a high-temperature liquid metal liquid level sensor and a preparation method thereof, and belongs to the field of high-temperature resistant sensitive coils. In order to solve the problem that the existing liquid metal liquid level sensor has poor insulation and different packaging materials can generate thermal stress in a high-temperature environment, the sensitive coil comprises a winding sensitive coil, a porous polyimide film layer and an alumina coating layer; the outer surface of the winding sensitive coil is coated with the porous polyimide film layer, and the outer surface of the porous polyimide film layer is high-temperature sintered with the alumina coating layer; and the packaged sensitive coil can be in an insulating state under the condition of 500 DEG C. The application is used for the liquid level sensor of high-temperature liquid metal.

Description

Technical Field

[0001] This invention relates to a sensitive coil for a high-temperature liquid metal level sensor and its preparation method, belonging to the field of high-temperature resistant sensitive coils. Background Technology

[0002] Sodium-cooled fast reactors have unique applications in numerous fields such as seawater desalination, district heating, ship propulsion, and space propulsion, making them a hot research topic. They are used to equip deep space exploration, conventional nuclear submarines, other nuclear power plants, and commercial nuclear power plants. In liquid metal-cooled fast neutron reactors and experimental devices, there is a large amount of liquid sodium on the surface, requiring monitoring of its level to ensure the normal operation of the reactor and heat transfer system, to detect any overflows in the container, and to determine if there is any sodium leakage.

[0003] Liquid sodium, potassium, and sodium-potassium alloys possess characteristics such as high electrical conductivity, chemical reactivity, flammability, explosiveness, and the requirement for high system airtightness. Therefore, sodium level gauges differ significantly from other level gauges, and most sodium level sensors are developed based on sodium's high electrical conductivity technology. Based on the technical characteristics of large-range continuous level sensors used in advanced nuclear reactor condition monitoring, and considering the product characteristics and requirements of existing mutual inductance level sensors, there is an urgent need to improve high-temperature coil insulation and encapsulation technology to enhance the long-term stability and service life of the sensors. This will meet the parameter monitoring requirements for both normal and accidental reactor operation, and comprehensively improve the overall technical level of nuclear reactor safety monitoring sensors.

[0004] High temperatures reduce the insulation between coils, necessitating insulating encapsulation of the wound sensitive coils to improve their lifespan and overall performance. A comprehensive analysis of the sensor's harsh operating environment and usage requirements reveals that the coil encapsulation structure expands or contracts when the temperature changes. Because the different materials used in each layer of the encapsulation result in varying coefficients of expansion, they will expand and contract to different degrees under the same temperature load, leading to thermal stress. Summary of the Invention

[0005] The purpose of this invention is to solve the problems of poor insulation and thermal stress caused by different packaging materials in existing liquid metal level sensors under high temperature environments, and to provide a sensitive coil of a high temperature liquid metal level sensor and its preparation method.

[0006] The present invention discloses a sensitive coil for a high-temperature liquid metal level sensor, which comprises: a wound sensitive coil, a porous polyimide thin film layer, and an aluminum oxide coating;

[0007] The outer surface of the wound sensitive coil is coated with a porous polyimide film layer, and the outer surface of the porous polyimide film layer is sintered with an aluminum oxide coating at high temperature.

[0008] The encapsulated sensitive coil can remain in an insulating state at 500℃.

[0009] The method for preparing the sensitive coil of a high-temperature liquid metal level sensor according to the present invention specifically includes:

[0010] The wound sensitive coil is ultrasonically cleaned for 3 to 10 minutes.

[0011] A porous polyimide film layer is coated on the outer surface of the cleaned wound sensitive coil.

[0012] An alumina coating is sintered at high temperature on the outer surface of a porous polyimide film layer.

[0013] Preferably, coating the outer surface of the wound sensitive coil with a porous polyimide thin film layer specifically includes:

[0014] The wound sensitive coil is immersed in a polyamic acid solution for 0.5-3 hours, and the temperature of the polyamic acid solution is set to 40-65℃.

