Natural vibration pulse type pit heat exchange tube

Abstract

The invention relates to the technical field of efficient heat exchange equipment, in particular to a self-oscillation pulse type pit heat exchange tube, fluid firstly passes through a self-oscillation cavity and is accelerated at a contraction section to form high-speed jet flow, the high-speed jet flow enters an oscillation chamber and impacts a collision wall to generate self-oscillation, periodic pulsating flow is formed, the fluid is guided to form large vortexes, and the high-speed jet flow is formed. The water flows out of the expansion section and enters the pit pipe; when pulsating flow flows through the oval pits, fluid separation is triggered in the deep pit areas, small-scale vortexes are generated, the fluid separation and the small-scale vortexes are coupled to form a multi-scale vortex system, a boundary layer is thinned, turbulence energy is enhanced, and composite enhanced heat transfer of pulsating flow disturbance and pit vortex enhancement is achieved. Therefore, the effects of multi-scale vortex synergistic enhanced heat exchange, anti-fouling performance and passive enhancement are achieved.

Description

Technical Field

[0001] This invention relates to the field of high-efficiency heat exchange equipment technology, and in particular to a self-oscillating pulse-type recessed heat exchange tube. Background Technology

[0002] In industrial production, heat exchangers are core equipment for energy exchange, commonly used in industrial processes such as cooling, heating, concentration, evaporation, and separation. Their efficiency directly affects energy utilization. Shell-and-tube heat exchangers, in particular, are highly adaptable to various environments, offer high safety and stability, and can utilize a wide range of raw materials, making them common in energy-intensive and inefficient industrial sectors. Heat exchange tubes are the core heat exchange components of shell-and-tube heat exchangers. Traditional bare tube heat exchangers suffer from low heat exchange efficiency and high flow resistance. Currently, improving the heat exchange performance of shell-and-tube heat exchangers mainly relies on enhanced heat transfer technologies. Existing technologies such as corrugated tubes and threaded tubes improve heat transfer performance by altering the tube surface structure, but still face challenges such as high pressure loss and insufficient fouling resistance. Therefore, developing high-efficiency, low-resistance heat exchange tubes is a key measure to effectively enhance the heat exchange performance of shell-and-tube heat exchangers.

[0003] Enhanced heat transfer technology is mainly divided into passive and active enhanced heat transfer technologies. Passive enhanced heat transfer technology refers to altering the shape of the heat exchange tubes without applying external force, thereby changing the heat exchange surface and flow channel shape, causing significant disturbance in the boundary layer fluid and achieving enhanced heat transfer. Examples include corrugated tubes, threaded tubes, internally inserted tubes, spiral grooved tubes, transverse grooved tubes, and finned tubes. Active enhanced heat transfer technology is more complex. It uses external energy to transform fluid flow into vortex flow, increasing the flow velocity and improving the heat transfer coefficient. Simultaneously, vortex flow can reduce fouling thickness, thus improving the heat transfer coefficient. To achieve better enhanced heat transfer effects, two or more enhanced heat transfer technologies are combined; this is called composite enhanced heat transfer technology. With the continuous advancement of enhanced heat transfer technology, numerous methods have emerged. Combining mature, simple, and low-energy-consumption enhanced heat transfer technologies, utilizing synergistic effects to overcome the performance bottlenecks of single technologies, and achieving higher overall heat transfer efficiency has made composite enhanced heat transfer technology a core technology in the field of enhanced heat transfer technology.

