CN109946103B - Geothermal parameter testing system and method based on middle-deep buried pipe heat exchanger - Google Patents
Geothermal parameter testing system and method based on middle-deep buried pipe heat exchanger Download PDFInfo
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Abstract
The invention provides a geothermal parameter testing system and method based on a medium-deep buried pipe heat exchanger, and belongs to the technical field of geothermal heat and geothermal energy utilization. The method takes a medium-deep buried pipe heat exchanger as a main technical platform, tests a change curve of the temperature of circulating water along with time under a zero load state, solves a heat transfer inverse problem based on a heat transfer model of the medium-deep buried pipe heat exchanger, determines local geothermal flow and borehole bottom temperature, and can further obtain thermal physical parameters of a stratum. The method can provide necessary geothermal parameters for the medium-deep ground source heat pump technology and the heat storage technology taking underground rock and soil as heat storage media, and also provides an alternative method for measuring the geothermal flow.
Description
Technical Field
The disclosure relates to the technical field of geothermal energy utilization, in particular to a geothermal parameter testing system and method based on a medium-deep buried pipe heat exchanger.
Background
The statements in this section merely provide background information related to the present disclosure and may not necessarily constitute prior art.
The ground source heat pump system forms a ground buried pipe heat exchanger by burying a pipeline underground, so that the ground becomes a heat source of the heat pump system, the requirements of building refrigeration in summer and heating in winter and domestic hot water supply are met, the primary energy utilization rate can be effectively improved, and the emission of greenhouse effect gas CO2 and other pollutants is reduced, so that the energy-saving novel technology utilizing renewable energy sources is provided.
In the traditional shallow-layer ground heat exchanger system, the depth of a buried pipe is generally 80-150m, so that a ground source heat pump system or a heat storage system needs to occupy a large amount of land, and the shallow-layer ground heat exchanger system becomes a main obstacle for popularization and application of the energy-saving technologies; in addition, the temperature of these shallow rock soils is typically below 20 ℃, also affecting the efficiency of the ground source heat pump system or the thermal storage system. In recent years, the technology of the middle-deep buried pipe heat exchanger developed improves the depth of the traditional vertical buried pipe to 1500-2500m, the temperature of the bottom of a drilling hole can reach 40-90 ℃, and the defects of large occupied area and low ground temperature of the shallow buried pipe heat exchanger are overcome.
The high-temperature ground core continuously dissipates heat to the ground surface, so that the ground heat flow is generated, and the phenomenon that the temperature is higher as the ground layer is deeper is also caused. The geothermal flow, also called geothermal flow density, refers to the heat transferred from the earth's interior to the surface in the vertical direction per unit area per unit time.
In the heat transfer analysis of the shallow buried pipe heat exchanger, the temperature change of the stratum in the depth direction is only 2-3 ℃, so that the temperature change in the depth direction is ignored in related specifications and engineering practices at home and abroad, and the temperature is uniform when the stratum is not disturbed. This also means that the effect of the ground heat flow is neglected. The temperature difference between the upper and lower parts of the borehole in the middle-deep buried pipe heat exchanger can reach 25-75 ℃, and becomes one of the decisive factors influencing the performance of the middle-deep buried pipe heat exchanger, so that the local geothermal heat flow of the borehole in the heat transfer analysis of the middle-deep buried pipe heat exchanger cannot be ignored, and is necessary basic data for the performance analysis and design calculation of the middle-deep buried pipe heat exchanger.
In addition, the thermal response test of the shallow ground source heat pump buried pipe heat exchanger aims at a shallow ground source heat pump system, and the depth of a buried pipe does not exceed 150m, so that the influence of the ground heat flow and the ground temperature gradient is ignored in the methods, and the aim is to obtain the average heat conductivity of the stratum only, and certainly, the concept of the ground heat flow cannot be related. The geothermal flow is a necessary parameter for the heat transfer analysis of the middle-deep geothermal energy application, so the method adopting the shallow geothermal heat pump thermal response test can not meet the requirements of the heat transfer analysis, design and operation of the middle-deep buried pipe heat exchanger. The second is that the method of testing is fundamentally different. Existing proprietary methods for thermal response testing of shallow ground source heat pump systems must be provided with a source of heat (cold), typically an electrical heating element or a heat pump.