[0015] In a vacuum environment, the wound sensitive coil, after being impregnated with the solution, is heated to 60–83°C and kept at that temperature for 1–3 hours.

[0016] In a well-ventilated environment, the wound sensitive coil is heated to 100-120°C to obtain a wound sensitive coil coated with a porous polyimide film layer.

[0017] Preferably, the polyamic acid solution is placed in an impregnation tank.

[0018] Preferably, the method for preparing the polyamic acid solution includes:

[0019] The diamine and organic solvent are rapidly stirred for 10–60 min; the diamine is 5–40 mmol and the organic solvent is 40–120 ml.

[0020] Add 5-40 mmol of dianhydride in 3-10 portions, and continue stirring for 3-24 hours;

[0021] A polyamic acid solution with a solid content of 8 wt% to 25 wt% was obtained.

[0022] Preferably, the dianhydride is at least one of pyromellitic dianhydride and 3,3',4,4'-benzophenone tetracarboxylic dianhydride.

[0023] Preferably, the diamine is at least one of 4,4'-diaminodiphenyl ether and long-chain flexible aromatic diamine.

[0024] Preferably, the organic solvent is one or any combination of N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide and 1,4-butyrolactone.

[0025] Preferably, all solutions use the same solvent, which is one or any combination of water, ethanol, and acetone.

[0026] Preferably, the high-temperature sintering of the alumina coating on the outer surface of the porous polyimide film layer specifically includes:

[0027] The Al2O3 ceramic coating was milled in a ball mill for 1-2 hours and then dried.

[0028] A mixed silicate solution of Na2SiO3 and K2SiO3 in a solid content ratio of 1:1 to 1:2 was prepared as a binder.

[0029] The dried Al2O3 ceramic coating and binder are uniformly mixed in a mass ratio of 1:1 to 1:2 to obtain a ceramic slurry.

[0030] The ceramic slurry was sprayed onto the outer surface of the porous polyimide film layer using a spraying method.

[0031] Advantages of the present invention: The sensitive coil of the high-temperature liquid metal level sensor proposed in this invention is encapsulated with a polyimide porous material system. After curing, an alumina coating is prepared on the surface of the coil for reinforcement and encapsulation according to the requirements of high-temperature use. It can remain in an insulating state under high temperature of 500°C, and the encapsulated coil does not crack under high temperature.

[0032] After curing, the dielectric withstand voltage of the sensitive coil at room temperature is 500V@50Hz, and the insulation resistance is >500MΩ@500V. At a high temperature of 500℃ for 1000 hours, the insulation resistance is >100MΩ@50V. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the mutual inductance liquid level test principle based on eddy current loss. Detailed Implementation

[0034] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0036] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but this is not intended to limit the scope of the invention.

[0037] Example 1:

[0038] The sensitive coil of the high-temperature liquid metal level sensor described in this embodiment includes: a wound sensitive coil, a porous polyimide thin film layer, and an aluminum oxide coating.

[0039] The outer surface of the wound sensitive coil is coated with a porous polyimide film layer, and the outer surface of the porous polyimide film layer is sintered with an aluminum oxide coating at high temperature.

[0040] The encapsulated sensitive coil can remain in an insulating state at 500℃.

[0041] Example 2:

[0042] The method for preparing the sensitive coil of a high-temperature liquid metal level sensor described in this embodiment specifically includes:

[0043] The wound sensitive coil is ultrasonically cleaned for 3 to 10 minutes.

[0044] A porous polyimide film layer is coated on the outer surface of the cleaned wound sensitive coil.

[0045] An alumina coating is sintered at high temperature on the outer surface of a porous polyimide film layer.

[0046] Furthermore, coating the outer surface of the wound sensitive coil with a porous polyimide thin film layer specifically includes:

[0047] The wound sensitive coil is immersed in a polyamic acid solution for 0.5-3 hours, and the temperature of the polyamic acid solution is set to 40-65℃.

