CN109992846B - Simulation method for solar cross-season buried pipe heat storage - Google Patents

Simulation method for solar cross-season buried pipe heat storage Download PDF

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CN109992846B
CN109992846B CN201910193763.5A CN201910193763A CN109992846B CN 109992846 B CN109992846 B CN 109992846B CN 201910193763 A CN201910193763 A CN 201910193763A CN 109992846 B CN109992846 B CN 109992846B
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temperature
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heat
ground
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CN109992846A (en
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孙东亮
姚乐恒
李国龙
宇波
杨绪飞
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Beijing Institute of Petrochemical Technology
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Abstract

The invention discloses a simulation method for flow heat transfer numerical simulation of a solar cross-season ground heat exchanger, which comprises the following steps of firstly obtaining an energy equation; calculating to obtain a dimensionless number Nu related to fluid flow heat transfer, and deducing a fluid convective heat transfer coefficient h f (ii) a A given fluid domain initial temperature; the Crank-Nicolson format is constructed to be used as the fluid temperature and the heat convection coefficient h of the fluid f Forming a third type boundary condition at the inner wall surface of the ground heat exchanger; iteratively solving the derived energy equation by adopting a three-dimensional unstructured grid finite volume method to obtain a temperature field; after each iteration solution is finished, calculating the heat loss of the fluid with the unit length according to the temperature near the wall surface, and calculating the temperature of the fluid at the next moment by adopting an element thermal balance method; repeating the above operations until the temperature field of the calculation region reaches a steady state; and performing post-processing on the result to obtain the temperature distribution condition of the area. The method can efficiently and accurately predict the flowing and heat transfer states of the ground heat exchanger.

Description

Simulation method for solar cross-season buried pipe heat storage
Technical Field
The invention relates to the field of solar photo-thermal utilization, in particular to a simulation method for solar cross-season buried pipe heat storage.
Background
In recent years, most areas of China are deeply troubled by haze, and the health and living standard of the China are seriously threatened. Through investigation, coal-fired heating is one of the main reasons for causing haze. However, the existing method of replacing coal with gas and replacing coal with electricity has higher cost, and solar energy is used as clean, rich and cheap energy and occupies more and more share in energy consumption composition. The solar energy soil cross-season heat storage system just utilizes solar heat to heat a circulating medium in a system loop, and the circulating medium and the soil are subjected to heat and mass exchange through the buried pipe heat exchanger, so that the purpose of solar energy' summer Chu Dong is achieved.
Factors influencing the working performance of the ground heat exchanger are many and have complex relations, so that the heat exchange process between the ground heat exchanger and soil is difficult to accurately predict in the design process. Under the existing conditions, only experimental research or establishment of demonstration engineering research is unrealistic in the process of coupling and heat storage of the soil of the buried pipe, so that the test period is long, the investment is huge, and optimization research is difficult to develop aiming at a single system. In this case, based on knowledge of the relevant flow and heat transfer, a suitable mathematical model is established, and the use of numerical calculation methods to study the problems is extremely efficient and economical.
The core of the cross-season soil heat storage numerical simulation research is the flow heat exchange process in the buried pipe and the heat transmission process between the buried pipe and the surrounding soil. Because the fluid region in the pipe and the solid region outside the pipe need to be modeled simultaneously, the calculation amount of the whole numerical solving process is large, the calculation period is long, and the existing calculation method at home and abroad is difficult to meet the requirements of actual engineering.
Disclosure of Invention
Based on the problems in the prior art, the invention aims to provide a simulation method for solar cross-season buried pipe heat storage, which can accurately predict the value of the heat exchange process between the flowing process in the buried pipe and the soil of the buried pipe on the premise of high efficiency calculation.