The earth flow values of each location may vary greatly depending on factors such as the geologic structure. The measurement and accumulation of the distribution data of the earth heat flow in various places are basic works of national geology and geothermal investigation, and are the problems which are urgently needed to be solved in the current middle-deep geothermal utilization. However, determining the earth's heat flow for a particular location is a difficult and costly task. There are few related studies on the heat flow of the earth, the temperature distribution of the middle deep layer and the thermal physical parameter test of the rock stratum. Wherein, the application number is: 201610021294.5, patent name: a sectional type ground temperature gradient fitting method based on stratum non-integration surface is disclosed, and the method is used for respectively and independently fitting ground temperature gradients above and below ground temperature gradient critical surfaces according to stratum development characteristics of different areas, so that ground temperature gradients of different layers above and below are obtained, ground temperature field characteristics of new and old stratum can be truly reflected, and reliable basis is provided for oil gas and geothermal resource exploration and utilization. But special drilling is required to determine the well region stratum structure, the spreading and burial depth of stratum non-integration surfaces.
Because of the complexity and high cost of the middle-deep layer geothermal flow and stratum thermal property parameter test, the ground geothermal flow value of about 1200 data points is only about 1200 in 2015 on the vast country of China, the differential distribution is very uneven, the requirements of the investigation and research of the country resources can not be met far, and the urgent requirements of the engineering application of the middle-deep layer buried pipe heat exchanger can not be met.
Disclosure of Invention
In order to solve the problems, the geothermal parameter testing system and the geothermal parameter testing method based on the medium-deep buried pipe heat exchanger are provided, the geothermal parameter testing system is built based on the medium-deep buried pipe heat exchanger, the medium-deep buried pipe heat exchanger in the system can be used as a part of a testing system and also can be used as a heat source of a ground source heat pump system or a heat storage system, the utilization rate of the medium-deep buried pipe heat exchanger is improved, and the testing cost is reduced. Meanwhile, only the middle-deep buried pipe heat exchanger and the testing device are connected in the test, no heating element exists in the testing device, the connection with the ground source heat pump system or the heat storage system is cut off, zero-load operation of the middle-deep buried pipe heat exchanger is realized, the temperature change of circulating liquid can truly reflect geothermal parameters, and therefore obtained geothermal parameter data are more accurate.
In order to achieve the above purpose, the present disclosure adopts the following technical scheme:
one or more embodiments provide a geothermal parameter testing system based on a mid-deep buried pipe heat exchanger, which comprises a mid-deep buried pipe heat exchanger, a water inlet valve group, a water outlet valve group and a testing device, wherein the water inlet valve group is connected with a water inlet end of the mid-deep buried pipe heat exchanger, the water outlet valve group is connected with a water outlet end of the mid-deep buried pipe heat exchanger, the water inlet valve group is respectively connected with the testing device and the heat pump system, and the water outlet valve group is respectively connected with the testing device and the heat pump system; in the geothermal parameter testing stage, the water outlet valve group and the water inlet valve group are connected with a testing device and a middle-deep buried pipe heat exchanger, and the heat pump system is bypassed; when the test stage is not in, the water outlet valve group and the water inlet valve group are connected with the heat pump system and the middle-deep buried pipe heat exchanger to provide a heat source for the heat pump system.
The testing device comprises a testing pipeline, a circulating pump, a flowmeter, a temperature sensor and a controller, wherein the testing pipeline is connected with the middle-deep buried pipe heat exchanger, the circulating pump, the flowmeter and the temperature sensor are arranged on the testing pipeline, at least one temperature sensor is arranged at the water inlet end and the water outlet end of the middle-deep buried pipe heat exchanger, and the controller is respectively connected with the flowmeter and the temperature sensor.
Further, the medium-deep buried pipe heat exchanger is of a sleeve type structure and comprises an inner pipe and an outer pipe, the pipe orifice of the outer pipe is a water inlet end, the pipe orifice of the inner pipe is a water outlet end, and a backfill material layer is arranged outside the outer pipe.
Further, the outer tube is a steel tube; or/and the inner pipe is a plastic pipe with low heat conductivity or a composite pipe with a heat insulation layer.
Further, the depth of the medium-deep buried pipe heat exchanger is more than 1500m.
Furthermore, the water outlet valve group is a water outlet three-way valve, the water outlet end of the water inlet end of the water outlet three-way valve is connected with the water outlet end of the submerged pipe heat exchanger, and the water outlet end of the water outlet three-way valve is respectively connected with the testing device and the heat pump system.
Further, the water inlet valve group is a water inlet three-way valve, the water inlet end of the middle-deep buried pipe heat exchanger at the water outlet end of the water inlet three-way valve is connected with the testing device and the heat pump system respectively.
The testing method of the geothermal parameter testing system based on the medium-deep buried pipe heat exchanger comprises the following steps:
filling circulating water, and recovering the rock-soil temperature around the buried pipe heat exchanger to an undisturbed state;
starting a testing device, and collecting time-dependent change data and flow data of the temperature of circulating water at the inlet and outlet ends of the medium-deep buried pipe heat exchanger;
establishing a heat transfer calculation model of the heat transfer process of the medium-deep sleeve type buried pipe heat exchanger;
solving a heat transfer calculation model of the middle-deep buried pipe heat exchanger by adopting a numerical calculation method, and solving an inverse problem of the heat transfer calculation model of the middle-deep buried pipe heat exchanger according to data acquired in the test to obtain local geothermal flow and borehole bottom temperature;
and determining the thermophysical parameters of the stratum according to the obtained local geothermal flow and the temperature of the bottom of the borehole.
