CN104482792A - Axial symmetry type cross inner-fin heat transfer enhanced tube - Google Patents

Abstract

An axisymmetric cross-finned enhanced heat exchange tube, including a plurality of unit tubes arranged at intervals and rotating unit tubes, the rotating unit tubes are formed by rotating the unit tubes at a preset angle, and the unit tubes are rotated along the axis There are many pairs of upper and lower opposite fins and wide fins penetrating the cross-section of the heat exchange tube integrally connected with the side wall of the unit tube, the wide fins are located on the left and right sides of the unit tube, and the plurality of pairs The fins are located between the wide fins on the left and right sides, and each pair of up and down relative fins is axisymmetric, and the distance between the tops of each pair of fin plates is a preset distance L3; the wide fins and the fins ( Extending in the axial direction but not completely penetrating, so that there is a smooth segment L1 and an inner fin segment L2 with a preset length in the unit tube and the rotating unit tube; the heat exchange tube of the present invention can not only increase the condensation temperature for occasions with condensation phase heat transfer The wall surface for heat exchange, and greatly reduces the thickness of the non-condensable gas boundary layer, increasing the condensation heat transfer coefficient.

Description

An axisymmetric cross-finned heat exchange tube

technical field

The invention belongs to the technical field of heat exchange tubes, and relates to a unit structure of a heat exchanger, in particular to an axisymmetric intersecting fin reinforced heat exchange tube.

Background technique

Heat exchangers are widely used in various industries of the national economy, and are one of the most common equipment in energy, petroleum, chemical, metallurgy, power, light industry, food and even aerospace industries. It is not only widely used equipment to ensure process flow and conditions, but also an important equipment to develop secondary energy, realize heat recovery and save energy consumption. The development and design of advanced enhanced heat exchange tubes and the rational design, operation and improvement of heat exchange equipment are very important to save metal, energy, money and space.

Adding inner fins to the heat exchange tube can not only increase the heat exchange area to a certain extent, but also change the flow pattern and resistance distribution of the fluid in the tube, and improve the heat transfer coefficient.

The use of inner-finned heat exchange tubes can play two roles, one is to increase the heat transfer coefficient from the working medium in the tube to the tube wall; the other is to reduce the temperature of the tube wall. After the inner fins are incorporated in the tube, the equivalent diameter of the channel section decreases. Due to the decrease of the equivalent diameter and the increase of the heat transfer area of the inner wall, the heat transfer coefficient of the straight inner finned tube is much higher than that of the bare tube. Therefore, when the heat transfer is the same, the temperature of the tube wall can be kept lower than that of the bare tube, which can not only improve the convective heat transfer coefficient of the single-phase airflow, but also be suitable for occasions where condensation occurs. When there is condensation phase change heat, Lower metal wall temperature can obtain larger condensation amount and better condensation effect.

The use of inner-finned heat exchange tubes to replace ordinary bare tubes is a method to enhance the convective heat transfer of the fluid in the tubes, and it is suitable for the case where the thermal resistance inside the tube is greater than the thermal resistance outside the tube. The influence of the inner fin on the heat exchange intensity of the fluid in the heat exchange tube is realized from two aspects. One is that the inner fin divides the tube into many fluid channels with smaller equivalent diameters, which can increase the heat exchange area inside the tube; on the other hand, the reasonable configuration of the fins can also improve the flow conditions in the tube: Under a certain combination of numbers, a secondary flow that is conducive to heat exchange will be formed in the center of the tube and the space between the fins, which will significantly improve the heat exchange effect.

The most effective inner finned tube currently used is formed by two identical half shells inserted into each other by means of groove-shaped depressions and rib-shaped protrusions. In the cross-section of the half-shells, the fins are arranged in a comb shape perpendicular to the joint surface and extend to a position close to the joint surface. The inner finned tube must be used with the outer tube. The inner finned tube of this structure has a higher finning ratio, which can largely destroy the radial temperature distribution pattern without fins, increase the heat transfer area and convective heat transfer coefficient, and make a large number of low-temperature regions appear in the cross-sectional temperature field , but the structure still has the following deficiencies:

1. It is impossible to maximize the uniformity of the cross-sectional temperature field. The inner fin structure makes the high-temperature flue gas flow through the entire heat exchange tube only through fixed channels, and the heat exchange between high-temperature flue gas in different channels is less, especially the finless area in the center of the pipe is still a high-temperature air flow area, which cannot To achieve the maximum uniformity of the cross-sectional temperature field.

