CN111551288A - Prediction method for circulating liquid temperature of middle-deep layer U-shaped heat exchange well - Google Patents

Prediction method for circulating liquid temperature of middle-deep layer U-shaped heat exchange well Download PDF

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CN111551288A
CN111551288A CN202010402134.1A CN202010402134A CN111551288A CN 111551288 A CN111551288 A CN 111551288A CN 202010402134 A CN202010402134 A CN 202010402134A CN 111551288 A CN111551288 A CN 111551288A
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node
circulating liquid
nodes
temperature
heat exchange
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CN111551288B (en
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张文科
关春敏
孙炳岩
王建华
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Shandong Jianzhu University
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
    • G01K13/00—Thermometers specially adapted for specific purposes
    • G01K13/02—Thermometers specially adapted for specific purposes for measuring temperature of moving fluids or granular materials capable of flow
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24T—GEOTHERMAL COLLECTORS; GEOTHERMAL SYSTEMS
    • F24T10/00—Geothermal collectors
    • F24T10/10—Geothermal collectors with circulation of working fluids through underground channels, the working fluids not coming into direct contact with the ground
    • F24T10/13—Geothermal collectors with circulation of working fluids through underground channels, the working fluids not coming into direct contact with the ground using tube assemblies suitable for insertion into boreholes in the ground, e.g. geothermal probes
    • F24T10/15—Geothermal collectors with circulation of working fluids through underground channels, the working fluids not coming into direct contact with the ground using tube assemblies suitable for insertion into boreholes in the ground, e.g. geothermal probes using bent tubes; using tubes assembled with connectors or with return headers
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
    • G01K13/00—Thermometers specially adapted for specific purposes
    • G01K13/02—Thermometers specially adapted for specific purposes for measuring temperature of moving fluids or granular materials capable of flow
    • G01K13/026—Thermometers specially adapted for specific purposes for measuring temperature of moving fluids or granular materials capable of flow of moving liquids
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
    • G01K3/00—Thermometers giving results other than momentary value of temperature
    • G01K3/08—Thermometers giving results other than momentary value of temperature giving differences of values; giving differentiated values
    • G01K3/10—Thermometers giving results other than momentary value of temperature giving differences of values; giving differentiated values in respect of time, e.g. reacting only to a quick change of temperature
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
    • G01K3/00—Thermometers giving results other than momentary value of temperature
    • G01K3/08—Thermometers giving results other than momentary value of temperature giving differences of values; giving differentiated values
    • G01K3/14—Thermometers giving results other than momentary value of temperature giving differences of values; giving differentiated values in respect of space
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24T—GEOTHERMAL COLLECTORS; GEOTHERMAL SYSTEMS
    • F24T2201/00—Prediction; Simulation
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/10—Geothermal energy

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  • Combustion & Propulsion (AREA)
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  • General Engineering & Computer Science (AREA)
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  • Heat-Exchange Devices With Radiators And Conduit Assemblies (AREA)

Abstract

The invention relates to a method for predicting the temperature of a circulating liquid of a middle-deep U-shaped heat exchange well, wherein the middle-deep U-shaped heat exchange well comprises a descending pipe, a horizontal pipe and an ascending pipe, a plurality of nodes are arranged in the middle-deep U-shaped heat exchange well and around rock soil, the temperature information of the nodes at the inlet of the circulating liquid and around rock soil nodes at the initial moment is collected, the collected temperature information is substituted into a prediction model formed by node equations of the nodes in the middle-deep U-shaped heat exchange well, and the temperature information of the nodes at other positions of the middle-deep U-shaped heat exchange well and other moments is obtained. The method has the advantages of low equipment investment and capability of mastering the change rule of the temperature of the circulating liquid along with the position and the time.

Description

Prediction method for circulating liquid temperature of middle-deep layer U-shaped heat exchange well
Technical Field
The invention relates to the technical field of construction environment and energy application professional engineering, in particular to a method for predicting the temperature of circulating liquid of a middle-deep layer U-shaped heat exchange well.
Background
The statements herein merely provide background information related to the present disclosure and may not necessarily constitute prior art.
The ground source heat pump technology is popularized and applied due to the advantages of energy conservation and environmental protection, and the underground medium provides cold and heat for buildings in summer and winter respectively. The whole system consists of a ground heat exchanger, a heat pump unit and indoor tail end equipment, and the ground heat exchanger reflects the difference between a ground source heat pump and other types of heat pumps. In recent years, shallow geothermal energy within a range of 50m to 200m away from the ground is mainly used as a cold and heat source of the ground source heat pump, and a heat exchange tube is embedded by drilling to manufacture a ground heat exchanger. Because the drill hole is shallow, one project usually needs a plurality of ground heat exchangers to bear cold and heat loads so as to meet the cold and heat supply requirements of the building; therefore, the drilling and pipe burying are needed to be arranged on the land with a certain area, the heat transfer effect becomes poor when the cold and heat loads are unbalanced, especially for the area with single cooling or single heating, the annual change of the shallow underground temperature is obvious due to the fact that the heat discharged or absorbed underground, and the good energy supply effect cannot be guaranteed.
