Method and system for calculating and analyzing thermal stress of tube plate of nuclear-grade heat exchanger

Abstract

The invention discloses a nuclear-grade heat exchanger tube plate thermal stress calculation and analysis method and a nuclear-grade heat exchanger tube plate thermal stress calculation and analysis system. The nuclear-grade heat exchanger tube plate thermal stress calculation and analysis method comprises the steps that the range of working condition parameters and the change trend of the working condition parameters along with time are determined; determining a modeling range of a tube plate part of the heat exchanger, and establishing a three-dimensional solid model of a plurality of local areas of the tube plate part; dividing finite element grids for the three-dimensional solid model, and determining contact surfaces and fluid inlet / outlet boundary surfaces among the local areas; receiving parameter information of a fluid dynamics calculation model and a heat transfer and thermal stress conjugate calculation model set by a user; calculating a temperature field and a thermal stress field of a specific local area of the tube plate part during the transient period; and calculating the thermal stress extreme value and amplitude of the tube plate part and the secondary stress extreme value and amplitude during the transient period. By implementing the technical scheme of the invention, the thermal stress of the nuclear-grade heat exchanger tube plate under the specific operation condition can be accurately, conservatively and quickly calculated.

Description

Technical Field

[0001] The present invention relates to the technical field of heat exchanger design and operation safety, and in particular to a method and system for calculating and analyzing thermal stress of a nuclear-grade heat exchanger tube sheet. Background Art

[0002] Nuclear-grade heat exchanger tube sheets are thicker and serve as the boundary between the cold and hot fluids on the tube side and the shell side, and are in contact with the colder air outside. During harsher operating transients (such as rapid startup and shutdown), there is a large temperature difference in the axial and radial directions of the tube sheet, which causes greater thermal stress (under certain rapid temperature rise transients, the thermal stress of the tube sheet is more than ten times greater than the mechanical stress under the design conditions). Accurate calculation of tube sheet thermal stress plays an important engineering role in heat exchanger design, operational safety analysis, formulation of operating restrictions (such as heating and cooling rate limits), and thermal fatigue life prediction.

[0003] Although CFD (computational fluid dynamics) and structural mechanics finite element calculation methods and related software are increasingly used in scientific research, RCC-M and other specifications do not provide technical guidance on how to apply these methods and software in engineering. In particular, these specifications do not provide specific guidance on the calculation and analysis of thermal stress in nuclear-grade heat exchanger tube sheets. Summary of the invention

[0004] The technical problem to be solved by the present invention is that, in view of the defect that RCC-M and other specifications do not provide a method for calculating and analyzing the thermal stress of nuclear-grade heat exchanger tube sheets, a method and system for calculating and analyzing the thermal stress of nuclear-grade heat exchanger tube sheets are provided, so as to accurately, conservatively and quickly calculate the extreme values ​​and variation ranges of the thermal stress of nuclear-grade heat exchanger tube sheets under specific operating conditions, thereby providing a technical basis for nuclear-grade tube sheet design, operation safety analysis and full-life thermal fatigue life prediction.

[0005] The technical solution adopted by the present invention to solve the technical problem is: constructing a thermal stress calculation and analysis method for nuclear-grade heat exchanger tube sheets, comprising:

[0006] Step S10, by combing and analyzing the design transient operating conditions of the tube side and the shell side of the heat exchanger, determining the range of the operating parameters and their changing trends over time;

[0007] Step S20, determining a modeling range of the tube sheet portion of the heat exchanger, and establishing three-dimensional solid models of multiple local areas of the tube sheet portion according to the modeling range;

[0008] Step S30, dividing the three-dimensional solid model into finite element meshes to determine the contact surfaces between the local areas and the fluid inlet / outlet boundary surfaces;

[0009] Step S40, receiving parameter information of the fluid dynamics calculation model, the heat transfer and thermal stress conjugate calculation model set by the user;

[0010] Step S50, calculating the temperature field and thermal stress field of the specific local area of ​​the tube sheet during the transient period according to the set parameter information, the contact surface between the local areas and the fluid inlet / outlet boundary surface;

[0011] Step S60, calculating the extreme value and amplitude of thermal stress at the tube sheet during the transient period, and the extreme value and amplitude of secondary stress according to the temperature field and thermal stress field of the specific local area.

[0012] Preferably, in step S20, determining the modeling range of the tube sheet portion of the heat exchanger includes:

[0013] Step S21, the following simplified assumptions are made for the physical structure of the tube sheet of the heat exchanger: the screw portion inserted into the flange screw hole, the positioning pin portion, and the sealing gasket between the tube sheet and the flange form a continuous integrated component with the flange; the bolt protrusion portion is ignored; any gaps between components and between components and the fluid are ignored; the tube sheet, the shell side cylinder flange, and the water chamber flange do not form a continuous integrated component;