2. It is difficult to ensure sealing and good contact with the outer tube. The inner finned tube is made of two half-shells plugged together, so it is difficult to ensure sealing, so it must be used with the outer tube, and there is a problem of poor contact with the outer tube, which greatly reduces the heat exchange effect.

Contents of the invention

In order to overcome the deficiencies in the above-mentioned prior art, the object of the present invention is to provide an axisymmetric cross-finned heat exchange tube, which can generate the inlet section effect and wake flow equivalent to the internal flow of the tube during the flow of flue gas along the tube. (Generation of vortex) The effect of the combined effect is to continuously mix the flue gas with uneven temperature, so that the heat of a small amount of high-temperature flue gas is evenly distributed to a large amount of flue gas with a lower temperature, ensuring that the overall flue temperature is low and at the same time, the cross-section The uniform temperature field is maximized, and the disturbance is enhanced at the same time, which strengthens the heat transfer in the tube; it can also completely destroy the radial temperature distribution mode without fins, greatly increase the heat transfer area and fluid turbulence, and enhance the convective heat transfer coefficient , to achieve the best heat transfer effect; for occasions with condensation phase transfer heat, it can not only increase the wall surface of condensation heat transfer, but also greatly reduce the thickness of the non-condensable gas boundary layer, and increase the condensation heat transfer coefficient.

In order to achieve the above object, the technical scheme adopted in the present invention is:

An axisymmetric cross-inner fin enhanced heat exchange tube, including a plurality of unit tubes 1 arranged at intervals and a rotating unit tube 2, the rotating unit tube 2 is formed by rotating the unit tube 1 at a preset angle, the The unit tube 1 is integrally connected with the side wall of the unit tube 1 in the axial direction, and there are multiple pairs of fins 3 facing up and down and wide fins 4 penetrating through the cross section of the heat exchange tube. The wide fins 4 are located in the unit tube 1 The left and right sides of the left and right sides, the plurality of pairs of fins 3 are located between the wide fins 4 on the left and right sides, and each pair of fins 3 facing up and down is axisymmetric, and the distance between the tops of each pair of fins 3 The distance is a preset distance L3; the wide fins 4 and fins 3 extend axially but do not completely pass through, so that a smooth segment L1 and an inner fin segment L2 of a preset length are left in the unit tube 1 and the rotating unit tube 2 .

It also includes a plurality of unit tubes 1 arranged at intervals and the outer circumference of the rotating unit tube 2 and is in contact with the outer wall of the outer sleeve 5 .

The ratio of the smooth section L1 to the inner wing section L2 is 0.2-0.5.

The preset angle is 45°-90°.

The preset angle is 60° or 90°.

The preset distance L3 is 6-8 mm.

The number of the fins 3 changes according to the temperature of the flue gas fed in, and when the temperature is low, the number of the fins 3 increases.

The wide fins 4 and 3 are flat plates with holes, spherical bubbles, strip bubbles, waves, segmented zigzag fins or crossed zigzag fins.

The cross sections of the unit pipe 1 and the rotating unit pipe 2 are circular, elliptical, polygonal or square.

The material of the unit tube 1 , the rotating unit tube 2 , the fins 3 , the wide fins 4 and the outer casing 5 is cast aluminum, aluminum-silicon alloy, stainless steel or titanium alloy.

Compared with the prior art, the present invention has the following advantages:

1. A plurality of unit tubes 1 and rotating unit tubes 2 are arranged at intervals, and the cross-section of the enhanced heat exchange tubes changes periodically. When the flue gas flows along the tubes, an inlet section appears when it enters the adjacent smooth section from an inner fin section. effect (the velocity of the flue gas is close to the mainstream velocity), and the vortex appears when the flue gas enters the next inner fin section from the smooth section, so that the flue gas whose temperature has not been uniform in the inner fin tube section can be strongly mixed in the smooth section, and the flue gas The heat exchange is directly carried out inside, so that the heat of a small amount of high-temperature flue gas is evenly distributed to a large amount of lower-temperature flue gas, ensuring that the overall flue temperature is low, and at the same time, the cross-sectional temperature field is maximized, and the cross-section of the inner fin section is periodic. The change of also enhances the disturbance and strengthens the heat transfer in the tube.

