Method for determining temperature distribution of buried pipe type heat exchanger

Abstract

The invention relates to the technical field of ground source heat pumps, and discloses a buried pipe type heat exchanger temperature distribution determining method which is based on a U-shaped buried pipe heat exchange system and comprises the steps that an equilibrium equation is established, and initial conditions and boundary conditions are set; calculating thermal resistance of each part according to thermophysical parameters of rock soil and a system; determining an initial drilling wall temperature distribution and an initial fluid temperature distribution before the system begins to operate; determining the heat flux density of the rock soil converged outside the well in each small section of the U-shaped buried pipe; establishing a line source model equation set, and calculating drilling wall temperature distribution in a system operation process; well wall temperature distribution in the system operation process is substituted into the balance equation, and fluid temperature distribution and heat exchange amount in the system operation process are obtained; and performing cycle calculation according to the cycle index and the operation period. According to the method, the ground heat exchanger model is established through the virtual heat source method, the temperature distribution condition of rock soil and fluid in the well in the operation cycle is obtained, and the thermal behavior of the tube well in the drilled well is predicted.

Description

Technical Field

[0001] The present invention relates to the technical field of ground source heat pumps, and particularly to a method for determining the temperature distribution of a buried tube heat exchanger. Background Art

[0002] The U-shaped medium-deep buried tube heat exchanger is a device for efficiently extracting medium-deep geothermal energy, with the advantages of high heat transfer efficiency and small floor area. The analysis and optimization of its heat transfer performance are based on geotechnical thermal property tests and design theories. In recent years, researchers have made remarkable progress in this field. In the past few years of research, scholars have proposed various calculation methods to simplify the study of U-shaped medium-deep buried tube heat exchangers. For example, by dividing the calculation area into different pipe zones and solving two-dimensional unsteady problems in two-dimensional cylindrical coordinates, the calculation complexity is effectively reduced and the calculation efficiency is improved. In addition, another study combined specific engineering cases to establish a three-dimensional full-scale numerical calculation model to explore the influence of the buried pipe cementing layer on the heat transfer performance, further expanding the research scope. In addition, some journals focus on the influence of different geological structure stratifications on the performance of U-shaped buried tube heat exchangers. With the help of MATLAB software and a numerical heat transfer model based on longitudinal geotechnical stratification, researchers systematically analyzed the influence of factors such as circulation flow rate, inlet temperature, pipe length, and thermal conductivity of the insulation material on the heat transfer performance. The results show that optimizing the circulation flow rate, pipe length, and selecting appropriate insulation materials and backfill materials can significantly improve the performance of the heat exchanger.

[0003] However, existing research still faces some challenges, such as the complexity of modeling and large amount of calculation. Future research should focus on improving the calculation model to more comprehensively explore the performance of U-shaped medium-deep buried tube heat exchangers, thus promoting the further development and application of this field. Summary of the Invention

[0004] The present invention provides a method for determining the temperature distribution of a buried tube heat exchanger. By establishing a buried tube heat exchanger model using the virtual heat source method, the temperature distribution of the rock and soil and the fluid in the well during the operation period is obtained, and the thermal behavior of the pipe well in the drilling is predicted. According to the obtained fluid temperature distribution, the control variable method is used to adjust various thermal property parameters in turn, so as to analyze their thermal sensitivity and obtain various schemes for optimizing the heat transfer efficiency of the system. In addition, the established model includes a set of equations for solving the temperature distribution of the drilling wall derived from the semi-infinite line source model, which can be applied to the calculation of the temperature of the drilling wall with various structural characteristics.

[0005] The present invention provides a method for determining the temperature distribution of a buried tube heat exchanger, based on a U-shaped buried tube heat exchange system, including:

[0006] S1. Establish an equilibrium equation for the fluid in the four well sections of the U-shaped buried pipe, and set the initial conditions and boundary conditions; among them, the U-shaped buried pipe is divided into four parts: injection well, arc section, horizontal well, and production well according to its structural characteristics;

[0007] S2. Calculate the thermal resistance of each part according to the thermophysical parameters of the rock and soil and the system;

[0008] S3. Determine the initial drilling wall temperature distribution before the system starts to operate according to the boundary conditions and the thermal resistance of each part, and determine the initial fluid temperature distribution before the system starts to operate according to the equilibrium equation and the drilling wall temperature distribution;

[0009] S4. Divide the U-shaped buried pipe into several small segments, and determine the heat flux density flowing into the rock and soil outside each small segment according to the initial fluid temperature distribution;

[0010] S5. Establish a line source model equation set for the four parts of the U-shaped buried pipe in turn, and substitute the heat flux density into the line source model equation set to obtain the drilling wall temperature distribution during the operation of the system;

[0011] S6. Substitute the drilling wall temperature distribution during the operation of the system into the equilibrium equation to obtain the fluid temperature distribution and heat transfer amount during the operation of the system;

[0012] S7. Perform cyclic calculations according to the number of cycles and the operation period until the number of cycles reaches the operation period, then output the fluid temperature distribution, and adjust the values of the thermophysical parameters in turn to analyze the heat transfer situation of the system.