The purpose of the invention is realized by the following technical scheme:
the embodiment of the invention provides a simulation method of solar cross-season ground heat storage of a ground heat exchanger, which is used for carrying out simulation calculation on the heat storage of the ground heat exchanger and comprises the following steps:
step 1, acquiring relevant parameters of the ground heat exchanger;
step 2, obtaining an energy equation of a solid area of the ground heat exchanger by applying an energy conservation relation and a heat conduction Fourier law;
step 3, calculating by using a flowing heat transfer experience correlation Gnielinski formula and combining the physical property parameters of the fluid in the pipe to obtain a dimensionless number Nu related to the flowing heat transfer of the fluid f According to said dimensionless number Nu f Deducing the convective heat transfer coefficient h of the fluid f ；
Step 4, giving the initial temperature of the fluid domain of the ground heat exchanger
Figure GDA0003907357060000021
As the temperature of the fluid at the present moment
Figure GDA0003907357060000022
And the temperature of the fluid at the next moment
Figure GDA0003907357060000023
An initial value of (1);
step 5, adopting the current time temperature of the fluid
Figure GDA0003907357060000024
And temperature at the next moment
Figure GDA0003907357060000025
Constructing a Crank-Nicolson format as the fluid temperature, and forming a third type boundary condition at the inner wall surface of the pipeline of the ground heat exchanger with the fluid convection heat transfer coefficient;
step 6, carrying out iterative solution on the energy equation obtained in the step 1 by adopting a three-dimensional unstructured grid finite volume method to obtain temperature distribution;
step 7, after each iteration solution in the step 6 is finished, calculating the heat loss of the fluid with unit length according to the temperature of the position close to the wall surface of the pipeline of the buried pipe heat exchanger, and calculating the temperature of the fluid at the next moment by adopting a simple body thermal balance method
Figure GDA0003907357060000026
Step 8, repeating the operation of the steps 4 to 7 until the calculated temperature field of the solid area of the ground heat exchanger reaches a stable state;
and 9, performing post-processing on the result obtained by the solving to obtain the temperature distribution condition of the area.
According to the technical scheme provided by the invention, the simulation method for solar cross-season buried pipe heat storage provided by the embodiment of the invention has the beneficial effects that:
the convective heat transfer coefficient of the fluid near the wall surface is directly calculated through an empirical correlation method, the fluid temperature is obtained through a Crank-Nicolson format, the grid division of the fluid domain of the ground heat exchanger is not needed, the fluid flow and heat transfer related parameters of the inner wall surface of the ground pipe are not needed to be obtained through solving a turbulence model, the calculated amount of the problems is effectively reduced, the calculation efficiency is greatly improved, and the accurate prediction of the solar energy seasonal soil heat storage temperature field value is realized on the premise of ensuring the high efficiency of the method.
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In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on the drawings without creative efforts.
Fig. 1 is a schematic flow chart of a simulation method for solar cross-season buried pipe flow heat transfer according to an embodiment of the present invention;
FIG. 2 is a schematic diagram comparing the outlet temperature of the buried pipe obtained by the simulation method provided by the embodiment of the invention with the calculation result of the turbulence model;
fig. 3 is a schematic diagram comparing results obtained by a calculation method of an on-way fluid temperature and turbulence model according to a simulation method provided by an embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention are clearly and completely described below with reference to the specific contents of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments of the present invention without making any creative effort, shall fall within the protection scope of the present invention. Details which are not described in detail in the embodiments of the invention belong to the prior art which is known to the person skilled in the art.
