CN104236369B - Inner spiral outer crossed tunnel double-side reinforced boiling heat transfer pipe - Google Patents

Abstract

The invention provides a double-sided enhanced boiling heat transfer tube with an inner spiral outer cross tunnel, which includes a heat transfer tube base, an inner spiral groove is arranged on the inner surface of the heat transfer tube base, and the inner spiral groove is distributed in a spiral shape along the inner surface. The axis is coaxial with the axis of the heat transfer tube; the outer surface of the heat pipe base is provided with a plurality of fins distributed helically along the tube axis; the fins are independent of each other and form a three-dimensional extended curved surface of the entire outer surface of the heat transfer tube wall. The invention can greatly increase the heat transfer area, the fins can also destroy the stagnant boundary layer, and improve the coefficient of the boiling heat transfer film; the spiral grooves distributed in the tube can induce secondary separation flow, improve the turbulence degree of the liquid in the tube, and improve the heat transfer coefficient in the tube. Convective heat transfer film coefficient, and has a certain anti-fouling ability. The invention is suitable for strengthening the heat exchange between the liquid with low viscosity and certain impurities inside the tube and the liquid with high viscosity and high boiling point outside the tube, especially the liquid organic compound.

Description

Double-sided enhanced boiling heat transfer tube with inner spiral and outer cross tunnel

technical field

The invention relates to an enhanced heat transfer tube, in particular to a double-sided enhanced boiling transfer tube with an inner spiral outer cross tunnel that can greatly improve the film coefficient of boiling heat transfer outside the tube and convective heat transfer inside the tube, and has a certain anti-fouling ability. Heat pipe.

Background technique

Shell-and-tube heat exchangers are currently the most widely used heat exchangers. They are widely used in energy and power, petrochemical, pharmaceutical, metallurgical and other industrial fields, and their investment accounts for more than 35% of the total equipment investment. Therefore, they are used The design and improvement of shell and tube heat exchangers based on the principle of enhanced heat transfer become the key to energy saving, equipment utilization and availability. Among them, the design of efficient heat transfer tubes, the basic heat exchange elements of shell and tube heat exchangers, is the main way to achieve efficient heat exchange in heat exchangers.

To enhance the boiling heat transfer outside the tube, different measures can be taken for various factors that affect the boiling heat transfer efficiency, among which the most common is to change the roughness of the heating surface of the heat transfer tube (Cheng Lixin, Chen Tingkuan. Boiling heat transfer enhancement technology and Method [J]. Chemical Equipment Technology, 1999, 20 (1): 30-34), in order to form more vaporization cores, increase the probability of bubble generation, and achieve the effect of strengthening boiling heat transfer. Based on this concept, a batch of new and efficient enhanced heat transfer tubes have been developed, and some have also applied for patents, such as the more common heat exchange tubes with porous surfaces, T-shaped finned tubes and low-finned tubes. Each enhanced heat transfer tube has a corresponding enhanced heat transfer mechanism and has its corresponding application range. Heat Exchange Tubes with Porous Surfaces (Liao Lihua, Dong Qingbo, Shen Chuanwen, Bai Eryi, Wang Zhijuan. Research on Enhanced Boiling Heat Exchange of Aluminum Porous Surface Heat Exchange Tubes and Its Industrial Application [J]. Chemical Equipment Technology, 2003, 24(1): 27- 30) The surface of the heating surface is covered with a porous layer of metal powder. Compared with a smooth tube, the boiling heat transfer film coefficient can be increased by 5 to 6 times. However, the processing technology of this type of heat exchange tube is complicated and the cost is high. Compared with the smooth tube, the investment is also greatly improved. T-shaped finned tubes (Luo Guoqin, Lu Yingsheng, Zhuang Lixian, Deng Songjiu. Study on boiling heat transfer characteristics of T-shaped finned tubes [J]. Journal of Chemical Engineering of Universities, 1989, 3(2): 56-62) compared with smooth tubes , its boiling heat transfer coefficient and critical heat load have been significantly improved, and the processing is extremely simple, but there is a serious boiling hysteresis phenomenon in the initial boiling stage of the T-shaped finned tube, which greatly affects its enhanced performance. . The low-finned tube has a simple structure and is easy to process. Its boiling heat transfer film coefficient is higher than that of a smooth tube but lower than that of a T-shaped finned tube ^[3] , and the geometric parameters of the tubes that achieve the best strengthening effect under different conditions are often different (Dong Liang , Zhang Hongji, Cheng Junguo. The influence and optimization of low geometrical parameters on boiling heat transfer [J]. Journal of Chongqing University, 1990, 13(1): 35-41), which brings great inconvenience to practical application . The above-mentioned heat transfer tubes have a certain effect on improving the boiling heat transfer coefficient outside the tube, especially the T-shaped finned tube, whose heat transfer performance can approach or even exceed the level of the E tube. However, they can only enhance heat transfer on one side of the outer side of the tube, and have the disadvantage of not being able to enhance the convective heat transfer coefficient in the tube, which also limits their industrial application in some aspects to a certain extent, such as low-viscosity liquid in the tube , The outside of the tube is a place for heat exchange between liquids with high viscosity and high boiling point.

