CN106354984B - Temperature response calculation method of pile foundation spiral buried pipe under underground water seepage condition - Google Patents
Temperature response calculation method of pile foundation spiral buried pipe under underground water seepage condition Download PDFInfo
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Abstract
The invention discloses a temperature response calculation method of a pile foundation spiral buried pipe under an underground water seepage condition, which is a temperature response calculation method of a single pile foundation spiral buried pipe in an underground medium under the underground water three-dimensional seepage condition according to the temperature response of a heat source in the medium when underground water flows at an infinite uniform medium at a three-dimensional speed. When groundwater flows through the pile-buried pipe group at a three-dimensional speed, the temperature response generated at any point in the underground medium at any moment is the superposition of the effects of groundwater seepage and heat exchange of the pile-buried pipe group, and a calculation formula of the temperature response can be obtained. And in the process of obtaining the groundwater seepage velocity, setting the range of the groundwater flow velocity and the direction, continuously extracting numerical values from the range, arranging points around the drill hole, solving the sum of the variance of the calculated value and the experimental value of all the points in a certain time period, and obtaining the actual flow velocity and the actual direction of the groundwater when the sum of the variance of a plurality of the points reaches the minimum.
Description
Technical Field
The invention belongs to the technical field of construction environment and energy application professional engineering, and particularly relates to a temperature response calculation method of a pile foundation spiral buried pipe under a groundwater seepage condition.
Background
The ground source heat pump technology takes underground medium as a cold and heat source, and heat is discharged to the underground in summer and absorbed from the underground in winter respectively. The temperature of the underground medium fluctuates little all the year round, and is an ideal cold and heat source, so the heat pump has the advantages of energy saving and environmental protection, belongs to a renewable energy air conditioning system, and is widely applied. The geothermal heat exchanger part is a main mark of a ground source heat pump system different from other types of heat pump systems, and a mode of drilling and embedding a U-shaped heat exchange tube is usually adopted at present, so that the initial investment is too high, a certain amount of ground area is required to arrange the drilled holes, and the two defects become main obstacles for restricting the development of the ground source heat pump.
With the development of research on geothermal heat exchangers, bearing members of buildings, i.e. pile foundations, are considered for embedding heat exchange tubes, thereby creating a novel geothermal heat exchanger, which is called a "pile-in-pipe heat exchanger". The diameter of the pile foundation is far larger than that of the drilled hole, and the spiral pipe is usually arranged inside the pile foundation instead of the U-shaped pipe, so that the heat exchange capacity of the buried pipe per meter of pile is obviously stronger than that of the drilled hole. Because the number of pile foundations of the building is limited, the geothermal heat exchanger of the whole system can be composed of the energy piles and the drilling buried pipes, the energy piles bear part of cold and heat loads to the maximum extent, and the rest loads are taken charge of the drilling buried pipes, so that the cost of drilling is greatly reduced, and the ground area for arranging the drilling is also reduced.
As the length of the pile foundation exceeds ten meters and even reaches dozens of meters, the seepage phenomenon of underground water cannot be ignored, and particularly in areas with larger hydraulic gradient or abundant underground water resources, the influence of the seepage is more important. When underground water flows through the energy piles, the heat transfer mode of the pile foundation and the surrounding underground medium is changed from single pure heat conduction into composite heat exchange containing heat conduction and convection. The flow of underground water relieves the heat accumulation around the pile foundation, improves the heat transfer performance of the pile buried pipe and improves the heat exchange quantity of the pile buried pipe per meter. In the heat transfer process of the pile buried pipe, the temperature of the surrounding medium is constantly changed under the influence of the surrounding medium, and when the groundwater seepage phenomenon occurs, the temperature response degree of the underground medium is slowed down under the influence of the groundwater, which means that the groundwater reduces the influence of the heat transfer of the pile buried pipe on the underground space.
At present, the research on the pile buried pipe under the condition of groundwater seepage is less, and no method for calculating the medium temperature response of groundwater in the ground when the groundwater seeps in an underground space at a three-dimensional speed exists.
