Electric heating element with surface enhanced heat exchange structure and preparation method of electric heating element

Abstract

The invention belongs to the technical field of electric heating, and particularly relates to an electric heating element with a surface enhanced heat exchange structure and a preparation method of the electric heating element. The electric heating element sequentially comprises a conductive rod, a conductive tube, a high-heat-conductivity and high-insulation tube, a metal tube shell and a spiral rib from inside to outside, the spiral rib is additionally arranged on the metal tube shell with a common smooth surface, and mixing of the outer surface of the electric heating element in the flowing process is enhanced; the low-melting-point high-fluidity liquid metal is adopted as a gap filler between the metal tube shell and the high-heat-conduction high-insulation tube, so that the heat exchange capacity of the surface of the electric heating element is effectively enhanced, and the heat exchange efficiency is improved; according to the preparation method of the electric heating element, the spiral ribs on the surface of the electric heating element are subjected to cold machining through spiral drawing, the technology of multiple times of drawing and rotating is adopted, and in the process of compressing internal insulation powder, the purpose of integrally forming the spiral ribs of a metal pipe shell is achieved; the problems of poor rib height, poor dimensional precision, poor rib strength and the like caused by machining spiral ribs on the surface of the smooth electric heating element are solved, and the batch preparation efficiency of the electric heating element with the surface enhanced heat exchange structure is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electric heating, and particularly relates to an electric heating element with a surface-strengthened heat exchange structure and a preparation method thereof. BACKGROUND

[0002] The thermal-hydraulic characteristics research of the fuel assembly in the core of a reactor is of great significance for the safe operation of the reactor and the design of related systems. In a new-type reactor, the fuel element rods in a single-can fuel assembly are generally arranged in a triangular shape to reduce the volume ratio of the core working medium to the nuclear fuel, increase the burnup depth of the nuclear fuel, achieve long-term cycle operation, achieve efficient utilization of the nuclear fuel, and improve the economy of the reactor.

[0003] In an out-of-pile experiment, an electric heating element is often used to simulate a fuel element in the core. A metal tubular electric heating element is an electric heating element with a metal tube as an outer shell, an alloy electric heating wire as a heating body, a lead-out rod (wire) at one end or both ends, and dense insulation material filled in the metal tube to fix the heating body. This electric heating element has the characteristics of simple structure, high mechanical strength, high thermal efficiency, safety and reliability, simple installation, long service life, and is widely used in the fields of energy and chemical industry.

[0004] In a sodium-cooled liquid metal reactor, in order to simplify the design of the fuel assembly, a rib structure is often added outside the cladding of the fuel element. Therefore, in the out-of-pile experiment of the reactor, it is necessary to simulate the design structure of the ribbed cladding tube of the real fuel element. However, the outer surface of the current metal tubular electric heating element is usually a smooth cylindrical surface, which cannot guarantee the simulation of the ribbed cladding of the fuel element, and this is a key problem faced in the out-of-pile experiment of the reactor. SUMMARY

[0005] The application aims to provide an electric heating element with a surface-strengthened heat exchange structure and a preparation method thereof, and solve the problem of simulating the ribbed cladding of the fuel element and enhancing the surface heat exchange capacity of the fuel element in the prior art.

[0006] The technical solution for achieving the purpose of the application is as follows:

[0007] The application provides an electric heating element with a surface-strengthened heat exchange structure, which comprises, from inside to outside, an electrically conductive rod, an electrically conductive tube, a high-thermal-conductivity high-insulation tube, a metal tube shell, and a spiral rib.

[0008] The electrically conductive rod and the electrically conductive tube are filled with high-thermal-conductivity high-insulation powder.

[0009] The high-thermal-conductivity high-insulation tube and the metal tube shell are filled with liquid metal.

[0010] The spiral rib is spirally distributed on the outer surface of the metal tube shell, and the spiral rib is integrally formed with the metal tube shell.

[0011] Optionally, the electric heating element with surface reinforced heat exchange structure further comprises an electric heating alloy wire;

[0012] Two ends of the electric heating alloy wire are welded with the conductive rod and the conductive tube respectively;

[0013] The electric heating alloy wire is spirally wound outside the conductive rod;

[0014] High-thermal-conductivity and high-insulation powder is filled between the conductive rod and the electric heating alloy wire.