Contents of the invention

The purpose of the present invention is to avoid the shortcomings of the existing heat transfer tubes in some places mentioned in the above-mentioned background technology, and to provide a double-sided enhanced boiling heat transfer tube with inner spiral and outer cross tunnel, which can greatly improve the external temperature of the tube at the same time. The film coefficient of boiling heat transfer and convective heat transfer in the tube, and the double-sided enhanced heat transfer tube with a certain anti-fouling ability can directly meet the design requirements of current and future designs for heat transfer tubes in high-viscosity, high-boiling point heat exchangers.

The object of the present invention is achieved at least by one of the following technical solutions.

A double-sided enhanced boiling heat transfer tube with an inner spiral outer cross tunnel, including a heat transfer tube base, an inner helical groove is provided on the inner surface of the heat transfer tube base, and the inner helical groove is helically distributed along the inner surface. The axis of the heat pipe is coaxial; the outer surface of the heat pipe base is provided with a plurality of fins that are helically distributed along the tube axis; the fins are independent of each other, forming a three-dimensional extended curved surface of the entire outer surface of the heat transfer tube wall; the inner spiral The grooves, fins and heat transfer tube base are integrated structures without contact thermal resistance.

To further optimize the implementation, the fins on the outer surface of the heat transfer tube base are naturally formed by crossing the helical grooves of the left-handed arcuate section and the helical grooves of the right-handed arcuate section starting from the end surface of the tube, and the axial spacing of the fins 30-50mm, and the fin height is 3.0-8.0mm.

For further optimized implementation, the internal helical groove on the inner surface of the heat transfer tube base is left-handed or right-handed, the helix angle θ of the groove is 65°-85°, and the lead, that is, the pitch d, is 15-25mm , groove depth b = 1.5mm ~ 4.5mm.

For further optimized implementation, the pitch of the left-handed arcuate section helical groove forming the rib is equal to or unequal to the pitch of the right-handed arcuate section helical groove, the pitch c of the arcuate section helical groove is 30-50mm,

The diameter of the arcuate section is Φ=4.0-10mm, and the depth of the spiral groove of the arcuate section is e=3.0-8mm.

For further optimized implementation, the external volumes of the ribs are equal or unequal, but the heights of the ribs are equal, and the height h of the ribs is the same as the depth e of the arcuate section spiral groove.

For further optimized implementation, the axial cross-sectional shape of the spiral groove in the base of the heat transfer tube is one of semicircle and inverted triangle.

In a further optimized implementation, the fins are perpendicular to the outer wall of the tube, have an included angle of 75°-88° with the axis of the tube, and are arranged in a helical shape along the axis.

For further optimized implementation, the material of the heat transfer tube includes brass, red copper, soft aluminum or soft alloy materials.