Disclosure of Invention
The invention provides a temperature response calculation method of a pile foundation spiral buried pipe under the condition of underground water seepage in order to solve the problems.
In order to achieve the purpose, the invention adopts the following technical scheme:
a temperature response calculation method of a pile foundation spiral buried pipe under the condition of groundwater seepage comprises the following steps:
(1) on the premise that underground water flows through an infinite uniform medium at a three-dimensional speed, temperature response of a point heat source which is positioned in the medium and radiates heat at a certain strength at any point in the medium is confirmed;
(2) constructing a temperature response heat transfer model when underground water flows through a single pile buried pipe at a three-dimensional speed, and obtaining the temperature response of any point except the spiral pipe in a semi-infinite medium after a heat exchange pipe with a certain spiral distance, spiral radius and length is buried in a pile foundation to form a pile foundation spiral buried pipe geothermal heat exchanger;
(3) measuring points are arranged around the borehole heat exchanger for temperature response test, a finite long-line heat source seepage model is utilized to calculate the flow rate of underground water in a reverse direction, and a temperature response result is calculated by combining the constructed response model.
In the step (1), the Green function is changed according to the Green function of the point heat source generating temperature response in the infinite medium in a pure heat conduction mode, and the temperature response caused by the point heat source when the underground water flows through the underground medium in a three-dimensional flowing mode is obtained.
In the step (1), on the premise that the underground water flows through an infinite uniform medium at a three-dimensional speed, the distribution of the underground medium is uniform and the porosity of the underground medium is consistent, and the temperature response of a point heat source located at (x ', y, z') at a certain time at any point (x, y, z) in the infinite space is calculated according to the porosity, the volume specific heat capacity of the underground solid medium, the volume specific heat capacity of the underground water, and the heat conductivity of the underground solid medium and the underground water.
In the step (2), after the spiral heat exchange tubes are arranged on the pile foundation, when underground water flows through a single pile buried tube at a three-dimensional flow rate, the influence of heat conduction and convection is comprehensively considered, an energy equation is established, and corresponding initial and boundary conditions are listed; the influence of the constant temperature of the ground on the spiral buried pipe of the limited long pile foundation is considered, and the influence of each parameter of the spiral pipe and the pile foundation in the heat exchange process is considered.
In the step (2), a virtual heat source method is utilized, namely a spiral pipe which can constantly generate heat exists in the underground medium, a spiral pipe which can constantly absorb heat exists in the virtual other half infinite medium which takes the ground as a symmetrical plane, namely, a spiral line heat source and a spiral line heat sink exist at the same time, so that after a temperature response expression of the pile foundation spiral buried pipe geothermal heat exchanger with limited length on the underground medium under the three-dimensional underground water seepage condition is obtained, the temperature response of any point in the underground medium at any time except for the heat exchange pipe when the three-dimensional underground water flows through a single pile foundation spiral buried pipe can be calculated.
In the step (2), according to the temperature response of a single pile foundation spiral buried pipe at any point (x, y, z) in the underground space except the spiral pipe under the condition of groundwater seepage, the temperature response of a pile foundation buried pipe group at the point is determined by considering the superposition of the temperature responses of a plurality of pile foundation buried pipes at the point and combining the spacing and the arrangement mode of the pile buried pipes.
In the step (3), the specific process includes:
and (3-1) uniformly arranging measuring points along the periphery of the borehole heat exchanger and the depth direction, and installing thermocouples or thermal resistors at the measuring points.
(3-2) setting the range of the flow velocity and the direction angle of the underground water, and extracting data from the set range;
(3-3) calculating the excess temperature of points distributed around the drill hole by adopting a drilling and pipe burying underground water seepage calculation model;
(3-4) calculating the variance between the theoretical calculation value and the actual value of each arrangement point, judging whether the variance sum of the arrangement points which accord with the set value number reaches the minimum value, if so, outputting the current flow velocity and direction of the underground water, and if not, continuously extracting the numerical value from the range of the flow velocity and the direction of the underground water for iterative calculation.