[0015] Optionally, one end of the metal tube shell is sealed with the conductive tube through an insulating end plug, and the other end is sealed through a stainless steel sealing head.

[0016] The conductive rod adopts low-resistivity material, which can be copper-based or nickel-based material.

[0017] Optionally, the high-thermal-conductivity and high-insulation powder and the high-thermal-conductivity and high-insulation tube adopt one or any two or three of magnesium oxide, boron nitride and silicon carbide.

[0018] The liquid metal filled between the high-thermal-conductivity and high-insulation tube and the metal tube shell is selected from low-melting-point alloy, which can be tin bismuth or indium tin.

[0019] Optionally, the electric heating alloy wire adopts high-resistance electric heating alloy satisfying GB / T 1234, and the structure form can also be an electric heating alloy strip.

[0020] The second aspect of the embodiments of the present application provides a preparation method of the electric heating element with surface reinforced heat exchange structure, for preparing the electric heating element with surface reinforced heat exchange structure, comprising the following steps:

[0021] Assembling the conductive rod, the electric heating alloy wire, the conductive tube, the high-thermal-conductivity and high-insulation tube, and the metal tube shell; filling the high-thermal-conductivity and high-insulation powder and compressing; installing the insulating end plug and the stainless steel sealing head for sealing;

[0022] Firstly drawing the electric heating element to draw out the metal tube shell with smooth surface into a rough state with straight ribs;

[0023] Secondly drawing the electric heating element to process the metal tube shell into straight rib structure;

[0024] Using a spinning device to spin and process the straight ribs into spiral ribs by torsion.

[0025] Optionally, the rib height of the processed metal tube shell is S, and the wall thickness is h.

[0026] The outer diameter of the metal tube shell with smooth surface before processing is greater than or equal to h+3mm, and the wall thickness is greater than or equal to S+h+1mm.

[0027] Optionally, the first drawing die is provided with rib grooves with the same shape and number as the straight rib;

[0028] The first drawing is uniform drawing, and the speed is 0.5 m / min-3 m / min; after the first drawing, the outer diameter of the metal tube shell is reduced by more than or equal to 10%, and the wall thickness is reduced by more than or equal to 10%;

[0029] The second drawing die has the same structure as the first drawing die, and the rib groove section size is smaller than that of the first drawing die;

[0030] After the second drawing, the straight rib section size is reduced.

[0031] Optionally, the compression amount of the high-thermal-conductivity high-insulation powder is not less than 24%.

[0032] The beneficial technical effects of the present application are that the electric heating element with a surface-strengthened heat exchange structure and the preparation method thereof provided by the embodiments of the present application have the following beneficial technical effects: the electric heating element comprises, from inside to outside, an electrically conductive rod, an electrically conductive tube, a high-thermal-conductivity high-insulation tube, a metal tube shell, and a spiral rib. The low-melting-point high-flowability liquid metal is used as a gap filler between the metal tube shell and the high-thermal-conductivity high-insulation tube, which can effectively reduce the interfacial thermal resistance between the two materials, improve the overall thermal conductivity of the electric heating element, and enhance the heat exchange efficiency of the electric heating element. The spiral rib is added to the ordinary smooth surface metal tube shell, which enhances the mixing of the electric heating element outer surface during the flow process, reduces the fluid temperature in the dense area of the electric heating element, improves the reliability and stability of the electric heating element in this area, and effectively enhances the heat exchange capacity of the electric heating element surface. A preparation method of the electric heating element with a spiral rib on the surface by cold working through spiral drawing is proposed. The process of multiple drawing and rotation is adopted to compress the internal insulation powder, so as to achieve the purpose of integral forming of the spiral rib of the metal tube shell, solve the problems of rib height difference, poor size precision, and poor rib strength caused by machining the spiral rib on the smooth surface of the electric heating element, and improve the batch preparation efficiency of the electric heating element with a surface-strengthened heat exchange structure. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 A structure schematic diagram of the electric heating element with a surface-strengthened heat exchange structure provided by the embodiments of the present application is shown in the figure;

[0034] Figure 2 A surface straight rib structure schematic diagram of the electric heating element with a surface-strengthened heat exchange structure provided by the embodiments of the present application is shown in the figure;