[0013] Further, the step S7 specifically includes:

[0014] S701. Record the number of times of obtaining the fluid temperature distribution and heat transfer amount during the operation of the system as the number of cycles, and judge whether the number of cycles is greater than or equal to the set operation period;

[0015] S702. If the number of cycles is less than the set operation period, return to step S4;

[0016] S703. If the number of cycles is greater than or equal to the set operation period, output the fluid temperature distribution, and adjust the values of the thermophysical parameters in turn to analyze the heat transfer situation of the system.

[0017] Further, in the step S1, the equilibrium equation is:

[0018]

[0019] Among them, except for the parameters that have been explained, the other several in the lower right corner represent positions: 1 - injection well, r - arc section, 2 - horizontal well, 3 - production well, b - drilling wall; z represents the longitudinal depth, unit m; x represents the horizontal length, unit m; θ represents the continuously changing central angle of the arc section, unit °; ρ represents the density of the fluid in the pipeline, unit kg / m 3 ; c represents the specific heat capacity of the fluid in the pipeline, unit J / kg·℃; V represents the volume flow rate of the fluid in the pipeline, unit m 3 / s; T b represents the temperature of the drilling wall, unit ℃; R x represents the thermal resistance of each well section, unit k / w.

[0020] Furthermore, in the step S1, the initial conditions are:

[0021] t = 0, circulating fluid:

[0022]

[0023] t = 0, drilling wall:

[0024]

[0025] Among them, the specific expressions of each well section are:

[0026] Injection well:

[0027] Arc section:

[0028] Horizontal well:

[0029] Production well:

[0030] The boundary conditions are:

[0031]

[0032] z = H1, T1 = T r

[0033] z = H 1+πr / 2 , T r = T2, T2 = T3

[0034] Among them, T0 represents the average surface temperature, unit ℃; k geo represents the geothermal gradient, unit ℃ / m; z represents the longitudinal depth, unit m; T io represents the outlet temperature of the injection well, unit ℃; T ao represents the outlet temperature of the arc well, unit ℃; H1 represents the depth of the injection well, unit m; r represents the radius length of the arc section, unit m; Tin Represents the fluid temperature at the system inlet, unit: °C; T out Represents the fluid temperature at the system outlet, unit: °C.

[0035] Furthermore, in step S2, the calculation formula for each part of the thermal resistance is:

[0036] R x = R i + R m + R o

[0037] Among them, the specific expressions for each part of the thermal resistance are:

[0038]

[0039] Among them, R i Represents the convective heat transfer between the fluid in the pipe and the inner wall of the pipe; R m Represents the heat conduction in the pipe material; R o Represents the heat conduction between the rock and soil outside the well and the backfill material; r x,i Is the inner radius of the buried pipe, unit: m; r x,o Is the outer radius of the buried pipe, unit: m; r b Is the drilling radius, unit: m; h f Is the convective heat transfer coefficient of the fluid in the pipe, unit: W / ㎡·K; k b Is the thermal conductivity of the backfill material, unit: W / m·K; k p Is the thermal conductivity of the pipe material, unit: W / m·K.

[0040] Furthermore, in step S4, the calculation formula for the heat flux density is:

[0041]

[0042] Among them, m represents the segmentation order; Represents the fluid outlet temperature in a small segment divided in the spatial dimension, unit: °C; Represents the fluid inlet temperature in a small segment divided in the spatial dimension, unit: °C; Represents the heat flow outside the system within this segment range, unit: kW; Represents the heat flux density within the same range, unit: kW / m; l represents the length of the small segment, unit: m;

[0043] Based on the fluid temperature distribution obtained after each cycle, determine the inlet and outlet fluid temperatures of several small segments here, and the calculated heat flux density is used for the next cycle to calculate the temperature distribution of the drilling wall, thus forming an iterative calculation.

[0044] Furthermore, in step S5, the line source model equations are:

[0045] Injection well:

[0046]

[0047] Arc section:

[0048]

[0049] Horizontal well:

[0050]

[0051]

[0052] Production well:

[0053]

[0054] Wherein, s represents the line source length, in m; T0 represents the annual average ground surface temperature, in °C; T a represents the amplitude of temperature oscillation, in °C; ω represents the angular frequency; a z represents the thermal diffusivity of the rock and soil in the z direction, in m² / s; k x k y k z are respectively the thermal conductivities of the rock and soil in the x, y, and z directions, in W / m·K; t represents the time difference; k zx represents the ratio of the thermal conductivity of the rock and soil in the z direction to that in the x direction, κ zy Similarly; β represents the central angle of the arc section, in °; a x represents the thermal diffusivity of the rock and soil in the x direction, in m 2 / s; κ xy represents the ratio of the thermal conductivity of the rock and soil in the x direction to that in the y direction, k xz Similarly.

