Heat transfer enhanced tube with variable diameter cyclone generating mechanism and cracking furnace

Abstract

The present application relates to the field of fluid heat transfer technology, and discloses a reinforced heat transfer pipe with a variable-diameter rotational flow generating mechanism and a cracking furnace, the reinforced heat transfer pipe with the variable-diameter rotational flow generating mechanism comprises a hollow tubular pipe body, a variable-diameter rotational flow generating mechanism is arranged on the inner wall of the pipe body, the variable-diameter rotational flow generating mechanism comprises at least one spiral blade, and at least part of the radial dimension of each spiral blade is arranged in a gradually changing manner in the axial direction of the pipe body; the reinforced heat transfer pipe provided by the present application can stably construct a flow field structure of a rigid rotational flow built-in high-energy secondary vortex by precisely controlling fluid flow behavior, realize deep matching of fluid mechanics characteristics and heat exchange characteristics, promote the orderly performance of heat exchange behavior, improve the fluid passability of the reinforced heat transfer element itself, effectively reduce the operating pressure drop of the equipment, weaken the stress of the connecting part between the heat transfer element and the pipe wall, greatly improve the impact resistance and operation reliability, and effectively inhibit the pipe wall fouling behavior and prolong the operation cycle of the device.

Description

Technical Field

[0001] This invention relates to the field of fluid heat transfer technology, and more specifically to an enhanced heat transfer tube and a pyrolysis furnace with a variable diameter swirl generation mechanism. Background Technology

[0002] Convective heat transfer of fluids within pipes is a common process in process industries. The development of related heat transfer enhancement technologies is of great practical significance for improving heat transfer efficiency (rate, intensity, and uniformity), promoting industrial production quality and efficiency, saving energy and reducing consumption, and ultimately improving energy utilization efficiency. The heat transfer process within pipes includes two aspects: first, thinning and disrupting the boundary layer to promote heat transfer between the pipe wall and the fluid near the wall surface; second, enhancing the heat interaction between the fluid in the central region and the fluid near the wall surface. The former limits the intensity of fluid heat transfer, while the latter determines the rate and uniformity of fluid heat transfer. Over the years, industry scholars have developed numerous heat transfer enhancement technologies from the perspectives of both reactors and internal components, including elliptical tubes, twisted tubes, shrink-expansion tubes, dimple tubes, plum blossom tubes, ribbed tubes, nail-head tubes, finned tubes, grooved tubes, spiral ribbons, and vortex generators, aiming to improve the heat transfer effect of fluids within pipes by increasing the heat transfer area or improving the convective heat transfer coefficient. Among the aforementioned technologies for enhancing heat transfer, insertable internal components, characterized by their simple structure, miniaturization, ease of implementation, and ability to induce vortex flow, have attracted particular attention. In fact, vortex flow is an ideal fluid disturbance behavior. High-speed vortex flow generates a large radial pressure gradient and a high tangential shear velocity, effectively enhancing radial mixing of the fluid and thinning the fluid boundary layer on the heat exchanger tube wall. This significantly improves heat transfer flux while maintaining good heat transfer uniformity.

[0003] In the prior art, spiral ribbons are considered an ideal vortex / vortex generation mechanism. US4466567 discloses a technical solution for welding a solid ribbon to the inner wall of a heat transfer tube, which is the first to propose a spiral ribbon configuration. US005850831A discloses a spiral ribbon configuration with alternating torsion ratios to enhance the heat transfer performance of solar heat receiving tubes. US006615911B1 discloses a spiral ribbon with transverse louvered grids, which can improve the cooling effect of electrical appliances when connected to the inner wall of a liquid phase cooling pipe. US4832114 discloses a ribbon structure with axially elongated slots, but it is fixed to a rotating shaft drive component on the axis of the heat transfer tube, which greatly limits its applicable working conditions. US 20200271402A1 discloses a spiral ribbon with a small radial dimension and asymmetrical wall connection to enhance the heat transfer tube, which greatly reduces fluid resistance, but this configuration is essentially a special type of the hollow spiral ribbon disclosed in US4466567. US 4119390 discloses a spiral ribbon for an open liquid phase cooling channel for gas turbine blades, wherein the outer edge of the configuration has axially staggered notches; US20110094721 A1 discloses a ribbon configuration composed of rectangular vortex generators, which is set in the central region of the heat transfer tube and can efficiently induce vortices, thereby achieving enhanced heat transfer effect; US 9676689 B2 discloses a spiral ribbon with openings; US20140127091A1 discloses a hollow spiral ribbon configuration with openings.

[0004] To overcome the thermal stress effect between the spiral ribbon and the heat transfer tube, CN 109724444 B, CN 109724446 B, and CN 109724448 B disclose a spiral structure composed of multiple fins; CN 112745884 B discloses a spiral ribbon and fin combination heat transfer enhancement mechanism to suppress coking and carburizing behavior on the heat transfer tube wall; Xu Fang et al. (Applied Thermal Engineering, 2022, 207: 118170) proposed a spiral ribbon with a serrated opening on the outer edge to enhance wall disturbance and thus promote heat transfer; Wang Juan et al. (Journal of Process Engineering, 2020, 20(05): 510-520) proposed a spiral ribbon with a serrated opening on the inner edge, but this configuration intensifies the fluid turbulence behavior of the tube section where the element is located at the cost of severe energy dissipation, and does not significantly improve the heat transfer enhancement effect of the fluid downstream of the spiral ribbon.

[0005] Furthermore, the aforementioned spiral ribbon configuration generally suffers from the following four problems in industrial heat transfer enhancement applications: 1) The fluid dynamics and heat transfer characteristics within the tube under the spiral ribbon effect are difficult to match deeply. The spiral ribbon causes the fluid to form a high-intensity rigid vortex, resulting in severe shearing and scouring of the tube wall. This can effectively thin and disrupt the laminar boundary layer, promoting the effective input of heat from outside the tube or the tube wall to the fluid near the inner wall. However, it is impossible to control the radial velocity vector to balance the heat interaction between the fluid in the central region and the fluid near the wall, easily generating a severe central poor heat transfer zone, leading to a large radial temperature gradient, and making it difficult to guarantee heat transfer efficiency and uniformity. 2) The challenge of reliable and reasonable arrangement of spiral ribbons in heat transfer tubes. The arrangement of spiral ribbons in heat transfer tubes usually includes two methods: built into the central region of the tube and directly connected to the tube wall. The former requires the introduction of supporting components, resulting in a reduction in the fluid flow area; the latter is simple and reliable, but stress-strain effects are easily generated between the spiral ribbon and the tube wall, especially under high-speed impact, making long-term stable operation impossible to guarantee, and it is difficult to adapt to complex and harsh working conditions. 3) For heat exchange systems prone to scaling, the centrifugal force generated by the swirling flow can easily cause scale particles or precursor components to move, aggregate, and deposit towards the tube wall, eventually forming a scale layer and deteriorating heat transfer. 4) The spiral loop has high form resistance, which can easily lead to a large pressure drop in the equipment, limiting the operational flexibility of the heat transfer tube to some extent.

[0006] Taking the development and application of enhanced heat transfer technology for ethylene cracking furnace tubes as an example, this process involves a high-throughput, fouling-prone, and extremely harsh high-temperature heat exchange system with highly coupled reaction behaviors. CN 1133862 C discloses a twisted-plate cast tube, a technology derived from the swirl cooling technology of aero-engine blades. However, the two technologies differ significantly in their heat transfer enhancement objectives. The swirl cooling technology of aero-engine blades only needs to reduce the tube wall temperature without considering the uniformity of fluid temperature, and the equipment structure has no significant thermal stress strain. In contrast, ethylene cracking furnace tubes need to reduce the tube wall temperature, ensure the mechanical properties of the furnace tube, and simultaneously consider the heating rate, intensity, and uniformity of the fluid to improve the yield of the target cracking reaction products. Therefore, although the twisted-plate cast tube produces a good enhanced heat transfer effect and effectively inhibits coking on the tube wall during industrial implementation, the thermal stress effect is significant due to long-term resistance to high-temperature environments (>1000℃) and high-speed impacts, making the furnace tube prone to cracking. In response to this, CN 103791753 B and US20140127091 A1 further proposed hollow twisted plate reinforced furnace tubes. Industrial application results show that this configuration can overcome the thermal stress strain effect on its own and avoid the undesirable phenomenon of coke layer falling off the tube wall and blocking the furnace tube. However, the fluid inside the tube still has a large radial temperature gradient, especially the axial low temperature zone. The aforementioned basic research and industrial application results indicate that constructing a reaction environment deeply matched to the thermal pyrolysis reaction-heat transfer-mass transfer characteristics requires overcoming several challenging problems: First, reducing the shape resistance of the twisted plates to increase raw material processing capacity and reduce equipment pressure drop; second, mitigating the strong shearing action between the twisted plates and the tube wall caused by high-speed fluid impact to avoid the risk of spalling and ensure long-term, stable, and reliable operation of the furnace tube; third, eliminating the poor heat transfer zone at the axis of the heat transfer tube and suppressing the coking reaction on the tube wall; fourth, ensuring that the twisted plate configuration adapts to the heat transfer requirements along the pyrolysis furnace tube, that is, prioritizing heat transfer efficiency and uniformity on the upstream side of the furnace tube to achieve rapid and uniform heating and reaction of the raw material gas, while focusing on suppressing pyrolysis coking on the downstream side to prevent tube wall overheating; and fifth, arranging the same configuration along the entire process. The twisted plates cause the fluid impact stress and pressure drop to be relatively concentrated on the first twisted plate near the heat transfer tube inlet, resulting in the first twisted plate being in a more severe working environment. Since the operating cycle of the pyrolysis furnace tube is determined by the performance of any twisted plate, the pyrolysis furnace tube will be shut down if any twisted plate peels off or causes the furnace tube to crack. Therefore, the performance of the twisted plates in the pyrolysis furnace tube should be kept uniform. At the same time, the twisted plates arranged along the flow path allow the fluid flowing through to obtain a uniform tangential shear velocity. However, the fluid temperature near the twisted plates in the upstream tube is lower, the reaction depth is smaller, and the coking rate at the tube wall is lower, so a large wall scouring rate is not required. As a result, the fluid flow characteristics controlled by the twisted plates are difficult to match the depth of the local heat transfer and mass transfer requirements of the heat transfer tube. Summary of the Invention

[0007] This invention aims to at least partially solve one of the technical problems in related technologies. Therefore, the objective of this invention is to provide an enhanced heat transfer tube and a pyrolysis furnace with a variable-diameter swirling flow generation mechanism. This enhanced heat transfer tube with the variable-diameter swirling flow generation mechanism constructs a flow field structure with a rigid swirling flow and built-in high-energy secondary vortex by precisely controlling the fluid flow behavior, achieving a deep match between fluid dynamics and heat transfer characteristics. Simultaneously, it improves the fluid permeability of the enhanced heat transfer element itself, effectively reduces the operating pressure drop of the equipment, weakens the stress at the connection between the heat transfer element and the tube wall, and significantly improves impact resistance and operational reliability.

