Octagonal finned tube with base tube arranged in rhombus shape

Abstract

An octagonal finned tube with a base tube arranged in a rhombus shape comprises the oval base tube and octagonal fins connected to the outer side of the base tube. The heat exchange tubes are elliptical tubes, so that the flowing resistance of a working medium is reduced; the heat exchange tube bundle is arranged in a rhombus mode, and the finned tube structure is more compact; and the fins are octagonal fins, so that the low heat transfer efficiency of the fins caused by heat transfer deterioration at the corners of the fins is improved. The octagonal finned tube is good in heat exchange performance and small in flow resistance loss, and the enhanced heat exchange effect on the smoke side is more obvious under the condition that the Reynolds number is smaller than 12500.

Description

Technical Field

[0001] The invention belongs to the technical field of heat exchange devices, and particularly relates to an octagonal fin tube with a base tube arranged in a rhombus. Background Art

[0002] Flue gas heat exchangers are key equipment for achieving efficient heat conversion of flue gas in thermal power plants. Developing efficient flue gas heat exchangers is a key measure to achieve efficient energy utilization. In the application of waste heat recovery of flue gas containing fly ash particles, H-type finned tubes are widely used due to their excellent anti-fouling and anti-erosion properties. In order to further improve the performance of the heat exchanger, researchers have designed new heat exchange fins such as 4-H, or added vortex generators or slots to traditional H-type fins, which can effectively enhance heat transfer. However, once such fins accumulate dust, the vortex generators and grooves may fail, thereby aggravating the accumulation of dust. When elliptical tubes are used instead of circular tubes, the accumulation of dust in the heat exchanger is reduced, and the flow resistance loss of the working fluid is reduced. Therefore, it is crucial to improve the comprehensive performance of the flue gas heat exchanger by reasonably designing the fin structure or adjusting the tube bundle layout. Studies have found that there are areas of heat transfer deterioration at the corners of H-type fins, and H-type finned tubes are usually arranged in a sequential manner, and their heat transfer performance is not optimal. Summary of the invention

[0003] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide an octagonal fin tube with a base tube arranged in a rhombus, and further optimize and improve the H-type fin tube, so as to improve its heat exchange performance as much as possible while taking into account its resistance loss.

[0004] In order to achieve the above object, the technical solution adopted by the present invention is:

[0005] An octagonal fin tube with a base tube arranged in a rhombus shape comprises a plurality of elliptical base tubes arranged in rows and columns, wherein four adjacent elliptical base tubes in the rows and columns are arranged in a rhombus shape;

[0006] An octagonal fin is vertically connected to the outer side of each elliptical base tube, and the smoke flow direction is perpendicular to two opposite sides of the octagonal fin. Along the smoke flow direction, the octagonal fin is divided into two symmetrical and mutually isolated parts.

[0007] In one embodiment, the major axis of the elliptical base tube is located on the axis of symmetry of the two parts.

[0008] In one embodiment, the row direction of the smoke flow direction is defined, and the direction perpendicular to the smoke flow direction is defined as the column direction. In the multiple elliptical base tubes arranged in the rows and columns, the ratio of the row spacing to the column spacing is 2:1.

[0009] In one embodiment, the ratio of the major axis to the minor axis of the elliptical base tube is 2:1.

[0010] In one embodiment, in the octagonal fin, two opposite sides are parallel to the smoke flow direction, two opposite sides are perpendicular to the smoke flow direction, the angle between the two opposite sides and the smoke flow direction is an acute angle α, and the angle between the last two opposite sides and the smoke flow direction is an obtuse angle β, α+β=180°.

[0011] In one embodiment, in the octagonal fin, the sum of the lengths of the four sides parallel or perpendicular to the flue gas flow direction is m, and the sum of the lengths of the other four sides is n, m:n=23:

[0012] In one embodiment, m:a=46:27, where a is the length of the elliptical base tube.

[0013] In one embodiment, the side length of the rhombus is 110 mm.