Preferably, the outer fins of the tube and the tube base are of an integrated structure without contact thermal resistance. And the fins outside the tube are independent of each other, distributed in a spiral shape along the outer surface of the substrate, perpendicular to the outer wall of the tube, and the included angle with the axis of the tube is 75° to 88°, thus forming a complete three-dimensional expansion on the outer surface of the tube wall surface. The intersecting tunnel spaces are formed by the gaps between the independent ribs, and the height of each rib is the same as the depth of the arcuate section spiral groove, which is 3.0mm-8.0mm. This structure can greatly increase the boiling heat transfer surface area, and the higher the height of the fins, the larger the outer surface area of the fins, and the better the boiling heat transfer performance. In addition, the gap between the fins is adjustable, and parameters can be adjusted according to different working conditions and different heat transfer fluid viscosities, so as to maximize the effect of liquid surface tension and strengthen the gas-liquid phase shear. The force acts on the turbulence of the fluid film on the heat transfer tube to enhance the heat transfer effect. The helical groove with this structure can induce secondary flow such as helical flow and boundary layer separation flow. While greatly improving the convective heat transfer film coefficient in the tube, it also has a certain anti-fouling ability.

The spiral groove in the pipe can be left-handed or right-handed, the helix angle θ of the groove is 65°-85°, the lead (or pitch) d is 15-25mm, and the groove depth b = 1.5 mm to 4.5 mm.

The main material of the heat transfer tube can be brass, red copper, soft aluminum and other non-ferrous metals or soft alloy materials.

The main preferred implementation parameters of the present invention are as follows:

Heat transfer tube outer diameter D: 100 ~ 200mm

Tube wall thickness δ: 10~20mm

Concave bow-shaped left-handed thread helix angle α: 75°～88°

Concave bow-shaped right-hand thread helix angle β: 95°～110°

Helix angle θ of spiral groove: 65°～85°

The lead (or pitch) d of the spiral groove on the inner surface: 15~25mm

Diameter Φ of arcuate section: 4.0～10mm

Helical groove depth e of arcuate section: 3.0-8mm.

The height h of the ribs: the same as the depth e of the spiral groove of the arcuate section

The pitch c of the arcuate section spiral groove: 30~50mm

Groove depth b of the spiral groove on the inner surface: 1.5-4.5 mm.

Principle of the present invention and effect are as follows:

The mechanism of the present invention's enhanced boiling heat transfer outside the tube is: the liquid outside the tube is heated by the liquid inside the tube. During the boiling process, there is a certain temperature difference in the direction of the curved surface of the fins, and the temperature difference will cause the liquid in the two fins to Create natural convection. At the same time, the curved surface of the fins provides the nucleation center of the air bubbles, which promotes the nucleation and growth of the air bubbles. When the air bubbles generated on the curved surface of the fins grow to a certain extent, they will leave the heated surface and float from the inside to the outside, and then rupture. Such behavior of bubbles not only disturbs the thin layer of liquid close to the surface, but also intensifies the overall convective turbulence of the liquid. In addition, the axially spirally distributed rib structure outside the pipe of the present invention also limits the escape of bubbles generated in the tunnel outside the pipe, making the bubbles move in a circular direction along the curved surface of the tunnel wall. The opportunity for the bubbles to contact with the curved surface of the inner wall of the tunnel is strengthened in this annular flow process, thereby increasing the boiling heat transfer film coefficient.

The mechanism of the invention to enhance convective heat transfer in the tube is: the spiral groove on the inner wall of the tube will cause a part of the liquid close to the wall to generate an additional spiral flow, which will increase the liquid flow rate and make the liquid move in a spiral shape, thereby reducing the thermal resistance. The convective heat transfer film coefficient is increased. At the same time, another part of the liquid near the wall is affected by the convex rib of the spiral groove, and a reverse pressure gradient is generated on the downstream surface of the rib, causing a secondary separation flow. The separated flow will promote radial mixing of the liquid in the tube, increasing the mixing degree of the main fluid and the boundary layer flow, thereby accelerating the heat transfer rate from the liquid to the wall.

The anti-fouling mechanism in the pipe of the present invention is: the inner wall of the pipe is provided with a helical groove with a semicircular and inverted triangular cross-section. The helical flow in the axial direction leads to additional separation flow, which has a good scouring effect on the inner wall of the tube, reduces the possibility of medium deposition to a certain extent, and fully prolongs the induction period of fine particle scaling in the liquid. On the other hand, the helical groove with a semicircular or inverted triangular cross-section has a large local curvature gradient in the direction of the pipe axis, which can also force the formed scale layer to crack again and fall off from the inner wall of the pipe to cooperate with the role of additional separation flow , can achieve a certain anti-fouling effect.