[0014] Step S22, determining the axial modeling range of the tube sheet of the heat exchanger, wherein the axial modeling range includes: a section of the upper part of the water chamber cylinder, the water chamber cylinder flange, the tube sheet, a section of the heat transfer tube, the shell side cylinder flange and a section of the lower part of the shell side cylinder, and the tube side fluid and the shell side fluid in these components; the total length of the shell side cylinder flange and the lower part of the shell side cylinder is the same as the length of the heat transfer tube, and the length is greater than the effective mixing length of the shell side fluid and less than The total length of the upper section of the water chamber cylinder and the water chamber cylinder flange is greater than the effective mixing length of the fluid in the water chamber on the tube side and less than Wherein, R is the average radius of the tube sheet portion; t is the thickness of the tube sheet portion;

[0015] Step S23, determining the horizontal modeling range of the tube sheet portion of the heat exchanger according to the following method: the length and width of the horizontal modeling range are both less than Within the horizontal modeling range, the number of heat transfer tubes is less than 1 / 10 of the total number, is greater than 3, and includes at least 1 inner circle heat transfer tube; the horizontal modeling range includes the outer wall in contact with the cold fluid; the horizontal modeling range is adjacent to the partition in the tube side water chamber, or is located on both sides of the partition.

[0016] Preferably, the step S40 includes:

[0017] Step S41, receiving a turbulent viscosity model set by a user;

[0018] Step S42, receiving the regional material characteristic parameters set by the user;

[0019] Step S43, receiving the boundary conditions set by the user;

[0020] Step S44, receiving the thermal stress calculation formula set by the user.

[0021] Preferably, the step S42 includes:

[0022] Step S421, receiving the values ​​of the characteristic parameters of the metal component set by the user, wherein the characteristic parameters of the metal component include: density, specific heat, thermal conductivity, elastic modulus and thermal expansion coefficient, wherein the values ​​of density, specific heat and thermal conductivity are taken as the values ​​at the highest temperature during the design transient period; the values ​​of elastic modulus and thermal expansion coefficient are taken as the values ​​at room temperature;

[0023] Step S422, receiving the values ​​of the fluid physical property parameters set by the user, wherein the fluid physical property parameters include density, viscosity, specific heat and thermal conductivity, and the values ​​of the fluid physical property parameters are functions of temperature and pressure in a supercooled state, and are functions of temperature or pressure in a saturated state.

[0024] Preferably, in step S44, the formula for the thermal stress distribution S(t,n) of the tube sheet area at the set time step t is:

[0025]

[0026] Where t is the time step, n is the unit number, N is the unit number set, C is the thermal stress concentration factor, α is the thermal expansion coefficient of the material, E is the elastic modulus of the material, and T(t,n) is the temperature at unit n at time step t.

[0027] Preferably, the step S60 includes:

[0028] Step S61, calculating the extreme value of thermal stress in a specific local area of ​​the tube sheet;

[0029] Step S62, calculating the variation amplitude of thermal stress in a specific local area of ​​the tube sheet;

[0030] Step S63, calculating the secondary stress extreme value of a specific local area of ​​the tube sheet;

[0031] Step S64, calculating the variation amplitude of the secondary stress in a specific local area of ​​the tube sheet.

[0032] Preferably, the step S61 includes:

[0033] Step S611, dividing the thermal stress of a specific local area of ​​the tube sheet into a secondary stress Q and a peak stress F, wherein the secondary stress includes: the sum of the film stress and the bending stress caused by the radial temperature difference of the tube sheet, and the equivalent linear part of the stress distribution caused by the axial non-uniform temperature distribution of the tube sheet;

[0034] Step S612: Calculate the maximum value of thermal stress (Q+F) and thermal stress

[0035] max

[0036] Minimum force (Q+F) min :

[0037]

[0038] Where T is the time step set; n is the unit number; N is the unit number set; S(t,n) is the thermal stress distribution of the tube sheet area under time step t;

[0039] Step S613, determining the time step t where the maximum value of the thermal stress is located max and unit number n max , and the time step t where the thermal stress minimum is located min and unit number n min .

[0040] Preferably, in step S63, the tube sheet region specific unit n is calculated according to the following steps: spc Secondary stress at:

[0041] Step S631, determining a radial temperature difference calculation path;

[0042] Step S632, calculating the sum of the membrane stress and the bending stress caused by the radial temperature difference of the tube sheet according to Formula 3:

[0043]

[0044] Where Q1 is the sum of the film stress and bending stress caused by the radial temperature difference of the tube sheet; α is the thermal expansion coefficient of the material; E is the elastic modulus of the material; T is the unit n spc The temperature at the radial path; n is the unit number on the radial path; N is the set of unit numbers; T(n) is the temperature distribution along the radial path;

[0045] Step S633, determining the axial temperature difference calculation path;

[0046] Step S634, calculate the equivalent linear part of the stress distribution caused by the axial non-uniform temperature distribution of the tube sheet according to Formula 4:

[0047]

[0048] Among them, Q2 is the equivalent linear part of the stress distribution caused by the axial non-uniform temperature distribution of the tube sheet; ν is the Poisson's ratio of the material; ΔT1 is the temperature difference between the upper and lower sides of the tube sheet when assuming an equivalent linear temperature distribution in the wall thickness direction; d is the thickness of the tube sheet; the origin of the x-axis is located at the midpoint of the wall thickness, and the x value ∈ [-d / 2, +d / 2]; f(x) is the axial temperature distribution;

[0049] Step S635, calculate the secondary stress Q using Formula 6:

[0050] Q=Q1+Q2 Formula 6.