Further, the method for establishing the heat transfer calculation model of the heat transfer process of the medium-deep sleeve type buried pipe heat exchanger comprises the following steps:
step 31, respectively establishing a heat conduction control equation of the rock and soil layer, a control equation of the circulation liquid temperature of the outer tube of the sleeve and a control equation of the circulation liquid temperature of the inner tube of the sleeve;
step 32, the control equation initial conditions and boundary conditions in step 31 are given.
Further, the method for solving the heat transfer calculation model of the middle-deep buried pipe heat exchanger by adopting a numerical calculation method solves the inverse problem of the heat transfer calculation model of the middle-deep buried pipe heat exchanger according to the data collected in the test, and the method for obtaining the local geothermal flow and the temperature of the bottom of the borehole comprises the following steps:
step 41, establishing a differential equation set corresponding to each control equation in step 31 under cylindrical coordinates by adopting a finite difference method;
step 42, solving a differential equation set by adopting a catch-up method to obtain a theoretical model calculation value;
and 43, solving a heat transfer inverse problem according to the acquired inlet and outlet temperature response data and the acquired theoretical model calculation value, and determining the geothermal flow and the borehole bottom temperature value.
Further, the rock-soil temperature around the mid-deep buried pipe heat exchanger is recovered to an undisturbed state, so that any one of the following conditions is satisfied:
the middle-deep buried pipe heat exchanger is used for completing the construction of drilling, pipe laying and backfilling for more than 30 days, and the recovery state is kept undisturbed by temperature;
the middle-deep buried pipe heat exchanger is leisure for more than 10 days after the last zero load test operation is finished, and the recovery state is kept undisturbed by temperature;
the medium-deep buried pipe heat exchanger is leisure for more than 90 days after finishing the heat supply or heat storage operation in the previous season, and the recovery state is kept undisturbed by temperature.
Compared with the prior art, the beneficial effects of the present disclosure are:
(1) The middle-deep buried pipe heat exchanger in the test system is only used as a part of the test system when the test is performed, and is connected with the heat pump system or the heat storage system to provide a heat source for the heat pump system or the heat storage system in a period of no test, so that waste caused by idle of the middle-deep buried pipe heat exchanger is avoided, the cost of geothermal parameter test is greatly reduced, and the utilization rate of the middle-deep buried pipe heat exchanger is improved. In the non-test stage, the deep buried pipe heat exchanger is used as a heat source of a ground source heat pump system or a heat storage system to generate continuous economic and environmental benefits, so that the economical efficiency of the deep buried pipe heat exchanger in construction is greatly improved.
(2) According to the geothermal parameter testing method, only the middle-deep buried pipe heat exchanger and the testing device are connected in the geothermal parameter testing, no heating element is arranged in the testing device, the ground source heat pump system or the heat storage system is cut off, zero-load operation of the middle-deep buried pipe heat exchanger is realized, the geothermal parameter can be truly reflected by temperature change, and therefore the obtained geothermal parameter data are more accurate. The test process is simple and convenient, the test time is short, about 6-10 hours is needed, and the high-accuracy medium-deep geothermal parameter test can be realized.
(3) The medium-deep buried pipe heat exchanger can adopt a sleeve type structure, has a regular shape, is easier to establish a heat transfer model, adopts a finite difference method to solve the heat transfer model, realizes high-efficiency calculation, and can simplify the measurement and analysis of medium-deep geothermal flow and stratum thermophysical parameters.
Drawings
The accompanying drawings, which are included to provide a further understanding of the disclosure, illustrate and explain the disclosure, and do not constitute a limitation on the disclosure.
FIG. 1 is a schematic diagram of a system according to one or more embodiments;
wherein: 1. the heat pump system comprises a circulating pump, 2, a flowmeter, 3, a temperature sensor, 4, an inner pipe, 5, an outer pipe, 6, a backfill material layer, 7, a stratum around the heat exchanger, 8, a test pipeline, 9, a water outlet valve group, 10, a water inlet valve group, 11 and a heat pump system.
The specific embodiment is as follows:
the disclosure is further described below with reference to the drawings and examples.
It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the present disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments in accordance with the present disclosure. As used herein, the singular is also intended to include the plural unless the context clearly indicates otherwise, and furthermore, it is to be understood that the terms "comprises" and/or "comprising" when used in this specification are taken to specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof. It should be noted that, without conflict, the embodiments of the present disclosure and features of the embodiments may be combined with each other. The embodiments will be described in detail below with reference to the accompanying drawings.