With the exploration of geothermal energy technology, a middle-deep ground source heat pump system is proposed and applied to practical engineering, and a buried pipe heat exchanger with the depth of 1500-; because the diameter of the drilled hole and the buried pipe is larger and the depth of the drilled hole and the buried pipe is far greater than that of the buried pipe in a shallow layer, one buried pipe heat exchanger can bear the heating amount of thousands of square meters or even tens of thousands of square meters of building area, and the land area for arranging more buried pipes is saved; the temperature of the medium-deep underground medium is far higher than that of shallow geology, and the underground temperature changes little year by year in areas with unbalanced cold and heat loads or single heat supply without affecting the performance of the system. Compared with a shallow ground source heat pump system and a heating system which extracts middle-deep underground water as a low-temperature heat source of a heat pump at present, the middle-deep buried pipe adopts a closed heat exchanger to extract the geothermal energy stored in the rock with the depth of 1500-. In order to ensure the structural stability of the underground heat exchange device, a sleeve structure is generally adopted, namely an inner pipe and an outer pipe with the same circle center are adopted, the outer pipe and the inner pipe are respectively a steel pipe and a plastic pipe, the steel pipe is used as a protective part outside the sleeve to play a good role in fixing, the heat conductivity coefficient of the steel pipe is higher, the hardness of the steel pipe is high, and the heat exchange between circulating liquid in the pipe and an underground medium is facilitated. The plastic pipeline has small heat conductivity coefficient and can realize the heat preservation effect. The circulating liquid flows into the sleeve from the gap between the inner pipe and the outer pipe, and returns to flow out from the inner pipe after sufficient heat exchange with the underground medium.
Because the heat supply capacity of the single-drilling middle-deep-layer sleeve heat exchanger is limited, the heat supply requirement when the building area is large is difficult to meet, in order to further enhance the heat exchange capacity of the middle-deep-layer buried pipe and improve the utilization effect of the middle-deep-layer geothermal energy, two vertical drilling buried pipes with the depth of 1500-3000m can be horizontally connected at the bottom, namely, the mode of horizontal drilling buried pipe is adopted at the bottom, and three sections of drilling buried pipes form a U-shaped well buried pipe heat exchanger. The drill hole can be directly made of a steel pipe without a sleeve. And circulating liquid flows in from the steel pipe of one vertical drilling hole, sequentially passes through the vertical steel pipe, the horizontal steel pipe and the vertical steel pipe, flows out from the steel pipe in the other vertical drilling hole, and then enters the next circulation.
The inventor finds that for monitoring the circulating liquid temperature of the middle-deep U-shaped well, a large number of temperature monitoring elements need to be arranged in the middle-deep U-shaped well, the arrangement of the temperature monitoring elements is inconvenient due to the deep burial depth of the middle-deep U-shaped well, the required number of the temperature monitoring elements is large, the equipment investment is large, the temperature change trend of the circulating liquid cannot be predicted, and particularly the temperature change of the circulating liquid after one year or even several years is difficult to obtain data through experiments.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a method for predicting the temperature of the circulating liquid of a middle-deep layer U-shaped heat exchange well, which can obtain the temperatures of other positions of the U-shaped heat exchange well and the temperatures of a plurality of moments in the future through the temperature at a circulating liquid inlet, does not need to arrange a large number of temperature monitoring elements and reduces equipment investment.
In order to achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, an embodiment of the invention provides a method for predicting temperature of a circulating fluid of a middle-deep-layer U-shaped heat exchange well, wherein the middle-deep-layer U-shaped heat exchange well comprises a descending pipe, a horizontal pipe and an ascending pipe, a plurality of nodes are arranged in the middle-deep-layer U-shaped heat exchange well and around the middle-deep-layer U-shaped heat exchange well, temperature information of nodes at a circulating fluid inlet and around rock nodes at the initial moment is collected, and the collected temperature information is substituted into a prediction model formed by node equations of the nodes in the middle-deep-layer U-shaped heat exchange well, so that temperature information of nodes at other positions of the middle-deep-layer U-.