2. The design of the inner fins 3 and wide fins 4 of the unit tube 1 and the rotating unit tube 2 makes the heat exchange tube have a high finning ratio, combined with the design of the smooth section, it can completely destroy the radial direction without fins. The temperature distribution mode greatly increases the heat transfer area and fluid turbulence, enhances the convective heat transfer coefficient, effectively reduces the flue gas temperature, and achieves a uniform cross-sectional temperature field as much as possible.

3. The unit tube is a circumferentially closed overall structure, which can be directly poured. The manufacturing process is simple, and there is no sealing problem. It does not need an outer tube and can be used directly as a heat exchange tube.

4. The design of the outer sleeve 5 can be adapted to different working fluids and different heat transfer conditions by changing the thickness and material, thereby achieving enhanced heat transfer.

5. The design of the inner wide fin 4 of the unit tube 1 and the rotating unit tube 2, in the case of the outer tube 5, enables the inner finned tube and the outer tube to be closely matched, and the interference fit is realized due to heating expansion during work, preventing the The heat exchange effect caused by poor contact between the inner and outer tubes is reduced, and the wide fin plate 4 itself also serves as a heat exchange surface, which increases the heat exchange area and strengthens the heat exchange. For occasions with condensation phase transfer heat, it can not only increase the wall surface of condensation heat transfer, but also greatly reduce the thickness of the non-condensable gas boundary layer and increase the condensation heat transfer coefficient.

Description of drawings

Fig. 1a is a schematic structural view of an axisymmetric intersected inner-fin enhanced heat exchange tube of the present invention.

Fig. 1b is a cross-sectional view along A-A direction of Fig. 1a.

Fig. 1c is a cross-sectional view along B-B direction of Fig. 1a.

Fig. 1d is a cross-sectional view along C-C direction of Fig. 1a.

Fig. 1e is a sectional view along the D-D direction of Fig. 1a.

Fig. 2 is a right side view of the axisymmetric intersected inner-fin enhanced heat exchange tube with an outer sleeve of the present invention.

Detailed ways

The present invention will be described in more detail below in conjunction with the accompanying drawings.

As shown in Fig. 1a, Fig. 1b, Fig. 1c, Fig. 1d, Fig. 1e and Fig. 2, an axisymmetric cross-finned heat exchange tube of the present invention includes a plurality of unit tubes 1 arranged at intervals and a rotating unit Pipe 2, the rotating unit pipe 2 is formed by rotating the unit pipe 1 at a preset angle. The unit tube 1 is integrally connected with the side wall of the unit tube 1 along the axial direction, and there are multiple pairs of fins 3 facing up and down and wide fins 4 penetrating the cross section of the heat exchange tube. 1, the plurality of pairs of fins 3 are located between the wide fins 4 on the left and right sides, and each pair of fins 3 facing up and down is axisymmetric, and between the tops of each pair of fin plates 3 The distance is the preset distance L3, the design of fin 3 and wide fin 4 makes the heat exchange tube have a high finning ratio, combined with the design of the smooth section can completely destroy the radial temperature distribution mode in the case of no fins , greatly increasing the heat transfer area and fluid turbulence, enhancing the convective heat transfer coefficient, effectively reducing the flue gas temperature, and achieving a uniform cross-sectional temperature field as much as possible. The wide fins 4 and 3 extend in the axial direction but do not penetrate completely, so that a smooth segment L1 and an inner fin segment L2 of a preset length are left in the unit tube 1 and the rotating unit tube 2, and a plurality of unit tubes 1 and The rotating unit tube 2 is arranged at intervals, and the cross-section of the enhanced heat exchange tube changes periodically, and the inlet section effect occurs when the flue gas flows from an inner finned section to the adjacent smooth section during the flow along the tube (the flue gas velocity is close to the mainstream velocity ), and a vortex occurs when the flue gas enters the next inner finned section from the smooth section, so that the flue gas that has not achieved uniform temperature in the inner finned tube section can be strongly mixed in the smooth section, and the heat exchange is directly performed inside the flue gas, making a small amount of The heat of high-temperature flue gas is evenly distributed to a large number of lower-temperature flue gases to ensure that the overall flue temperature is low and at the same time maximize the uniformity of the cross-sectional temperature field. In-tube heat exchange.

