Electric radiant tube facilitating prolonging of service life and method

Abstract

According to the electric radiant tube beneficial to prolonging the service life and the method disclosed by the invention, the electric heating wires of the electric radiant tube are arranged in a non-uniform distribution manner along the circumferential direction of the ceramic body supporting sheet; according to the method, the fracture toughness of a ceramic body is taken as a constraint lower limit, the allowable maximum area of a single ceramic body supporting piece is taken as a constraint upper limit, uniform temperature field distribution is taken as a target function, the distribution of the heating wires on the single ceramic body supporting piece is optimized, and the distribution of the heating wires is determined according to an optimization result. According to the electric radiant tube beneficial to prolonging the service life and the method, on the basis of optimizing the influence of the uniformity of the temperature field on the heating effect, the tensile strength and the cost of the ceramic body are considered, the service life of the radiant tube is prolonged on the whole, and the response to process requirements is guaranteed.

Description

Technical Field

[0001] The present invention belongs to the technical field of industrial electric heating, and particularly relates to an electric radiant tube and method conducive to improving the service life. Background Art

[0002] The radiant tube is an indirect heating element widely used in industrial furnaces. There are many problems with traditional gas radiant tubes in industrial applications, such as a relatively high exhaust gas temperature, uneven temperature distribution on the wall surface of the radiant tube, and a large amount of combustion product emissions. Although technical optimization measures have been proposed for gas radiant tubes, due to the use of gas in the gas radiant tube, the problem of NOx emissions always exists.

[0003] The electric radiant tube can not only improve the heating efficiency but also fundamentally solve the problem of NOx emissions. The electric radiant tubes used in industry are mainly cage-type electric radiant tubes, which mainly consist of a radiant tube sleeve, a ceramic body, and heating wires. The ceramic body mainly serves as a support for the heating wires. When the electric radiant tube is working, the surface temperature of the heating wires can reach about 1200°C.

[0004] When designing the existing electric radiant tubes, the basic design principle followed is: meeting the power requirement + uniform distribution of heating wires to form uniform heat supply. However, in actual use, the fatigue cycle of the radiant tube is about several months to one year, showing a deviation from the theoretical fatigue cycle, and the degree of deviation shows a random distribution.

[0005] The invention application with the application number: CN201110163899.5 discloses a "radiant tube heating device", including a double A-type radiant tube, including an intermediate tube, a first side tube, and a second side tube. The first side tube and the intermediate tube form a closed first flue gas circulation channel, and the second side tube and the intermediate tube form a closed second flue gas circulation channel. On the same side of the radiant tube, there are respectively extended outward an intermediate installation pipe, a first installation pipe, and a second installation pipe. The heat exchanger includes a first heat exchanger and a second heat exchanger; the burner is fixedly arranged in the intermediate installation pipe, and the first heat exchanger and the second heat exchanger are respectively connected to the burner through air ducts. It makes the temperature distribution of the radiant tube uniform, reduces the flame temperature, and reduces the emission of NOx; and increases the heat exchange area, can effectively increase the air preheating temperature and reduce the exhaust gas temperature, and the thermal efficiency is increased. Moreover, it prolongs the service life of the radiant tube and improves the temperature uniformity of the radiant tube.

[0006] The invention application with the application number CN201811570700.9 discloses "a method and device for controlling the temperature of an electric radiation tube". By collecting the current strip information in the vertical annealing furnace; determining the output limit of the electric radiation tube in the vertical annealing furnace; collecting the strip temperature setting value of the strip in the current processing section; obtaining the tube temperature reference value of the electric radiation tube in the current processing section according to the strip temperature setting value of the strip in the current processing section; and obtaining the temperature setting value of the electric radiation tube of the strip in the current processing section according to the tube temperature reference value, the position corresponding to the roll chamber in the current processing section, and the strip temperature setting value of the previous processing section. Summary of the Invention

[0007] To solve the above problems, the present invention provides an electric radiation tube and method that are beneficial to improving the service life. The technical solutions are as follows:

[0008] An electric radiation tube includes a U-shaped electric heating wire 1, a ceramic body for supporting the U-shaped electric heating wire 1 and forming an insulating layer between the U-shaped electric heating wires, and a sleeve 4 sleeved on the ceramic body. The ceramic body includes a ceramic body support shaft 2 and ceramic body support pieces 3. A hole is opened at the center of the ceramic body support piece 3, and the ceramic body support shaft 2 passes through the hole of the ceramic body support piece 3. The ceramic body support pieces 3 are multiple and are axially spaced along the ceramic body support shaft 2.

[0009] The U-shaped electric heating wire 1 is non-uniformly distributed along the circumferential direction of the ceramic body support piece 3.

[0010] Furthermore,

[0011] The U-shaped electric heating wire 1 is arranged in a one-turn manner along the circumferential direction of the ceramic body support piece 3.

[0012] According to this non-uniform distribution, specifically:

[0013] The holes opened on the ceramic body support piece 3 for arranging the electric heating wire are such that the setting positions of each hole are equidistant from the center of the ceramic body support piece 3. Along the path from the bottom end to the top end of the ceramic body support piece 3 in the circumferential direction, the arc lengths between adjacent holes are arranged in a manner that gradually increases the sparsity.