[0004] In recent years, there has been much research and development on enhanced heat transfer technology. On the one hand, passive enhanced heat transfer technology has been used. Patent No. CN201720538979.7 discloses a spiral deep pit tube, patent No. CN201720109234.9 discloses an ellipsoidal pit heat transfer tube, and patent No. CN201810424654.5 discloses a droplet-shaped pit heat transfer tube. These pit heat transfer tubes have simple structures and can improve heat transfer efficiency to a certain extent, but the efficiency improvement is limited. They are not combined with dynamic pulsating flow and cannot give full play to the coupling enhancement effect of multi-scale eddies. On the other hand, active heat transfer enhancement technology has been utilized. Patent No. CN201910851413.3 discloses a heat exchange device and heat exchange device group based on vibration-enhanced heat transfer. However, it requires external energy to ensure the continuity of fluid vortex, which cannot fundamentally solve the energy problem. Patent No. CN202210743331.9 discloses a small-scale resonant flue gas / water heat exchange device, and Patent No. CN202322703632.1 discloses a pulsed flow enhanced heat transfer heat exchanger. These devices utilize a chamber structure that does not require external pulsed excitation to form a pulsed flow to improve the heat transfer effect of the fluid. However, when used alone, the vortex distribution is uneven, and the synergistic effect with the pit structure has not been fully developed. There are still research gaps in the heat transfer mechanism, structural parameter optimization, and engineering application of the composite structure of self-excited oscillation cavity and pit tube. Summary of the Invention

[0005] The purpose of this invention is to provide a self-oscillating pulsed concave heat exchange tube, which utilizes composite enhanced heat transfer technology and the synergistic effect of self-excited oscillation cavity and elliptical concave to achieve multi-scale vortex enhanced heat transfer, reduce pressure loss, and improve overall heat transfer performance.

[0006] To achieve the above objectives, the present invention provides a self-excited pulsed pit heat exchange tube, comprising a self-excited oscillation chamber and a pit tube, wherein the self-excited oscillation chamber is connected to the pit tube, and the outer surface of the pit tube has a plurality of elliptical pits. The self-excited oscillation chamber comprises a contraction section, an oscillation chamber, and an expansion section connected sequentially along the fluid flow direction. The oscillation chamber is provided with a collision wall, and the outlet of the expansion section is connected to the pit tube.

[0007] The recessed tube is a circular tube with a wall thickness of 1 mm. The outer diameter D of the recessed tube is determined according to the Reynolds number calculation formula.

[0008] In the formula, Re is the Reynolds number, ranging from 10,000 to 45,000; μ is the kinematic viscosity of the fluid inside the heat exchange tube; ρ is the density of the fluid inside the tube; and v is the flow velocity of the fluid inside the tube.

[0009] The grooved tube has three elliptical grooves distributed circumferentially on the same cross section. The included angle between adjacent elliptical grooves on the same cross section is 120°. The included angle between adjacent elliptical grooves on adjacent cross sections is 60°, and they are evenly distributed along the axial direction.

[0010] The ratio of the major axis to the minor axis of the elliptical recess is 1 to 2, the ratio of the protrusion height of the elliptical recess to the outer diameter D of the recess tube is 0.15 to 0.25, and the ratio of the rising distance between the two recesses to the outer diameter D of the recess tube is 1 to 1.75.

[0011] The inlet diameter of the contraction section is the same as the outer diameter of the concave tube, the ratio of the inlet diameter of the expansion section to the outlet diameter of the contraction section is 1.1 to 1.6, the ratio of the diameter of the oscillation chamber to the outlet diameter of the contraction section is 4 to 9, and the aspect ratio of the oscillation cavity is 0.1 to 0.7.

[0012] The inlet length of the contraction section is 10mm, the outlet length of the contraction section is 20mm, and the taper between the inlet and outlet of the contraction section is 30°.

[0013] The included angle of the collision walls is 120°.