[0048] In a vacuum environment, the wound sensitive coil, after being impregnated with the solution, is heated to 60–83°C and kept at that temperature for 1–3 hours.

[0049] In a well-ventilated environment, the wound sensitive coil is heated to 100-120°C to obtain a wound sensitive coil coated with a porous polyimide film layer.

[0050] Furthermore, the polyamic acid solution is placed in an impregnation tank.

[0051] Furthermore, the method for preparing the polyamic acid solution includes:

[0052] The diamine and organic solvent are rapidly stirred for 10–60 min; the diamine is 5–40 mmol and the organic solvent is 40–120 ml.

[0053] Add 5-40 mmol of dianhydride in 3-10 portions, and continue stirring for 3-24 hours;

[0054] A polyamic acid solution with a solid content of 8 wt% to 25 wt% was obtained.

[0055] Furthermore, the dianhydride is at least one of pyromellitic dianhydride and 3,3',4,4'-benzophenone tetracarboxylic dianhydride.

[0056] Furthermore, the diamine is at least one of 4,4'-diaminodiphenyl ether and a long-chain flexible aromatic diamine.

[0057] Furthermore, the organic solvent is one or any combination of N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, and 1,4-butyrolactone.

[0058] Furthermore, all solutions use the same solvent, which is one or any combination of water, ethanol, and acetone.

[0059] Furthermore, the high-temperature sintered alumina coating on the outer surface of the porous polyimide film layer specifically includes:

[0060] The Al2O3 ceramic coating was milled in a ball mill for 1-2 hours and then dried.

[0061] A mixed silicate solution of Na2SiO3 and K2SiO3 in a solid content ratio of 1:1 to 1:2 was prepared as a binder.

[0062] The dried Al2O3 ceramic coating and binder are uniformly mixed in a mass ratio of 1:1 to 1:2 to obtain a ceramic slurry.

[0063] The ceramic slurry was sprayed onto the outer surface of the porous polyimide film layer using a spraying method.

[0064] In this embodiment, the pretreatment of the wound sensitive coil is as follows: the sensitive coil is first ultrasonically cleaned for 3 to 10 minutes, preferably 5 minutes. This removes oil or dust from the coil surface, ensuring that the polyimide film can adhere evenly to the coil surface.

[0065] In this embodiment, the specific method for insulating and encapsulating the sensitive coil with porous polyimide colloid material is as follows: a polyamic acid solution is placed in an impregnation tank, a layer of polyamic acid solution is adhered to the surface of the conductor, and the coil is impregnated in the solution at 40-65°C for 0.5-3 hours, preferably 55°C; the turns and layers are uniformly coated with polyimide colloid, and the coil is vacuum heated to 60-83°C, preferably 70°C; and kept at this temperature for 1-3 hours, preferably 2 hours; then it is ventilated and heated to 100-120°C, preferably 110°C; thus obtaining a sensitive coil coated with porous polyimide.

[0066] In this embodiment, the ceramic coating film on the surface is prepared by spraying a dense Al2O3 film onto the surface of the polyimide encapsulated coil. The Al2O3 ceramic coating is mixed, ball-milled for 1-2 hours, and then dried for later use. A mixed silicate solution of Na2SiO3:K2SiO3 = 1:1 to 1:2 (solid content ratio) is prepared as a binder. The Al2O3 ceramic coating and the binder are mixed uniformly at a mass ratio of 1:1 to 1:2 to obtain a homogeneous and stable ceramic slurry. The Al2O3 ceramic coating is then sprayed onto the surface of the cured porous polyimide coil.

[0067] In this embodiment, the preparation method of polyamic acid solution is as follows: 5-40 mmol of diamine and 40-120 ml of organic solvent are rapidly stirred for 10-60 min, and then 5-40 mmol of dianhydride is added in 3-10 portions. After stirring for 3-24 h, the mixture is stopped to obtain polyamic acid solution with a solid content of 8 wt%-25 wt%.