And in the step (3-1), arranging corrosion-resistant thermocouples or thermal resistors around the borehole heat exchanger, and recording the change of the temperature of the arranged points along with time by using a data acquisition instrument.
And (3-2) continuously extracting the flow velocity and the angle within respective ranges, and substituting the flow velocity and the angle into a finite long-line heat source seepage model for calculation.
And (3) in the step (3-3), calculating and obtaining the temperature response value of the arranged points around the drill hole by utilizing a relatively mature finite long-line heat source seepage model of the drill hole buried pipe under the condition of groundwater seepage and combining the magnitude and the direction of the groundwater flow velocity continuously extracted in the step (3-2).
in the step (3-4), the variance sum is made to take the first derivatives of the magnitude u of the groundwater flow speed and the two direction angles α and beta, when the three first derivatives are all smaller than the set value, the first derivative is considered to be approximately zero, and at this time, the variance sum at the point has reached the minimum.
The invention has the beneficial effects that:
(1) when the pile foundation spiral buried pipe is used as a geothermal heat exchanger to exchange heat with underground media, after the seepage effect of underground water is considered, the temperature change of any position in the underground media except for the heat exchange pipe at any moment can be directly obtained by calculation, and a large number of thermal resistors or thermocouples do not need to be buried on site. The temperature change of an underground medium caused by a plurality of pile buried pipes under the underground water seepage condition is mastered by a calculation method for obtaining the temperature response of one pile buried pipe under the underground water seepage action;
(2) the heat exchange capacity of the geothermal heat exchanger is enhanced by the seepage of the underground water, the heat exchange amount of the heat exchanger per meter is increased, the relationship between the heat exchange amount of the pile foundation spiral buried pipe and the flow velocity of the underground water is revealed through the technical scheme of the invention, and the influence of different underground water flow velocities on pile foundation buried pipes with different geometric size parameters is analyzed;
(3) the economical efficiency of the whole ground source heat pump air conditioning system is improved due to the seepage effect of the underground water, and the heat exchange quantity born by the pile foundation buried pipe is increased due to the seepage effect of the underground water, so that the cold and heat loads born by the drilling buried pipe can be reduced, and the investment cost of drilling can be reduced. The main purpose of adopting the pile-buried pipe is to reduce the initial investment of the system, further consider the influence of seepage and further contribute to the research of the pile-buried pipe;
(4) in order to be matched with the application of the calculation method, the seepage velocity of the underground water must be obtained firstly, and the flow velocity of the underground water can be obtained without direct measurement by providing a reverse reasoning calculation method. Seepage velocity is usually small, direct measurement is difficult, and underground environment is complex and difficult to arrange instruments for measuring flow velocity. Therefore, the method is also of great significance for obtaining the seepage velocity of the underground water;
(5) the temperature response of any point in the underground medium is the result of the combined action of the pile-buried pipe groups with certain arrangement shapes under the underground water seepage condition, the actions of the pipe groups arranged in different shapes are different at the same point and at the same seepage speed, and the difference of the generated temperature responses of the pipe groups in various arrangement modes at the same underground water seepage speed can be analyzed according to a calculation method of the temperature response, so that the arrangement modes of the pipe groups are optimized.
Drawings
FIG. 1 is a schematic diagram of heat exchange of a pile foundation spiral buried pipe under a groundwater seepage condition;
FIG. 2 is a schematic diagram showing an angle between the seepage velocity of groundwater and a coordinate axis;
FIG. 3 is a schematic view of the arrangement of the measurement points around the borehole;
fig. 4 is a schematic flow chart of the reverse reasoning algorithm.
Wherein: 1 starting point h of spiral tube 12 underground water seepage, 3 building pile foundation, 4 spiral heat exchange tubes, 5 underground medium and 6 spiral tube end point h 27 spiral tube distance b,8 groundwater seepage, 9 an included angle β between the groundwater seepage speed and the Z axis, 10 an included angle beta between the projection of the groundwater seepage speed on the XOZ surface and the X axis, 11 drilled holes and 12 measured points arranged around the drilled holes.
