Reinforced heat exchange structure of freezing pipe of metro connecting channel and manufacturing and control method of reinforced heat exchange structure

Abstract

The invention discloses a subway connection channel freezing pipe enhanced heat exchange structure and a manufacturing and control method thereof.The heat exchange structure comprises a hollow pipe body, a heat conduction pipe is coaxially sleeved with the pipe body, a plurality of closely-adjacent hexagonal grooves are formed in the cross section of the pipe wall of the heat conduction pipe, a honeycomb structure is formed, and the honeycomb structure is filled with a phase change material; an inner corrugated pipe is coaxially sleeved with the heat conduction pipe and is a hollow pipe body, and a plurality of protruding edges are continuously arranged around the inner wall of the corrugated pipe and extend along the axis of the heat conduction pipe. Spiral fins are wound outside the pipe body, and a gap is reserved between every two adjacent spiral fins; wherein one end of the pipe body is closed, and the other end is communicated with a brine branch; and the interior of the pipe body is used for introducing cooling liquid so as to cool the peripheral environment of the pipe body. The problems that an existing traditional smooth freezing pipe is smooth in surface and limited in heat exchange area, and saline water in the pipe mostly flows in a laminar flow state, so that the convective heat exchange coefficient is insufficient are solved.

Description

Technical Field

[0001] This invention belongs to the field of underground engineering construction technology, specifically relating to a reinforced heat exchange structure for a freezing pipe in a subway connecting passage and its manufacturing and control methods. Background Technology

[0002] The freezing method for subway connecting tunnel construction is an important technique in underground engineering. It involves artificially freezing water in the ground to form a frozen curtain with sufficient strength and sealing, ensuring the safety of tunnel excavation and structural construction. The freezing pipe, as the core component of the freezing system, directly determines the formation speed, uniformity, and construction efficiency of the frozen curtain through its heat exchange performance. In subway connecting tunnel construction, the freezing pipe must efficiently transfer cold energy under complex geological conditions to meet the requirements of rapid construction and safety assurance.

[0003] In existing technologies, the freezing method for subway connecting passage construction typically uses smooth, low-carbon seamless steel pipes as freezing pipes. These smooth freezing pipes circulate low-temperature brine internally, transferring cold energy to the surrounding soil, causing the moisture in the soil to freeze and form a freezing curtain. Traditional freezing pipes are hollow cylinders, typically with an outer diameter of 89-127 mm and a wall thickness of 5-8 mm. The material is mostly low-carbon steel with a thermal conductivity of approximately 50 W / m·K. Inside the pipe, a brine circulation system delivers low-temperature brine at a flow rate of 0.1-0.3 m / s. The cold energy is conducted through the pipe wall to the surrounding soil, causing the soil moisture to transform into ice, forming a freezing wall.

[0004] To improve freezing efficiency, existing technologies often employ methods such as increasing the number of freezing pipes or lowering the brine temperature. However, these measures typically result in low cold energy utilization, prolonged freezing time, and high construction energy consumption. Furthermore, traditional smooth freezing pipes have low heat exchange efficiency due to their smooth surface, limited heat exchange area, and the fact that the brine flow inside the pipe is mostly laminar, leading to insufficient convective heat transfer coefficients. This makes it difficult to meet the technical requirements for rapid and uniform freezing under complex geological conditions. Summary of the Invention

[0005] The purpose of this invention is to provide a heat exchange enhancement structure for a freezing pipe in a subway connecting passage, as well as its manufacturing and control methods, to solve the problem that existing traditional smooth freezing pipes have insufficient convective heat transfer coefficients due to their smooth surface, limited heat exchange area, and laminar flow of brine inside the pipe.

[0006] The present invention adopts the following technical solution: a frozen pipe enhanced heat exchange structure for subway connecting passages, including a hollow tube body, a heat-conducting pipe coaxially installed inside the tube body, and multiple closely adjacent hexagonal grooves on the cross-section of the tube wall of the heat-conducting pipe forming a honeycomb structure, the honeycomb structure being filled with phase change material. The heat pipe is coaxially fitted with an inner bellows, which is a hollow tube with multiple protruding ribs continuously arranged around the inner wall. The protruding ribs extend along the axis of the heat pipe. The tube body is wound with spiral ribs, with gaps between adjacent spiral ribs; One end of the pipe is closed, while the other end is used to connect to the brine branch; the inside of the pipe is used to introduce coolant to cool its surrounding environment.