[0051] The present invention also constructs a nuclear-grade heat exchanger tube sheet thermal stress calculation and analysis system, including a processor and a memory storing a computer program. The processor implements the steps of the nuclear-grade heat exchanger tube sheet thermal stress calculation and analysis method described above when executing the computer program.

[0052] By implementing the technical solution of the present invention, the thermal stress of the tube sheet of a nuclear-grade heat exchanger under specific operating conditions can be calculated accurately, conservatively and quickly, thereby providing a technical basis for tube sheet design, operation safety analysis and full-life thermal fatigue life prediction. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 is a flow chart of a method for calculating and analyzing thermal stress of a tube sheet of a nuclear-grade heat exchanger according to an embodiment of the present invention;

[0054] Figure 2 is a graph showing the change of water temperature at the inlet of the water chamber on the tube side of the RRA heat exchanger over time under the preheating condition in an embodiment of the present invention;

[0055] Figure 3 Schematic diagram of the radial modeling range of the tube sheet of the RRA heat exchanger in the embodiment of the present invention;

[0056] Figure 4 is a solid model diagram of a local area of ​​a tube sheet of an RRA heat exchanger in an embodiment of the present invention;

[0057] Figure 5 is a curve diagram showing the change of the maximum temperature difference and the maximum thermal stress in the RRA heat exchanger tube sheet slice area over time under the preheating condition in the embodiment of the present invention;

[0058] Figure 6 is a curve diagram showing the change of the temperature along the radial position on the vertical surface of the RRA heat exchanger tube sheet slice at 2833 seconds under the preheating condition in the embodiment of the present invention;

[0059] Figure 7 It is a curve diagram of the temperature change along the axial position on the vertical surface 2 of the RRA heat exchanger tube sheet slice at 300 seconds under the non-preheating startup condition in the embodiment of the present invention. DETAILED DESCRIPTION

[0060] The following will be combined with the accompanying drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by relevant technical personnel in the field without making creative work are within the scope of protection of the present invention.

[0061] like Figure 1 As shown, the thermal stress calculation and analysis method of the nuclear-grade heat exchanger tube sheet of this embodiment includes:

[0062] Step S10, determining the range of operating parameters and their changing trends over time by combing and analyzing the designed transient operating conditions of the tube side and the shell side of the heat exchanger;

[0063] Step S20, determining a modeling range of the tube sheet portion of the heat exchanger, and establishing three-dimensional solid models of multiple local areas of the tube sheet portion according to the modeling range;

[0064] Step S30, dividing the three-dimensional solid model into finite element meshes to determine the contact surfaces between the local areas and the fluid inlet / outlet boundary surfaces;

[0065] Step S40, receiving parameter information of the fluid dynamics calculation model, the heat transfer and thermal stress conjugate calculation model set by the user;

[0066] Step S50, calculating the flow field, temperature field and thermal stress field of the specific local area of ​​the tube sheet during the transient period according to the set parameter information, the contact surface between the local areas and the fluid inlet / outlet boundary surface;

[0067] Step S60, calculating the extreme value and amplitude of thermal stress at the tube sheet during the transient period, and the extreme value and amplitude of secondary stress according to the temperature field and thermal stress field of the specific local area.

[0068] Further, step S10 includes:

[0069] Step S11, sorting out and analyzing the design transient operating conditions of the system to which the tube side and the shell side of the heat exchanger belong;

[0070] Step S12, analyzing the thermal hydraulic state of the tube side of the heat exchanger under various design transient conditions, determining the variation range and heating / cooling rate of the tube side temperature, pressure and flow rate, and the variation curve of the tube side temperature, pressure and flow rate over time;

[0071] Step S13, analyzing the thermal-hydraulic state of the shell side of the heat exchanger under various design transient conditions, determining the variation range and heating / cooling rate of the shell side temperature, pressure and flow, and the variation curve of the shell side temperature, pressure and flow over time.

[0072] Further, in step S20, determining the modeling range of the tube sheet portion of the heat exchanger includes:

[0073] Step S21, the following simplified assumptions are made for the physical structure of the tube sheet of the heat exchanger: the screw portion inserted into the flange screw hole, the positioning pin portion, and the sealing gasket between the tube sheet and the flange form a continuous integrated component with the flange; the bolt protrusion portion is ignored; any gaps between components and between components and the fluid are ignored; the tube sheet, the shell side cylinder flange, and the water chamber flange do not form a continuous integrated component;

[0074] Step S22, determining the axial modeling range of the tube sheet of the heat exchanger, and the axial modeling range includes: a section of the upper part of the water chamber cylinder, the water chamber cylinder flange, the tube sheet, a section of the heat transfer tube, the shell side cylinder flange and a section of the lower part of the shell side cylinder, and the tube side fluid and the shell side fluid in these components; the total length of the shell side cylinder flange and the lower part of the shell side cylinder is the same as the length of the heat transfer tube, and the length is greater than the effective mixing length of the shell side fluid, and less than The total length of the upper section of the water chamber cylinder and the water chamber cylinder flange is greater than the effective mixing length of the fluid in the water chamber on the tube side and less than Wherein, R is the average radius of the tube sheet portion; t is the thickness of the tube sheet portion;