[0014] This invention discloses a self-oscillating pulsed concave heat exchange tube. Fluid first passes through the self-excited oscillation chamber, where it accelerates in the contraction section to form a high-speed jet. Upon entering the oscillation chamber, it impacts the collision wall, generating self-excited oscillation and forming a periodic pulsating flow. This guides the fluid to form large vortices, which flow out from the expansion section and into the concave tube. As the pulsating flow passes through the elliptical concave, fluid separation occurs in the deep concave region, generating small-scale vortices. These vortices couple to form a multi-scale vortex system, thinning the boundary layer and enhancing turbulent kinetic energy, achieving a composite enhanced heat transfer effect of "pulsating flow disturbance and concave vortex reinforcement." Thus, multi-scale vortex synergistic heat transfer is achieved: the pulsating flow generated by self-excited oscillation couples with the vortex induced by the elliptical concave, forming a synergistic effect of large and small-scale vortices, improving heat transfer efficiency by approximately 5% compared to a single concave tube. Anti-fouling performance: the periodic pulsating flow and the scaling effect of the concave enhance the scouring of the tube wall by the fluid, inhibiting scaling and extending the heat exchanger cleaning cycle. Passive heat transfer: No external energy input is required; efficient heat transfer is achieved solely through structural design, meeting the requirements for energy conservation and emission reduction. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0016] Figure 1 This is a schematic diagram of the overall structure of the self-oscillating pulse-type concave heat exchange tube of the present invention.

[0017] Figure 2 This is a cross-sectional schematic diagram of the self-excited oscillation cavity of the present invention.

[0018] Figure 3 This is a front view of the self-oscillating pulse-type pitted heat exchanger tube of the present invention.

[0019] Figure 4 This is a schematic diagram of the structure of the recessed tube of the present invention.

[0020] Figure 5 This is a left view of the self-oscillating pulse-type pitted heat exchanger tube of the present invention.

[0021] Figure 6 This is the invention Figure 4 Sectional view at point AA.

[0022] Figure 7 This is the invention Figure 4 Sectional view at BB.

[0023] Figure 8 This is a cross-sectional view of the self-oscillating pulse-type pitted heat exchanger tube of the present invention.

[0024] In the diagram: 101-Self-excited oscillation cavity, 102-Dimpled tube, 103-Contraction section, 104-Oscillation chamber, 105-Expansion section, 106-Collision wall. Detailed Implementation

[0025] The embodiments of the present invention are described in detail below. Examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, but should not be construed as limiting the present invention.

[0026] Please see Figures 1 to 8 The present invention provides a self-oscillating pulsed pit heat exchange tube, including a self-excited oscillation chamber 101 and a pit tube 102. The pit tube 102 has a plurality of elliptical pits. The self-excited oscillation chamber 101 includes a contraction section 103, an oscillation chamber 104 and an expansion section 105.

[0027] In this specific embodiment, the self-excited oscillation chamber 101 is connected to the pitted tube 102. The outer surface of the pitted tube 102 has a plurality of elliptical pits. The self-excited oscillation chamber 101 includes a contraction section 103, an oscillation chamber 104, and an expansion section 105 connected in sequence along the fluid flow direction. The oscillation chamber 104 is provided with a collision wall 106. The outlet of the expansion section 105 is connected to the pitted tube 102.

[0028] The self-oscillating pulsed concave heat exchange tube is composed of the self-excited oscillation chamber 101 and the concave tube 102. The self-excited oscillation chamber 101 includes the contraction section 103, the oscillation chamber 104, the collision wall 106 and the expansion section 105. The whole material is Q235A steel.

[0029] The recessed tube 102 is a circular tube with a wall thickness of 1 mm. The outer diameter D of the recessed tube 102 is determined according to the Reynolds number calculation formula.

[0030] In the formula, Re is the Reynolds number, ranging from 10,000 to 45,000; μ is the kinematic viscosity of the fluid inside the heat exchange tube; ρ is the density of the fluid inside the tube; and v is the flow velocity of the fluid inside the tube.

[0031] Secondly, three elliptical recesses are circumferentially distributed on the same cross section of the recessed tube 102. The included angle between adjacent elliptical recesses on the same cross section is 120°, and the staggered included angle between adjacent elliptical recesses on adjacent cross sections is 60°, and they are evenly distributed along the axial direction. The ratio of the major axis to the minor axis of the elliptical recess is 1~2, the ratio of the protrusion height of the elliptical recess to the outer diameter D of the recessed tube 102 is 0.15~0.25, and the ratio of the rising distance between two recesses to the outer diameter D of the recessed tube 102 is 1~1.75.

