A method for fast mapping of heat exchanger grids in a nuclear power system

Abstract

This invention discloses a rapid mesh mapping method for heat exchangers in nuclear power systems, comprising the following steps: 1. Modeling and meshing the internal and external fluid domains of the heat exchanger using SolidWorks software; 2. Obtaining the coordinates of all primary side meshes and calculating the maximum center-to-center distance between adjacent meshes in three directions; 3. Marking all secondary side meshes within the range centered on the primary side mesh coordinates and with the center-to-center distance equal to half the side length; 4. Assigning cyclic numbers to the primary and secondary side meshes and counting the corresponding primary and secondary side mesh counts; 5. Writing the primary and secondary side mesh marking process into the initialization macro built into Fluent software, using the predefined macro to read the mesh coordinate parameters, performing initialization operations, and then realizing the retrieval and marking of primary and secondary side meshes. This invention solves the problem of mesh mismatch when calculating the coupling between internal and external fluids in heat transfer tubes, and still provides reasonable marking results even when the internal and external fluid meshes are divided in different ways and when the number and arrangement of heat transfer tube meshes vary significantly.

Description

Technical Field

[0001] This invention belongs to the technical field of nuclear reactor thermal-hydraulic calculation methods, specifically relating to a fast mesh mapping method for heat exchangers in nuclear power systems. Background Technology

[0002] The Passive Residual Heat Removal System (PRHRS), a crucial dedicated safety facility in third-generation advanced nuclear power plants such as AP1000 and Hualong One, is responsible for removing core heat during reactor start-up and shutdown, transient conditions, and accidents. The main equipment in this system is the passive C-type heat exchanger (PRHR HX), designed to be immersed in a refueling tank integrated within the containment. Once the passive C-type heat exchanger is operational, heat exchange occurs between the primary and secondary fluids through bundled C-shaped heat transfer tubes. Accurate numerical simulation of this process helps reduce experimental costs and provides a reference for optimizing the arrangement of heat transfer tubes. However, due to the large number of heat transfer tubes in actual structures, detailed modeling of the C-type heat exchanger and the secondary fluid domain as a whole is challenging and would significantly increase the mesh size, consuming computational resources that are currently prohibitive. Therefore, appropriate simplification is necessary during the modeling process.

[0003] To address this issue, some common approaches include: reducing the number of heat transfer tubes to a few and performing detailed modeling and analysis to study the heat transfer characteristics of the primary and secondary flow. However, this method requires a very small number of heat transfer tubes, which is far removed from practical engineering problems and is therefore only used as a scientific research method. Another common approach is to not create a solid model of the primary heat transfer tubes, but only mark the positions of the heat transfer tubes in the secondary water area based on their geometry and position parameters. The flow inside the heat transfer tubes is considered one-dimensional, and the heat transfer from the fluid inside the tubes to the secondary side is manually calculated as the heat source term for the secondary tube bundle region to study the thermal-hydraulic characteristics of the secondary fluid. This method greatly simplifies the modeling process and improves computational efficiency, but because the primary fluid domain is not modeled, it cannot simulate the three-dimensional flow of the fluid inside the tubes. To simultaneously simulate the three-dimensional flow of the primary and secondary fluid domains, it is necessary to create a solid model of the primary fluid domain. Modeling the primary and secondary fluid domains separately can solve this problem. Furthermore, since the two fluid domains use two independent meshes, the number of meshes can be selectively reduced during mesh generation, improving computational speed. However, this method requires high accuracy in the marking process and results of the primary side heat transfer tube bundle in the secondary side fluid domain.