Compared with prior art, advantage and beneficial effect of the present invention are:

1. The fins on the outer side of the tube wall and the spiral groove inside the tube are formed by multiple times of non-cutting rolling, so that the fins are continuously distributed and integrated with the tube base, completely without contact thermal resistance. Independent fins are used outside the tube to enhance boiling heat transfer, and spiral grooves are used inside the tube to enhance convective heat transfer, which can fully meet the requirements for enhanced heat transfer inside and outside the tube.

2. The special spiral groove structure in the tube of the present invention can generate additional separation flow and longitudinal eddy current in the process of liquid flow in the tube, which has the effect of washing the wall surface, making the inner wall surface of the tube less prone to fouling, thereby ensuring long-lasting and good convective heat transfer performance in the tube , has a certain anti-scale and anti-scale performance.

3. Compared with smooth tubes with the same diameter parameters, the present invention can increase the boiling heat transfer film coefficient outside the single tube by more than 200%, and the convective heat transfer film coefficient inside the tube can be increased by more than 125% under boiling heat transfer conditions. The total heat transfer coefficient can be increased by more than 85%, while the increase of the pressure drop in the tube is less than 5%, which is not very obvious.

4. Under the same heat exchanging conditions, the heat exchanging area can be reduced by adopting the present invention, and the materials of pipes, tube plates, cylinders, and the entire processing and assembling man-hours can be correspondingly reduced, so that the structure of the heat exchanger is compact and the manufacturing cost is reduced. .

As a high-efficiency double-sided enhanced boiling heat transfer tube, the invention can be widely used in the occasion of boiling heat transfer of high-viscosity and high-boiling point liquids. For example, the heat exchange element of the reboiler that uses the liquid with low viscosity and certain impurities in the tube to heat the liquid with high viscosity and high boiling point (especially liquid organic compound) outside the tube is very suitable for adopting the present invention.

Description of drawings

Fig. 1 is a three-dimensional structure diagram of the heat transfer tube of the embodiment.

Fig. 2 is a partial three-dimensional structure diagram of the heat transfer tube of the embodiment.

Fig. 3 is a partial cross-sectional view of the heat transfer tube of the embodiment in the frontal direction.

Fig. 4 is a partial cross-sectional view of the heat transfer tube in the plan view direction of the embodiment.

Fig. 5 is a schematic axial cross-sectional view of the heat transfer tube of the embodiment.

Fig. 6 is a schematic axial cross-sectional view of the heat transfer tube of the embodiment in a direction 90° from the viewing angle of Fig. 5 .

Fig. 7 is an axial view of the heat transfer tube of the embodiment.

In the figure: 1-fins; 2-heat transfer tube base; 3-semi-circular section inner spiral groove; D-heat transfer tube outer diameter; δ-tube wall thickness; angle; β-the helix angle of the arcuate right-handed thread outside the tube; θ-the helix angle of the helical groove inside the tube; b-the groove depth of the helical groove on the inner surface; c-the pitch of the helical groove on the arcuate section; d-the inner surface The lead (or pitch) of the helical groove; Φ-the diameter of the arcuate section. e - Helical groove depth of arcuate section. h - the height of the fin.

detailed description

The implementation of the invention will be further described below in conjunction with the drawings and examples, but the implementation and protection of the invention are not limited thereto. Processes that are not specifically described in detail below can be performed by those skilled in the art with reference to the prior art.

As shown in Figure 1, the three-dimensional structural diagram of the heat transfer tube, as shown in Figure 2, the local three-dimensional structural diagram, a double-sided enhanced boiling heat transfer tube with an inner spiral and an outer cross tunnel, including a heat transfer tube matrix 2, which forms a spiral along the outer surface of the matrix The ribs 1 distributed in a shape, the helical grooves 3 distributed along the inner surface of the matrix in a semi-circular cross-section. Wherein, the outer fins 1 of the tube are naturally formed by crossing the helical grooves with a left-handed arcuate section and the helical grooves with a right-handed arcuate section starting from the end face of the tube; Concave single-head or multi-head spiral grooves are formed.