[0075] Step S23, determining the horizontal modeling range of the tube sheet portion of the heat exchanger according to the following method: the length and width of the horizontal modeling range are both less than Within the horizontal modeling range, the number of heat transfer tubes is less than 1 / 10 of the total number, is greater than 3, and includes at least 1 inner circle heat transfer tube; the horizontal modeling range includes the outer wall in contact with the cold fluid; the horizontal modeling range is adjacent to the partition in the tube side water chamber, or is located on both sides of the partition.

[0076] Further, step S30 includes:

[0077] Step S31, dividing the components and fluid regions in the three-dimensional solid model into unstructured finite element grids; wherein the grid density of the tube sheet region and the water chamber flange region is greater than the grid density of other components and fluid regions;

[0078] Step S32, determining the contact surfaces between components and between components and fluid;

[0079] Step S33, determining the surface where the fluid inlet / outlet boundary is located.

[0080] Further, step S40 includes:

[0081] Step S41, receiving a turbulent viscosity model set by a user;

[0082] Step S42, receiving the regional material characteristic parameters set by the user;

[0083] Step S43, receiving the boundary conditions set by the user;

[0084] Step S44, receiving the thermal stress calculation formula set by the user.

[0085] Further, step S42 includes:

[0086] Step S421, receiving the values ​​of the characteristic parameters of the metal component set by the user, wherein the characteristic parameters of the metal component include: density, specific heat, thermal conductivity, elastic modulus and thermal expansion coefficient, wherein the values ​​of density, specific heat and thermal conductivity are taken as the values ​​at the highest temperature during the design transient period; the values ​​of elastic modulus and thermal expansion coefficient are taken as the values ​​at room temperature;

[0087] Step S422, receiving the value of the fluid physical property parameter set by the user. The fluid physical property parameter includes density, viscosity, specific heat and thermal conductivity. The value of the fluid physical property parameter is a function of temperature and pressure in a supercooled state, and is a function of temperature or pressure in a saturated state.

[0088] Further, step S43 includes:

[0089] S431, receiving the inlet boundary and outlet boundary conditions of the tube side and shell side fluids set by the user, wherein the inlet boundary type is set to a velocity boundary; the outlet boundary type is set to a pressure boundary, the fluid temperature and velocity on the inlet boundary are functions of time; and the fluid pressure on the outlet boundary is a function of time;

[0090] S432, receiving a boundary condition between an unmodeled area and a modeled area set by a user, and setting the boundary between the unmodeled area and the modeled area as an adiabatic boundary;

[0091] S433, receiving a contact boundary condition between the outer wall of the component and the air set by the user, wherein the convective heat transfer coefficient value of the contact boundary between the outer wall of the component and the air is set to the value of the steel-air convective heat transfer coefficient at room temperature;

[0092] S434, receiving contact boundary conditions between solid and solid regions and between solid and fluid regions. The boundaries are set as coupling boundaries.

[0093] Further, in step S44, the formula for the thermal stress distribution S(t,n) of the tube sheet area at the set time step t is:

[0094]

[0095] Where t is the time step, n is the unit number, N is the unit number set, C is the thermal stress concentration factor, α is the thermal expansion coefficient of the material, E is the elastic modulus of the material, and T(t,n) is the temperature at unit n at time step t.

[0096] Further, step S60 includes:

[0097] Step S61, calculating the extreme value of thermal stress in the tube sheet area;

[0098] Step S62, calculating the variation amplitude of thermal stress in the tube sheet area;

[0099] Step S63, calculating the secondary stress extreme value of the tube sheet area;

[0100] Step S64, calculating the secondary stress variation amplitude in the tube sheet area.

[0101] Furthermore, the step S61 includes:

[0102] Step S611, dividing the thermal stress of the tube sheet area into secondary stress Q and peak stress F. The secondary stress includes: the sum of the film stress and bending stress caused by the radial temperature difference of the tube sheet, and the equivalent linear part of the stress distribution caused by the axial non-uniform temperature distribution of the tube sheet;

[0103] Step S612: Calculate the maximum value of thermal stress (Q+F) and thermal stress

[0104] Minimum value of max force (Q+F) min :

[0105]

[0106] Where T is the time step set; n is the unit number; N is the unit number set; S(t,n) is the thermal stress distribution of the tube sheet area under time step t;

[0107] Step S613, determining the time step t where the maximum value of the thermal stress is located max and unit number n max , and the time step t where the thermal stress minimum is located min and unit number n min .

[0108] Further, in step S62, according to the maximum value of thermal stress (Q+F), the minimum value of thermal stress

[0109] max

[0110] Value (Q+F) min Calculate the magnitude of thermal stress changes.