[0008] To achieve the above objectives, the first aspect of the present invention provides an enhanced heat transfer tube with a variable diameter swirl generating mechanism, the enhanced heat transfer tube comprising a hollow tubular tube body, wherein a variable diameter swirl generating mechanism is provided on the inner wall of the tube body, the variable diameter swirl generating mechanism comprising at least one helical blade, wherein at least a portion of the radial dimension of each helical blade is arranged in a gradually changing manner in the axial direction of the tube body.

[0009] Preferably, the twist angle of the helical blade is 90°-1080°, more preferably 180°-360°.

[0010] Preferably, the height of the helical blade in the axial direction of the tube body is 1-10 times the inner diameter of the tube body.

[0011] Preferably, the radial dimensions of the inflow end and the outflow end of the spiral blade are 0-0.5 times the inner diameter of the tube body, more preferably 0-0.4 times.

[0012] Preferably, the radial dimension of the incoming flow end of the helical blade is smaller than the radial dimension of the outgoing flow end.

[0013] Preferably, the thickness of the helical blades is set to be equal or gradually varying along the axial direction of the tube body.

[0014] Preferably, the thickness of the incoming flow end of the helical blade is 0-2 times the thickness of its outgoing flow end.

[0015] Preferably, the thickness of the helical blades gradually decreases along the flow direction of the fluid within the tube.

[0016] Preferably, the thickness of the outflow end of the spiral blade is 0.2-2 times the wall thickness of the tube body, and the thickness of the outflow end of the spiral blade is 0.1-0.2 times the inner diameter of the tube body.

[0017] Preferably, the thickness of the helical blades is set to be equal or gradually varying in the radial direction of the tube body.

[0018] Preferably, the spiral blade has a first side and a second side disposed opposite to each other. The first side is connected to the inner wall of the tube body. The thickness of the first side is 0.2-2 times the wall thickness of the tube body and 0.1-0.2 times the inner diameter of the tube body. The thickness of the second side is 0-1 times the thickness of the first side.

[0019] Preferably, the helical blade has a first helical twisted section near its inflow end and a second helical twisted section near its outflow end, wherein the helix angle of the first helical twisted section is 0.1-5 times the helix angle of the second helical twisted section.

[0020] Preferably, the helix angle of the first helical twisted segment is greater than the helix angle of the second helical twisted segment.

[0021] Preferably, in the axial direction of the tube body, the first spiral twisted section is a variable diameter twisted section, and the second spiral twisted section is a constant diameter twisted section.

[0022] Preferably, the variable diameter swirl generating mechanism includes multiple helical blades, wherein the helical blades arranged in parallel along the circumference of the tube have the same helical twist direction; the helical blades arranged along the axial direction of the tube have opposite helical twist directions.

[0023] Preferably, multiple variable diameter swirl generating mechanisms are provided, and the multiple variable diameter swirl generating mechanisms are spaced apart along the axial direction of the pipe body.

[0024] Preferably, the distance between two adjacent variable-diameter swirl generating mechanisms is 10-100 times the inner diameter of the tube.

[0025] Preferably, the spiral twisting directions of the spiral blades of two adjacent variable diameter swirl generating mechanisms are opposite.

[0026] Preferably, the spiral blade is provided with jet holes.

[0027] Preferably, the jet hole is a louver type or a planar hole type.

[0028] Preferably, the size of the jet hole is 0.02-0.2 times the inner diameter of the tube body.

[0029] Preferably, the number of jet holes is 1-12.

[0030] Preferably, the jet holes are arranged in 1-3 rows in the radial direction of the tube body. A second aspect of the invention provides a pyrolysis furnace, the pyrolysis furnace including a radiation chamber, wherein at least one radiation furnace tube assembly is installed in the radiation chamber, the radiation furnace tube assembly including a plurality of radiation furnace tubes arranged in sequence and heat transfer tubes communicating with adjacent radiation furnace tubes, the heat transfer tubes being the aforementioned enhanced heat transfer tubes.

[0031] The enhanced heat transfer tube with a variable diameter swirl generation mechanism provided by this invention has the following beneficial effects:

[0032] 1. By setting at least a portion of the radial dimension of at least one helical blade constituting the variable diameter vortex generating mechanism in a gradually changing manner along the axial direction of the pipe body, the shape resistance of the variable diameter vortex generating mechanism is reduced, the fluid throughput capacity is improved, and the operating pressure drop of the equipment is reduced, thereby effectively improving the production capacity.

[0033] 2. By gradually varying the radial dimensions of at least a portion of the spiral blades along the axial direction of the tube, the unobstructed flow area of ​​the fluid changes, thereby inducing a symmetrically distributed secondary vortex with high vortex intensity, large size, and stable motion in the central region of the tube. This can improve heat transfer intensity and reduce or even eliminate the radial temperature gradient. In addition, the above structure can also slow down the direct impact of high-speed fluid on the spiral blades and improve the overall impact resistance of the vortex generating mechanism.

[0034] 3. In a pipe body equipped with the variable diameter swirling flow generating mechanism described in this invention, the fluid turbulence intensity in the central region of the pipe body is small, while the fluid swirling intensity in the near-wall region is large, which can suppress energy dissipation and fully ensure the formation of tangential velocity of the fluid near the pipe wall.

[0035] 4. Based on the enhanced heat exchange tube provided by the present invention, the flow field in the tube body downstream of the variable diameter swirling generator is a rigid swirling flow structure with multiple high-energy secondary vortices. This flow structure is closely matched with the heat exchange characteristics, greatly improving the heat exchange effect and realizing the fine control of the cracking reaction process.

[0036] 5. Based on the enhanced heat transfer tube provided by the present invention, mass transfer can be accelerated under the disturbance of high-energy secondary vortex. In particular, the scale particles or precursor components that accumulate near the heat transfer tube wall under the action of centrifugal force are re-entrained into the central region of the heat transfer tube, thereby inhibiting the formation of scale on the tube wall and extending the scale removal cycle of the enhanced heat transfer tube. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of a conventional hollow vortex generator mechanism;

[0038] Figure 2 This is a schematic diagram of the structure of an enhanced heat transfer tube provided in Embodiment 1 of the present invention;

[0039] Figure 3 This is a schematic diagram comparing the thickness of the incoming and outgoing ends of the helical blades. Figure 3 (a) are equal along the axial direction; Figure 3 (b) is a gradual change along the axial direction;

[0040] Figure 4This is a comparison diagram of the eddy current field structure characteristics of the enhanced heat transfer tube and the bare tube in Embodiment 1 of the present invention, wherein... Figure 4 (a) is a light tube; Figure 4 (b) The enhanced heat transfer tube provided in Example 1;

[0041] Figure 5 This is a comparison diagram of the axial fluid temperature distribution of the enhanced heat transfer tube provided in Embodiment 1 of the present invention, a bare tube, and a heat transfer tube with a conventional hollow swirl generation mechanism.

[0042] Figure 6 This is a comparison diagram of the radial distribution of fluid temperature at the end outlet of the enhanced heat transfer tube provided in Embodiment 1 of the present invention, a bare tube, and a heat transfer tube with a conventional hollow swirl generating mechanism.

[0043] Figure 7 This is a schematic diagram of the structure of an enhanced heat transfer tube provided in Embodiment 2 of the present invention;

[0044] Figure 8 This is a schematic diagram of the structure of an enhanced heat transfer tube provided in Embodiment 3 of the present invention;

[0045] Figure 9 This is a schematic diagram of the structure of an enhanced heat transfer tube provided in Embodiment 4 of the present invention;

[0046] Figure 10 This is a schematic diagram of the structure of an enhanced heat transfer tube provided in Embodiment 5 of the present invention;

[0047] Figure 11 The radial dimension of the variable diameter swirl generation mechanism of the enhanced heat transfer tube in Embodiment 5 of the present invention has a nonlinear gradual change rate along the axial direction.

[0048] Figure 12 This is a schematic diagram of the structure of an enhanced heat transfer tube provided in Embodiment 6 of the present invention;

[0049] Figure 13 This is a comparison diagram of the radial velocity distribution in the middle of the pipe section where the variable diameter swirl generator is located in Embodiment 6 and Embodiment 1 of the present invention;

[0050] Figure 14 This is a comparison diagram of the radial temperature distribution of the fluid in a local pipe section downstream of the variable diameter swirl generator in Embodiment 6 and Embodiment 1 of the present invention (at 10 times the inner diameter of the pipe body);

[0051] Figure 15 This is a schematic diagram of the structure of an enhanced heat transfer tube provided in Embodiment 7 of the present invention;

[0052] Figure 16 This is a comparison of the local flow-heat transfer characteristics (at 6 times the inner diameter of the pipe) between Embodiment 7 and Embodiments 1 and 6 of the present invention. Figure 16(a) shows the axial distribution of fluid temperature in a local pipe section downstream of the variable diameter vortex generator; Figure 16 (b) shows the radial distribution of the fluid radial velocity in a local pipe section downstream of the variable diameter vortex generator;

[0053] Figure 17 This is a schematic diagram of the structure of an enhanced heat transfer tube provided in Embodiment 8 of the present invention;

[0054] Figure 18 This refers to the axial distribution of fluid temperature at the axis of the enhanced heat transfer tube in Embodiments 8 and 2 of the present invention;

[0055] Figure 19 This is a comparison of the enhanced flow-heat transfer characteristics of Embodiment 8 and Embodiment 2 of the present invention, wherein... Figure 19 (a) The radial distribution of fluid temperature in the downstream pipe section (30 times the inner diameter of the pipe body) of the variable diameter vortex generator; Figure 19 (b) The radial distribution of the fluid radial velocity in the downstream pipe section (30 times the inner diameter of the pipe body) of the variable diameter vortex generator;

[0056] Figure 20 This is a schematic diagram of the structure of an enhanced heat transfer tube provided in Embodiment 9 of the present invention;

[0057] Figure 21 This is a comparison diagram of the vortex field structure characteristics of the enhanced heat transfer tube in Embodiment 9 and Embodiment 1 of the present invention;

[0058] Figure 22 This is a comparison diagram of the axial distribution of the average fluid temperature in the cross section of the enhanced heat transfer tube in Embodiment 9 and Embodiment 1 of the present invention;

[0059] Figure 23 This is a schematic diagram of the structure of an enhanced heat transfer tube provided in Embodiment 10 of the present invention;

[0060] Figure 24 This is a comparison diagram of the radial distribution of the fluid tangential velocity at the end outlet of the enhanced heat transfer tube in Embodiments 10 and 9 of the present invention;

[0061] Figure 25 This is a schematic diagram of the structure of an enhanced heat transfer tube provided in Embodiment 11 of the present invention;

[0062] Figure 26 This refers to the axial distribution of fluid temperature at the axis of the enhanced heat transfer tube in Embodiments 11 and 9 of the present invention;

[0063] Figure 27 These are schematic diagrams of the structures in embodiments 12-15 of the present invention;

[0064] Figure 28This is a comparison diagram of the axial fluid temperature distribution of the enhanced heat transfer tube in Embodiment 12 of the present invention, compared with that of a bare tube and a heat transfer tube with a conventional hollow swirl generation mechanism.