[0055] Furthermore, in the step S6, the calculation of the fluid temperature distribution and the heat exchange amount is as follows:

[0056]

[0057] Wherein, represents the temperature of the inlet fluid after circulation, in °C; represents the temperature of the outlet fluid after circulation, in °C; Q (n) represents the heat exchange amount of the system after each circulation, in kw; a new outlet temperature is obtained at the end of each circulation, and the heat exchange amount of the system is calculated and its change situation is analyzed accordingly.

[0058] The present invention also provides a device for determining the temperature distribution of a buried tube heat exchanger, based on a U-shaped buried tube heat exchange system, including:

[0059] A first establishment module, configured to establish an equilibrium equation for the fluid in the four well sections of the U-shaped buried pipe, and set initial conditions and boundary conditions; wherein, the U-shaped buried pipe is divided into four parts: an injection well, an arc section, a horizontal well, and a production well according to its structural characteristics;

[0060] A first calculation module, configured to calculate the thermal resistance of each part according to the thermal physical properties of the rock and soil and the system;

[0061] A first determination module, configured to determine the initial drilling wall temperature distribution before the system starts running according to the boundary conditions and the thermal resistance of each part, and determine the initial fluid temperature distribution before the system starts running according to the equilibrium equation and the drilling wall temperature distribution;

[0062] A second determination module, configured to divide the U-shaped buried pipe into several small segments, and determine the heat flux density flowing into the rock and soil outside each small segment according to the initial fluid temperature distribution;

[0063] A second establishment module, configured to sequentially establish a line source model equation set for the four parts of the U-shaped buried pipe, and substitute the heat flux density into the line source model equation set to obtain the drilling wall temperature distribution during the operation of the system;

[0064] A second calculation module, configured to substitute the drilling wall temperature distribution during the operation of the system into the equilibrium equation to obtain the fluid temperature distribution and the heat exchange amount during the operation of the system;

[0065] A circulation module, configured to perform circulation calculations according to the number of circulation times and the operation period, and when the number of circulation times reaches the operation period, output the fluid temperature distribution, and sequentially adjust the values of the thermal physical property parameters to analyze the heat exchange situation of the system.

[0066] The present invention also provides a computer device, including a memory and a processor, wherein the memory stores a computer program, and when the processor executes the computer program, the steps of the above method are implemented.

[0067] The present invention also provides a computer-readable storage medium, on which a computer program is stored, and when the computer program is executed by a processor, the steps of the above method are implemented.

[0068] The beneficial effects of the present invention are:

[0069] The present invention uses the virtual heat source method and regards the system as a semi-infinite line heat source, programs the objective function using Matlab, and finally can output the fluid temperature distribution and the heat exchange amount of the system during the entire operation cycle. For the solution of the temperature distribution of the drilling wall, a set of line source model equations is derived, realizing the coupled calculation of the heat exchange process between the rock and soil outside the well and the fluid inside the well. It can be applied to buried pipe systems with various structural characteristics other than U-shaped pipe wells. While ensuring the numerical accuracy of the system temperature distribution, it shortens the calculation time of software simulation, provides various solutions for optimizing the heat exchange efficiency, and lays a foundation for the establishment of a ground source heat pump system. Brief Description of the Drawings

[0070] Figure 1 It is a schematic flow chart of the method for determining the temperature distribution of the buried tube heat exchanger of the present invention.

[0071] Figure 2 It is a schematic diagram of the specific technical route of the present invention.

[0072] Figure 3 It is a schematic structural diagram of the U-shaped buried tube heat exchange system of the present invention.

[0073] Figure 4 It is a schematic diagram of the composition of the heat exchange process of the present invention.

[0074] Figure 5 It is a simplified diagram of the well section of the present invention.

[0075] Figure 6 It is a schematic structural diagram of the device for determining the temperature distribution of the buried tube heat exchanger of the present invention.

[0076] The realization, functional features and advantages of the object of the present invention will be further described with reference to the embodiments and the accompanying drawings. Detailed Embodiments

[0077] It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0078] The ground heat exchanger model established by the virtual heat source method in the present invention obtains the temperature distribution of the rock and soil and the fluid in the pipe during the operation period, realizes the prediction of the heat behavior of the buried pipe in the drilling, and analyzes the influence degree of various thermal physical parameters on the heat exchange efficiency of the system. First, an equilibrium equation for the fluid in the pipe is established, and the temperature distribution of the rock and soil and the fluid temperature distribution before the system operation are determined by using the initial conditions. Then, based on the derived line source model formula, the temperature distribution during the system operation is calculated. By the method of controlling variables, various thermal physical parameters are adjusted in turn, and their thermal sensitivities are analyzed to obtain various schemes for optimizing the heat exchange efficiency of the system. While ensuring the numerical accuracy of the system temperature distribution, the calculation time of the software simulation is shortened, and various schemes for optimizing the heat exchange efficiency are provided, laying a foundation for the establishment of the ground source heat pump system.

