Method for parallel computing simulation of heat exchange process of single and double U-shaped buried pipes in geothermal reservoir

Abstract

The invention discloses a method for simulating the heat exchange process of a single U-shaped buried pipe and double U-shaped buried pipes in a geothermal reservoir through parallel calculation. Circulating fluid in U-shaped pipes and pipe walls are simplified into one-dimensional heat exchange pipes; utilizing the one-dimensional heat exchange tube simplification unit to take a pipeline as a curve in a three-dimensional model to carry out pipeline flow model modeling; a parallel finite element calculation method is adopted in the pipeline flow model, and joint solving is conducted on the interior and the exterior of the pipeline; finally, factor sensitivity analysis is conducted by changing different working condition parameters, circulating fluid in the U-shaped pipe and the pipe wall are simplified into a one-dimensional heat exchange pipe, a one-dimensional linear grid unit is used for explicitly representing a three-dimensional pipe volume unit, and coupling is conducted through linear unit nodes and a three-dimensional grid unit outside the pipe; according to the method, a parallel finite element calculation method is adopted to integrate fluid flow and a heat transfer module, the problems of flow and convective heat transfer in the U-shaped pipe and pipe wall heat conduction are solved in a combined mode, the solving efficiency of the three-dimensional finite element numerical model is improved, and the system, the equipment and the medium for achieving the method are further included.

Description

Technical Field

[0001] The present invention relates to the technical field of geothermal reservoir heat extraction, and in particular to a method for parallel computing simulation of the heat exchange process of single and double U-shaped buried pipes in geothermal reservoirs, which is used to analyze the heat exchange of single and double U-shaped buried pipes under rock and soil stratification seepage conditions. Background Art

[0002] The buried pipe heat transfer process is a complex non-steady-state process with a large spatial span and a long action time. By establishing a theoretical and numerical model of buried pipe heat transfer under rock and soil stratification and seepage conditions in geothermal reservoirs, we can more accurately describe the heat transfer process of buried pipe heat exchangers under actual complex geological conditions, and scientifically predict the long-term performance of ground-source heat pump systems under complex conditions, providing a theoretical basis and technical support for the optimized design and efficient operation of ground-source heat pump systems.

[0003] Theoretical heat transfer models are generally based on necessary assumptions, making it difficult to accurately describe every specific heat transfer detail of a ground pipe heat exchanger, and will deviate to varying degrees from the actual heat transfer process. Numerical heat transfer models, based on numerical methods such as finite element method (FEM), finite difference method (FDM), and finite volume method (FVM), can accurately describe the entire area inside and outside the ground pipe borehole. They can be used to study the heat transfer problems of ground pipe heat exchangers under various complex conditions, such as variable heat flow, uneven initial temperature, groundwater seepage, and inhomogeneous rock and soil media. Initially, models were mainly one- and two-dimensional models. These models ignored circumferential or axial heat transfer and were therefore unable to accurately predict the heat transfer characteristics of ground pipe heat exchangers or obtain the vertical distribution pattern of the fluid temperature within the pipe. To more accurately describe the heat transfer process, researchers have established different three-dimensional transient numerical models based on various software platforms to further study the heat transfer patterns of vertical ground pipe heat exchangers. However, during the construction of the vertical buried heat exchanger numerical model, the division of grid units in different regions was not given much consideration, and the calculation results of each region were not clearly distinguished.

[0004] Vertical buried heat exchangers typically consist of single or double U-shaped high-density polyethylene pipes and surrounding backfill material placed in boreholes 20 to 200 meters deep and 0.15 to 0.75 meters in diameter. Unlike the flow and heat transfer problems encountered in conventional systems, the vertical U-shaped buried heat exchanger tubes exhibit significant dimensional differences in the axial and radial directions, and feature a large aspect ratio (on the order of 5000), distinguishing them from traditional flow and heat transfer devices. Therefore, in numerical calculations, using conventional meshing methods to address flow and heat transfer within U-shaped tubes inevitably requires a large number of meshes, resulting in excessive consumption of computational resources and time. Furthermore, mesh quality is often difficult to guarantee when meshing such slender structures, making convergence of the computational results difficult. For example, patent application number CN202411290081.3 discloses a temperature prediction method for the fluid in the tube based on the double U-tube vertical medium-deep ground heat exchanger fluid model. The temperature distribution of the circulating fluid in the tube is realized through the U-tube buried pipe heat exchanger prediction model. However, the problem is that the circulating fluid in the tube and the tube wall are relatively complex, resulting in a waste of computing resources, and the convergence of the calculation results cannot be guaranteed. Summary of the Invention

