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CN-121997400-A - Construction of heat transfer model of buried pipe heat exchanger and hole depth determination method of buried pipe heat exchanger

CN121997400ACN 121997400 ACN121997400 ACN 121997400ACN-121997400-A

Abstract

The application discloses a construction method of a heat transfer model of a buried pipe heat exchanger and a method for determining the hole depth of the buried pipe heat exchanger, and aims to solve the technical problem that the hole depth of a conventional buried pipe heat exchanger is unreasonable. According to the technical scheme, based on the heat transfer model of the ground heat exchanger, the better burial depth range is gradually thinned by adopting an interval approximation method, so that the optimal layout hole depth in the specific depth range is found, simplicity and science are realized, the accuracy of predicting the performance of the ground heat exchanger can be improved, and the efficiency and the reliability of a ground source heat pump system are further improved.

Inventors

  • SHI YONGXIA
  • REN SHENGWEI
  • YUE YANG
  • SONG XUE
  • Qu Jingdai
  • Cui Guocan
  • WANG WENJUAN
  • LI XIAOHUI
  • Yan yucai
  • JIN WANGLIN

Assignees

  • 河南省地质局生态环境地质服务中心

Dates

Publication Date
20260508
Application Date
20241211

Claims (10)

  1. 1. A construction method of a heat transfer model of a buried pipe heat exchanger comprises the following steps: (1) Determining a drilling depth range of a region to be determined, respectively analyzing hydrogeological conditions, rock-soil body thermophysical characteristics and ground temperature field characteristics in the range, and meshing the region to be determined; (2) Carrying out aquifer generalization according to the hydrogeological conditions and the thermophysical characteristics of the rock-soil mass, and vertically dividing the aquifer into a shallow aquifer temperature-changing zone, a shallow aquifer temperature-increasing zone, a weak permeable layer and a deep aquifer temperature-increasing zone; (3) Setting a solution condition, characterizing a water-bearing layer source sink item of a region to be determined, and constructing a steady flow model on the basis of the characterization, so as to simulate and obtain initial flow field distribution of the model under the given condition; (4) Characterizing the buried pipe heat exchanger and surrounding rock and soil mass based on the solving conditions, and establishing a heat transmission control equation to construct and obtain a heat transfer model of the buried pipe heat exchanger; the buried pipe heat exchanger is characterized by adopting a one-dimensional finite element method, and the control equation is as follows: ; ; ; ; ; ; ; ; Wherein, ρ r 、c r is the heat capacity of the fluid in the tube, ε g is the porosity of the backfill, ρ g 、c g is the heat capacity of the backfill, u is the flow rate of the circulating fluid in the tube, ∇ is the heat dispersion flux of the differential operator, and Λ r is the heat dispersion flux of the fluid in the tube; -the convective heat transfer coefficient between the fluid in the double U heat exchange tube and the wall of the inlet tube; -a convective heat transfer coefficient between the fluid in the double U heat exchange tube and the tube wall of the tube; -the convective heat transfer coefficient between the two tubes; -the coefficient of convective heat transfer of backfill material to the surrounding soil; The surrounding rock-soil body adopts a three-dimensional finite element processing method, and the heat transmission control equation is as follows: ; ; ; The method comprises the steps of s-water storage coefficient, dimensionless, superscript f-representing liquid, superscript s-representing soil, H-water head, Q-flow, beta-thermal expansion coefficient, Q-Darcy flow rate, ∇ -vector differential operator, T-temperature, epsilon-porosity, rho-density, c-specific heat capacity, H-heat source and sink, lambda-thermal conductivity, alpha L-longitudinal heat dispersion, alpha T-transverse heat dispersion and I-unit characteristic matrix.
  2. 2. The method of claim 1, wherein in step (2), the aqueous medium of the shallow aquifer temperature zone comprises silt, middlings, and fine sand.
  3. 3. The method of claim 1, wherein in step (2), the shallow aquifer-containing aqueous medium comprises fine sand, silt and silt.
  4. 4. A method of construction according to claim 1, wherein in step (2) the layer of water-impermeable rock comprises a thick layer of silty clay and/or a thin layer of silty clay.
  5. 5. The method of claim 1, wherein in step (2), the aqueous medium of the deep aquifer heating zone comprises a thin layer of fine sand, silt and/or silty clay.
  6. 6. The construction method according to claim 1, wherein in the step (3), the solution condition is that the surface layer temperature takes the annual average temperature of the area to be determined, the geothermal constant temperature zone takes 17.3 ℃, and each layer down takes a value according to the depth from the constant temperature zone and the ground temperature increasing rate.
  7. 7. The method of claim 1, wherein in step (3), the flow boundaries are generalized in the horizontal direction to be a replenishment boundary, a drainage boundary, and a zero flow boundary, and in the vertical direction to be a flux boundary surface and a water barrier boundary surface.
  8. 8. The construction method according to claim 1, wherein in the step (3), the surface and lower boundary of the area to be determined are generalized to be a constant temperature boundary.
  9. 9. The construction method according to claim 1, wherein in the step (1), triangle mesh division is performed on the super mesh surface using a triangule algorithm in the area to be determined.
  10. 10. A method for determining the hole depth of a buried pipe heat exchanger comprises the following steps: (1) Setting a simulation period based on the heat transfer model of the buried pipe heat exchanger, setting single-hole operation power and circulation flow rate of a heat exchange hole, and simulating through a circulation time sequence to establish a geothermal prediction model; (2) Based on the geothermal prediction model, respectively simulating and contrasting outlet temperatures of different buried depths of the buried pipes at specific intervals in a heating period and a cooling period, and respectively calculating inlet and outlet temperature differences of the buried pipes with different buried depths; (3) Drawing a 'temperature difference-depth' diagram, and respectively calculating slopes of different burial depth intervals of a refrigerating period and a heating period in an annual period; (4) Determining the period of slope change along with depth, further refining the lower limit of the burial depth interval where the minimum absolute value of slope is located in the period, further reducing the burial depth interval, simulating the outlet temperatures of different burial depths of the buried pipes in the period, then respectively calculating the inlet and outlet temperature differences of the buried pipe bodies of different burial depths, and drawing a 'temperature difference-depth' diagram; (5) And taking the intermediate value of two adjacent buried depth intervals with the largest gradient absolute value difference in the temperature difference-depth line graph as the optimal hole depth.