[0007] Furthermore, the spiral ribs have a spiral angle of 15°-45°, a height of 5-15mm, a thickness of 1-3mm, and a spacing of 10-30mm between adjacent spiral ribs.

[0008] Furthermore, the cross-sectional shape of the convex ridge is a triangle with its vertex pointing towards the central axis of the tube, and the vertex is arc-shaped. The maximum height of the convex ridge is 2-5mm, and the wavelength is 10-20mm.

[0009] Furthermore, a highly thermally conductive putty is filled between the tube body and the heat-conducting tube.

[0010] Furthermore, a graphene coating is applied to the surface of the spiral ribs.

[0011] Furthermore, the heat pipe is made of copper, aluminum, or carbon fiber, and the hollow volume of the heat pipe accounts for 10%-30%.

[0012] Furthermore, a flow meter and a temperature measuring device are installed at the end of the pipe that connects to the brine branch.

[0013] The second technical solution adopted in this invention is a manufacturing method for a frozen pipe enhanced heat exchange structure for subway connecting passages. Based on the frozen pipe enhanced heat exchange structure for subway connecting passages, an inner corrugated pipe is formed by cold rolling or hydraulic forming process, spiral ribs are processed on the outer wall of the pipe body by spiral welding or 3D printing, and phase change material is filled into the heat pipe by vacuum injection process.

[0014] The third technical solution adopted in this invention is a control method for a frozen pipe enhanced heat exchange structure in a subway connecting passage, specifically including: The flow rate of coolant in the pipe and the temperature change inside the pipe are collected by a flow meter and a temperature sensor. Based on temperature changes, the flow meter is adjusted to ensure the flow rate inside the pipe reaches the level required to meet freezing conditions.

[0015] The beneficial effects of this invention are: 1. This invention significantly increases the heat exchange area and enhances the turbulence of brine inside the pipe by setting spiral ribs on the outer surface of the pipe body and continuously setting prisms on the inner corrugated pipe, thereby effectively accelerating the construction progress of the subway connecting passage.

[0016] 2. This invention uses a high thermal conductivity aluminum alloy or copper alloy tube body, combined with a graphene coating and a phase change material embedded in the heat pipe, to reduce thermal resistance and improve the efficiency of cold energy utilization, thus promoting green and low-carbon construction.

[0017] 3. By setting up a phase change material layer with spiral ribs and a honeycomb structure, combined with a differential temperature strategy, this invention is adaptable to complex geological conditions such as clay layers and water-rich sand layers. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the enhanced heat exchange structure of the freezing pipe in the subway connecting passage of the present invention.

[0019] The components include: 1. tube body; 2. spiral fins; 3. inner corrugated tube; 4. heat pipe; and 5. phase change material. Detailed Implementation

[0020] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0021] This invention improves a heat exchange structure for frozen pipes in subway connecting passages, such as... Figure 1 As shown, it includes a hollow tube 1, which is made of aluminum alloy or copper alloy with a thermal conductivity ≥200W / m·K. A heat-conducting tube 4 is coaxially installed inside the tube 1. The cross-section of the tube wall of the heat-conducting tube 4 has multiple closely adjacent hexagonal grooves forming a honeycomb structure. The honeycomb structure is filled with a phase change material 5. The freezing point of the phase change material 5 is -5℃ to -10℃, and the latent heat of phase change is ≥150kJ / kg. The honeycomb structure is used to increase the contact area between the phase change material 5 and the tube 1, as well as with the surrounding soil.

[0022] The heat pipe 4 is coaxially fitted with an inner corrugated pipe 3, which is a hollow tube with multiple protruding ribs continuously arranged around the inner wall. The protruding ribs extend along the axis of the heat pipe 4. The outside of the tube body 1 is wound with spiral ribs 2, with gaps between adjacent spiral ribs 2. One end of the tube body 1 is closed, and the other end is used to connect with the brine branch. Coolant is introduced into the tube body 1 to cool the surrounding soil environment.