In the technical scheme disclosed in one or more embodiments, as shown in fig. 1, a geothermal parameter testing system based on a middle-deep buried pipe heat exchanger comprises the middle-deep buried pipe heat exchanger, a water inlet valve set 10 and a water outlet valve set 9, wherein the water inlet valve set 10 is connected with a water inlet end of the middle-deep buried pipe heat exchanger, the water outlet valve set 9 is connected with a water outlet end of the middle-deep buried pipe heat exchanger, the water inlet valve set 10 is respectively connected with a testing device and a heat pump system 11, and the water outlet valve set 9 is respectively connected with the testing device and the heat pump system 11; in the geothermal parameter testing stage, the water outlet valve group and the water inlet valve group are connected with a testing device and a middle-deep buried pipe heat exchanger, and the heat pump system is bypassed; when the test stage is not in, the water outlet valve group and the water inlet valve group are connected with the heat pump system and the middle-deep buried pipe heat exchanger to provide a heat source for the heat pump system.
The heat pump system in this embodiment may include any system of a heat pump, and may be a ground source heat pump system and a heat storage system, where the ground source heat pump system uses a rock mass, groundwater or surface water as a low-temperature heat source, and is a heating air conditioning system composed of a water source heat pump unit, a geothermal energy exchange system, and a system in a building. The middle-deep buried pipe heat exchanger in the test system of the embodiment can be used as a part of the test system, and the heat pump system 11 is connected to provide a heat source for the middle-deep buried pipe heat exchanger in a non-test period, so that waste caused by idle middle-deep buried pipe heat exchanger devices is avoided, the utilization rate of the middle-deep buried pipe heat exchanger is improved, and the utilization rate of primary energy is improved. The middle-deep buried pipe heat exchanger can be connected in the ground source heat pump system 11 or the heat storage system in a stage of not testing, and is connected in series with a heat pump or other heat exchangers to form a closed loop to provide a heat source.
The testing device comprises a testing pipeline 8, a circulating pump 1, a flowmeter 2, a temperature sensor 3 and a controller, wherein the testing pipeline 8 is connected with the middle-deep buried pipe heat exchanger, the circulating pump 1, the flowmeter 2 and the temperature sensor 3 are arranged on the testing pipeline 8, at least one temperature sensor 3 is arranged at the water inlet end and the water outlet end of the middle-deep buried pipe heat exchanger, and the controller is respectively connected with the flowmeter and the temperature sensor 3.
The flow meter 2 and the temperature sensor 3 may be connected to the controller by means of a data collector.
The circulation pump 1 can be driven by a driving motor, and the driving motor of the circulation pump can adopt a variable frequency motor to drive the circulation pump to adjust the flow of circulating water. The flowmeter 2 collects flow data of the test pipeline and transmits the data to the controller, and the controller stores the collected data and controls the circulating pump driving motor to work according to the collected flow data so that the flow is in a set range. The temperature sensors 3 arranged at the water inlet end and the water outlet end of the medium-deep buried pipe heat exchanger respectively detect water outlet temperature data of water inlet temperature changing along with time, and the detected temperature data are transmitted to the controller, and the controller stores and displays the data. The specific model of the controller can be STC15W408 singlechip.
In the geothermal parameter test, only the middle-deep buried pipe heat exchanger and the test device are connected, no heating element exists in the test device, the ground source heat pump system or the heat storage system is cut off, zero-load operation of the middle-deep buried pipe heat exchanger is realized, and the geothermal parameter can be truly reflected by temperature change, so that the obtained geothermal parameter data is more accurate.
As a further improvement, the medium-deep buried pipe heat exchanger can adopt a sleeve type structure, and comprises an inner pipe 4 and an outer pipe 5, wherein the pipe orifice of the outer pipe is a water inlet end, the pipe orifice of the inner pipe is a water outlet end, and a backfill material layer 6 is arranged outside the outer pipe. The backfill material layer 6 is arranged between the medium deep buried pipe heat exchanger and the stratum 7 around the heat exchanger. In the medium-deep buried pipe heat exchanger of the embodiment, circulating medium (such as circulating water) flows in and out of the outer pipe 5 and the inner pipe 4, the structure of the sleeve type is convenient to construct, the shape is more regular, a heat transfer model is easier to build, and the analysis of geothermal parameters can be simplified.
The outer tube 5 can be made of steel tube, the tube wall of the inner tube 4 has good heat insulation performance, and the inner tube 4 can be made of plastic tube with low heat conductivity or composite tube with heat insulation layer. The depth of borehole burial is now typically 1500-2500m; deeper depths may also be employed where technical and economic considerations permit. Pure water can be adopted as a circulating medium in the medium-deep buried pipe heat exchanger.