As shown in fig. 1, an embodiment of the present invention provides a simulation method for solar cross-season ground pipe heat storage, which is used for performing simulation calculation on heat storage of a ground pipe heat exchanger, and includes the following steps:
step 1, acquiring relevant parameters of the ground heat exchanger;
step 2, applying an energy conservation relation and a heat conduction Fourier law to a solid area of the ground heat exchanger to obtain an energy equation; the solid region refers to: the pipe wall of the ground heat exchanger, the drilling backfill material and the soil;
step 3, combining the fluid physical property parameters in the pipe to calculate and obtain a dimensionless number Nu related to fluid flow heat transfer based on the flow heat transfer empirical correlation Gnielinski formula f According to said dimensionless number Nu f Deducing the convective heat transfer coefficient h of the fluid f ；
Step 4, giving the initial temperature of the fluid domain of the ground heat exchanger
Figure GDA0003907357060000031
As the temperature of the fluid at the present moment
Figure GDA0003907357060000032
And fluid temperature at the next time
Figure GDA0003907357060000033
An initial value of (1);
step 5, adopting the current time temperature of the fluid
Figure GDA0003907357060000034
And temperature at the next moment
Figure GDA0003907357060000035
Structural Crand the ank-Nicolson format is used as the fluid temperature, and forms a third type of boundary condition at the inner wall surface of the pipeline of the ground heat exchanger with the fluid convection heat transfer coefficient, wherein the third type of boundary condition is as follows: and calculating the solution condition in the heat conduction process. Under the condition, the convective heat transfer coefficient and the fluid temperature of the fluid are given, so that the heat conduction is solved;
step 6, carrying out iterative solution on the energy equation obtained in the step 1 by adopting a three-dimensional unstructured grid finite volume method to obtain temperature distribution; the iterative solution of the energy equation comprises the following steps: (1) discretizing an energy equation; (2) setting an iteration initial test condition, an iteration definite solution condition, an iteration convergence condition, a maximum iteration step number and a time step length, and then starting to solve an energy equation;
step 7, after each iteration solution in the step 6 is finished, calculating the heat loss of the fluid with unit length according to the temperature of the position close to the wall surface of the pipeline of the buried pipe heat exchanger, and calculating the temperature of the fluid at the next moment by adopting a simple body thermal balance method
Figure GDA0003907357060000041
Step 8, repeating the operation of the steps 4 to 6 until the calculated temperature field of the solid area of the ground heat exchanger reaches a stable state;
and 9, performing post-processing on the result obtained by the solving to obtain the temperature distribution condition of the area.
In step 1 of the method, obtaining relevant parameters of the ground heat exchanger includes: pipe diameter, branch spacing, borehole diameter, borehole depth, circulating medium flow rate, and inlet temperature.
In step 2 of the above-described method,
the energy conservation relation is as follows: the increase rate of the thermodynamic energy in the infinitesimal body is equal to the work of net heat flow, volume force and surface force entering the infinitesimal body on the infinitesimal body, wherein the infinitesimal body is a unit body represented by each grid after the solid area of the ground heat exchanger is subjected to grid division;
the energy equation expressed by the specific enthalpy h and the temperature T of the fluid is obtained as follows:
Figure GDA0003907357060000042
in the above formula (1), λ is the thermal conductivity of the fluid, S h The internal heat source of the fluid, Φ is the portion of the mechanical energy converted into thermal energy due to viscous action, called dissipation function (dissipation function), whose calculation is as follows:
Figure GDA0003907357060000043
in the above formula (2), pdivU is the work of surface force on the fluid micro-element, and this parameter is ignored; simultaneously taking h = c for ideal gas, liquid and solid p T, get c p As a constant, the dissipation function Φ is taken into the source term S T Middle (S) T ＝S h + Φ), yielding:
Figure GDA0003907357060000044
for the solution of the soil side solid area, the simplified energy equation is:
Figure GDA0003907357060000051
in the above formula (1), λ is the thermal conductivity of the fluid; t is the temperature; t is time; u is the vector velocity; rho is density; c P Is the specific heat capacity of the soil (a constant is taken during calculation); s T As a source term, these parameters are for the soil since the solution is for soil side solids.
In step 3 of the method, the gnilinski formula is as follows:
Figure GDA0003907357060000052
in the above formula (5), d is the nominal diameter of the pipeline, l is the length of the pipeline, and f is the resistance coefficient of the flow in the pipeline, and the calculation formula is as follows:
f＝(1.82lgRe-1.64) -2 ；(6)
for the medium circulating in the tube:
Figure GDA0003907357060000053
according to Nu f Number-defined formula:
Figure GDA0003907357060000054
obtaining the convective heat transfer coefficient h of the inner wall surface of the pipeline of the buried pipe heat exchanger f 。
In step 5 of the above-described method,
the third type of boundary conditions of the inner wall surface of the pipeline of the ground heat exchanger are as follows:
Figure GDA0003907357060000055
in the above-mentioned formula (9),
Figure GDA0003907357060000056
is the temperature gradient at the wall, T w Is the wall temperature, T f Is the temperature of the fluid in the pipe, T f Comprises the following steps:
Figure GDA0003907357060000057
in step 6 of the above method, the three-dimensional unstructured grid of the three-dimensional unstructured grid finite volume method is a hexahedral grid.
