CN114491949A - Simplified calculation method of sleeve type buried pipe heat exchanger - Google Patents
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- CN114491949A CN114491949A CN202111606442.7A CN202111606442A CN114491949A CN 114491949 A CN114491949 A CN 114491949A CN 202111606442 A CN202111606442 A CN 202111606442A CN 114491949 A CN114491949 A CN 114491949A
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- 238000004364 calculation method Methods 0.000 title claims abstract description 36
- 238000000034 method Methods 0.000 claims abstract description 20
- 239000000463 material Substances 0.000 claims abstract description 17
- 239000002689 soil Substances 0.000 claims abstract description 16
- 230000008569 process Effects 0.000 claims abstract description 14
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 14
- 230000008859 change Effects 0.000 claims abstract description 8
- 230000000704 physical effect Effects 0.000 claims abstract description 8
- 239000011435 rock Substances 0.000 claims abstract description 7
- 239000012530 fluid Substances 0.000 claims description 12
- 230000015572 biosynthetic process Effects 0.000 claims description 3
- 230000008878 coupling Effects 0.000 claims description 3
- 238000010168 coupling process Methods 0.000 claims description 3
- 238000005859 coupling reaction Methods 0.000 claims description 3
- 230000009286 beneficial effect Effects 0.000 description 2
- 230000008901 benefit Effects 0.000 description 2
- 230000004075 alteration Effects 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 238000010030 laminating Methods 0.000 description 1
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- 230000004048 modification Effects 0.000 description 1
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- G—PHYSICS
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- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F2113/00—Details relating to the application field
- G06F2113/08—Fluids
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F2113/00—Details relating to the application field
- G06F2113/14—Pipes
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
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Abstract
The invention relates to the technical field of geothermal resource development and utilization, and discloses a simplified calculation method of a sleeve type buried pipe heat exchanger, which comprises the following steps: 1) the thermal physical properties of backfill materials and surrounding rock and soil are uniform, the thermal physical property parameters of the backfill materials do not change along with the change of radial and vertical sizes, and the influence of underground water seepage and soil moisture transfer is ignored; 2) there is no heat conduction in the vertical direction, i.e. the heat transfer process is a two-dimensional heat transfer problem along the radial direction of the buried pipe. According to the simplified calculation method of the sleeve type buried pipe heat exchanger, by adopting the calculation method, the grid division in the heat transfer calculation process of the sleeve type buried pipe heat exchanger can be reduced, and meanwhile, the complicated three-dimensional unsteady heat transfer problem is simplified into the two-dimensional unsteady heat transfer problem, so that the simplified calculation of the sleeve type buried pipe heat exchanger can be carried out under different conditions, the calculation efficiency is improved, and certain practical use value and popularization value are achieved.
Description
Technical Field
The invention relates to the technical field of geothermal resource development and utilization, in particular to a simplified calculation method of a sleeve type buried pipe heat exchanger.
Background
The geothermal energy is a clean and environment-friendly renewable energy source, the competitiveness in the field of clean energy utilization is increasingly strong, at present, the system can be divided into an open type ground source heat pump system and a closed type ground source heat pump system according to the exploitation form of geothermal resources, the open type ground source heat pump system needs to extract underground water, the influence of the stability of water temperature and water quantity and policy protection is large, and the system is difficult to develop in cities; and closed ground source heat pump system adopts the form of ground heat exchanger, divide into shallow layer buried pipe and well deep layer buried pipe, and well deep layer ground source heat pump system buried pipe degree of depth can reach more than 1500 ~ 2500m, and the temperature of ground layer in the make full use of stratum can realize "getting heat and not getting water", has unique advantage, can effectively guarantee the stability of secret heat transfer, is a novel clean heating technique.
The ground source heat pump system of the medium-deep sleeve type ground source adopts a form of a ground pipe to mine medium-deep geothermal resources, generally in a form of a coaxial sleeve type heat exchanger, cold water flows in from an inlet of an outer sleeve, heat exchange between the cold water and a surrounding rock-soil layer is completed through heat conduction and convection heat exchange in the descending process of the cold water in the outer sleeve, and the cold water reaches the bottom of the sleeve and then flows out upwards from an inner pipe channel to a wellhead.
