Determination method of convection heat transfer coefficient and equivalent heat transfer area of ​​water cooling after rolling

Abstract

The present invention provides a method for determining the water-cooled convection heat transfer coefficient and equivalent heat transfer area for post-rolling cooling, and relates to the field of hot rolling technology. First, key production process parameters of the post-rolling cooling process of hot-rolled strip steel and geometric parameters and thermophysical parameters of the strip steel are collected; the value range of the water-cooled convection heat transfer coefficient and the corresponding equivalent heat transfer area of ​​the upper and lower surfaces of the strip steel are determined to form a search space; multiple groups of parameter combinations of the water-cooled convection heat transfer coefficient and the corresponding equivalent heat transfer area of ​​the upper and lower surfaces of the strip steel are randomly selected in the search space as feasible solutions to the problem; the strip steel is divided into multiple samples along the length direction, and the three-dimensional heat transfer of the post-rolling cooling process is simplified to a one-dimensional heat transfer problem along the thickness direction, a one-dimensional non-steady-state heat conduction differential equation is established and solved to obtain the final cooling temperature of all strip steel samples, and the fitness of this group of feasible solutions is calculated; and then the water-cooled convection heat transfer coefficient and the corresponding equivalent heat transfer area of ​​the post-rolling cooling process are obtained.

Description

Technical Field

[0001] The invention relates to the technical field of hot rolling, and in particular to a method for determining a post-rolling cooling water-cooling convection heat transfer coefficient and an equivalent heat exchange area. Background Art

[0002] Post-rolling cooling is the last major production process of the hot rolling production line. Its main function is to cool the strip from the final rolling temperature to the coiling temperature by setting the cooling path. During the cooling process, the high-temperature austenite structure inside the steel decomposes and transforms into low-temperature ferrite or martensite structure according to different cooling paths and cooling rates. The volume fraction and grain size of the low-temperature phase directly affect the mechanical properties of the steel. Therefore, precise control of the cooling path and target temperature of the cooling process is crucial to product quality. The heat exchange of the strip in the cooling zone mainly includes radiation heat exchange in the air cooling zone and forced convection heat exchange in the water cooling zone. Among them, forced convection heat exchange of cooling water is the most important heat exchange method and the only controllable means. Therefore, determining the high-precision convection heat transfer coefficient and equivalent heat exchange area is crucial to the high-precision control of the post-rolling cooling temperature and the quality of hot-rolled products.

[0003] At present, there are few methods for determining the heat transfer coefficient of post-rolling cooling in China, and the publicly published research is more about the determination method of the convective heat transfer coefficient of other working conditions and cooling conditions. The Chinese patent "CN 117929461 A Experimental method and system for measuring natural convection and forced convection heat transfer coefficients" obtains the temperature changes of the workpiece during natural convection and forced convection cooling in the air by installing thermocouples inside the workpiece, and then obtains the heat transfer coefficients of natural convection and forced convection when the workpiece is air-cooled by "energy conservation". However, this method does not consider the influence of uneven temperature distribution inside the workpiece and the influence of changes in thermophysical parameters caused by temperature changes, so the heat transfer coefficient calculated by this method has a large error. The Chinese patent "CN 118191007 A An experimental device and method for measuring the convective heat transfer coefficient of a flat plate surface" adopts a double-sided structure of two identical experimental pieces symmetrically clamping the heating plate to achieve symmetrical heating, and blows air on both sides in the flow channel, so that the heat generated by the heating plate is evenly dispersed to both sides, and half of the total heat generation is used as the heat flux value for calculating the heat transfer of the flat plate surface on one side. This solves the problem of large heat loss caused by the inability to insulate one side of the heating plate in the traditional single-sided heating method, greatly reduces non-adiabatic loss and system error, and thus improves the accuracy of the experiment. Similarly, this method requires obtaining real-time temperature changes on the surface of the workpiece, and ignores the influence of temperature changes on thermal physical parameters. Based on the basic theory of heat transfer, the Chinese patent "CN 1588023 A A method for testing convective heat transfer coefficient and its convective heat transfer coefficient sensor" designs a sensor that can directly measure the convective heat transfer coefficient of the convective heat transfer surface. Its basic principle is basically the same as the aforementioned patent, and it also needs to obtain real-time temperature changes inside the workpiece, and also ignores the uneven temperature distribution inside the workpiece and the influence of temperature on thermal physical parameters. The Chinese patent "CN 114460129 A A method for obtaining the convective heat transfer coefficient of solid three-dimensional thermal conductivity" constructs a temperature cost function and a Lagrangian function for measuring the convective heat transfer coefficient by measuring the real-time temperature changes of the solid surface to be tested and the surrounding fluid within a certain period of time, and then obtains the optimal convective heat transfer coefficient through the Newton iteration method. The Chinese patent "CN 115060618 A Device and method for determining the convective heat transfer coefficient during thermal shock cooling" uses a temperature sensor to measure the temperature data inside the rock sample at different times during thermal shock. By assigning values ​​to the numerical model according to actual experimental conditions, the true thermal shock process is inverted by means of numerical simulation, and the value of the convective heat transfer coefficient in the numerical simulation is continuously corrected, so that the measured curve and the numerical simulation curve coincide perfectly, and finally the convective heat transfer coefficient of the rock during thermal shock under determined parameters is obtained.