[0023] In some embodiments, the spiral fins 2 have a spiral angle of 15°-45°, a height of 5-15mm, a thickness of 1-3mm, and a spacing of 10-30mm between adjacent spiral fins 2. In locations requiring higher cooling efficiency, the spiral fins can be arranged more densely and at higher elevations.

[0024] In some embodiments, the cross-sectional shape of the convex ridge is a triangle with its vertex pointing to the central axis of the tube body 1, the vertex being arc-shaped, the maximum height of the convex ridge being 2-5mm, and the wavelength being 10-20mm.

[0025] In some embodiments, a highly thermally conductive putty is filled between the tube body 1 and the heat-conducting pipe 4 to reduce contact thermal resistance.

[0026] In some embodiments, a graphene coating is applied to the surface of the spiral rib 2 to improve thermal conductivity.

[0027] In some embodiments, the heat pipe 4 is made of copper, aluminum or carbon fiber, and the hollow volume of the heat pipe 4 accounts for 10%-30%.

[0028] In some embodiments, a flow meter and a temperature measuring device are provided at the end of the pipe body 1 that connects to the brine branch. The thermocouples in the temperature measuring device can be multiple and arranged in an array.

[0029] The present invention also provides a method for manufacturing a reinforced heat exchange structure for a frozen pipe in a subway connecting passage. The inner corrugated pipe 3 is formed by cold rolling or hydroforming process, and spiral ribs 2 are processed on the outer wall of the pipe body 1 by spiral welding or 3D printing. The heat pipe 4 is filled with phase change material 5 by vacuum injection process, and the cooling rate is controlled during the filling process to avoid phase separation.

[0030] The present invention also provides a control method for the enhanced heat exchange structure of the freezing pipe in a subway connecting passage, specifically including: collecting the flow rate of the coolant in the pipe body 1 and the temperature change inside the pipe body 1 through a flow meter and a temperature sensor; and adjusting the flow meter according to the temperature change to achieve the flow rate required to meet the freezing conditions inside the pipe body 1.

[0031] The method of using the enhanced heat exchange structure of the freezing pipe in the subway connecting passage of this invention is as follows: In the construction of subway connecting passages in general clay layers, the enhanced heat exchange structure of the freezing pipe is vertically arranged around the perimeter of the connecting passage and connected to a low-temperature brine circulation system for continuous cyclic freezing. During the initial freezing period, it operates at full power for the first 7 days to form an initial frozen wall thickness of 0.5m. Subsequently, during the maintenance period, the brine temperature is adjusted to -20℃, and the soil temperature field is monitored using thermocouple arrays spaced every 0.5m. After the frozen curtain is completed, tunnel excavation and lining pouring are carried out. Throughout the process, CFD software is used to simulate the temperature field in real time and optimize the brine flow rate. Example

[0032] The standard composite structure freezing pipe of this invention is used for the construction of subway connecting passages in general clay layers. This embodiment provides a standard composite freezing pipe suitable for the freezing method construction of subway connecting passages in general clay layers. Its structural parameters are configured for medium strength, and the material selection is mainly aluminum alloy. It is suitable for clay layers with a moisture content of 20%-25%.

[0033] Specific structure: like Figure 1 As shown, the freezing tube includes a tube body 1, spiral fins 2, an inner corrugated tube 3, a phase change material 5, and a heat-conducting tube 4. The tube body 1 is a hollow cylinder with an outer diameter of 108 mm, a wall thickness of 7 mm, and a length of 5 m. It is made of 6061 aluminum alloy with a thermal conductivity of approximately 200 W / m·K. Continuous spiral fins 2 are arranged on the outer surface of the tube body 1, with a spiral angle of 25°, a fin height of 8 mm, a fin thickness of 2 mm, and a fin spacing of 20 mm. The grooves between adjacent spiral fins 2 are 3 mm wide and 1 mm deep, used to guide the flow of brine to enhance heat dissipation. The inner corrugated pipe 3 has a convex ridge depth of 3mm. Phase change material 5, 15mm thick, is filled inside the pipe body 1. It uses an ethylene glycol-water mixture as the phase change material, with a freezing point of -5℃ and a latent heat of phase change of 180kJ / kg. A honeycomb-shaped heat-conducting pipe structure with a porosity of 30% is employed to increase the contact area with the pipe body 1 and the surrounding soil. The heat-conducting pipe 4, made of aluminum wire, forms a continuous heat-conducting channel, accounting for 20% of the volume. High thermal conductivity mortar, with a thermal conductivity of 5W / m·K, is filled between the pipe body 1 and the heat-conducting pipe 4 to reduce contact thermal resistance. The spiral fins 2 are coated with a graphene coating of 0.1mm thickness, improving thermal conductivity by 15%.