[0005] To overcome the limitations of existing buried pipe heat exchange models, the present invention aims to provide a parallel computing method for simulating the heat exchange process of single and double U-shaped buried pipes in geothermal reservoirs. The circulating fluid in the U-shaped pipe and the pipe wall are simplified into a one-dimensional heat exchange pipe. The three-dimensional pipe volume unit is explicitly represented by a one-dimensional linear grid unit, and is coupled with the three-dimensional grid unit outside the pipe through the linear unit node. A parallel finite element calculation method is used to integrate the fluid flow and heat transfer modules, and the flow and convective heat transfer problems in the U-shaped pipe and the heat conduction problems of the pipe wall are jointly solved, thereby improving the solution efficiency of the three-dimensional finite element numerical model.

[0006] To achieve the above object, the technical solution of the present invention is as follows:

[0007] A method for parallel computing simulation of a heat exchange process of single and double U-shaped buried pipes in a geothermal reservoir, comprising the following steps:

[0008] Step 1: Simplify the pipe volume unit

[0009] The parallel finite element method is used to discretize the pipe volume unit, and the circulating fluid in the U-tube and the tube wall are simplified into a one-dimensional heat exchange tube, that is, a one-dimensional heat exchange tube simplified unit;

[0010] Step 2: Pipeline flow model construction

[0011] Establish a pipeline flow model in the three-dimensional modeling, and use the one-dimensional heat exchange tube simplified unit to model the pipeline as a curve in the three-dimensional model;

[0012] Step 3: Jointly solve the inside and outside of the tube

[0013] Outside the pipe, the temperature response in the geotechnical medium is calculated by solving the transient three-dimensional heat conduction or heat-permeability coupling equations. Inside the pipe, the flow equations and energy equations of the circulating fluid are coupled to calculate the temperature and velocity distribution of the fluid inside the U-shaped pipe. Finally, a parallel finite element calculation method is used in the pipeline flow model to jointly solve the inside and outside of the pipe.

[0014] Step 4: Perform factor sensitivity analysis by changing different operating parameters.

[0015] The specific steps of simplifying the pipeline volume unit in step 1 are as follows:

[0016] (1) Using the parallel finite element method, the circulating fluid in the U-shaped tube and the tube wall are discretized to form a one-dimensional linear finite element unit;

[0017] (2) Inserting U-shaped circular arc curve elements between discrete one-dimensional linear finite element grids;

[0018] (3) The one-dimensional linear finite element unit and the U-shaped arc curve unit are renumbered so that the finite element unit number and the node number are continuous, thereby forming a simplified one-dimensional heat exchange tube, namely, a one-dimensional heat exchange tube simplified unit.

[0019] The specific steps of constructing the pipeline flow model in step 2 are:

[0020] (1) Use 3D modeling to build the wellbore and backfill material;

[0021] (2) The outside of the tube is still in three-dimensional form, and the inside and wall of the tube are simplified using one-dimensional heat exchange tube units, that is, the tube is modeled as a curve in the three-dimensional model to obtain a geometric model;

[0022] (3) Input the working condition parameters into the geometric model and give them physical meaning, establish the overall layered rock and soil seepage model, and obtain the pipeline flow model.

[0023] The specific steps in step three are:

[0024] (1) In the part outside the pipe, the energy equation of the rock and soil medium outside the pipe is established based on the porous media heat transfer theory, where the rock and soil medium includes the backfill material in the surrounding hole and the underground stratification and seepage rock and soil medium outside the hole; the energy equation of the rock and soil medium outside the pipe is expressed as:

[0025]

[0026] Where, ρ g is the reservoir fluid density, kg / m 3 ;c p,g is the constant-pressure specific heat capacity of the formation fluid, J / (kg·K); T wis the formation fluid temperature, °C; u g is the reservoir fluid velocity, m / s; λ g is the thermal conductivity of the fluid outside the heat exchange tube; Q wall is the heat transferred from geothermal fluid to the heat medium through the heat exchange tube wall, J;

[0027]

[0028] Where, (ρc p ) eff is the effective specific heat capacity at constant pressure, J / (℃·m 3 );λ eff is the effective thermal conductivity, W / (m·℃); T r is the formation temperature;