[0065] Figure 29 This is a comparison diagram of the radial distribution of fluid temperature at the end outlet of the enhanced heat transfer tube in Embodiment 12 of the present invention and that of a conventional hollow vortex generator.

[0066] Figure 30 This is a comparison diagram of the pressure drop distribution trends of each swirl generator in the enhanced heat transfer tube and the conventional swirl generator in Embodiment 12 of the present invention.

[0067] Figure 31 This is a comparison diagram of the differences in fluid swirling shear velocity at the tube wall under the action of various swirling generation mechanisms in the enhanced heat transfer tube of Embodiments 12 and 13 of the present invention.

[0068] Explanation of reference numerals in the attached figures

[0069] 1. Pipe body; 2. Variable diameter swirl generator; 201. First side; 202. Second side; 21. First helical blade; 211. First variable diameter section; 2111. First inlet end; 2112. First outlet end; 212. Second variable diameter section; 2121. Second inlet end; 2122. Second outlet end; 22. Second helical blade; 23. Outlet end; 231. Second helical twist section; 24. Inlet end; 241. First helical twist section; 25. 1. Positive pressure side; 26. Back pressure side; 3. Jet hole; 4. Conventional hollow vortex generator; 5. First vortex generator; 6. Second vortex generator; 7. Third vortex generator; 8. Fourth vortex generator; 9. First interval; 10. Second interval; 11. Third interval; 12. Fifth vortex generator; 13. Fourth interval; 210. Helical blade one; 220. Helical blade two; 230. Helical blade three; 240. Helical blade four. Detailed Implementation

[0070] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0071] The present invention provides an enhanced heat transfer tube with a variable diameter swirl generating mechanism. The enhanced heat transfer tube includes a hollow tubular tube body 1. A variable diameter swirl generating mechanism 2 is provided on the inner wall of the tube body 1. The variable diameter swirl generating mechanism 2 includes at least one helical blade. At least a portion of the radial dimension of each helical blade is arranged in a gradually changing manner in the axial direction of the tube body 1.

[0072] The concept of this invention includes improving the structure of the helical blades constituting the variable diameter swirl generator 2, thereby achieving precise control over the flow behavior of the fluid, constructing a flow field structure with a rigid swirl containing a high-energy secondary vortex, and achieving a deep match between the fluid dynamics characteristics and heat transfer characteristics; at the same time, it improves the fluid's own permeability, effectively reduces the pressure drop of the equipment, weakens the stress at the connection between the swirl generator and the pipe body, and significantly improves the impact resistance and operational reliability. Specifically, according to the enhanced heat transfer tube provided by the present invention, when fluid enters the enhanced heat transfer tube and flows through the variable diameter swirling flow generating mechanism 2, the fluid in the central region of the tube body 1 is not obstructed by the variable diameter swirling flow generating mechanism 2 and passes through rapidly in an approximately plug flow form, or in a rigid swirling flow form under the viscous shearing action of the fluid near the wall of the tube body 1. Meanwhile, the fluid near the wall of the tube body 1, upon encountering the positive pressure side 25 of the variable diameter swirling flow generating mechanism 2, experiences a rapid decrease in its axial velocity component and an increase in its tangential velocity component. Furthermore, under the viscous shearing action of the high-speed fluid in the central region of the tube body 1, the fluid near the wall of the tube body 1 bypasses the positive pressure side 25 to obtain a radial velocity component. Simultaneously, the variable diameter swirling flow generating mechanism 2... A low-pressure zone is formed at the back-pressure side 26 of mechanism 2. High-speed fluid in the central region of pipe 1 moves towards this low-pressure zone under the influence of the pressure difference. The fluid forms a symmetrical secondary vortex under the combined action of the positive-pressure side 25 and the back-pressure side 26 of the variable-diameter vortex generating mechanism 2. Simultaneously, because at least a portion of the radial dimensions of the helical blades are gradually varied along the axial direction of pipe 1, the area of ​​the low-axial velocity component fluid region at the positive-pressure side 25 of the variable-diameter vortex generating mechanism 2 continuously increases (the tangential and radial velocity components of the fluid in this region continuously increase). The area of ​​the low-pressure zone at the back-pressure side 26 also increases, and a large amount of fluid in the central region of pipe 1 moves towards the vicinity of the pipe wall, ultimately increasing the vortex intensity. It is easy to understand that, according to Bernoulli's equation (Equation 1), compared to... Figure 1 In the conventional hollow vortex generator shown, the variable diameter vortex generator 2 of the present invention reduces the pressure drop energy loss, thereby increasing the fluid kinetic energy (the axial velocity component decreases, but the tangential and radial velocity components continuously increase), thus providing energy for the formation of high-energy vortices.

[0073]

[0074] In equation (1), p is the fluid pressure, ρ is the fluid density, u is the fluid velocity, h is the tube length, and g is the gravitational acceleration.

[0075] Under the aforementioned hydrodynamic characteristics, firstly, the high-intensity swirling flow formed on the positive pressure side 25 of the helical blade is released downstream at its outlet 23, forming a rigid swirling flow and applying a high-intensity shear force to the inner wall of the pipe body 1. This effectively thins and disrupts the laminar boundary layer, promotes heat transfer between the pipe wall and the fluid near the pipe wall, and increases the renewal rate and frequency of wall components, shortening the residence time of scaling particles or scaling precursors, thereby effectively inhibiting scale formation and growth. Secondly, the fluid on the back pressure side 26 of the helical blade and the central region of the pipe body 1... Due to the significant velocity difference and the shearing effect within the fluid, a secondary longitudinal vortex is first induced on the back pressure side 26 of the inflow end 24. This vortex gradually develops as it spirals axially, following the gradual change in the radial dimension of the variable-diameter vortex generator 2. Both the vortex size and intensity continuously increase, and it gradually moves towards the axis of the tube body 1. At the outflow end 23 of the helical blades, it is further released downstream in a stable helical motion. This vortex, embedded within a rigid vortex, effectively enhances the heat exchange between the fluid in the wall region and the fluid in the central region of the tube body 1. It should be noted that in this invention, the secondary vortex's axial movement along the tube body is helical rather than linear, and the axis of the secondary vortex's helical motion is the axis of the tube body 1. Ultimately, the fluid leaving the variable-diameter swirling generator 2 achieves ideal swirling intensity near the inner wall of the tube 1, while a high-energy secondary longitudinal vortex with specific size and vortex intensity is formed in the central region of the tube 1. This balances the heat transfer between the high-temperature wall of the tube 1 and the fluid near the wall, as well as the heat-mass interaction between the fluid near the wall and the fluid in the central region, greatly improving the fluid heat exchange efficiency, intensity, and uniformity, and effectively suppressing the formation of scale on the wall.

[0076] In this invention, by gradually varying the radial dimensions of at least a portion of the spiral blades constituting the variable-diameter vortex generator 2 along the axial direction of the tube body 1, the form resistance of the variable-diameter vortex generator 2 is reduced, thereby improving fluid throughput and reducing the operating pressure drop of the equipment, effectively increasing production capacity. Furthermore, by gradually varying the radial dimensions of the spiral blades, the unobstructed flow area of ​​the fluid changes, inducing symmetrically distributed secondary vortices with high vortex intensity, large size, and stable motion in the central region of the heat transfer tube, which can improve heat transfer intensity and reduce or even eliminate the radial temperature gradient. In addition, the above structure can also slow down the direct impact of high-speed fluid on the spiral blades, improving the overall impact resistance of the variable-diameter vortex generator 2. Further, within the tube body 1 equipped with the variable-diameter vortex generator 2 described in this invention, the fluid turbulence intensity in the central region of the tube body is low, while the fluid vortex intensity near the wall is high, which can suppress energy dissipation and fully ensure the formation of fluid tangential velocity.

[0077] In the enhanced heat transfer tube provided by the present invention, the flow field in the tube body 1 after the variable diameter swirl generator 2 is a rigid swirling flow structure with multiple high-energy secondary vortices. This flow structure is well-suited to the heat transfer characteristics, which greatly improves the heat transfer effect. In addition, the disturbance effect of the high-energy secondary vortices can accelerate mass transfer, especially by re-entraining the scale particles or precursor components that have accumulated near the heat transfer tube wall under the action of centrifugal force into the central region, thereby inhibiting the formation of scale on the tube wall and extending the scale removal cycle of the heat transfer tube.

[0078] In this invention, in order to improve the disturbance effect of the variable diameter swirl generating mechanism 2 on the fluid inside the tube 1, the twist angle of the helical blade is 90°-1080°, more preferably 180°-360°; for example, the twist angle of the helical blade is 180°, 210°, 240°, 270°, 300°, 330° or 360°.

[0079] In some embodiments, the height of the helical blade in the axial direction of the tube body 1 is 1-10 times the inner diameter of the tube body 1. In particular, by controlling the height of the helical blade in the axial direction of the tube body 1 to 1-5 times the inner diameter of the tube body 1, an ideal swirling velocity can be obtained over a shorter axial distance.

[0080] In some embodiments, the radial dimensions of the inflow end 24 and the outflow end 23 of the helical blade are 0-0.5 times, more preferably 0-0.4 times, the inner diameter of the tube body 1.

[0081] In some embodiments, the radial dimension of the inlet end 24 of the helical blade is smaller than the radial dimension of the outlet end 23. This effectively avoids the impact of the fluid on the side of the variable diameter swirl generator 2 near the center region of the pipe body 1, and minimizes the concentration of impact stress at the inlet end 24 and its transmission as shear stress to the connection between the inlet end 24 and the pipe body 1. It should be noted that when the radial dimension of the helical blade is gradually changed along the axial direction of the pipe body 1, the present invention does not impose special limitations on the form of the gradual change, such as whether the gradual change rate is linear or nonlinear, or whether the gradual change pattern is continuous or intermittent.

[0082] In some embodiments, the thickness of the helical blades is set to be equal or gradually varied in the axial direction of the tube body 1. It should be noted that when the thickness of the helical blades is set to be gradually varied in the axial direction of the tube body 1, the present invention does not impose any special limitation on the gradual variation form, for example, its gradual variation rate is linear or nonlinear.

[0083] In some embodiments, the thickness of the inflow end 24 of the helical blade is 0-2 times the thickness of its outflow end 23, more preferably 1-1.5 times; furthermore, the thickness of the helical blade gradually decreases along the flow direction of the fluid within the pipe body 1, which can fully ensure the connection strength between the inflow end 24 of the helical blade and the pipe body 1, further attenuate the fluid impact on the inflow end 24 of the helical blade, weaken the stress effect between it and the pipe body 1, and avoid the problem of pipe wall cracking of the pipe body 1.