[0034] Manufacturing method: The inner corrugated tube 3 is formed by cold rolling or hydroforming process, the spiral ribs 2 are processed on the outer wall of the tube body 1 by winding welding or 3D printing, and the heat pipe 4 is filled with phase change material 5 by vacuum injection process. The surface of the spiral rib 2 was sandblasted to improve the roughness Ra to 3.2μm, and a graphene coating 8 was applied using chemical vapor deposition with a thickness of 0.1mm. Preparation of heat pipe 4: Aluminum wire with a diameter of 1mm is woven into a mesh structure, accounting for 20% of the volume, and the surface is anodized to improve compatibility with phase change materials; Quality inspection: The welding quality of the spiral rib 2 was inspected by ultrasonic testing, a water pressure test was conducted at a pressure of 2MPa for 10 minutes, and the structural dimensional accuracy was verified by a 3D laser scanner.

[0035] Application method: In the construction of subway connecting passages in general clay layers, the freezing pipes are vertically arranged around the perimeter of the connecting passage at a spacing of 1.2m and a depth of 20m. They are connected to a low-temperature brine circulation system for continuous cyclic freezing. During the initial freezing period, the system operates at full power for the first 7 days, forming an initial frozen wall thickness of 0.5m. Subsequently, during the maintenance period, the brine temperature is adjusted to -20℃, and the soil temperature field is monitored using thermocouple arrays spaced 0.5m apart. After the frozen curtain is fully formed, tunnel excavation and lining pouring are carried out. The entire process incorporates real-time temperature field simulation using CFD software to optimize the brine flow rate.

[0036] Experimental data and simulation results: Laboratory model test at a 1:10 scale, using sand to simulate clay with a moisture content of 22%: The average heat transfer coefficient of this freezing pipe is 285 W / m²·K, which is 58% higher than the 180 W / m²·K of the traditional smooth freezing pipe. The time required to reach a frozen wall thickness of 5 cm is 12 hours, which is 42% shorter than the traditional pipe. Numerical simulation using ANSYS Fluent, a three-dimensional unsteady-state model, considering the phase change enthalpy-porosity method: The temperature field shows a 35% increase in isotherm density, and the circumferential thickness difference of the frozen wall is <2 mm, which is better than the <5 mm of the traditional pipe. Energy consumption simulation shows that under the same freezing effect, the brine temperature can be increased by 6℃, and energy consumption can be reduced by 18%. Example

[0037] Variable cross-section composite freezing pipe used in the construction of subway connecting passages in water-rich sandy layers This embodiment targets water-rich sand layers with a moisture content >30%, emphasizing enhanced heat transfer at the bottom, and selecting copper alloys to improve thermal conductivity.

[0038] Specific structure: The tube body 1 is a hollow cylinder with an outer diameter of 108 mm, a wall thickness of 7 mm, and a length of 6 m. It is made of copper alloy with a thermal conductivity of 385 W / m·K. It employs a variable cross-section design along the axial direction: the bottom 1 m section has densely packed spiral fins 2 with a height of 12 mm and a spacing of 15 mm; the upper 5 m section has a height of 6 mm and a spacing of 25 mm; the spiral angle is 35°, the fin thickness is 2 mm, and the width between adjacent spiral fins 2 is 4 mm, with a depth of 1.5 mm. The phase change material 5 is 20 mm thick and uses a special frozen phase change material, paraffin-based composite, with a freezing point of -8℃ and a latent heat of phase change of 200 kJ / kg. The heat-conducting pipe 4 is made of carbon fiber, accounting for 25% of the volume, forming a continuous heat-conducting channel. High thermal conductivity putty with a thermal conductivity of 6 W / m·K is filled between the tube body 1 and the heat-conducting pipe 4. The surface of the spiral fins 2 is coated with a graphene coating with a thickness of 0.15 mm.