[0014] Furthermore,

[0015] The U-shaped electric heating wire 1 is arranged in a two-turn manner along the circumferential direction of the ceramic body support piece 3.

[0016] According to this non-uniform distribution, specifically:

[0017] In the first turn, the holes opened on the ceramic body support piece 3 for arranging the electric heating wire are such that the setting positions of each hole are equidistant from the center of the ceramic body support piece 3.

[0018] On the second circle, the openings for arranging the heating wires on the ceramic support plate 3 are arranged at equal distances from the center of the ceramic support plate 3.

[0019] On the first circle and the second circle, the arc lengths between adjacent openings are arranged in a manner of increasing sparseness along the path from the bottom end of the ceramic support plate 3 to the top end of the ceramic support plate 3 along the circumferential direction.

[0020] Furthermore,

[0021] The U-shaped heating wire 1 is arranged in a circle along the circumference of the ceramic support plate 3.

[0022] The non-uniform distribution is as follows:

[0023] The openings for disposing the heating wires on the ceramic support plate 3 are arranged at equal distances from the center of the ceramic support plate 3.

[0024] The openings distributed along the circumferential direction are divided into a pair of openings with the shortest distance from the top of the ceramic support plate 3 and other openings;

[0025] The arc length between a pair of openings that are at the shortest distance from the top of the ceramic support plate 3 is set according to the first arc length;

[0026] For the remaining openings, the arc length between two adjacent openings is set according to the second arc length;

[0027] The length of the first arc is 2.5 to 3 times the length of the second arc.

[0028] Further,

[0029] The U-shaped heating wire 1 is arranged in two circles along the circumference of the ceramic support plate 3.

[0030] The non-uniform distribution is as follows:

[0031] On the first circle, the openings for arranging the heating wires on the ceramic support plate 3 are arranged at equal distances from the center of the ceramic support plate 3.

[0032] On the second circle, the openings for arranging the heating wires on the ceramic support plate 3 are arranged at equal distances from the center of the ceramic support plate 3.

[0033] The openings in the first circle distributed along the circumference are evenly distributed with equal arc lengths;

[0034] The second circle of openings distributed along the circumferential direction is divided into a pair of openings with the shortest distance from the top of the ceramic support plate 3 and other openings;

[0035] Set the arc length between the pair of openings with the smallest distance from the top of the ceramic body support piece 3 according to the first arc length;

[0036] For the remaining openings, set the arc length between adjacent two openings according to the second arc length;

[0037] The first arc length is 3.5 to 5 times the second arc length.

[0038] Furthermore,

[0039] The diameter of the heating wire is 5 - 5.5 mm.

[0040] Furthermore,

[0041] The diameter of the heating wire is 6 - 7 mm.

[0042] Furthermore,

[0043] The shortest arc length between adjacent openings is 15 - 18 mm.

[0044] Furthermore,

[0045] The shortest arc length between adjacent openings is 7 - 10 mm, and the distance between the first and second circles is 10 - 15 mm.

[0046] Furthermore,

[0047] The second arc length is 15 - 18 mm.

[0048] Furthermore,

[0049] The second arc length is 7 - 10 mm, and the distance between the first and second circles is 10 - 15 mm.

[0050] A method for improving the service life of an electric radiation tube,

[0051] Taking the fracture toughness of the ceramic body as the lower constraint limit, taking the maximum allowable area of a single ceramic body support piece as the upper constraint limit, and taking the uniform distribution of the overall temperature field of the radiation tube as the objective function, optimize the distribution of the heating wire on a single ceramic body support piece, and determine the distribution of the heating wire according to the optimization result.

[0052] Furthermore,

[0053] The optimization of the distribution of the heating wire on a single ceramic body support piece specifically includes the following steps:

[0054] S11: Determine the shortest distance between adjacent two heating wires according to the fracture toughness of the ceramic body, and determine the area of the ceramic body support piece according to the maximum allowable area of a single ceramic body support piece;

[0055] S12: Using the determined shortest distance and area as the initial values, for the openings on the ceramic body support sheet for arranging the heating wires, the set positions of each opening are equidistant from the center of the ceramic body support sheet. Along the path from the bottom end to the top end of the ceramic body support sheet in the circumferential direction, the arc length between adjacent openings increases in a gradually increasing sparsity manner. Iterate on the distance between adjacent heating wires and the area of a single ceramic body support sheet, and calculate the temperature field distribution of the radiant tube after each iteration;

[0056] S13: Based on the point values of the temperature field distribution of the radiant tube calculated, determine whether the temperature field distribution under the current iteration meets the requirements through the set temperature field uniformity objective function. If it does not meet the requirements, continue the iteration until it meets the requirements and terminate the iteration, and determine the current value as the final set value.

[0057] Furthermore,

[0058] The heating wires are arranged in a single circle or two circles along the circumferential direction of the ceramic body support sheet.