The specific implementation mode is as follows:
the invention will be further explained with reference to the drawings.
The pile foundation and the spiral heat exchange tube buried in the pile foundation all have corresponding geometric dimensions, and the diameter and the length of the pile foundation, the spiral diameter, the spiral space, the spiral length and other parameters all influence the heat exchange of the pile buried tube. The subterranean medium can be considered to be a homogeneous medium having the same thermophysical parameters. The invention provides an analytic calculation method for temperature response generated by an energy pile under the condition of groundwater seepage, which can obtain the temperature response at any point in an underground medium except a spiral heat exchange pipe under the action of heat conduction and convection composite heat exchange when groundwater flows through a pile foundation spiral buried pipe with different geometric parameters.
In addition, the flow velocity of the underground water is a vector comprising the magnitude and the direction, the direct measurement of the flow velocity is very difficult work, and the seepage velocity of the underground water is small and is not easy to measure. Therefore, the invention discloses a reverse reasoning method for calculating the seepage velocity of underground water, including the size and the direction of the underground water. The obtained groundwater flow speed is substituted into the method for calculating the temperature response of the underground medium, and the temperature change of the underground medium at any point and any time can be obtained. According to the invention, the relationship between the heat exchange quantity of the pile foundation spiral buried pipe and the flow velocity of underground water can be analyzed.
The heat exchange of the pile foundation spiral buried pipe heat exchanger under the condition of groundwater seepage requires the relevant dimensional parameters and the thermophysical parameters of the underground medium to be determined. FIG. 1 is a schematic diagram of a pile foundation buried pipe under the condition of groundwater seepage, circulating liquid flows back and forth between a spiral heat exchange pipe and a heat pump unit, and the temperature and the flow of an inlet and an outlet of the pile foundation buried pipe when the circulating liquid flows through the spiral heat exchange pipe can be measured by a thermometer and a flowmeter, so that the heat exchange quantity q per meter of the pile foundation buried pipe can be calculatedl。
The subsurface medium is uniformly distributed and has a porosity of epsilon. RhoscsIs the volumetric specific heat capacity, ρ, of the subsurface solid mediumwcwIs the volumetric specific heat capacity of groundwater. k is a radical ofsAnd kwRespectively representing the thermal conductivity of the solid underground medium and the underground water. Thus, the total volumetric specific heat capacity and thermal conductivity of the subsurface medium is shown in equation (1):
the velocity u of groundwater seepage is a vector including magnitude and direction, its velocity division in the x, y and z directionsDegree is respectively u1,u2And u3. The spiral pipe is buried in the pile foundation, the radius and the distance of the spiral pipe are r0And b of the first and second groups,
representing its helix angle. The initial position and the final position of the heat exchange tube from the ground are respectively h1And h2Therefore, the corresponding helix angles are:
and
the helical tubes are helically wound at intervals and angles along the pile foundation surface. q. q.slThe heat transfer quantity of each meter of the pipe laying heat exchanger is obtained. In the actual heat exchange process, circulating liquid enters along the spiral pipe and then flows out along the central straight pipe section to return to the heat pump unit. The initial temperature and the non-initial temperature of the underground medium are respectively t0And t, in the whole heat exchange process, the temperature of the ground is kept constant, and the thermophysical parameters of the underground medium and the underground water are kept unchanged. (x ', y, ' z ') represents the coordinates of any point on the heat source of the spiral pipe, and (x, y, z) represents the coordinates of any point in the subsurface medium other than the heat source. Tau refers to any time period in the heat exchange process; t-t ═ t0The excess temperature is also called as temperature response, namely the temperature change of any point in the underground medium at any time caused by the pile burying pipe under the condition of underground water seepage.
According to analysis, a mathematical model is established for the heat transfer process of the pile foundation spiral buried pipe geothermal heat exchanger under the condition of groundwater seepage, and the mathematical model comprises an energy equation and corresponding initial and boundary conditions. As shown in formula (2), r is the radial distance from any point in the underground medium to the central axis of the pile foundation buried pipe, and δ (x-x ', y-y ', z-z ') is the dirac function.