The invention has the beneficial effects that:
according to the method for predicting the temperature of the circulating fluid of the middle-deep U-shaped heat exchange well, temperature information of other nodes and specific time of the U-shaped heat exchange well can be obtained through the node equations of a plurality of nodes by acquiring the temperature information of the circulating fluid inlet and the initial time of the nodes of peripheral rock soil, the temperature of the circulating fluid at the corresponding position in the U-shaped heat exchange well can be mastered, the change rule of the temperature along with time can be mastered, a large number of temperature monitoring elements are not required to be arranged, equipment investment is reduced, observation and research of whether the temperature change of the circulating fluid is reasonable or not are facilitated, and the heat supply capacity of a heat exchanger.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate embodiments of the application and, together with the description, serve to explain the application and are not intended to limit the application.
Fig. 1 is a schematic structural view of a deep U-shaped heat exchange well in embodiment 1 of the present invention;
fig. 2 is a schematic node distribution diagram according to embodiment 1 of the present invention;
the method comprises the following steps of 1, a downcomer, 2, a horizontal pipe, 3, an ascending pipe, 4, a descending drill hole, 5, a horizontal drill hole, 6, an ascending drill hole, 7, rock soil, 8, the ground and 9, a backfill material.
Detailed Description
It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the 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 application 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 example embodiments according to the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.
For convenience of description, the words "up", "down", "left" and "right" in the present invention, if any, merely indicate correspondence with up, down, left and right directions of the drawings themselves, and do not limit the structure, but merely facilitate the description of the invention and simplify the description, rather than indicate or imply that the referenced device or element must have a particular orientation, be constructed and operated in a particular orientation, and thus should not be construed as limiting the invention.
As introduced by the background art, for the middle-deep layer U-shaped well heat exchanger, a large number of temperature monitoring elements are required to be arranged for temperature monitoring, the equipment investment is high, and the prediction of the temperature of the circulating liquid after a long time in the future cannot be performed.
In example 1 of a typical embodiment of the present application, a method for predicting temperature of circulating fluid in a heat exchanger of a middle-deep U-shaped well includes dividing a plurality of nodes in the middle-deep U-shaped heat exchange well and around the heat exchange well, collecting temperature information of nodes at a circulating fluid inlet and around the nodes at the initial time, and substituting the collected temperature information into a prediction model formed by node equations of the nodes in the middle-deep U-shaped heat exchange well to obtain temperature information of circulating fluid nodes at other positions of the middle-deep U-shaped heat exchange well and around the other time.
As shown in fig. 1, the heat exchanger of the U-shaped well in the middle deep layer is buried in rock soil 7 and comprises three pipe sections, namely a down pipe 1, a horizontal pipe 2 and an up pipe 3, wherein the down pipe is positioned in a down hole 4, the horizontal pipe is positioned in a horizontal hole 5, the up pipe is positioned in an up hole 6, and backfill materials 9 are arranged between the pipe walls of the down pipe, the horizontal pipe and the up pipe and the hole wall of the hole. The downcomers and risers extend above ground level 8.
When the circulating liquid of the heat exchanger of the middle-deep U-shaped well works, the circulating liquid flows in from the top end of the downcomer, passes through the downcomer, the horizontal pipe and the riser and flows out from the top end of the riser.
The node arrangement is as shown in figure 2, the node arrangement method in the middle-deep layer U-shaped well heat exchanger is that the distance step length between two adjacent nodes is determined △ z according to actual needs, the length of a down pipe is H1The length of the horizontal pipe is H2The length of the riser pipe is H3. And (3) taking the ratio of the length of each pipe section to the distance step length, and then taking an integer part to obtain the number of the nodes of each pipe section.
The total number of nodes n in the downcomer, the horizontal pipe and the riser1、n2、n3Are respectively H1/△z、H2/△z、H3The value of/△ z being an integer part, e.g. H1If/△ z is 100.7, then n1Using the same method to obtain n as 1002、n3. The descending pipe is provided with nodes in sequence from the circulating liquid inlet position, the horizontal pipe is provided with nodes in sequence from the circulating liquid inlet position, and the ascending pipe is provided with nodes in sequence from the circulating liquid inlet position.
The nodes in the downcomer, horizontal and riser are numbered.
In the downcomer, the node at the inlet position of the circulating liquid of the downcomer is a No. 0 node, and the other nodes are numbered as No. 1, No. 2, No. … k, No. … n in sequence according to the flowing direction of the circulating liquid1Node number, where k is greater than or equal to 0 and less than or equal to n1。
In the horizontal pipe, the node at the inlet position of the circulating liquid in the horizontal pipe is the node No. 0, and the other nodes are numbered as No. 1, No. 2, No. … k, No. … n according to the flowing direction of the circulating liquid2Node number, where k is greater than or equal to 0 and less than or equal to n2。
In the ascending pipe, the node of the circulating liquid inlet position of the ascending pipe is n3Number node, the rest are sequentially connected according to the flowing direction of the circulating liquidNode number n3Number-1, n3Node No. … 0 of-2 … k, where 0 ≦ k ≦ n3。
The rock soil around the downcomer, the horizontal pipe and the ascending pipe is also divided into a plurality of nodes.