As a further improvement, the medium-deep buried pipe heat exchanger is selected for testing, and a switching device connected with a ground source heat pump system is further arranged, wherein the switching device is any switching device, can be a manual or automatic device, the switching device of the embodiment is a water outlet valve group 9 and a water inlet valve group 10, and valves arranged on the water outlet valve group 9 and the water inlet valve group 10 can be manual valves or electromagnetic valves, and particularly can be three-way valves. The water outlet valve group 9 is a water outlet three-way valve, the water outlet end of the water outlet three-way valve is connected with the water outlet end of the submerged heat exchanger, and the water outlet end of the water outlet three-way valve is respectively connected with the testing device and the heat pump system 11. The water inlet valve group 10 is a water inlet three-way valve, the water outlet end of the water inlet three-way valve is connected with the water inlet end of the medium-deep buried pipe heat exchanger, and the water inlet end of the water inlet three-way valve is respectively connected with the testing device and the heat pump system 11. The three-way valve in the embodiment can be replaced by two valves, and the two valves are adopted to replace the three-way valve to be connected to form two branches which can be communicated with the three-way valve. When the three-way valve is an electromagnetic valve, the controller can be connected, and the conduction state of the three-way valve can be controlled by setting a key.
Example 2
The embodiment provides a test method of a geothermal parameter test system based on a mid-deep buried pipe heat exchanger according to embodiment 1, comprising the following steps:
step 1, circulating water is filled, and the rock-soil temperature around the medium-deep buried pipe heat exchanger is recovered to a state of no interference; the circulating water may be pure water.
And (3) recovering the rock-soil temperature around the middle-deep buried pipe heat exchanger to an undisturbed state, filling circulating water, and connecting the middle-deep buried pipe heat exchanger and the testing device.
The rock-soil temperature around the medium-deep buried pipe heat exchanger is recovered to an undisturbed state, and any one of the following conditions can be satisfied:
(1) the middle-deep buried pipe heat exchanger completes the construction of drilling, pipe descending and backfilling for more than 30 days, and the recovery state is kept undisturbed by temperature.
(2) The middle-deep buried pipe heat exchanger is leisure for more than 10 days after the last zero load test operation is completed, and the recovery state is kept free from temperature disturbance.
(3) The medium-deep buried pipe heat exchanger is leisure for more than 90 days after finishing the heat supply or heat storage operation in the previous season, and the recovery state is kept undisturbed by temperature.
In the test, only the middle-deep buried pipe heat exchanger and the test device are connected, no heating element exists in the test device, the ground source heat pump system or the heat storage system is cut off, zero-load operation of the middle-deep buried pipe heat exchanger is realized, the temperature change can truly reflect geothermal parameters, and therefore the obtained geothermal parameter data are more accurate.
Step 2, starting a testing device, and collecting time-dependent change data and flow data of the temperature of circulating water at the inlet end and the outlet end of the medium-deep buried pipe heat exchanger;
and opening the circulating pump, and simultaneously starting the controller and the data acquisition device to acquire data. Circulating water flows into the medium-deep buried pipe heat exchanger from the outer pipe and flows out from the inner pipe, and the circulating flow is kept within a set range in the whole test process. And measuring the flow of the circulating water and the power consumption of the water pump, and continuously recording the change of the temperature of the circulating water at the inlet and the outlet of the buried pipe heat exchanger along with the time. The circulating water temperature will exhibit a periodic oscillation of decaying amplitude during the first hours, and will then enter a smooth and slow warm-up phase. After the temperature rising stage is determined to be entered, the circulating pump is turned off, and the data acquisition process is finished.
Step 3, establishing a heat transfer calculation model of the heat transfer process of the medium-deep sleeve type buried pipe heat exchanger;
the method for establishing the heat transfer calculation model of the heat transfer process of the medium-deep sleeve type buried pipe heat exchanger comprises the following steps:
step 31, respectively establishing a heat conduction control equation of the rock and soil layer, a control equation of the circulation liquid temperature of the outer tube of the sleeve and a control equation of the circulation liquid temperature of the inner tube of the sleeve;
the heat transfer in the rock soil around the buried pipe heat exchanger of the embodiment can be described by two-dimensional transient heat conduction in cylindrical coordinates, and a heat conduction control equation of the rock soil layer is as follows:
wherein a is the thermal diffusivity of the rock and soil, t is the temperature of the rock and soil, tau is time, r is a radial index, and z is an axial coordinate.