[0035] Figure 3 An internal temperature distribution diagram of the electric heating element with a surface-strengthened heat exchange structure provided by the embodiments of the present application is shown in the figure;

[0036] In the figure: 1 - electrically conductive rod; 2 - electrically conductive tube; 3 - insulating end plug; 4 - electric heating alloy wire; 5 - high thermal conductivity and high insulation powder; 6 - high thermal conductivity and high insulation tube; 7 - metal tube shell; 8 - spiral rib; 9 - stainless steel sealing head; 10 - straight rib. DETAILED DESCRIPTION

[0037] In order for those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the following described embodiments are only part of the embodiments of the present application, not all. Based on the embodiments described in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0038] The electric heating element with surface-strengthened heat exchange structure and the preparation method thereof provided by the embodiments of the present application increase spiral ribs on the ordinary smooth surface metal tube shell, strengthen the mixing of the outer surface of the electric heating element during the flow process, can effectively enhance the heat exchange capacity of the surface of the electric heating element, and improve the heat exchange efficiency.

[0039] Based on the above, in order to clearly and specifically describe the above advantages of the present application, the specific embodiments of the present application will be described below in conjunction with the accompanying drawings.

[0040] Reference is made to Figure 1 The figure is a structural schematic diagram of an electric heating element with surface-strengthened heat exchange structure provided by the embodiments of the present application.

[0041] The electric heating element with surface-strengthened heat exchange structure provided by the embodiments of the present application comprises, from inside to outside, an electrically conductive rod 1, an electrically conductive tube 2, a high thermal conductivity and high insulation tube 6, a metal tube shell 7, and a spiral rib 8.

[0042] The electrically conductive rod 1 and the electrically conductive tube 2 are filled with high thermal conductivity and high insulation powder 5;

[0043] The high thermal conductivity and high insulation tube 6 and the metal tube shell 7 are filled with liquid metal;

[0044] The spiral rib 8 is spirally distributed on the outer surface of the metal tube shell 7, and the spiral rib 8 is integrally formed with the metal tube shell 7.

[0045] Preferably, the material of the metal tube shell 7 can be stainless steel, zirconium and zirconium alloy, ferrite martensite alloy steel, and oxide dispersion reinforced iron-chromium-aluminum stainless steel.

[0046] The spiral rib 8 can be one or more, preferably four.

[0047] In some possible implementation manners of the embodiments of the present application, the electric heating element further comprises an electric heating alloy wire 4.

[0048] Two ends of the electric heating alloy wire 4 are welded with the conductive rod 1 and the conductive tube 2 respectively;

[0049] The electric heating alloy wire 4 is spirally wound outside the conductive rod 1;

[0050] The conductive rod 1 and the electric heating alloy wire 4 are filled with the high-thermal-conductivity and high-insulation powder 5.

[0051] In some possible implementation manners of the embodiment, one end of the metal tube shell 7 is sealed with the conductive tube 2 through the insulating end plug 3, and the other end is sealed through the stainless steel sealing head 9.

[0052] In some possible implementation manners of the embodiment, the conductive rod 1 adopts a low-resistivity material, which can be a copper-based or nickel-based material.

[0053] In some possible implementation manners of the embodiment, the high-thermal-conductivity and high-insulation powder 5 and the high-thermal-conductivity and high-insulation tube 6 adopt one or any two or three of magnesium oxide, boron nitride and silicon carbide.

[0054] The high-thermal-conductivity and high-insulation tube 6 and the metal tube shell 7 are filled with a liquid metal, which is selected to be a low-melting-point alloy, such as tin-bismuth or indium-tin.

[0055] It should be noted that, since the high-thermal-conductivity and high-insulation tube 6 and the metal tube shell 7 are two different materials and have inconsistent expansion coefficients, a gap is formed at high temperature, thereby forming a surface thermal resistance between the two materials. In the embodiment, a liquid metal with good fluidity is filled in the gap between the high-thermal-conductivity and high-insulation tube 6 and the metal tube shell 7, so as to reduce the interface thermal resistance and improve the overall thermal conductivity. The tin-bismuth or indium-tin material has the advantages of low melting point and high boiling point, which ensures that the filling can be realized at room temperature, and the material is not easy to boil at high temperature, thereby ensuring the stability of the internal pressure of the electric heating alloy tube.

