Downhole efficient heat exchange device suitable for medium-deep layer geothermal exploitation

Abstract

The utility model discloses an underground efficient heat exchange device suitable for medium-deep layer geothermal exploitation. Comprising a spiral inner rib heat exchange enhancement outer sleeve and a spiral outer rib heat insulation inner sleeve which are coaxially arranged in a drilled deep heating stratum in a sleeving manner, a smooth outer sleeve and a heat insulation inner sleeve which are coaxially arranged in a shallow variable-temperature stratum and a drilled constant-temperature stratum in a sleeving manner, a first heat exchanger, a second heat exchanger and a heat pump unit, the heat insulation inner sleeve is coaxially connected with the spiral outer rib heat insulation inner sleeve; the smooth outer sleeve is coaxially connected with the spiral inner rib enhanced heat exchange outer sleeve; the top end of the spiral inner rib enhanced heat exchange outer sleeve is open and the bottom end is closed; the top end and the bottom end of the spiral outer rib heat insulation inner sleeve are open; the spiral inner rib enhanced heat exchange outer sleeve, the spiral outer rib heat insulation inner sleeve, the smooth outer sleeve and the heat insulation inner sleeve jointly form a sleeve structure with a closed bottom end and an open top. The utility model can effectively solve the problem of low heat transfer performance of the existing mid-deep geothermal heat exchange technology.

Description

Technical Field

[0001] This utility model relates to the field of geothermal energy development technology, specifically to a downhole high-efficiency heat exchange device suitable for medium-deep geothermal development. Background Technology

[0002] Medium-deep geothermal heating technology has developed rapidly in northern my country. It not only occupies a small area but also has a high heat exchange power per meter, effectively making up for the shortcomings of shallow geothermal energy in the development and utilization process. However, the high cost still restricts the large-scale promotion of medium-deep geothermal energy.

[0003] Existing medium-deep geothermal heating technologies are divided into hydrothermal development technologies and heat exchanger development technologies. Hydrothermal development technologies are constrained by geological resource conditions and cannot be widely adopted. Heat exchanger development technologies have wider applicability and are not constrained by resource conditions; however, compared to hydrothermal development technologies, their economic efficiency is relatively poor. Therefore, to reduce dependence on natural resources during medium-deep geothermal development, heat exchanger development technologies need to be upgraded to improve their techno-economic efficiency. Currently, existing medium-deep geothermal heat exchanger development technologies use coaxial tube heat exchangers and U-shaped heat exchangers as core heat exchange components. The heat exchanger tubes often use oil-filled tubing with bare tube walls, resulting in low heat transfer performance. Summary of the Invention

[0004] The purpose of this invention is to provide a downhole high-efficiency heat exchange device suitable for medium-deep geothermal development, in order to address the problem of low heat transfer performance in existing medium-deep geothermal heat exchange development technologies.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] A high-efficiency downhole heat exchange device suitable for medium-deep geothermal development includes a spiral inner-ribbed reinforced heat exchange outer sleeve and a spiral outer-ribbed heat-insulating inner sleeve, coaxially fitted in the deep, warming formation of the borehole; a smooth outer sleeve and a heat-insulating inner sleeve, coaxially fitted in the shallow, variable-temperature formation and the constant-temperature formation of the borehole; and a first heat exchanger, a second heat exchanger, and a heat pump unit; wherein:

[0007] The inner heat-insulating tube is coaxially connected to the upper end of the spiral outer heat-insulating tube, and both have the same inner and outer diameters; the smooth outer tube is coaxially connected to the upper end of the spiral inner heat-exchange reinforced outer tube, and both have the same inner and outer diameters; the top end of the spiral inner heat-exchange reinforced outer tube is open and the bottom end is closed, while the top and bottom ends of the spiral outer heat-insulating tube are both open; the spiral inner heat-exchange reinforced outer tube, the spiral outer heat-insulating tube, the smooth outer tube, and the inner heat-insulating tube together form a tube structure with a closed bottom and an open top;

[0008] The top of the smooth outer sleeve is connected to the primary side inlet pipe of the first heat exchanger and the primary side inlet pipe of the second heat exchanger via the geothermal well outlet pipe, and the top of the heat-insulating inner sleeve is connected to the primary side outlet pipe of the first heat exchanger and the primary side outlet pipe of the second heat exchanger via the geothermal well outlet pipe.