As a preferred embodiment of the present invention, it also includes an outer sleeve 5 arranged on the outer circumference of a plurality of unit tubes 1 and rotating unit tubes 2 arranged at intervals and in contact with their outer walls. The design of the outer sleeve 5 can be adapted to different working fluids and different heat transfer conditions by changing the thickness and material, thereby achieving enhanced heat transfer. In the case of the outer tube 5, the design of the wide fin 4 enables the inner finned tube and the outer tube to be closely matched, and an interference fit is achieved due to thermal expansion during work, preventing the heat transfer effect from being reduced due to poor contact between the inner and outer tubes, and at the same time The wide fin plate 4 itself also acts as a heat exchange surface, which increases the heat exchange area and strengthens the heat exchange. For occasions with condensation phase heat transfer, it can not only increase the wall surface for condensation heat exchange, but also greatly reduce the thickness of the non-condensable gas. The thickness of the boundary layer increases the condensation heat transfer coefficient.

As a preferred embodiment of the present invention, the ratio of the smooth section L1 to the inner wing section L2 is 0.2-0.5. This ratio enables the flue gas to enter the next inner fin section as soon as possible while sufficiently mixing in the smooth section to achieve heat transfer enhancement.

As a preferred embodiment of the present invention, the preset angle is 45°-90°. Further, the preset angle is 60° or 90°. The preset angle makes the cross-section of the inner fin section change periodically, which further enhances the disturbance, strengthens the heat transfer in the tube, and reduces the temperature difference inside the flue gas in the tube.

As a preferred embodiment of the present invention, the preset distance L3 is 6-8 mm.

As a preferred embodiment of the present invention, the number of the fins 3 changes according to the temperature of the flue gas fed in, and the number of the fins 3 increases when the temperature is low. It can maintain a relatively high flue gas flow rate while achieving a gradual reduction in the volume of the flue gas, especially under the condition that the flue gas condensation requires the flue gas to tear the liquid film, and can significantly increase the convection and condensation heat transfer coefficients.

As a preferred embodiment of the present invention, the wide fins 4 and fins 3 are flat plates with holes, spherical bubbles, strip bubbles, waves, segmented zigzag fins or cross zigzag fins to increase Heat transfer area and enhanced disturbance.

As a preferred embodiment of the present invention, the cross-sections of the unit pipe 1 and the rotating unit pipe 2 are circular, elliptical, polygonal or square. Different cross-sections can be adapted to different placement spaces, and the arrangement of heat exchange tubes can be adjusted

As a preferred embodiment of the present invention, the material of the unit tube 1 , the rotating unit tube 2 , the fins 3 , the wide fins 4 and the outer casing 5 is cast aluminum, aluminum-silicon alloy, stainless steel or titanium alloy. Compared with traditional cast iron or stainless steel heat exchange tubes, the application of cast aluminum or aluminum-silicon alloy to heat exchange tubes has the following advantages: the thermal conductivity of aluminum is 8 times that of stainless steel, and it gives a greater impact on the design of combustion chambers and waterways. Space; in terms of corrosion resistance, aluminum can effectively prevent acid corrosion and oxygen corrosion, and has high reliability; from the perspective of raw material prices, processability and processing costs, aluminum has absolute advantages. Friction stir welding can be preferably used for the connection part of the enhanced heat exchange tube, which does not need to consume electrodes and coatings, is efficient and environmentally friendly, and other butt welding methods can also be used, such as: automatic submerged arc welding, tungsten inert gas shielded welding ( TIG), molten inert gas welding (MIG) or active gas welding (MAG) and other welding methods.

working principle

There are three ways to transfer heat energy: heat conduction, heat convection and heat radiation. Among them, the heat transfer by heat conduction is Φ=hAΔt. The main influencing factors are temperature difference, heat transfer area and flow rate. When the temperature difference remains unchanged, increasing the flow rate and heat transfer area can effectively increase the heat transfer.

The high-temperature flue gas passes through the axisymmetric cross-finned heat exchange tube, and the low-temperature fluid flows outside the tube. The heat of the high-temperature flue gas is transferred to the tube wall through heat conduction, and the tube wall transfers the heat to the low-temperature fluid outside the tube through heat conduction, thus Reduce the temperature of the flue gas and increase the temperature of the fluid outside the pipe.