[0004] Therefore, developing a method for rapid mesh mapping of heat exchangers in nuclear power systems is of great significance for conducting accurate three-dimensional numerical simulations of heat exchangers in nuclear power systems and improving computational efficiency. Summary of the Invention

[0005] The purpose of this invention is to provide a method for rapid mesh mapping of heat exchangers in nuclear power systems. This method reads the coordinate parameters of the primary and secondary side meshes, performs multiple iterations to automatically mark the secondary side tube bundle region mesh, and uses Fluent user-defined memory to store the marking information. Based on the overall marking, it performs local fine-grained "one-to-many" marking, realizing the automatic and accurate marking function between the primary and secondary side meshes. This avoids the complexity of manual marking, enhances the program's versatility, and improves calculation accuracy.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for fast mesh mapping of heat exchangers in nuclear power systems, characterized by comprising the following steps:

[0008] Step 1: Use SolidWorks software to model the heat transfer tubes and the secondary fluid domain outside the tubes of the heat exchanger of the nuclear power system. Use the mesh generation tool ICEM to generate the mesh. During the mesh generation process, choose to generate a structured mesh or an unstructured mesh according to the actual situation.

[0009] Step 2: Using the built-in mesh loop format and predefined macros in Fluent software, read the coordinates of the center of all primary side meshes and store them in three one-dimensional arrays x1[n1], y1[n1], and z1[n1]. Assuming that the meshes retrieved consecutively during the loop reading of the primary side meshes are adjacent, the maximum distance between the centers of adjacent meshes in the three directions is calculated by the following formula:

[0010]

[0011] In the formula: subscript 1 represents the primary side variable identifier, and n1 is the total number of primary side grids, which is dimensionless;

[0012] —Identifier of the first-order lateral coordinate array, Take x, y, z, and m;

[0013] —The identifier of the first-order lateral coordinate array when looping to the i-th grid. This represents the identifier of the side coordinate array when looping to the (i+1)th grid, m;

[0014] —Maximum distance between the centers of adjacent grid cells, in meters;

[0015] To ensure that the value obtained from equation (1) is a valid value between adjacent grids, the following constraint conditions are used for validity determination:

[0016]

[0017] Where: P1——the distance between the centers of adjacent heat transfer tubes, m; d1——the diameter of the heat transfer tube, m;

[0018] Equation (1) will only be calculated when the coordinates of two consecutively retrieved grids satisfy equation (2). By solving the common constraints of equations (1) and (2), the calculated value is guaranteed to be the maximum distance between the centers of adjacent grids.

[0019] Step 3: After obtaining the volume center coordinate array of the primary side mesh and the maximum volume center spacing in three dimensions, the secondary side mesh is marked using a cuboid marking method. Specifically, a cuboid spatial region is formed with the coordinates of the primary side mesh as the center and the maximum volume center spacing as half the side length. The coordinates of all meshes in the secondary side fluid domain are read iteratively, and all secondary side meshes within the spatial region are numerically marked using user-defined memory in the Fluent software, as described below:

[0020]

[0021] In the formula: —The secondary coordinate identifier, m;

[0022] By using the double loop method, when traversing the first-side coordinate array, a second-side mesh loop is performed for each first-side mesh, and the mesh is marked by Equation (3). After the loop ends, the mesh of the tube bundle region is marked in the second-side fluid domain.

[0023] Step 4: To characterize the correspondence between primary and secondary side meshes and achieve accurate marking between them, based on the marking results in Step 3, and according to the different numbers of meshes in the primary and secondary side bundle regions, the side with fewer meshes is selected as the benchmark. The number of meshes on the other side corresponding to each mesh on that side is counted. Simultaneously, these corresponding meshes are assigned the same label number. For ease of subsequent management and retrieval, the label number is defined as the cyclic number when the mesh is retrieved + 1, i.e.:

[0024]

[0025] a[n]=a[n]+1 (5)

[0026] In the formula: —The label number of the nth cyclic grid coordinate, dimensionless;

[0027] a[n] — Counts the number of grids on the other side corresponding to the nth cyclic reference grid;

[0028] Because the grid is closely spaced, the same grid may be marked repeatedly during the labeling process. This problem can also lead to errors in counting the number of grid cells. Therefore, when assigning labels and numbers to the grid cells, all grid cells must first be labeled separately. Set the value to 0 and use the following description:

[0029] when hour:

[0030]

[0031] when hour:

[0032]

[0033] When a[k] > 1:

[0034]

[0035] a[k]=a[k]-1 (9)

[0036] a[n]=a[n]+1 (10)

[0037] In the formula: k — the label number assigned to the nth cyclic grid, which is dimensionless;

[0038] When the searched grid already has a label number, the grid is re-labeled by equations (7) to (10), and the value of the corresponding statistical array is changed. After all grids have been cycled, the primary and secondary grids are accurately searched by their respective label numbers, and the number of corresponding grids on the other side is counted, which is convenient for parameter averaging in subsequent calculations.