[0059] Furthermore,

[0060] The optimization of the distribution of the heating wires on a single ceramic body support sheet specifically includes the following steps:

[0061] S21: Determine the shortest distance between adjacent two heating wires according to the fracture toughness of the ceramic body, and determine the area of the ceramic body support sheet according to the maximum allowable area of a single ceramic body support sheet;

[0062] S22: Using the determined shortest distance and area as the initial values, for the openings on the ceramic body support sheet for arranging the heating wires, the set positions of each opening are equidistant from the center of the ceramic body support sheet. Divide the circumferentially distributed openings into a pair of openings with the smallest distance from the top end of the ceramic body support sheet and other openings; in a way that the arc length between the pair of openings with the smallest distance from the top end of the ceramic body support sheet is greater than the arc length between adjacent two of the other openings, iterate on the distance between adjacent heating wires and the area of a single ceramic body support sheet, and calculate the temperature field distribution of the radiant tube after each iteration;

[0063] S23: Based on the point values of the temperature field distribution of the radiant tube calculated, determine whether the temperature field distribution under the current iteration meets the requirements through the set temperature field uniformity objective function. If it does not meet the requirements, continue the iteration until it meets the requirements and terminate the iteration, and determine the current value as the final set value.

[0064] Furthermore,

[0065] The heating wires are arranged in a single circle or two circles along the circumferential direction of the ceramic body support sheet.

[0066] Further,

[0067] When the heating wire is arranged in a single loop along the ceramic body support sheet, for the case of "using the openings provided on the ceramic body support sheet for arranging the heating wire, the setting positions of each opening are equidistant from the center of the ceramic body support sheet, dividing the circumferentially distributed openings into a pair of openings with the smallest distance from the top end of the ceramic body support sheet and other openings; and iterating the distance between adjacent heating wires and the area of a single ceramic body support sheet in such a way that the arc length between the pair of openings with the smallest distance from the top end of the ceramic body support sheet is greater than the arc length between two adjacent other openings", it is carried out under the constraint that the arc length between the pair of openings with the smallest distance from the top end of the ceramic body support sheet is 2.5 to 3 times greater than the arc length between two adjacent other openings.

[0068] Further,

[0069] When the heating wire is arranged in two loops along the ceramic body support sheet, the "using the openings provided on the ceramic body support sheet for arranging the heating wire, the setting positions of each opening are equidistant from the center of the ceramic body support sheet, dividing the circumferentially distributed openings into a pair of openings with the smallest distance from the top end of the ceramic body support sheet and other openings; and iterating the distance between adjacent heating wires and the area of a single ceramic body support sheet in such a way that the arc length between the pair of openings with the smallest distance from the top end of the ceramic body support sheet is greater than the arc length between two adjacent other openings" is specifically as follows: for the openings provided on the ceramic body support sheet of the first loop for arranging the heating wire, with the setting positions of each opening being equidistant from the center of the ceramic body support sheet, the circumferentially distributed openings are evenly distributed according to equal arc lengths. For the openings provided on the ceramic body support sheet of the first loop for arranging the heating wire, with the setting positions of each opening being equidistant from the center of the ceramic body support sheet, the circumferentially distributed openings are divided into a pair of openings with the smallest distance from the top end of the ceramic body support sheet and other openings; and iterating the distance between adjacent heating wires and the area of a single ceramic body support sheet in such a way that the arc length between the pair of openings with the smallest distance from the top end of the ceramic body support sheet is greater than the arc length between two adjacent other openings.

[0070] Further,

[0071] The "the arc length between the pair of openings with the smallest distance from the top end of the ceramic body support sheet is greater than the arc length between two adjacent other openings" is specifically: the arc length between the pair of openings with the smallest distance from the top end of the ceramic body support sheet is 3.5 to 5 times greater than the arc length between two adjacent other openings.

[0072] Further,

[0073] The so-called "taking the fracture toughness of the ceramic body as the lower limit of constraint" specifically means:

[0074] First, calculate the corresponding stress field distribution based on the current temperature field distribution to obtain the stress values at each calculation node;

[0075] Secondly, substitute the maximum stress value into the following formula, and then compare the calculation result with the fracture toughness value. When the calculation result is less than the fracture toughness value, the constraint is satisfied; otherwise, it is not satisfied.

[0076]

[0077] In the above formula,

[0078] K: Stress intensity index under the current temperature field distribution;

[0079] σ: Maximum stress value under the current temperature field distribution, unit: Pa;

[0080] α: Correction coefficient;

[0081] σbb: Flexural strength of the ceramic body, unit: Pa.

[0082] Furthermore,

[0083] The value range of the correction coefficient α is: [1 - 4].

[0084] Furthermore,

[0085] The so-called "taking the uniform temperature field distribution as the objective function" specifically means:

[0086] Establish the first objective function based on the skewness between the temperature mean value and the target temperature value falling within [10, 20];

[0087] Establish the second objective function based on the temperature fluctuation amplitude falling within [20, 30],

[0088] Complete the establishment of the objective function with the first objective function and the second objective function forming a logical AND relationship.

[0089] An electric radiation tube and method for improving the service life according to the present invention, while optimizing the influence of the temperature field uniformity on the heating effect, takes into account the tensile strength and cost of the ceramic body, and overall improves the service life of the radiation tube and ensures the response to process requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0090] Figure 1 It is a schematic structural diagram of the electric radiation tube in the present invention;

[0091] Figure 2 It is a schematic diagram of the optimization steps of the electric heating wire distribution on a single ceramic body support sheet based on the gradually increasing sparsity in the present invention;

[0092] Figure 3 This is a schematic diagram of the optimization steps for the distribution of heating wires on a single ceramic body support sheet based on the missing heating wire type in the present invention.