[0029] (2) In the pipe part, the flow equation and energy equation of the fluid in the pipe are established according to the non-isothermal pipe flow theory, and the flow state and stress distribution of the fluid in the U-shaped pipe are obtained;

[0030] The flow equation is shown in equations (3) and (4):

[0031]

[0032] The energy equation is shown in formula (5):

[0033]

[0034] Where A p is the cross-sectional area of the heat exchange tube, m 2 ρ f is the fluid density, kg / m 3 ;u f is the fluid velocity, m / s; p is the well pressure, Pa; d p is the inner diameter of the tube, m; c p,f is the constant pressure specific heat capacity of the fluid, J / (kg·℃); T f is the temperature of the fluid, °C; λ f is the thermal conductivity of the fluid in the heat exchange tube, W / (m·℃); Q wall is the heat transferred from geothermal fluid to the heat medium through the heat exchange tube wall, J;

[0035] In formula (4), f D is the Darcy friction factor, according to the Churchill model:

[0036]

[0037] Where Re is the Reynolds number; e is the roughness of the inner tube;

[0038] In formula (5), Qwall :

[0039] Q wall =(hZ) eff (T ext -T f ) (7)

[0040] Where, T ext is the temperature outside the heat exchange tube wall, °C; (hZ) eff is the total equivalent heat transfer coefficient, including the thermal resistance of the tube wall and the convection thermal resistance of the inner and outer walls, W / (m·℃); Z is the circumference of the tube wall, m; h is the forced convection heat transfer coefficient, W / (m 2 ·℃), calculated by formula (8):

[0041]

[0042] Where Nu is the Nusselt number, λ f is the thermal conductivity of the fluid in the heat exchange tube. For a circular tube, (hZ) eff It can be calculated by formula (9):

[0043]

[0044] Where h int is the convection heat transfer coefficient in the tube, W / (m·℃); h ext is the convection heat transfer coefficient outside the tube, W / (m·℃); r i With r o are the inner and outer diameters of the circular tube, respectively. The convection heat transfer coefficient inside and outside the tube is expressed by the Nusselt number Nu int and Nu ext calculate:

[0045]

[0046] Where λ g is the thermal conductivity of the fluid outside the heat exchange tube; Nu int It can be calculated by Gnielinski formula:

[0047]

[0048] Where Pr is the Prandtl number, and the applicable range of the equation is: Re = 3000 ~ 6 × 10 6 , Pr = 0.5 ~ 2000. For the natural convection outside the heat exchange tube, it can be calculated by the model proposed by Churchill and Chu:

[0049]

[0050] Where Ra is the Rayleigh number, Ra = Pr Gr; Gr is the dimensionless Grashof number, which represents the ratio of buoyancy to viscous force. The applicable range of formula (12) is Ra < 10 12 ;

[0051] (3) The parallel finite element calculation method is used to combine the rock and soil medium outside the pipe and the circulating fluid medium inside the pipe to obtain the overall control equation group, which is as follows:

[0052] First, the temperature of the fluid inside the pipe and the temperature of the rock and soil outside the pipe are calculated separately. Then, the parallel finite element method is used to jointly solve the temperatures between different media according to the physical field to obtain the transient temperature changes of the fluid in the calculation model and the transient temperature changes in the rock and soil.

[0053] The specific steps in step 4 are:

[0054] (1) The outlet temperature and heat transfer capacity under different conditions are obtained by changing different operating parameters. Different operating parameters are factors that affect the heat transfer characteristics of the buried pipe. The operating parameters include well parameters and operating parameters. The well parameters include the thermal conductivity of rock and soil stratification, rock and soil density and specific heat capacity, thermal conductivity of backfill materials, groundwater seepage velocity, aquifer location, and geothermal gradient; the operating parameters include the injection temperature of the circulating fluid, the injection flow rate, and the system operation time.

[0055] (2) Using the grey correlation analysis method, the influence degree of each factor on thermal mining efficiency is ranked;

[0056] (3) Orthogonal test method was used for random grouping, and the optimal parameter combination was obtained based on heat transfer capacity and heat transfer efficiency.

[0057] The present invention also includes:

[0058] A system includes a processor capable of running the method for parallel computing to simulate the heat exchange process of single and double U-shaped buried pipes in a geothermal reservoir.