As shown in Figure 1, the outer surface of the pipe wall is the rib of the present invention, and the inner surface is a spiral groove. For the sake of clarity, Figure 2 provides a local three-dimensional structure diagram of the present invention, and Figure 3 provides Partial sectional view of the present invention's front view direction, Fig. 4 has provided the partial sectional view of the present invention's top view direction, Fig. 5, Fig. 6 have provided the axial sectional schematic view of the present invention under the direction of different viewing angles, Fig. 7 has provided the shaft of the present invention to the view. The invention combines the advantages of porous surface heat exchange tubes, T-shaped finned tubes and low-finned tubes in boiling heat transfer and convective heat transfer, and avoids their shortcomings.

In the embodiment of the present invention, two cross-distributed inner concave arcuate threads with the same pitch and opposite direction of rotation are provided on the outer surface of the heat transfer tube. The inner concave arcuate threads cut the outer surface of the tube into many spirally distributed ribs. The fins constitute a three-dimensionally expanded concave surface outside the tube. Each fin is integrated with the outer wall of the heat transfer tube, and is connected with four surrounding fins at the bottom of the groove, and each fin is perpendicular to the tube wall (see Figures 1-6). The higher the height of the fins outside the tube, the larger the specific surface area of the three-dimensionally expanded surface, and the higher the heat transfer enhancement coefficient of boiling outside the tube, but it also increases the resistance of the fluid outside the tube. Therefore, the height of each fin can be taken as 3.0mm-8.0mm (slightly smaller than the diameter Φ of the arcuate section), and the axial spacing c=30-50mm.

There are single or multiple left-handed helical grooves or right-handed helical grooves on the inner surface of the heat transfer tube (see Figures 1-6 for details). The deeper the spiral groove in the tube, the smaller the lead (or pitch), the greater the enhanced convective heat transfer coefficient in the tube, but it also increases the pressure drop of the fluid in the tube. Therefore, the helix angle θ of each spiral groove can be taken as 65°-85°, the lead (or pitch) d can be taken as 15-25mm, and the groove depth b=1.5mm-4.5mm.

The implementation of the present invention can use the smooth pipe as the blank, and use a special pipe rolling machine to carry out extrusion and little or no cutting. The spiral groove 3 inside the pipe and the fins 1 outside the pipe are separately processed and formed.

A feasible processing method is to place the copper or aluminum smooth tube on a special rolling machine, and insert the smooth tube into a special mold arranged in an equilateral triangle, clamp the mold radially along the tube, start the rolling machine, The three sets of molds rotate synchronously to the left, and the gradually tightened molds can cause plastic deformation of the pipe wall metal and make the pipe produce left-handed and axial movements, thereby forming a concave left-handed arcuate cross-section spiral groove. After this process is completed, put the pipe processed by this process into the same mold (it can also be replaced with another set of molds), clamp the mold, and start the pipe rolling machine. At this time, the three sets of molds are clockwise rotated synchronously. , can form a right-handed helical groove with an arcuate cross-section that intersects with the helical groove with an arcuate cross-section formed in the previous step and has an opposite direction of rotation. The diameter of the cross-section of the two helical grooves is Φ. After this process is completed, replace the mold with a roller with a cylindrical outer surface, insert the pipe processed by the previous two processes, clamp and rotate the roller, and slowly pull out the pipe along the axial direction. With the increase, the metal flows radially and axially. Through these three steps of processing, the ribs (1) distributed in a spiral shape on the outer side of the tube can be formed. Finally, insert a semicircular or triangular special hobbing knife into the tube for extrusion and less cutting. The hobbing knife can form a left-handed spiral groove by extruding the material on the inner wall of the tube. If the pipe is rotated in the opposite direction, The right-handed helical grooves are formed by extruding the material of the inner wall of the tube by the hobbing knife, which can form the helical groove surface of the inner wall of the tube. After the above several processing steps, the smooth tube blank can be processed into the present invention.

The following is a specific example of the present invention, and the specific parameters of the heat transfer tube are shown in Table 1.