In step 7 of the above-described method,
calculating according to a heat conduction Fourier law to obtain that the heat loss at the position close to the wall surface of the pipeline of the ground heat exchanger is as follows:
Figure GDA0003907357060000058
in the above formula (10) A pipe_wall Is the unit area of the long wall surface of the tube,
Figure GDA0003907357060000061
the temperature of two adjacent nodes at the pipe wall is shown, and delta is the grid size at the position close to the wall surface;
the element heat balance method comprises the following steps:
Figure GDA0003907357060000062
in the above-mentioned formula (11),
Figure GDA0003907357060000063
is the internal energy of the element at the current moment,
Figure GDA0003907357060000064
Figure GDA0003907357060000065
the heat introduced to the upper surface of the element at this time,
Figure GDA0003907357060000066
Figure GDA0003907357060000067
for the heat conducted off the lower surface at this moment,
Figure GDA0003907357060000068
Figure GDA0003907357060000069
the heat quantity led out from the wall surface,
Figure GDA00039073570600000610
Figure GDA00039073570600000611
the internal energy of the element body at the next moment,
Figure GDA00039073570600000612
Figure GDA00039073570600000613
is the mass flow rate of the fluid, t iteration Is the inner iteration duration; by
Figure GDA00039073570600000614
Deducing the fluid temperature in the next time element
Figure GDA00039073570600000615
The element is a unit body which is formed by axially dividing a fluid area of the buried pipe heat exchanger into a plurality of parts, wherein the length of each part is preferably 1% of the buried depth of the buried pipe. The more the number of the divided parts is, the more accurate the calculation result is, but the calculation time is increased correspondingly.
In step 9 of the method, the post-processing of the result obtained by the solution is as follows: after the calculation reaches convergence, the temperature value of the required part is output, and a temperature profile or a line graph is generated for analysis.
In the above method, in steps 1 to 9, the iterative solution for solving the soil-side heat conduction process is an outer iteration, and the iterative solution for solving the fluid temperature is an inner iteration.
According to the method, due to the fact that grid division is not needed to be carried out on the fluid domain, parameters related to fluid flow and heat transfer at the inner wall surface of the buried pipe are not needed to be obtained through solving the turbulence model, the fact that the flow in the pipe can be solved without introducing the turbulence model in numerical solution is achieved, calculation efficiency is improved to a great extent, numerical values of the flow process in the buried pipe and the heat exchange process between soil of the buried pipe can be accurately predicted, and the method is efficient and accurate.
The embodiments of the present invention are described in further detail below.
Fig. 1 is a schematic flow chart of a simulation method for flow heat transfer of a buried pipe according to an embodiment of the present invention, where the simulation method includes the following steps:
step 1, acquiring relevant parameters of the ground heat exchanger;
step 2, firstly, according to a heat transfer theory, an energy equation is obtained by applying an energy conservation law and a heat conduction Fourier law to a solid area;
selecting an energy conservation law:
according to the conservation relation: the energy equation expressed by the specific enthalpy h and the temperature T of the fluid can be obtained by [ rate of increase of thermodynamic energy in the infinitesimal body ] = [ net heat flux into the infinitesimal body ] + [ work done by volume force and surface force on the infinitesimal body ]:
Figure GDA0003907357060000071
where λ is the thermal conductivity of the fluid, S h The internal heat source of the fluid, Φ is the portion of the mechanical energy converted into heat energy due to viscous action, called dissipation function (dispersion function), and is calculated as follows:
Figure GDA0003907357060000072
wherein pdivU is the work done by surface force on the fluid micro-elements, and can be generally ignored; simultaneously, h = c can be taken for ideal gas, liquid and solid p T, further take c p Is constant and incorporates a dissipation function Φ into the source term S T Middle (S) T ＝S h + Φ), yielding:
Figure GDA0003907357060000073
for the solution of the soil side solid area, the energy equation can be further simplified:
Figure GDA0003907357060000074
