Radiant tube

Abstract

The present invention provides a radiant tube having a heat transfer promoter with a simple structure and the ability to further improve heat transfer efficiency. The heat transfer promoter (4) has a main body (41) disposed on the center side of the pipe (1) and a plurality of protrusions (42) protruding from the main body (41) toward the inner wall surface (1a) of the pipe (1). Multiple protrusions (42) are formed on the outer periphery of the main body (41) in a manner arranged along the circumferential direction of the pipe (1). The multiple protrusions (42) are composed of multiple first protrusions (42a) and other second protrusions (42b). The front end of the first protrusion (42a) is opposed to the inner wall surface (1a) of the pipe (1) with a gap (ΔL). The number of first protrusions (42a) is set to be greater than the number of second protrusions (42b). When the ratio of the equivalent diameter (ΔL / Dt) of the gap relative to the portion of the pipe (1) in which the heat transfer promoter (4) is arranged is set to 100% as x [%), the following formula is satisfied: 0.3% <x<7%。

Description

Technical Field

[0001] This invention relates to a radiant tube having a heat transfer enhancer. Background Technology

[0002] A radiant tube includes a pipe forming the main body of the tube and a gas generating unit, such as a burner disposed at the inlet side of the pipe to generate combustion gases. The radiant tube indirectly heats an object outside the pipe through the radiant heat from the pipe heated by the combustion gases generated by the gas generating unit.

[0003] The radiant tube allows the combustion gases generated by the gas generator to flow along a gas flow path formed by the pipes. As a result, the pipes become hot due to heat transfer from the combustion gases. At this point, the radiant tube transfers heat from the combustion gases to the pipes. On the outlet side (downstream side) of the pipe, where the combustion gas temperature decreases, the radiant heat transfer decreases, and the surface temperature of the pipes drops. Therefore, to improve the heat transfer efficiency of the combustion gases to the pipes on the downstream side (outlet side) of the radiant tube and to increase the thermal utilization rate of the radiant tube, a heat transfer promoter is sometimes installed on the downstream side of the pipes.

[0004] For example, Patent Document 1 discloses a heat transfer promoter disposed in the rear half of the radiant tube's piping, with plate-shaped guide vanes forming a spiral flow path for the combustion gas as the structure of the heat transfer promoter. According to this technology, in the rear half of the radiant tube's piping, the combustion gas flows toward the pipe outlet while rotating in a spiral, thereby increasing the relative velocity between the pipe and the combustion gas, and thus increasing the convective heat transfer coefficient.

[0005] However, in the method described in Patent Document 1, the structure of the heat transfer promoter needs to be complex in order to make the combustion gas rotate in a spiral shape. Therefore, the manufacturing cost of the heat transfer promoter described in Patent Document 1 is high, requiring a cheaper heat transfer promoter.

[0006] In contrast, Patent Document 2 discloses a heat transfer promoter with a cross-shaped cross-section. This heat transfer promoter has four plate-like partitions, and multiple heat transfer promoters with a cross-shaped cross-section are embedded in series within a pipe, staggered by 45 degrees each time. According to this structure, since multiple heat transfer promoters are embedded in the pipe, a spiral airflow can be formed inexpensively. However, the heat transfer efficiency of the cross-shaped heat transfer promoter described in Patent Document 2 is not high enough, and further improvement is required.

[0007] Furthermore, Patent Document 3 proposes a star-shaped heat transfer promoter that specifies the ratio of the cross-sectional area of ​​the heat transfer promoter to the cross-sectional area of ​​the radiant tube, and the ratio of the perimeter of the heat transfer promoter cross-section to the perimeter of the radiant tube cross-section, in order to improve heat transfer efficiency and suppress the increase in pressure loss caused by the insertion of the heat transfer promoter, and can be manufactured inexpensively.

[0008] Existing technical documents

[0009] Patent documents

[0010] Patent Document 1: Japanese Patent Application Publication No. 57-112694

[0011] Patent Document 2: Japanese Utility Model Application Publication No. 63-173613

[0012] Patent Document 3: Japanese Patent Application Publication No. 2017-83127 Summary of the Invention

[0013] The problem that the invention aims to solve

[0014] Patent Document 3 aims to improve the heat transfer coefficient by reducing the flow path area. In this technology, the gas velocity along the flow direction of the pipe is increased. However, in this technology, since the front end of the protrusion constituting the heat transfer promoter contacts the inner wall surface of the pipe, the flow path cross-sections formed between adjacent protrusions become disconnected, suppressing the flow in the swirling direction.

[0015] That is, in Patent Document 3, although the heat transfer promoter has a simple shape and can be manufactured inexpensively, a large heat transfer coefficient cannot be obtained due to the truncation of each flow path cross-section. In addition, in Patent Document 3, when considering the actual use of radiant tubes, the amount of deformation due to thermal deformation of the radiant tube and the heat transfer promoter also needs to be taken into account.

[0016] The present invention was made in view of the above-mentioned problems, and its object is to provide a radiant tube with a simple structure and a heat transfer promoter that can further improve the heat transfer efficiency.

[0017] Methods for solving problems

[0018] The inventors conducted numerical simulations comparing heat transfer efficiency based on the waste heat reduction rate of the radiant tube, using a heat transfer promoter with multiple protrusions as shown in Patent Document 3. Furthermore, the inventors evaluated the pressure loss caused by inserting the heat transfer promoter into the pipe in this experiment. Based on the results of these numerical simulations, the inventors discovered that maintaining a specific distance (gap ΔL) between the inner surface of the radiant tube and the protruding tips of the heat transfer promoter is effective in improving heat transfer efficiency in a heat transfer promoter with multiple protrusions on its outer periphery.