[0056] In one example, the electric heating alloy wire 4 adopts a high-resistance electric heating alloy satisfying GB / T 1234, and the structure form can also be an electric heating alloy belt.

[0057] The electric heating element with the surface-strengthened heat exchange structure provided in the above embodiment has a smooth cylindrical outer surface of the metal tube shell 7 without protruding ribs at the initial assembly. The high-thermal-conductivity and high-insulation powder 5 seriously reduces the internal thermal conductivity and insulation, and therefore needs to be compacted through a certain method.

[0058] Therefore, the application further provides a preparation method of the electric heating element with the surface reinforced heat exchange structure, which is applied to the preparation of any one of the electric heating elements with the surface reinforced heat exchange structure provided in the above embodiments. The high-thermal-conductivity and high-insulation powder 5 is made to form the spiral rib 8 on the surface of the metal tube shell 7 in the process of densification by the method of rotary drawing, so that the processing steps of the metal tubular electric heating element with the surface reinforced heat exchange structure are optimized, and the overall preparation efficiency is improved.

[0059] The preparation method of the electric heating element with the surface reinforced heat exchange structure provided in the application includes the following steps:

[0060] The electrically conductive rod 1, the electric heating alloy wire 4, the electrically conductive tube 2, the high-thermal-conductivity and high-insulation tube 6, and the metal tube shell 7 are assembled; the high-thermal-conductivity and high-insulation powder 5 is filled and compressed; the insulating end plug 3 and the stainless steel sealing head 9 are installed and sealed. It can be understood that the outer diameter of the metal tube shell 7 is greater than the finally required outer diameter at this time;

[0061] The electric heating element is subjected to first drawing, and the metal tube shell 7 with a smooth surface is drawn into a blank state with straight ribs 10;

[0062] The electric heating element is subjected to second drawing, and the metal tube shell 7 is processed into a straight rib 10 structure. The straight rib 10 structure is as shown in Figure 2 ;

[0063] The spiral rib 8 is processed on the metal tube shell 7 by torsion of the straight rib 10 by using a spinning device.

[0064] In some possible implementation manners of the application, the rib height of the processed metal tube shell 7 is S, and the wall thickness is h;

[0065] The outer diameter of the metal tube shell 7 with a smooth surface before processing is ≥h+3mm, and the wall thickness is ≥S+h+1mm.

[0066] It can be understood that, since it is necessary to extrude the rib height on the metal tube blank and then draw the metal tube blank by using a drawing outer die with a pass to reduce the outer diameter and the wall thickness of the blank, it is necessary to design the wall tube to have sufficient outer diameter and wall thickness.

[0067] In some possible implementation manners of the application, the first drawing die is provided with rib grooves with the same shape and number as the straight rib 10.

[0068] The first drawing is uniform drawing at a speed of 0.5m / min-3m / min. The outer diameter of the metal tube shell 7 is reduced by ≥10% after the first drawing, and the wall thickness is reduced by ≥10%.

[0069] The second drawing die is the same structure as the first drawing die, and the rib groove cross-sectional size is smaller than the first drawing die;

[0070] After the second drawing, the straight rib 10 cross-sectional size is reduced.

[0071] It should be noted that the rib groove on the first drawing die needs to be designed to be consistent with the shape and number of the straight rib, which is used to extrude the rib from the smooth metal tube shell. In the embodiment of the application, the rib groove cross-sectional shape is square, and the square straight rib is extruded; a hydraulic drawing machine or a chain drawing machine is used for uniform speed drawing; in order to ensure that the metal is fully filled and the rib is completely formed, the outer diameter reduction of the metal tube shell 7 is ≥10%, and the wall thickness reduction rate is greater than or equal to 10%.

[0072] The purpose of the second drawing is to reduce the cross-sectional size of the straight rib 10; the design principle is to make the deformation elongation rate of the straight rib 10 consistent with the elongation rate of the metal tube, so as to ensure the overall plastic deformation of the rib and the metal tube; during the drawing process, the rib on the metal tube moves forward in the rib groove, and the rib will only deform after the inner wall of the metal tube contacts the core die; after drawing, the metal tube wall becomes uniform under the extrusion deformation of the outer die and the core die, the shape of the rib does not change, the outer diameter and wall thickness of the metal tube shell 7 are further reduced, and the cross-sectional size is reduced.

