Concentric double-pipe heat exchanger

Abstract

The utility model discloses a concentric double-pipe heat exchanger, and mainly relates to the field of concentric buried pipe heat exchangers. Comprising an outer pipe, an inner pipe, an annular cavity channel and an outflow channel, the inner pipe, the annular cavity channel and the outflow channel are coaxially suspended in the outer pipe, a vacuum heat preservation layer is arranged on the inner wall of the top of the inner pipe, the outflow channel is of a reducing structure with the thick bottom and the thin upper portion, the outer side of the bottom of the outer pipe is of a round-basin-shaped outwards-protruding structure, and a drainage structure used for reducing heat loss is arranged at the inner bottom of the outer pipe. And the drainage structure comprises a curved surface formed by sweeping an outer convex sine line around the circular surface of the central shaft of the outer tube and a columnar bulge at the central position. The utility model has the beneficial effects that the heat exchange area of the buried pipe at the highest soil temperature is increased through the convex structure and the drainage structure, the circulating working medium flows annularly, the buffering and drainage of the working medium in the whole circumferential direction are realized, the dynamic energy dissipation of the fluid and the impact damage of the fluid to the outer pipe are reduced, the heat preservation and heat insulation are better, and the service life is prolonged. And the stability of the outer pipe buried in the soil area is improved.

Description

TECHNICAL FIELD

[0001] The utility model relates to concentric buried pipe heat exchanger field, specifically a concentric double pipe heat exchanger. BACKGROUND

[0002] The 2023 World Geothermal Congress clearly pointed out that the "heat extraction without water extraction" type buried pipe heat exchanger should be actively explored and developed, and its heat extraction efficiency should be continuously improved. The concentric double pipe buried heat exchanger is most commonly used in the process of medium-deep geothermal exploitation. The traditional concentric double pipe heat exchanger has a relatively simple structure and is composed of an inner pipe and an outer pipe. Although it can extract geothermal energy, its heat extraction efficiency is relatively low, and the backfilling method generally uses cementing water, which reduces the thermal conductivity of the surrounding area. Therefore, the structure of the concentric double pipe heat exchanger should be improved, and the backfilling method should be improved to achieve the purpose of strengthening heat exchange.

[0003] Patent No. 202323409952.2 discloses a reinforced heat transfer type concentric double pipe heat exchanger with fins, which specifically discloses an inner pipe and an outer pipe structure. The inner wall of the outer pipe is provided with spaced and circumferential corrugated fins, and the bottom closed end of the outer pipe is provided with a drainage structure. The length of the middle inner convex strip structure in the drainage structure is equal to the diameter of the inner wall of the outer pipe, which divides the bottom annular cavity space into two areas. The outer wall of the inner pipe is provided with spiral fins arranged in a spiral manner, and the inner pipe wall is provided with a thermal insulation layer and a heat insulation layer. The flowing working medium enters from the outer pipe annular cavity and flows into the inner pipe channel through the drainage structure.

[0004] Although the above-mentioned patent can realize the utilization of medium-deep geothermal energy under the condition of "heat extraction without water extraction" and improve the heat exchange efficiency to a certain extent, when the flowing working medium flows in a ring shape, the strip area still has a large flow loss, and the impact pressure of the flowing working medium on the pipe wall is increased, which is not conducive to long-term sustainable utilization. Moreover, the heat loss of the inner pipe is mainly concentrated in the upper part, and the thermal insulation and heat insulation of the whole pipe are not economical. In addition, the further fixation of the outer wall of the outer pipe is not considered. Therefore, in summary, the effect of the prior art in actual use is still not ideal. UTILITY MODEL CONTENTS

[0005] The utility model aims at providing a concentric double pipe heat exchanger, which increases the buried pipe heat exchange area at the highest soil temperature through the outer convex structure and the drainage structure, makes the circulating working medium flow in a ring shape, realizes the buffering and drainage of the working medium in the whole circumferential direction, reduces the kinetic energy dissipation of the fluid and the impact damage of the fluid on the outer pipe, better insulates and heats, and improves the stability of the outer pipe buried in the soil.