[0093] In the figure,

[0094] 1 - Heating wire;

[0095] 2 - Ceramic body support shaft;

[0096] 3 - Ceramic body support sheet;

[0097] 4 - Sleeve. Specific embodiments

[0098] Next, a kind of electric radiant tube and method for improving service life according to the present invention will be further specifically described according to the drawings in the specification and the specific embodiments. The following understanding can be combined with Figure 1 , 2 , 3 for implementation.

[0099] Design concept, working principle and process:

[0100] The technical solution aims at such an electric radiant tube, which includes a U-shaped heating wire 1, a ceramic body for supporting the U-shaped heating wire 1 and forming an insulating layer between the U-shaped heating wires, and a sleeve 4 sleeved on the ceramic body. The ceramic body includes a ceramic body support shaft 2 and a ceramic body support sheet 3. A hole is opened at the center of the ceramic body support sheet 3, and the ceramic body support shaft 2 passes through the hole of the ceramic body support sheet 3. The ceramic body support sheets 3 are multiple and are axially spaced along the ceramic body support shaft 2. Some who use two ceramic body support sheets together as one ceramic sheet to enhance stability are also regarded as the electric radiant tube aimed at by the technical solution.

[0101] As described in the background art section, when the existing electric radiation tubes are designed, the basic design principle followed is: meeting the power requirement + uniform distribution of the heating wire to form uniform heat supply. The problems existing in this setting method are as described in the background art section. At the same time, it is found in actual operation that: since the radiation tubes in the furnace are divided into the side close to the heated workpiece and the side close to the furnace wall, and the heat exchange on the side close to the heated workpiece is more sufficient than that on the side close to the furnace wall, the overall temperature distribution of the radiation tubes is uneven, thus affecting the heating effect. Therefore, how to solve the deviation between the actual fatigue cycle and the theoretical fatigue cycle, and the deviation degree is random, and at the same time, how to solve the problem of uneven temperature distribution in the actual use of the radiation tubes have become two major problems that need to be solved urgently. It should be noted here that: for the convenience of understanding this technical solution, the side close to the furnace wall after the radiation tube is placed is uniformly defined as the upper end (or top end), and the side close to the heated workpiece is defined as the lower end (or bottom end). The lowest end and the highest end of the ceramic body support piece described in the text are based on this setting as the reference standard.

[0102] This technical solution innovatively proposes to take the fracture toughness of the ceramic body as the lower limit of the constraint, the maximum allowable area of a single ceramic body support piece as the upper limit of the constraint, and the uniform distribution of the overall temperature field of the radiation tube as the objective function, to optimize the distribution of the heating wire on a single ceramic body support piece, and determine the distribution of the heating wire according to the optimization result. The constraint of the fracture toughness of the ceramic body is established by comparing the maximum stress with the bending strength to form a more stringent constraint, so as to reach a safer and more reliable distance, so as to ensure that the service life of the ceramic body is not affected by the distribution distance of the heating wire, but only restricted by its own material properties; at the same time, in order to prevent the constraint established in this way from being too strict, a correction coefficient α is further set to facilitate the adaptive adjustment of the actual situation. Specifically:

[0103] First, calculate the corresponding stress field distribution based on the current temperature field distribution to obtain the stress values at each calculation node;

[0104] Secondly, substitute the maximum stress value into the following formula, and then compare the calculation result with the fracture toughness value. When the calculation result is less than the fracture toughness value, the constraint is satisfied, otherwise it is not satisfied;

[0105]

[0106] In the above formula,

[0107] K: Stress intensity index under the current temperature field distribution;

[0108] σ: Maximum stress value under the current temperature field distribution, unit: Pa;

[0109] α: Correction coefficient;

[0110] σbb: Flexural strength of the ceramic body, unit: Pa.

[0111] The value range of the correction coefficient α is: [1 - 4].

[0112] The reason for introducing the constraint lower limit based on the fracture toughness of the ceramic body is that the thermal conductivity of the ceramic body is very low, making it difficult for heat to transfer, resulting in an increase in the internal temperature gradient, thereby increasing the thermal stress; and the uneven temperature distribution caused by external environmental reasons will exacerbate this situation, leading to the actual maximum stress exceeding the allowable stress of the material itself.

[0113] Since in the process of optimizing the uniform distribution of the temperature field, the fracture toughness constraint of the ceramic body and the allowable maximum area constraint of a single ceramic body support sheet are introduced, this technical solution performs a certain degree of "relaxation treatment" on the objective function, that is, by establishing the first objective function with the skewness between the temperature mean and the target temperature value falling within [10, 20]; establishing the second objective function with the temperature fluctuation amplitude falling within [20, 30], and completing the establishment of the objective function with the relationship of "and" composed of the first objective function and the second objective function.

[0114] The fracture toughness value used to judge whether the fracture toughness of the ceramic body meets the constraint is determined according to the current ceramic body material, the maximum operating area of a single ceramic body support sheet is determined according to the process requirements, and the target temperature value in the first objective function is determined according to the process requirements, and all are pre-entered into L4. The above process involves the solution of the temperature field and the stress field. The solution process is based on the idea of using difference to approximate the differential, discretizing the constitutive equation, and then completing it based on the numerical solution. It is completed by using Fluent finite element analysis. Since both the single ceramic body piece and the radiation tube are set with regular symmetric structures and are in the case of having heat sources in the internal field, based on this, the corresponding simplification treatments are first carried out on the heat conduction differential equation and the stress constitutive equation.