According to the formula (2), the temperature response of any point in the underground medium except the heat exchange pipe at any time can be calculated, and the temperature response is also the heat influence on the underground space when the pile foundation spiral buried pipe and the underground medium exchange heat under the action of underground water seepage. The geometric parameters of the pile foundation and the spiral pipe can be arbitrarily selected, and as long as the structural size of a certain pile foundation spiral pipe-laying heat exchanger and the flow rate of underground water are known, the temperature response value can be obtained according to the formula (2); it is also within the meaning of the invention that it can be used to calculate the temperature response of any size of pipe in a pile. The number of the pile foundations of the building is a plurality, which means that the number of the spiral pipe laying heat exchangers of the pile foundations is a plurality, if the drill pipe laying heat exchangers are not considered, the temperature response of any point in the underground medium is the superposition of the temperature response generated by the pile pipes at the point, so the total temperature response generated by the pile pipes can be superposed according to the calculation method of one pile pipe laying in the groundwater seepage process.
The groundwater flow velocity is vector, the magnitude and direction of which depend on the local hydraulic gradient, and the magnitude of which is usually in the range of 10-8m/s～10-1the research of the current borehole buried pipe in the groundwater seepage is mature, a finite long-line heat source seepage model can be used for calculating the temperature response of the borehole buried pipe geothermal heat exchanger in the surrounding underground medium under the groundwater seepage condition, in order to reversely calculate the flow velocity and the direction of the underground water, a theoretical calculation and experimental measurement mode can be adopted, the seepage velocity of the underground water is unknown, but the seepage velocity of the underground water is known within a certain range according to local hydraulic data, so the flow velocity range of the underground water is set firstly, in addition, the direction of the underground water is also unknown, as the hydraulic gradient is generally in three-dimensional distribution, the seepage velocity of the underground water is also in three-dimensional distribution, namely, the seepage velocity of the underground water has the component velocity along the x, y and z directions, the flow velocity direction is mainly determined by two parameters, namely, the included angle α between the flow velocity and the z axis, and the included angle beta between the projection of the flow velocity on the xoy surface and the x axis are β, and the specific values of the two angles are β, but the ranges of α and beta are not more than 0 and not more than pi 2.Uniformly arranging five points around the drill hole buried pipe, wherein the five points are equidistant from the center of the drill hole and have equal included angles with each other as shown in figure 3, and the five points are arranged along the periphery of the drill hole buried pipe in a horizontal plane; five points are uniformly arranged on the corresponding horizontal plane every several meters in the depth direction of the drilling hole, thermocouples are buried at the points, and the change of the temperature response along with the time can be obtained by the thermocouples. In addition, the flow velocity and the angle are continuously extracted within respective ranges and are substituted into a finite long-line heat source seepage model, and when the difference value between the temperature response obtained by calculation at each point and the temperature response measured by the thermocouple reaches the minimum, the flow velocity and the angle extracted from the ranges are the actual value of the groundwater seepage velocity; the corresponding calculation is shown in equation (3):
and k represents the sequence number of each moment in the data acquisition stage. Thetacal,kRepresents the temperature response calculated by a mathematical formula of a linear heat source seepage model at the kth moment, and thetaexp,kIt represents the experimentally collected temperature response value at the kth time. The time interval is set in the experimental process, and the data acquisition instrument records data at regular intervals, wherein the data comprises experimental data from the moment k to the moment n, wherein the moment k is 1. Equation (3) gives the sum of the variances of the experimental values and the theoretical calculated values at any one of the arranged points during the time period of data acquisition. When the sum of the variances of most points arranged around the drill hole reaches the minimum value at the same time, the value extracted from the range of the flow velocity size and the flow direction is the actual value, which means that the reverse reasoning calculation is carried out through continuous iteration until the flow velocity size and the flow direction of the underground water can be obtained when the sum of the variances reaches the minimum value.
