Variable-pitch turbulator for industrial boiler smoke tubes

Abstract

This utility model pertains to thermal power engineering, specifically to devices for enhancing heat exchange in the fire tubes and flame tubes of steam and hot water boilers. It can be used to improve the efficiency of heat transfer from combustion products to the coolant. The utility model is intended for installation inside the fire tubes of industrial boilers to increase the heat transfer coefficient and can be used in both new production and the modernization of existing boiler equipment. The technical result consists of increasing the thermal efficiency of the fire tube by enhancing heat exchange (increasing the heat transfer coefficient) while simultaneously reducing hydraulic resistance. 2 ill.

Description

[0001] The utility model relates to the field of thermal power engineering, namely to devices for intensifying heat exchange in smoke tubes and fire tubes of steam and hot water boilers, and can be used to increase the efficiency of heat transfer from combustion products to the coolant.

[0002] The utility model is intended for installation inside the smoke tubes of industrial boilers in order to increase the heat transfer coefficient and can be used both in new production and in the modernization of existing boiler equipment.

[0003] Smoothbore fire tubes are used in conventional steam and hot water boiler designs to increase the heating surface. However, these tubes have a significant drawback: low heat transfer intensity due to the presence of a laminar boundary layer near the inner wall of the tube, which prevents efficient heat transfer from the hot gases to the wall.

[0004] There is a wide range of technical solutions for intensifying heat exchange in pipes, each of which has significant drawbacks when applied to the operating conditions of boiler installations.

[0005] A heat exchanger tube turbulization device, described in Author's Certificate SU 1476300 A2 (published April 30, 1989), comprises a wire spring spiral with a variable pitch, secured at one end to the tube sheet and equipped at the other with a weight in the form of a ring with inclined holes. The device is designed to disrupt the boundary layer by vibration of the spiral caused by the gas flow. A disadvantage of this design is low operational reliability due to the presence of moving elements (weight, ring), which are subject to wear and seizure under high-temperature, dusty flow conditions. Furthermore, the device's efficiency is unstable over time, and the vibration created does not allow for precise control of hydraulic resistance along the length of the tube.

[0006] A turbulator is known from the author's certificate SU 1753959 A3 (published August 7, 1992), installed in the exhaust duct with complete closure. The device has a tapered inlet section with a swirler in the form of a conical visor with radial slots and bends, as well as a diffuser outlet section.

[0007] The disadvantage of this solution is its narrow specialization—it is designed for installation at the combustion chamber outlet, not within multiple smoke tubes. This design creates significant localized hydraulic resistance and does not ensure uniform heat transfer along the entire length of the tube.

[0008] A heat exchange unit is known according to patent RU 2179689 C2 (published 02 / 20 / 2002), which includes a hot water boiler with smoke tubes, which are equipped with turbulators.

[0009] A drawback is that the description of the installation does not reveal the design features of the turbulators themselves. The mention of them is general, preventing any conclusions about the technical solutions aimed at improving heat transfer efficiency. Presumably, it uses known types of turbulators with their inherent drawbacks.

[0010] A smoke tube for a heat exchanger is known according to patent RU 2197683 C2 (published 01 / 27 / 2003), containing a turbulator located inside along the entire length in the form of a wire spiral, as well as multi-start grooves on the inner surface of the tube with a profile made in the form of a radial conjugation of two straight beams with an angle of no more than 90°.

[0011] The disadvantage of this design is its high technological complexity and, consequently, high manufacturing costs. Precise machining of the pipe's inner surface is required to create profiled grooves and synchronize them with the installed spiral. Furthermore, the spiral has a constant pitch, which prevents optimization of the heat exchange process along the pipe's length, taking into account changes in temperature and gas flow velocity.

[0012] A cast iron gas hot water heating boiler is known according to patent RU 224410 U1 (published 03 / 21 / 2024), in which turbulators are located in the space between the needle-shaped projections of the cast iron heat exchanger, made in the form of horizontal twisted plates held by vertical bars.

[0013] The disadvantage is that this turbulator design is designed for the specific geometry of a cast iron sectional heat exchanger and is not intended for installation inside round fire tubes, which are standard components of most industrial boilers. Using this design in fire tubes is impossible without significant modifications.

[0014] A turbulence device is known from the author's certificate SU 1302132 A1 (published April 7, 1987). It contains a spring-loaded wire spiral, rigidly fixed at one end to the tube sheet and equipped with a ring-shaped weight at the other end.

[0015] The disadvantages are similar to those described for SU 1476300: the presence of moving elements, low reliability, instability of the effect over time.

[0016] A turbulent device for a heat exchange pipe is known, according to patent RU 2714469 C2 (published February 17, 2020), comprising a connecting unit and a spiral tape rotatably connected to it. The connecting unit includes a housing with a plug, an internal bearing with a shaft extending from the housing, and external shaped elements for securing the housing in the pipe. The spiral tape is designed as a helical conoid, the twist pitch of which is determined by a calculation formula taking into account the flow rate and the internal diameter of the pipe.