[0115] The simplified partial differential equation group is specifically as follows:

[0116]

[0117]

[0118]

[0119] ρ: Density, kg / m3;

[0120] c: Specific heat, J / (kg·K);

[0121] T: Temperature, K;

[0122] r: Radius, mm;

[0123] λr: Radial thermal conductivity, W / (m·K);

[0124] Radian in cylindrical coordinate system, rad;

[0125] u: Velocity in the x - direction in a two - dimensional coordinate system, m / s;

[0126] v: Velocity in the y - direction in a two - dimensional coordinate system, m / s;

[0127] α: Coefficient of thermal expansion, 1 / K;

[0128] In this technical solution, the distribution of heating wires on a single ceramic body support sheet based on gradually increasing sparsity and the distribution of heating wires on a single ceramic body support sheet based on missing heating wires can be formed. According to their own optimization, both of these situations can achieve the technical objectives of this technical solution.

[0129] The distribution of heating wires on a single ceramic body support sheet with gradually increasing sparsity refers to: when the heating wires are distributed in a circle along the circumference of the ceramic body support sheet, for the openings on the ceramic body support sheet 3 for arranging the heating wires, the setting positions of each opening are equidistant from the center of the ceramic body support sheet 3. On the path from the bottom end to the top end of the ceramic body support sheet 3 along the circumference, the arc length between adjacent openings is set in a way that the sparsity gradually increases;

[0130] Or, when the heating wires are distributed in two circles along the circumference of the ceramic body support sheet, on the first circle, for the openings on the ceramic body support sheet 3 for arranging the heating wires, the setting positions of each opening are equidistant from the center of the ceramic body support sheet 3. On the second circle, for the openings on the ceramic body support sheet 3 for arranging the heating wires, the setting positions of each opening are equidistant from the center of the ceramic body support sheet 3. On the first circle and the second circle, on the path from the bottom end to the top end of the ceramic body support sheet 3 along the circumference, the arc length between adjacent openings is set in a way that the sparsity gradually increases.

[0131] The distribution of heating wires on a single ceramic body support sheet with missing heating wires refers to: when the heating wires are distributed in a circle along the circumference of the ceramic body support sheet, for the openings on the ceramic body support sheet 3 for arranging the heating wires, the setting positions of each opening are equidistant from the center of the ceramic body support sheet 3. The openings distributed along the circumference are divided into a pair of openings with the smallest distance from the top end of the ceramic body support sheet 3 and other openings; the arc length between the pair of openings with the smallest distance from the top end of the ceramic body support sheet 3 is set according to the first arc length; for the remaining openings, the arc length between adjacent two openings is set according to the second arc length; and at the same time, the first arc length is set to be 2.5 - 3 times the second arc length;

[0132] Alternatively, when the heating wire is distributed in two circumferential turns along the ceramic body support sheet, on the first turn, for the openings provided on the ceramic body support sheet 3 for arranging the heating wire, the setting positions of each opening are equidistant from the center of the ceramic body support sheet 3; on the second turn, for the openings provided on the ceramic body support sheet 3 for arranging the heating wire, the setting positions of each opening are equidistant from the center of the ceramic body support sheet 3. The openings distributed along the circumferential direction of the first turn are evenly distributed with equal arc lengths; the openings distributed along the circumferential direction of the second turn are divided into a pair of openings with the smallest distance from the topmost end of the ceramic body support sheet 3 and other openings; for the arc length between the pair of openings with the smallest distance from the topmost end of the ceramic body support sheet 3, it is set according to the first arc length; for the remaining openings, the arc length between adjacent two openings is set according to the second arc length; and at the same time, the first arc length is set to be 3.5 to 5 times the second arc length.

[0133] At the same time, for the heating wire distributions on a single ceramic body support sheet based on the gradually increasing sparsity type and the heating wire distribution on a single ceramic body support sheet based on the missing heating wire type as described above, respective design considerations are made for the corresponding heating wire diameters according to the circumferential turns of the heating wire along the ceramic body support sheet, so as to establish the adaptation of the heating wire to different single powers. Specifically: for the case of circumferential single-turn distribution, the corresponding heating wire diameter is set to 5 - 5.5 mm; for the case of circumferential two-turn distribution, the corresponding heating wire diameter is set to 6 - 7 mm.

[0134] For the heating wire distribution on a single ceramic body support sheet based on the gradually increasing sparsity type as described above, the specific optimization process is as follows:

[0135] S11: Determine the shortest distance between adjacent two heating wires according to the fracture toughness of the ceramic body, and determine the area of the ceramic body support sheet according to the allowable maximum area of a single ceramic body support sheet;

[0136] S12: Taking the determined shortest distance and area as initial values, for the openings provided on the ceramic body support sheet for arranging the heating wire, the setting positions of each opening are equidistant from the center of the ceramic body support sheet, and on the path from the bottommost end to the topmost end of the ceramic body support sheet along the circumferential direction, the arc length between adjacent openings increases in a gradually increasing sparsity manner, iterate on the distance between adjacent heating wires and the area of a single ceramic body support sheet, and calculate the temperature field distribution of the radiant tube after each iteration;

[0137] S13: Based on the values of each point of the calculated temperature field distribution of the radiant tube, judge whether the temperature field distribution under the current iteration meets the requirements through the set temperature field uniformity objective function. If it does not meet the requirements, continue the iteration until it meets the requirements and terminate the iteration, and determine the current value as the final set value.