[0111] Further, in step S63, the tube sheet region specific unit n is calculated according to the following steps: spc Secondary stress at:

[0112] Step S631, determining a radial temperature difference calculation path;

[0113] Step S632, calculating the sum of the membrane stress and the bending stress caused by the radial temperature difference of the tube sheet according to Formula 3:

[0114]

[0115] Where Q1 is the sum of the film stress and bending stress caused by the radial temperature difference of the tube sheet; α is the thermal expansion coefficient of the material; E is the elastic modulus of the material; T is the unit n spc The temperature at the radial path; n is the unit number on the radial path; N is the set of unit numbers; T(n) is the temperature distribution along the radial path;

[0116] Step S633, determining the axial temperature difference calculation path;

[0117] Step S634, calculate the equivalent linear part of the stress distribution caused by the axial non-uniform temperature distribution of the tube sheet according to Formula 4:

[0118]

[0119] Among them, Q2 is the equivalent linear part of the stress distribution caused by the axial non-uniform temperature distribution of the tube sheet; ν is the Poisson's ratio of the material; ΔT1 is the temperature difference between the upper and lower sides of the tube sheet when the equivalent linear temperature distribution in the wall thickness direction is assumed; d is the thickness of the tube sheet; the origin of the x-axis is located at the midpoint of the wall thickness, and the x value ∈ [-d / 2, +d / 2]; f(x) is the axial temperature distribution; ΔT1 is the temperature difference between the upper and lower sides of the tube sheet;

[0120] Step S635, calculate the secondary stress Q using Formula 6:

[0121] Q=Q1+Q2 Formula 6.

[0122] The following is an example of the thermal stress calculation and analysis of the RRA (residual heat removal) heat exchanger tube sheet of the CPR1000 nuclear power unit.

[0123] In step S10, the design transient operating conditions of the tube side and shell side of the heat exchanger are sorted out and analyzed to determine the range of the operating parameters and their changing trends over time. Specifically, the design transient operating condition data (such as lists, classifications, basic conditions and assumptions, etc.) of the systems to which the tube side and shell side of the RRA heat exchanger belong are collected, and the thermal-hydraulic states of the tube side under 7 operating conditions and the shell side under 1 operating condition are analyzed to obtain the range of the thermal-hydraulic parameters of the tube side and shell side and their changing trend curves over time.

[0124] Under the preheating condition, the range of thermal hydraulic parameters of the RRA heat exchanger tube side is shown in Table 1. The change of water temperature at the inlet of the water chamber on the RRA heat exchanger tube side with time is shown in Table 1. Figure 2 As shown in the figure, the inlet water temperature of the RRA heat exchanger shell side is 293.15K, the inlet water velocity is 0.548m / s, and the pressure is 8.0bar.

[0125]

[0126]

[0127] Table 1

[0128] In step S20, the modeling range of the tube sheet of the heat exchanger is determined, and based on the modeling range, a three-dimensional solid model of multiple local areas of the tube sheet is established. Specifically, it is assumed that the screw part inserted into the flange screw hole, the positioning pin part and the sealing gasket between the tube sheet and the flange form a continuous integrated component with the flange; the protruding part of the bolt (such as the nut) is ignored; any gaps between components and between components and the fluid are ignored; the tube sheet, the shell side cylinder flange and the water chamber flange do not constitute a continuous integrated component.

[0129] The axial modeling range of the local area includes: a section of the upper part of the water chamber cylinder, the water chamber cylinder flange, the tube sheet, a section of the heat transfer tube, the shell side cylinder flange and a section of the lower part of the shell side cylinder, as well as the tube side fluid and shell side fluid in these components. The total axial height is 900mm. Among them, the tube sheet height is 200mm, the shell side cylinder flange and the lower section of the shell side cylinder height are 300mm, and the upper section of the water chamber cylinder and the water chamber cylinder flange height are 400mm.

[0130] Local area radial modeling range: take the area surrounded by the 270° axis of the tube sheet (coincides with the axis of the partition plate in the water chamber), the angle line of 60° with the axis and the arc line of the outer edge of the tube sheet (this area contains 10 heat transfer tubes), such as Figure 3 Area A10 is shown.

[0131] The three-dimensional solid model includes six local areas, namely local areas A1-A6. Figure 4As shown. Among them, local area A1 is the area where the tube sheet and a small section at the bottom of a heat transfer tube are modeled as a whole, called the "slice area" (plate1); local area A2 is the area where the tube sheet and 9 heat transfer tubes are modeled as a whole (plate2); local area A3 is the area where the water chamber and its flange are modeled as a whole (bowl); local area A4 is the area where the shell and its flange are modeled as a whole (barrel); local area A5 is the area where the hot fluid on the tube side is modeled as a whole (priwater); local area A6 is the area where the cold fluid on the shell side is modeled as a whole (secwater). The geometric features of the three-dimensional solid model of the local area of ​​the tube sheet of the RRA heat exchanger mentioned above are consistent with the requirements of steps S21, S22, and S23. In addition, a three-dimensional solid modeling software is used to establish three-dimensional solid models of each local area of ​​the tube sheet.