[0039] Manufacturing method: The inner corrugated tube 3 is formed by cold rolling or hydroforming process, the spiral ribs 2 are processed on the outer wall of the tube body 1 by winding welding or 3D printing, and the heat pipe 4 is filled with phase change material 5 by vacuum injection process. The surface of the spiral rib 2 is chemically treated and coated with graphene coating 8; carbon fiber heat pipe 4 is prepared with a braiding density of 200 g / m² and surface treated with silane coupling agent; and filled with high thermal conductivity putty.

[0040] Quality inspection: X-ray inspection of the printed layer bonding, air pressure test at 3MPa, and optical measurement to verify the accuracy of the variable cross-section.

[0041] Application method: During construction in water-rich sand layers, freezing pipes were spaced 1.0m apart and laid at a depth of 25m. The brine temperature was -28℃, and the flow velocity was 0.4m / s. A differential temperature strategy was adopted, with the brine temperature at the bottom at -30℃ and at the top at -25℃. A groundwater flow model was used to monitor the impact of seepage. High flow was initially used to form a 1m thick frozen wall, and the flow rate was reduced by 20% during the maintenance period. Real-time adjustments were made based on temperature sensor feedback during excavation.

[0042] Experimental data and simulation results: Laboratory tests simulating water-rich sand reduced freezing time by 48% and groundwater carried away less cold by 25%. Simulating COMSOL, a multiphysics coupling model including Darcy flow, showed: frozen wall development velocity at the bottom increased by 40%, overall uniformity difference <1.5mm; energy consumption decreased by 22%, and brine temperature increased by 8℃. Example

[0043] High-strength composite structure freezing pipes are used for auxiliary freezing construction in deep foundation pits. This embodiment is applicable to deep foundation pits with an auxiliary freezing depth >30m, mixed strata, and adopts high-strength materials and modular design, with structural parameters biased towards durability.

[0044] Specific structure: The tube body 1 has an outer diameter of 114mm, a wall thickness of 8mm, and a length of 8m. It is modularly assembled, with each 4m section made of high thermal conductivity steel with added Cu, and a thermal conductivity of 70W / m·K. The spiral fins 2 have an angle of 20°, a height of 10mm, a thickness of 3mm, and a spacing of 25mm. The channel width between adjacent spiral fins 2 is 3.5mm and the depth is 1.2mm. The phase change material 5 is 25mm thick, an inorganic salt hydrate, with a freezing point of -10℃, a latent heat of 160kJ / kg, and a porosity of 35%. The heat-conducting pipe 4 is a copper mesh, accounting for 15% of the volume. The putty 7 has a thermal conductivity of 4.5W / m·K. The fins 2 are coated with a nano-ceramic coating 10, 0.2mm thick, which improves wear resistance.

[0045] Manufacturing method: The inner corrugated tube 3 is formed by cold rolling or hydroforming process, the spiral ribs 2 are processed on the outer wall of the tube body 1 by winding welding or 3D printing, and the heat pipe 4 is filled with phase change material 5 by vacuum injection process. Sandblasting of the spiral ribs; The heat pipe 4 of the copper mesh skeleton is electroplated with Ni; and filled with putty.

[0046] The phase change material is a salt hydrate heated to 50°C, thickener added; segmented vacuum filling, cooling at 3°C / min; annealing and curing.

[0047] Testing: Metallographic analysis of the connection, durability cycle test of 50 freeze-thaw cycles.

[0048] Application method: Deep foundation pits are assisted by freezing, arranged in a ring array with a spacing of 1.5m and a depth of 35m; brine at -26℃ with a flow rate of 0.2m / s; modules are spliced ​​using flange connections; layout is combined with BIM simulation; stress field is monitored during the maintenance period; and excavation is carried out in layers.

[0049] Experimental data and simulation results: Laboratory-scale mixed soil simulation: heat transfer coefficient increased by 45% to 260 W / m²·K; freezing time was shortened by 35%; durability degradation was <5% per 100 cycles. ABAQUS simulation with coupled stress: stable temperature field, uniform wall thickness (<3 mm difference); energy consumption reduced by 16%. On-site foundation pit: construction period shortened by 28 days; safety accident rate reduced by 60%.