[0138] Regarding the distribution of heating wires on a single ceramic body support sheet based on the missing heating wire type as described above, the specific optimization process is as follows:

[0139] S21: Determine the shortest distance between two adjacent heating wires according to the fracture toughness of the ceramic body, and determine the area of the ceramic body support sheet according to the maximum allowable area of a single ceramic body support sheet;

[0140] S22: Take the determined shortest distance and area as the initial values. For the openings on the ceramic body support sheet for arranging the heating wires, the setting positions of each opening are equidistant from the center of the ceramic body support sheet. Divide the circumferentially distributed openings into a pair of openings with the smallest distance from the top end of the ceramic body support sheet and other openings; in a way that the arc length between the pair of openings with the smallest distance from the top end of the ceramic body support sheet is greater than the arc length between two adjacent other openings, iterate on the distance between adjacent heating wires and the area of a single ceramic body support sheet, and calculate the temperature field distribution of the radiation tube after each iteration;

[0141] S23: Based on the values of each point of the calculated temperature field distribution of the radiation tube, judge whether the temperature field distribution under the current iteration meets the requirements through the set temperature field uniformity objective function. If it does not meet the requirements, continue to iterate until it meets the requirements and terminate the iteration, and determine the current value as the final set value.

[0142] When the heating wires are arranged in two circles on the ceramic body support sheet, the description in S22 "For the openings on the ceramic body support sheet for arranging the heating wires, the setting positions of each opening are equidistant from the center of the ceramic body support sheet. Divide the circumferentially distributed openings into a pair of openings with the smallest distance from the top end of the ceramic body support sheet and other openings; in a way that the arc length between the pair of openings with the smallest distance from the top end of the ceramic body support sheet is greater than the arc length between two adjacent other openings, iterate on the distance between adjacent heating wires and the area of a single ceramic body support sheet" is specifically: For the openings on the ceramic body support sheet of the first circle for arranging the heating wires, with the setting positions of each opening being equidistant from the center of the ceramic body support sheet, evenly distribute the circumferentially distributed openings according to equal arc lengths. For the openings on the ceramic body support sheet of the first circle for arranging the heating wires, with the setting positions of each opening being equidistant from the center of the ceramic body support sheet, divide the circumferentially distributed openings into a pair of openings with the smallest distance from the top end of the ceramic body support sheet and other openings; in a way that the arc length between the pair of openings with the smallest distance from the top end of the ceramic body support sheet is greater than the arc length between two adjacent other openings, iterate on the distance between adjacent heating wires and the area of a single ceramic body support sheet.

[0143] When the heating wire is arranged in a two-loop manner along the ceramic body support sheet, the "openings for arranging the heating wire opened on the ceramic body support sheet, the setting positions of each opening are equidistant from the center of the ceramic body support sheet, and the circumferentially distributed openings are divided into a pair of openings with the smallest distance from the top end of the ceramic body support sheet and other openings; iterating the distance between adjacent heating wires and the area of a single ceramic body support sheet in such a way that the arc length between the pair of openings with the smallest distance from the top end of the ceramic body support sheet is greater than the arc length between adjacent two of the other openings" described in S22 is specifically as follows: For the openings for arranging the heating wire opened on the ceramic body support sheet in the first loop, with the setting positions of each opening being equidistant from the center of the ceramic body support sheet, the circumferentially distributed openings are evenly distributed according to equal arc lengths. For the openings for arranging the heating wire opened on the ceramic body support sheet in the first loop, with the setting positions of each opening being equidistant from the center of the ceramic body support sheet, the circumferentially distributed openings are divided into a pair of openings with the smallest distance from the top end of the ceramic body support sheet and other openings; iterating the distance between adjacent heating wires and the area of a single ceramic body support sheet in such a way that the arc length between the pair of openings with the smallest distance from the top end of the ceramic body support sheet is greater than the arc length between adjacent two of the other openings. The "the arc length between the pair of openings with the smallest distance from the top end of the ceramic body support sheet is greater than the arc length between adjacent two of the other openings" specifically means that the arc length between the pair of openings with the smallest distance from the top end of the ceramic body support sheet is 3.5 to 5 times greater than the arc length between adjacent two of the other openings.

[0144] It should be noted that: Whether it is the optimization result obtained based on step S13 or the optimization result obtained based on step S23, it can only guarantee a feasible solution, but not necessarily the optimal solution. If you want to further find a better solution, or want to confirm whether the current feasible solution is a relatively good solution. You can also establish further optimization based on constraints such as minimum variance and minimum fluctuation amplitude, so as to find a better solution or the optimal solution among the feasible solutions.

Claims

1. An electric radiation tube, comprising a U-shaped heating wire (1), a ceramic body for supporting the U-shaped heating wire (1) and forming an insulating layer between the U-shaped heating wires, and a sleeve (4) sleeved on the ceramic body, wherein the ceramic body comprises a ceramic body support shaft (2) and a ceramic body support plate (3), a hole is opened in the center of the ceramic body support plate (3), the ceramic body support shaft (2) passes through the hole of the ceramic body support plate (3), and the ceramic body support plates (3) are distributed in a plurality of axially spaced intervals along the ceramic body support shaft (2), characterized in that: The U-shaped heating wire (1) is distributed non-uniformly along the circumference of the ceramic support plate (3).