The buried pipe heat exchanger is an important component of a ground source heat pump system of a middle-deep buried pipe, and is characterized in that a method for calculating the heat exchange performance of the double-pipe buried pipe heat exchanger comprises a numerical method and an analytical method, a heat transfer model is constructed, the numerical model is solved through a finite difference method, and a complex partial differential problem is converted into a solving problem of a linear equation set.
Disclosure of Invention
Technical problem to be solved
Aiming at the defects of the prior art, the invention provides a simplified calculation method of a sleeve type buried pipe heat exchanger, which has the advantages of improving the calculation efficiency and the like and solves the problem of low calculation efficiency.
(II) technical scheme
In order to achieve the purpose of improving the calculation efficiency, the invention provides the following technical scheme: a simplified calculation method for a double pipe subterranean heat exchanger comprising the steps of:
1) the thermal physical properties of backfill materials and surrounding rock and soil are uniform, the thermal physical property parameters of the backfill materials do not change along with the change of radial and vertical sizes, and the influence of underground water seepage and soil moisture transfer is ignored;
2) the heat conduction phenomenon does not exist in the vertical direction, namely, the heat transfer process is a two-dimensional heat transfer problem along the radial direction of the buried pipe;
3) the temperature of the fluid inside the buried pipe is uniform, and the problem of heat backflow of the fluid inside and outside the inner sleeve of the double-pipe heat exchanger is not considered;
4) there is no thermal contact resistance between the contact surfaces, i.e. there is no contact gap between the materials.
Preferably, the thermal resistance R per unit length between the fluid in the casing pipe type buried pipe heat exchanger pipe and the rock-soil layer can be calculated by the following formula:
thermal resistance Rf between the wall surface and the circulation working medium by convective heat transfer:
wherein r1 is the inner diameter of the outer sleeve, and m and hf are the convection heat transfer coefficient between the wall surface and the circulating working medium.
Sleeve-type outer sleeve thermal resistance R1:
wherein r1 is the inner diameter of the outer sleeve in m; r2 is the outer diameter of the outer sleeve, in m; λ 1 is the thermal conductivity of the outer jacket tube, in W/(m · k).
Backfill material thermal resistance R2:
wherein r1 is the inner diameter of the outer sleeve in m; r2 is the outer diameter of the outer sleeve, in m; λ 2 is the thermal conductivity of the outer jacket tube, in W/(m · k).
Sleeve-type outer sleeve thermal resistance R3:
wherein r3 is the borehole aperture in m; r4 is the buried pipe influence radius in m; and lambda 3 is the thermal conductivity coefficient of stratum rock and soil, and the unit W/(m.k).
The heat resistance per unit length of the ground heat exchanger is as follows:
R＝Rf+R1+R2+R3
the heat exchange quantity of the buried pipe in unit length is as follows:
wherein Tw is the initial formation temperature in units of; ti1 is the pipe section inlet temperature in units of ℃; to1 is the tube section outlet temperature in degrees Celsius.
Each pipe section is a continuous flow coupling heat exchange process, the outlet temperature of the previous pipe section is the inlet temperature of the next pipe section, namely:
To1＝Ti2
the heat exchange load calculation of the buried pipe meets the following requirements:
Q＝Cw×m×(To-Ti)
wherein: cw is the specific heat capacity of the circulating working medium, and the unit kJ/(kg. DEG C); and m is the mass flow of the fluid and has a unit of kg/s.
(III) advantageous effects
Compared with the prior art, the invention provides a simplified calculation method of a sleeve type buried pipe heat exchanger, which has the following beneficial effects:
according to the simplified calculation method of the sleeve type buried pipe heat exchanger, by adopting the calculation method, the grid division in the heat transfer calculation process of the sleeve type buried pipe heat exchanger can be reduced, and meanwhile, the complicated three-dimensional unsteady heat transfer problem is simplified into the two-dimensional unsteady heat transfer problem, so that the simplified calculation of the sleeve type buried pipe heat exchanger can be carried out under different conditions, the calculation efficiency is improved, and certain practical use value and popularization value are achieved.