According to the inlet temperature t of the circulating liquid flowing through the spiral heat exchange tube1And outlet temperature t2And the mass flow m of the circulating liquid and the depth h of the spiral pipe in the pile foundation2-h1And calculating the heat exchange quantity of each meter of spiral pipe, as shown in formula (4):
ql＝Cp×m×(t2-t1)/(h2-h1) (4)
the groundwater is percolated in a three-dimensional manner with the velocity quantities of the percolation velocity u in the x, y and z directions being u, respectively1,u2And u3The radius and the pitch of the spiral pipe are respectively r0And b, the helix angle is
The initial position and the final position of the heat exchange tube from the ground are respectively h1And h2The diameter and depth of the pile foundation are respectively rpAnd H. During the arrangement of the heat exchange pipes, the diameter of the spiral pipe is usually slightly smaller than that of the pile foundation, and a certain distance is kept between the pipe and the bottom of the pile foundation. The traditional Green function is deformed, and the temperature response caused by a point heat source when underground water flows through an underground medium in a three-dimensional flowing mode can be obtained:
equation (5) is a new Green function, U, after deformation on the basis of pure heat conduction1、U2And U3The component velocities of the groundwater along the x, y and z axes, respectively. For a point heat source located at (x ', y, z ') in a porous medium during groundwater seepage, the temperature response expression caused by heating from the moment tau ' until the moment tau at any point (x, y, z) in an infinite space still adopts the formula (5), except that the U in the formula (5) is used1＝u1ρwcw/ρc,U2＝u2ρwcw/ρc,U3＝u3ρwcwAnd/[ rho ] c. And u1、u2And u3Three partial velocities of actual groundwater.
In order to obtain the temperature response of the pile spiral buried pipe generated in the three-dimensional space, in the implementation process of the scheme of the invention, the pile buried pipe can be assumed to be infinitely long, the heat transfer along the depth direction can be ignored, and only the heat transfer along the x and y directions of the horizontal plane is considered, which means that the influence of the ground is ignored. According to the formulas (2) and (5), a temperature response calculation formula of the pile embedded pipe with infinite length under the condition of groundwater seepage can be obtained, as shown in the formula (6):
on the basis of the formula (6), the heat exchange of the finite long pile buried pipe during groundwater seepage is further considered, the temperature of the ground is constant, and the initial positions of the spiral pipes in the pile foundations are h respectively1And h2. The result of the pipe burying of the infinite long pile lays a foundation for the finite research.
According to the formulas (2) and (5), a virtual heat source method, a so-called virtual heat source method, is adopted, that is, a spiral pipe with constant heat generation exists in an underground medium, and a spiral pipe with constant heat absorption exists in a virtual semi-infinite medium taking the ground as a symmetrical plane. So that there are so-called helical heat sources and helical heat sinks. The single pile foundation spiral buried pipe exchanges heat with an underground medium from a time tau' under the condition of underground water seepage, and the calculation formula of the temperature response caused by any point (x, y, z) except the spiral pipe in the underground space at the time of tau is as follows:
wherein the content of the first and second substances,
z’＝z’。
formula (7) lists the temperature response of a finite length pile buried pipe caused by groundwater seepage, and for any point, the temperature response is the superposition of the temperature responses caused by a plurality of pile buried pipes or pile buried pipe groups at the point, so that the temperature response expression (8) caused by the pile buried pipe group at any point (x, y, z) is as follows:
because the pile foundations are aligned with each other with the same depth coordinates, the difference is in their horizontal plane coordinates, i.e. the difference between the x and y directions.
According to the temperature response calculation formula of the pile-buried spiral pipe under the action of groundwater seepage, the flow velocity of groundwater must be obtained, and the temperature response value can be calculated. According to the introduced reverse reasoning calculation method, the corresponding reverse calculation flow is shown in fig. 4.