[0019] Furthermore, the inventors have observed that it is preferable to simply place the heat transfer promoter within the pipeline while forming the aforementioned gap ΔL. Moreover, the inventors have observed that in the above structure, the pressure loss is similarly small to that of the heat transfer promoter described in Patent Document 3, and the heat transfer promoter can be manufactured inexpensively.

[0020] Here, the term "heat transfer efficiency" in this invention refers to the efficiency of heat transfer to the radiant tube from the heat originating from the combustion gases through the pipes, and the waste heat discharged as sensible heat from the exhaust gas. If the amount of waste heat discharged without heat transfer from the exhaust gas to the pipes decreases, the heat transfer efficiency increases.

[0021] Furthermore, to solve the problem, one aspect of the present invention is a radiant tube having a pipe heated by a fluid gas flowing within it, and one or more heat transfer promoters arranged along the axis of the pipe within the pipe. The key point is that each heat transfer promoter has a main body portion disposed on the central side of the pipe, and a plurality of protrusions protruding from the main body portion toward the inner wall surface of the pipe. These protrusions are formed on the outer periphery of the main body portion in a manner arranged along the circumferential direction of the pipe. Each protrusion is composed of a plurality of first protrusions and other second protrusions. The front end of each first protrusion faces the inner wall surface of the pipe with a gap ΔL. The number of first protrusions is set to be greater than the number of second protrusions. When the ratio (ΔL / Dt) of the gap ΔL to the equivalent diameter Dt of the pipe portion in which the heat transfer promoters are disposed is set to 100% as x [%), the following formula (1) is satisfied.

[0022] 0.3% <x<7%···(1)。

[0023] Invention Effects

[0024] According to the method of the present invention, it is possible to provide a radiant tube with a heat transfer promoter that improves heat transfer efficiency and can be manufactured inexpensively. Attached Figure Description

[0025] [ Figure 1 [This is a diagram used to illustrate the configuration of a radiant tube based on an embodiment of the present invention.]

[0026] [ Figure 2 ] is used for the purpose of Figure 1 The diagram illustrates the cross-section of the pipe and the heat transfer promoter of this embodiment, cut at section AA′.

[0027] [ Figure 3 This is a schematic diagram of the swirling flow R formed near the inner wall surface when viewed from the axial direction of the pipeline.

[0028] [ Figure 4 The figures shown illustrate an example of a cavity being formed in a heat transfer enhancer. (a) is a plan view taken from the direction of gas flow, and (b) is a B-B′ cross-sectional view of (a).

[0029] [ Figure 5 [Enlarged view illustrating an example where a notch is provided in the second protrusion.]

[0030] [ Figure 6 [This is a diagram illustrating the heat transfer enhancer used in Example 1 (a previous example).]

[0031] [ Figure 7 [This is a diagram illustrating the heat transfer enhancer used in Example 2.]

[0032] [ Figure 8 [This is a diagram used to illustrate the heat transfer enhancer in Example 3.]

[0033] [ Figure 9 [This is a diagram used to illustrate the heat transfer enhancer in Example 4.]

[0034] [ Figure 10 [Figure showing the results of verifying the effects of the present invention]

[0035] [ Figure 11 [This is a graph showing the results of verifying the effect of gap ΔL.]

[0036] [ Figure 12 This is a diagram illustrating the results of verifying the effects of different pipe cross-sections. Detailed Implementation

[0037] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0038] The accompanying drawings are schematic, and the size, length ratio, etc., of the components differ from reality. Furthermore, the embodiments shown below exemplify the configuration used to concretize the technical concept of the present invention; the materials, shapes, and structures of the constituent components in the technical concept of the present invention are not limited to those described below. Various modifications can be made to the technical concept of the present invention within the technical scope defined by the claims.

[0039] (constitute)

[0040] like Figure 1As shown, the radiant tube 100 of this embodiment includes: a conduit 1 for supplying combustion gas (hereinafter simply referred to as gas), a radiant tube burner 2 for generating combustion gas within the conduit 1, and heat transfer promoters 4. The radiant tube 100 may include various waste heat recovery devices 5 such as heat exchangers and regenerative burners, as well as other known components, or it may not include such components. A heat exchanger is a device that performs heat exchange between the combustion gas flowing through the radiant tube 100 and the combustion air. In this embodiment, an example is shown where multiple heat transfer promoters 4 are arranged coaxially side-by-side, and the protrusions 42 of these multiple heat transfer promoters 4 are arranged side-by-side along the conduit.

[0041] (Pipeline 1)

[0042] like Figure 1 As shown, the pipe 1 in this embodiment is formed into a roughly W-shaped zigzag shape when viewed from the side. That is, the pipe 1 has four straight pipe sections 1A to 1D arranged side by side, and the ends of adjacent straight pipe sections 1A to 1D are connected to each other by curved pipe sections 1E to 1G that extend in an arc shape to form a gas flow path. Reference numeral 6 is a partition member to prevent narrowing between adjacent straight pipe sections. Reference numeral 7 is a support member supported on the protrusion 3A to prevent the pipe 1 from shifting downward.

[0043] In addition, by fixing the inlet side of the upstream straight pipe section 1A and the outlet of the downstream straight pipe section 1D to the furnace wall 3, the pipe 1 is supported on the furnace wall 3.