In the working condition that circulating water flows into the outer pipe and flows out of the inner pipe (the outer inlet and the inner outlet), heat transfer equations of fluid in the inner pipe and the outer pipe are respectively established as follows:
the control of the temperature of the circulating liquid of the sleeve pipe outer pipe adopts a one-dimensional transient heat transfer model, and the control equation is as follows:
wherein t is f1 For the outer tube fluid temperature, t f2 At the inner tube fluid temperature t b To the temperature of the borehole wall, R 1 R is the thermal resistance between the borehole wall and the outer tube fluid 2 Mc is the heat capacity of the circulating fluid and C is the heat resistance between the inner tube and the outer tube 1 The heat capacity of the outer tube per unit length, z is the axial coordinate and τ is time.
The temperature control equation of the circulating fluid in the sleeve pipe is as follows:
wherein C is 2 Heat capacity of inner tube per unit length, t f1 For the outer tube fluid temperature, t f2 For the inner tube fluid temperature, mc is the heat capacity of the circulating fluid, R 2 The thermal resistance between the inner tube and the outer tube is represented by z, which is the axial coordinate, and τ, which is the time.
Step 32, the control equation initial conditions and boundary conditions in step 31 are given. The initial condition may be an initial temperature distribution in the rock and soil without interference, and specifically may be:
wherein q is g Is the heat flow of the earth, h a Is the surface convection heat transfer coefficient, t a J is the number of formations, H j Depth of the j-th layer, k j Is the thermal conductivity of the j-th layer.
The initial temperature distribution in the formation depends on the local earth flow value and the earth thermal conductivity, which also determines the subsequent heat transfer process.
The boundary conditions may be: the far boundary and the bottom boundary of the cylindrical region adopt a constant temperature boundary condition; the surface adopts convection boundary conditions.
The control equation in step 31 gives the initial conditions and boundary conditions as the heat transfer calculation model of the present embodiment.
In this embodiment, geothermal test parameters are obtained, and the basic calculation method is to solve the inverse problem of heat transfer. Various optimization and parameter estimation algorithms can be employed to solve the inverse heat transfer problem. In the method, according to the difference of the algorithm and the required precision, the temperature of the bottom of the drill hole can be measured by adopting a single method, and then the ground heat flow is determined by solving the inverse problem; the inverse problem can also be solved by the method, directly determining the borehole bottom temperature, the geothermal flow and more other relevant parameters.
And 4, solving a heat transfer inverse problem according to the acquired data and a heat transfer calculation model of the middle-deep buried pipe heat exchanger, namely adopting a parameter estimation algorithm to enable the parameter (the ground heat flow and the borehole bottom temperature) value closest to the curve calculated by the actual measurement data and the theoretical model to be the obtained parameter estimation value. Therefore, the local geothermal heat value and the drilling bottom temperature value are tested by measuring the inlet and outlet circulating water temperature of the sleeve type buried pipe heat exchanger. The specific steps can be as follows:
step 41, quickly and effectively solving a mathematical model, namely solving a positive problem, is the basis for data processing of solving an inverse problem. In the embodiment, a finite difference method is adopted to carry out numerical solution on the mathematical model. The finite difference method is adopted to establish a differential equation set corresponding to each control equation in the step 31, the differential format adopts a cross direction method, the obtained differential equation set can adopt any time step, and the differential equation of a typical node can be as follows:
differential equation for internal nodes of the rock mass:
wherein t is the temperature, B z 、B r And P is a time step length number, and i and j are node coordinates.
Differential equation of the temperature of the casing tube circulating fluid:
wherein B is 1 、B 3 、B 4 Is the coefficient, t f1 For the outer tube fluid temperature, t f2 The temperature of the fluid in the inner pipe is t, P is the time step number, and i and j are node coordinates.
Differential equation of the temperature of the circulating fluid in the sleeve:
wherein t is f1 For the outer tube fluid temperature, t f2 For the inner tube fluid temperature, B 2 、B 5 And B 4 Is a coefficient, t is a temperature, P is a time step number, j is a node coordinate,
and 42, solving the differential equation set, namely directly solving by adopting a catch-up method to obtain a theoretical model calculation value and a theoretical calculation value of the temperature of the rock stratum and the circulating liquid. The temperature of each point in the rock and the temperature of the circulating water in the inner pipe and the outer pipe can be determined to change along with time. This is the basis for solving the inverse problem of heat transfer. In embodiments, a finite difference method may be used to solve the heat transfer model; the inverse problem of heat transfer can be solved by using a Tikhonov regularization method.
In this embodiment, the differential equation set obtained by the corresponding heat transfer model is directly solved by adopting a catch-up method, and any time step can be adopted, so that convergence of numerical calculation can be ensured. These features ensure the computational heat transfer problem, i.e., the quick and efficient solution of the above heat transfer model.
And 43, solving a heat transfer inverse problem according to the acquired inlet and outlet temperature response data and the acquired theoretical model calculation value, and determining the geothermal flow and the borehole bottom temperature value.