[0079] As Figure 1-2 shown, the present invention provides a method for determining the temperature distribution of a buried pipe heat exchanger, which is based on a U-shaped buried pipe heat exchange system and includes:

[0080] S1. Establish an equilibrium equation for the fluid in the four well sections of the U-shaped buried pipe, and set the initial conditions and boundary conditions of the whole system; among them, as Figure 3-4 shown, the U-shaped pipe is divided into four parts according to its structural characteristics, and named as the injection well, the arc section, the horizontal well, and the production well in the order of fluid flow in the pipe.

[0081] In the present invention, the following settings are made: there is no heat interference phenomenon between the injection well, the arc section, the horizontal well, and the production well that make up the system. The porous medium rock and soil is regarded as a saturated state, that is, there is no air in the rock and soil, and the heat exchange process is heat conduction. The temperature distribution near the system is affected by the geothermal gradient and is not regarded as a uniform situation. The thermal physical properties of the circulating fluid, the backfill material, and the pipe material are uniform and the values do not change with factors such as temperature and pressure; there is no contact thermal resistance between different media. The surface temperature is regarded as a fixed value, and the value is obtained by consulting the average annual temperature of the specific project location over the years. The velocity and temperature at the cross-section where the circulating fluid is located are consistent and there is no leakage phenomenon.

[0082] Regarding the parameter annotation in all subsequent formulas, the superscript (n) represents the current cycle number, and the subscript, except for the parameters that have been explained, represents the position in other cases: 1 - injection well, r - arc section, 2 - horizontal well, 3 - production well, b - drilling wall. In step S4, due to the segmented idea, except for the above annotations, the subscript m represents the segmentation order.

[0083] According to the structural characteristics of the U-shaped pipe well, the fluid equilibrium equations in the four well sections are established in turn, and the equilibrium equation is:

[0084]

[0085] Among them, except for the parameters that have been explained, the other several represent positions: 1 - injection well, r - circular arc section, 2 - horizontal well, 3 - production well, b - drilling wall; z represents the longitudinal depth, unit m; x represents the horizontal length, unit m; θ represents the continuously changing central angle of the arc section, unit °; ρ represents the density of the fluid in the pipeline, unit kg / m 3 ; c represents the specific heat capacity of the fluid in the pipeline, unit J / kg·℃; V represents the volume flow rate of the fluid in the pipeline, unit m 3 / s; T b represents the temperature of the drilling wall, unit ℃; R x represents the thermal resistance of each well section, unit k / w.

[0086] The control conditions are shown in equations (5)-(9):

[0087] 1. The initial conditions are:

[0088] t = 0, circulating fluid:

[0089]

[0090] t = 0, drilling wall:

[0091]

[0092] Regarding equation (6), the specific expressions of each well section are shown in equations (6.1)-(6.4):

[0093] Injection well:

[0094] Circular arc section:

[0095] Horizontal well:

[0096] Production well:

[0097] 2. The boundary conditions are:

[0098]

[0099] z = H1, T1 = T r (8)

[0100] z = H 1+πr / 2 , T r = T2, T2 = T3 (9)

[0101] Among them, T0 represents the average surface temperature, unit ℃; k geo represents the geothermal gradient, unit ℃ / m; z represents the longitudinal depth, unit m; T io represents the outlet temperature of the injection well, unit ℃; Tao represents the outlet temperature of the arc well, in °C; H1 represents the depth of the injection well, in m; r represents the radius of the arc segment, in m; T in Indicates the system inlet fluid temperature, unit: °C; T out Indicates the system outlet fluid temperature, unit: °C.

[0102] S2. Calculate the thermal resistance of each part based on the thermophysical parameters of the rock and soil and the system. Determine the thermophysical parameters according to the specific rock and soil types at different depths, and do not regard them as uniform.

[0103] The calculation formula is:

[0104] R x =R i +R m +R o (10) Regarding formula (10), the specific expressions of the thermal resistance of each part are shown in formulas (10.1)-(10.3):

[0105]

[0106]

[0107] Among them, R i Represents the convection heat transfer between the fluid in the pipe and the inner wall of the pipe; R m Represents the heat conduction in the pipe; R o Represents the heat conduction between the rock and backfill material outside the well; r x,i is the inner radius of the buried pipe, in m; r x,o is the outer radius of the buried pipe, in m; r b is the drilling radius, in m; h f is the convection heat transfer coefficient of the fluid in the tube, in W / m 2 ·K; k b is the thermal conductivity of the backfill material, in W / m·K; k is the thermal conductivity of the pipe, in W / m·K.

[0108] S3. Determine the initial borehole wall temperature distribution before the system starts to operate according to the boundary conditions and the thermal resistance of each part, and determine the initial fluid temperature distribution before the system starts to operate according to the equilibrium equation and the borehole wall temperature distribution.