[0039] Step 5: Using the user-defined function function in Fluent software, the primary and secondary side mesh marking process is written into the built-in initialization macro in Fluent software. In equations (1) and (2), the predefined macro is used to read the mesh coordinate parameters. After the initialization operation is performed in Fluent software, the retrieval and marking of the primary and secondary side meshes are realized.

[0040] Compared with the prior art, the present invention has the following advantages:

[0041] 1) The method of the present invention uses an array to extract the primary side grid coordinates and then compares and retrieves the secondary side grid coordinates with the primary side array coordinates. This avoids the situation in the prior art where the specific heat transfer tube geometry and spatial distribution are required when marking the primary side heat transfer tube region in the secondary side fluid domain. Only a few heat transfer tube geometric features are needed to achieve automatic marking in the program, reducing manual operation.

[0042] 2) Based on the original overall marking, a specific marking function for each grid has been implemented. At the same time, the corresponding number of primary and secondary side grids can be counted, which improves the marking accuracy, simplifies the retrieval process, and helps to carry out subsequent coupled calculation analysis.

[0043] (3) The method has a clear approach, a simple calculation process, and strong program versatility. It can be applied to the marking process of fluid domains inside and outside the tubes of various heat exchangers. Attached Figure Description

[0044] Figure 1a and Figure 1b These are schematic cross-sectional views of the nine C-shaped heat transfer tubes and a diagram showing the markings on the secondary heat transfer tubes.

[0045] Figure 2a and Figure 2b The diagrams show 100 C-shaped heat transfer tubes and the marking results of the secondary side heat transfer tubes.

[0046] Figure 3 This is a flowchart of the method of the present invention. Detailed Implementation

[0047] The following combination Figure 3 The flowchart shown is as follows: Figure 1a The invention will be further described in detail using the marking process of the nine C-shaped heat transfer tubes shown as an example.

[0048] This invention discloses a method for fast mesh mapping of heat exchangers in nuclear power systems, comprising the following steps:

[0049] Step 1: Model the heat transfer tubes and the secondary fluid domain outside the tubes of the C-shaped heat exchanger in the nuclear power system using SolidWorks software. Use the ICEM meshing tool to generate the mesh. During mesh generation, you can choose to create a structured or unstructured mesh based on the actual situation. Figure 1a The modeling cross-sectional view of the heat transfer tube and its upper and lower chambers is given. In this example, the secondary side fluid domain is a cuboid water body with a regular shape and is meshed using a structured grid. The primary side is meshed using an unstructured grid to simplify the meshing process.

[0050] Step 2: Using the built-in mesh loop format and predefined macros in Fluent software, read the coordinates of the center of all primary side meshes and store them in three one-dimensional arrays x1[n1], y1[n1], and z1[n1]. If the meshes retrieved consecutively during the primary side mesh reading are adjacent, the maximum distance between the centers of adjacent meshes in the three directions is calculated by the following formula:

[0051]

[0052] In the formula: subscript 1 represents the primary side variable identifier, and n1 is the total number of primary side grids, which is dimensionless;

[0053] —Identifier of the first-order lateral coordinate array, Take x, y, z, and m;

[0054] —The identifier of the first-order lateral coordinate array when looping to the i-th grid. This represents the identifier of the side coordinate array when looping to the (i+1)th grid, m;

[0055] —Maximum distance between the centers of adjacent grid cells, in meters.