[0032] The outer diameter D of the recessed tube 102 is 20 mm, and the wall thickness is 1 mm. The major axis a of the elliptical recess is 16 mm, the minor axis b is 10 mm, the protrusion height d is 5 mm, the rising distance P between two recesses is 25 mm, three elliptical recesses are evenly distributed in the same cross section, the included angle β between adjacent elliptical deep recesses in the same cross section is 120°, the staggered included angle θ between adjacent circumferential elliptical deep recesses in adjacent cross sections is 60°, and they are evenly distributed along the axial direction.

[0033] Meanwhile, the inlet diameter of the contraction section 103 is the same as the outer diameter of the recessed tube 102; the ratio of the inlet diameter of the expansion section 105 to the outlet diameter of the contraction section 103 is 1.1~1.6; the ratio of the diameter of the oscillation chamber 104 to the outlet diameter of the contraction section 103 is 4~9; and the length-to-diameter ratio of the oscillation cavity is 0.1~0.7. The inlet length of the contraction section 103 is 10mm, the outlet length of the contraction section 103 is 20mm, and the taper between the inlet and outlet of the contraction section 103 is 30°.

[0034] In addition, the included angle of the collision wall 106 is 120°.

[0035] The inlet diameter d0 of the contraction section 103 of the self-excited oscillation chamber 101 is 20 mm, the outlet diameter d1 of the contraction section 103 (i.e., the inlet diameter of the oscillation chamber 104) is 15 mm, the taper ω between the inlet and outlet of the contraction section 103 is 30°, the diameter D of the oscillation chamber 104 is 90 mm, the length L of the oscillation chamber 104 is 22.5 mm, the included angle α of the collision wall 106 is 120°, the inlet diameter d2 of the expansion section 105 (i.e., the outlet diameter of the oscillation chamber 104) is 20 mm, and the outlet of the expansion section 105 is connected to the concave tube 102.

[0036] In terms of processing technology, the surface of the tube is plastically processed by rolling or extrusion dies to form an array of elliptical pits, ensuring the dimensional accuracy of the pits and the smoothness of the surface. In addition, a welding process is used to embed the prefabricated chamber structure into the tube inlet section, ensuring a smooth flow transition and reducing flow dead zones.

[0037] Using a self-oscillating pulsed concave heat exchange tube in this embodiment, the fluid first passes through the self-excited oscillation chamber 101, which can form a pulsating flow without an external vibration source, thereby increasing the Reynolds number of the fluid, forming turbulence, and generating vortices to disturb the internal fluid. Then, it passes through the concave tube 102. Based on the theory of vortex interaction, multi-scale vortices are formed under the disturbance of the concave element, and the boundary layer is thinned. According to the knowledge of convective heat transfer, when the boundary layer is thinned, the thermal resistance will decrease, accelerating the heat exchange process between the hot and cold fluids, and the heat transfer coefficient will increase, thereby achieving the purpose of composite enhanced heat transfer.

[0038] The above-mentioned fluid heat exchange and flow process was simulated numerically. The fluid inside the heat exchange tube was set to water, the inlet velocity was 1.5 m / s, the inlet fluid temperature was 288 K (15 °C), and the heat exchange tube wall temperature was 368 K (95 °C). The Nusselt coefficient Nu and the resistance coefficient f of the heat exchange tube of the present invention were compared with those of the smooth tube, the single-dimpled tube 102 (without the self-excited oscillation cavity 101), and the heat exchange tube of the present invention. Finally, the heat exchange efficiency under each working condition was judged by the comprehensive evaluation coefficient PEC, as shown in the following formula:

[0039] In the formula, Nu is the average Nusselt coefficient of the heat exchanger tube wall. Let f be the average Nusselt coefficient of the heat exchanger wall surface of the tube, and let f be the average resistance coefficient of the heat exchanger wall surface of the tube. This represents the average resistance coefficient of the heat exchanger wall surface of the tube.