[0004] The above studies provide reference value and ideas for determining the convective heat transfer coefficient of the post-rolling cooling process to a certain extent. However, the above studies all need to obtain the real-time temperature changes inside the workpiece during the cooling or heating process, and the acquisition of real-time temperature data requires the installation of thermocouples inside the workpiece, which is destructive to the workpiece. In addition, the workpieces in the above studies are all stationary and the heat exchange area does not need to be determined because the volume of the workpiece is fixed. However, in the hot rolling production of strip steel, only the temperature of a few key positions can be obtained in the post-rolling cooling area. In addition, the rolling speed and its variation are large, and the rolling speed and its variation will affect the flow state of the cooling water on the surface of the strip, thereby further affecting the size of the convective heat transfer coefficient. Therefore, the post-rolling cooling water cooling convective heat transfer coefficient and its equivalent heat transfer area cannot be obtained by the existing method of measuring the heat transfer coefficient of the stationary workpiece surface. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a method for determining the convective heat transfer coefficient and equivalent heat exchange area of ​​post-rolling cooling water cooling in view of the deficiencies in the above-mentioned prior art. By converting the measurement of the convective heat transfer coefficient, an inverse problem of heat conduction, into a problem of solving the optimization of heat conduction under flexible constraints, the convective heat transfer coefficient and equivalent heat exchange area of ​​post-rolling cooling water cooling suitable for industrial production are obtained.

[0006] The method for determining the convection heat transfer coefficient and equivalent heat transfer area of ​​post-rolling cooling water cooling comprises the following steps:

[0007] Step 1: Collect key production process parameters of the hot rolled strip cooling process after rolling and the geometric parameters and thermophysical parameters of the strip;

[0008] The key production process parameters of the strip cooling process after rolling include the measured temperature of each pyrometer, rolling speed, header configuration and nozzle spacing. The geometric parameters of the strip include the thickness and density of the strip. The thermophysical parameters of the strip include thermal diffusivity, specific heat capacity, thermal conductivity and density.

[0009] Step 2: Determine the value range of the water-cooled convection heat transfer coefficient and the corresponding equivalent heat transfer area on the upper and lower surfaces of the strip, and form a search space;

[0010] Step 3: Randomly select multiple sets of parameter combinations of water-cooled convective heat transfer coefficients and corresponding equivalent heat transfer areas on the upper and lower surfaces of the strip in the search space as feasible solutions to the problem of solving the water-cooled convective heat transfer coefficient and equivalent heat transfer area for post-rolling cooling;

[0011] Step 4: Divide the strip into multiple samples along the length direction, simplify the three-dimensional heat transfer in the post-rolling cooling process into a one-dimensional heat transfer problem along the thickness direction, establish a one-dimensional unsteady-state heat conduction differential equation and solve it;

[0012] Step 4.1: Divide the strip into a plurality of strip samples along the length direction according to a fixed sampling period;

[0013] Step 4.2: Simplify the three-dimensional heat transfer in the post-rolling cooling process into a one-dimensional heat transfer problem along the thickness direction, and establish a one-dimensional unsteady-state heat conduction differential equation, as shown in the following formula:

[0014] ;in, is the strip density, is the specific heat capacity, is the thermal conductivity, t For cooling time, T is the strip temperature, x is the thickness direction coordinate, h is the strip thickness, , ;