[0044] Furthermore, the heated body is indirectly heated by the radiant tube 100 by being conveyed along the arrangement direction of the plurality of straight tube sections 1A to 1D. Figure 2 In the example, the direction of transport of the heated body is indicated by the mark 50. Figure 1 The example shows the case where multiple straight tube sections 1A to 1D are arranged in a vertical direction, but the arrangement of multiple straight tube sections 1A to 1D can also be in a horizontal direction.

[0045] Here, the shape of the radiator 100 is not limited to a roughly W-shaped shape when viewed from the side. The shape of the radiator 100 can also be other shapes such as U-shaped or straight.

[0046] In this embodiment, the pipe 1 has at least one straight pipe section 1D with a heat transfer promoter 4, and the opening cross-section is as follows: Figure 2 As shown, the example illustrates the case of an ellipse with different minor and major axes. It should be noted that, as... Figure 2As shown, it is preferable to arrange the pipe with the major axis facing upwards and downwards. When the opening cross-section of the straight pipe section 1D is an elliptical shape with different minor and major axes, it is preferable that the entire pipe 1 is an elliptical shape with different minor and major axes. However, the present invention can be applied even if the opening cross-section of the pipe 1 is a circle or a rectangle or other cross-sectional shapes.

[0047] (Radiant tube burner 2)

[0048] The gas generating section 2A of the radiant tube burner 2 is disposed on the inlet side of the pipeline 1. The gas generating section 2A injects fuel gas and combustion air along the extension direction of the pipeline 1 to generate combustion gas. The generated combustion gas flows from the inlet side to the outlet side in the pipeline 1 and transfers heat to the pipeline 1.

[0049] The gas generating unit 2A is only required to generate combustion gas that flows in the pipeline 1; there are no particular limitations, and any known burner can be used.

[0050] (Heat transfer enhancer 4)

[0051] The heat transfer enhancer 4 is positioned closer to the outlet side than the middle of the extension direction of the radiant tube 100 within the pipe 1. The heat transfer enhancer 4 is installed within the pipe 1 to improve the heat transfer efficiency of the radiant tube 100.

[0052] Next, the heat transfer promoter 4 of this embodiment will be described.

[0053] In this embodiment, a plurality of heat transfer promoters 4 are arranged coaxially along the axis of the pipe 1. Furthermore, the plurality of heat transfer promoters 4 appropriately adjust the waste heat reduction rate and pressure loss of the radiant tube 100.

[0054] Each heat transfer promoter 4 has a main body 41 located at the center side of the cross section of the pipe 1 (the axial side of the pipe 1), and a plurality of protrusions 42 that are integral with the main body 41 and protrude from the main body 41 toward the inner wall surface 1a of the pipe 1.

[0055] Multiple protrusions 42 are integrally formed on the outer periphery of the main body 41 in a manner arranged along the circumferential direction of the pipe 1. Furthermore, each heat transfer promoter 4 is disposed within the pipe 1 such that the protrusions 42 of each heat transfer promoter 4 are aligned in the long side direction of the pipe 1. Preferably, the heat transfer promoters 4 are disposed in a manner where adjacent heat transfer promoters 4 abut against each other.

[0056] Each protrusion 42 protrudes radially outward from the main body 41 toward the pipe 1. Viewed axially from the pipe 1, as... Figure 2As shown, the shape becomes such that the width along the circumferential direction of the pipe 1 decreases the further away from the main body 41 (the closer to the wall of the pipe 1). However, each protrusion 42 is configured to have the same shape along the axial direction of the pipe 1. As a result, a space is formed between two adjacent protrusions 42 in the circumferential direction of the pipe 1, where the distance between the two adjacent protrusions 42 increases the further away from the main body 41. It should be noted that the outline of the cross-sectional shape of each protrusion 42 may not be a straight line.

[0057] Furthermore, the multiple protrusions 42 of the heat transfer promoter 4 are classified into multiple first protrusions 42a and second protrusions 42b. The front end of the first protrusion 42a does not contact the inner wall surface 1a of the pipe 1, and the front end of the first protrusion 42a is arranged opposite to the inner wall surface 1a of the pipe 1 in the radial direction of the pipe 1 with a gap ΔL.

[0058] On the other hand, in this embodiment, the front end of the protrusion 42 of the second protrusion 42b contacts the inner wall surface 1a of the pipe 1. In this case, the heat transfer promoter 4 can be positioned within the pipe 1 (positioned in the direction perpendicular to the axis of the pipe 1) by means of the second protrusion 42b. It should be noted that, in this case, the number of second protrusions 42b is preferably two or more.

[0059] However, as long as the heat transfer promoter 4 can be positioned in the pipe 1 by other means (positioning in the direction perpendicular to the axis of the pipe 1), it is not necessary to make the second protrusion 42b contact the inner wall surface 1a of the pipe 1.

[0060] Preferably, the number of second protrusions 42b is relatively small. In this embodiment, the number of second protrusions 42b is less than the number of first protrusions 42a. Preferably, the number of second protrusions 42b is less than 1 / 3 of the number of first protrusions 42a, more preferably less than 1 / 4. However, in order to use the second protrusions 42b for positioning the heat transfer promoter 4 within the pipe 1, the number of second protrusions 42b needs to be two or more. Figure 2 In the example shown, there are two second protrusions 42b. The heat transfer promoter 4 is supported on the pipe 1 by its own weight through the two second protrusions 42b located on the lower side.

[0061] In addition, in this embodiment, the gap ΔL between the front end of the first protrusion 42a and the inner wall surface 1a of the pipe 1 opposite to the front end is defined as follows.