[0084] In some embodiments, the thickness of the outflow end 23 of the helical blade is 0.2-2 times the wall thickness of the tube body 1, and the thickness of the outflow end 23 of the helical blade is 0.1-0.2 times the inner diameter of the tube body 1.

[0085] In some embodiments, the thickness of the helical blades is set in a uniform or gradually varying manner in the radial direction of the tube body 1. It should be noted that when the thickness of the helical blades is set in a gradually varying manner in the radial direction of the tube body 1, the present invention does not impose any special limitation on the form of the gradual change, for example, the gradual change rate is linear or nonlinear.

[0086] In some embodiments, the helical blade has a first side 201 and a second side 202 disposed opposite to each other. The first side 201 is connected to the inner wall of the tube body 1. The thickness of the first side 201 is 0.2-2 times the wall thickness of the tube body 1, and the thickness of the first side 201 is 0.1-0.2 times the inner diameter of the tube body 1. The thickness of the second side 202 is 0-1 times the thickness of the first side 201, more preferably 0.5-1 times.

[0087] It is understood that in this invention, the gradual change in the thickness of the spiral blades can adapt to the axial evolution of the fluid impact force, thereby effectively reducing the (thermal) stress at the connection between the swirling mechanism and the tube body 1, extending the life of the heat transfer tube and the safe operation cycle.

[0088] In some embodiments, the helical blade has a first helical twisted section 241 near its inflow end 24 and a second helical twisted section 231 near its outflow end 23. The helix angle of the first helical twisted section 241 is 0.1-5 times the helix angle of the second helical twisted section 231. It should be noted that, in this invention, the helix angle refers to the angle between the tangent of the helix and the plane perpendicular to the axis of the helical blade. It can be found that the larger the helix angle, the greater the height along the axial direction of the tube body 1 when the helical blade is twisted by the same angle.

[0089] In some embodiments, the helix angle of the first helical twisted section 241 is greater than that of the second helical twisted section 231. With this structural configuration, the generation rate of tangential swirling flow varies along the axial direction of the pipe body 1 when the near-wall fluid passes through the pipe section containing the helical blades. Specifically, the swirling flow generation rate in the region containing the first helical twisted section 241 is less than that in the region containing the second helical twisted section 231, resulting in a pressure drop distribution along the pipe exhibiting a "small at first, then large" trend. Furthermore, the enhanced heat transfer pipe provided by this invention can mitigate the impact of high-speed fluid on the inflow end 24 of the helical blades and effectively disperse the shear stress at the connection between the helical blades and the pipe body 1, making the pressure drop distribution along the pipe more gradual and enhancing the overall reliability of the variable-diameter swirling flow generating mechanism 2.

[0090] It is understood that in the heat transfer tube provided by the present invention, at least a portion of the radial dimensions of the helical blades are arranged in a gradually changing manner in the axial direction of the tube body 1, that is, the helical blades can be configured as locally variable diameter. In some embodiments, in the axial direction of the tube body 1, the first helical twisted section 241 is a variable diameter twisted section, and the second helical twisted section 231 is a constant diameter twisted section.

[0091] In some embodiments, the variable diameter swirl generator 2 includes a plurality of helical blades, wherein the helical blades arranged in parallel along the circumference of the tube body 1 have the same helical twist direction; and the helical blades arranged along the axial direction of the tube body 1 have opposite helical twist directions.

[0092] In some embodiments, the variable diameter swirl generating mechanism 2 includes four helical blades, namely helical blade one 210, helical blade two 220, helical blade three 230 and helical blade four 240; wherein, helical blade one 210 and helical blade two 220 are arranged side by side along the circumference of the tube body 1, and helical blade three 230 and helical blade four 240 are arranged side by side along the circumference of the tube body 1; the helical twisting direction of helical blade one 210 and helical blade two 220 is the same and opposite to the helical twisting direction of helical blade three 230 and helical blade four 240.

[0093] In the above embodiments of the present invention, by improving the rotation direction of the helical blades constituting the variable diameter vortex generating mechanism 2, a flow field structure with multiple high-energy secondary vortices with opposite rotation directions built into the rigid vortex is constructed, enhancing the radial mixing of the fluid, thereby finely controlling the fluid flow behavior and achieving a deep match between fluid dynamics, heat transfer, and mass transfer characteristics; at the same time, it improves the permeability of the component itself, increases production capacity, and significantly improves impact resistance and operational reliability. Specifically, according to the enhanced heat transfer tube provided by the present invention, when the fluid enters the enhanced heat transfer tube and flows through the variable diameter vortex generating mechanism 2, the fluid in the axial region of the tube body 1 is not hindered by the variable diameter vortex generating mechanism 2 and passes through in an approximately plug flow form, or in a rigid vortex form under the viscous shearing action of the fluid near the wall of the tube body 1; while the fluid near the wall of the tube body 1 flows axially through the tube section where helical blade 1 210 and helical blade 220 are located, and the tube section where helical blade 3 230 and helical blade 4 240 are located. Upon encountering the positive pressure side of helical blades 210 and 220, the axial velocity component of the fluid decreases sharply, while the tangential velocity component increases. Furthermore, under the viscous shearing action of the high-speed fluid in the axial region of pipe 1, the fluid near the wall of pipe 1 circumvents the positive pressure side, thus acquiring a radial velocity component. Simultaneously, a low-pressure zone is formed at the negative pressure side of helical blades 210 and 220. The high-speed fluid in the central region of pipe 1 moves towards this low-pressure zone under the influence of the pressure difference. Ultimately, the fluid passes through the positive pressure side of helical blades 210 and 220. The combined effect of the positive and negative pressure sides of blade 220 forms a symmetrical secondary vortex. Simultaneously, because at least a portion of the radial dimensions of the helical blades are gradually varied along the axial direction of tube 1, the area of ​​the low axial velocity component fluid region on the positive pressure side of helical blade 210 and helical blade 220 continuously increases (the tangential and radial velocity components of the fluid in this region continuously increase), and the area of ​​the low-pressure region on the negative pressure side also increases. A large amount of fluid in the central region of tube 1 moves towards the vicinity of the tube wall, ultimately increasing the vortex intensity. It is easy to understand that, according to Bernoulli's equation, compared to... Figure 1In the conventional hollow vortex generator shown, the variable diameter vortex generator 2 of the present invention reduces the pressure drop energy loss, which greatly increases the fluid kinetic energy (the axial velocity component decreases, but the tangential and radial velocity components continuously increase), thereby providing energy for the formation of high-energy vortices. Furthermore, when encountering helical blades 230 and 240 along the axial direction of pipe 1, which rotate in the opposite direction to helical blades 210 and 220, the already formed symmetrical secondary vortex undergoes rigid rotational motion and is not hindered by helical blades 230 and 240. The fluid near the wall of pipe 1 then comes into further contact with the positive pressure side of helical blades 230 and 240. The axial velocity component of the fluid decreases, while the tangential velocity vector first decreases and then gradually increases after reversal. Under the viscous shearing action of the high-speed fluid in the axial region of pipe 1, the fluid near the wall of pipe 1 travels around the positive pressure side, thus acquiring a radial velocity component. At the same time, a low-pressure zone is formed on the back pressure side of helical blades 230 and 240, and the fluid in pipe 1... Under the influence of pressure difference, the high-speed fluid in the core region moves towards the low-pressure region. Ultimately, under the combined action of the positive and negative pressure sides of the three spiral blades 230 and the four spiral blades 240, the fluid forms a symmetrical secondary vortex. The direction of rotation of this symmetrical secondary vortex is opposite to that of the symmetrical secondary vortex formed at the one spiral blade 210 and the two spiral blades 220. At the same time, because at least part of the radial dimension of the spiral blades is gradually changed in the axial direction of the tube body 1, the area of ​​the low axial velocity component fluid region at the positive pressure side of the three spiral blades 230 and the four spiral blades 240 continuously increases (the tangential velocity component and radial velocity component of the fluid in this region continuously increase), and the area of ​​the low-pressure region on the negative pressure side also increases. A large amount of fluid in the central region of the tube body 1 moves towards the vicinity of the tube wall, and the vortex intensity continuously increases.

[0094] Under the aforementioned hydrodynamic characteristics, firstly, the high-intensity swirling flow formed on the positive pressure side of helical blade 1 210 and helical blade 220, after leaving the outflow end 1 and outflow end 2, is hindered by helical blade 3 230 and helical blade 4 240, and rapidly attenuates at the inflow end 3 and inflow end 4. Subsequently, under the action of the positive pressure side of helical blade 3 230 and helical blade 4 240, it gradually forms a rigid swirling flow with opposite directions of rotation, and finally releases to the downstream pipe section at the outflow end 3 and outflow end 4. This rigid swirling flow can apply a high-intensity shear force to the wall of pipe body 1, effectively thinning and destroying the laminar boundary layer, promoting heat transfer between the pipe wall and the fluid near the pipe wall, and increasing the renewal rate and frequency of wall components, shortening the residence time of scale particles or scale precursors, thereby effectively inhibiting the formation and growth of scale. Secondly, a significant velocity difference exists between the fluid in the central region of pipe 1 and the back pressure side of helical blades 1 (210) and 220, and due to internal fluid shearing, symmetrical secondary longitudinal vortices with the same rotation direction are induced first on the back pressure side of inflow end 1 and inflow end 2. These vortices gradually develop along the axial direction as the radial dimensions of helical blades 1 (210) and 220 gradually change, increasing in both size and intensity. They also gradually move radially towards the axis of pipe 1 and are released in a stable helical motion at outflow end 1 and outflow end 2. Similarly, a significant velocity difference also exists between the fluid in the central region of pipe 1 on the back pressure side of helical blades 3 (230) and 4 (240), and due to internal fluid shearing, symmetrical secondary longitudinal vortices with the same rotation direction are induced on the back pressure side of inflow end 3 and inflow end 4. The side induces secondary longitudinal vortices with the same rotation direction. As these vortices advance axially, they gradually develop with the gradual change in the radial dimensions of the three helical blades 230 and the four helical blades 240. The size and intensity of the vortices increase, and they gradually move radially towards the axis of the tube body 1. They are then released downstream in a stable helical motion at the three and four outlet ends. Since the rotation direction of the secondary vortices released from the three and four outlet ends is opposite to that of the secondary vortices released from the one and two outlet ends, and their interaction is weak, the fluid can stably maintain multiple secondary vortexes with opposite rotation directions in a large space within the downstream tube body 1 of the variable diameter vortex generator 2. Furthermore, since they are built into a rigid vortex, the fluid transfer behavior between the wall region and the central region of the tube body 1 can be effectively enhanced. Ultimately, the fluid leaving the variable-diameter swirling generator 2 achieves ideal swirling intensity near the inner wall of the tube 1. In the central region of the tube 1, multiple high-energy secondary longitudinal vortices with opposite directions of rotation are formed, thus taking into account both the heat transfer between the high-temperature wall surface of the tube 1 and the fluid near the wall surface, and the heat-mass interaction between the fluid near the wall surface of the tube 1 and the fluid in the central region. This greatly improves the fluid heat exchange efficiency, intensity, and uniformity, and effectively inhibits the formation of scale.