A plurality of nodes of the peripheral rock soil of the downcomer are arranged along the axis direction of the downcomer, the distance step length of the two adjacent nodes is the same as that of the two adjacent nodes in the downcomer, and the serial numbers of the two nodes positioned on the same horizontal plane in the downcomer and the nodes of the peripheral rock soil are the same, namely, the nodes of the rock soil corresponding to the node k in the downcomer are positioned on the same horizontal plane, and the serial numbers are also the node k.
A plurality of nodes of the peripheral rock soil of the horizontal pipe are arranged along the axis direction of the horizontal pipe, the distance step length of the two adjacent nodes is the same as that of the two adjacent nodes in the horizontal pipe, and the serial numbers of the two nodes positioned on the same vertical surface in the horizontal pipe and the nodes of the peripheral rock soil of the horizontal pipe are the same, namely, the nodes of the rock soil corresponding to the node k in the horizontal pipe are positioned on the same vertical surface with the node k, and the serial numbers of the nodes are also the number k.
A plurality of nodes of the peripheral rock soil of the ascending pipe are arranged along the axial direction of the ascending pipe, the distance step length of the two adjacent nodes is the same as that of the two adjacent nodes in the ascending pipe, and the serial numbers of the two nodes positioned on the same horizontal plane in the ascending pipe and the nodes of the peripheral rock soil are the same, namely, the nodes of the rock soil corresponding to the k-number nodes in the ascending pipe are positioned on the same horizontal plane, and the serial numbers are also k-numbers.
After the nodes are arranged on rock soil on the periphery of the U-shaped heat exchange well in the middle-deep layer and each pipeline thereof, a node equation is established for each node in the descending pipe, the horizontal pipe and the ascending pipe.
The method for establishing the node equations of the nodes in the downcomer, the horizontal pipe and the riser comprises the following steps: and establishing an energy control equation for each node inside the heat exchange well, and bringing the thermal resistance between the circulating liquid with a unit length and the hole wall of the drilled hole of the heat exchange well, the thermal capacity of a backfill material in the drilled hole of the heat exchange well and the mass flow specific heat capacity of the circulating liquid into the established energy control equation to obtain the node equation of each node.
The energy control equation of the node of the downcomer is as follows:
Figure BDA0002489889900000061
wherein C is1Is the sum of the thermal capacities of the backfill material in the down-hole per unit length, R1Is the thermal resistance between the wall of the descending borehole per unit length and the circulating fluid, tf1Is the temperature value of the circulating liquid in the downcomer, tb1The temperature value of the hole wall rock soil drilled by the downcomer is shown, z is a vertical coordinate value of a k-number node in the downcomer, and tau represents time.
Figure BDA0002489889900000071
Wherein d is1iIs the internal diameter of the downcomer, d1oOutside diameter of the downcomer, p1c1The volumetric specific heat capacity of the downcomer, db1To reduce the diameter of the borehole, pg1cg1The volumetric specific heat capacity, rho, of the backfill material in the downcomerwcwThe volume specific heat capacity of the circulating liquid can be measured in advance.
Figure BDA0002489889900000072
Wherein d is1iIs the internal diameter of the downcomer, d1oOutside diameter of the downcomer, λp1Is the heat conductivity coefficient of the downcomer, lambdag1The heat conductivity coefficient of the backfill material in the descending tube, h1The heat convection coefficient between the downcomer and the circulating liquid.
C＝mCw(kJ/s.K) (4)
m is the mass flow of the circulating liquid in the downcomer, CwSpecific heat capacity of the circulating liquid.
The equations (2), (3) and (4) are substituted into the energy control equation (1) of each node of the downcomer, and the node equation of each node in the downcomer can be obtained.
1) The node number at the circulating liquid inlet of the downcomer is 0, and k is 0
The node equation for node 0 is:
Figure BDA0002489889900000073
Figure BDA0002489889900000074
and
Figure BDA0002489889900000075
respectively represents the temperature of a k-type (0-type) node in the descending pipe and the ascending pipe at the p +1 moment,
Figure BDA0002489889900000076
indicating the temperature of the k-th (0) node in the downcomer at time p.
Figure BDA0002489889900000077
The temperature of the rock-soil node (the node on the ground) of the hole wall corresponding to the No. 0 node of the downcomer at the time point p is represented.