[0017] A disadvantage of this design is the presence of moving components (bearings, rotating spiral belt), which significantly reduces operational reliability when operating in high-temperature, dusty combustion product flows typical of industrial boiler fire tubes. The bearing assembly requires precision manufacturing and protection from contamination, which complicates the design and increases the cost of both manufacturing and maintenance. The device is not static—its operation is based on the rotation of the spiral, which does not ensure stable turbulence under variable boiler operating conditions and can lead to heat transfer instability. The spiral pitch is determined by a formula that does not account for changes in temperature and gas velocity along the length of the tube, reducing heat transfer efficiency in certain sections.The device is attached to only one end of the pipe (via a coupling), which does not guarantee reliable alignment and fixation along the entire length, especially under vibration and thermal deformation. Furthermore, the screw conoid lacks a central rod, reducing the rigidity of the structure and potentially causing it to deform under the flow.

[0018] The closest analogue (prototype) for the utility model is a turbulent device according to the author's certificate SU 1476300 A2, as containing a spiral with a variable pitch and intended for installation inside a heat exchange pipe.

[0019] However, the prototype has the following disadvantages:

[0020] 1. The presence of moving elements (ring-shaped load), which reduces reliability in high-temperature and dusty conditions.

[0021] 2. The operating principle is based on the vibration of the spiral, which does not provide a stable and uniform effect on the boundary layer along the length of the pipe.

[0022] 3. Changing the spiral pitch is aimed at creating resonance, rather than optimizing hydraulic resistance and heat transfer.

[0023] 4. The design is difficult to manufacture and configure.

[0024] Thus, there is an objective need to create a turbulator for smoke tubes that is free from the above mentioned disadvantages, has a simple and reliable design, and ensures uniform intensification of heat exchange along the length of the tube with reduced hydraulic resistance.

[0025] The technical problem that the utility model is aimed at solving is the creation of a static turbulator with a variable spiral pitch, ensuring optimal turbulence of the flow of combustion products in each section of the pipe, taking into account changes in their temperature and speed, while simultaneously reducing hydraulic resistance compared to the prototype.

[0026] The technical result consists in increasing the thermal efficiency of the smoke tube by intensifying heat exchange (increasing the heat transfer coefficient) while simultaneously reducing hydraulic resistance.

[0027] Design characteristics of the claimed turbulator:

[0028] - the presence of a central rod made of a metal rod with a diameter of 4-8 mm;

[0029] - spiral winding made of a metal rod with a diameter of 4-8 mm, fixed on a central rod;

[0030] - the winding pitch decreases from the inlet end (hot gas inlet side) to the outlet;

[0031] - in the input zone, the step is from 2 to 3 internal pipe diameters (D);

[0032] - in the main zone, the step is from 1 to 2 D;

[0033] - in the output zone, the step is from 0.5 to 1 D;

[0034] - the turbulator has no moving elements (it is static), it is attached to the pipe by means of centering elements (for example, spring rings) at the ends of the rod.

[0035] Operating parameters (for pipe with inner diameter 50mm):

[0036] - the length of the turbulator corresponds to the length of the pipe;

[0037] - maximum spiral pitch (at the input) - 100-150 mm;

[0038] - minimum step (at output) - 25-50 mm;

[0039] - the ratio of the maximum step to the minimum - from 3:1 to 6:1;

[0040] - winding profile height - from 0.5 to 0.8 of the inner radius of the pipe.

[0041] The essence of the utility model is explained by drawings.

[0042] Fig. 1 shows the general view of a turbulator with a variable spiral pitch, installed in a smoke tube (longitudinal section), where: 1 - smoke tube; 2 - turbulator; 3 - central rod; 4 - spiral winding; 5 - inlet zone (large pitch); 6 - main zone (medium pitch); 7 - outlet zone (fine pitch); 9 - direction of combustion product flow.

[0043] Fig. 2 shows a longitudinal section of the turbulator indicating the change in the spiral pitch, where: 3 - central rod; 4 - spiral winding; 5 - input zone with pitch (large pitch); 6 - main zone (medium pitch); 7 - output zone (fine pitch); 9 - flow direction.

[0044] The essence of the utility model is as follows.

[0045] The turbulator (2) is designed as a spiral winding (4) secured to a central rod (3). The central rod (3) is made of a metal rod (e.g., stainless steel) and serves to rigidify the structure and ensure the alignment of the spiral within the pipe. The spiral winding (4) is made of a metal rod with a diameter of 4-8 mm (wire can also be used) and is wound onto the rod with a variable pitch, which smoothly decreases from the inlet zone (5) to the outlet zone (7). In the preferred embodiment, the pitch of the spiral varies linearly.

[0046] In the inlet zone (5), where combustion products have the highest temperature (250-300°C) and high initial turbulence, the S1 spiral pitch is selected in the range of 2-3 pipe internal diameters (D). This allows for moderate additional turbulence without causing excessive hydraulic resistance.

[0047] In the main zone (6), where the temperature and flow velocity decrease (150-200°C), the S2 pitch is reduced to 1-2 internal diameters, enhancing turbulence and maintaining a high heat transfer coefficient.

[0048] In the outlet zone (7), where the gases are maximally cooled (100-150°C) and the velocity is minimal, the pitch S3 is 0.5-1 of the internal diameter, creating the most intense vortex formation necessary for efficient heat exchange in the final section of the pipe.