[0056] In practice, continuous retrieval of non-adjacent grids must be considered. To ensure that the value obtained from equation (1) is a valid value between adjacent grids, the following constraints are used for validity determination:

[0057]

[0058] Where: P1——the distance between the centers of adjacent heat transfer tubes, m; d1——the diameter of the heat transfer tube, m.

[0059] When the coordinates of two consecutively retrieved grids satisfy equation (2), equation (1) is calculated. By solving the common constraints of equations (1) and (2), the calculated value is guaranteed to be the maximum distance between the centers of adjacent grids. Due to the existence of equation (2), the situation where the distance between the centers of adjacent grids is too large when the primary side grid is divided into unstructured grids is also constrained, thus avoiding abnormal marking range of the secondary side grid and improving marking accuracy.

[0060] Step 3: After obtaining the volume center coordinate array of the primary side mesh and the maximum volume center spacing in three dimensions, the secondary side mesh is marked using a cuboid marking method. Specifically, a cuboid spatial region is formed with the coordinates of the primary side mesh as the center and the maximum volume center spacing as half the side length. The coordinates of all meshes in the secondary side fluid domain are read iteratively, and all secondary side meshes in the spatial region are numerically marked using user-defined memory in the Fluent software. The mathematical description is as follows:

[0061]

[0062] In the formula: —The secondary lateral coordinate identifier, m.

[0063] By using the double loop method, when traversing the primary side coordinate array, a secondary side grid loop is performed for each primary side grid, and the grid is marked by Equation (3). After the loop ends, the grid of the tube bundle region is marked in the secondary side fluid domain.

[0064] Step 4: After the overall marking is completed, compare the number of primary and secondary side grids in the tube bundle region. If the number of secondary side grids is greater than the number of primary side grids, then, using the primary side grids as a baseline, count the number of secondary side grids corresponding to each primary side grid. Assign the same marker number to these corresponding grids. For ease of subsequent management and retrieval, the marker number is defined as the cyclic number when the grid is retrieved + 1, i.e.:

[0065]

[0066] a2[n]=a2[n]+1 (5)

[0067] In the formula: —The label number of the nth cyclic grid coordinate, dimensionless.

[0068] a2[n] — Counts the number of secondary side grids corresponding to the first side grid of the nth cycle.

[0069] Because the grid is closely spaced, the same grid may be marked repeatedly during the labeling process. This problem can also lead to errors in counting the number of grid cells. To solve this problem, when assigning labels and numbers to the grid cells, all grid cells must first be labeled... Set the value to 0 and use the following description:

[0070] when hour:

[0071]

[0072] when hour:

[0073]

[0074] When a2[k] > 1:

[0075]

[0076] a2[k]=a2[k]-1 (9)

[0077] a2[n]=a2[n]+1 (10)

[0078] In the formula: k — the label number assigned to the nth cyclic grid, which is dimensionless.

[0079] When the searched grid already has a label number, the grid is relabeled using equations (7) to (10), and the value of the corresponding statistical quantity array is changed. After all grids have been cycled, the primary and secondary side grids can be accurately found by their respective label numbers. At the same time, the secondary side grids corresponding to each primary side grid are statistically analyzed, which facilitates parameter averaging in subsequent calculations.

[0080] Step 5: Using the user-defined function function in Fluent software, the primary and secondary side mesh marking process is written into the built-in initialization macro in Fluent software. In Equations (1) and (2), the predefined macro is used to read the mesh coordinate parameters. After the initialization operation is performed in Fluent, the retrieval and marking of the primary and secondary side meshes are realized. Figure 1b The marked positions of the heat transfer tubes in the secondary fluid domain are given. Figure 3 A flowchart illustrating the entire marking process is provided.

[0081] The method of this invention was used to perform a labeling analysis on a C-shaped heat exchanger with a similar structure containing 100 heat transfer tubes. Figure 2a The arrangement of 100 heat transfer tubes is given. Figure 2b The final labeling results are shown.

[0082] The parts of this invention not described in detail are common knowledge to those skilled in the art.