2).0＜k＜n1In time, the node equation of node k is:
Figure BDA0002489889900000081
Figure BDA0002489889900000082
represents the temperature of the node k-1 in the downcomer at the moment p +1,
Figure BDA0002489889900000083
represents the temperature of the k-node of the downcomer at the moment p +1,
Figure BDA0002489889900000084
indicating the temperature of the k-node in the downcomer at time p,
Figure BDA0002489889900000085
the temperature of the corresponding inner node of the rock and soil of the hole wall of the drill hole around the k-shaped node of the downcomer at the time p is represented.
3) The node number of the circulating liquid outlet of the downcomer is n1In this case, k is n1The nodal equation is:
Figure BDA0002489889900000086
Figure BDA0002489889900000087
represents the temperature of the node k-1 in the downcomer at the moment p +1,
Figure BDA0002489889900000088
denotes the downcomer k number (n)1Number) the temperature of the node at time p +1,
Figure BDA0002489889900000089
denotes the number k (n) in the downcomer1Number) node temperature at time p.
Wherein the content of the first and second substances,
Figure BDA00024898899000000810
c is the specific heat capacity of the mass flow of the circulating liquid, C1The sum of heat capacities of filling materials in a drill hole in which the downcomer is located, Q is the heat exchange amount born by the middle-deep U-shaped well, and the sum is preset, △ z is the distance step length of adjacent nodes, △ tau is the time step length set when the node temperature at the future moment is predicted, and R is1Is the thermal resistance between the circulating liquid in the downcomer and the wall of the borehole.
The energy control equation of the nodes in the horizontal pipe is as follows:
Figure BDA00024898899000000811
wherein C is2Is the sum of the heat capacities, R, of the backfill material in a horizontal borehole per unit length2Is the thermal resistance between the wall of the horizontal bore hole per unit length and the circulating fluid, tf2Is the temperature value of the circulating liquid in the horizontal pipe, tb2Temperature value, x, of a bore wall rock for drilling a horizontal pipeAnd tau represents time, and is the horizontal coordinate value of a k node in the horizontal pipe.
Figure BDA00024898899000000812
Wherein d is2iIs the inner diameter of the horizontal tube, d2oIs the outer diameter of the horizontal tube, ρ2c2Is the volumetric specific heat capacity of the horizontal tube, db2Diameter of horizontal bore hole, pg2cg2The volumetric specific heat capacity, rho, of the backfill material in the horizontal tubewcwThe volume specific heat capacity of the circulating liquid can be measured in advance.
Figure BDA0002489889900000091
Wherein d is2iIs the inner diameter of the horizontal tube, d2oOutside diameter of the downcomer, λp2Is the thermal conductivity, lambda, of the horizontal tubeg2Is the heat conductivity coefficient of the backfill material in the horizontal pipe, h2The heat convection coefficient between the horizontal pipe and the circulating liquid.
C＝mCw(kJ/s.K) (11)
m is the mass flow of the circulating liquid in the horizontal pipe, CwSpecific heat capacity of the circulating liquid.
Substituting equations (9), (10), (11) into equation (8) can obtain the node equation of each node in the downcomer.
1) The node number at the circulating liquid inlet of the horizontal pipe is 0, and k is 0
The node equation for node 0 is:
Figure BDA0002489889900000092
Figure BDA0002489889900000093
represents the temperature of the k-number (0) node in the horizontal pipe at the moment of p +1,
Figure BDA0002489889900000094
is a node (n) at the circulating liquid outlet of a downcomer1Number) temperature at time p + 1.
2)0＜k＜n2In time, the node equation of node k is:
Figure BDA0002489889900000095
Figure BDA0002489889900000096
and
Figure BDA0002489889900000097
respectively shows the temperature of the node k-1 and the node k at the moment p +1 of the horizontal pipe,
Figure BDA0002489889900000098
the temperature of the inner node of the rock and soil of the hole wall of the peripheral borehole corresponding to the k node in the horizontal pipe at the time of p is shown,
Figure BDA0002489889900000099
indicating the temperature of the k-node in the horizontal pipe at time p.
3) The node number of the circulating liquid outlet of the horizontal pipe is n2In this case, k is n2The nodal equation is:
Figure BDA0002489889900000101
Figure BDA0002489889900000102
and
Figure BDA0002489889900000103
respectively represent node k-1 and node k (n)2Number) the temperature of the node at time p +1,
Figure BDA0002489889900000104
denotes the number k (n) in the horizontal tube2Number) node corresponding peripheral borehole wall rockThe temperature of the node in the soil at time p,
Figure BDA0002489889900000105
denotes the number k (n) in the horizontal tube2Number) node temperature at time p.