[0095] In this invention, by alternating the rotation directions of the helical blades constituting the variable diameter swirling flow generating mechanism 2 along the axial direction of the tube body 1, the overall shape resistance of the variable diameter swirling flow generating mechanism 2 is reduced, and the fluid throughput capacity is further improved, effectively enhancing the production capacity of the enhanced heat transfer tube. Furthermore, by alternating the rotation directions of the helical blades constituting the swirling flow generating element along the axial direction in a clockwise-counterclockwise manner, multiple symmetrically distributed secondary vortices with high vortex strength, large size, stable motion, and opposite rotation directions are induced in the central region of the enhanced heat transfer tube, greatly promoting radial mixing behavior, thereby improving the heat transfer rate and intensity, and reducing or even eliminating the radial temperature gradient. In addition, the above structure can also slow down the direct impact of high-speed fluid on the variable diameter swirling flow generating mechanism 2 and avoid stress concentration on helical blade 1 210 and helical blade 220, instead distributing it relatively evenly to helical blade 1 210, helical blade 220, helical blade 3 230, and helical blade 4 240, improving the overall impact resistance of the variable diameter swirling flow generating mechanism 2.

[0096] In some embodiments, multiple variable diameter swirl generating mechanisms 2 are provided, and the multiple variable diameter swirl generating mechanisms 2 are spaced apart along the axial direction of the tube body 1; the distance between two adjacent variable diameter swirl generating mechanisms 2 is 10-100 times the inner diameter of the tube body 1; more preferably, it is 30-80 times.

[0097] It is understood that in the tube body 1, the fluid passing through the variable diameter swirling generator 2 experiences a decrease in both swirling and turbulent intensity. Upon entering the next variable diameter swirling generator 2, further eddy current intensification occurs. Arranging multiple variable diameter swirling generators 2 at axial intervals in the tube body 1 ensures that the heat transfer and mass transfer requirements of the fluid are met. Alternatively, the variable diameter swirling generator 2 described in this invention and a conventional hollow swirling generator 4 in the art can be arranged axially in the tube body 1.

[0098] It is understood that in this invention, by arranging swirling flow generating mechanisms of different configurations along the axial direction of the tube body 1, a deep match between the fluid turbulence intensity, swirling flow intensity, and heat exchange requirements within different heat transfer tube sections is achieved, such as... Figure 27 As shown.

[0099] It should be noted that in the tube body 1 of the present invention, the spiral twisting direction of the spiral blades of two adjacent variable diameter swirl generating mechanisms 2 can be the same, or, preferably, the spiral twisting direction of the spiral blades of two adjacent variable diameter swirl generating mechanisms 2 is opposite.

[0100] In some embodiments, the tube body 1 is provided with a first swirl generating mechanism 5, a second swirl generating mechanism 6, a third swirl generating mechanism 7, and a fourth swirl generating mechanism 8 spaced apart along its axial direction; the first swirl generating mechanism 5, the second swirl generating mechanism 6, the third swirl generating mechanism 7, and the fourth swirl generating mechanism 8 each include at least one helical blade, and at least a portion of the radial dimension of the helical blade included in at least one of the first swirl generating mechanism 5, the second swirl generating mechanism 6, the third swirl generating mechanism 7, and the fourth swirl generating mechanism 8 is arranged in a gradually changing manner along the axial direction of the tube body 1. The solutions provided in the above embodiments precisely control the balance between the rigid vortex intensity and the secondary vortex intensity, so that the fluid dynamics characteristics match and adapt to the heat transfer requirements along the cracking reaction process. In particular, they prioritize ensuring the secondary vortex intensity on the upstream side of the heat exchange tube, improve the heat transfer rate and uniformity, and achieve rapid heating and reaction of the raw gas. On the downstream side, they prioritize ensuring the rigid vortex intensity, enhance the vortex shear effect of the tube wall, and suppress the fundamental technical goal of side reactions and coking and coke layer growth at the high-temperature tube wall. At the same time, under the premise of improving fluid flowability, they change the pressure drop distribution along the process, reduce the stress at the connection between the heat transfer element and the tube wall under high-speed impact, significantly improve the impact resistance, and ensure the long-term and reliable operation of the cracking furnace.

[0101] It is understandable that after the fluid leaves the first swirling generator 5, the rigid swirling intensity and the symmetrically distributed secondary vortex intensity gradually decrease along the axial direction of the pipe body 1. Before the symmetrically distributed double vortex decreases to a single vortex, it enters at least the second swirling generator 6 to undergo swirling enhancement. After the same attenuation process occurs, it enters at least the third swirling generator 7 and the fourth swirling generator 8 in sequence to undergo swirling enhancement.

[0102] In some embodiments, the radial dimensions of the outflow ends 23 of the helical blades included in the first swirl generating mechanism 5, the second swirl generating mechanism 6, the third swirl generating mechanism 7, and the fourth swirl generating mechanism 8 are different. Specifically, the radial dimension of the outflow end 23 of the first swirl generating mechanism 5 is 0.6-1 times the radial dimension of the outflow end 23 of the second swirl generating mechanism 6, the radial dimension of the outflow end 23 of the second swirl generating mechanism 6 is 0.6-1 times the radial dimension of the outflow end 23 of the third swirl generating mechanism 7, and the radial dimension of the outflow end 23 of the third swirl generating mechanism 7 is 0.6-1 times the radial dimension of the outflow end 23 of the fourth swirl generating mechanism 8.

[0103] In some embodiments, the helix angles of the first swirl generating mechanism 5, the second swirl generating mechanism 6, the third swirl generating mechanism 7, and the fourth swirl generating mechanism 8 are 5°-85°; further, the helix angle of the first swirl generating mechanism 5 is 0.5-3 times that of the second swirl generating mechanism 6, the helix angle of the second swirl generating mechanism 6 is 0.5-3 times that of the third swirl generating mechanism 7, and the helix angle of the third swirl generating mechanism 7 is 0.5-3 times that of the fourth swirl generating mechanism 8; preferably, the helix angles of the first swirl generating mechanism 5, the second swirl generating mechanism 6, the third swirl generating mechanism 7, and the fourth swirl generating mechanism 8 decrease sequentially.

[0104] It is understood that in this invention, by setting different configurations of swirling flow generating mechanisms along the axial direction of the tube body 1, the balance control of the rigid swirling flow intensity and the symmetrically distributed secondary vortex intensity along the axial direction of the tube body 1 can be achieved. That is, as the rigid swirling flow intensity increases along the axial direction of the tube body 1, the intensity, shape, size and motion mode of the secondary vortex are stably maintained, and finally the deep matching between the fluid turbulence intensity, swirling flow intensity and heat exchange requirements in different heat transfer tube sections is achieved.

[0105] In some embodiments, the first vortex generating mechanism 5 and the second vortex generating mechanism 6 form a first interval 9, the second vortex generating mechanism 6 and the third vortex generating mechanism 7 form a second interval 10, and the third vortex generating mechanism 7 and the fourth vortex generating mechanism 8 form a third interval 11; the first interval 9, the second interval 10 and the third interval 11 are 10-100 times the inner diameter of the tube body 1; preferably, the first interval 9 is 0.5-2 times the second interval 10, and the second interval 10 is 0.5-2 times the third interval 11; more preferably, the first interval 9, the second interval 10 and the third interval 11 decrease sequentially.

[0106] Understandably, as the fluid temperature gradually increases along the axial direction of pipe 1, the rate of coke formation and the rate of coke layer growth at the pipe 1 wall increase along the path. The fluid needs to achieve a greater rigid swirling intensity to enhance its scouring effect on the pipe 1 wall, thereby reducing the coke deposition rate and inhibiting the increase in coke layer thickness. However, according to the principle of energy conservation, the increase in the rigid swirling intensity inevitably leads to a decrease in the intensity of the secondary vortex, resulting in a shorter attenuation distance of the secondary vortex. Therefore, in order to maintain a symmetrically distributed double-vortex flow structure within the rigid swirling flow within pipe 1, the first interval 9, the second interval 10, and the third interval 11 decrease along the axial direction, thereby ensuring that the heat exchange-reaction-mass transfer requirements of the fluid on the upstream and downstream sides of pipe 1 are met.

[0107] The solution provided by this invention features a simple swirl generator, which is easy to manufacture and readily adapts for industrial modification. It can be achieved by simply replacing the heat transfer tubes in existing equipment.

[0108] In some embodiments, the spiral blade is provided with a jet hole 3; in the present invention, by providing a jet hole 3, on the one hand, the flow area of ​​the fluid can be increased and the flow resistance can be reduced, and on the other hand, some fluid can pass through the jet hole 3 to form a high-speed jet, which intensifies the fluid disturbance and promotes the heat exchange between the fluid near the inner wall surface of the tube body 1 and the fluid in the central region.

[0109] It should be noted that the present invention does not impose any special limitations on the external shape of the jet hole 3. In some embodiments, the jet hole 3 is a louver type or a planar hole type, and the planar hole type can be circular, elliptical, square, rhomboid, trapezoidal or other irregular shapes. In some embodiments, the size of the jet hole 3 is 0.02-0.2 times the inner diameter of the tube body 1, more preferably 0.02-0.1 times. In some embodiments, the number of jet holes 3 is 1-12, preferably 2-10. In some embodiments, the jet holes 3 are arranged in 1-3 rows in the radial direction of the tube body 1.

[0110] The present invention also provides a pyrolysis furnace, comprising a radiation chamber in which at least one radiation furnace tube assembly is installed. The radiation furnace tube assembly includes a plurality of sequentially arranged radiation furnace tubes and heat transfer tubes connecting adjacent radiation furnace tubes. These heat transfer tubes are enhanced heat transfer tubes provided by the present invention. By installing the enhanced heat transfer tubes provided by the present invention in the radiation chamber of the pyrolysis furnace, not only can the heat transfer effect of the fluid be improved, promoting precise control of reaction behavior, but also the operating pressure drop of the equipment can be reduced, increasing production capacity. Furthermore, since the thermal stress of the heat transfer tubes is reduced and the formation of scale on the tube walls is suppressed, the operating cycle of the pyrolysis furnace can also be increased.

[0111] The enhanced heat transfer tube provided by the present invention will be further described below through specific embodiments.