[0062] That is, when the ratio of the gap ΔL to the equivalent diameter Dt of the straight pipe section 1D of the pipeline 1 with the heat transfer promoter 4 is set to 100% as x, the gap ΔL is set to satisfy the following formula (1).

[0063] 0.3% <x<7%···(1)

[0064] Furthermore, it is more preferable to satisfy the following equation (2).

[0065] 0.5% <x<4.5%···(2)

[0066] More specifically, an example of the heat transfer promoter 4 in this embodiment will be described.

[0067] As described above, each heat transfer promoting body 4 is composed of a main body 41 and a plurality of protrusions 42 protruding from the outer periphery of the main body 41 toward the inner wall surface 1a.

[0068] like Figure 2 As shown, the main body 41 is constructed of a columnar shape having an elliptical cross-section similar to or approximating the elliptical cross-section of the opening of the pipe 1. Furthermore, the main body 41 is arranged such that the axis (long side direction) of the columnar shape is parallel to the axis of the pipe 1.

[0069] By utilizing the area of ​​the main body 41 that restricts the flow of gas within the pipe 1, the flow velocity of the gas flowing on the outer periphery (outer diameter side) of the main body 41 increases.

[0070] Furthermore, by providing multiple protrusions 42 on the outer periphery of the main body 41, the gas flowing around the outer periphery of the main body 41 is divided into multiple parts along the circumferential direction by the protrusions 42, and the gas flows in the space between adjacent protrusions 42 respectively.

[0071] In this embodiment, the protrusion 42 has a roughly triangular cross-section (triangular when viewed from the axial direction of the pipe 1), and its base is integrally formed with the outer periphery of the main body 41. In addition, the protrusion 42 has a thick plate shape with the same cross-sectional shape in the direction parallel to the axis of the pipe 1 along its long side (rectangular when viewed from the side).

[0072] Between adjacent protrusions 42 along the circumferential direction of pipe 1 (viewed from the axial direction of pipe 1), such as Figure 2 As shown, a space S with a cross-sectional triangular shape is formed, which becomes wider the further away from the main body 41.

[0073] With the multiple protrusions 42, the gas flowing around the outer periphery of the main body 41 is less likely to become a swirling flow, and flows laminarly along the axis of the tube 1 along the space S. That is, by providing multiple protrusions 42, separate gas flow paths are formed in the circumferential direction between the protrusions 42, allowing the gas to flow in each gas flow path.

[0074] exist Figure 2In this configuration, the two lower protrusions 42 are made longer than the other protrusions 42, thus forming a second protrusion 42b. The front ends of these two protrusions 42b abut against the lower surface of the inner wall of the pipe 1, thereby supporting the heat transfer facilitator 4 in a predetermined position within the pipe 1. It should be noted that when the uppermost protrusion 42 also abuts against the inner wall of the pipe 1 as a second protrusion 42b, the heat transfer facilitator 4 is stably positioned within the pipe 1. However, it is preferable to have a smaller number of second protrusions 42b.

[0075] Here, as Figure 2 As shown, it is preferable that the center of gravity P2 of the heat transfer promoter 4 disposed in the pipe 1 is aligned with the center of gravity P1 of the opening section of the pipe 1 by means of multiple second protrusions 42b. If the centers of gravity P1 and P2 of the two 1 and 4 are aligned, the center of gravity P2 of the heat transfer promoter 4 is aligned with the center of gravity of the section of the radiant tube 100 perpendicular to the combustion flow direction, which can suppress the displacement of the heat transfer promoter 4 in the direction of gravity and eliminate the reduction in heat transfer performance. It should be noted that aligning the center of gravity of the heat transfer promoter 4 with the center of gravity of the section of the radiant tube 100 perpendicular to the combustion flow direction is particularly effective when the radiant tube has an elliptical shape.

[0076] Furthermore, in this embodiment, in addition to the protrusion 42 that constitutes the second protrusion 42b, a first protrusion 42a is constituted, and the lengths of the first and second protrusions and the size of the main body 41 are set so that a gap ΔL is formed between the front ends of the plurality of first protrusions 42a and the inner surface of the pipe 1.

[0077] The gap ΔL satisfies the condition of equation (1) above.

[0078] (effect)

[0079] Next, the function of the heat transfer promoter 4 in this embodiment will be explained.

[0080] By utilizing the area of ​​the main body 41 that restricts the flow of gas within the pipe 1, the flow velocity of the gas flowing on the outer periphery (outer diameter side) of the main body 41 increases. In this embodiment, by aligning or approximating the centroid of the cross-section of the main body 41 with or near the centroid of the cross-section of the pipe 1, the distribution of the gas flowing on the outer periphery of the main body 41 becomes more uniform.

[0081] Furthermore, multiple protrusions 42 divide the space around the main body 41 into multiple spaces along the circumferential direction of the pipe 1. That is, independent gas flow paths are formed between adjacent protrusions 42, allowing gas to flow in each gas flow path.

[0082] Here, when the ratio of the cross-sectional area of ​​the heat transfer promoter 4 to the opening cross-sectional area of ​​the pipe 1 section where the heat transfer promoter 4 is arranged is set as A, and the ratio of the perimeter of the cross-section of the heat transfer promoter 4 to the perimeter of the opening cross-section of the pipe 1 section where the heat transfer promoter 4 is arranged is set as B, the heat transfer promoter 4 preferably satisfies the following equations (3) and (4) relative to the pipe 1.

[0083] A≤0.53···(3)

[0084] (1-A) －4 / 5 ×AB≥2.48···(4)

[0085] Equations (3) and (4) will be explained.