[0015] Step 4.3: Determine the initial conditions and boundary conditions at each moment of each strip sample's movement in the cooling zone;

[0016] Step 4.3.1: Take the initial cooling temperature as the initial condition of the strip steel sample;

[0017] Step 4.3.2: According to the opening and closing status of the cooling valve, the entire post-rolling cooling area is divided into an air cooling area and a water cooling area;

[0018] The conditions for determining whether the upper surface of the strip sample is in the air cooling area or the water cooling area are as follows:

[0019] ; Among them, pos is the position of the strip sample at a certain moment, is the distance from the center of the movable valve to the first pyrometer, is the equivalent heat exchange area of ​​the water cooling zone on the upper surface of the strip;

[0020] The judgment conditions for the lower surface of the strip sample to be in the air cooling zone and the water cooling zone are the same as those for the upper surface;

[0021] Step 4.3.3: In the air cooling area, the third type of boundary conditions are used to calculate the heat transfer coefficients of the upper and lower surfaces of the strip steel sample;

[0022] The heat transfer coefficient of the upper and lower surfaces of the strip steel sample in the air cooling area is calculated by the Stefan-Boltzmann law as shown in the following formula:

[0023] ;in, and are the heat transfer coefficients of the upper and lower surfaces of the strip steel sample in the air cooling area, and are the radiation coefficients of the upper and lower surfaces of the strip, is the Boltzmann constant, is the ambient air temperature;

[0024] Step 4.3.4: In the water cooling area, the water cooling convection heat transfer coefficient of the upper and lower surfaces of the strip is the feasible solution in step 3;

[0025] Step 4.4: Mesh the strip sample along the thickness direction;

[0026] Step 4.5: Use implicit difference to solve the one-dimensional unsteady-state heat conduction differential equation in step 4.2, and obtain the temperature distribution of the strip sample along the thickness direction at any time, as shown in the following formula:

[0027] ;in, and are the convective heat transfer coefficients of the upper and lower surfaces of the strip steel sample, , , , , , , , and are the Biot numbers of the upper and lower surfaces of the strip steel sample, is the Fourier number; is the distance between two grid nodes; To calculate the time step; , and are the upper and lower surfaces of the strip sample at the next moment and the i Node temperature; , and They are the upper and lower surfaces of the strip sample at the current moment and the i Node temperature; is the cooling medium temperature;

[0028] Step 5: Taking a set of feasible solutions in step 3 as boundary conditions, calculate the final cooling temperature of all strip samples according to step 4, and calculate the fitness of the set of feasible solutions, as shown in the following formula:

[0029] ;in, is the fitness value, m is the number of samples divided, and are the calculated final cooling temperature and measured temperature of the upper surface of the j-th strip steel sample, respectively;

[0030] Step 6: Calculate the fitness of all feasible solutions in step 3 as boundary conditions, and continue to randomly select multiple groups of parameter combinations within the neighborhood of the feasible solution with the smallest fitness as feasible solutions for solving the problem of post-rolling cooling water cooling convection heat transfer coefficient and equivalent heat transfer area;

[0031] Step 7: Repeat steps 5 and 6 until the maximum number of searches is reached, and the feasible solution with the minimum fitness is obtained, and then the water cooling convection heat transfer coefficient and its corresponding equivalent heat transfer area of ​​the post-rolling cooling process are obtained.

[0032] The beneficial effects of adopting the above technical solution are:

[0033] The method for determining the convective heat transfer coefficient and equivalent heat transfer area of ​​post-rolling cooling water cooling provided by the present invention converts the measurement of the convective heat transfer coefficient, which is an inverse problem of heat conduction, into an optimization problem of heat conduction under flexible constraints, so that the convective heat transfer coefficient and its equivalent heat transfer area of ​​the water cooling process can be obtained with fewer temperature measurement points. Compared with the measurement method of the convective heat transfer coefficient in the public research, the advantage of the present invention is that it does not need to measure the real-time temperature changes of multiple points inside the workpiece, and is suitable for the calculation of the heat transfer coefficient of high-speed moving workpieces such as post-rolling cooling. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 A flow chart of a method for determining a post-rolling cooling water cooling convection heat transfer coefficient and an equivalent heat transfer area provided in an embodiment of the present invention;