[0050] Experimental Comparison Table To verify the performance advantages of the enhanced heat exchange structure of the freezing pipe in the subway connecting passage of the present invention, laboratory model tests and field tests were conducted to compare the performance of the composite structure freezing pipe of the present invention with that of the traditional smooth freezing pipe. The experimental data and simulation results are shown in the table below. For specific implementation methods, please refer to Examples 1, 2, and 3.

[0051]

[0052] illustrate: The table above compares the performance of the composite structure freezing pipe of this invention with that of a traditional smooth freezing pipe through laboratory model tests. Example 1 is for clay layers, Example 2 is for water-rich sand layers, and Example 3 is for mixed strata in deep foundation pits. The results show that the freezing pipe of this invention increases the heat transfer coefficient by 45%-75%, shortens the freezing time by 35%-48%, reduces energy consumption by 16%-22%, shortens the construction period by 10-28 days, and reduces the accident rate by 50%-70%.

Claims

1. A frozen pipe enhanced heat exchange structure for subway connecting passages, characterized in that, It includes a hollow tube (1), and a heat-conducting tube (4) is coaxially installed inside the tube (1). The heat-conducting tube (4) has multiple closely adjacent hexagonal grooves on its cross-section to form a honeycomb structure. The honeycomb structure is filled with phase change material (5). The heat pipe (4) is coaxially fitted with an inner corrugated pipe (3). The corrugated pipe (3) is a hollow tube with multiple protruding ribs continuously arranged around the inner wall. The protruding ribs extend along the axis of the heat pipe (4). The tube body (1) is wound with spiral ribs (2) on the outside, and there is a gap between adjacent spiral ribs (2); One end of the pipe (1) is closed, and the other end is used to connect with the brine branch; the inside of the pipe (1) is used to introduce coolant to cool and reduce the temperature of its surrounding environment.

2. The enhanced heat exchange structure for freezing pipes in subway connecting passages according to claim 1, characterized in that, The spiral rib (2) has a spiral angle of 15°-45°, a height of 5-15mm, a thickness of 1-3mm, and a spacing of 10-30mm between adjacent spiral ribs (2).

3. The enhanced heat exchange structure for freezing pipes in subway connecting passages according to claim 1 or 2, characterized in that, The cross-sectional shape of the convex ridge is a triangle with its vertex pointing to the central axis of the tube (1), and the vertex is arc-shaped. The maximum height of the convex ridge is 2-5mm, and the wavelength is 10-20mm.

4. The enhanced heat exchange structure for freezing pipes in subway connecting passages according to claim 3, characterized in that, High thermal conductivity putty is filled between the tube body (1) and the heat-conducting tube (4).

5. The enhanced heat exchange structure for freezing pipes in subway connecting passages according to claim 3, characterized in that, The surface of the spiral rib (2) is coated with a graphene coating.

6. The enhanced heat exchange structure for freezing pipes in subway connecting passages according to claim 3, characterized in that, The heat pipe (4) is made of copper, aluminum or carbon fiber, and the hollow volume of the heat pipe (4) accounts for 10%-30%.

7. The enhanced heat exchange structure for freezing pipes in subway connecting passages according to claim 3, characterized in that, A flow meter and a temperature measuring device are installed at one end of the pipe (1) that is connected to the brine branch.

8. A method for manufacturing a frozen pipe enhanced heat exchange structure for a subway connecting passage, characterized in that, Based on the subway connecting passage freezing pipe enhanced heat exchange structure according to any one of claims 1-7, the inner corrugated pipe (3) is formed by cold rolling or hydraulic forming process, the spiral ribs (2) are processed on the outer wall of the pipe body (1) by spiral welding or 3D printing method, and the heat pipe (4) is filled with phase change material (5) by vacuum injection process.

9. A control method for a frozen pipe enhanced heat exchange structure in a subway connecting passage, characterized in that, The enhanced heat exchange structure for the subway connecting passage freezing pipe as described in claim 7 specifically includes: The flow rate of the coolant in the pipe (1) and the temperature change inside the pipe (1) are collected by a flow meter and a temperature sensor. Based on the temperature change, the flow meter is adjusted to ensure that the flow rate inside the pipe (1) meets the freezing conditions.

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