[0086] Here, the area of ​​the opening section formed by the installation portion of pipe 1 is defined as α. Furthermore, the cross-sectional area of ​​the heat transfer facilitator 4 is defined as β. In this case, A is (β / α). Additionally, the perimeter of the opening section of the installation portion of pipe 1 (the inner perimeter of pipe 1) is defined as c. Furthermore, the perimeter of the heat transfer facilitator 4 is defined as d. In this case, B is (d / c).

[0087] Furthermore, in the heat transfer promoter 4 of this embodiment, A and B are preferably designed to satisfy the above-described formulas (3) and (4). The inventors conducted research and found that if A exceeds 0.53, the pressure loss is large, significantly inhibiting the flow of combustion gases. Therefore, as specified in formula (3), A is preferably 0.53 or less. More preferably, A is 0.46 or less.

[0088] Furthermore, the above formula (4) was discovered by the inventors of this application based on general convective heat transfer theory, considering that if the cross-sectional area of ​​the heat transfer promoter 4 is reduced, the gas flow rate slows down, the effect of convective heat transfer weakens, and the heat transfer area is proportional to the outer perimeter of the heat transfer promoter 4. Moreover, the inventors of this application confirmed that the desired heat transfer efficiency can be obtained by having the left side of formula (4) be 2.48 or higher.

[0089] In addition, one feature of this embodiment is that a predetermined gap ΔL is provided between the first protrusion 42a and the inner wall surface 1a of the pipe 1.

[0090] By setting the aforementioned gap ΔL near the inner wall surface 1a of pipe 1, such as Figure 3 As shown, a swirling flow (R) of the combustion flow is formed near the inner wall of pipe 1 in the direction of circumference.

[0091] Here, if the velocity of the combustion flow in the direction of flow is set as Vx, and the velocity of the cross section perpendicular to the flow direction is set as Vy and Vz, then the velocity V of the combustion flow can be expressed by the following equation (5).

[0092] V = √(Vx) 2 +Vy 2 +Vz 2 (5)

[0093] As can be seen from equation (5), the increased velocity V increases the amount of swirling flow R formed near the inner wall of pipe 1, and in this embodiment, the heat transfer efficiency is further improved.

[0094] Furthermore, the swirling flow R becomes stronger, especially when the flow transitions from a curved surface to a straight surface. The part where the flow transitions from a curved surface to a straight surface is... Figure 1 For example, in the transition section from the curved section 1G to the straight section 1D, in Figure 1 Stagnation easily occurs in the upper space near the A-A′ section position. This is due to the flow deviation caused by the stripping of the combustion flow on the curved surface. Therefore, in heat transfer promoters where there is no gap ΔL based solely on the present invention or where the gap is smaller than the gap ΔL based on the present invention, different amounts of combustion gas flow in the divided spaces S, resulting in reduced heat transfer efficiency. On the other hand, by setting an appropriate gap ΔL, the flow rates in the multiple spaces S divided by the protrusion 42 naturally become equal. In this embodiment, the protrusion 42 that divides the gas flow has a shape that becomes narrower the closer it is to the inner wall surface 1a of the pipe 1. Therefore, as Figure 3 As shown, swirling flow is also easily generated in each space S divided by the protrusion 42, and the heat transfer efficiency from the combustion flow to the heat transfer promoter increases.

[0095] Furthermore, in this embodiment, the cross-section of each space S divided by the protrusion 42 is wider the closer it is to the inner wall surface 1a of the pipe 1, and the less influence of the wall surface, resulting in relatively low flow resistance. Therefore, the gas flowing between the protrusions 42 flows further outward than towards the center. As a result, more gas contributes to the swirling flow R formed near the inner wall surface 1a of the pipe 1.

[0096] In particular, in this embodiment, the shape of the protrusion 42 is not a rectangular cross-section, but rather a roughly triangular shape whose circumferential width narrows as it approaches the inner wall of the pipe 1. Therefore, for the cross-section of each space S divided by the protrusion 42, compared to the case where the protrusion 42 is rectangular, the circumferential expansion per unit length can be set to be larger as it moves radially outward. As a result, the gas flowing between the protrusions 42 flows further outward than towards the center, thereby facilitating the formation of a swirling flow R near the inner wall surface 1a of the pipe 1.

[0097] It should be noted that the protrusion 42 is preferably in a shape in which the roots of adjacent protrusions 42 are connected to each other (the part on the side of the main body) (a continuous shape).

[0098] Furthermore, if the cross-section of the space S formed between the protrusions 42 is set to a triangular shape, the heat transfer promoter 4, the combustion gas, and the wall of the pipe 1 will always be side by side, so it will not hinder the radiative heat transfer from the combustion gas, which is the heat source, to the pipe.

[0099] Here, in order to generate the aforementioned swirling flow R near the inner wall surface 1a of the pipe 1, a specified gap ΔL is required between the protrusion 42 of the heat transfer promoter 4 and the inner wall surface 1a of the pipe 1. The specified gap ΔL refers to the gap width or more of the region near the wall surface, which is called the viscous sublayer, where the velocity of the combustion gas is close to 0.

[0100] In the flow within a typical industrial radiant tube, the width of the viscous sublayer is greater than 0.3% of the equivalent diameter, and if it is 0.5% of the equivalent diameter, it is well within the transition region.

[0101] Therefore, in this embodiment, the 100th percentile x of the ratio (ΔL / Dt) of the gap ΔL to the equivalent diameter Dt of the portion of the pipe 1 in which the heat transfer promoter 4 is disposed is set to be greater than 0.3%, preferably greater than 0.5%.