[0112] Example 1

[0113] In this embodiment, a tube 1 with an inner diameter of 51 mm and a length of 3.6 m is used as the research object. A variable diameter swirl generator 2 is added at a distance of 1 m from the fluid inlet of the tube 1. The fluid flow-heat transfer characteristics in the heat transfer tube are systematically investigated. The specific working conditions are as follows: the fluid medium is air, the fluid linear velocity is 75 m / s, the fluid inlet temperature is 873.15 K, the tube wall temperature is 1118 K, and the outlet gauge pressure is 1 atm.

[0114] like Figure 2As shown, in this embodiment, the variable-diameter vortex generating mechanism 2 consists of two sets of helical blades, namely a first helical blade 21 and a second helical blade 22. The first helical blade 21 and the second helical blade 22 have the same twist angle of 180°. The heights of the first helical blade 21 and the second helical blade 22 in the axial direction of the tube body 1 are three times the inner diameter of the tube body 1. The radial dimensions of the inflow end 24 of the first helical blade 21 and the second helical blade 22 are 0.02 times the inner diameter of the tube body 1, and the radial dimensions of the outflow end 23 are 0.25 times the inner diameter of the tube body 1. Within the tube body 1, along the flow direction of the fluid, the radial dimension gradually changes in a continuous manner with a linear rate of change. Within the tube body 1, along the flow direction of the fluid, the thickness of both the first helical blade 21 and the second helical blade 22 gradually decreases with a linear rate of change. The thickness of the inflow end 24 of the first helical blade 21 and the second helical blade 22 is 1.5 times the thickness of their respective outflow end 23. The thickness of the outflow end 23 of the first helical blade 21 and the second helical blade 22 is 0.6 times the wall thickness of the tube body 1 and 0.1 times the inner diameter of the tube body 1. The thickness of the first helical blade 21 and the second helical blade 22 is linearly and gradually varied in the radial direction of the tube body 1. The first helical blade 21 and the second helical blade 22 each have a first side 201 and a second side 202 arranged opposite to each other. The first side 201 is connected to the inner wall of the tube body 1. The thickness of the second side 202 is 0.5 times the thickness of the first side 201. The thickness of the first side 201 is 0.6 times the wall thickness of the tube body 1 and 0.1 times the inner diameter of the tube body 1. The first helical blade 21 and the second helical blade 22 each have a first helical twisted section 241 near their respective inflow end 24 and a second helical twisted section 231 near their respective outflow end 23. In the first helical blade 21, the helix angle of the first helical twisted section 241 is equal to that of the second helical twisted section 231, which is 38.5°; in the second helical blade 22, the helix angle of the first helical twisted section 241 is equal to that of the second helical twisted section 231, which is 38.5°. The first helical blade 21 and the second helical blade 22 are arranged side by side in the circumferential direction of the tube body 1.

[0115] The test results of the relevant fluid flow-heat transfer characteristics are summarized in Table 1. The conventional hollow vortex generator mechanism, such as... Figure 1 As shown. Figure 4 The diagram shown is a characteristic image of the vortex field structure of the enhanced heat transfer tube in this embodiment. Figure 4 It can be seen that the variable-diameter vortex generator 2 in this embodiment induces an ideal rigid vortex with built-in symmetrical secondary vortexes. For example... Figure 5 The diagram shown is an axial temperature distribution of the fluid in the central region of the enhanced heat transfer tube in this embodiment, compared to a bare tube (such as...). Figure 5a) In this embodiment, the temperature of the fluid at the axial center of the enhanced heat transfer tube is significantly increased by more than 20°C, effectively eliminating the low-temperature zone in the center. Compared with conventional hollow vortex generators (such as...), this significantly improves the temperature of the fluid at the axial center of the enhanced heat transfer tube. Figure 5 b) The temperature rise curve of the fluid at the shaft center shows a stable upward trend without significant fluctuations, indicating a stable and orderly heat exchange process. Figure 6 The diagram shows a comparison of the radial temperature distribution of the fluid at the outlet of the enhanced heat transfer tube in this embodiment. It confirms that the enhanced heat transfer tube provided in this embodiment can reduce the radial temperature gradient while improving the heat transfer intensity, thereby achieving good heat transfer uniformity.

[0116] Example 2

[0117] Combination Figure 7 The structure of the enhanced heat transfer tube used in this embodiment is basically the same as that in Embodiment 1. The difference is that in this embodiment, the helix angle of the first helical twisted section 241 in the first helical blade 21 and the second helical blade 22 is 46.7° and the helix angle of the second helical twisted section 231 is 27.9°.

[0118] The working principle of this embodiment is basically similar to that of Embodiment 1. The difference is that, through the above structural arrangement, when the near-wall fluid in the tube body 1 passes through the section where the variable-diameter swirling flow generating mechanism 2 is located, the generation rate of the tangential swirling flow varies along the axial direction. Specifically, the swirling flow generation rate in the region where the first helical twisted section 241 is located is less than that in the region where the second helical twisted section 231 is located, resulting in a pressure drop distribution along the friction path that shows a "small at first, then large" trend. Compared with the enhanced heat transfer tube of Embodiment 1, the enhanced heat transfer tube provided in this embodiment slows down the impact of high-speed fluid on the first helical twisted section 241 of the two helical blades and effectively disperses the shear stress at the connection between the helical blades and the tube body 1, making the pressure drop distribution along the friction path more gradual and enhancing the overall reliability of the heat transfer element. The relevant fluid flow-heat transfer characteristic test results are summarized in Table 1.

[0119] Example 3

[0120] Combination Figure 8This embodiment has a structure that is basically the same as the enhanced heat transfer tube used in Embodiment 1. The difference is that in this embodiment, the first helical twisted section 241 is a variable diameter twisted section and the second helical twisted section 231 is a constant diameter twisted section in the axial direction of the tube body 1. More specifically, within the tube body 1 along the fluid flow direction, the radial dimension of the first helical twisted section 241 linearly increases from 0.02 times the inner diameter of the tube body 1 at the inlet end 24 to 0.25 times the inner diameter of the tube body 1, and its length is 0.7 times the height of the variable diameter vortex generating mechanism 2; the radial dimension of the second helical twisted section 231 is 0.25 times the inner diameter of the tube body 1, and its length is 0.3 times the height of the variable diameter vortex generating mechanism 2. With the above structural limitations, compared with the enhanced heat transfer tube provided in Embodiment 1, the rigid vortex intensity of the fluid flowing near the tube wall through the variable diameter vortex generating mechanism 2 is further improved in this embodiment. The relevant fluid flow-heat transfer characteristic test results are summarized in Table 1.

[0121] Example 4

[0122] Combination Figure 9 The structure of the enhanced heat transfer tube used in this embodiment is basically the same as that in Embodiment 3. The difference is that in this embodiment, jet holes 3 are respectively provided on the second helical twisted section 231 of the first helical blade 21 and the second helical blade 22. The jet holes 3 are circular holes, the diameter of the jet holes 3 is 0.04 times the inner diameter of the tube body 1, and there are 6 jet holes 3 arranged in 2 rows in the radial direction of the tube body 1. The relevant fluid flow-heat transfer characteristic test results are summarized in Table 1.

[0123] Example 5

[0124] Combination Figure 10 The structure of the enhanced heat transfer tube used in this embodiment is basically the same as that in Embodiment 2. The difference is that in this embodiment, as shown in the example... Figure 11 As shown, the radial dimensions of the first helical blade 21 and the second helical blade 22 increase non-linearly along the axial direction. In this embodiment, the rate of increase of the radial dimension of the first helical twisted section 241 along the fluid flow direction is less than the rate of increase of the radial dimension of the second helical twisted section 231. The working principle of this embodiment is basically similar to that of Embodiment 2. The difference is that the formation and development rates of the high-energy secondary vortex on the back pressure side 26 of the first helical blade 21 and the second helical blade 22 differ along the axial direction. Specifically, the rate of increase of the size and intensity of the high-energy secondary vortex shows a trend of "low at first and then high". The relevant fluid flow-heat transfer characteristic test results are summarized in Table 1.

[0125] Example 6

[0126] Combination Figure 12This embodiment has a structure that is basically the same as the enhanced heat transfer tube used in Embodiment 1. The difference is that in this embodiment, the radial dimension of the first helical blade 21 and the second helical blade 22 changes intermittently, so that the unobstructed flow area of ​​the fluid exhibits a multi-segment "gradual contraction-sudden expansion" change. Inside the tube body 1, along the flow direction of the fluid, the first helical blade 21 and the second helical blade 22 are respectively composed of a first variable diameter section 211 and a second variable diameter section 212. The heights of the first variable diameter section 211 and the second variable diameter section 212 are equal, and the twist angles of the first variable diameter section 211 and the second variable diameter section 212 are both 90°. The first variable diameter section 211 has a first inflow end 2111 and a first outflow end 2112, and the second variable diameter section 212 has a second inflow end 2121 and a second outflow end 2122. The radial dimensions of the first inflow end 2111 and the second inflow end 2121 are equal, both being 0.02 times the inner diameter of the pipe body 1; the radial dimensions of the first outflow end 2112 and the second outflow end 2122 are equal, both being 0.25 times the inner diameter of the pipe body 1.

[0127] Based on the above structure, the working principle of this embodiment is basically similar to that of Embodiment 1. The difference is that the unobstructed flow area of ​​the fluid exhibits a change of "gradual contraction-sudden expansion-gradual contraction-sudden expansion". When the fluid flows through the variable diameter vortex generator 2, the variable diameter vortex generator 2 can simultaneously induce high-energy secondary vortices on the back pressure side 26 of the first inflow end 2111 and the second inflow end 2121, and release the high-energy secondary vortices on the back pressure side 26 of the first outflow end 2112 and the second outflow end 2122. This effectively increases the number of high-energy secondary longitudinal vortices in the central region of the tube body 1, enhances the turbulence intensity, and further improves the heat transfer driving force between the fluid near the wall surface of the tube body 1 and the fluid in the central region, improves the heat transfer uniformity, effectively reduces the radial temperature gradient, and even eliminates the low-temperature fluid zone in the axial region of the tube body 1. Figure 13 As shown, compared to Example 1, Example 6 allows the fluid to achieve a greater radial velocity, which is beneficial for heat transfer from the high-temperature pipe wall to the low-temperature axial region. For example... Figure 14 The diagram shows a comparison of the radial temperature distribution of the fluid in a local section downstream of the variable-diameter swirl generator (at 10 times the inner diameter of the pipe body) in Example 6 and Example 1. Example 6 is significantly superior to Example 1. The test results of the relevant fluid flow-heat transfer characteristics are summarized in Table 1.

[0128] Example 7

[0129] Combination Figure 15The structure of the enhanced heat transfer tube used in this embodiment is basically the same as that in Embodiment 6. The difference is that in this embodiment, in the first diameter-changing section 211, the radial dimension of the first inflow end 2111 is larger than the radial dimension of the first outflow end 2112; and in the second diameter-changing section 212, the radial dimension of the second inflow end 2121 is larger than the radial dimension of the second outflow end 2122. In the above structure, the radial dimensions of the first inflow end 2111 and the second inflow end 2121 are equal, both being 0.25 times the inner diameter of the tube body 1; the radial dimensions of the first outflow end 2112 and the second outflow end 2122 are equal, both being 0.02 times the inner diameter of the tube body 1.