[0035] Figure 2 A schematic diagram of the distribution of equipment and the division of heat exchange areas in the post-rolling cooling process provided by an embodiment of the present invention;

[0036] Figure 3 A schematic diagram of rolling speed variation over time provided by an embodiment of the present invention;

[0037] Figure 4 A schematic diagram of mesh division in the thickness direction provided by an embodiment of the present invention;

[0038] Figure 5 A schematic diagram of the change in fitness of parameter combinations corresponding to the iterative process provided by an embodiment of the present invention;

[0039] Figure 6 A schematic diagram comparing the calculated temperature and the measured temperature of all samples of a whole coil of steel strip, for the water-cooling convection heat transfer coefficient and the equivalent heat transfer area determined by the method of the present invention, provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0040] The specific implementation of the present invention is further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0041] This embodiment verifies the effectiveness of the present invention in solving the post-rolling cooling water cooling convection heat transfer coefficient and its equivalent heat transfer area and the accuracy of the solved parameters. Combined with the distribution of post-rolling cooling equipment and the specific cooling process of a hot-rolled strip production line, the implementation process of the method for determining the post-rolling cooling water cooling convection heat transfer coefficient and equivalent heat transfer area of ​​the present invention is further explained.

[0042] In this embodiment, the method for determining the post-rolling cooling water cooling convection heat transfer coefficient and the equivalent heat transfer area is as follows: Figure 1 As shown, the following steps are included:

[0043] Step 1: Collect key production process parameters of the hot rolled strip cooling process after rolling and the geometric parameters and thermophysical parameters of the strip;

[0044] The key production process parameters of the strip cooling process after rolling include the measured temperature of each pyrometer, rolling speed, header configuration and nozzle spacing. The geometric parameters of the strip include the thickness and density of the strip. The thermophysical parameters of the strip include thermal diffusivity, specific heat capacity, thermal conductivity and density.

[0045] In this embodiment, HP345 steel strip with a thickness of 9.85 mm is used as an example for illustration. The thermal properties of HP345 steel strip are shown in Table 1.

[0046] Table 1 Thermal properties of HP345 steel strip

[0047]

[0048] In this embodiment, the opening state of the header in the post-rolling cooling zone and the heat exchange mode between the strip and the surrounding environment are as follows: Figure 2 As shown, two pyrometers are installed in the cooling area, denoted by 1#PY and 2#PY respectively, which are used to measure the upper surface temperature of the strip sample directly below them. The two pyrometers are 23.56m apart. According to the cooling water opening position, the upper surface area is divided into three areas along the rolling direction: air cooling area Lt1, water cooling area Lt and air cooling area Lt2. The lower surface area of ​​the strip sample is also divided into three areas along the rolling direction: air cooling area Lb1, water cooling area Lb and air cooling area Lb2. 1#Nozzle~5#Nozzle are nozzles with a nozzle spacing of 0.38m. The distance between pyrometer 1#PY and 4#Nozzle is 10.26m, and the distance between pyrometer 2#PY and 4#Nozzle is 13.3m.

[0049] Step 2: Determine the value range of the water-cooled convection heat transfer coefficient and the corresponding equivalent heat transfer area on the upper and lower surfaces of the strip, and form a search space;

[0050] In this embodiment, the water-cooled convection heat transfer coefficient of the upper and lower surfaces of the strip and the corresponding equivalent heat transfer area are determined based on production experience as shown in Table 2;

[0051] Table 2 Undetermined parameter search space

[0052] parameter significance Value range <![CDATA[ht(W·m -2 ·℃ -1 )]]> Upper surface water cooling heat transfer coefficient [1000,1000000,100] <![CDATA[hb(W·m -2 ·℃ -1 )]]> Lower surface water cooling heat transfer coefficient [1000,1000000,100] Lt (m) Upper surface water cooling equivalent heat exchange area [0.38,0.76,0.01] Lb(m) Equivalent heat exchange area of ​​lower surface water cooling [0.76,1.14,0.01]

[0053] Step 3: In the search space determined in step 2, multiple groups of parameter combinations of water-cooled convection heat transfer coefficients and corresponding equivalent heat transfer areas of the upper and lower surfaces of the strip are randomly selected as feasible solutions to the problem of solving the water-cooled convection heat transfer coefficient and equivalent heat transfer area of ​​post-rolling cooling;