[0102] On the other hand, if the gap ΔL is too wide, the heat transfer area, especially the convective heat transfer area from the combustion flow to the heat transfer promoter, becomes smaller. Therefore, the aforementioned x is set to be less than 7%, preferably less than 4.5%.

[0103] Here, any known material can be used as the material constituting the heat transfer promoter 4. For example, refractory insulating bricks, heat-resistant metals, ceramics, castables, etc. can be used as this material. In order to reduce manufacturing costs and suppress deformation of the radiant tube 100 caused by the weight of the heat transfer promoter 4, inexpensive and lightweight refractory insulating bricks are preferred.

[0104] As explained above, in this embodiment, the heat transfer promoter 4 is designed with the specific shape described above. This reduces the cross-sectional area of ​​the flow path, thereby increasing the flow velocity of the combustion gas. Furthermore, in this embodiment, the heat transfer area of ​​the heat transfer promoter 4 can be increased without suppressing the swirling flow R of the combustion gas near the inner wall surface, thus improving heat transfer efficiency. Furthermore, the heat transfer promoter 4 of this embodiment has a simple shape, making it inexpensive to manufacture. Additionally, by inserting the heat transfer promoter 4 into the radiant tube 100, the combustion gas can be agitated in the same way as in the prior art. In the above description, a heat transfer promoter 4 with a uniform cross-section along the flow path was used; however, by making the upstream side of the exhaust gas tapered along the flow path, the agitation of the combustion gas can be further promoted, and the heat transfer efficiency can be further improved.

[0105] [Regarding equivalent diameter]

[0106] The equivalent diameter Dt can be calculated from the circumference L of the inner wall and the cross-sectional area Sa of the opening of pipe 1 perpendicular to the flow direction using the following formula.

[0107] Dt=(4·Sa) / L

[0108] [Approximate method for finding the viscous sublayer in circular pipe flow]

[0109] The coefficient of friction f of the pipe is expressed by the following formula according to the Courbert formula.

[0110]

[0111] Here, ε: surface roughness, Re: Reynolds number (obtained by (u·Dt) / v).

[0112] Furthermore, if the pressure drop per unit length on the cross-section of the circular tube is denoted as ΔP, it can be expressed as ΔP = 1 / 2(f·(1 / Dt)·ρ·u) 2 ).

[0113] The shear stress τ0 generated per unit length on the inner wall surface 1a of pipe 1 is equal to the pressure drop ΔP, and therefore can be described as follows.

[0114] Sa·ΔP=L·τ0

[0115] τ0=(Sa / (2·I·Dt))f·ρ·u 2

[0116] Friction speed u * It can be manifested as

[0117] The range of the viscous sublayer is u * (y / v) < 5.

[0118] Therefore, in this embodiment, the gap ΔL only needs to be larger than the viscous sublayer, so it can be set as follows.

[0119]

[0120] (Modified Example)

[0121] (1) The cross-sectional shape of the front end of the protrusion 42 is preferably a chamfered shape or a curved surface shape such as an arc.

[0122] The protrusion in the heat transfer promoter 4 is located near the inner wall surface 1a of the pipe 1. By making its front end chamfered or similar shape to blunt the outline, the area of ​​the opposing part of the protrusion that is opposite to the inner wall surface 1a of the pipe 1 is made to function.

[0123] Therefore, the efficiency of heat transfer from the combustion gas to the heat transfer promoter 4 is improved, as the heat is transferred from the front end of the protrusion 42 near the inner wall surface 1a of the pipe 1 to the inner wall surface 1a of the pipe 1. That is, the heat transfer area from the heat transfer promoter 4 to the pipe 1 is increased, further demonstrating the heat transfer promotion effect.

[0124] (2) Heat transfer enhancer 4, for example, Figure 4 As shown in (b), the interior is a cavity that opens on the side along the direction of movement of the fluid flowing in pipe 1.

[0125] According to this structure, the heat transfer area of ​​the heat transfer promoter 4 can be maintained at a large extent, and the heat transfer promoter 4 can be made lightweight.

[0126] (3) As described above, the opening section of the part of the pipeline 1 in which the heat transfer promoter 4 is configured can also be set as an elliptical shape with different lengths of the minor axis and the major axis, with the major axis configured in the up and down direction.

[0127] The atmosphere in which the radiant tube 100 is configured is a high-temperature atmosphere, and a heat load is applied to the pipe 1. However, in this modified example, the rigidity of the pipe 1 is increased, and deformation of the pipe 1 can be suppressed even if the load or heat load of the heat transfer promoter 4 is applied to the pipe 1. This allows indirect heating from the radiant tube 100 to the heated body to be performed stably over a longer period of time.

[0128] (4) The number of the first protrusions 42a is preferably 8 or more and 25 or less. The more protrusions 42a there are, the more flow paths are formed on the outer periphery of the main body 41, and the easier it is to adjust the axial flow of the circumferential pipe 1. However, if there are too many, the flow path resistance may become high, so it is preferable to have 25 or less.

[0129] (5) In addition, it is preferable to arrange one or more first protrusions 42a between two adjacent second protrusions 42b.

[0130] It can suppress the reduction of the generation sites of the circumferential swirling flow R.

[0131] It should be noted that it can also be formed at the midpoint of the long side relative to the front end of the second protrusion 42b that contacts the surface of pipe 1. Figure 5 Such a notch 42Ba reduces the inhibition of the swirling flow R by the second protrusion 42b. The distance ΔL1 between the notch 42Ba and the inner wall surface 1a of the pipe 1 is set to be within the same range as the distance between the gap ΔL and the inner wall surface 1a. That is, it is preferably set to satisfy an equation equivalent to the above equation (1).