2. The electric radiation tube according to claim 1, characterized in that: The U-shaped heating wire (1) is arranged in a circle along the circumference of the ceramic support plate (3). The non-uniform distribution is as follows: The openings for distributing the heating wires on the ceramic support plate (3) are arranged at equal distances from the center of the ceramic support plate (3), and the arc lengths between adjacent openings are arranged in a manner of increasing sparseness along a path from the bottom end of the ceramic support plate (3) to the top end of the ceramic support plate (3) along a circumferential transition.

3. The electric radiation tube according to claim 1, characterized in that: The U-shaped heating wire (1) is arranged in two circles along the circumference of the ceramic support plate (3). The non-uniform distribution is as follows: On the first circle, the openings for arranging the heating wires on the ceramic support plate (3) are arranged at equal distances from the center of the ceramic support plate (3). On the second circle, the openings for disposing the heating wires on the ceramic support plate (3) are arranged at equal distances from the center of the ceramic support plate (3). On the first circle and the second circle, the arc lengths between adjacent openings are arranged in a manner of increasing sparseness along the path from the bottom end of the ceramic support plate (3) to the top end of the ceramic support plate (3) along the circumferential direction.

4. The electric radiation tube according to claim 1, characterized in that: The U-shaped heating wire (1) is arranged in a circle along the circumference of the ceramic support plate (3). The non-uniform distribution is as follows: The openings for disposing the heating wires on the ceramic support plate (3) are arranged at equal distances from the center of the ceramic support plate (3). Dividing the openings distributed along the circumferential direction into a pair of openings with the shortest distance from the top of the ceramic support plate (3) and other openings; The arc length between a pair of openings that are at the shortest distance from the top of the ceramic support plate (3) is set according to the first arc length; For the remaining openings, the arc length between two adjacent openings is set according to the second arc length; The length of the first arc is 2.5 to 3 times the length of the second arc.

5. The electric radiation tube according to claim 1, characterized in that: The U-shaped heating wire (1) is arranged in two circles along the circumference of the ceramic support plate (3). The non-uniform distribution is as follows: On the first circle, the openings for arranging the heating wires on the ceramic support plate (3) are arranged at equal distances from the center of the ceramic support plate (3). On the second circle, the openings for disposing the heating wires on the ceramic support plate (3) are arranged at equal distances from the center of the ceramic support plate (3). The openings in the first circle distributed along the circumference are evenly distributed with equal arc lengths; Dividing the second circle of openings distributed along the circumferential direction into a pair of openings with the shortest distance from the top of the ceramic support plate (3) and other openings; The arc length between a pair of openings that are at the shortest distance from the top of the ceramic support plate (3) is set according to the first arc length; For the remaining openings, the arc length between two adjacent openings is set according to the second arc length; The length of the first arc is 3.5 to 5 times the length of the second arc.

6. An electric radiation tube according to claim 2 or 4, characterized in that: The diameter of the heating wire is 5-5.5mm.

7. An electric radiation tube according to claim 3 or 5, characterized in that: The diameter of the heating wire is 6-7mm.

8. The electric radiation tube according to claim 2, characterized in that: The shortest arc length between adjacent openings is 15-18 mm.

9. The electric radiation tube according to claim 3, characterized in that: The shortest arc length between adjacent openings is 7-10 mm, and the distance between the first circle and the second circle is 10-15 mm.

10. The electric radiation tube according to claim 4, characterized in that: The length of the second arc is 15-18 mm.

11. The electric radiation tube according to claim 5, characterized in that: The length of the second arc is 7-10 mm, and the distance between the first circle and the second circle is 10-15 mm.

12. A method for increasing the service life of an electric radiant tube, characterized by: Taking the fracture toughness of the ceramic body as the lower constraint limit, the maximum allowable area of a single ceramic support plate as the upper constraint limit, and the uniform distribution of the overall temperature field of the radiant tube as the objective function, the distribution of the heating wires on a single ceramic support plate is optimized, and the distribution of the heating wires is determined based on the optimization results.

13. The method for increasing the service life of an electric radiant tube according to claim 12, characterized in that: The above-mentioned optimization of the distribution of the heating wires on a single ceramic support plate specifically includes the following steps: S11: Determine the shortest distance between two adjacent heating wires based on the fracture toughness of the ceramic body, and determine the area of the ceramic support sheet based on the maximum allowable area of a single ceramic support sheet; S12: Using the determined shortest distance and area as initial values, the distance between adjacent heating wires and the area of a single ceramic support sheet are iterated in a manner such that the arc lengths between adjacent openings along a path from the bottom end of the ceramic support sheet to the top end of the ceramic support sheet increase in sparseness, with the openings for distributing heating wires on the ceramic support sheet being equidistant from the center of the ceramic support sheet. The temperature field distribution of the radiant tube after each iteration is calculated. S13: Based on the calculated values of each point of the temperature field distribution of the radiation tube, determine whether the temperature field distribution under the current iteration meets the requirements through the set temperature field uniformity objective function. If it does not meet the requirements, continue to iterate until the requirements are met, terminate the iteration, and determine the current value as the final set value.