[0054] Step 4: Divide the strip into multiple samples along the length direction, simplify the three-dimensional heat transfer in the post-rolling cooling process into a one-dimensional heat transfer problem along the thickness direction, establish a one-dimensional unsteady-state heat conduction differential equation and solve it;

[0055] Step 4.1: Divide the strip into m samples, and the length of each sample is shown in the following formula:

[0056] (1);

[0057] in, is the length of the strip steel sample, in m; is the current rolling speed, in m / s; is a fixed sampling time, in seconds; in this embodiment, the rolling speed is as follows Figure 3 As shown, the sampling period is 0.1s;

[0058] Step 4.2: Since the width-to-thickness ratio of the strip is relatively large, and the heat exchange between the strip and the surrounding medium during the cooling process mainly occurs on the upper and lower surfaces, the three-dimensional heat transfer of the cooling process is simplified to a one-dimensional heat transfer problem along the thickness direction, and a one-dimensional unsteady-state heat conduction differential equation is established, as shown in the following formula:

[0059] (2);

[0060] in, is the density of the strip steel, in kg / m3; is the specific heat capacity, in J / (kg·℃); is thermal conductivity, unit is W / (m·℃); t is the cooling time, in seconds; T is the strip temperature, in °C; x is the thickness direction coordinate; h is the strip thickness in m, and ;

[0061] Step 4.3: Determine the initial conditions and boundary conditions at each moment of each strip sample's movement in the cooling zone;

[0062] Step 4.3.1: Take the initial cooling temperature (measured temperature of the first pyrometer 1#PY) as the initial condition of the strip steel sample, as shown in the following formula:

[0063] (3);

[0064] in, is the temperature of the steel strip sample in the thickness direction at time 0, in °C; is the initial cooling temperature of the strip sample, in °C;

[0065] Step 4.3.2: According to the opening and closing status of the cooling valve, the entire post-rolling cooling area is divided into an air cooling area and a water cooling area. The judgment conditions for the upper surface of the strip sample to be in the air cooling area or the water cooling area are as follows: ; Among them, pos is the position of the strip sample at a certain moment, in m; is the distance from the center of the movable valve to the first pyrometer, in meters. In this embodiment, The value is 10.26; is the equivalent heat exchange area of ​​the water cooling zone on the upper surface of the strip, in m;

[0066] The judgment conditions for the lower surface of the strip sample to be in the air cooling zone and the water cooling zone are the same as those for the upper surface;

[0067] Step 4.3.3: In the air cooling area, the heat exchange between the strip and the surrounding medium is mainly caused by self-radiation. The third type of boundary conditions are used to calculate the heat transfer coefficient of the upper and lower surfaces of the strip sample in this area;

[0068] The heat transfer coefficient of the upper and lower surfaces of the strip steel sample in the air cooling area is calculated by the Stefan-Boltzmann law as shown in the following formula:

[0069] (4);

[0070] in, and are the heat transfer coefficients of the upper and lower surfaces of the strip steel sample in the air cooling area, respectively; and are the radiation coefficients of the upper and lower surfaces of the strip, respectively. In this embodiment, and The average value is 0.8; is the Boltzmann constant, with a value of 5.67×10-8W / m 2 ℃ 4 ; is the ambient air temperature. In this embodiment, The value is 25℃;

[0071] Step 4.3.4: In the water cooling area, the water cooling convection heat transfer coefficient of the upper and lower surfaces of the strip is the feasible solution in step 3;

[0072] Step 4.4: Mesh the strip sample along the thickness direction;

[0073] The strip steel sample is meshed along the thickness direction using a method of dense division on the upper and lower surfaces and sparse division in the middle, such as Figure 4 The division method is shown in the following formula:

[0074] (5);

[0075] in, is the coordinate value of the grid node; is the number of grid nodes, n >1;

[0076] Step 4.5: Use implicit difference to solve the one-dimensional unsteady-state heat conduction differential equation (2) in step 4.2, and then you can get the temperature distribution of the strip sample along the thickness direction at any time, as shown in the following formula:

[0077] (6);