[0132] (6) The heated body is conveyed along the arrangement direction of multiple pipes 1A to 1D and indirectly heated by the radiant tube 100. It should be noted that when the cross-section of pipe 1 is elliptical, the heating efficiency is good when the major axis is set to the arrangement direction of pipe 1.

[0133] Preferably, the area of ​​the space between the protrusions 42 located on the side opposite to the heated body is set to be relatively larger than the area of ​​the space between the protrusions 42 located at other positions. For example, the pipe 1 is divided into four regions by two straight lines obtained by tilting the minor axis of the ellipse at ±45 degrees around the center of the ellipse. The area of ​​the space between the protrusions 42 located in each region is set such that the total area of ​​the space in the region located on the side opposite to the heated body (the region including the minor axis in the ellipse) is relatively larger than the total area of ​​the space in the other regions.

[0134] (Effect)

[0135] This implementation method achieves the following effects.

[0136] (1) In this embodiment, the radiant tube 100 includes a pipe 1 heated by a fluid gas flowing in the pipe 1, and one or more heat transfer promoters 4 arranged along the axis of the pipe 1 within the pipe 1. Each heat transfer promoter 4 includes a main body 41 disposed on the center side of the pipe 1 and a plurality of protrusions 42 protruding from the main body 41 toward the inner wall surface 1a of the pipe 1. The plurality of protrusions 42 are formed on the outer side of the main body 41 in a manner arranged along the circumferential direction of the pipe 1. In the Zhou, the multiple protrusions 42 are composed of multiple first protrusions 42a and other second protrusions 42b. The front end of the first protrusion 42a is opposite to the inner wall surface 1a of the pipe 1 with a gap ΔL. The number of first protrusions 42a is set to be more than the number of second protrusions 42b. When the ratio of the gap ΔL to the equivalent diameter Dt of the portion of the pipe 1 in which the heat transfer promoter 4 is arranged is set to 100% (ΔL / Dt), the following formula is satisfied.

[0137] 0.3% <x<7%

[0138] Based on this structure, a radiant tube 100 can be provided having a heat transfer promoter 4 that can improve heat transfer efficiency and be manufactured inexpensively.

[0139] In particular, according to this structure, even though the heat transfer promoter 4 is a simple structure, it is easy to form a swirling flow R that facilitates heat transfer near the inner wall surface 1a of the pipe 1, resulting in improved heat transfer efficiency.

[0140] (2) In this embodiment, the heat transfer promoter 4 is positioned relative to the pipe 1 by the front end of the second protrusion 42b abutting against the inner wall surface 1a of the pipe 1. In this case, the number of the second protrusions 42b is 2 or more.

[0141] According to this structure, a gap ΔL can be formed between the first protrusion 42a and the inner wall surface 1a, and the heat transfer promoter 4 can be easily disposed in the pipe 1.

[0142] The front end of the second protrusion 42b may not abut against the inner wall surface 1a of the pipe 1. In this case, the gap between the front end of the second protrusion 42b and the inner wall surface 1a of the pipe 1 may not satisfy the gap ΔL.

[0143] (3) In this embodiment, the heat transfer promoter 4 is arranged such that the center of gravity P2 of the heat transfer promoter 4 is consistent with the center of gravity P1 of the opening section of the pipe 1.

[0144] By arranging the heat transfer promoter 4 in a manner where the centers of gravity of both are aligned, the center of gravity of the heat transfer promoter 4 is aligned with the center of gravity of the cross section of the radiant tube 100 perpendicular to the combustion flow direction, which can suppress the offset of the heat transfer promoter 4 in the direction of gravity and eliminate the reduction in heat transfer performance.

[0145] (4) In this embodiment, the cross-sectional shape of each protrusion 42 is such that the width of the protrusion 42 is smaller along the circumferential direction of the pipe 1 as it moves further away from the main body 41 in the radial direction of the pipe 1. A space is formed between two adjacent protrusions 42 in the circumferential direction of the pipe 1, and the distance between two adjacent protrusions 42 is wider as it moves further away from the main body 41.

[0146] According to this structure, even if a space is formed between the two protrusions 42, the distance between the two adjacent protrusions 42 is wider the further away from the main body 41, the airflow will flow further to the outer periphery compared to the case where the protrusions 42 are plate-shaped. This allows for the more reliable formation of a swirling flow R formed by the gap ΔL at the front end of the protrusions 42, resulting in further improved heat transfer efficiency.

[0147] (5) In this embodiment, the front end of the protrusion 42 is chamfered or curved.

[0148] According to this structure, the heat transfer efficiency from the protrusion 42 to the pipe 1 is further improved.

[0149] (6) The interior of the heat transfer promoter 4 is a cavity, which can be a shape in which the surface opposite to the direction of movement of the fluid flowing in the pipe 1 is closed.

[0150] Based on this structure, the heat transfer promoter 4 can be made lighter, and the deformation of the pipeline 1 caused by heat load can be further suppressed.

[0151] (7) In this embodiment, the opening cross-section of the pipe 1 portion equipped with the heat transfer promoter 4 is elliptical. The shortest minor axis of the ellipse and the major axis, which is orthogonal to the minor axis, are different in size. Preferably, the major axis of the ellipse faces the vertical direction.

[0152] According to this structure, the rigidity of the pipe 1 is improved, further suppressing the deformation of the pipe 1 caused by heat load, and further improving the heat transfer efficiency of the heat transfer promoter 4 in this embodiment.