And arranging a corrosion-resistant thermocouple or thermal resistor along the depth direction of the drill hole, and recording the change of the temperature of the arranged point along with time by adopting a data acquisition instrument. When the variance sum of the difference value between the theoretical calculation value and the experimental data of each point reaches the minimum, the value extracted from the size and the direction of the flow velocity of the underground water is the actual flow velocity value of the underground water. The number of points arranged around the drill hole is large, five points are uniformly arranged every several meters in the depth direction, the variance sum of the five points of each layer can be minimized, a plurality of horizontal planes are arranged in the depth extending direction, the total number of the points is large, the variance sum of all the points cannot be minimized, and when the variance sum of most points can be minimized at the same time, the flow velocity and the direction of the underground water can be considered to be obtained.
theoretically, three first derivatives are zero at the same time for the same point, but the probability of the first derivative being zero is extremely small due to errors in actual calculation and experiments, a smaller value can be set, if all three first derivatives are at the same time at the smaller value, the first derivative can be considered to be approximately zero, and at this time, the sum of the variances for the point is minimized, and formula (9) lists corresponding expressions for these.
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 temperature response calculation method of a pile foundation spiral buried pipe under the condition of groundwater seepage is characterized by comprising the following steps: the method comprises the following steps:
(1) on the premise that underground water flows through an infinite uniform medium at a three-dimensional speed, temperature response of a point heat source which is positioned in the medium and radiates heat at a certain strength at any point in the medium is confirmed;
(2) constructing a response model when underground water flows through a single pile buried pipe at a three-dimensional speed, and obtaining the temperature response of any point except the spiral pipe in a semi-infinite medium after a heat exchange pipe with a certain spiral distance, spiral radius and length is buried in a pile foundation to form a pile foundation spiral buried pipe geothermal heat exchanger; the response model is as follows:
wherein, theta is t-t0The excess temperature is expressed and can be called as temperature response, tau refers to any time in the heat exchange process, rho c is the volume specific heat capacity of the underground medium, and rhowcwIs the volume specific heat capacity of the groundwater, u1,u2And u3The component velocities of the groundwater seepage velocity in the x, y and z directions respectively, (x ', y ', z ') represents the coordinate of any point on the spiral pipe heat source, (x, y, z) represents the coordinate of any point in the underground medium except the heat source, qlIs the heat exchange amount per meter of spiral tube, r0Is the radius of the spiral tube,
for helix angle, δ (x-x ', y-y ', z-z ') is the Dirac function, h1And h2In the direction of depth of the pile-burying tubeStart-stop coordinates;
(3) measuring points are arranged along the periphery and the depth direction of the drill hole buried pipe, temperature response data are recorded, a finite long-line heat source seepage model is combined, the flow rate of underground water is calculated reversely, the flow rate and the angle are extracted continuously in respective ranges and are substituted into the finite long-line heat source seepage model, when the difference value between the temperature response obtained by calculation at each point and the temperature response measured by a thermocouple reaches the minimum, the flow rate and the angle extracted from the ranges are the actual value of the underground water seepage speed, and therefore the parameters of the underground water flow speed are provided for the temperature response calculation method of the pile foundation spiral buried pipe under the underground water seepage condition.
2. The method for calculating the temperature response of the pile foundation spiral buried pipe under the condition of groundwater seepage according to claim 1, wherein the method comprises the following steps: in the step (1), the Green function is changed according to the Green function of the point heat source generating temperature response in the infinite medium in a pure heat conduction mode, and the temperature response caused by the point heat source when the underground water flows through the underground medium in a three-dimensional flowing mode is obtained.
3. The method for calculating the temperature response of the pile foundation spiral buried pipe under the condition of groundwater seepage according to claim 1, wherein the method comprises the following steps: in the step (1), on the premise that the underground water flows through an infinite uniform medium at a three-dimensional speed, the distribution of the underground medium is uniform and the porosity of the underground medium is consistent, and the temperature response of a point heat source located at (x ', y, z') at a certain time at any point (x, y, z) in the infinite space is calculated according to the porosity, the volume specific heat capacity of the underground solid medium, the volume specific heat capacity of the underground water, and the heat conductivity of the underground solid medium and the underground water.