Drawings
FIG. 1 is a model schematic view of a simplified calculation method for a double pipe type ground heat exchanger according to the present invention;
fig. 2 is a heat transfer model diagram of a casing pipe type ground heat exchanger according to the present invention.
In the figure: 1 inner pipe pipeline, 2 inner pipe walls, 3 outer sleeve pipe pipelines, 4 outer sleeve pipe walls, 5 backfill materials and 6 rock-soil layers.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments 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 of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
In the calculation process, the double-pipe type ground heat exchanger is simplified into 5 layers according to geological and geotechnical characteristics, and each layer is regarded as a two-dimensional unsteady heat transfer process for calculation.
Because the depth of the sleeve type ground heat exchanger is usually 200-3000 m, and the aperture of a drilled hole is small, compared with the depth of a drilled hole, the depth of the sleeve type ground heat exchanger can be regarded as a two-dimensional unsteady heat transfer process for calculation.
This patent simplifies 2500 m's sleeve type buried pipe heat exchanger into 5 laminatings according to the stratum lithology, and cold water flows in from the outer tube entry, and cold water descends the in-process in the outer tube and accomplishes heat exchange through heat conduction and convection heat transfer and around the ground layer, upwards flows out to the well head from the inner tube passageway again after reaching the sleeve pipe bottom.
The outlet temperature of each layer is the inlet temperature of the next layer.
During calculation, the influence of the convective heat transfer of the circulating working medium in the pipe, the heat conduction of the pipe wall of the outer sleeve, the heat conduction of the backfill material and the heat conduction of the stratum on the heat transfer of the sleeve type buried pipe heat exchanger is mainly considered.
A simplified calculation method for a double pipe type ground heat exchanger includes the following steps:
1) the thermal physical properties of backfill materials and surrounding rock and soil are uniform, the thermal physical property parameters of the backfill materials do not change along with the change of radial and vertical sizes, and the influence of underground water seepage and soil moisture transfer is ignored;
2) the heat conduction phenomenon does not exist in the vertical direction, namely, the heat transfer process is a two-dimensional heat transfer problem along the radial direction of the buried pipe;
3) the temperature of the fluid inside the buried pipe is uniform, and the problem of heat backflow of the fluid inside and outside the inner sleeve of the double-pipe heat exchanger is not considered;
4) there is no thermal contact resistance between the contact surfaces, i.e. there is no contact gap between the materials.
A simplified calculation method for a sleeve type ground heat exchanger is characterized in that the thermal resistance R per unit length between fluid in a sleeve type ground heat exchanger tube and a rock-soil layer can be calculated by adopting the following formula:
thermal resistance Rf of convection heat exchange between the wall surface and the circulating working medium:
wherein r1 is the inner diameter of the outer sleeve, and m and hf are the convection heat transfer coefficient between the wall surface and the circulating working medium.
Sleeve-type outer sleeve thermal resistance R1:
wherein r1 is the inner diameter of the outer sleeve in m; r2 is the outer diameter of the outer sleeve, in m; λ 1 is the thermal conductivity of the outer jacket tube, in W/(m · k).
Backfill material thermal resistance R2:
wherein r1 is the inner diameter of the outer sleeve in m; r2 is the outer diameter of the outer sleeve, in m; λ 2 is the thermal conductivity of the outer jacket tube, in W/(m · k).
Sleeve-type outer sleeve thermal resistance R3:
wherein r3 is the borehole aperture in m; r4 is the buried pipe influence radius in m; and lambda 3 is the thermal conductivity coefficient of stratum rock and soil, and the unit W/(m.k).
The heat resistance per unit length of the ground heat exchanger is as follows:
R＝Rf+R1+R2+R3
the heat exchange quantity of the buried pipe in unit length is as follows:
wherein Tw is the initial formation temperature in units of; ti1 is the pipe section inlet temperature in units of ℃; to1 is the tube section outlet temperature in degrees Celsius.
Each pipe section is a continuous flow coupling heat exchange process, the outlet temperature of the previous pipe section is the inlet temperature of the next pipe section, namely:
To1＝Ti2
the heat exchange load calculation of the buried pipe meets the following requirements:
Q＝Cw×m×(To-Ti)
wherein: cw is the specific heat capacity of the circulating working medium, and the unit kJ/(kg. DEG C); and m is the mass flow of the fluid and has unit kg/s.