[0073] In some possible implementations of the embodiment of the application, the compression amount of the high-thermal-conductivity high-insulation powder 5 is not less than 24%.

[0074] The preparation method of the electric heating element with the surface-strengthened heat exchange structure provided in the embodiment of the application will be described below in combination with a specific example:

[0075] The size (outer diameter x wall thickness) of the metal tube shell 7 with a smooth surface is 27.3 x 2.5 mm;

[0076] The metal tube shell 7 is lubricated, the hydraulic press head is reduced in diameter, the reduction amount is greater than 3 mm, the length of the reduced diameter section is 150 mm, and the drawing is prepared;

[0077] The electric heating element is drawn for the first time, the first drawing die with a hole type has four rib grooves on the inner wall, which are uniformly and symmetrically distributed, and the rib groove depth is 1 mm; the electric heating element with the surface-strengthened heat exchange structure with a straight rib on the outer wall is drawn, the outer diameter of the electric heating element is 25 mm, the tube wall thickness is 2.0 mm, there are four straight ribs on the surface, and the rib height is 1 mm;

[0078] The electric heating element is drawn for the second time, the second drawing die with a hole type has a diameter of 19 mm and four rib grooves with a groove depth of 0.88 mm; after drawing, the outer diameter of the electric heating element is 19 mm, the wall thickness is 0.75 mm, there are four straight ribs on the surface, and the rib height is 0.88 mm;

[0079] Optionally, the heating element is drawn a third time. The third drawing die with holes has a diameter of 17mm, four ribs, and a groove depth of 0.82mm. After drawing, the heating element has an outer diameter of 17mm, a wall thickness of 0.65mm, and four straight ribs on the surface with a rib height of 0.82mm. A heating element with straight ribs that meets the size requirements is produced.

[0080] A spinning device is used for spinning. The outer mold of the spinning device has a diameter of 17mm, 4 ribs, and a groove depth of 0.82mm. The linear drawing speed is 700mm / min, and the rotation speed of the thin-walled metal tube with straight ribs is 360° / min, which twists the tube into a helix with a pitch of 300mm to obtain an electric heating element with helical ribs.

[0081] The final product is an electric heating element with a surface-enhanced heat transfer structure. Its outer diameter is 17mm, and it has two helical straight ribs, each square with a height of 0.82mm. The outer metal tube shell 7 is made of 1Cr18Ni9Ti stainless steel. The high thermal conductivity and high insulation tube 6 inside the metal tube is made of boron nitride, with an outer diameter of 20mm. A tin-bismuth alloy is filled into the 1.15mm gap formed between the high thermal conductivity and high insulation tube 6 and the outer metal tube shell 7. After filling, the temperature between the outer metal tube shell and the boron nitride tube decreases significantly, reducing the interfacial thermal resistance. Figure 3 As shown.

[0082] The embodiments of this application have the following beneficial effects:

[0083] (1) Spiral ribs were added to the ordinary smooth surface metal tube shell to enhance the mixing of the outer surface of the heating element during the flow process, which can effectively enhance the heat exchange capacity of the heating element surface and improve the heat exchange efficiency.

[0084] (2) Using low-melting-point, high-fluidity liquid metal as a filler between the metal tube shell and the high thermal conductivity and high insulation tube can effectively reduce the interfacial thermal resistance between the two materials, improve the overall thermal conductivity of the heating element, and enhance the heat exchange efficiency of the heating element.

[0085] (3) The tin-bismuth or indium-tin liquid metal filled between the metal tube shell and the high thermal conductivity and high insulation tube has the advantages of low melting point and high boiling point, which ensures that filling can be achieved at room temperature. At the same time, it is not easy to boil at high temperature, which ensures the stability of the pressure inside the electric heating alloy tube.

[0086] (4) A method for preparing electric heating elements by spiral drawing and cold processing of spiral ribs on the surface of electric heating elements is proposed, which solves the problems of uneven rib height, poor dimensional accuracy and poor rib strength caused by machining spiral ribs on the surface of smooth electric heating elements.

[0087] The application has been described in detail with reference to the accompanying drawings and embodiments, but the application is not limited to the above-mentioned embodiments, and various changes can be made within the knowledge of those skilled in the art without departing from the purpose of the application. The contents not described in detail in the application can adopt the prior art.