step 3, calculating a dimensionless number related to fluid flow heat transfer based on a flow heat transfer experience correlation Gnielinski formula and fluid physical property parameters in a pipeNu f Deducing the convective heat transfer coefficient h of the fluid f ；
In this step, a dimensionless number Nu is used f To characterize the flow heat transfer state of turbulent flow in the pipe, nu f The number is calculated by the flow heat transfer correlation for turbulent flow in the pipe, gnielinski formula:
Figure GDA0003907357060000075
wherein d is the nominal diameter of the pipeline, l is the length of the pipeline, f is the resistance coefficient of the flow in the pipeline, and the calculation formula is as follows:
f＝(1.82lgRe-1.64) -2 (6)
in particular, for a medium circulating in a pipe,
Figure GDA0003907357060000076
according to Nu f Number-defined formula:
Figure GDA0003907357060000077
the heat convection coefficient h of the inner wall surface of the buried pipe can be obtained f ；
Step 4, giving the initial temperature of the fluid domain
Figure GDA0003907357060000081
As the temperature of the fluid at the present moment
Figure GDA0003907357060000082
And the temperature of the fluid at the next moment
Figure GDA0003907357060000083
The initial value of (1);
in this step, since the method described in the present invention has no grid of fluid domains, the fluid temperature is a hypothetical fluid temperature, as is the case in the following, given the temperature of the fluid domain for subsequent calculations to be performed;
step 5, using the flowBody current time temperature
Figure GDA0003907357060000084
And temperature at the next moment
Figure GDA0003907357060000085
The Crank-Nicolson format is constructed to be used as the fluid temperature and the heat convection coefficient h of the fluid f Forming a third type of boundary condition at the inner wall surface of the ground heat exchanger;
a third class of boundary conditions for the inner wall surface of a conduit can be expressed as:
Figure GDA0003907357060000086
wherein,
Figure GDA0003907357060000087
is the temperature gradient at the wall, T w Is the wall temperature, T f To the fluid temperature inside the pipe, it can be expressed in particular as:
Figure GDA0003907357060000088
step 6, solving the energy equation obtained in the step 1 by adopting a three-dimensional unstructured grid finite volume method to obtain temperature distribution;
the three-dimensional unstructured grid adopted in the step 5 is a hexahedral grid so as to ensure the convergence and stability of the calculation process;
step 7, after each iteration solution in the step 5 is finished, calculating the heat loss of the fluid with the unit length according to the temperature at the position close to the wall surface through a heat conduction Fourier law, and calculating the temperature of the fluid at the next moment by adopting an element thermal balance method
Figure GDA00039073570600000819
；
The expression of the heat conduction Fourier law of heat loss at the near wall surface is as follows:
Figure GDA0003907357060000089
wherein A is pipe_wall Is the unit area of the long wall surface of the tube,
Figure GDA00039073570600000810
the temperature of two adjacent nodes at the pipe wall is shown, and delta is the grid size at the position close to the wall surface;
the expression of the element heat balance method is as follows:
Figure GDA00039073570600000811
wherein,
Figure GDA00039073570600000812
is the internal energy of the element at the current moment,
Figure GDA00039073570600000813
Figure GDA00039073570600000814
the heat introduced to the upper surface of the element at this time,
Figure GDA00039073570600000815
Figure GDA00039073570600000816
for the heat conducted off the lower surface at this moment,
Figure GDA00039073570600000817
Figure GDA00039073570600000818
the heat quantity led out from the wall surface,
Figure GDA0003907357060000091
Figure GDA0003907357060000092
the internal energy of the element body at the next moment,
Figure GDA0003907357060000093
Figure GDA0003907357060000094
is the mass flow rate of the fluid, t iteration Is the inner iteration duration;
by
Figure GDA0003907357060000095
The temperature of the fluid in the body at the next moment can be deduced
Figure GDA0003907357060000096
Step 8, repeating the operations of the steps 4 to 6 until the temperature field of the calculation area reaches a stable state;
and 9, performing post-processing on the result obtained by the solving to obtain the temperature distribution condition of the area.
In specific implementation, in the steps 1 to 9, the iterative solution for solving the soil-side heat conduction process is an outer iteration, and the iterative solution for solving the fluid temperature is an inner iteration.