[0068] In this embodiment, the dianhydride is pyromellitic dianhydride or / and 3,3',4,4'-benzophenone tetracarboxylic dianhydride.

[0069] In this embodiment, the diamine is 4,4'-diaminodiphenyl ether or / and long-chain flexible aromatic diamine.

[0070] In this embodiment, the organic solvent is one or any combination of N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, and 1,4-butyrolactone (GBL).

[0071] In this embodiment, the coagulation bath is one or any combination of water, ethanol, and acetone.

[0072] like Figure 1 The diagram shown is a schematic of the mutual inductance liquid level test principle based on eddy current loss.

[0073] The sensor utilizes the mutual inductance principle of the excitation winding and the output winding. The probe length depends on the object being measured. High-temperature wires, wound in parallel and circumferentially, serve as the excitation winding and the output winding, respectively, and are wound on the DT4 electromagnet core. This constitutes the sensitive element of the mutual inductance continuous liquid sodium metal level sensor. The sensitive element is externally encapsulated in a stainless steel housing.

[0074] In use, the sensor is inserted into a stainless steel blind tube (Ф18mm) sealed at one end, which is then immersed in liquid sodium metal.

[0075] When the sensor is powered on and completely submerged in the liquid, a sinusoidal AC excitation voltage of a certain frequency is applied to the excitation winding A. The induced electromotive force generated in the output winding B due to the excitation winding A at this time is called the primary induced electromotive force, which can be approximately expressed as:

[0076]

[0077] Where M represents the mutual inductance of the output windings;

[0078] ω represents the angular frequency of the excitation signal;

[0079] R2 represents the resistance of the output winding;

[0080] L2 represents the inductance of the output winding.

[0081] When the liquid metal level rises, the induced electromotive force (EMF) generated in the output winding B due to the eddy currents in the liquid metal conductor is called the secondary induced EMF. At this time, the total EMF in the output winding B is the superposition of the primary and secondary induced EMFs. Ignoring eddy current losses, the total EMF in the output winding B can be expressed as:

[0082]

[0083] As the excitation winding is submerged in sodium metal, induced eddy currents are generated in the sodium. The magnetic field formed by these eddy currents causes the mutual inductance of the output winding to decrease. Ignoring eddy current and hysteresis losses within the iron core and neglecting magnetic field disturbances near the free surface of the liquid metal, the induced voltage in the output winding decreases linearly with the increase in the sodium metal level. The total output electromotive force can be expressed as:

[0084]

[0085] Where N1 represents the number of turns in the excitation winding;

[0086] N2 represents the number of turns in the output winding;

[0087] μ0 represents the vacuum permeability;

[0088] μ rIndicates the relative permeability of the iron core;

[0089] R represents the winding radius;

[0090] L represents the winding length;

[0091] Indicates the excitation winding current;

[0092] This refers to induced eddy currents in liquid metal.

[0093] Since the eddy current intensity in liquid metal can be expressed as:

[0094]

[0095] Where K represents the height to which the sensor is submerged;

[0096] H represents a constant.

[0097] Therefore, in the excitation current Under the condition of constant frequency and constant current, the following qualitative relationship exists:

[0098]

[0099] Where A and B both represent coefficients that vary with the temperature of the measured medium.

[0100] In other words, there is a linear relationship between the output voltage of the liquid metal level sensor and the liquid level.

[0101] While the invention has been described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the invention. Therefore, it should be understood that many modifications can be made to the exemplary embodiments, and other arrangements can be designed without departing from the spirit and scope of the invention as defined by the appended claims. It should be understood that different dependent claims and features described herein can be combined in ways different from those described in the original claims. It is also understood that features described in conjunction with individual embodiments can be used in other described embodiments.