[0040] The simulation results show that the self-oscillating pulsed concave heat exchange tube formed by combining the self-excited oscillation cavity 101 and the concave tube 102 can effectively improve the heat exchange efficiency, which is about 25% higher than that of the bare tube and about 5% higher than that of the concave tube 102 alone. It is an effective study to realize composite enhanced heat exchange technology.

[0041] In terms of anti-fouling performance, the pulsating flow and the expansion and contraction of the pipe enhance the scouring effect on the pipe wall, making it difficult for scale to form on the inner wall. This avoids the situation where scale reduces heat exchange efficiency as the service time increases, thus exhibiting anti-fouling performance.

[0042] This invention is applicable to condensers in petrochemicals, steam heat exchangers in power plants, evaporators in air conditioning systems, etc., and is especially suitable for high-viscosity fluids and conditions prone to scaling. It can significantly reduce equipment size and metal consumption, and lower operating costs.

[0043] In summary, this invention, through the innovative combination of the self-excited oscillation cavity 101 and the elliptical recess, breaks through the performance bottleneck of traditional enhanced heat transfer tubes, providing a new technical solution for the research of composite enhanced heat transfer technology and the design of high-efficiency heat exchangers.

[0044] The above-disclosed embodiments are merely one or more preferred embodiments of this application and should not be construed as limiting the scope of this application. Those skilled in the art can understand that all or part of the processes for implementing the above embodiments and equivalent changes made in accordance with the claims of this application still fall within the scope of this application.

Claims

1. A self-oscillating pulse-type recessed heat exchange tube, characterized in that, It includes a self-excited oscillation chamber and a pitted tube. The self-excited oscillation chamber is connected to the pitted tube. The outer surface of the pitted tube has multiple elliptical pits. The self-excited oscillation chamber includes a contraction section, an oscillation chamber, and an expansion section connected in sequence along the fluid flow direction. The oscillation chamber is provided with a collision wall. The outlet of the expansion section is connected to the pitted tube.

2. The self-oscillating pulse-type recessed heat exchange tube as described in claim 1, characterized in that, The recessed tube is a circular smooth tube with a wall thickness of 1 mm. The outer diameter D of the recessed tube is determined according to the Reynolds number calculation formula. In the formula, Re is the Reynolds number, ranging from 10,000 to 45,000; μ is the kinematic viscosity of the fluid inside the heat exchange tube; ρ is the density of the fluid inside the tube; and v is the flow velocity of the fluid inside the tube.

3. The self-oscillating pulse-type recessed heat exchange tube as described in claim 1, characterized in that, The concave tube has three elliptical concaves distributed circumferentially on the same cross section. The included angle between adjacent elliptical concaves on the same cross section is 120°. The included angle between adjacent elliptical concaves on adjacent cross sections is 60°, and they are evenly distributed along the axial direction.

4. The self-oscillating pulse-type recessed heat exchanger tube as described in claim 3, characterized in that, The ratio of the major axis to the minor axis of the elliptical recess is 1 to 2, the ratio of the protrusion height of the elliptical recess to the outer diameter D of the recess tube is 0.15 to 0.25, and the ratio of the rising distance between the two recesses to the outer diameter D of the recess tube is 1 to 1.

75.

5. The self-oscillating pulse-type recessed heat exchanger tube as described in claim 1, characterized in that, The inlet diameter of the contraction section is the same as the outer diameter of the concave tube, the ratio of the inlet diameter of the expansion section to the outlet diameter of the contraction section is 1.1 to 1.6, the ratio of the diameter of the oscillation chamber to the outlet diameter of the contraction section is 4 to 9, and the length-to-diameter ratio of the oscillation cavity is 0.1 to 0.

7.

6. The self-oscillating pulse-type recessed heat exchanger tube as described in claim 5, characterized in that, The inlet length of the contraction section is 10mm, the outlet length of the contraction section is 20mm, and the taper between the inlet and outlet of the contraction section is 30°.

7. The self-oscillating pulse-type recessed heat exchanger tube as described in claim 1, characterized in that, The included angle of the collision wall is 120°.

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