[0132] In step S30, the three-dimensional solid model is divided into finite element meshes to determine the contact surfaces between local areas and the fluid inlet / outlet boundary surfaces. Specifically, a finite element meshing software is used to divide the six areas in the local area solid model of the tube sheet of the RRA heat exchanger into unstructured finite element meshes, specify the contact surfaces between metal parts and between metal parts and fluids, and specify the surfaces where the inlet boundary and outlet boundary of the tube sheet parts are located. The meshes of the tube sheet slice area and the water chamber flange area of ​​interest are divided densely.

[0133] In step S40, the parameter information of the fluid dynamics calculation model, heat transfer and thermal stress conjugate calculation model set by the user is received. Specifically, the turbulent viscosity model option and the near-wall processing method option are set. The density, specific heat and thermal conductivity values ​​of the metal part 00Cr19Ni10 stainless steel are taken as the values ​​at 180°C during the transient operation. The elastic modulus and thermal expansion coefficient of 00Cr19Ni10 stainless steel are taken as the values ​​at 20°C. According to the IAPWS-IF97 calculation relationship, a computer program for calculating the density, viscosity, specific heat and thermal conductivity values ​​of supercooled water is written in C language.

[0134] Set the following 4 types of boundary conditions:

[0135] Type 1 boundary (inlet and outlet boundaries of the tube and shell side fluids): The inlet boundary type is set to velocity boundary; the outlet boundary type is set to pressure boundary. The fluid temperature and velocity on the inlet boundary are functions of time. The fluid pressure on the outlet boundary is a function of time. Use C language to write a computer program to calculate the thermal hydraulic parameter values ​​of the inlet and outlet boundaries.

[0136] Type 2 boundaries (boundaries between unmodeled and modeled regions): These boundaries are assumed to be adiabatic (i.e., the heat flux is taken as 0.0 W / m 2 ).

[0137] Type 3 boundary (contact boundary between the outer wall of the component and the air): Set the convection heat transfer coefficient value of this type of boundary to 7.0 W / (m 2 K).

[0138] Type 4 boundaries (contact boundaries between solid-solid regions and solid-fluid regions): Set all of these boundaries as coupled boundaries.

[0139] According to the above formula 1, a computer program is written in C language to calculate the maximum temperature difference, minimum temperature difference and thermal stress distribution in the tube sheet area under a specific time step.

[0140] In step S50, the flow field, temperature field and thermal stress field of the specific local area of ​​the tube sheet during the transient period are calculated according to the set parameter information, the contact surface between the local areas and the fluid inlet / outlet boundary surface.

[0141] Specifically, the calculation steps include steady-state calculation and transient calculation. The purpose of steady-state calculation is to obtain the state parameters at the initial moment of the operating condition (t = 0 seconds) so as to start transient calculation under this state. The purpose of transient calculation is to obtain the flow field, temperature field and thermal stress field at each time step during the transient operation.

[0142] Before starting steady-state and transient calculations, set iterative calculation options; set monitoring parameters at locations of interest (such as water temperature and water velocity at the inlet and outlet of the pipe side) to facilitate checking the rationality of these parameters during and after the calculation.

[0143] In step S60, based on the temperature field and thermal stress field of the specific local area, the extreme value and amplitude of thermal stress at the tube sheet portion during the transient period, as well as the extreme value and amplitude of secondary stress are calculated.

[0144] Specifically, according to step S61, the maximum value (Q+F) and minimum value (Q+F) of thermal stress in the tube sheet area are calculated.

[0145] max value (Q+F) min , and determine the time step where the extreme value is located (t max and t min ) and unit number (n max and n min ).

[0146] The maximum temperature difference and maximum thermal stress of the tube sheet slice area change with time under preheating conditions, such as Figure 5As shown in Figure 2, the maximum value of thermal stress and secondary stress in the tube sheet section area appears at 2833 seconds, and the minimum value appears at 0 seconds. The maximum value of thermal stress in the tube sheet section area is 976.6MPa, and the minimum value is 0.0MPa.

[0147] Assuming that the position of the minimum thermal stress in the tube sheet area is the same as the position of the maximum thermal stress during the transient period, the maximum thermal stress amplitude Δ(Q+F) in the tube sheet section area is 976.6MPa under the preheating condition.

[0148] Let a specific unit n spc =n max According to step S63, calculate the maximum secondary stress Q of the tube sheet area under specific operating conditions max The calculation process is as follows:

[0149] (1) Determine the radial temperature difference calculation path

[0150] The temperature change along the radial position on the vertical surface of the slice at 2833 seconds under the preheating condition is as follows: Figure 6 shown.

[0151] (2) Calculate Q1 according to formula 3

[0152] At 2833 seconds under preheating conditions, Q1=482.4MPa.

[0153] (3) Determine the axial temperature difference calculation path

[0154] The temperature change along the axial position on the vertical surface 2 of the slice at 300 seconds without preheating is as follows: Figure 7 On the two marked curves, the temperature difference between the upper and lower surfaces is the largest (the temperature difference is about 100K).

[0155] (4) Calculate ΔT1 according to Formula 5; calculate Q2 according to Formula 4

[0156] At 2833 seconds under preheating conditions, Q2 = 93.6 MPa.