[0130] The working principle of this embodiment is basically the same as that of embodiment 6. The difference is that the unobstructed flow area of ​​the fluid exhibits a change of "sudden contraction-gradual expansion-sudden contraction-gradual expansion", which causes the fluid to quickly form a high-energy secondary vortex on the back pressure side 26 of the first inflow end 2111. Subsequently, its vortex volume and size decrease along the axial direction in the heat transfer tube section where the variable diameter vortex generating mechanism 2 is located. Figure 16 (a) indicates that, compared to Examples 1 and 6, the temperature of the fluid in the central region can be further increased within a limited area downstream of the variable-diameter vortex generator in Example 7. And from... Figure 16 As shown in the radial velocity distribution diagram (b), it can be observed that the fluid near the pipe wall in Example 7 achieves a greater radial velocity, which significantly promotes the transfer of heat from the pipe wall to the central region. Ultimately, this results in a significant increase in the heating rate of the fluid in the central region and an effective reduction in the radial temperature gradient. The relevant fluid flow-heat transfer characteristic test results are summarized in Table 1.

[0131] Example 8

[0132] Combination Figure 17 The structure of the enhanced heat transfer tube used in this embodiment is basically the same as that in embodiment 2. The difference is that in this embodiment, the radial dimension of the incoming flow end 24 of the variable diameter swirl generator 2 is 0.1 times the inner diameter of the tube body 1, the radial dimension of the middle part is 0.02 times the inner diameter of the tube body 1, and the radial dimension of its outgoing flow end 23 is 0.25 times the inner diameter of the tube body 1, so that the radial dimension of the first helical blade 21 and the second helical blade 22 both decrease first and then increase.

[0133] The working principle and beneficial effects of this embodiment are similar to those of Embodiments 2, 6, and 7. The difference lies in that the unobstructed flow area of ​​the fluid within the heat transfer tube where the variable-diameter vortex generator 2 is located undergoes a "sudden contraction-gradual expansion-gradual contraction-sudden expansion" change, thus providing sufficient space for the stable development of the high-energy secondary vortex. This allows the high-energy secondary vortex to rapidly form on the back pressure side 26 of the incoming flow end 24, and its intensity and size continuously increase during its movement towards the central region, and it is efficiently released at the outgoing flow end 23. This process will cause a significant change in the fluid temperature rise curve. Figure 18 The diagram shows the axial temperature distribution of the fluid at the center of the enhanced heat transfer tube. Compared to Example 2, Example 8 allows the fluid at the center to obtain a higher temperature within a range of 25 to 40 times the inner diameter of the tube 1 downstream of the variable diameter swirling flow generator. Figure 19 (a) Further, a radial temperature distribution diagram within this interval (30 times the inner diameter of the tube 1) is given. It can be observed that the radial temperature distribution of the fluid in this Example 8 is more uniform. The essential reason is that the fluid under the action of Example 8 has a greater radial velocity, which intensifies the radial mixing behavior of the fluid (e.g., Figure 19 (b) effectively promoted the transport of heat from the pipe wall to the central region. The test results of the relevant fluid flow-heat transfer characteristics are summarized in Table 1.

[0134] Example 9

[0135] like Figure 20As shown, in this embodiment, the variable diameter swirl generator 2 is composed of a first spiral blade 210, a second spiral blade 220, a third spiral blade 230, and a fourth spiral blade 240. The first spiral blade 210 and the second spiral blade 220 are arranged side-by-side along the circumference of the tube body 1 with the same spiral twisting direction; the third spiral blade 230 and the fourth spiral blade 240 are arranged side-by-side along the circumference of the tube body 1 with the same spiral twisting direction; the first spiral blade 210 and the fourth spiral blade 240 are arranged along the axial direction of the tube body 1 with opposite spiral twisting directions; the second spiral blade 220 and the third spiral blade 230 are arranged along the axial direction of the tube body 1 with opposite spiral twisting directions; the first spiral blade 210 has an inlet end and an outlet end; the second spiral blade 220 has an inlet end and an outlet end; the third spiral blade 230 has an inlet end and an outlet end; and the fourth spiral blade 240 has an inlet end and an outlet end. The outflow end of helical blade 210 is connected to the inflow end of helical blade 240, and the outflow end of helical blade 220 is connected to the inflow end of helical blade 230. The helical twist angles of helical blades 210, 220, 230, and 240 are the same, at 90°. The heights of helical blades 210, 220, 230, and 240 along the axial direction of the tube body 1 are equal, being 0.5 times the height of the variable-diameter vortex generator 2. Helical blades 210, 220, 230, and 240 have the same helix angle of 38.5°. The radial dimensions of inlet ends 1, 2, 3, and 4 are equal, being 0.02 times the inner diameter of pipe body 1. The radial dimensions of outlet ends 1, 2, 3, and 4 are also equal, being 0.25 times the inner diameter of pipe body 1. Within pipe body 1, along the fluid flow direction, the radial dimension gradually changes in a continuous manner with a linear rate of change. Within pipe body 1, along the fluid flow direction, the thicknesses of helical blades 1 (210), 2 (220), 3 (230), and 4 (240) all gradually decrease with a linear rate of change. The thicknesses of inlet end 1, inlet end 2, inlet end 3, and inlet end 4 are 1.5 times the thicknesses of outlet end 1, outlet end 2, outlet end 3, and outlet end 4, respectively. The thicknesses of outlet end 1, outlet end 2, outlet end 3, and outlet end 4 are all 0.6 times the wall thickness of pipe body 1 and 0.1 times the inner diameter of pipe body 1. The thicknesses of spiral blade 1 (210), spiral blade 2 (220), spiral blade 3 (230), and spiral blade 4 (240) are linearly and gradually varied in the radial direction of pipe body 1. Spiral blade 1 210, spiral blade 220, spiral blade 3 230 and spiral blade 4 240 each have a first side 201 and a second side 202 arranged opposite to each other. The first side 201 is connected to the inner wall of the tube body 1. The thickness of the second side 202 is 0.5 times the thickness of the first side 201. The thickness of the first side 201 is 0.6 times the wall thickness of the tube body 1 and 0.1 times the inner diameter of the tube body 1.

[0136] Figure 21 The diagram shows a comparison of the flow field structure features of Embodiment 9 and Embodiment 1. It can be seen that the enhanced heat transfer tube provided in Embodiment 9 forms an ideal rigid vortex field with multiple secondary vortices of opposite directions inside. Figure 22 This is a comparison diagram of the axial distribution of the average cross-sectional temperature of the fluid in the enhanced heat transfer tube of Example 9 and Example 1. The temperature rise trend of the fluid in the enhanced heat transfer tube of Example 9 is consistent with that of Example 1, but the fluid temperature at the same cross-section is higher, confirming that this example has a better heat transfer intensity. The relevant fluid flow-heat transfer characteristic test results are summarized in Table 1.

[0137] Example 10

[0138] Combination Figure 23 The structure of the enhanced heat transfer tube used in this embodiment is basically the same as that in Embodiment 9. The difference is that in this embodiment: the radial dimensions of the inlet end three and the outlet end two are equal, which is 0.15 times the inner diameter of the tube body 1; and the radial dimensions of the inlet end four and the outlet end one are equal, which is 0.15 times the inner diameter of the tube body 1. Figure 24 As shown, compared to Example 9, the fluid near the tube wall at the outlet section of the enhanced heat transfer tube provided in Example 10 exhibits a greater tangential swirling shear velocity. The relevant fluid flow-heat transfer characteristic test results are summarized in Table 1.

[0139] Example 11

[0140] Combination Figure 25 The structure of the enhanced heat transfer tube used in Embodiment 11 is basically the same as that in Embodiment 9. The difference is that in this embodiment: the outflow end of the spiral blade 210 and the inflow end of the spiral blade 240 are not connected, and there is a 90° angle between them; the outflow end of the spiral blade 220 and the inflow end of the spiral blade 230 are not connected, and there is a 90° angle between them. Figure 26 As shown, compared to Example 9, the enhanced heat transfer tube provided in Example 11 enables the fluid to have a faster heat transfer rate within the axial space of 1.3m downstream of the variable diameter swirling flow generator 2. The relevant fluid flow-heat transfer characteristic test results are summarized in Table 1.

[0141] Example 12

[0142] Combination Figure 27In this embodiment, a tube 1 with an inner diameter of 51 mm and a length of 11 m is used as the research object. A first vortex generating mechanism 5 is added at a distance of 40 times the inner diameter of the tube 1 inlet; a second vortex generating mechanism 6 is added at a distance of 80 times the inner diameter of the tube 1 inlet; a third vortex generating mechanism 7 is added at a distance of 120 times the inner diameter of the tube 1 inlet; and a fourth vortex generating mechanism 8 is added at a distance of 160 times the inner diameter of the tube 1 inlet. The system tests the fluid flow-heat transfer characteristics in the enhanced heat transfer tube. The specific operating conditions are: the fluid medium is air, the fluid linear velocity is 75 m / s, the fluid inlet temperature is 873.15 K, the tube wall temperature is 1118 K, and the outlet absolute pressure is 1 atm.

[0143] In this embodiment, the first swirl generating mechanism 5, the second swirl generating mechanism 6, the third swirl generating mechanism 7, and the fourth swirl generating mechanism 8 are all variable-diameter swirl generating mechanisms 2 in Embodiment 1. The first swirl generating mechanism 5 and the second swirl generating mechanism 6 form a first interval 9, the second swirl generating mechanism 6 and the third swirl generating mechanism 7 form a second interval 10, and the third swirl generating mechanism 7 and the fourth swirl generating mechanism 8 form a third interval 11. The first interval 9 is twice the size of the second interval 10, and the second interval 10 is twice the size of the third interval 11.

[0144] like Figure 28 A comparison diagram of the axial distribution of fluid temperature at the axial center of Embodiment 12, a bare tube, and a heat transfer tube with a conventional hollow swirl generator is provided. It can be observed that the axial oscillation of the fluid temperature at the axial center in Embodiment 12 is weaker, indicating that the heat transfer process is orderly, stable, and precisely controlled. In actual industrial implementation, this can also effectively prevent physical oscillation behavior of the heat transfer tube. Combined with… Figure 29 The comparison diagram of the radial distribution of fluid temperature at the outlet section of the enhanced heat transfer tube shows that the radial temperature gradient of this embodiment 12 is smaller, and the heat transfer uniformity is improved. Figure 30The pressure drop distribution trends of each swirl generator in this embodiment 12 and the enhanced heat transfer tube with a conventional swirl generator were compared. It can be observed that the pressure drop of the first swirl generator in this embodiment (214 Pa) is significantly lower than that of the first swirl generator in the enhanced heat transfer tube with a conventional hollow swirl generator (285 Pa) by 24.9%, thus avoiding pressure drop concentration at the first swirl generator. At the same time, the maximum pressure drop difference between the first swirl generator and other swirl generators decreased from 145 Pa to 105 Pa, a reduction of 27%. Since the operating cycle of the heat transfer tube is determined by the performance degradation of any swirl generator, that is, the failure of any swirl generator (including furnace tube cracking or detachment) will lead to the failure of the heat transfer tube. Therefore, the enhanced heat transfer tube of this embodiment 12 can fully ensure the uniformity of the performance and reliability of each swirl generator, thereby extending the operating cycle.