[0109] S4. Divide the U-shaped buried pipe into several small sections, such as Figure 5 As described above, the temperature is regarded as continuous at the segmented position, and the heat flux density of the rock and soil outside the well in each small section is determined according to the initial fluid temperature distribution. The calculation formula is:

[0110]

[0111] Among them, m represents the segmentation order; represents the fluid outlet temperature in the small segment divided in the spatial dimension, with the unit of °C; represents the fluid inlet temperature in the small segment divided in the spatial dimension, with the unit of °C; represents the heat flux outside the system within this segment range, with the unit of kW; represents the heat flux density within the same range, with the unit of kW / m; l represents the length of the small segment, with the unit of m;

[0112] Based on the fluid temperature distribution obtained after each cycle, the inlet and outlet fluid temperatures of several small segments here are determined, and the solved heat flux density is used for the next cycle of calculating the wellbore wall temperature distribution, thereby forming an iterative calculation.

[0113] S5. Establish a line source model equation set for four parts of the U-shaped buried pipe in sequence, and substitute the heat flux density into the line source model equation set to obtain the wellbore wall temperature distribution during the operation of the system.

[0114] According to the structural characteristics of the U-shaped pipe well, establish a line source model for the heat exchange of the wellbore wall for four well sections in sequence. The formula derivation idea adopted when establishing the line source model can also be applied to pipe wells with various other structural characteristics; the line source model equation set is:

[0115] Injection well:

[0116]

[0117] Arc section:

[0118]

[0119] Horizontal well:

[0120]

[0121] Production well:

[0122]

[0123] Among them, s represents the line source length, with the unit of m; T0 represents the annual average surface temperature, with the unit of °C; T a represents the amplitude of temperature oscillation, with the unit of °C; ω represents the angular frequency; a z represents the thermal diffusivity of the rock and soil in the z direction, with the unit of m² / s; k x 、k y 、k z are the thermal conductivities of the rock and soil in the x, y, and z directions respectively, with the unit of W / m·K; t represents the time difference; κ zx represents the ratio of the thermal conductivity of the rock and soil in the z direction to the thermal conductivity in the x direction, k zySimilarly, β represents the central angle of the circular arc segment, in °; a x represents the thermal diffusivity of the geotechnical material in the x-direction, in m 2 / s; κ xy represents the ratio of the thermal conductivity of the geotechnical material in the x-direction to that in the y-direction, κ xz Similarly.

[0124] S6. Substitute the temperature distribution of the drilling wall during the operation of the system into the above equilibrium equation to obtain the fluid temperature distribution and heat transfer amount during the operation of the system; the calculation formula is:

[0125]

[0126] where, represents the temperature of the inlet fluid after circulation, in °C; represents the temperature of the outlet fluid after circulation, in °C; Q (n) represents the heat transfer amount of the system after each circulation, in kw; a new outlet temperature is obtained at the end of each circulation, and the heat transfer amount of the system is calculated and its change situation is analyzed accordingly.

[0127] S7. Perform iterative calculations according to the number of cycles and the operation period until the number of cycles reaches the operation period, then output the fluid temperature distribution, and adjust the values of the thermophysical parameters in turn to analyze the heat transfer situation of the system.

[0128] Specifically including:

[0129] S701. Record the number of times of obtaining the fluid temperature distribution and heat transfer amount during the operation of the system as the number of cycles, and judge whether the number of cycles is greater than or equal to the set operation period;

[0130] S702. If the number of cycles is less than the set operation period, return to step S4;

[0131] S703. If the number of cycles is greater than or equal to the set operation period, output the fluid temperature distribution, and adjust the values of the thermophysical parameters in turn to analyze the heat transfer situation of the system.

[0132] As described in the above step process, the specific calculation steps of the method for determining the temperature distribution of the buried tube heat exchanger are exemplified as follows:

[0133] Step 1: On the premise that the formula is established and improved, first calculate the system thermal resistance according to formula (10); secondly, calculate the temperature of the drilling wall under the action of the infinite source model at the initial moment Given an inlet fluid temperature at the initial moment and determine it by the combined action of the initial conditions in formulas (5)-(6); finally, calculate the temperature distribution of the fluid in the tube at the initial moment Substitute all the required parameters into the fluid balance equations (1)-(4) in the tube and determine them in combination with the boundary conditions (7)-(9).

[0134] Step 2: After knowing the temperature distribution in the pipe at the initial moment, firstly based on the idea of segmenting the pipeline, the inlet and outlet fluid temperatures of each small section can be obtained. Secondly, according to equations (11)-(12), the corresponding rock and soil heat flow of each section is calculated and heat flux This value will be used for the first cycle; finally, the borehole wall temperature distribution under the wired source model is calculated for the first cycle. Substitute all the required heat flux densities into the line source model equations (13)-(16) and calculate them together to determine them.