[0078] in, and are the convective heat transfer coefficients of the upper and lower surfaces of the strip steel sample, , , , , , , , and is the Biot number of the upper and lower surfaces of the strip sample, is the Fourier number; and are the convective heat transfer coefficients of the upper and lower surfaces, W / (m²·℃); is the distance between two grid nodes, in meters; is the calculation time step, in seconds; , and are the upper and lower surfaces of the strip sample at the next moment and the i Node temperature, in °C; , and They are the upper and lower surfaces of the strip sample at the current moment and the i Node temperature, in °C; is the cooling medium temperature, in °C;

[0079] Step 5: Taking a set of feasible solutions in step 3 as boundary conditions, iterate sequentially according to formula (6) in step 4.5 to calculate the final cooling temperature of all strip samples and the fitness of the set of feasible solutions, as shown in the following formula:

[0080] (7);

[0081] in, is the fitness value, m is the number of samples divided, and Respectively j The calculated final cooling temperature and the measured temperature on the upper surface of the strip steel sample, i.e. j The calculated and measured temperatures of the upper surface of each sample passing through the second pyrometer are in °C;

[0082] Step 6: Calculate the fitness of each feasible solution in step 3 as the boundary condition, and continue to randomly select multiple groups of parameter combinations within the neighborhood of the feasible solution with the smallest fitness as feasible solutions for solving the problem of post-rolling cooling water cooling convection heat transfer coefficient and equivalent heat transfer area;

[0083] Step 7: Repeat steps 5 and 6 until the maximum number of searches is reached, and the feasible solution with the minimum fitness is obtained, and then the water cooling convection heat transfer coefficient and its corresponding equivalent heat transfer area of ​​the post-rolling cooling process are obtained.

[0084] In this embodiment, the corresponding fitness of the feasible solution in each iteration process is as follows: Figure 5 As shown in Table 3, the parameter combination corresponding to the minimum fitness is the water-cooled convection heat transfer coefficient and equivalent heat transfer area in this example. The feasible solution with the minimum fitness is used in step 4. The comparison between the calculated temperature and the measured temperature of all strip steel samples is shown in Table 3. Figure 6 As shown;

[0085] Table 3 Parameter combinations corresponding to the minimum fitness

[0086]

[0087] The present invention aims to solve the problem that the water-cooling convective heat transfer coefficient and its equivalent heat transfer area in the post-rolling cooling process cannot be directly measured. By converting the measurement of the convective heat transfer coefficient, an inverse problem of heat conduction, into an optimization problem of heat conduction under flexible constraints, the parameter combination that minimizes the mean square error between the calculated temperature and the measured temperature is obtained through multiple iterative searches as the convective heat transfer coefficient and equivalent heat transfer area of ​​the water-cooling process. Compared with the determination method of the convective heat transfer coefficient in existing reports, the present invention can obtain the convective heat transfer coefficient and equivalent heat transfer area of ​​the water-cooling process with only limited measured values, and the method is suitable for working conditions such as post-rolling cooling where the workpiece runs at a high speed. The final calculation results show that the calculated temperature of the water-cooling convective heat transfer coefficient and the equivalent heat transfer area determined by this method is in good agreement with the measured temperature, indicating that the method is not only feasible, but also has high accuracy in the obtained parameters.

[0088] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope defined by the claims of the present invention.

Claims

1. A method for determining the convection heat transfer coefficient and equivalent heat transfer area of ​​post-rolling cooling water cooling, characterized in that: The following steps are involved: Step 1: Collect key production process parameters of the hot rolled strip cooling process after rolling and the geometric parameters and thermophysical parameters of the strip; Step 2: Determine the value range of the water-cooled convection heat transfer coefficient and the corresponding equivalent heat transfer area on the upper and lower surfaces of the strip, and form a search space; Step 3: Randomly select multiple sets of parameter combinations of water-cooled convective heat transfer coefficients and corresponding equivalent heat transfer areas on the upper and lower surfaces of the strip in the search space as feasible solutions to the problem of solving the water-cooled convective heat transfer coefficient and equivalent heat transfer area for post-rolling cooling; Step 4: Divide the strip into multiple samples along the length direction, simplify the three-dimensional heat transfer in the post-rolling cooling process into a one-dimensional heat transfer problem along the thickness direction, establish a one-dimensional unsteady-state heat conduction differential equation and solve it; Step 5: Taking a set of feasible solutions in step 3 as boundary conditions, calculate the final cooling temperature of all strip samples according to step 4, and calculate the fitness of the set of feasible solutions; Step 6: Calculate the fitness of all feasible solutions in step 3 as boundary conditions, and continue to randomly select multiple groups of parameter combinations within the neighborhood of the feasible solution with the smallest fitness as feasible solutions for solving the problem of post-rolling cooling water cooling convection heat transfer coefficient and equivalent heat transfer area; Step 7: Repeat steps 5 and 6 until the maximum number of searches is reached, and the feasible solution with the minimum fitness is obtained, and then the water cooling convection heat transfer coefficient and its corresponding equivalent heat transfer area of ​​the post-rolling cooling process are obtained.