The 9 steps described in the embodiment simulate the heat transfer process between the soil of the ground pipe in the solar cross-season soil heat storage process, and the specific dimensions and physical parameters of the simulated ground pipe heat exchanger are shown in tables 1 and 2.
Figure GDA0003907357060000097
Figure GDA0003907357060000098
Fig. 2 is a schematic diagram showing comparison between the outlet temperature of the ground buried pipe and the calculation result of the turbulence model obtained by the simulation method of the embodiment of the invention, and fig. 2 is a diagram comparing the fluid temperature at the outlet of the U-shaped pipe at one side of the double-U type ground buried pipe heat exchanger obtained by the calculation of the embodiment of the invention with the calculation result of the traditional simulation method using the turbulence model Standard k-e model. As shown in fig. 2, the results obtained by simulation in the embodiment of the present invention are better matched with the turbulence model, and the accuracy of the simulation method established by the present invention is verified.
Fig. 3 is a schematic diagram showing a comparison between the on-way fluid temperature obtained by the simulation method in the embodiment of the present invention and the result obtained by the conventional numerical calculation method, and fig. 3 is a schematic diagram showing a comparison between the on-way fluid temperatures obtained by different simulation methods, and as shown in fig. 3, the maximum deviation between the result obtained by the simulation method in the embodiment of the present invention and the result obtained by the conventional numerical calculation method is 0.025%, the average deviation is 0.02%, the two are in good agreement, and the accuracy of the simulation method established by the present invention is further verified.
Details which are not described in detail in the embodiments of the invention belong to the prior art which is known to the person skilled in the art.
In conclusion, the method provided by the embodiment of the invention simulates the flowing heat transfer process of the buried pipe heat exchanger by using numerical simulation, can conveniently obtain the temperature of the fluid in the buried pipe and the temperature distribution of the soil, does not need to perform grid division and calculation on a fluid domain, can greatly reduce the calculation amount of solar cross-season soil heat storage, and shortens the research and development period.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims (5)

1. A simulation method for solar cross-season ground pipe heat storage is characterized by being used for carrying out simulation calculation on heat storage of a ground pipe heat exchanger and comprising the following steps of:
step 1, acquiring relevant parameters of the ground heat exchanger, namely acquiring the relevant parameters of the ground heat exchanger comprises the following steps: pipe diameter, branch pipe spacing, bore diameter, bore depth, circulating medium flow rate and inlet temperature;
step 2, obtaining an energy equation of a solid area of the ground heat exchanger by applying an energy conservation relation and a heat conduction Fourier law, wherein the energy conservation relation is as follows: the increase rate of the thermodynamic energy in the infinitesimal body is equal to the work of net heat flow, volume force and surface force entering the infinitesimal body on the infinitesimal body, wherein the infinitesimal body is a unit body represented by each grid after the solid area of the ground heat exchanger is subjected to grid division;
the energy equation obtained is:
Figure FDA0003907357050000011
in the above formula (4), λ is the thermal conductivity of the fluid; t is the temperature; t is time; u is the vector velocity; rho is density; c. C P The specific heat capacity of the soil; s. the T Is a source item;
step 3, calculating by using a flowing heat transfer experience correlation Gnielinski formula and combining the physical property parameters of the fluid in the pipe to obtain a dimensionless number Nu related to the flowing heat transfer of the fluid f According to said dimensionless number Nu f Deducing the convective heat transfer coefficient h of the fluid f The flow heat transfer experience correlation Gnielinski formula is as follows:
Figure FDA0003907357050000012
in the above formula (5), d is the nominal diameter of the pipeline, l is the length of the pipeline, f is the resistance coefficient of the flow in the pipeline, and the calculation formula of f is as follows: f = (1.82 lgRe-1.64) -2 ；(6)
For the medium circulating in the tube:
Figure FDA0003907357050000013
according to the dimensionless number Nu f Number-defined formula:
Figure FDA0003907357050000014
obtaining the convective heat transfer coefficient h of the inner wall surface of the pipeline of the ground heat exchanger f ；