[0059] A device comprising:

[0060] Memory: used to store the computer program of the method for parallel computing simulation of heat exchange process of single and double U-shaped buried pipes in geothermal reservoirs;

[0061] Processor: used to implement the method of parallel computing simulation of single and double U-shaped buried pipe heat exchange process in geothermal reservoir when executing the computer program.

[0062] A computer-readable storage medium stores a computer program, which, when executed by a processor, implements the method for parallel computing simulation of single and double U-shaped buried pipe heat exchange processes in geothermal reservoirs.

[0063] Compared with the prior art, the present invention has the following beneficial effects:

[0064] 1. In step 2 of the present invention, three-dimensional modeling is used to establish the wellbore and backfill material portion. A simplified one-dimensional heat exchange tube unit is used inside the tube, while a three-dimensional unit is still used outside the tube. The pipeline is modeled as a curve in the three-dimensional model to obtain a geometric model. While ensuring the accuracy of the calculation results, the problem of low mesh quality caused by the large aspect ratio of the heat exchange tube can be solved. The three-dimensional finite element numerical model is solved in parallel, significantly improving the calculation efficiency.

[0065] 2. In step three of the present invention, the temperature response in the rock and soil medium is calculated by solving the transient three-dimensional heat conduction or heat-permeability coupling equation in the part outside the pipe; in the part inside the pipe, the flow equation and energy equation of the circulating fluid medium in the pipe are coupled to calculate the temperature and velocity distribution of the fluid in the U-shaped pipe; finally, a parallel finite element calculation method is used in the pipeline flow model to jointly solve the inside and outside of the pipe, thereby improving the solution efficiency of the three-dimensional finite element numerical model.

[0066] In summary, the present invention considers the seepage heat transfer problem between the buried heat exchanger and the surrounding layered rock and soil media, couples multiple physical fields such as heat transfer, seepage, and fluid flow, and facilitates the fluid flow and heat transfer analysis of the buried heat exchanger. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] Figure 1 This is a calculation flow chart of step three of the present invention for solving the buried pipe heat exchange model using parallel finite element method.

[0068] Figure 2 Schematic diagram of geometric modeling of single and double U-shaped buried pipes, where Figure 2 (a) is a schematic diagram of the cross section of a single U-shaped buried pipe; Figure 2 (b) is a schematic diagram of the cross section of a single U-shaped buried pipe; Figure 2 (c) is a schematic diagram of the longitudinal section of the U-shaped buried pipe.

[0069] Figure 3 Schematic diagram of the coupling between one-dimensional linear element nodes and three-dimensional mesh elements outside the pipe.

[0070] Figure 4 It is the grid division diagram of single and double U-shaped buried pipes, where Figure 4 (a) is the grid decomposition diagram of a single U-shaped buried pipe; Figure 4 (b) in the figure is the grid decomposition diagram of the double U-shaped buried pipe.

[0071] Figure 5 The temperature change curves of the wellbore and the surrounding geothermal reservoir along the X direction of the temperature measuring line at different time periods are shown, which are the temperature changes on the 1st day, the 10th day, the 60th day and the 120th day respectively. DETAILED DESCRIPTION

[0072] The present invention will be described in detail below with reference to the accompanying drawings.

[0073] A method for parallel computing simulation of a heat exchange process of single and double U-shaped buried pipes in a geothermal reservoir, comprising the following steps:

[0074] Step 1: Simplify the pipe volume unit. Use the parallel finite element method to discretize the pipe volume unit and simplify the circulating fluid in the U-shaped tube and the tube wall into a one-dimensional heat exchange tube.

[0075] In the above step 1, the specific steps of simplifying the pipeline volume unit are as follows, refer to Figure 2 :

[0076] (1) Using the parallel finite element method, the circulating fluid in the U-shaped tube and the tube wall are discretized to form a one-dimensional linear finite element unit;

[0077] (2) Inserting U-shaped circular arc curve elements between discrete one-dimensional linear finite element grids;

[0078] (3) The one-dimensional linear finite element unit and the U-shaped arc curve unit are renumbered so that the finite element unit number and the node number are continuous, thereby forming a simplified one-dimensional heat exchange tube, namely, a one-dimensional heat exchange tube simplified unit.

[0079] Step 2: Establish a pipeline flow model in the 3D modeling. Use one-dimensional linear units to model the pipeline as a curve in the 3D model. Coupling the linear unit nodes with the 3D mesh units outside the pipe is beneficial for meshing the finite diameter 3D pipeline.