[0135] Step 3: After knowing the temperature distribution of the borehole wall during the first cycle, calculate the temperature distribution of the fluid in the pipe after the first cycle Substitute all the parameters into the fluid balance equations (1)-(4) in the tube and combine them with the boundary conditions (7)-(9) to determine them. After calculating the fluid temperature distribution of this cycle through joint solution, use the outlet fluid temperature Combined with formula (17), the heat exchange Q of the system after this cycle is calculated: (1) .

[0136] Step 4: Given the temperature distribution in the pipe at the end of the first cycle, repeat the idea of step 2 and determine the inlet and outlet fluid temperatures of each small section after this cycle based on the pipeline segmentation idea. Then, according to equations (11)-(12), the corresponding rock and soil heat flow of each section is calculated: Its density Similarly, this value is substituted into the line source model equations (13)-(16) to calculate the borehole wall temperature distribution during the second cycle: Substituting all the parameters into the fluid balance equations (1)-(4), the temperature distribution of the fluid in the tube after the second cycle can be determined. And the system heat transfer Q (2) .

[0137] Step 5: When the number of loops is less than the system operation cycle, repeat the ideas from step 2 to step 3 and record the data each time; when the number of loops is greater than the system operation cycle, exit the iterative calculation and output all calculation results.

[0138] Step 6: After verifying the results of the iterative calculation, adjust the various parameters that affect the heat transfer of the system according to the control variable method. After running and outputting the data, analyze its impact trend and impact degree.

[0139] like Figure 6As shown in the figure, the present invention also provides a device for determining the temperature distribution of a buried pipe heat exchanger, which is based on a U-shaped buried pipe heat exchange system and includes:

[0140] A first establishment module 1, configured to establish an equilibrium equation for the fluid in the four well sections of the U-shaped buried pipe, and set initial conditions and boundary conditions; wherein, the U-shaped buried pipe is divided into four parts, namely an injection well, an arc section, a horizontal well, and a production well, according to its structural characteristics;

[0141] A first calculation module 2, configured to calculate the thermal resistance of each part according to the thermal physical properties of the rock and soil and the system;

[0142] A first determination module 3, configured to determine the initial temperature distribution of the drilling wall before the system starts to operate according to the boundary conditions and the thermal resistance of each part, and determine the initial fluid temperature distribution before the system starts to operate according to the equilibrium equation and the temperature distribution of the drilling wall;

[0143] A second determination module 4, configured to divide the U-shaped buried pipe into several small sections, and determine the heat flux density of the rock and soil outside each small section flowing into according to the initial fluid temperature distribution;

[0144] A second establishment module 5, configured to establish a line source model equation set for the four parts of the U-shaped buried pipe in sequence, and substitute the heat flux density into the line source model equation set to obtain the temperature distribution of the drilling wall during the operation of the system;

[0145] A second calculation module 6, configured to substitute the temperature distribution of the drilling wall during the operation of the system into the equilibrium equation to obtain the fluid temperature distribution and the heat exchange amount during the operation of the system;

[0146] A circulation module 7, configured to perform circulation calculations according to the number of circulation times and the operation period, and output the fluid temperature distribution until the number of circulation times reaches the operation period, and adjust the values of the thermal physical properties parameters in sequence to analyze the heat exchange situation of the system.

[0147] In one embodiment, the circulation module 7 specifically includes:

[0148] A recording unit, configured to record the number of times of obtaining the fluid temperature distribution and the heat exchange amount during the operation of the system as the number of circulation times, and determine whether the number of circulation times is greater than or equal to the set operation period;

[0149] A return unit, configured to return to step S4 when the number of circulation times is less than the set operation period;

[0150] An output unit, configured to output the fluid temperature distribution when the number of circulation times is greater than or equal to the set operation period, and adjust the values of the thermal physical properties parameters in sequence to analyze the heat exchange situation of the system.

[0151] Each of the above modules and units is used to correspondingly execute each step in the above method for determining the temperature distribution of the buried tube heat exchanger. The specific implementation manner refers to the method embodiments described above and will not be elaborated here.

[0152] As Figure 3 shown, the present invention also provides a computer device, which may be a server, and its internal structure may be as Figure 3 shown. The computer device includes a processor, a memory, a network interface, and a database connected through a system bus. Among them, the processor of the computer device is used to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system, a computer program, and a database. The internal memory provides an environment for the operation of the operating system and the computer program in the non-volatile storage medium. The database of the computer device is used to store all data required for the process of the method for determining the temperature distribution of the buried tube heat exchanger. The network interface of the computer device is used to communicate with an external terminal through a network connection. When the computer program is executed by the processor, it implements the method for determining the temperature distribution of the buried tube heat exchanger.

[0153] Those skilled in the art can understand that Figure 3 the structure shown in

[0154] is only a block diagram of a part of the structure related to the solution of the present application, and does not constitute a limitation on the computer device to which the solution of the present application is applied.