Step 4, giving the initial temperature of the fluid domain of the ground heat exchanger
Figure FDA0003907357050000015
As the temperature of the fluid at the present moment
Figure FDA0003907357050000016
And fluid temperature at the next time
Figure FDA0003907357050000017
An initial value of (1);
step 5, adopting the current time temperature of the fluid
Figure FDA0003907357050000021
And temperature at the next moment
Figure FDA0003907357050000022
Constructing a Crank-Nicolson format as the fluid temperature, and forming a third boundary condition at the inner wall surface of the pipeline of the ground heat exchanger with the fluid convection heat transfer coefficient, wherein the third boundary condition of the inner wall surface of the pipeline of the ground heat exchanger is as follows:
Figure FDA0003907357050000023
in the above-mentioned formula (9),
Figure FDA0003907357050000024
is the temperature gradient at the wall, T w Is the wall temperature, T f Is the temperature of the fluid in the pipe, T f Comprises the following steps:
Figure FDA0003907357050000025
step 6, carrying out iterative solution on the energy equation obtained in the step 2 by adopting a three-dimensional unstructured grid finite volume method to obtain temperature distribution;
step 7, after each iteration solution in the step 6 is finished, calculating the heat loss of the fluid with unit length according to the temperature of the position close to the wall surface of the pipeline of the buried pipe heat exchanger, and calculating the temperature of the fluid at the next moment by adopting a simple body thermal balance method
Figure FDA0003907357050000026
Calculating according to a heat conduction Fourier law to obtain that the heat loss at the position close to the wall surface of the pipeline of the ground heat exchanger is as follows:
Figure FDA0003907357050000027
in the above formula (10) A pipe_wall Is the unit area of the long wall surface of the tube,
Figure FDA0003907357050000028
T i n the temperature of two adjacent nodes at the pipe wall is shown, and delta is the grid size at the position close to the wall surface;
the element heat balance method comprises the following steps:
Figure FDA0003907357050000029
in the above-mentioned formula (11),
Figure FDA00039073570500000210
the internal energy of the cell body at the current moment,
Figure FDA00039073570500000211
Figure FDA00039073570500000212
the heat introduced to the upper surface of the element at this time,
Figure FDA00039073570500000213
Figure FDA00039073570500000214
the heat conducted away from the lower surface at this time,
Figure FDA00039073570500000215
Figure FDA00039073570500000216
the heat quantity led out from the wall surface,
Figure FDA00039073570500000217
Figure FDA00039073570500000218
the internal energy of the element body at the next moment,
Figure FDA00039073570500000219
Figure FDA00039073570500000220
is the mass flow rate of the fluid, t iteration Is the inner iteration duration; by
Figure FDA00039073570500000221
Deducing the fluid temperature T in the next time element i n+1 (ii) a The element body is a unit body which axially divides a fluid area of the ground heat exchanger into a plurality of parts, wherein each part represents the unit body;
step 8, repeating the operation of the steps 4 to 7 until the calculated temperature field of the solid area of the ground heat exchanger reaches a stable state;
and 9, performing post-processing on the result obtained by the solving to obtain the temperature distribution condition of the area.
2. The simulation method of solar cross-season buried pipe thermal storage according to claim 1, wherein in the step 6 of the method, the three-dimensional unstructured grid of the three-dimensional unstructured grid finite volume method is a hexahedral grid.
3. The method for simulating solar trans-seasonal ground pipe thermal storage according to claim 1, wherein in step 5 of the method, the third type of boundary condition is a solution condition when calculating a heat conduction process.
4. The method for simulating solar cross-season buried pipe thermal storage according to claim 1, wherein in step 6 of the method, the step of iteratively solving an energy equation comprises:
(1) Discretizing an energy equation;
(2) And (4) solving the energy equation after giving an iteration initial condition, an iteration definite solution condition, an iteration convergence condition, the maximum iteration step number and a time step length.
5. The simulation method of solar trans-seasonal buried pipe thermal storage according to claim 1, wherein in the method, in the steps 1 to 9, the iterative solution for solving the soil-side thermal conduction process is an outer iteration, and the iterative solution for solving the fluid temperature is an inner iteration.
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