Figure BDA0002489889900000106
C is the specific heat capacity of the mass flow of the circulating liquid, C2Q is the heat exchange amount born by the U-shaped well in the middle deep layer, △ z is the distance step length of adjacent nodes, △ tau is the time step length set when the node temperature at the future moment is predicted, and R is the sum of the heat capacities of filling materials in the drill hole in which the horizontal pipe is positioned2Is the thermal resistance between the circulating liquid in the horizontal pipe and the wall of the hole of the drill hole.
The nodal energy control equation in the riser is:
Figure BDA0002489889900000107
wherein C is3Is the sum of the heat capacities of the backfill material per unit length of the raised borehole, R3Is the thermal resistance between the wall of the raised borehole per unit length and the circulating fluid, tf3Is the temperature value of the circulating liquid in the riser, tb3The temperature value of hole wall rock soil drilled in the ascending pipe is shown, z is a vertical coordinate value of a k node in the ascending pipe, and tau represents time.
Figure BDA0002489889900000108
Wherein d is3iFor the inner diameter of the riser, d3oIs the outside diameter of the riser, ρ3c3Is the volumetric specific heat capacity of the riser, db3To increase the diameter of the borehole, pg3cg3The volumetric specific heat capacity, rho, of the backfill material in the riserwcwThe volume specific heat capacity of the circulating liquid can be measured in advance.
Figure BDA0002489889900000109
Wherein d is3iFor the inner diameter of the riser, d3oIs the outer diameter of the riser pipe, lambdap3Is the heat conductivity coefficient, lambda, of the riserg3The heat conductivity of the backfill material in the riser, h3The heat convection coefficient of the ascending pipe and the circulating liquid.
C＝mCw(kJ/s.K) (18)
m is the mass flow of the circulating liquid in the riser, CwSpecific heat capacity of the circulating liquid.
Substituting the equations (16), (17) and (18) into the equation (15) can obtain the node equation of each node in the downcomer.
1) The circulating liquid inlet node of the riser is numbered n3Number k ═ n3
The node equation for node 0 is:
Figure BDA0002489889900000111
Figure BDA0002489889900000112
the temperature of the k-node of the rising pipe at the moment p +1,
Figure BDA0002489889900000113
the temperature of the node at the outlet of the circulating liquid of the horizontal pipe at the moment p + 1.
2)0＜k＜n3In time, the node equation of node k is:
Figure BDA0002489889900000114
Figure BDA0002489889900000115
and
Figure BDA0002489889900000116
respectively represents the temperature of a node k +1 and a node k of the ascending pipe at the moment p +1,
Figure BDA0002489889900000117
represents the temperature of the k-node of the riser at time p,
Figure BDA0002489889900000118
and the temperature of the rock-soil inner node of the hole wall of the drill hole on the periphery corresponding to the k node of the ascending pipe at the moment p is shown.
3) The node number of the circulating liquid outlet of the ascending pipe is No. 0, at the moment, k is 0, and the node equation is as follows:
Figure BDA0002489889900000119
Figure BDA00024898899000001110
and
Figure BDA00024898899000001111
respectively represents the temperature of a node k +1 and a node k of the ascending pipe at the moment p +1,
Figure BDA00024898899000001112
represents the temperature of the k-node of the riser at time p,
Figure BDA00024898899000001113
and (3) representing the temperature of a node p in the rock and soil of the peripheral drilling hole wall corresponding to the ascending pipe circulating liquid inlet node.
Figure BDA00024898899000001114
C is the specific heat capacity of the mass flow of the circulating liquid, C3Q is the heat exchange amount born by the U-shaped well in the middle deep layer, △ z is the distance step length of adjacent nodes, △ tau is the time step length set when the node temperature at the future moment is predicted, and R is the sum of the heat capacities of the filling materials in the drill hole in which the ascending pipe is positioned3Is the thermal resistance between the circulating liquid in the riser and the wall of the borehole.
And (3) forming a prediction model by combining equations of formula (5), formula (6), formula (7), formula (12), formula (13), formula (14), formula (19), formula (20) and formula (21).
The initial moment is 0 moment, namely p is 0, temperature information of nodes in rock and soil at the periphery drill hole wall corresponding to a descending pipe circulating liquid inlet (namely a descending pipe node 0) and a descending pipe node 0 at the 0 moment is acquired by using external temperature acquisition equipment, the cut-off moment of the predicted temperature is set (namely the calculation of how many time steps are required to be carried out is set), and after the set of equations is substituted, the set of equations solves the temperature information of all the nodes in the descending pipe, the horizontal pipe and the ascending pipe and the information of a plurality of step length moment nodes by adopting a catch-up method.
In this embodiment, the zero point of the coordinate system of the node energy control equation in the Z direction is located on the ground, and the zero point in the X direction is located at the midpoint of the connecting line of the axes of the downcomer and the riser.