[0006] To achieve the above-mentioned purpose, the utility model realizes the following technical scheme:

[0007] A concentric sleeve type heat exchanger comprises an outer tube and an inner tube coaxially suspended inside the outer tube, a ring cavity channel for circulating working medium inflow is formed between the outer wall of the inner tube and the inner wall of the outer tube, the inner cavity of the inner tube forms an outflow channel for the circulating working medium after heat exchange, the inner wall of the top of the inner tube is provided with a vacuum insulation layer, the outflow channel forms a variable-diameter structure with a large bottom and a small upper part, the outer side of the bottom of the outer tube is in a circular basin shape, the inner bottom of the outer tube is provided with a flow guide structure for reducing heat loss, and the flow guide structure comprises a curved surface swept by an outer convex sinusoidal line around the outer tube center axis and a columnar protrusion at the center position.

[0008] Further, the inner tube is of an elliptical cross section, and the outer tube is of a circular cross section.

[0009] Further, the inner wall of the bottom of the outer tube is provided with staggered reinforced heat transfer elements, and the reinforced heat transfer elements are ellipsoidal protrusions.

[0010] Further, a plurality of protruding teeth are arranged on the outer wall of the bottom of the outer tube, and the plurality of protruding teeth are uniformly arranged along the circumference of the outer tube.

[0011] Further, the cross section of the curved surface is arc-shaped.

[0012] Further, the circulating working medium is water, supercritical carbon dioxide or a refrigerant.

[0013] Further, the upper part of the outer side of the outer tube is backfilled with a material with a low thermal conductivity, and the bottom of the outer side of the outer tube is backfilled with a material with a high thermal conductivity.

[0014] Compared with the prior art, the beneficial effects of the utility model are as follows:

[0015] 1. The inner diameter of the top region of the inner tube is reduced by the vacuum insulation layer, the outflow direction of the circulating working medium in the inner tube is tapered, the flow speed of the circulating working medium returning to the ground in the inner tube is accelerated by utilizing the narrow tube effect, so that the heat loss time of the circulating working medium is reduced, the upper part where the heat loss is more concentrated is further insulated by the vacuum insulation layer, and the economic effect is better.

[0016] 2. The inner wall of the lower part of the outer tube is provided with a plurality of staggered reinforced heat transfer elements, the disturbance to the fluid in the main heat extraction section is enhanced, the thermal boundary layer is destroyed to improve the heat extraction effect.

[0017] 3. The outer wall of the outer tube is provided with a fixing structure, the position of the buried pipe in the drilling hole is fixed by the protruding teeth, the heat exchange area of the high heat extraction section of the outer tube is increased, and the heat extraction amount is further improved.

[0018] 4. The drainage structure of the bottom of the outer tube comprises a curved surface formed by a convex sinusoidal line around the outer tube center axis circle surface and a columnar protrusion at the center position, which on the one hand increases the heat exchange area of the buried tube bottom, and on the other hand reduces the impact of the fluid in the annular cavity passage on the bottom of the outer tube through the curvature of the curved surface, thereby reducing the kinetic energy dissipation and tube bottom wear caused by the impact of the fluid on the bottom, and realizing the drainage function of the fluid from the annular cavity passage into the outflow passage in the inner tube;

[0019] 5. The outer part of the outer tube buried tube and the gap between the drill hole are backfilled in sections, and through the different thermal conductivities, the heat extraction amount of the heat extraction section is improved, the heat loss of the heat loss section is reduced, which is of great significance for efficient utilization of high deep geothermal energy. BRIEF DESCRIPTION OF DRAWINGS

[0020] FIG. 1 is a schematic diagram of the structure of the outer tube of the present application. Figure 1

[0021] FIG. 2 is a schematic diagram of the structure of the inner tube of the present application. Figure 2 FIG. 3 is a schematic diagram of the structure of the annular cavity passage of the present application.

[0022] Figure 3 FIG. 4 is a schematic diagram of the structure of the outflow passage of the present application.

[0023] FIG. 5 is a schematic diagram of the structure of the drainage structure of the present application. Figure 4 FIG. 6 is a schematic diagram of the outer tube external structure of the present application.

[0024] Reference signs shown in the drawings:

[0025] 1. Outer tube; 2. Inner tube; 3. Annular cavity passage; 4. Outflow passage; 5. Vacuum insulation layer; 6. Drainage structure; 7. Curved surface; 8. Columnar protrusion; 9. Convex structure; 10. Heat transfer enhancement element; 11. Convex tooth. DETAILED DESCRIPTION

[0026] The present application will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present application and not to limit the scope of the present application. In addition, it should be understood that after reading the content taught by the present application, those skilled in the art can make various changes or modifications to the present application, and these equivalent forms also fall within the scope defined by the present application.