[0009] The user-side water outlet pipe is connected to the secondary side water inlet pipe of the first heat exchanger and the condenser side water inlet pipe of the heat pump unit, respectively; the user-side water inlet pipe is connected to the secondary side water outlet pipe of the first heat exchanger and the condenser side water outlet pipe of the heat pump unit, respectively.

[0010] The secondary side outlet of the second heat exchanger is connected to the evaporator side inlet pipe of the heat pump unit, and the secondary side inlet of the second heat exchanger is connected to the evaporator side outlet pipe of the heat pump unit.

[0011] A ground-source circulating pump is installed at the inlet end of the geothermal well outlet pipe, and a primary-side water inlet control valve for the second heat exchanger is installed at the outlet end of the geothermal well outlet pipe.

[0012] A primary-side inlet control valve is installed on the primary-side inlet pipe of the first heat exchanger, and a primary-side outlet control valve is installed on the primary-side outlet pipe of the first heat exchanger; a secondary-side outlet control valve is installed on the secondary-side outlet pipe of the first heat exchanger, and a secondary-side inlet control valve is installed on the secondary-side inlet pipe of the first heat exchanger; a condenser-side outlet control valve is installed on the condenser-side outlet pipe of the heat pump unit, and a condenser-side inlet control valve is installed on the condenser-side inlet pipe of the heat pump unit; a user-side circulating pump is installed on the user-side outlet pipe.

[0013] Furthermore, the spiral inner rib reinforced heat exchange outer tube and the smooth outer tube, as well as the spiral outer rib heat insulation inner tube and the heat insulation inner tube, are all connected by threaded sealing.

[0014] Furthermore, the spiral inner rib reinforced heat exchange outer tube is made of a high thermal conductivity metal tube; the outer wall of the spiral inner rib reinforced heat exchange outer tube is uniformly coated with a graphene coating, and the inner wall is provided with rectangular high thermal conductivity spiral inner ribs.

[0015] Furthermore, the rectangular high thermal conductivity spiral inner ribs are 16 to 20 pieces, the height and width of the ribs are preferably 3mm, and the spiral angle is preferably 30°.

[0016] Furthermore, the spiral outer rib heat-insulating inner sleeve is filled with aerogel as a heat-insulating material; the outer wall of the spiral outer rib heat-insulating inner sleeve is provided with rectangular spiral outer ribs.

[0017] Furthermore, the rectangular spiral outer ribs consist of 16 to 20 pieces, with a rib height and width of 3 mm and a spiral angle of 30°.

[0018] Furthermore, a low-density, low-thermal-conductivity composite cementing material is filled between the smooth outer casing and the shallow, variable-temperature formation.

[0019] Furthermore, the space between the spiral inner rib reinforced heat exchange outer tube and the constant temperature formation and the deep heating formation is filled with conventional high-density thermal conductivity composite cementing material.

[0020] Compared with the prior art, this utility model has the following beneficial technical effects:

[0021] Compared with the currently used medium-deep coaxial casing heat exchangers, the downhole high-efficiency heat exchange device of this invention increases the wetted perimeter of the annulus and decreases the equivalent diameter by adding rectangular spiral fins to the inner wall of the outer casing and the outer wall of the inner casing, thereby expanding the heat exchange area between the fluid and the outer casing wall. Furthermore, the spiral fin structure causes the fluid flow to rotate, enhancing turbulence intensity. Both of these enhanced heat transfer effects help reduce the temperature of the inner wall of the outer casing and increase the heat transfer coefficient between the inner wall and the fluid. The uniform coating of graphene on the outer wall of the casing enhances the heat absorption capacity of the heat exchange device from the surrounding high-temperature rock and soil, thereby increasing the heat exchange power of the geothermal well and improving the technical and economic feasibility of medium-deep heat exchange development technology. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the overall structure of the high-efficiency downhole heat exchange device for medium-deep geothermal development according to this utility model.