[0157] (5) Calculate Q according to formula 6 max

[0158] At 2833 seconds under preheating conditions, Q max =576.0MPa.

[0159] Let a specific unit n spc =n min According to step S63, calculate the minimum value Q of the secondary stress in the tube sheet area under specific operating conditions min . At 0 seconds in preheating condition, Q1=Q2=Q min =0.0MPa.

[0160] The maximum secondary stress amplitude ΔQ in the tube sheet area during the transient period is calculated. Under the preheating condition, the maximum secondary stress amplitude ΔQ in the tube sheet section area is 576.0 MPa.

[0161] The present invention also constructs a nuclear-grade heat exchanger tube sheet thermal stress calculation and analysis system, including a processor and a memory storing a computer program. When the processor executes the computer program, the steps of the nuclear-grade heat exchanger tube sheet thermal stress calculation and analysis method described above are implemented.

[0162] Furthermore, in order to obtain the calculation results quickly, a parallel calculation analysis of thermal stress of nuclear-grade heat exchanger tube sheet is carried out on a parallel computing cluster system composed of homogeneous computers. The hardware system of the parallel computing system includes: 6 H3C servers, 1 H3C disk array cabinet, some high-speed network equipment and displays, etc. These computers are contained in a local area network with a C / S architecture. Among them, 1 server is used as a login node, 1 server is used as a database node, and the other servers are used as computing nodes.

[0163] The software system of the parallel computing system includes: SuSE operating system, self-compiled CFD finite element calculation package, H3C cloud platform software package, PVM (parallel virtual machine) software package and parallel operation program, etc.

[0164] The parallel operation program source code is written in C language based on the message management function library in the parallel computing support software package. The parallel operation program has the functions of task control, task division, task load statistics, task scheduling, task synchronization and task communication. The further description of the parallel operation program function is shown in Table 2:

[0165]

[0166]

[0167]

[0168] Table 2

[0169] The above description is only a preferred embodiment of the present invention and cannot be used to limit the claims of the present invention. For various types of shell and tube heat exchangers, the present invention can have various modifications and variations. Any modification, equivalent replacement or improvement made within the principle and technical essence of the present invention is included in the scope of the claims of the present invention.

Claims

1. A method for calculating and analyzing thermal stress of tube sheets of nuclear-grade heat exchangers, characterized in that: include: Step S10, by combing and analyzing the design transient operating conditions of the tube side and the shell side of the heat exchanger, determining the range of the operating parameters and their changing trends over time; Step S20, determining a modeling range of the tube sheet portion of the heat exchanger, and establishing three-dimensional solid models of multiple local areas of the tube sheet portion according to the modeling range; Step S30, dividing the three-dimensional solid model into finite element meshes to determine the contact surfaces between the local areas and the fluid inlet / outlet boundary surfaces; Step S40, receiving parameter information of the fluid dynamics calculation model, the heat transfer and thermal stress conjugate calculation model set by the user; Step S50, calculating the temperature field and thermal stress field of the specific local area of ​​the tube sheet during the transient period according to the set parameter information, the contact surface between the local areas and the fluid inlet / outlet boundary surface; Step S60, calculating the extreme value and amplitude of thermal stress at the tube sheet during the transient period, and the extreme value and amplitude of secondary stress according to the temperature field and thermal stress field of the specific local area.

2. The method for calculating and analyzing thermal stress of tube sheets of nuclear-grade heat exchangers according to claim 1, characterized in that: In the step S20, determining the modeling range of the tube sheet portion of the heat exchanger includes: Step S21, the following simplified assumptions are made for the physical structure of the tube sheet of the heat exchanger: the screw portion inserted into the flange screw hole, the positioning pin portion, and the sealing gasket between the tube sheet and the flange form a continuous integrated component with the flange; the bolt protrusion portion is ignored; any gaps between components and between components and the fluid are ignored; the tube sheet, the shell side cylinder flange, and the water chamber flange do not form a continuous integrated component; Step S22, determining the axial modeling range of the tube sheet of the heat exchanger, wherein the axial modeling range includes: a section of the upper part of the water chamber cylinder, the water chamber cylinder flange, the tube sheet, a section of the heat transfer tube, the shell side cylinder flange and a section of the lower part of the shell side cylinder, and the tube side fluid and the shell side fluid in these components; the total length of the shell side cylinder flange and the lower part of the shell side cylinder is the same as the length of the heat transfer tube, and the length is greater than the effective mixing length of the shell side fluid and less than The total length of the upper section of the water chamber cylinder and the water chamber cylinder flange is greater than the effective mixing length of the fluid in the water chamber on the tube side and less than Wherein, R is the average radius of the tube sheet portion; t is the thickness of the tube sheet portion; Step S23, determining the horizontal modeling range of the tube sheet portion of the heat exchanger according to the following method: the length and width of the horizontal modeling range are both less than Within the horizontal modeling range, the number of heat transfer tubes is less than 1 / 10 of the total number, is greater than 3, and includes at least 1 inner circle heat transfer tube; the horizontal modeling range includes the outer wall in contact with the cold fluid; the horizontal modeling range is adjacent to the partition in the tube side water chamber, or is located on both sides of the partition.