[0080] In the step 2, the specific steps of constructing the pipeline flow model are as follows: Figure 3 and Figure 4 :

[0081] (1) Use 3D modeling to build the wellbore and backfill material;

[0082] (2) The outside of the tube is still in three-dimensional form, and the inside and wall of the tube are simplified using one-dimensional heat exchange tube units, that is, the tube is modeled as a curve in the three-dimensional model to obtain a geometric model;

[0083] (3) Input the working condition parameters into the geometric model and give them physical meaning, establish the overall layered rock and soil seepage model, and obtain the pipeline flow model.

[0084] Step 3: Outside the tube, calculate the temperature response in the geotechnical medium by solving the transient three-dimensional heat conduction or heat-permeability coupling equation. Inside the tube, couple the flow equation and energy equation of the circulating fluid medium to calculate the temperature and velocity distribution of the fluid in the U-tube. Finally, use the parallel finite element calculation method in the pipeline flow model to jointly solve the fluid flow and convective heat transfer in the U-tube, as well as the heat conduction problem of the tube wall.

[0085] In step 3, the specific steps of using the parallel finite element calculation method to integrate the fluid flow and heat transfer modules are as follows:

[0086] (1) In the part outside the pipe, the energy equation of the rock and soil medium outside the pipe is established based on the porous media heat transfer theory, where the rock and soil medium includes the backfill material in the surrounding hole and the underground stratification and seepage rock and soil medium outside the hole; the energy equation of the rock and soil medium outside the pipe is expressed as:

[0087]

[0088] Where, ρ g is the reservoir fluid density, kg / m 3 ;c p,g is the constant-pressure specific heat capacity of the formation fluid, J / (kg·K); T w is the formation fluid temperature, °C; u g is the reservoir fluid velocity, m / s; λ g is the thermal conductivity of the fluid outside the heat exchange tube; Q wall The heat transferred from geothermal fluid to the heat medium through the heat exchange tube wall, J.

[0089]

[0090] Where, (ρc p ) eff is the effective specific heat capacity at constant pressure, J / (℃·m 3 );λ eff is the effective thermal conductivity, W / (m·℃); T r is the formation temperature.

[0091] (2) In the pipe part, the flow equation and energy equation of the fluid in the pipe are established according to the non-isothermal pipe flow theory, and the flow state and stress distribution of the fluid in the U-shaped pipe are obtained;

[0092] The flow equation is shown in equations (3) and (4):

[0093]

[0094] The energy equation is shown in formula (5):

[0095]

[0096] Where A p is the cross-sectional area of the heat exchange tube, m 2 ρ f is the fluid density, kg / m 3 ;u f is the fluid velocity, m / s; p is the well pressure, Pa; d p is the inner diameter of the tube, m; c p,f is the constant pressure specific heat capacity of the fluid, J / (kg·℃); T f is the temperature of the fluid, °C; λ f is the thermal conductivity of the fluid in the heat exchange tube, W / (m·℃); Q wall The heat transferred from geothermal fluid to the heat medium through the heat exchange tube wall, J.

[0097] In formula (4), f D is the Darcy friction factor, according to the Churchill model:

[0098]

[0099] Where Re is the Reynolds number; e is the roughness of the inner tube.

[0100] In formula (5), Q wall :

[0101] Q wall =(hZ) eff (T ext -T f ) (7)

[0102] Where, T ext is the temperature outside the heat exchange tube wall, °C; (hZ) eff is the total equivalent heat transfer coefficient, including the thermal resistance of the tube wall and the convection thermal resistance of the inner and outer walls, W / (m·℃); Z is the circumference of the tube wall, m; h is the forced convection heat transfer coefficient, W / (m 2 ·℃), calculated by formula (8):

[0103]

[0104] Where Nu is the Nusselt number, λ f is the thermal conductivity of the fluid in the heat exchange tube. For a circular tube, (hZ) eff It can be calculated by formula (9):

[0105]

[0106] Where h int is the convection heat transfer coefficient in the tube, W / (m·℃); h ext is the convection heat transfer coefficient outside the tube, W / (m·℃);

[0107] r i With r o are the inner and outer diameters of the circular tube respectively. The convection heat transfer coefficient inside and outside the tube is calculated by the Nusselt number Nu int and Nu ext calculate:

[0108]

[0109] Where λ g is the thermal conductivity of the fluid outside the heat exchange tube; Nu int It can be calculated by Gnielinski formula:

[0110]

[0111] Where Pr is the Prandtl number, and the applicable range of the equation is: Re = 3000 ~ 6 × 10 6 , Pr = 0.5 ~ 2000. For the natural convection outside the heat exchange tube, it can be calculated by the model proposed by Churchill and Chu:

[0112]

[0113] Where Ra is the Rayleigh number, Ra = Pr Gr; Gr is the dimensionless Grashof number, which represents the ratio of buoyancy to viscous force. The applicable range of formula (12) is Ra < 10 12 .