[0049] When the boiler is operating, combustion products enter the smoke tube (1) and wash the turbulator (2). Thanks to the variable pitch of the spiral:

[0050] - moderate turbulence is created at the inlet section without creating excessive hydraulic resistance;

[0051] - in the middle part, turbulence increases, compensating for the decrease in flow speed;

[0052] - maximum turbulence is achieved at the outlet section, ensuring efficient heat exchange at low gas temperatures.

[0053] The choice of the central rod diameter in the range of 4-8 mm is determined by the calculation of the relative overlap of the pipe section and bending rigidity:

[0054]

[0055] which does not lead to a significant increase in hydraulic resistance.

[0056] Moment of inertia of the rod cross-section at d ст ≥4 mm provides a deflection of less than 0.5% of the pipe length at maximum flow rates.

[0057] The declared ranges of the spiral pitch S=(0.5÷3)D are consistent with the formula for determining the pitch for turbulent devices (see patent RU 2714469 C2):

[0058]

[0059] where k=0.05÷0.2 is the coefficient determining the pitch variation limits. At flow velocity ν=10÷30 m / s and D=0.05 m, the calculated pitch value is in the range of 0.025-0.15 m (0.5-3 D).

[0060] The smooth pitch control ensures continuous adaptation of the turbulator to changing hydrodynamic conditions along the length of the pipe. The absence of moving parts guarantees high reliability and durability.

[0061] Implementation of a utility model.

[0062] In practice, the claimed turbulator is manufactured as follows. The central rod (3) is cut from a hollow rod of the required length. One end of a metal rod with a diameter of 4-8 mm is secured to the rod, after which it is wound with a variable pitch. In the preferred embodiment, the spiral pitch changes linearly from the inlet to the outlet. To ensure pitch accuracy, tooling with a programmable winding pitch is used. The finished turbulator is equipped with centering elements (e.g., spring rings or radial projections) at the ends of the rod.

[0063] The turbulator is installed in the smoke tube (1) by inserting it into the tube until the centering elements stop. Axial fixation is ensured by friction or additional locking elements.

[0064] During boiler operation, combustion products move along the pipe (1) in direction (9). Passing through the spiral coil (4) with a variable pitch, the flow repeatedly changes direction and swirl intensity. At the inlet section, with a coarse pitch, moderate turbulence is created without significant resistance. In the middle section, with a decreasing pitch, the intensity of vortex formation increases, compensating for the decrease in flow velocity. At the outlet section, with a minimal pitch, maximum turbulence is achieved, ensuring efficient heat exchange at low gas temperatures.

[0065] Tests of a prototype turbulator with variable pitch (S1=120 mm, S2=75 mm, S3=40 mm for a pipe with an internal diameter of 50 mm) as part of an industrial boiler showed:

[0066] - increase in heat transfer coefficient by 5.2% compared to constant pitch turbulator;

[0067] - 12% reduction in hydraulic resistance compared to a constant pitch turbulator;

[0068] - equalization of the pipe wall temperature along the length (the temperature difference decreased from 80°C to 45°C);

[0069] - reduction in the intensity of soot deposits by 25% due to the absence of stagnant zones.

[0070] Thus, the stated technical result is achieved.

[0071] The utility model is new because, at the priority date, no turbulence device for industrial boiler smoke tubes was known, made in the form of a spiral with a variable pitch decreasing from the input zone (2-3 internal diameters of the tube) to the output zone (0.5-1 internal diameter of the tube), with rigid fastening on a central rod and the absence of moving elements, intended for static installation inside the tube.

[0072] The utility model is industrially applicable, as it can be manufactured using standard materials (stainless or carbon steel) and known coil winding technologies, and its design and operating principle allow achieving the stated technical result when installed in both new and existing boilers.

Claims

1. A turbulator for industrial boiler smoke tubes with a variable spiral pitch, characterized in that it is made static and contains a central rod made of a metal rod with a diameter of 4-8 mm, as well as a spiral winding made of a metal rod with a diameter of 4-8 mm, fixed on the central rod, wherein the winding pitch decreases from the inlet end of the turbulator facing towards the flow of combustion products, to the outlet end, wherein the winding has an inlet zone with a spiral pitch from 2 to 3 internal diameters of the pipe, a main zone with a spiral pitch from 1 to 2 internal diameters of the pipe, an outlet zone with a spiral pitch from 0.5 to 1 internal diameter of the pipe, centering elements fixed on the ends of the central rod and made with the possibility of axial fixation of the turbulator inside the pipe.

2. A turbulator according to paragraph 1, characterized in that the spiral winding is made with a smooth change in pitch along the entire length of the turbulator according to a linear law.

3. A turbulator according to paragraph 1, characterized in that the central rod is made hollow.

4. A turbulator according to paragraph 1, characterized in that the ratio of the maximum pitch of the spiral to the minimum is from 3:1 to 6:

1.

5. A turbulator according to paragraph 1, characterized in that the height of the winding profile is from 0.5 to 0.8 of the internal radius of the pipe.

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