Claims

1. A heating element with a surface-enhanced heat transfer structure, characterized in that, The heating element comprises, from the inside out, a conductive rod (1), a conductive tube (2), a high thermal conductivity and high insulation tube (6), a metal tube shell (7), and a spiral rib (8); The space between the conductive rod (1) and the conductive tube (2) is filled with highly thermally conductive and highly insulating powder (5); Liquid metal is filled between the high thermal conductivity and high insulation tube (6) and the metal tube shell (7); The spiral ribs (8) are spirally distributed on the outer surface of the metal tube shell (7), and the spiral ribs (8) are integrally formed with the metal tube shell (7).

2. The electric heating element with a surface-reinforced heat transfer structure according to claim 1, characterized in that, It also includes an electrothermal alloy wire (4); The two ends of the electrothermal alloy wire (4) are respectively welded to the conductive rod (1) and the conductive tube (2); The heating alloy wire (4) is spirally wound around the outside of the conductive rod (1); The conductive rod (1) and the heating alloy wire (4) are filled with a highly thermally conductive and highly insulating powder (5).

3. The electric heating element with a surface-reinforced heat transfer structure according to claim 1, characterized in that, One end of the metal tube shell (7) is sealed to the conductive tube (2) by an insulating end plug (3), and the other end is sealed by a stainless steel sealing head (9).

4. The electric heating element with a surface-reinforced heat transfer structure according to claim 1, characterized in that, The conductive rod (1) is made of a low resistivity material, which can be copper-based or nickel-based.

5. The electric heating element with a surface-reinforced heat transfer structure according to claim 1, characterized in that, The high thermal conductivity and high insulation powder (5) and the high thermal conductivity and high insulation tube (6) are made of one or any two or three of magnesium oxide, boron nitride, and silicon carbide. The liquid metal filling the space between the high thermal conductivity and high insulation tube (6) and the metal tube shell (7) is a low melting point alloy, which may be tin-bismuth or indium-tin.

6. The electric heating element with a surface-reinforced heat transfer structure according to claim 2, characterized in that, The heating alloy wire (4) is made of a high-resistance heating alloy that meets GB / T 1234, and its structure can also be a heating alloy strip.

7. A method for preparing an electric heating element with a surface-reinforced heat transfer structure, characterized in that, The method for preparing the electric heating element with surface-reinforced heat transfer structure according to any one of claims 1-6 comprises the following steps: Assemble the conductive rod (1), heating alloy wire (4), conductive tube (2), high thermal conductivity and high insulation tube (6), and metal tube shell (7); fill with high thermal conductivity and high insulation powder (5) and compress; install insulating end plug (3) and stainless steel sealing head (9) for sealing; The heating element is pulled for the first time, and the smooth metal tube shell (7) is pulled into a blank state with straight ribs (10). The heating element is drawn a second time to process the metal tube shell (7) into a straight rib (10) structure; Spiral ribs (8) are formed on the metal tube shell (7) by spinning using a spinning device and twisting the straight ribs (10).

8. The method for preparing an electric heating element with a surface-reinforced heat transfer structure according to claim 7, characterized in that, The rib height of the processed metal tube shell (7) is S, and the wall thickness is h; Before processing, the outer diameter of the smooth metal tube shell is ≥h+3mm, and the wall thickness is ≥S+h+1mm.

9. The method for preparing an electric heating element with a surface-reinforced heat transfer structure according to claim 7, characterized in that, The first drawing die is equipped with rib grooves of the same shape and number as the straight ribs (10); The first drawing is a uniform drawing at a speed of 0.5 m / min to 3 m / min; after the first drawing, the outer diameter reduction of the metal tube shell (7) is ≥10%, and the wall thickness reduction rate is greater than or equal to 10%. The second drawing die has the same structure as the first drawing die, but the cross-sectional dimensions of the rib groove are smaller than those of the first drawing die. After the second drawing, the cross-sectional dimensions of the straight rib (10) become smaller.

10. The method for preparing an electric heating element with a surface-reinforced heat transfer structure according to claim 7, characterized in that, The high thermal conductivity and high insulation powder (5) has a compression weight of not less than 24%.

Images