[0155] Those of ordinary skill in the art can understand that all or part of the processes of implementing the methods in the above embodiments can be completed by instructing relevant hardware through a computer program. The computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above methods. Among them, any reference to a memory, storage, database, or other medium provided in this application and used in the embodiments can include non-volatile and / or volatile memories. Non-volatile memory can include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM), or flash memory. Volatile memory can include random access memory (RAM) or external cache memory. By way of illustration and not limitation, RAM is available in many forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double data rate SDRAM (SSRSDRAM), enhanced SDRAM (ESDRAM), synchronous link DRAM (SLDRAM), Rambus direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and Rambus dynamic RAM (RDRAM), etc.

[0156] It should be noted that in this text, the term "including", "comprising", or any other variant thereof is intended to cover non-exclusive inclusion, such that a process, apparatus, article, or method that includes a series of elements includes not only those elements but also other elements not expressly listed, or elements that are inherent to such process, apparatus, article, or method. Without further limitation, an element defined by the statement "including one..." does not exclude the existence of additional identical elements in the process, apparatus, article, or method that includes such element.

[0157] The above are only the preferred embodiments of the present invention, and do not limit the patent scope of the present invention. Any equivalent structural or equivalent process transformation made by using the specification and drawings of the present invention, or directly or indirectly applied in other related technical fields, shall equally be included in the patent protection scope of the present invention.

Claims

1. A method for determining the temperature distribution of a buried tube heat exchanger, characterized in that, Based on a U-shaped buried pipe heat exchange system, including: S1. Establish an equilibrium equation for the fluid in the four well sections of the U-shaped buried pipe, and set initial conditions and boundary conditions; among them, the U-shaped buried pipe is divided into four parts according to its structural characteristics: injection well, arc section, horizontal well, and production well; S2. Calculate the thermal resistance of each part according to the thermal physical properties of the rock and soil and the system; S3. Determine the initial drilling wall temperature distribution before the system starts to operate according to the boundary conditions and the thermal resistance of each part, and determine the initial fluid temperature distribution before the system starts to operate according to the equilibrium equation and the drilling wall temperature distribution; S4. Divide the U-shaped buried pipe into several small sections, and determine the heat flux density of the rock and soil outside each small section flowing in according to the initial fluid temperature distribution; S5. Establish a line source model equation set for the four parts of the U-shaped buried pipe in turn, and substitute the heat flux density into the line source model equation set to obtain the drilling wall temperature distribution during the operation of the system; S6. Substitute the drilling wall temperature distribution during the operation of the system into the equilibrium equation to obtain the fluid temperature distribution and heat exchange amount during the operation of the system; S7. Perform iterative calculations according to the number of cycles and the operation period until the number of cycles reaches the operation period, output the fluid temperature distribution, and adjust the values of the thermal physical properties parameters in turn to analyze the heat exchange situation of the system.

2. The method for determining the temperature distribution of the buried tube heat exchanger according to claim 1, characterized in that The specific steps of S7 include: S701. Record the number of times of obtaining the fluid temperature distribution and heat exchange amount during the operation of the system as the number of cycles, and judge whether the number of cycles is greater than or equal to the set operation period; S702. If the number of cycles is less than the set operation period, return to step S4; S703. If the number of cycles is greater than or equal to the set operation period, output the fluid temperature distribution, and adjust the values of the thermal physical properties parameters in turn to analyze the heat exchange situation of the system.

3. The method for determining the temperature distribution of the buried tube heat exchanger according to claim 1, wherein In step S1, the equilibrium equation is: Among them, except for the parameters that have been explained, the other several represent positions: 1 - injection well, r - arc section, 2 - horizontal well, 3 - production well, b - drilling wall; z represents the longitudinal depth, unit m; x represents the horizontal length, unit m; θ represents the continuously changing central angle of the arc-shaped well section, unit °; ρ represents the density of the fluid in the pipeline, unit kg / m 3 ; c represents the specific heat capacity of the fluid in the pipeline, unit J / kg·℃; V represents the volume flow rate of the fluid in the pipeline, unit m 3 / s; T b represents the drilling wall temperature, unit ℃; R x represents the thermal resistance of each well section, unit k / w.

4. The method for determining the temperature distribution of the buried tube heat exchanger according to claim 3, characterized in that, In step S1, the initial conditions are: t = 0, circulating fluid: t = 0, drilling wall: Among them, the specific expressions of each well section are: Injection well: Arc segment: Horizontal well: Production well: The boundary conditions are: z = H1, T1 = T r z = H 1+πr / 2 , T r = T2, T2 = T3 Among them, T0 represents the average surface temperature, with the unit of °C; k geo represents the geothermal gradient, with the unit of °C / m; z represents the vertical depth, with the unit of m; T io represents the outlet temperature of the injection well, with the unit of °C; T ao represents the outlet temperature of the arc-shaped well, with the unit of °C; H1 represents the depth of the injection well, with the unit of m; r represents the radius length of the arc section, with the unit of m; T in represents the temperature of the fluid at the inlet of the system, with the unit of °C; T out represents the temperature of the fluid at the outlet of the system, with the unit of °C.