[0023] Figure 2(a) is a perspective view of a medium-deep geothermal coaxial tube heat exchanger with spiral fins added;

[0024] Figure 2(b) shows a cross-section of a medium-deep geothermal coaxial tube heat exchanger with spiral fins added;

[0025] Figure 3 A schematic diagram of the spiral inner rib reinforced heat exchange outer tube;

[0026] Figure 4 This is a schematic diagram of the spiral outer rib thermal insulation inner sleeve;

[0027] Figure 5(a) is a cloud map of fluid temperature distribution in the inner tube of a medium-deep geothermal coaxial tube heat exchanger with added spiral fins.

[0028] Figure 5(b) is a cloud map of the fluid temperature distribution inside the inner tube of a conventional coaxial tube heat exchanger;

[0029] Figure 6(a) shows the fluid streamlines inside a medium-deep geothermal coaxial tube heat exchanger with added spiral fins;

[0030] Figure 6(b) is a flow diagram of fluid flow inside a conventional coaxial tube heat exchanger.

[0031] The labels in the diagram represent the following: 1-Shallow variable-temperature formation, 2-Isothermal formation, 3-Deep heating formation, 4-Helical inner rib reinforced heat exchange outer casing, 5-Helical outer rib insulated inner casing, 6-Conventional density high thermal conductivity composite cementing material, 7-Smooth outer casing, 8-Insulated inner casing, 9-Low density low thermal conductivity composite cementing material, 10-Geothermal well inlet pipe, 11-Geothermal well outlet pipe, 12-Ground source side circulation pump, 13-First heat exchanger primary side inlet control valve, 14-First heat exchanger primary side outlet control valve, 15-Second heat exchanger primary side inlet pipe, 16-Second heat exchanger primary side outlet pipe, 17-Second heat exchanger primary side outlet control valve, 18-Second heat exchanger primary side inlet control valve, 19-Second heat exchanger 20 - Evaporator side water outlet pipe of heat pump unit; 21 - Evaporator side water inlet pipe of heat pump unit; 22 - Intermediate circulation pump; 23 - Heat pump unit; 24 - Condensate side water inlet control valve of heat pump unit; 25 - Condensate side water outlet control valve of heat pump unit; 26 - Condensate side water inlet pipe of heat pump unit; 27 - Condensate side water outlet pipe of heat pump unit; 28 - User side circulation pump; 29 - User side water outlet pipe; 30 - User side water inlet pipe; 31 - Secondary side water inlet pipe of first heat exchanger; 32 - Secondary side water outlet pipe of first heat exchanger; 33 - Secondary side water inlet control valve of first heat exchanger; 34 - Secondary side water outlet control valve of first heat exchanger; 35 - First heat exchanger; 36 - Primary side water outlet pipe of first heat exchanger; 37 - Primary side water inlet pipe of first heat exchanger.

[0032] 401 - Spiral inner rib reinforced heat exchange outer tube body; 402 - Rectangular high thermal conductivity spiral inner rib; 501 - Spiral outer rib heat insulation inner tube body; 502 - Rectangular spiral outer rib.

[0033] The present invention will be further explained below with reference to the accompanying drawings and specific embodiments. Detailed Implementation

[0034] It should be noted that all components and equipment used in this utility model, unless otherwise specified, are those known in the art. For example, the user heating equipment uses conventional fan coil units or water heaters. The first heat exchanger 35 and the second heat exchanger 19 both use conventional plate heat exchangers known in the art. The smooth outer sleeve 7 and the heat-insulating inner sleeve 8 use conventional pipe materials known in the art. The ground source side circulation pump 12, the user side circulation pump 28, and the intermediate circulation pump 22 all use conventional variable frequency circulation pumps known in the art.