[0114] (3) The parallel finite element calculation method is used to combine the rock and soil medium outside the pipe and the circulating fluid medium inside the pipe to obtain the overall control equation group, which is as follows:

[0115] First, the temperature of the fluid inside the pipe and the temperature of the rock and soil outside the pipe are calculated separately. Then, the parallel finite element method is used to jointly solve the temperatures between different media according to the physical field to obtain the transient temperature changes of the fluid in the calculation model and the transient temperature changes in the rock and soil.

[0116] The overall control equations are obtained as follows Figure 1 As shown, the steps include:

[0117] ①Evenly distribute the one-dimensional linear finite element units and the three-dimensional tetrahedral finite element units to each processor in the parallel computing system;

[0118] ② Calculate the fluid temperature inside the pipe and the rock and soil temperature outside the pipe on each processor;

[0119] ③ Using the parallel finite element method, the temperatures between different media are jointly solved according to the physical field in the parallel computing system to obtain the overall control equations.

[0120] The specific steps of using the parallel finite element calculation method to solve the temperature and velocity distribution of the fluid in the U-shaped tube and the temperature response in the rock and soil are as follows:

[0121] (1) Using parallel computing methods, solve the overall control equations of the computational model to obtain the transient temperature changes, velocity changes of the fluid in the computational model, and the transient temperature changes in the rock and soil;

[0122] (2) transmitting the calculated temperature and speed change data to each processor in the parallel computing system;

[0123] (3) Perform post-processing on each processor to calculate the temperature and velocity distribution of the fluid in the model and the temperature response in the rock and soil (such as Figure 5 shown).

[0124] Step 4: Conduct a sensitivity analysis of factors by varying operating parameters. This involves combining the multi-physics coupled numerical model with a sensitivity analysis of factors by varying wellbore and operating parameters. This analysis comprehensively examines the impact of geothermal thermal properties and buried pipe heat transfer characteristics on geothermal reservoir thermal extraction efficiency.

[0125] In step 4, the specific steps for performing factor sensitivity analysis by changing different well parameters and operating parameters are as follows:

[0126] (1) The outlet temperature and heat transfer capacity under different conditions are obtained by changing different operating parameters. Different operating parameters are factors that affect the heat transfer characteristics of the buried pipe. The operating parameters include well parameters and operating parameters. The well parameters include the thermal conductivity of rock and soil stratification, rock and soil density and specific heat capacity, thermal conductivity of backfill materials, groundwater seepage velocity, aquifer location, and geothermal gradient; the operating parameters include the injection temperature of the circulating fluid, the injection flow rate, and the system operation time.

[0127] By changing different parameters, the outlet temperature and heat transfer under different conditions can be obtained. The expressions are:

[0128] Q r =c×m×Δt=1.163×Q×Δt (13)

[0129] Where: Q r is the heat transfer capacity, kW; c is the specific heat capacity of the circulating fluid, J / (kg·℃); Q is the flow rate, m 3 / h; Δt is the water temperature difference between the inlet and outlet, ℃.

[0130] In step 4, the specific steps of comprehensively studying the influence of the thermal physical properties of rock and soil and the heat transfer characteristics of buried pipes on the heat extraction efficiency of geothermal reservoirs are as follows:

[0131] (1) Using the grey correlation analysis method, the influence degree of each factor on thermal mining efficiency was ranked;

[0132] (2) Orthogonal test method was used for random grouping, and the optimal parameter combination was obtained based on heat transfer capacity and heat transfer efficiency.

[0133] The present invention also includes:

[0134] A system includes a processor capable of running the method for parallel computing to simulate the heat exchange process of single and double U-shaped buried pipes in a geothermal reservoir.