Claims

1. A method for fast mesh mapping of heat exchangers in a nuclear power system, characterized in that, Includes the following steps: Step 1: Use SolidWorks software to model the heat transfer tubes and the secondary fluid domain outside the tubes of the heat exchanger of the nuclear power system. Use the mesh generation tool ICEM to generate the mesh. During the mesh generation process, choose to generate a structured mesh or an unstructured mesh according to the actual situation. Step 2: Use the built-in mesh loop format and predefined macros in Fluent software to read the coordinates of the volume centers of all primary side meshes and store them in three one-dimensional arrays. In this context, assuming that the meshes retrieved consecutively during a single cyclic read of the side mesh are adjacent, the maximum body center distance between adjacent meshes in the three directions is calculated using the following formula: （1） In the formula: the subscript 1 represents the identifier of the primary side variable. The total number of side grids in a single step is dimensionless. —Identifier of the first-order lateral coordinate array, Pick , ; — Loop to the 1st The identifier of the first lateral coordinate array for each grid cell. Indicates the loop reaches the 1st... Each grid cell is identified by a lateral coordinate array. ; —Maximum distance between the centers of adjacent grid cells, ; To ensure that the value obtained from equation (1) is a valid value between adjacent grids, the following constraint conditions are used for validity determination: （2） In the formula: — Spacing between adjacent heat transfer tubes ; —Heat transfer tube diameter, ; Equation (1) will only be calculated when the coordinates of two consecutively retrieved grids satisfy equation (2). By solving the common constraints of equations (1) and (2), the calculated value is guaranteed to be the maximum distance between the centers of adjacent grids. Step 3: After obtaining the volume center coordinate array of the primary side mesh and the maximum volume center spacing in three dimensions, the secondary side mesh is marked using a cuboid marking method. Specifically, a cuboid spatial region is formed with the coordinates of the primary side mesh as the center and the maximum volume center spacing as half the side length. The coordinates of all meshes in the secondary side fluid domain are read iteratively, and all secondary side meshes within the spatial region are numerically marked using user-defined memory in the Fluent software, as described below: （3） In the formula: —Secondary lateral coordinate identifier, ; By using the double loop method, when traversing the first-side coordinate array, a second-side mesh loop is performed for each first-side mesh, and the mesh is marked by Equation (3). After the loop ends, the mesh of the tube bundle region is marked in the second-side fluid domain. Step 4: To characterize the correspondence between primary and secondary side meshes and achieve accurate marking between them, based on the marking results in Step 3, and according to the different numbers of meshes in the primary and secondary side bundle regions, the side with fewer meshes is selected as the benchmark. The number of meshes on the other side corresponding to each mesh on that side is counted. Simultaneously, these corresponding meshes are assigned the same label number. For ease of subsequent management and retrieval, the label number is defined as the cyclic number when the mesh is retrieved + 1, i.e.: （4） （5） In the formula: ——No. The dimensionless label number for each cyclic grid coordinate; ——Statistics The number of grids on the other side corresponding to each cyclic reference grid; Because the grid is closely spaced, the same grid may be marked repeatedly during the labeling process. This problem can also lead to errors in counting the number of grid cells. Therefore, when assigning labels and numbers to the grid cells, all grid cells must first be labeled separately. Set the value to 0 and use the following description: when hour: （6） when hour: （7） when hour: （8） （9） （10） In the formula: ——No. Each cyclic grid has been assigned a dimensionless label number; When the searched grid already has a label number, the grid is re-labeled by equations (7) to (10), and the value of the corresponding statistical quantity array is changed. After all grids have been cycled, the primary and secondary grids are accurately searched by their respective label numbers, and the number of corresponding grids on the other side is counted, which is convenient for parameter averaging in subsequent calculations. Step 5: Using the user-defined function function in Fluent software, the process of marking the primary and secondary side meshes, i.e., the process of steps 2 to 4, is written into the built-in initialization macro in Fluent software. In equations (1) and (2), the predefined macro is used to read the mesh coordinate parameters. After the initialization operation is performed in Fluent software, the retrieval and marking of the primary and secondary side meshes are realized.

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