[0035] The borehole used in this invention is a conventional drilling technique with a depth of 200m to 4000m. The geological structure around the borehole is divided into three layers from top to bottom: shallow variable temperature layer 1, constant temperature layer 2, and deep warming layer 3.

[0036] This utility model provides a downhole high-efficiency heat exchange device suitable for medium-deep geothermal development, such as... Figures 1 to 4 As shown, it includes a spiral inner rib reinforced heat exchange outer sleeve 4 and a spiral outer rib insulated inner sleeve 5, coaxially fitted within the deep heated formation 3 of the borehole; a smooth outer sleeve 7 and an insulated inner sleeve 8, coaxially fitted within the shallow variable-temperature formation 1 and the constant-temperature formation 2 of the borehole; and a first heat exchanger 35, a second heat exchanger 19, and a heat pump unit 23. Wherein:

[0037] The inner heat-insulating sleeve 8 is coaxially connected to the upper end of the spiral outer rib heat-insulating sleeve 5, and the inner and outer diameters of the two are the same; the smooth outer sleeve 7 is coaxially connected to the upper end of the spiral inner rib heat-exchange outer sleeve 4, and the inner and outer diameters of the two are the same; the top end of the spiral inner rib heat-exchange outer sleeve 4 is open and the bottom end is closed, and the top end and bottom end of the spiral outer rib heat-insulating sleeve 5 are both open; the spiral inner rib heat-exchange outer sleeve 4, the spiral outer rib heat-insulating sleeve 5, the smooth outer sleeve 7 and the inner heat-insulating sleeve 8 together form a sleeve structure with a closed bottom and an open top.

[0038] The top of the smooth outer sleeve 7 is connected to the primary side inlet pipe 37 of the first heat exchanger and the primary side inlet pipe 15 of the second heat exchanger via the geothermal well outlet pipe 11, respectively. The top of the heat-insulating inner sleeve 8 is connected to the primary side outlet pipe 36 of the first heat exchanger and the primary side outlet pipe 16 of the second heat exchanger via the geothermal well inlet pipe 10.

[0039] User-side water outlet pipe 29 is connected to the secondary side water inlet pipe 31 of the first heat exchanger and the condenser side water inlet pipe 26 of the heat pump unit, respectively; user-side water inlet pipe 30 is connected to the secondary side water outlet pipe 32 of the first heat exchanger and the condenser side water outlet pipe 27 of the heat pump unit, respectively.

[0040] The secondary side outlet of the second heat exchanger 19 is connected to the evaporation side inlet pipe 21 of the heat pump unit, and the secondary side inlet of the second heat exchanger 19 is connected to the evaporation side outlet pipe 20 of the heat pump unit.

[0041] A ground source side circulation pump 12 is installed at the inlet end of the geothermal well outlet pipe 11, and a second heat exchanger primary side water inlet control valve 18 is installed at the outlet end of the geothermal well outlet pipe 11.

[0042] A primary-side inlet water control valve 13 is installed on the primary-side inlet water pipe 37 of the first heat exchanger, and a primary-side outlet water control valve 14 is installed on the primary-side outlet water pipe 36 of the first heat exchanger; a secondary-side outlet water control valve 34 is installed on the secondary-side outlet water pipe 32 of the first heat exchanger, and a secondary-side inlet water control valve 33 is installed on the secondary-side inlet water pipe 31 of the first heat exchanger; a condenser-side outlet water control valve 25 is installed on the condenser-side outlet water pipe 27 of the heat pump unit, and a condenser-side inlet water control valve 24 is installed on the condenser-side inlet water pipe 26 of the heat pump unit; a user-side circulating pump 28 is installed on the user-side outlet water pipe 29.

[0043] In a preferred embodiment of this utility model, the spiral inner rib reinforced heat exchange outer sleeve 4 and the smooth outer sleeve 7, and the spiral outer rib heat insulation inner sleeve 5 and the heat insulation inner sleeve 8 are all connected by threaded sealing.