[0014] The octagonal finned tube with a rhombus-shaped base tube of the present invention can be used in a flue gas heat exchanger. Specifically, the flue gas heat exchanger using the octagonal finned tube can be arranged on the flue gas side under the working condition of Reynolds number less than 12500.

[0015] Compared with traditional H-shaped fins, firstly, the heat transfer deterioration area at the corners of the octagonal fins of the present invention is improved, thereby improving the heat transfer efficiency of the fins; secondly, the heat exchange tubes of the present invention adopt elliptical base tubes instead of round tubes, thereby reducing the flow resistance of the flue gas and increasing the heat exchange area; finally, compared with the sequential arrangement of the heat exchange tube bundles, the heat exchange tubes of the present invention adopt a diamond arrangement, which can improve the flow hysteresis caused by the sequential arrangement, while making the fin tube arrangement more compact.

[0016] Experiments have shown that the enhanced heat exchange effect on the flue gas side of the octagonal fin tube heat exchanger of the present invention is more obvious when the Reynolds number is less than 12500. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a schematic diagram of an octagonal fin tube with a rhombus arrangement as the base tube of the present invention.

[0018] Figure 2 This is a front view of an octagonal fin tube with a rhombus-shaped base tube according to the present invention.

[0019] Figure 3 It is a left side view of an octagonal fin tube with a rhombus arrangement as the base tube of the present invention.

[0020] Figure 4 The schematic diagram of the arrangement of the octagonal finned tubes with a rhombus arrangement is shown in FIG. DETAILED DESCRIPTION

[0021] The present invention is described in detail below in conjunction with the accompanying drawings:

[0022] In order to improve the heat exchange performance of the fin-tube heat exchanger and reduce the flow resistance loss on the flue gas side, the present invention provides an octagonal fin tube with a base tube arranged in a rhombus. An elliptical base tube is selected and arranged in a rhombus, and octagonal fins are used at the same time, which work synergistically to achieve the above purpose.

[0023] like Figure 1 to Figure 4 As shown, the base tube of the present invention adopts an octagonal fin tube arranged in a rhombus, including a plurality of heat exchange tubes. The heat exchange tube of the present invention is specifically an elliptical base tube 1. Compared with the traditional round tube, the elliptical base tube 1 can reduce the flow resistance of the flue gas and increase the heat exchange area. In the present invention, the flue gas flow direction is along the long axis direction of the cross section of the elliptical base tube 1.

[0024] The diamond arrangement of the present invention means that the elliptical base tubes 1 are arranged in rows and columns in the form of multiple rows and columns, and the four elliptical base tubes 1 between adjacent rows and columns are arranged in a diamond shape, that is, the centers of the four elliptical base tubes 1 are respectively located at the four vertices of a diamond. Compared with the traditional sequential arrangement, the diamond arrangement is not only more compact, but also can strengthen the disturbance of the working medium, so that the area of ​​slow flow at the tail of the base tube is reduced, thereby improving the flow hysteresis phenomenon.

[0025] The octagon of the present invention refers to an octagonal fin 2 connected to the outside of the elliptical base tube 1. The octagonal fin 2 is arranged perpendicular to the elliptical base tube 1 and is an octagon as a whole, with two opposite sides perpendicular to the direction of smoke flow. Along the direction of smoke flow, the octagonal fin 2 is divided into two mutually isolated parts, and the two parts are symmetrical about the direction of smoke flow. In the present invention, mutual isolation is interpreted in a narrow sense, which only means that the two parts of the octagonal fin 2 are not directly connected. In fact, each part is respectively connected to the outside of the same elliptical base tube 1. This is from Figure 1 , Figure 2 , Figure 4 The octagonal fin 2 has a slotted area similar to the single H-type fin, but the single H-type fin has a heat transfer deterioration area (i.e., the boundary) where the fin temperature is too high. For this reason, the octagonal fin 2 is used. The larger corners of the fin can effectively prevent the fin temperature from being too high. Therefore, the heat transfer deterioration area of ​​the corners is improved, thereby improving the heat transfer efficiency of the fin.