[0145] The test results of the relevant fluid flow-heat transfer characteristics are summarized in Table 2.

[0146] Example 13

[0147] Combination Figure 27 The variable-diameter swirl generator configuration and heat transfer tube structure used in this embodiment 13 are basically the same as those in embodiment 12. The difference is that in this embodiment: the radial dimension of the outflow end 23 of the first swirl generator 5 is 0.25 times the inner diameter of the tube body 1; the radial dimension of the outflow end 23 of the second swirl generator 6 is 0.35 times the inner diameter of the tube body 1; the radial dimension of the outflow end 23 of the third swirl generator 7 is 0.4 times the inner diameter of the tube body 1; and the radial dimension of the outflow end 23 of the fourth swirl generator 8 is 0.45 times the inner diameter of the tube body 1.

[0148] Figure 31 By comparing the fluid swirling shear velocities under the action of the various swirling generating mechanisms arranged along the pipe body 1 in Embodiment 13 and Embodiment 12, it can be observed that Embodiment 13 can form a larger tangential scouring velocity at the wall of the pipe body 1 compared with Embodiment 12, and the velocity increases along the fluid flow direction in the pipe body 1. This adapts to the evolution trend of the coking reaction behavior gradually intensifying along the axial direction, which is conducive to the timely removal of coking particles and thus inhibits the growth of coke layer on the pipe wall.

[0149] The test results of the relevant fluid flow-heat transfer characteristics are summarized in Table 2.

[0150] Example 14

[0151] Combination Figure 27The structure of the heat transfer tube used in this embodiment 14 is basically the same as that in embodiment 12. The difference is that in this embodiment, the spiral rotation direction of the first swirl generating mechanism 5 and the third swirl generating mechanism 7 is clockwise, and the spiral rotation direction of the second swirl generating mechanism 6 and the fourth swirl generating mechanism 8 is counterclockwise.

[0152] The test results of the relevant fluid flow-heat transfer characteristics are summarized in Table 2.

[0153] Example 15

[0154] Combination Figure 27 The structure of the heat transfer tube used in Embodiment 15 is basically the same as that in Embodiment 12. The difference is that in this embodiment: the first interval 9, the second interval 10, and the third interval 11 are not equal, and the second interval 10 is 0.88 times the first interval 9, and the third interval 11 is 0.88 times the second interval 10; and a fifth vortex generating mechanism 12 is added, forming a fourth interval 13, which is 0.8 times the third interval 11. The relevant fluid flow-heat transfer characteristic test results are summarized in Table 2.

[0155] Table 1. Test results of fluid flow-heat transfer characteristics of a single variable-diameter swirl generator enhanced heat exchange tube in Examples 1-11

[0156]

[0157] It should be noted that in Table 1 above, the inner diameter of the tube is 51mm and the length is 3.6m; the conventional hollow vortex generator is built into the tube with an inner diameter of 51mm and a length of 3.6m, and its arrangement position is the same as that of the variable diameter vortex generator 2 in Example 1.

[0158] Table 2. Test results of fluid flow-heat transfer characteristics in the enhanced heat transfer tubes in Examples 12-15.

[0159]

[0160] It should be noted that in Table 2 above, the inner diameter of the light tube is 51mm and the length is 11m; the configuration of the conventional hollow vortex generator is the same as that of the conventional hollow vortex generator in Table 1, and it is built into a tube with an inner diameter of 51mm and a length of 11m. The arrangement position is the same as that of the first vortex generator 5, the second vortex generator 6, the third vortex generator 7 and the fourth vortex generator 8 in Example 12.

[0161] In the above results, the higher the heat exchange load, the better, and the lower the pressure drop, the better.

[0162] Based on the above experimental data, it can be seen that the enhanced heat transfer tube provided by the present invention can significantly improve the heat exchange effect and has the advantage of reducing equipment operating pressure.

[0163] Application Example 1

[0164] This application example 1 provides a cracking furnace equipped with the variable-diameter cyclone generator and heat transfer tubes described in Example 1. Its operational performance was compared and examined under actual industrial production conditions. Specifically, the cracking feedstock was light hydrocarbons, with a residence time of approximately 0.15 seconds. The furnace heating fuel gas (methane, hydrogen) flow rate maintained the furnace temperature at 1273 K. Operational data shows that, under the same feed and heating conditions, compared to cracking furnace tubes equipped with conventional hollow cyclone generators, the coking behavior on the furnace tube walls in this application example was suppressed (as shown in Table 3), the industrial operating cycle was extended to 100 days, and the ethylene yield increased to 33.82%.

[0165] Table 3: Performance Comparison of Application Example 1

[0166] Runtime, days ethylene yield light tube 60 - Conventional hollow vortex generator 90 33.35 Application Example 1 100 33.82

[0167] The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings and examples. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention. To avoid unnecessary repetition, the present invention will not describe the various possible combinations separately. However, these simple modifications and combinations should also be considered as the content disclosed in the present invention and all fall within the protection scope of the present invention.

Claims

1. A heat transfer tube with a variable diameter swirl generation mechanism, characterized in that, The enhanced heat transfer tube includes a hollow tubular tube body (1), and a variable diameter swirl generating mechanism (2) is provided on the inner wall of the tube body (1). The variable diameter swirl generating mechanism (2) includes at least one helical blade, and at least part of the radial dimension of each helical blade is gradually arranged in the axial direction of the tube body (1). The helical blade has a first helical twisted section (241) near its inflow end (24) and a second helical twisted section (231) near its outflow end (23). The helix angle of the first helical twisted section (241) is 0.1-5 times that of the helix angle of the second helical twisted section (231). The helix angle of the first helical twisted section (241) is not equal to that of the second helical twisted section (231). The variable diameter swirl generating mechanism (2) includes multiple helical blades, wherein the helical blades arranged in parallel along the circumference of the tube body (1) have the same helical twist direction; the helical blades arranged along the axial direction of the tube body (1) have opposite helical twist directions. The spiral blade is provided with jet holes (3), which are louver type or planar hole type. The size of the jet holes (3) is 0.02-0.2 times the inner diameter of the tube body (1), and the number is 1-12. In addition, 1-3 rows are provided in the radial direction of the tube body (1).

2. The enhanced heat transfer tube with a variable diameter swirl generation mechanism according to claim 1, characterized in that, The helix angle of the first helical twist segment (241) is greater than that of the second helical twist segment (231).

3. The enhanced heat transfer tube with a variable diameter swirl generation mechanism according to claim 1, characterized in that, The twist angle of the helical blade is 90°-1080°.

4. The enhanced heat transfer tube with a variable diameter swirl generation mechanism according to claim 3, characterized in that, The twist angle of the helical blade is 180°-360°.

5. The enhanced heat transfer tube with a variable diameter swirl generation mechanism according to claim 1, characterized in that, The height of the helical blade in the axial direction of the tube body (1) is 1-10 times the inner diameter of the tube body (1).

6. The enhanced heat transfer tube with a variable diameter swirl generation mechanism according to claim 1, characterized in that, The radial dimensions of the inflow end (24) and the outflow end (23) of the spiral blade are 0-0.5 times the inner diameter of the tube body (1), respectively.

7. The enhanced heat transfer tube with a variable diameter swirl generation mechanism according to claim 6, characterized in that, The radial dimensions of the inflow end (24) and the outflow end (23) of the spiral blade are 0-0.4 times the inner diameter of the tube body (1), respectively.

8. The enhanced heat transfer tube with a variable diameter swirl generation mechanism according to claim 1, characterized in that, The radial dimension of the incoming flow end (24) of the helical blade is smaller than the radial dimension of the outgoing flow end (23).

9. The enhanced heat transfer tube with a variable diameter swirl generation mechanism according to claim 1, characterized in that, The thickness of the spiral blades is set to be equal or gradually varied along the axial direction of the tube body (1).

10. The enhanced heat transfer tube with a variable diameter swirl generation mechanism according to claim 9, characterized in that, The thickness of the spiral blades gradually decreases along the flow direction of the fluid within the tube (1).

11. The enhanced heat transfer tube with a variable diameter swirl generation mechanism according to claim 1, characterized in that, The thickness of the outflow end (23) of the spiral blade is 0.2-2 times the wall thickness of the tube body (1), and the thickness of the outflow end (23) of the spiral blade is 0.1-0.2 times the inner diameter of the tube body (1).

12. The enhanced heat transfer tube with a variable diameter swirl generation mechanism according to claim 1, characterized in that, The thickness of the spiral blades is equal or gradually varied in the radial direction of the tube body (1); the spiral blades have a first side (201) and a second side (202) arranged opposite to each other, the first side (201) is connected to the inner wall of the tube body (1), the thickness of the first side (201) is 0.2-2 times the wall thickness of the tube body (1) and 0.1-0.2 times the inner diameter of the tube body (1), and the thickness of the second side (202) is 0-1 times the thickness of the first side (201).

13. The enhanced heat transfer tube with a variable diameter swirl generation mechanism according to claim 1, characterized in that, In the axial direction of the tube body (1), the first spiral twisted section (241) is a variable diameter twisted section, and the second spiral twisted section (231) is a constant diameter twisted section.

14. The enhanced heat transfer tube with a variable diameter swirl generation mechanism according to claim 1, characterized in that, Multiple variable diameter swirl generating mechanisms (2) are provided, and the multiple variable diameter swirl generating mechanisms (2) are spaced apart along the axial direction of the tube body (1).

15. The enhanced heat transfer tube with a variable diameter swirl generation mechanism according to claim 14, characterized in that, The distance between two adjacent variable diameter swirl generators (2) is 10-100 times the inner diameter of the tube (1).

16. The enhanced heat transfer tube with a variable diameter swirl generation mechanism according to claim 14, characterized in that, The spiral twisting directions of the spiral blades of two adjacent variable diameter swirling generators (2) are opposite.

17. A pyrolysis furnace, characterized in that, The pyrolysis furnace includes a radiation chamber, in which at least one radiation furnace tube assembly is installed. The radiation furnace tube assembly includes a plurality of radiation furnace tubes arranged in sequence and a heat transfer tube communicating with adjacent radiation furnace tubes. The heat transfer tube is an enhanced heat transfer tube as described in any one of claims 1-16.

Images