14. The method for increasing the service life of an electric radiant tube according to claim 13, characterized in that: The heating wire is arranged in one circle or two circles along the circumference of the ceramic support plate.

15. The method for increasing the service life of an electric radiant tube according to claim 12, characterized in that: The above-mentioned optimization of the distribution of the heating wires on a single ceramic support plate specifically includes the following steps: S21: determining the shortest distance between two adjacent heating wires based on the fracture toughness of the ceramic body, and determining the area of the ceramic support sheet based on the maximum allowable area of a single ceramic support sheet; S22: Using the determined shortest distance and area as initial values, the openings for distributing the heating wires on the ceramic support plate are arranged at equal distances from the center of the ceramic support plate, and the circumferentially distributed openings are divided into a pair of openings with the shortest distance from the top of the ceramic support plate and the other openings; The distance between adjacent heating wires and the area of a single ceramic support plate are iterated in such a way that the arc length between a pair of openings with the shortest distance from the top of the ceramic support plate is greater than the arc length between two adjacent openings of other openings, and the temperature field distribution of the radiant tube after each iteration is calculated; S23: Based on the calculated values of each point of the temperature field distribution of the radiation tube, determine whether the temperature field distribution under the current iteration meets the requirements through the set temperature field uniformity objective function. If it does not meet the requirements, continue to iterate until the requirements are met, terminate the iteration, and determine the current value as the final set value.

16. The method for increasing the service life of an electric radiant tube according to claim 15, characterized in that: The heating wire is arranged in one circle or two circles along the circumference of the ceramic support plate.

17. The method for increasing the service life of an electric radiant tube according to claim 16, characterized in that: When the heating wire is arranged in a circle along the ceramic support plate, the openings for arranging the heating wire on the ceramic support plate are arranged at equal distances from the center of the ceramic support plate, and the openings distributed along the circumference are divided into a pair of openings with the smallest distance from the top of the ceramic support plate and the other openings; In the case of "iterating the distance between adjacent heating wires and the area of a single ceramic support sheet in a manner such that the arc length between a pair of openings at the shortest distance from the top of the ceramic support sheet is greater than the arc length between two adjacent openings of other openings", the method is performed under the constraint that the arc length between a pair of openings at the shortest distance from the top of the ceramic support sheet is greater than the arc length between two adjacent openings of other openings by 2.5 to 3 times.

18. The method for increasing the service life of an electric radiant tube according to claim 16, characterized in that: When the heating wire is arranged in two circles along the ceramic support plate, the openings for arranging the heating wire on the ceramic support plate are arranged at equal distances from the center of the ceramic support plate, and the openings distributed along the circumference are divided into a pair of openings with the smallest distance from the top of the ceramic support plate and the other openings; The distance between adjacent heating wires and the area of a single ceramic support sheet are iterated in such a way that the arc length between a pair of openings at the smallest distance from the top of the ceramic support sheet is greater than the arc length between two adjacent openings of the other openings. Specifically, for the openings for arranging heating wires on the first circle of the ceramic support sheet, the distance between the openings and the center of the ceramic support sheet is made equal, and the openings distributed along the circumference are evenly distributed according to equal arc lengths. For the openings for arranging heating wires on the first circle of the ceramic support sheet, the distance between the openings and the center of the ceramic support sheet is made equal, and the openings distributed along the circumference are divided into a pair of openings at the smallest distance from the top of the ceramic support sheet and other openings. The distance between adjacent heating wires and the area of a single ceramic support plate are iterated in such a way that the arc length between a pair of openings with the smallest distance from the top of the ceramic support plate is greater than the arc length between two adjacent openings of other openings.

19. The method for increasing the service life of an electric radiant tube according to claim 18, characterized in that: The phrase "the arc length between a pair of openings at the shortest distance from the top of the ceramic body support plate is greater than the arc length between two adjacent openings of the other openings" specifically means that the arc length between a pair of openings at the shortest distance from the top of the ceramic body support plate is 3.5 to 5 times greater than the arc length between two adjacent openings of the other openings.

20. The method for increasing the service life of an electric radiant tube according to claim 12, characterized in that: The aforementioned “fracture toughness of the ceramic body as the lower limit” is specifically: First, the corresponding stress field distribution is calculated based on the current temperature field distribution to obtain the stress value on each calculation node; Secondly, substitute the maximum stress value into the following formula, and then compare the calculated result with the fracture toughness value. If the calculated result is less than the fracture toughness value, the constraint is satisfied, otherwise it is not satisfied. In the above formula, K: stress intensity index under the current temperature field distribution; σ: maximum stress value under the current temperature field distribution, unit: Pa; α: correction coefficient; σbb: flexural strength of ceramic body, unit: Pa.

21. The method for increasing the service life of an electric radiant tube according to claim 20, characterized in that: The value range of the correction coefficient α is: [1-4].

22. The method for increasing the service life of an electric radiant tube according to claim 12, characterized in that: The "uniform distribution of temperature field as the objective function" is specifically: The first objective function is established with the skewness between the mean temperature and the target temperature falling into [10, 20]; The second objective function is established with the temperature fluctuation amplitude falling into [20, 30]. The establishment of the objective function is completed by forming a relationship between the first objective function and the second objective function.

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