2. The method for determining the post-rolling cooling water cooling convection heat transfer coefficient and equivalent heat transfer area according to claim 1, characterized in that: The key production process parameters of the strip cooling process after rolling include the measured temperature of each pyrometer, rolling speed, header configuration and nozzle spacing; the geometric parameters of the strip include strip thickness and density; the thermophysical parameters of the strip include thermal diffusivity, specific heat capacity, thermal conductivity and density.

3. The method for determining the post-rolling cooling water cooling convection heat transfer coefficient and equivalent heat transfer area according to claim 2, characterized in that: The specific method of step 4 is: Step 4.1: Divide the strip into a plurality of strip samples along the length direction according to a fixed sampling period; Step 4.2: Simplify the three-dimensional heat transfer in the post-rolling cooling process into a one-dimensional heat transfer problem along the thickness direction, and establish a one-dimensional unsteady-state heat conduction differential equation; Step 4.3: Determine the initial conditions and boundary conditions at each moment of each strip sample's movement in the cooling zone; Step 4.4: Mesh the strip sample along the thickness direction; Step 4.5: Use implicit difference to solve the one-dimensional unsteady-state heat conduction differential equation in step 4.2 to obtain the temperature distribution of the strip sample along the thickness direction at any time.

4. The method for determining the post-rolling cooling water cooling convection heat transfer coefficient and equivalent heat transfer area according to claim 3, characterized in that: The one-dimensional unsteady-state heat conduction differential equation in step 4.2 is as follows: ;in, is the strip density, is the specific heat capacity, is the thermal conductivity, t For cooling time, T is the strip temperature, x is the thickness direction coordinate, h is the strip thickness, , .

5. The method for determining the post-rolling cooling water cooling convection heat transfer coefficient and equivalent heat transfer area according to claim 4, characterized in that: The specific method of step 4.3 is: Step 4.3.1: Take the initial cooling temperature as the initial condition of the strip steel sample; Step 4.3.2: According to the opening and closing status of the cooling valve, the entire post-rolling cooling area is divided into an air cooling area and a water cooling area; The conditions for determining whether the upper surface of the strip sample is in the air cooling area or the water cooling area are as follows: ; Among them, pos is the position of the strip sample at a certain moment, is the distance from the center of the movable valve to the first pyrometer, is the equivalent heat exchange area of ​​the water cooling zone on the upper surface of the strip; Step 4.3.3: In the air cooling area, the third type of boundary conditions are used to calculate the heat transfer coefficients of the upper and lower surfaces of the strip steel sample; Step 4.3.4: In the water-cooling area, the water-cooling convection heat transfer coefficient of the upper and lower surfaces of the strip is the feasible solution in step 3.

6. The method for determining the post-rolling cooling water convection heat transfer coefficient and equivalent heat transfer area according to claim 5, characterized in that: In step 4.3.2, the judgment conditions for whether the lower surface of the strip sample is in the air cooling zone and the water cooling zone are the same as the judgment conditions for the upper surface.

7. The method for determining the post-rolling cooling water cooling convection heat transfer coefficient and equivalent heat transfer area according to claim 6, characterized in that: The temperature distribution of the strip steel sample along the thickness direction at any time in step 4.5 is shown in the following formula: ;in, and are the convective heat transfer coefficients of the upper and lower surfaces of the strip steel sample, , , , , , , , and are the Biot numbers of the upper and lower surfaces of the strip steel sample, is the Fourier number; is the distance between two grid nodes; To calculate the time step; , and are the upper and lower surfaces of the strip sample at the next moment and the i Node temperature; , and They are the upper and lower surfaces of the strip sample at the current moment and the i Node temperature; is the cooling medium temperature.

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