According to the acquired data and the obtained theoretical model calculated value, solving the inverse problem of heat transfer of the medium-deep buried pipe heat exchanger by adopting a Tikhonov regularization method to obtain local geothermal flow and borehole bottom temperature. In the embodiment, a Tikhonov regularization method is adopted for optimization fitting, namely, the geothermal flow and the temperature value of the bottom of the drill hole which enable the measured data and the theoretical calculation data curve to be best fit are found.
According to the acquired data and a heat transfer calculation model of the middle-deep buried pipe heat exchanger, solving a heat transfer problem inverse problem, namely adopting a parameter estimation algorithm, so that the parameter (the geothermal flow and the borehole bottom temperature) value closest to the curve calculated by the actual measurement data and the theoretical model is the calculated parameter estimation value. Therefore, the local geothermal flow value and the temperature value of the bottom of the borehole are tested by measuring the inlet and outlet circulating water temperature of the sleeve type buried pipe heat exchanger.
In this embodiment, geothermal test parameters are obtained, and the basic calculation method is to solve the inverse problem of heat transfer. The mathematical model, i.e. the problem, is solved quickly and effectively, and is the basis of data processing. Various optimization and parameter estimation algorithms can be employed to solve the inverse heat transfer problem. In the problem, according to the difference of the algorithm and the required precision, the temperature of the bottom of the drill hole can be measured by adopting a single method, and then the ground heat flow is determined by solving the inverse problem; the borehole bottom temperature, geothermal flow and more other relevant parameters can also be determined directly by solving the inverse problem.
The solving method of the embodiment adopts a Tikhonov regularization method, converts the inverse problem of the heat transfer problem into a nonlinear optimization problem, and solves the earth heat flow value and the temperature value of the bottom of the drill hole. The positive problems in this embodiment are: and solving a time-dependent change curve of the circulating water temperature of the middle-deep sleeve type ground heat exchanger according to the assumed geothermal flow value, the assumed drilling bottom temperature value and the assumed circulating water flow. In this embodiment, the change curve of the circulating water temperature with time and the flow data are collected first, which are the detected data. The method for solving the inverse problem of heat transfer, namely the algorithm of parameter estimation, is utilized to ensure that the parameter (the geothermal flow and the temperature at the bottom of the drilling hole) value closest to the curve calculated by the actual measurement data and the theoretical model is the calculated parameter estimation value. Thereby realizing the test of the local geothermal heat value and the temperature value of the bottom of the drilling hole by measuring the temperature of the inlet and outlet circulating water of the sleeve type buried pipe heat exchanger
And 5, determining the average thermophysical parameters of the stratum according to the obtained local geothermal flow and the temperature of the bottom of the borehole.
The calculation can be made by the following formula:
wherein k is the average heat conductivity coefficient of the rock and soil layer, t h Is the temperature of the bottom of the drill hole, t 0 Is the surface temperature, H is the drilling depth, q g Is the geothermal flow.
According to the test system and the test method, the change of the inlet and outlet circulating liquid temperature along with time is measured when the buried pipe heat exchanger operates under the zero load condition, and the heat transfer inverse problem is solved according to a certain heat transfer model, so that the geothermal flow, the temperature of the bottom of a drilling hole and the thermal physical parameters of a stratum are determined. Within the scope of this spirit and principle, the construction and dimensions of the various borehole heat exchangers, the refinement of the heat transfer model, and the mathematical solution are all within the scope of the present application.
The foregoing description of the preferred embodiments of the present disclosure is provided only and not intended to limit the disclosure so that various modifications and changes may be made to the present disclosure by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present disclosure should be included in the protection scope of the present disclosure.
While the specific embodiments of the present disclosure have been described above with reference to the drawings, it should be understood that the present disclosure is not limited to the embodiments, and that various modifications and changes can be made by one skilled in the art without inventive effort on the basis of the technical solutions of the present disclosure while remaining within the scope of the present disclosure.