The temperature information of a plurality of positions of the circulating liquid and a plurality of moments in the future can be obtained by collecting information of one point, the change rule of the circulating liquid along with the temperature and the positions can be conveniently mastered, and the heat supply capacity of the U-shaped well in the middle and deep layers can be known. And a plurality of temperature detection elements are not required to be configured, so that the equipment investment is reduced.
Although the embodiments of the present invention have been described with reference to the accompanying drawings, it is not intended to limit the scope of the present invention, and it should be understood by those skilled in the art that various modifications and variations can be made without inventive efforts by those skilled in the art based on the technical solution of the present invention.

Claims (10)

1. A method for predicting the temperature of circulating liquid of a middle-deep U-shaped heat exchange well comprises a descending pipe, a horizontal pipe and an ascending pipe and is characterized in that a plurality of nodes are arranged in the middle-deep U-shaped heat exchange well and around rock soil, temperature information of the nodes at the inlet of the circulating liquid and around rock soil nodes at the initial moment is collected, the collected temperature information is substituted into a prediction model formed by node equations of the nodes in the middle-deep U-shaped heat exchange well, and temperature information of other position nodes and other moments of the middle-deep U-shaped heat exchange well is obtained.
2. The method for predicting the temperature of the circulating liquid of the middle-deep U-shaped heat exchange well according to claim 1, wherein the temperature information of the heat exchange well at the initial time of the circulating liquid inlet and the peripheral rock-soil node is substituted into the prediction model, and then the temperature information of the nodes at other positions of the heat exchange well and other times is solved by adopting a catch-up method.
3. The method for predicting the temperature of the circulating liquid of the middle-deep-layer U-shaped heat exchange well according to claim 1, wherein the middle-deep-layer U-shaped heat exchange well nodes are arranged in a mode that: and determining the distance step length of adjacent nodes, taking an integer from the ratio of the length of each pipe section of the heat exchange well to the distance step length to obtain the number of the nodes, and arranging a plurality of nodes along the axial direction of the pipe sections of the heat exchange well.
4. The method for predicting the temperature of the circulating fluid of the middle-deep U-shaped heat exchange well according to claim 3, wherein the arrangement mode of the inner nodes of the peripheral rock soil of the middle-deep U-shaped heat exchange well is as follows: the plurality of nodes are arranged in a dividing mode along the axis direction of each pipe section of the heat exchange well, and the distance step length of every two adjacent nodes is equal to that of every two adjacent nodes in the heat exchange well.
5. The method for predicting the temperature of the circulating liquid of the middle-deep U-shaped heat exchange well according to claim 4, wherein the nodes in the downcomer, the horizontal pipe and the riser and the nodes in the peripheral rock and soil are numbered, wherein the nodes in the downcomer, the horizontal pipe and the riser and the peripheral rock and soil which are positioned on the same horizontal plane are numbered the same, and the nodes in the horizontal pipe and the peripheral rock and soil which are positioned on the same vertical plane are numbered the same.
6. The method for predicting the temperature of the circulating liquid of the middle-deep U-shaped heat exchange well as recited in claim 1, wherein the node equation is established by the following steps: and establishing an energy control equation for each node of the middle-deep layer U-shaped heat exchange well, and bringing the thermal resistance between the unit length of the circulating liquid and the hole wall of the drilled hole of the heat exchange well, the thermal capacity of the backfill material in the drilled hole of the heat exchange well and the mass flow specific heat capacity of the circulating liquid into the established energy control equation to obtain the node equation of each node.
7. The method for predicting the temperature of the circulating liquid of the middle-deep U-shaped heat exchange well as recited in claim 6,
the energy control equation of the inner node of the downcomer is as follows:
Figure FDA0002489889890000021
the energy control equation of the nodes in the horizontal pipe is as follows:
Figure FDA0002489889890000022
the energy control equation of the nodes in the ascending pipe is as follows:
Figure FDA0002489889890000023
c is the specific heat capacity of the mass flow of the circulating liquid, C1、C2、C3The sum of the heat capacities of the filling materials in the drill holes in which the downcomer, the horizontal pipe and the riser are respectively positioned, R1、R2、R3Thermal resistances between the circulating liquid in the downcomer, the horizontal pipe and the riser and the wall of the borehole, tf1、tf2、tf3The temperatures of circulating liquid in the downcomer, the horizontal pipe and the riser are respectively; t is tb1、tb2、tb3The temperatures of the hole wall rock soil of the drill holes of the downcomer, the horizontal pipe and the ascending pipe respectively.