Claims

1. A sensitive coil for a high-temperature liquid metal level sensor, characterized in that, It includes: Winding of a sensitive coil, a porous polyimide thin film layer, and an alumina coating; The outer surface of the wound sensitive coil is coated with a porous polyimide film layer, which has a thermal stress buffering function to alleviate the thermal stress generated at high temperature due to the mismatch of the thermal expansion coefficients of the materials. The outer surface of the porous polyimide film layer is sintered with an alumina coating at high temperature, forming an organic-inorganic composite insulating structure. The encapsulated sensitive coil has an insulation resistance greater than 100MΩ in a 500℃ high-temperature liquid metal environment, and its surface shows no cracks after 1000 hours of high-temperature testing.

2. A method for fabricating the sensitive coil of a high-temperature liquid metal level sensor, characterized in that, Specifically, it includes: The wound sensitive coil is ultrasonically cleaned for 3-10 minutes. The outer surface of the cleaned wound sensitive coil is impregnated with a polyamic acid solution and cured by step temperature increase to form a porous polyimide film layer with thermal stress buffering function. A ceramic slurry is sprayed onto the outer surface of a porous polyimide film layer and then sintered at high temperature to form an alumina coating, thus forming an organic-inorganic composite insulation structure.

3. The method for preparing the sensitive coil of a high-temperature liquid metal level sensor according to claim 2, characterized in that, The coating of the outer surface of the wound sensitive coil with a porous polyimide thin film specifically includes: The wound sensitive coil is immersed in a polyamic acid solution for 0.5-3 hours, and the temperature of the polyamic acid solution is set to 40-65℃. In a vacuum environment, the wound sensitive coil, after being impregnated with the solution, is heated to 60~83℃ and kept at that temperature for 1~3 hours; In a well-ventilated environment, the wound sensitive coil is heated to 100~120℃ to obtain a wound sensitive coil coated with a porous polyimide film layer.

4. The method for preparing the sensitive coil of a high-temperature liquid metal level sensor according to claim 2, characterized in that, The polyamic acid solution is placed in an impregnation tank.

5. The method for preparing the sensitive coil of a high-temperature liquid metal level sensor according to claim 3, characterized in that, The method for preparing the polyamic acid solution includes: The diamine and organic solvent are rapidly stirred for 10-60 min; the diamine is 5-40 mmol and the organic solvent is 40-120 ml. Add 5-40 mmol of dianhydride in 3-10 portions and continue stirring for 3-24 hours; A polyamic acid solution with a solid content of 8wt%~25wt% was obtained.

6. The method for preparing the sensitive coil of a high-temperature liquid metal level sensor according to claim 5, characterized in that, The dianhydride is at least one of pyromellitic dianhydride and 3,3',4,4'-benzophenone tetracarboxylic dianhydride.

7. The method for preparing the sensitive coil of a high-temperature liquid metal level sensor according to claim 5, characterized in that, The diamine is at least one of 4,4'-diaminodiphenyl ether and long-chain flexible aromatic diamine.

8. The method for preparing the sensitive coil of a high-temperature liquid metal level sensor according to claim 5, characterized in that, The organic solvent is one or any combination of N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide and 1,4-butyrolactone.

9. The method for preparing the sensitive coil of a high-temperature liquid metal level sensor according to claim 5, characterized in that, All solutions use the same solvent, which is one or any combination of water, ethanol, and acetone.

10. The method for preparing the sensitive coil of a high-temperature liquid metal level sensor according to claim 2, characterized in that, The high-temperature sintering of the alumina coating on the outer surface of the porous polyimide film layer specifically includes: The Al2O3 ceramic coating was milled for 1-2 hours using a mixing ball mill, and then dried. A mixed silicate solution of Na2SiO3 and K2SiO3 with a solid content ratio of 1:1 to 1:2 was prepared as a binder. The dried Al2O3 ceramic coating and binder are uniformly mixed in a mass ratio of 1:1 to 1:2 to obtain a ceramic slurry. The ceramic slurry was sprayed onto the outer surface of the porous polyimide film layer using a spraying method.

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