[0044] As a preferred embodiment of this utility model, the spiral inner rib reinforced heat exchange outer tube 4 is made of a high thermal conductivity metal tube, which is integrally formed from high thermal conductivity metal materials such as carbon steel and alloy steel; its outer wall is uniformly coated with a graphene coating, and the inner wall of the spiral inner rib reinforced heat exchange outer tube 401 is provided with rectangular high thermal conductivity spiral inner ribs 402, preferably 16 to 20 pieces, the height and width of the ribs are preferably 3mm, and the spiral angle is preferably 30°.

[0045] In a preferred embodiment of this utility model, the spiral outer rib heat-insulating inner sleeve 5 is made from the same sleeve as the heat-insulating inner sleeve 8 as the base material, and is filled with aerogel for heat insulation. The outer wall of the spiral outer rib heat-insulating inner sleeve 501 is provided with (preferably welded) rectangular spiral outer ribs 502. The rectangular spiral outer ribs 502 are made of carbon steel or alloy steel, preferably 16 to 20 pieces, the height and width of the ribs are preferably 3mm, and the spiral angle is preferably 30°.

[0046] In a preferred embodiment of this utility model, a low-density, low-thermal-conductivity composite cementing material 9 is filled between the smooth outer casing 7 and the shallow temperature-varying formation 1. The low-density, low-thermal-conductivity backfill material 9 is made of loess, sand, clay, bentonite, and other soil materials backfilled and compacted.

[0047] In a preferred embodiment of this utility model, a conventional high-density thermally conductive composite cementing material 6 is filled between the spiral inner rib reinforced heat exchange outer tube 4 and the constant temperature formation 2 and the deep heating formation 3. The conventional high-density thermally conductive composite cementing material 6 is a composite cementing material made of ordinary cementing cement, copper powder, carbon fiber, alumina, etc., and has high thermal conductivity.

[0048] This utility model has two working modes for the downhole high-efficiency heat exchange device suitable for medium-deep geothermal development: high-temperature heating mode and medium-low temperature heating mode.

[0049] High-temperature heating mode: When the outlet water temperature of the downhole high-efficiency heat exchanger is ≥50℃, the geothermal well is connected to the first heat exchanger 35. The specific connection method is as follows: the geothermal well outlet pipe 11 is connected to the primary side inlet pipe 13 of the first heat exchanger; the geothermal well inlet pipe 10 is connected to the primary side outlet pipe 36 of the first heat exchanger. The user-side outlet pipe 29 is connected to the secondary side inlet pipe 31 of the first heat exchanger; the user-side inlet pipe 30 is connected to the secondary side outlet pipe 32 of the first heat exchanger; the primary side inlet control valve 13, the primary side outlet control valve 14, the secondary side inlet control valve 33, and the secondary side outlet control valve 34 of the first heat exchanger are opened, and the ground source side circulation pump 12 and the user-side circulation pump 28 are started for heating, while the remaining control valves and circulation pumps are closed.

[0050] Medium and low temperature heating mode: When the outlet water temperature of the downhole high-efficiency heat exchanger is <50℃, the geothermal well is connected to the second heat exchanger 19, and the second heat exchanger 19 is connected to the heat pump unit 23. The specific connection method is as follows: the geothermal well outlet water pipe 11 is connected to the primary side inlet water pipe 15 of the second heat exchanger; the geothermal well inlet water pipe 10 is connected to the primary side outlet water pipe 16 of the second heat exchanger. The heat pump unit 23 is connected to the second heat exchanger 19 via the heat pump unit evaporator side outlet water pipe 20 and the heat pump unit evaporator side inlet water pipe 21; the user side outlet water pipe 29 is connected to the unit condenser side inlet water pipe 26; the user side inlet water pipe 30 is connected to the heat pump unit condenser side outlet water pipe 27; the second heat exchanger primary side inlet water control valve 18, the second heat exchanger primary side outlet water control valve 17, the heat pump unit condenser side inlet water control valve 24, and the heat pump unit condenser side outlet water control valve 25 are opened, and the ground source side circulation pump 12 and the user side circulation pump 28 are started to provide heat, while the remaining control valves and circulation pumps are closed.