[0026] In the following description, for the convenience of description, the two parts obtained by dividing the octagonal fin 2 are named as the first part 21 and the second part 22, respectively. The first part 21 and the second part 22 are provided with a first empty slot 23, an elliptical base tube 1 and a second empty slot 24. Figure 2 As shown. Thus, a windward area 3 is formed on the windward side of the first part 21 and the second part 22, and a leeward area 4 is formed on the leeward side. The first part 21 and the second part 22 are symmetrical along the long axis of the cross section of the elliptical base tube 1, and both are hexagonal in shape (one side is concave to connect with the elliptical base tube 1).

[0027] As a preferred embodiment of the present invention, the performance of the heat exchanger with different elliptical base tube axial ratios (1:1 to 3:1) under the same Reynolds number conditions was compared. The results showed that the axial ratio of the elliptical base tube 1 was 2:1, and at this time, the comprehensive performance of the finned tube heat exchanger was optimal. When the axial ratio of the elliptical base tube changed from 1:1 (i.e., circular tube) to 3:1, the pressure drop of the finned tube bundle was significantly reduced, but as the axial ratio increased, the change in the short radius size of the elliptical base tube was no longer obvious, and the change in the flue gas flow cross-sectional area decreased, so the pressure drop reduction trend gradually slowed down. Compared with the circular tube, the pressure drop on the flue gas side of the heat exchanger was reduced by 42.5%, and the temperature distribution of the fins was more uniform.

[0028] As a preferred embodiment of the present invention, the ratio of the row spacing to the column spacing of the elliptical base tube 1 is 2:1, so that the fin tube heat exchanger has a better comprehensive heat exchange performance. The heat exchanger corresponding to this structure has a relatively high fin efficiency and a relatively small resistance loss, so it has a better comprehensive performance.

[0029] As a preferred embodiment of the present invention, the ratio of the outer fin side length of the octagonal fin 2 along the flow direction to the length of the semi-major axis of the cross section of the elliptical base tube 1 is 1:1, so that the fin-tube heat exchanger has a better comprehensive heat exchange performance. This is because under this structural condition, the heat exchanger has both good fin efficiency and pressure drop.

[0030] As a preferred embodiment of the present invention, the octagonal fin 2 has a regular shape to achieve better heat exchange performance. Specifically, every two of the eight sides are a parallel pair, and among the four pairs of sides, the first pair of sides is parallel to the direction of smoke flow, and the first empty slot 23 and the second empty slot 24 are located between the first pair of sides, and the smoke flows through the first empty slot 23 and the second empty slot 24 in sequence. The second pair of sides is perpendicular to the direction of smoke flow, and the sum of the angle between the third pair of sides and the direction of smoke flow and the angle between the fourth pair of sides and the direction of smoke flow is 180°. This regular shape is not only conducive to processing and manufacturing, but also can achieve a regular heat exchange effect.

[0031] As a preferred embodiment of the present invention, the sum of the lengths of the first pair of sides and the second pair of sides is defined as m, and the sum of the lengths of the third pair of sides and the fourth pair of sides is defined as n. When m:n=23: When m:a=46:27, where a is the length of the elliptical base tube 1, a better heat transfer effect is achieved. The reason is that when the value of m:n increases, the heat transfer area decreases, the disturbance effect on the fluid is more obvious, and the comprehensive performance coefficient is improved. However, there is a maximum value, that is, m:n=23: When m:a=46:27, the heat exchange effect is optimal.

[0032] As a preferred embodiment of the present invention, the diamond side length of the diamond arrangement structure is 110 mm. At this time, the heat exchanger has a good heat exchange-pump power ratio and heat exchange specific volume power. This is because the increase in the diamond side length increases the flow area of ​​the heat exchanger, and the flow rate of the fluid between the tubes decreases, which directly leads to a decrease in the heat transfer coefficient and pressure drop; in addition, the rear tube is gradually removed from the tail flow area of ​​the front tube, and the heat transfer performance and pressure drop of the rear tube increase, and gradually approach a single tube. When the diamond side length is 110 mm, the comprehensive performance of the heat exchanger is the best.