[0135] A device comprising:

[0136] Memory: used to store the computer program of the method for parallel computing simulation of heat exchange process of single and double U-shaped buried pipes in geothermal reservoirs;

[0137] Processor: used to implement the method of parallel computing simulation of single and double U-shaped buried pipe heat exchange process in geothermal reservoir when executing the computer program.

[0138] A computer-readable storage medium stores a computer program, which, when executed by a processor, implements the method for parallel computing simulation of single and double U-shaped buried pipe heat exchange processes in geothermal reservoirs.

Claims

1. A method for parallel computing simulation of heat exchange process of single and double U-shaped buried pipes in geothermal reservoirs, characterized in that: The following steps are involved: Step 1: Simplify the pipe volume unit The parallel finite element method is used to discretize the pipe volume unit, and the circulating fluid in the U-tube and the tube wall are simplified into a one-dimensional heat exchange tube, that is, a one-dimensional heat exchange tube simplified unit; Step 2: Pipeline flow model construction Establish a pipeline flow model in the three-dimensional modeling, and use the one-dimensional heat exchange tube simplified unit to model the pipeline as a curve in the three-dimensional model; Step 3: Jointly solve the inside and outside of the tube Outside the pipe, the temperature response in the geotechnical medium is calculated by solving the transient three-dimensional heat conduction or heat-permeability coupling equations. Inside the pipe, the flow equations and energy equations of the circulating fluid are coupled to calculate the temperature and velocity distribution of the fluid inside the U-shaped pipe. Finally, a parallel finite element calculation method is used in the pipeline flow model to jointly solve the inside and outside of the pipe. Step 4: Perform factor sensitivity analysis by changing different operating parameters.

2. A method for simulating the heat exchange process of single and double U-shaped buried pipes in a geothermal reservoir by parallel computing according to claim 1, characterized in that: The specific steps of simplifying the pipeline volume unit in step 1 are as follows: (1) Using the parallel finite element method, the circulating fluid in the U-shaped tube and the tube wall are discretized to form a one-dimensional linear finite element unit; (2) Inserting U-shaped circular arc curve elements between discrete one-dimensional linear finite element grids; (3) The one-dimensional linear finite element unit and the U-shaped arc curve unit are renumbered so that the finite element unit number and the node number are continuous, thereby forming a simplified one-dimensional heat exchange tube, namely, a one-dimensional heat exchange tube simplified unit.

3. A parallel computing method for simulating heat exchange processes of single and double U-shaped buried pipes in geothermal reservoirs according to claim 1, characterized in that: The specific steps of constructing the pipeline flow model in step 2 are: (1) Use 3D modeling to build the wellbore and backfill material; (2) The outside of the tube is still in three-dimensional form, and the inside and wall of the tube are simplified using one-dimensional heat exchange tube units, that is, the tube is modeled as a curve in the three-dimensional model to obtain a geometric model; (3) Input the working condition parameters into the geometric model and give them physical meaning, establish the overall layered rock and soil seepage model, and obtain the pipeline flow model.