[0051] Compared with the currently used medium-deep coaxial shell heat exchangers, this invention, by adding rectangular spiral fins to the inner wall of the outer shell and the outer wall of the inner shell, increases the wetted perimeter of the annular region and reduces the equivalent diameter, while simultaneously expanding the heat exchange area between the fluid and the outer shell wall. Furthermore, the spiral fin structure causes the fluid flow to rotate (as shown in Figure 6(a)), enhancing turbulence intensity. Both of these enhanced heat transfer effects help reduce the temperature of the inner wall of the outer shell and increase the heat transfer coefficient between the inner wall and the fluid. The uniform coating of graphene on the outer wall of the tube enhances the heat absorption capacity of the heat exchange device from the surrounding high-temperature rock and soil, thereby increasing the heat exchange power of the geothermal well and improving the technical and economic feasibility of medium-deep heat exchange development technology. To further illustrate the superiority of this technology, numerical simulations are used to compare the improved technical effects with those of ordinary medium-deep shell heat exchangers.

[0052] The basic parameters for model calculation are as follows:

[0053] ① Ordinary medium-deep shell-and-tube heat exchanger: outer tube specifications Φ177.8×159.42mm, inner tube specifications Φ114.3×76mm, outer tube thermal conductivity 46W / (m·K); inner tube thermal conductivity 0.02W / (m·K); tube length 1m, circulation flow rate 30m³ / h 3 / h, inlet water temperature set at 10℃, outer casing wall temperature at 100℃.

[0054] ② The heat exchanger designed in this utility model has the following specifications: outer tube Φ177.8×159.42mm, inner tube Φ114.3×76mm, outer tube thermal conductivity 46W / (m·K); inner tube thermal conductivity 0.02W / (m·K); tube length 1m, fin height 3mm, fin width 3mm, fin quantity 20, spiral angle 30°. Circulation flow rate 30m³ / h. 3 / h, inlet water temperature set at 10℃, outer casing wall temperature at 100℃.

[0055] The calculation results are shown in Figures 5(a) and 5(b): the outlet water temperature of the coaxial shell heat exchanger for medium-deep geothermal ...