In the single-phase heat exchange process, the inlet section effect occurs when the flue gas flows from an inner finned section to the adjacent smooth section (the velocity of the flue gas is close to the mainstream velocity), while the flue gas enters the next smooth section from the smooth section. The eddy current appears in the inner fin section, so that the enhanced heat transfer in the tube is very significant. When the high-temperature flue gas flows through the inner fin section, the fin 3 and the wide fin plate 4 divide the high-temperature gas in the heat exchange tube into several heat exchange areas, which greatly increases the heat exchange area and strengthens the heat exchange; A flow field with a relatively high flow rate is formed in the flow space, and the existence of fins and various shapes processed on the fins strengthens the turbulence, enhances the turbulent flow, and further strengthens the flow heat transfer.

In the heat exchange process with condensing phase change, several unit tubes 1 and rotating unit tubes 2 are arranged alternately, and the inlet section effect and wake effect caused by the periodic change of the cross section enhance the disturbance of the fluid in the tube, and it is easier to thin the tube. The thickness of the boundary layer of condensable gas, the water vapor in the mainstream of flue gas can condense on the fin wall as long as it passes through the thinner boundary layer of non-condensable gas. Due to the division effect of the fins, the inner fin section divides the high-temperature flue gas into thin layers, which greatly reduces the thickness of the non-condensable gas boundary layer and significantly weakens the resistance of the non-condensable gas boundary layer to the condensation of water vapor. At the same time, after the heat exchange is enhanced, the surface temperature of the fins decreases, which further provides the power of temperature difference for the condensation of water vapor in the flue gas. Discharge, perforate the surface of the fin, or make the fin into bubbling, corrugated, and segmented, crossed sawtooth fins and other structures to further destroy the thickness of the liquid film and reduce the heat transfer and mass transfer resistance of the liquid film , so that the condensation heat transfer is further enhanced.

Claims (10)

1. An axisymmetric cross-finned heat exchange tube is characterized in that: it includes a plurality of unit tubes (1) and rotating unit tubes (2) arranged at intervals, and the rotating unit tubes (2) are made of The unit tube (1) is rotated at a preset angle, and the unit tube (1) is integrally connected with the side wall of the unit tube (1) along the axial direction. The wide fins (4) of the tube cross section, the wide fins (4) are located on the left and right sides in the unit tube (1), and the multiple pairs of fins (3) are located on the left and right sides Between the fins (4), and each pair of fins (3) facing up and down is axisymmetric, and the distance between the tops of each pair of fin plates (3) is a preset distance L3; the wide fins (4) and the fins The sheet (3) extends in the axial direction but does not penetrate completely, so that a smooth section L1 and an inner fin section L2 of a predetermined length are left in the unit tube (1) and the rotating unit tube (2). 2. An axisymmetric cross-inner fin enhanced heat exchange tube according to claim 1, characterized in that it also includes a plurality of unit tubes (1) arranged at intervals and the outer circumference of the rotating unit tubes (2) circle and contact the outer casing (5) with its outer wall. 3 . The axisymmetric intersected inner fin enhanced heat exchange tube according to claim 1 , wherein the ratio of the smooth segment L1 to the inner fin segment L2 is 0.2-0.5. 4 . The axisymmetric intersected inner-fin enhanced heat exchange tube according to claim 1 , wherein the predetermined angle is 45°-90°. 5 . The axisymmetric cross-inner-fin enhanced heat exchange tube according to claim 4 , wherein the preset angle is 60° or 90°. 6 . The axisymmetric intersected inner-fin enhanced heat exchange tube according to claim 1 , wherein the preset distance L3 is 6-8 mm. 6 . 7. An axisymmetric intersected fin-enhanced heat exchange tube according to claim 1, characterized in that: the number of the fins (3) changes according to the temperature of the flue gas passing through, and when the temperature is low, The number of fins (3) increases. 8. An axisymmetric cross-inner fin enhanced heat exchange tube according to claim 1, characterized in that: the wide fins (4) and fins (3) are flat plates with holes, spherical bubbles , strip bubbles, waves, segmented zigzag fins or cross zigzag fins. 9. An axisymmetric cross-finned heat exchange tube according to claim 1, characterized in that: the cross-sections of the unit tubes (1) and the rotating unit tubes (2) are circular, oval shape, polygon or square. 10. An axisymmetric cross-finned heat exchange tube according to claim 2, characterized in that: said unit tube (1), rotating unit tube (2), fins (3), wide fins The sheet (4) and the outer sleeve (5) are made of cast aluminum, aluminum-silicon alloy, stainless steel or titanium alloy.