Description

Construction of heat transfer model of buried pipe heat exchanger and hole depth determination method of buried pipe heat exchanger The application aims at the application number 202411822020.7, the construction of the heat transfer model of the buried pipe heat exchanger and the method for determining the hole depth of the buried pipe heat exchanger, and the application date of the parent application is 2024.12.11. Technical Field The invention relates to the technical field of geothermal energy utilization, in particular to a method for constructing a heat transfer model of a buried pipe heat exchanger and determining the hole depth of the buried pipe heat exchanger. Background The buried pipe ground source heat pump system is a high-efficiency energy-saving environment-friendly air conditioning system which utilizes underground shallow geothermal resources to supply heat and refrigerate, and the performance of a buried pipe heat exchanger which is a core component directly influences the efficiency and reliability of the whole system. The buried pipe heat exchanger utilizes the constant temperature characteristic of underground soil and the natural flow of underground water to realize the heat storage and extraction by burying a pipeline in the ground. In practical applications, the performance of the borehole heat exchanger is closely related to the choice of hole depth. The traditional method for determining the hole depth of the buried pipe heat exchanger mainly depends on engineering experience and estimation, and has larger uncertainty, so that the drilling depth is often unreasonable (the drilling is too shallow, the heat exchange requirement of a system can not be met, the system efficiency is low, and the drilling is too deep, so that the resource waste is caused, the construction and operation cost of the system is increased), and the heat exchange efficiency and the operation cost of the system are further affected. Therefore, the scientific and accurate buried pipe heat exchanger hole depth determining method is developed, and has important significance for improving the efficiency and reliability of a ground source heat pump system. The information disclosed in this background section is only for enhancement of understanding of the background of the disclosure and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art that is well known to a person skilled in the art. Disclosure of Invention In view of at least one of the above technical problems, the present disclosure provides a method for constructing a heat transfer model of a buried pipe heat exchanger and determining a hole depth of the buried pipe heat exchanger, which adopts a method of interval approximation to gradually refine a preferred buried depth range, so that the hole depth is optimally distributed in a specific depth range, and a more accurate scientific basis is provided for the design of the buried pipe heat exchanger. According to one aspect of the disclosure, a method for constructing a heat transfer model of a buried pipe heat exchanger is provided, which comprises the following steps: (1) Determining a drilling depth range of a region to be determined, respectively analyzing hydrogeological conditions, rock-soil body thermophysical characteristics and ground temperature field characteristics in the range, and meshing the region to be determined; (2) Carrying out aquifer generalization according to the hydrogeological conditions and the thermophysical characteristics of the rock-soil mass, and vertically dividing the aquifer into a shallow aquifer temperature-changing zone, a shallow aquifer temperature-increasing zone, a weak permeable layer and a deep aquifer temperature-increasing zone; (3) Setting a solution condition, characterizing a water-bearing layer source sink item of a region to be determined, and constructing a steady flow model on the basis of the characterization, so as to simulate and obtain initial flow field distribution of the model under the given condition; (4) Characterizing the buried pipe heat exchanger and surrounding rock and soil mass based on the solving conditions, and establishing a heat transmission control equation to construct and obtain a heat transfer model of the buried pipe heat exchanger; the buried pipe heat exchanger is characterized by adopting a one-dimensional finite element method, and the control equation is as follows: ; ; ; ; ; ; ; ; Wherein, ρ r、cr is the heat capacity of the fluid in the tube, ε g is the porosity of the backfill, ρ g、cg is the heat capacity of the backfill, u is the flow rate of the circulating fluid in the tube, ∇ is the heat dispersion flux of the differential operator, and Λ r is the heat dispersion flux of the fluid in the tube; -the convective heat transfer coefficient between the fluid in the double U heat exchange tube and the wall of the inlet tube; -a convective heat transfer coefficient be