Table 1

The above-mentioned three-dimensionally expanded concave curved surface outside the tube of the present invention can provide the nucleation center of the bubbles during boiling, and promote the nucleation and growth of the bubbles. At the same time, it is also conducive to disturbing the flow pattern of the liquid, reducing the thickness of the bottom layer of laminar flow and thermal resistance, so it has a high coefficient of boiling heat transfer film outside the tube. Furthermore, the production by rolling tube method can ensure the structural integrity of the surface of the outer fins of the tube, the surface of the inner groove of the tube and the tube base, and completely eliminate the quality problems such as the increase of thermal resistance caused by the metal powder covering the surface of the heating surface. And shape dislocation and other disadvantages. The invention has the characteristics of high heat transfer coefficient, large specific heat transfer surface and anti-fouling, and is suitable for strengthening the heat exchange of the liquid with low viscosity and certain impurities inside the tube and the liquid with high viscosity and high boiling point outside the tube, and can be widely used in Heat exchange of various high-viscosity oils in the fields of power energy, petrochemical industry, etc., to replace smooth tubes or low-fin threaded tubes, porous surface heat exchange tubes, etc.

Application examples

Now take the transformation of reboiler for ethanol distillation in chemical plant as an example:

The heat transfer efficiency of the copper smooth tube reboiler in a chemical plant is low, which makes it impossible to heat ethanol to the set temperature, which affects the normal production of ethanol distillation. Make the present invention with smooth copper tube now, structural parameter is as the concrete example of the above-mentioned present invention, to replace the original smooth tube in the reboiler, carry out technological transformation.

After technical transformation, under the same working condition, the total heat transfer coefficient of the reboiler of the present invention is 50%-75% higher than that of the original smooth tube reboiler. This shows that: when other conditions are the same, the total heat transfer efficiency of the present invention is higher than that of the smooth tube. This is because the fins outside the heat transfer tube of the present invention are distributed in a spiral shape along the tube wall, and the three-dimensionally expanded concave surface formed by the fins provides the bubble nucleation center when ethanol boils, and this special internal The concave surface is easy to induce separation flow, which can reduce the thickness of the ethanol laminar bottom layer and the contact thermal resistance with the outer wall of the tube, and the specific surface area is 3.5 times that of a smooth tube. For ethanol, this form of three-dimensional extended concave surface enhanced boiling heat transfer performance is better than low-fin spiral tubes, porous surface heat exchange tubes, etc.

Claims (3)

1. A double-sided enhanced boiling heat transfer tube with an inner spiral outer cross tunnel, including a heat transfer tube base, characterized in that the inner surface of the heat transfer tube base is provided with inner helical grooves, and the inner helical grooves are helically distributed along the inner surface , the spiral axis is coaxial with the axis of the heat transfer tube; the outer surface of the heat transfer tube base is provided with a plurality of fins that are helically distributed along the tube axis; Curved surface; the fins on the outer surface of the heat transfer tube base are naturally formed from the end surface of the tube, the spiral grooves in the left-handed arcuate section and the spiral grooves in the right-handed arcuate section cross each other, and the axial spacing of the fins is 30~ 50mm, the fin height is 3.0~8.0mm; the inner spiral groove on the inner surface of the heat transfer tube base is left-handed or right-handed, the helix angle θ of the groove is 65°~85°, and its lead is The pitch d is 15~25mm, the groove depth b =1.5mm~4.5mm; the pitch of the left-handed arcuate section spiral groove forming the rib is equal to or unequal to the pitch of the right-handed arcuate section spiral groove, and the arcuate section spiral groove The pitch of the groove c=30~50mm, the diameter of the arcuate section Φ=4.0~10mm, the depth of the spiral groove of the arcuate section e=3.0~8mm; the shape and volume of the fins are equal or unequal, but the height of the fins is equal, The height h of the fins is the same as the depth e of the arcuate section spiral grooves; the axial cross-sectional shape of the spiral grooves in the base of the heat transfer tube is one of semicircle and inverted triangle; the fins and the tube The outer wall is vertical, the included angle with the pipe axis is 75°~88°, and arranged in a helical shape along the axis direction. 2. The inner spiral outer cross tunnel double-sided enhanced boiling heat transfer tube according to claim 1, characterized in that the material of the heat transfer tube includes brass, red copper, soft aluminum or soft alloy materials. 3. The inner spiral outer cross tunnel double-sided enhanced boiling heat transfer tube according to claim 1 or 2, characterized in that the inner spiral grooves, fins and heat transfer tube matrix are an integrated structure without contact heat resistance.