4. The method for calculating the temperature response of the pile foundation spiral buried pipe under the condition of groundwater seepage according to claim 1, wherein the method comprises the following steps: in the step (2), after the spiral heat exchange tubes are arranged on the pile foundation, when underground water flows through a single pile buried tube at a three-dimensional flow rate, the influence of heat conduction and convection is comprehensively considered, an energy equation is established, and corresponding initial and boundary conditions are listed; the influence of the constant temperature of the ground on the spiral buried pipe of the limited long pile foundation is considered, and the influence of each parameter of the spiral pipe and the pile foundation in the heat exchange process is considered.
5. The method for calculating the temperature response of the pile foundation spiral buried pipe under the condition of groundwater seepage according to claim 1, wherein the method comprises the following steps: in the step (2), after the temperature response expression of the finite pile foundation spiral buried pipe geothermal heat exchanger to the underground medium under the three-dimensional underground water seepage condition is obtained, the temperature response of any point in the underground medium at any time except the heat exchange pipe when the three-dimensional underground water flows through a single pile foundation spiral buried pipe can be calculated.
6. The method for calculating the temperature response of the pile foundation spiral buried pipe under the condition of groundwater seepage according to claim 1, wherein the method comprises the following steps: in the step (2), a virtual heat source method is utilized, namely a spiral pipe which can generate heat constantly exists in the underground medium, a spiral pipe which can absorb heat constantly exists in the virtual other half infinite medium which takes the ground as a symmetrical plane, namely a spiral heat source and a spiral heat sink exist simultaneously, and according to the temperature response caused by any point (x, y, z) except the spiral pipe in the underground space under the condition that a single pile foundation spiral buried pipe is in underground water seepage, the temperature response caused by a plurality of pile foundation buried pipes at the point is considered to be superposed, and the temperature response caused by the pile buried pipe group at the point is determined by combining the distance and the arrangement mode between the pile buried pipes.
7. The method for calculating the temperature response of the pile foundation spiral buried pipe under the condition of groundwater seepage according to claim 1, wherein the method comprises the following steps: in the step (3), the specific process includes:
(3-1) uniformly arranging measuring points along the periphery of the borehole heat exchanger and the depth direction, and mounting thermocouples or thermal resistors at the measuring points;
(3-2) setting the range of the flow velocity and the direction angle of the underground water, and extracting data from the set range to calculate;
(3-3) calculating the excess temperature of points distributed around the drill hole by adopting a drilling and pipe burying underground water seepage calculation model;
(3-4) calculating the variance between the theoretical calculation value and the actual value of each distribution point, judging whether the variance sum of the distribution points which accord with the set value number reaches the minimum value, if so, outputting the current flow rate and direction of the underground water, and if not, continuously extracting the numerical value from the range of the flow rate and direction of the underground water for iterative calculation.
8. The method for calculating the temperature response of the pile foundation spiral buried pipe under the condition of groundwater seepage according to claim 7, wherein the method comprises the following steps: in the step (3-1), corrosion-resistant thermocouples or thermal resistors are arranged around the borehole heat exchanger and in the depth direction, and a data acquisition instrument is adopted to record the change of the temperature of the arranged points along with time; meanwhile, in the step (3-2), the flow velocity and the angle are continuously extracted within respective ranges and substituted into a finite long-line heat source seepage model for calculation.
9. The method for calculating the temperature response of the pile foundation spiral buried pipe under the condition of groundwater seepage according to claim 7, wherein the method comprises the following steps: in the step (3-3), a temperature response value of a point arranged around the drill hole is calculated and obtained by utilizing a finite long-line heat source seepage model of the drill hole buried pipe under the condition of groundwater seepage and combining the flow speed and the direction of the groundwater continuously extracted in the step (3-2).
10. the method for calculating the temperature response of the pile-foundation spiral buried pipe under the groundwater seepage condition as claimed in claim 7, wherein in the step (3-4), the variance sum is taken as the first derivative for the magnitude u of the groundwater flow speed and the two direction angles α and β, and when the three first derivatives are all smaller than the set value, the first derivative is considered to be approximately zero, and at this time, the variance sum for the point is minimized.
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