5. The method for determining the temperature distribution of the buried tube heat exchanger according to claim 1, characterized in that In step S2, the calculation formula for the thermal resistance of each part is: R x = R i + R m + R o Among them, the specific expressions of the thermal resistance of each part are: Among them, R i represents the convective heat transfer between the fluid inside the pipe and the inner wall of the pipe; R m represents the heat conduction inside the pipe material; R o represents the heat conduction between the soil outside the well and the backfill material; r x,i is the inner radius of the buried pipe, with the unit of m; r x,o is the outer radius of the buried pipe, with the unit of m; r b is the drilling radius, with the unit of m; h f is the convective heat transfer coefficient of the fluid inside the pipe, with the unit of W / ㎡·K; k b is the thermal conductivity of the backfill material, with the unit of W / m·K; k p is the thermal conductivity of the pipe material, with the unit of W / m·K.

6. The method for determining the temperature distribution of the buried tube heat exchanger according to claim 2, characterized in that In step S4, the calculation formula for the heat flux density is: Among them, m represents the segmentation order; represents the fluid outlet temperature within the small segment divided in the spatial dimension, with the unit of °C; represents the fluid inlet temperature within the small segment divided in the spatial dimension, with the unit of °C; represents the heat flux outside the system within this segment range, with the unit of kW; represents the heat flux density within the same range, with the unit of kW / m; l represents the length of the small segment, with the unit of m; Based on the fluid temperature distribution obtained after each cycle, determine the inlet and outlet fluid temperatures of several small sections here, and the solved heat flux density is used for the drilling wall temperature distribution in the next cycle, thus forming an iterative calculation.

7. The method for determining the temperature distribution of the buried tube heat exchanger according to claim 1, wherein In step S5, the line source model equation set is: Injection well: Arc section: Horizontal well: Production well: Among them, s represents the length of the line source, with the unit of m; T0 represents the annual average surface temperature, with the unit of °C; T a represents the amplitude of temperature oscillation, with the unit of °C; ω represents the angular frequency; a z represents the thermal diffusivity of the rock and soil in the z direction, with the unit of m² / s; k x 、k y 、k z are the thermal conductivities of the rock and soil in the x, y, and z directions respectively, with the unit of W / m·K; t represents the time difference; κ zx represents the ratio of the thermal conductivity of the rock and soil in the z direction to that in the x direction, κ zy Similarly; β represents the central angle of the arc segment, with the unit of °; a x represents the thermal diffusivity of the rock and soil in the x direction, with the unit of m² / s; κ xy represents the ratio of the thermal conductivity of the rock and soil in the x direction to that in the y direction, κ xz Similarly.

8. The method for determining the temperature distribution of the buried tube heat exchanger according to claim 2, wherein In step S6, the calculation of the fluid temperature distribution and heat exchange amount is: Among them, represents the temperature of the inlet fluid after circulation, in °C; represents the temperature of the outlet fluid after circulation, in °C; Q (n) represents the heat exchange amount of the system after each circulation, in kW; a new outlet temperature is obtained at the end of each circulation, and the heat exchange amount of the system is calculated and its change situation is analyzed accordingly.

9. A device for determining the temperature distribution of a buried tube heat exchanger, characterized in that, Based on a U-shaped buried pipe heat exchange system, including: The first establishment module is used to establish an equilibrium equation for the fluid in the four well sections of the U-shaped buried pipe, and set initial conditions and boundary conditions; among them, the U-shaped buried pipe is divided into four parts according to its structural characteristics: injection well, arc section, horizontal well, and production well; The first calculation module is used to calculate the thermal resistance of each part according to the thermal physical properties of the rock and soil and the system; The first determination module is configured to determine the initial temperature distribution of the drilling wall before the system starts to operate according to the boundary conditions and the thermal resistances of each part, and determine the initial fluid temperature distribution before the system starts to operate according to the balance equation and the temperature distribution of the drilling wall; The second determination module is configured to divide the U-shaped buried pipe into several small segments, and determine the heat flux density of the surrounding rock and soil outside each small segment flowing into the pipe according to the initial fluid temperature distribution; The second establishment module is configured to successively establish a system of line source model equations for four parts of the U-shaped buried pipe, and substitute the heat flux density into the system of line source model equations to obtain the temperature distribution of the drilling wall during the operation of the system; The second calculation module is configured to substitute the temperature distribution of the drilling wall during the operation of the system into the balance equation to obtain the fluid temperature distribution and the heat exchange amount during the operation of the system; The loop module is configured to perform loop calculations according to the number of loops and the operation period. When the number of loops reaches the operation period, the fluid temperature distribution is output, and the values of the thermophysical parameters are adjusted in sequence to analyze the heat exchange situation of the system.

10. A computer device, comprising a memory and a processor, the memory storing a computer program, characterized in that, When the processor executes the computer program, it implements the steps of the method according to any one of claims 1 to 8.

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