The invention has the beneficial effects that: by the simplified calculation method, the thermal resistance of the sleeve type ground heat exchanger can be calculated according to the thermophysical properties of the stratum temperature, the backfill material, the ground pipe and the circulating working medium, the heat exchange quantity, the inlet and outlet temperature of the circulating working medium and the flow of the circulating working medium in the pipeline can be further calculated, the grid division in the heat transfer calculation process of the sleeve type ground heat exchanger can be reduced, and meanwhile, the complicated three-dimensional unsteady heat transfer problem is simplified into the two-dimensional unsteady heat transfer problem, so that the simplified calculation can be carried out on the sleeve type ground heat exchanger under different conditions, the calculation efficiency is improved, and the method has certain practical use value and popularization value.
Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.
Claims (2)
1. A simplified calculation method for a double-pipe type ground heat exchanger is characterized by comprising the following steps:
1) the thermal physical properties of backfill materials and surrounding rock and soil are uniform, the thermal physical property parameters of the backfill materials do not change along with the change of radial and vertical sizes, and the influence of underground water seepage and soil moisture transfer is ignored;
2) the heat conduction phenomenon does not exist in the vertical direction, namely, the heat transfer process is a two-dimensional heat transfer problem along the radial direction of the buried pipe;
3) the temperature of the fluid inside the buried pipe is uniform, and the problem of heat backflow of the fluid inside and outside the inner sleeve of the double-pipe heat exchanger is not considered;
4) there is no thermal contact resistance between the contact surfaces, i.e. there is no contact gap between the materials.
2. A simplified calculation method for a double pipe borehole heat exchanger according to claim 1, characterised in that: the thermal resistance R of the unit length between the fluid in the tube of the sleeve-type buried tube heat exchanger and the rock-soil layer can be calculated by adopting the following formula:
thermal resistance Rf of convection heat exchange between the wall surface and the circulating working medium:
wherein r1 is the inner diameter of the outer sleeve, and m and hf are the convection heat transfer coefficient between the wall surface and the circulating working medium;
sleeve-type outer sleeve thermal resistance R1:
wherein r1 is the inner diameter of the outer sleeve in m; r2 is the outer diameter of the outer sleeve, in m; λ 1 is the thermal conductivity of the outer sleeve, with the unit W/(m · k);
backfill material thermal resistance R2:
wherein r1 is the inner diameter of the outer sleeve in m; r2 is the outer diameter of the outer sleeve, in m; λ 2 is the thermal conductivity of the outer sleeve, with the unit W/(m · k);
sleeve-type outer sleeve thermal resistance R3:
wherein r3 is the borehole aperture in m; r4 is the buried pipe influence radius in m; lambda 3 is the thermal conductivity coefficient of stratum rock and soil, and the unit W/(m.k);
the heat resistance per unit length of the ground heat exchanger is as follows:
R＝Rf+R1+R2+R3
the heat exchange quantity of the buried pipe in unit length is as follows:
wherein Tw is the initial formation temperature in units of; ti1 is the pipe section inlet temperature in units of ℃; to1 is the pipe section outlet temperature in units of ℃;
each pipe section is a continuous flow coupling heat exchange process, the outlet temperature of the previous pipe section is the inlet temperature of the next pipe section, namely:
To1＝Ti2
the heat exchange load calculation of the buried pipe meets the following requirements:
Q＝Cw×m×(To-Ti)
wherein: cw is the specific heat capacity of the circulating working medium, and the unit kJ/(kg. DEG C); and m is the mass flow of the fluid and has unit kg/s.
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| Application Number | Priority Date | Filing Date | Title |
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| CN202111606442.7A CN114491949A (en) | 2021-12-26 | 2021-12-26 | Simplified calculation method of sleeve type buried pipe heat exchanger |
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| CN202111606442.7A CN114491949A (en) | 2021-12-26 | 2021-12-26 | Simplified calculation method of sleeve type buried pipe heat exchanger |
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Application publication date: 20220513 |