4. A method for simulating the heat exchange process of single and double U-shaped buried pipes in a geothermal reservoir by parallel computing according to claim 1, characterized in that: The specific steps in step three are: (1) In the part outside the pipe, the energy equation of the rock and soil medium outside the pipe is established based on the porous media heat transfer theory, where the rock and soil medium includes the backfill material in the surrounding hole and the underground stratification and seepage rock and soil medium outside the hole; the energy equation of the rock and soil medium outside the pipe is expressed as: Where, ρ g is the reservoir fluid density, kg / m 3 ;c p,g is the constant-pressure specific heat capacity of the formation fluid, J / (kg·K); T w is the formation fluid temperature, °C; u g is the reservoir fluid velocity, m / s; λ g is the thermal conductivity of the fluid outside the heat exchange tube; Q wall is the heat transferred from geothermal fluid to the heat medium through the heat exchange tube wall, J; Where, (ρc p ) eff is the effective specific heat capacity at constant pressure, J / (℃·m 3 );λ eff is the effective thermal conductivity, W / (m·℃); T r is the formation temperature; (2) In the pipe part, the flow equation and energy equation of the fluid in the pipe are established according to the non-isothermal pipe flow theory, and the flow state and stress distribution of the fluid in the U-shaped pipe are obtained; The flow equation is shown in equations (3) and (4): The energy equation is shown in formula (5): Where A p is the cross-sectional area of the heat exchange tube, m 2 ; ρ f is the fluid density, kg / m 3 ;u f is the fluid velocity, m / s; p is the well pressure, Pa; d p is the inner diameter of the tube, m; c p,f is the constant pressure specific heat capacity of the fluid, J / (kg·℃); T f is the temperature of the fluid, °C; λ f is the thermal conductivity of the fluid in the heat exchange tube, W / (m·℃); Q wall is the heat transferred from geothermal fluid to the heat medium through the heat exchange tube wall, J; In formula (4), f D is the Darcy friction factor, according to the Churchill model: Where Re is the Reynolds number; e is the roughness of the inner tube; In formula (5), Q wall : Q wall =(hZ) eff (T ext -T f ) (7) Where, T ext is the temperature outside the heat exchange tube wall, °C; (hZ) eff is the total equivalent heat transfer coefficient, including the thermal resistance of the tube wall and the convection thermal resistance of the inner and outer walls, W / (m·℃); Z is the circumference of the tube wall, m; h is the forced convection heat transfer coefficient, W / (m 2 ·℃), calculated by formula (8): Where Nu is the Nusselt number, λ f is the thermal conductivity of the fluid in the heat exchange tube; for circular tubes, (hZ) eff It can be calculated by formula (9): Where h int is the convection heat transfer coefficient in the tube, W / (m·℃); h ext is the convection heat transfer coefficient outside the tube, W / (m·℃); r i With r o are the inner and outer diameters of the circular tube, respectively. The convection heat transfer coefficient inside and outside the tube is expressed by the Nusselt number Nu int and Nu ext calculate: Where λ g is the thermal conductivity of the fluid outside the heat exchange tube; Nu int It can be calculated by Gnielinski formula: Where Pr is the Prandtl number, and the applicable range of the equation is: Re = 3000 ~ 6 × 10 6 , Pr = 0.5 ~ 2000; For the natural convection outside the heat exchange tube, it can be calculated by the model proposed by Churchill and Chu: Where Ra is the Rayleigh number, Ra = Pr Gr; Gr is the dimensionless Grashof number, which represents the ratio of buoyancy to viscous force. The applicable range of formula (12) is Ra < 10 12 ; (3) The parallel finite element calculation method is used to combine the rock and soil medium outside the pipe and the circulating fluid medium inside the pipe to obtain the overall control equation group, which is as follows: First, the temperature of the fluid inside the pipe and the temperature of the rock and soil outside the pipe are calculated separately. Then, the parallel finite element method is used to jointly solve the temperatures between different media according to the physical field to obtain the transient temperature changes of the fluid in the calculation model and the transient temperature changes in the rock and soil.

5. The method for simulating the heat exchange process of single and double U-shaped buried pipes in a geothermal reservoir by parallel computing according to claim 1, characterized in that: The specific steps in step 4 are: (1) The outlet temperature and heat transfer capacity under different conditions are obtained by changing different operating parameters. Different operating parameters are factors that affect the heat transfer characteristics of the buried pipe. The operating parameters include well parameters and operating parameters. The well parameters include the thermal conductivity of rock and soil stratification, rock and soil density and specific heat capacity, thermal conductivity of backfill materials, groundwater seepage velocity, aquifer location, and geothermal gradient; the operating parameters include the injection temperature of the circulating fluid, the injection flow rate, and the system operation time. (2) Using the grey correlation analysis method, the influence degree of each factor on thermal mining efficiency is ranked; (3) Orthogonal test method was used for random grouping, and the optimal parameter combination was obtained based on heat transfer capacity and heat transfer efficiency.

6. A system, characterized in that: The invention comprises a processor capable of running the method for simulating the heat exchange process of single and double U-shaped buried pipes in a geothermal reservoir by parallel computing as described in any one of claims 1 to 5.

7. A device, characterized in that include: Memory: a computer program for storing the method for parallel computing simulation of heat exchange process of single and double U-shaped buried pipes in geothermal reservoirs according to any one of claims 1 to 5; Processor: used to implement the method of parallel computing simulation of single and double U-shaped buried pipe heat exchange process in geothermal reservoir when executing the computer program described in any one of claims 1-5.

8. A computer-readable storage medium, characterized in that The computer-readable storage medium stores a computer program, which, when executed by a processor, implements the method of parallel computing for simulating the heat exchange process of single and double U-shaped buried pipes in a geothermal reservoir according to any one of claims 1 to 5.

Images