3. The method for calculating and analyzing thermal stress of nuclear-grade heat exchanger tube sheets according to claim 1, characterized in that: The step S40 comprises: Step S41, receiving a turbulent viscosity model set by a user; Step S42, receiving the regional material characteristic parameters set by the user; Step S43, receiving the boundary conditions set by the user; Step S44, receiving the thermal stress calculation formula set by the user.

4. The method for calculating and analyzing thermal stress of nuclear-grade heat exchanger tube sheets according to claim 3, characterized in that: The step S42 comprises: Step S421, receiving the values ​​of the characteristic parameters of the metal component set by the user, wherein the characteristic parameters of the metal component include: density, specific heat, thermal conductivity, elastic modulus and thermal expansion coefficient, wherein the values ​​of density, specific heat and thermal conductivity are taken as the values ​​at the highest temperature during the design transient period; the values ​​of elastic modulus and thermal expansion coefficient are taken as the values ​​at room temperature; Step S422, receiving the values ​​of the fluid physical property parameters set by the user, wherein the fluid physical property parameters include density, viscosity, specific heat and thermal conductivity, and the values ​​of the fluid physical property parameters are functions of temperature and pressure in a supercooled state, and are functions of temperature or pressure in a saturated state.

5. The method for calculating and analyzing thermal stress of nuclear-grade heat exchanger tube sheets according to claim 3, characterized in that: In step S44, the formula for the thermal stress distribution S(t,n) of the tube sheet area at the set time step t is: Where t is the time step, n is the unit number, N is the unit number set, C is the thermal stress concentration factor, α is the thermal expansion coefficient of the material, E is the elastic modulus of the material, and T(t,n) is the temperature at unit n at time step t.

6. The method for calculating and analyzing thermal stress of nuclear-grade heat exchanger tube sheets according to claim 1, characterized in that: The step S60 comprises: Step S61, calculating the extreme value of thermal stress in a specific local area of ​​the tube sheet; Step S62, calculating the variation amplitude of thermal stress in a specific local area of ​​the tube sheet; Step S63, calculating the secondary stress extreme value of a specific local area of ​​the tube sheet; Step S64, calculating the variation amplitude of the secondary stress in a specific local area of ​​the tube sheet.

7. The method for calculating and analyzing thermal stress of nuclear-grade heat exchanger tube sheets according to claim 6, characterized in that: The step S61 comprises: Step S611, dividing the thermal stress of a specific local area of ​​the tube sheet into a secondary stress Q and a peak stress F, wherein the secondary stress includes: the sum of the film stress and the bending stress caused by the radial temperature difference of the tube sheet, and the equivalent linear part of the stress distribution caused by the axial non-uniform temperature distribution of the tube sheet; Step S612, calculate the maximum value (Q+F) and minimum value (Q+F) of thermal stress in the tube sheet area according to Formula 2. min : Where T is the time step set; n is the unit number; N is the unit number set; S(t,n) is the thermal stress distribution of the tube sheet area under time step t; Step S613, determining the time step t where the maximum value of the thermal stress is located max and unit number n max , and the time step t where the thermal stress minimum is located min and unit number n min .

8. The method for calculating and analyzing thermal stress of nuclear-grade heat exchanger tube sheets according to claim 6, characterized in that: In step S63, the tube sheet region specific unit n is calculated according to the following steps: spc Secondary stress at: Step S631, determining a radial temperature difference calculation path; Step S632, calculating the sum of the membrane stress and the bending stress caused by the radial temperature difference of the tube sheet according to Formula 3: Where Q1 is the sum of the film stress and bending stress caused by the radial temperature difference of the tube sheet; α is the thermal expansion coefficient of the material; E is the elastic modulus of the material; T is the unit n spc The temperature at the radial path; n is the unit number on the radial path; N is the set of unit numbers; T(n) is the temperature distribution along the radial path; Step S633, determining the axial temperature difference calculation path; Step S634, calculate the equivalent linear part of the stress distribution caused by the axial non-uniform temperature distribution of the tube sheet according to Formula 4: Among them, Q2 is the equivalent linear part of the stress distribution caused by the axial non-uniform temperature distribution of the tube sheet; ν is the Poisson's ratio of the material; ΔT1 is the temperature difference between the upper and lower sides of the tube sheet when assuming an equivalent linear temperature distribution in the wall thickness direction; d is the thickness of the tube sheet; the origin of the x-axis is located at the midpoint of the wall thickness, and the x value ∈ [-d / 2, +d / 2]; f(x) is the axial temperature distribution; Step S635, calculate the secondary stress Q using Formula 6: Q=Q1+Q2 Formula 6.

9. A nuclear grade heat exchanger tube sheet thermal stress calculation and analysis system, comprising a processor and a memory storing a computer program, characterized in that: The processor implements the steps of the nuclear-grade heat exchanger tube sheet thermal stress calculation and analysis method as described in any one of claims 1 to 8 when executing the computer program.

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