[0033] The flow and heat transfer performance of the heat exchanger under different structural parameters was studied by numerical simulation. The flue gas inlet temperature was 700K and the flow rate was 4.5-14.5 m·s -1 Based on the flue gas inlet velocity range and the outer diameter of the fin tube heat exchanger base tube, the calculated Re range is 8000-26000, which has reached the turbulent range. Therefore, the RNG k-ε turbulence model is used for calculation. The SIMPLE algorithm is used to process the coupling process between pressure and velocity, and the convection term adopts the second-order upwind discrete format. Based on this, the flue gas side convection heat transfer coefficient h and fin efficiency η of the heat exchanger under five groups of flow conditions are compared. f Within the parameter range studied, the fin efficiency increased by an average of 2.2%, and the flue gas side convective heat transfer coefficient increased by 46.0%, 41.1%, 27.2%, 25.9% and 25.0%, respectively. It can be seen that the flue gas side convective heat transfer coefficient increased by a maximum of 46.0%.

[0034] The enhanced heat exchange effect of the octagonal fin-tube heat exchanger of the present invention on the flue gas side is more obvious when the Reynolds number is less than 12500. This is because as the Reynolds number increases, the disturbance between the working fluids increases, thereby enhancing the heat exchange; but when the Reynolds number increases to a certain extent, the degree of disturbance between the working fluids gradually weakens, and the ability to enhance heat exchange by simply increasing the flow rate is limited.

Claims

1. A base tube adopts an octagonal fin tube arranged in a rhombus, characterized in that: It comprises a plurality of elliptical base tubes (1) arranged in rows and columns, wherein four adjacent elliptical base tubes (1) in the rows and columns are arranged in a rhombus shape; An octagonal fin (2) is vertically connected to the outside of each elliptical base tube (1); the smoke flow direction is perpendicular to two opposite sides of the octagonal fin (2); and along the smoke flow direction, the octagonal fin (2) is divided into two symmetrical and mutually isolated parts.

2. According to claim 1, the base tube is an octagonal fin tube arranged in a rhombus, characterized in that: The major axis of the elliptical base tube (1) is located on the symmetry axis of the two parts.

3. According to claim 1, the base tube is an octagonal fin tube arranged in a rhombus, characterized in that: The row direction is defined as the direction of smoke flow, and the direction perpendicular to the smoke flow is defined as the column direction. In the plurality of elliptical base tubes (1) arranged in rows and columns, the ratio of the row spacing to the column spacing is 2:

1.

4. According to claim 1, 2 or 3, the base tube is an octagonal fin tube arranged in a rhombus, characterized in that: The ratio of the major axis to the minor axis of the elliptical base tube (1) is 2:

1.

5. According to claim 1, the base tube is an octagonal fin tube arranged in a rhombus, characterized in that: In the octagonal fin (2), two opposite sides are parallel to the smoke flow direction, two opposite sides are perpendicular to the smoke flow direction, the angle between the two opposite sides and the smoke flow direction is an acute angle α, and the angle between the last two opposite sides and the smoke flow direction is an obtuse angle β, α+β=180°.

6. According to claim 5, the base tube is an octagonal fin tube arranged in a rhombus, characterized in that: In the octagonal fin (2), the sum of the lengths of the four sides parallel or perpendicular to the flue gas flow direction is m, and the sum of the lengths of the remaining four sides is n.

7. According to claim 6, the base tube is an octagonal fin tube arranged in a rhombus, characterized in that: m:a=46:27, wherein a is the length of the elliptical base tube (1).

8. The base tube according to claim 1, 2, 3, 5, 6 or 7 is an octagonal fin tube arranged in a rhombus, characterized in that: The side length of the rhombus is 110 mm.

9. Use of the octagonal fin tube with a rhombus-arranged base tube as claimed in any one of claims 1 to 8 in a flue gas heat exchanger.

10. The use according to claim 9, characterized in that: The flue gas heat exchanger is arranged on the flue gas side under the working condition where the Reynolds number is less than 12500.

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