Claims

1. A high-efficiency downhole heat exchanger suitable for medium-deep geothermal development, characterized in that, Includes a spiral inner rib reinforced heat exchange outer sleeve (4) and a spiral outer rib insulated inner sleeve (5) coaxially fitted within the deep heated formation (3) of the borehole; a smooth outer sleeve (7) and an insulated inner sleeve (8) coaxially fitted within the shallow variable-temperature formation (1) and the constant-temperature formation (2) of the borehole; and a first heat exchanger (35), a second heat exchanger (19), and a heat pump unit (23); wherein: The inner heat-insulating sleeve (8) is coaxially connected to the upper end of the spiral outer rib heat-insulating sleeve (5) and the inner and outer diameters of the two are the same; the smooth outer sleeve (7) is coaxially connected to the upper end of the spiral inner rib heat-exchange outer sleeve (4) and the inner and outer diameters of the two are the same; the top end of the spiral inner rib heat-exchange outer sleeve (4) is open and the bottom end is closed, and the top end and bottom end of the spiral outer rib heat-insulating sleeve (5) are both open; the spiral inner rib heat-exchange outer sleeve (4), the spiral outer rib heat-insulating sleeve (5), the smooth outer sleeve (7) and the inner heat-insulating sleeve (8) together form a sleeve structure with the bottom closed and the top open; The top of the smooth outer sleeve (7) is connected to the primary side inlet pipe (37) of the first heat exchanger and the primary side inlet pipe (15) of the second heat exchanger via the geothermal well outlet pipe (11). The top of the heat-insulating inner sleeve (8) is connected to the primary side outlet pipe (36) of the first heat exchanger and the primary side outlet pipe (16) of the second heat exchanger via the geothermal well inlet pipe (10). The user-side water outlet pipe (29) is connected to the secondary side water inlet pipe (31) of the first heat exchanger and the condenser side water inlet pipe (26) of the heat pump unit, respectively; the user-side water inlet pipe (30) is connected to the secondary side water outlet pipe (32) of the first heat exchanger and the condenser side water outlet pipe (27) of the heat pump unit, respectively. The secondary side outlet of the second heat exchanger (19) is connected to the evaporation side inlet pipe (21) of the heat pump unit, and the secondary side inlet of the second heat exchanger (19) is connected to the evaporation side outlet pipe (20) of the heat pump unit. A ground source side circulation pump (12) is installed at the inlet end of the geothermal well outlet pipe (11), and a second heat exchanger primary side water inlet control valve (18) is installed at the outlet end of the geothermal well outlet pipe (11). A primary-side inlet water control valve (13) is installed on the primary-side inlet water pipe (37) of the first heat exchanger, and a primary-side outlet water control valve (14) is installed on the primary-side outlet water pipe (36) of the first heat exchanger; a secondary-side outlet water control valve (34) is installed on the secondary-side outlet water pipe (32) of the first heat exchanger, and a secondary-side inlet water control valve (33) is installed on the secondary-side inlet water pipe (31) of the first heat exchanger; a condenser-side outlet water control valve (25) is installed on the condenser-side outlet water pipe (27) of the heat pump unit, and a condenser-side inlet water control valve (24) is installed on the condenser-side inlet water pipe (26) of the heat pump unit; a user-side circulating pump (28) is installed on the user-side outlet water pipe (29).

2. The downhole high-efficiency heat exchange device for medium-deep geothermal development as described in claim 1, characterized in that, The spiral inner rib reinforced heat exchange outer sleeve (4) and the smooth outer sleeve (7), as well as the spiral outer rib heat insulation inner sleeve (5) and the heat insulation inner sleeve (8), are all connected by threaded seals.

3. The downhole high-efficiency heat exchange device for medium-deep geothermal development as described in claim 1, characterized in that, The spiral inner rib reinforced heat exchange outer tube (4) is made of a high thermal conductivity metal tube; the outer wall of the spiral inner rib reinforced heat exchange outer tube body (401) is uniformly coated with a graphene coating, and the inner wall is provided with rectangular high thermal conductivity spiral inner ribs (402).

4. The downhole high-efficiency heat exchange device for medium-deep geothermal development as described in claim 3, characterized in that, The rectangular high thermal conductivity spiral inner rib (402) consists of 16 to 20 pieces, with the rib height and width preferably being 3mm and the spiral angle preferably being 30°.

5. The downhole high-efficiency heat exchange device for medium-deep geothermal development as described in claim 1, characterized in that, The spiral outer rib heat insulation inner sleeve (5) is filled with aerogel; the outer wall of the spiral outer rib heat insulation inner sleeve body (501) is provided with rectangular spiral outer ribs (502).

6. The downhole high-efficiency heat exchange device for medium-deep geothermal development as described in claim 5, characterized in that, The rectangular spiral outer ribs (502) consist of 16 to 20 pieces, with a rib height and width of 3 mm and a spiral angle of 30°.

7. The downhole high-efficiency heat exchange device suitable for medium-deep geothermal development as described in any one of claims 1 to 6, characterized in that, The smooth outer casing (7) and the shallow variable temperature formation (1) are filled with a low-density, low-thermal-conductivity composite cementing material (9).

8. The downhole high-efficiency heat exchange device suitable for medium-deep geothermal development as described in any one of claims 1 to 6, characterized in that, The spiral inner rib reinforced heat exchange outer tube (4) is filled with conventional high-density thermal conductivity composite cementing material (6) between the constant temperature formation (2) and the deep heating formation (3).

Images