Claims (8)
1. The test method of the geothermal parameter test system based on the medium-deep buried pipe heat exchanger is characterized by comprising the following steps of:
filling circulating water, and recovering the rock-soil temperature around the buried pipe heat exchanger to an undisturbed state;
starting a testing device, and collecting time-dependent change data and flow data of the temperature of circulating water at the inlet and outlet ends of the medium-deep buried pipe heat exchanger;
establishing a heat transfer calculation model of the heat transfer process of the medium-deep sleeve type buried pipe heat exchanger;
solving a heat transfer calculation model of the middle-deep buried pipe heat exchanger by adopting a numerical calculation method, and solving an inverse problem of the heat transfer calculation model of the middle-deep buried pipe heat exchanger according to data acquired in the test to obtain local geothermal flow and borehole bottom temperature;
determining the thermophysical parameters of the stratum according to the obtained local geothermal flow and the temperature of the bottom of the borehole;
the thermophysical parameters of the stratum are determined according to the obtained local geothermal flow and the temperature of the bottom of the borehole, and the following formula is specifically adopted:
wherein k is the average heat conductivity coefficient of the rock and soil layer, t h Is the temperature of the bottom of the drill hole, t 0 Is the surface temperature, H is the depth of the borehole, q g Is the geothermal flow;
the geothermal parameter testing system based on the middle-deep buried pipe heat exchanger is adopted in the testing method, and comprises the middle-deep buried pipe heat exchanger, a water inlet valve bank, a water outlet valve bank and a testing device, wherein the water inlet valve bank is connected with the water inlet end of the middle-deep buried pipe heat exchanger, the water outlet valve bank is connected with the water outlet end of the middle-deep buried pipe heat exchanger, the water inlet valve bank is respectively connected with the testing device and the heat pump system, and the water outlet valve bank is respectively connected with the testing device and the heat pump system; in the geothermal parameter testing stage, the water outlet valve group and the water inlet valve group are connected with a testing device and a middle-deep buried pipe heat exchanger, and the heat pump system is bypassed; when the test stage is not performed, the water outlet valve group and the water inlet valve group are connected with the heat pump system and the middle-deep buried pipe heat exchanger to provide a heat source for the heat pump system;
the testing device comprises a testing pipeline, a circulating pump, a flowmeter, a temperature sensor and a controller, wherein the testing pipeline is connected with the middle-deep buried pipe heat exchanger;
the medium-deep buried pipe heat exchanger is of a sleeve type structure and comprises an inner pipe and an outer pipe, the pipe orifice of the outer pipe is a water inlet end, the pipe orifice of the inner pipe is a water outlet end, and a backfill material layer is arranged outside the outer pipe.
2. The test method of claim 1, wherein: the method for establishing the heat transfer calculation model of the heat transfer process of the medium-deep sleeve type buried pipe heat exchanger comprises the following steps:
step 31, respectively establishing a heat conduction control equation of the rock and soil layer, a control equation of the circulating fluid temperature of the outer tube of the sleeve and a control equation of the circulating fluid temperature of the inner tube of the sleeve;
step 32, the control equation initial conditions and boundary conditions in step 31 are given.
3. The test method of claim 1, wherein: the method for solving the inverse problem of the heat transfer calculation model of the middle-deep buried pipe heat exchanger by adopting a numerical calculation method comprises the steps of obtaining local geothermal flow and borehole bottom temperature according to the data acquired in the test, wherein the method comprises the following steps:
step 41, establishing a differential equation set corresponding to each control equation in step 31 under cylindrical coordinates by adopting a finite difference method;
step 42, solving a differential equation set by adopting a catch-up method to obtain a theoretical model calculation value;
and 43, solving a heat transfer inverse problem according to the acquired inlet and outlet temperature response data and the acquired theoretical model calculation value, and determining the geothermal flow and the borehole bottom temperature value.
4. The test method of claim 1, wherein: the rock-soil temperature around the middle-deep buried pipe heat exchanger is recovered to an undisturbed state, and any one of the following conditions is satisfied:
the middle-deep buried pipe heat exchanger is used for completing the construction of drilling, pipe laying and backfilling for more than 30 days, and the recovery state is kept undisturbed by temperature;
the middle-deep buried pipe heat exchanger is leisure for more than 10 days after the last zero load test operation is finished, and the recovery state is kept undisturbed by temperature;
the medium-deep buried pipe heat exchanger is leisure for more than 90 days after finishing the heat supply or heat storage operation in the previous season, and the recovery state is kept undisturbed by temperature.
5. The test method of claim 1, wherein: the outer tube is a steel tube; or/and the inner pipe is a plastic pipe with low heat conductivity or a composite pipe with a heat insulation layer.
6. The test method of claim 1, wherein: the depth of the medium-deep buried pipe heat exchanger is more than 1500m.
7. The test method of claim 1, wherein: the water outlet valve group is a water outlet three-way valve, the water outlet end of the water inlet end of the water outlet three-way valve is connected with the water outlet end of the submerged heat exchanger, and the water outlet end of the water outlet three-way valve is respectively connected with the testing device and the heat pump system.
8. The test method of claim 1, wherein: the water inlet valve group is a water inlet three-way valve, the water inlet end of the middle-deep buried pipe heat exchanger at the water outlet end of the water inlet three-way valve is connected with the testing device and the heat pump system respectively.
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| CN114201797A (en) * | 2021-11-25 | 2022-03-18 | 中国建筑科学研究院有限公司 | Design method and device for middle-deep buried pipe heat pump heating system |
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