8. The method for predicting the temperature of the circulating liquid of the middle-deep U-shaped heat exchange well as recited in claim 1,
the node equation at the circulating liquid inlet of the downcomer is as follows:
Figure FDA0002489889890000024
the node equation at the circulating liquid outlet of the downcomer is as follows:
Figure FDA0002489889890000025
the node equations at the other nodes of the downcomer are:
Figure FDA0002489889890000026
Figure FDA0002489889890000027
and
Figure FDA0002489889890000028
respectively shows the temperature of k nodes of the descending pipe and the ascending pipe at the moment of p +1,
Figure FDA0002489889890000029
represents the temperature of the k-node of the downcomer at the moment p,
Figure FDA00024898898900000210
the temperature of the inner node of the rock and soil on the wall of the drill hole corresponding to the periphery of the inlet node of the circulating liquid of the downcomer at the moment p is shown,
Figure FDA00024898898900000211
represents the temperature of the node k-1 of the downcomer at the moment p +1,
Figure FDA00024898898900000212
the temperature of the inner node of the rock-soil of the hole wall of the drill hole around the k-shaped node of the downcomer at the moment p is represented;
wherein the content of the first and second substances,
Figure FDA0002489889890000031
c is the specific heat capacity of the mass flow of the circulating liquid, C1Q is the sum of heat capacities of filling materials in the drill hole in which the downcomer is located, and Q is a U-shaped shape of a middle deep layerThe heat exchange quantity borne by the well, △ z is the distance step of adjacent nodes, △ tau is the time step, R1Is the thermal resistance between the circulating liquid in the downcomer and the wall of the borehole.
9. The method for predicting the temperature of the circulating liquid of the middle-deep U-shaped heat exchange well as recited in claim 1,
the node equation of the node at the inlet of the circulating liquid of the horizontal pipe is as follows:
Figure FDA0002489889890000032
the node equation of the node at the outlet of the horizontal pipe circulating liquid is as follows:
Figure FDA0002489889890000033
the equations for the remaining nodes of the level pipe are:
Figure FDA0002489889890000034
Figure FDA0002489889890000035
representing the temperature at time p +1 of the fluid node with index k in the horizontal pipe,
Figure FDA0002489889890000036
the temperature of a node at the circulating liquid outlet of the downcomer at the moment p +1, n1Is the total number of the descending pipe nodes,
Figure FDA0002489889890000037
and
Figure FDA0002489889890000038
respectively shows the temperature of the node k-1 and the node k at the moment p +1 of the horizontal pipe,
Figure FDA0002489889890000039
represents the number k in the horizontal tubeThe temperature of the inner node of the rock soil of the peripheral drilling hole wall corresponding to the node at the moment p,
Figure FDA00024898898900000310
representing the temperature of a k node in the horizontal pipe at the moment p;
Figure FDA00024898898900000311
c is the specific heat capacity of the mass flow of the circulating liquid, C2Is the sum of heat capacities of filling materials in the drill hole in which the horizontal pipe is positioned, Q is the heat exchange amount born by the U-shaped well in the middle deep layer, △ z is the distance step length of adjacent nodes, △ tau is the time step length, R is the time step length2Is the thermal resistance between the circulating liquid in the horizontal pipe and the wall of the hole of the drill hole.
10. The method for predicting the temperature of the circulating liquid of the middle-deep U-shaped heat exchange well as recited in claim 1,
the node equation of the node at the inlet of the circulating liquid of the ascending pipe is as follows:
Figure FDA00024898898900000312
the node equation of the node at the circulating liquid outlet of the ascending pipe is as follows:
Figure FDA0002489889890000041
the node equation of nodes at other positions of the ascending pipe is as follows:
Figure FDA0002489889890000042
Figure FDA0002489889890000043
the temperature of the k-node of the rising pipe at the moment p +1,
Figure FDA0002489889890000044
is a horizontal pipe circulating liquid outlet jointTemperature at point p +1, n2In order to be the number of horizontal pipe nodes,
Figure FDA0002489889890000045
and
Figure FDA0002489889890000046
respectively represents the temperature of a node k +1 and a node k of the ascending pipe at the moment p +1,
Figure FDA0002489889890000047
represents the temperature of the k-node of the riser at time p,
Figure FDA0002489889890000048
the temperature of the inner node of the peripheral rock soil corresponding to the k node of the ascending pipe at the time p is shown,
Figure FDA0002489889890000049
and (4) representing the temperature of a node p in the hole wall of the peripheral rock-soil drilling hole corresponding to the ascending pipe circulating liquid inlet node.
Figure FDA00024898898900000410
C is the specific heat capacity of the mass flow of the circulating liquid, C3Q is the heat exchange amount born by the U-shaped well in the middle deep layer, △ z is the distance step length of the adjacent nodes, △ tau is the time step length, R is the sum of the heat capacities of the filling materials in the drill hole in which the ascending pipe is positioned3Is the thermal resistance between the circulating liquid in the riser and the wall of the borehole.
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