[0027] ​​The utility model relates to a concentric sleeve pipe type heat exchanger, main body structure includes outer tube 1 and the inner tube 2 of coaxial suspension in the inside of outer tube 1, the outer tube 1 is circular section, and the outer tube 1 top end opening bottom end is closed, the inner tube 2 is oval section and is the through pipe of two end openings, the outer tube 1 adopts high hardness, strong ductility, good heat conductivity stainless steel suitable material, the inner tube 2 adopts the strong corrosion resistance, good toughness, high thermal resistance, thermal stability good polyethylene pipe (PE80 or PE100) or polybutene pipe (PB) suitable material, the outer wall between the inner tube 2 and the inner wall of outer tube 1 forms the annular cavity channel 3 for circulating working medium inflow, the inner cavity of inner tube 2 forms the outflow channel 4 for the outflow of circulating working medium after heat exchange, and circulating working medium enters the outflow channel 4 from the inner tube 2 bottom end opening after entering the annular cavity channel 3 from the outer tube 1 top end opening, and flows out from the inner tube 2 top end opening, realizes working medium circulation heat exchange, the inner wall of the inner tube 2 top is equipped with vacuum insulation layer 5, makes the outflow channel 4 form the reducing structure of bottom thick upper thin, that is, the direction along the outflow of circulating working medium is tapered, makes the upper portion of inner tube 2 form the narrow tube effect, increases the flow rate when the high-temperature fluid after heat extraction returns to the ground, to reduce the heat loss time, can also reduce the heat loss caused by the reverse heat transfer of high-temperature working medium in the annular cavity channel 3 after heat extraction through the outflow process in the outflow channel 4, simultaneously further reduces the heat loss by utilizing vacuum insulation layer, insulates the upper portion more concentrated for heat loss, and the economic effect is better, the outside of the bottom of outer tube 1 is the outer convex structure 9 of round basin shape, the inner bottom of outer tube 1 is equipped with the drainage structure 6 for reducing heat loss, the drainage structure 6 includes the curved surface 7 formed by the outer convex sinusoidal line around the outer tube 1 center axis circle surface sweep and the columnar protrusion 8 at the center position, the center axis of columnar protrusion 8 is coaxial with the center axis of inner tube 2, betterly drains working medium from the annular cavity channel 3 to the outflow channel 4, the section of curved surface 7 is two arc shapes bending towards the bottom, makes the section of curved surface 7 as a whole W-shaped, expands the heat exchange area of the inner bottom of outer tube 1, and realizes the drainage of working medium from the bottom of annular cavity channel 3 to the outflow channel 4 of inner tube 2, and the curved surface 7 after circle surface sweep is arc structure, reduces the impact wear of working medium to the bottom of outer tube 1, also reduces the kinetic energy dissipation of working medium, reaches the effect of reducing energy consumption.

[0028] In addition, since the inner tube 2 is of an oval cross section, the surface shape of the oval cross section pipe reduces the boundary layer thickness of the working medium when flowing through the outer tube 2, and easily forms turbulent flow, which can significantly improve the convective heat transfer coefficient, enhance the heat exchange efficiency, and reduce the scaling phenomenon outside the inner tube. In addition, compared with a circular tube, the resistance coefficient of the fluid working medium bypassing the oval tube is smaller, thereby reducing the pressure loss and saving the energy consumption of the pump to a certain extent. Finally, compared with a circular tube, the oval cross section tube can provide a larger heat exchange area under the same occupied space.

[0029] Preferably, the inner wall of the outer tube 1 near the bottom is provided with staggered heat transfer enhancement elements 10. The heat transfer enhancement elements 10 are ellipsoidal protrusions made of stainless steel. The ellipsoidal protrusions have a certain protrusion height, a semi-elliptical arc cross section, and an elliptical longitudinal section. The ellipsoidal protrusions are staggered on the inner wall of the outer tube 1. Obviously, their protrusion heights can be the same or different. By using the heat transfer enhancement elements 10, the circulating working fluid is passively agitated when injected into the annular cavity channel 3, which enhances the mixing rate between fluids, destroys the thermal boundary layer of the fluid near the wall, and achieves the purpose of enhancing heat transfer, so that the temperature distribution of the fluid at each position in the annular cavity channel 3 is more uniform.

[0030] Preferably, the outer tube 1 has multiple stainless steel protrusions 11 on its outer wall near the bottom. The multiple protrusions 11 are evenly arrayed along the circumference of the outer tube 1. On the one hand, this can further increase the heat exchange area at the bottom of the outer tube 1. On the other hand, it can fix the position of the buried tube in the borehole. The protrusion height and spacing of the protrusions 11 should take into account the fixation, the increase of the heat transfer area and the economy. Generally speaking, the higher and denser the protrusions, the larger the heat exchange area and the stronger the reinforcement. However, there will also be an imbalance problem of high cost. Therefore, in actual operation, the balance between cost and reinforcement and the increase of heat transfer area should be considered at the same time.

[0031] Preferably, the circulating working fluid is water, supercritical carbon dioxide, or a refrigerant.

[0032] Preferred options are listed below. Figure 1 As shown, the upper part of the outer side of the outer pipe 1 is backfilled with a material with low thermal conductivity, such as a thermal insulation backfill material made by mixing, molding, and sintering diatomaceous earth as the main raw material with some combustible materials. The thermal conductivity is much lower than that of the soil, thus avoiding reverse heat transfer between the circulating working fluid and the soil. The bottom of the outer side of the outer pipe 1 is backfilled with a material with high thermal conductivity, such as composite cementing cement (graphene, cement). By adjusting the mass content of each component, the thermal conductivity is made greater than that of the soil, thereby improving the heat exchange effect between the heat exchanger and the surrounding soil. The gap between the outer pipe 1 and the borehole is backfilled in upper and lower sections to maximize the utilization of medium-deep geothermal energy.

[0033] When this patented heat exchanger is in operation, the circulating working fluid is injected into the outer tube from the annular cavity channel 3. After passing through the arc-shaped buffer of the curved surface 7 and the guide of the columnar protrusion 8 to the outflow channel 4, it finally enters the outflow channel 4 from the bottom of the inner tube 2. After passing through the small-diameter tapered section at the top of the outflow channel 4, it is accelerated and returns to the ground, thus achieving the purpose of low kinetic energy loss and high-efficiency heat exchange of the working fluid.

[0034] The concentric double-pipe heat exchanger has the characteristics of high heat exchange efficiency, convenient assembly, firm positioning, low loss and the like, can be simply modified according to the existing concentric double-pipe heat exchanger, has low cost, has strong implementability, and has important significance for efficient utilization of medium-deep geothermal energy.

Claims

1. A concentric double-pipe heat exchanger comprising an outer pipe (1) and an inner pipe (2) coaxially suspended inside the outer pipe (1), a ring cavity passage (3) for circulating working medium inflow being formed between the outer wall of the inner pipe (2) and the inner wall of the outer pipe (1), and an outflow passage (4) for circulating working medium outflow after heat exchange being formed in the inner cavity of the inner pipe (2), characterized in that: The inner wall of the top of the inner tube (2) is provided with a vacuum insulation layer (5), so that the outflow channel (4) forms a variable-diameter structure with a wide bottom and a narrow top, the outer side of the bottom of the outer tube (1) is in a circular-pot-shaped convex structure (9), the inner bottom of the outer tube (1) is provided with a flow guide structure (6) for reducing heat loss, and the flow guide structure (6) comprises a curved surface (7) swept by an outer convex sinusoidal line around the central axis of the outer tube (1) and a columnar protrusion (8) at the center position.

2. A concentric double pipe heat exchanger as claimed in claim 1, wherein: The inner tube (2) is of an elliptical cross section, and the outer tube (1) is of a circular cross section.

3. A concentric double pipe heat exchanger as claimed in claim 1, wherein: The inner wall of the bottom of the outer tube (1) is provided with staggered reinforced heat transfer elements (10), and the reinforced heat transfer elements (10) are ellipsoidal protrusions.

4. The concentric tube heat exchanger of claim 1, wherein: A plurality of protruding teeth (11) are arranged on the outer wall of the bottom of the outer tube (1), and the plurality of protruding teeth (11) are uniformly arranged along the circumference of the outer tube (1).

5. The concentric double pipe heat exchanger of claim 1, wherein: The cross section of the curved surface (7) is arc-shaped.

6. A concentric double pipe heat exchanger as claimed in claim 1, wherein: The circulating working medium is water, supercritical carbon dioxide or a refrigerant.

7. The concentric double pipe heat exchanger of claim 1, wherein: The upper part of the outer side of the outer tube (1) is backfilled with a material with a low thermal conductivity, and the bottom of the outer side of the outer tube (1) is backfilled with a material with a high thermal conductivity.

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