[0153] For an ellipse, for example, (major axis Lb / minor axis La) is set to be greater than 1.1 and less than 1.6.

[0154] (8) Preferably, the cross-sectional shape of each heat transfer promoter 4 in the long side direction is the same, the shape of multiple heat transfer promoters 4 is the same, and the multiple heat transfer promoters 4 are arranged coaxially with the positions of their front ends side by side in the axial direction.

[0155] In this case, the swirling flow R can be generated more reliably only near the inner wall surface 1a of the pipe 1, and even the heat transfer promoter 4 with a simple structure can further improve the heat transfer efficiency.

[0156] [Example]

[0157] The following describes an embodiment based on the implementation method.

[0158] In this example, the heat transfer enhancer 4 used in the radiant tube 100 was evaluated using a combustion heat transfer simulation based on the following finite volume method.

[0159] (i) Pipeline 1

[0160] The shape of the extension direction of pipe 1 is as follows: Figure 1 As shown in the W shape, the opening cross-section of pipe 1 is an elliptical shape with a major axis of 236 mm and a minor axis of 188 mm. In addition, the total length of pipe 1 is set to 8900 mm.

[0161] (ii) Gas generating section 2A

[0162] As the gas generating unit 2A, a burner is used. The fuel used is a substance refined from the gas produced during the dry distillation of coal in a coke oven.

[0163] (iii) Heat transfer enhancer 4

[0164] Ten heat transfer promoters 4 are arranged from 300 mm to 950 mm from the outlet side of the radiant tube 100 located at the downstream straight section.

[0165] (iv) Waste heat reduction ratio

[0166] As the waste heat reduction ratio, the balance between the heat released from the test furnace and the heat from the exhaust is calculated, and the proportion of exhaust heat in the input heat is determined. Furthermore, when all the protrusions 42 of the heat transfer promoter 4 in Example 1 described later come into contact with the inner wall of the radiant tube 100 (refer to...) Figure 6 When the waste heat reduction rate is set to 1.00, this ratio is used to represent the waste heat reduction rate.

[0167] In this embodiment, a waste heat reduction ratio of 1.20 or higher, preferably 1.50 or higher, is considered to be of excellent heat transfer efficiency and is therefore acceptable.

[0168] First, the basic shape of the cross-sectional star-shaped heat transfer promoter 4 is studied.

[0169] Figure 6 Example 1 shown is an example in which the entire front end of the multiple front ends of the heat transfer promoter 4 is in contact with the inner wall of the pipe 1.

[0170] Figure 7 Example 2 shown is an example where the front end of the heat transfer promoter 4 is shortened equally. However, the heat transfer promoter 4 is biased towards the direction of gravity. That is, the center of gravity of the heat transfer promoter 4 is located below the center of the cross-section of the pipe 1.

[0171] Figure 8 Compared to Example 2, Example 3 only has two front ends of the same length as Example 1, which serve as the second protrusion 42b, so that the center of gravity of the heat transfer promoter 4 is aligned with the center of the pipe 1 (the center of gravity of the cross section on the cylinder perpendicular to the flow direction).

[0172] Figure 9 Example 4 shows an example where the front end of the protrusion 42 is chamfered in the same manner as in Example 3, with the same gap ΔL at the front end of the protrusion 42 as in Example 1. It should be noted that in the protrusion 42... Figure 9 In the shape shown, when the protrusion 42 is rounded, the amount of waste heat reduction is approximately the same as in Example 4.

[0173] The research results of Examples 1 to 4 above are shown in Figure 10 .exist Figure 10 In this case, the vertical axis represents the waste heat reduction ratio.

[0174] As can be seen from Figure 10 , as in Examples 2 to 4, by providing a gap ΔL at the front end of the protrusion 42, the waste heat reduction ratio is improved as compared with the state where the front end portion contacts the pipeline 1 (Example 1).

[0175] Furthermore, as shown in Examples 3 and 4, by making the centroid of the cross-section of the pipeline 1 coincide with or approximate to the centroid of the cross-section of the heat transfer promotion body 4, the waste heat reduction ratio is further improved, and the waste heat reduction ratio is 1.50 or more.

[0176] Next, based on the shape of Example 4, the gap ΔL between the front end portion of the heat transfer promotion body 4 formed in a star shape and the inner wall of the pipeline 1 is changed to study the waste heat reduction ratio.

[0177] The results are as shown in Figure 11 .

[0178] As can be seen from Figure 11 , if the gap ΔL at the front end of the protrusion 42 with respect to the equivalent diameter of the inner wall of the radiation pipe 100 satisfies 0.3 < x < 7, the waste heat reduction ratio is 1.3 times or more, showing a very high effect of improving the heat transfer efficiency. It is further preferable that the gap ΔL between the front end portion and the inner wall satisfies 0.5 < x < 4.5, and the waste heat reduction ratio is 1.5 times or more, showing an even higher effect of improving the heat transfer efficiency.

[0179] Next, a comparison was made between the case where the pipeline 1 has a circular shape with a diameter of 188 mm and the case where it has an elliptical shape.

[0180] In either case, based on the amount of waste heat when the front end portion of the heat transfer promotion body 4 contacts the wall surface of the pipeline 1, the gap ΔL at the front end of the protrusion 42 with respect to the equivalent diameter of the inner wall of the radiation pipe 100 is the same condition for the circle and the ellipse.

[0181] The comparison results are as shown in Figure 12 .

[0182] As can be seen from Figure 12 , regardless of whether the opening cross-section of the pipeline 1 is circular or elliptical, the waste heat reduction ratio is equally improved. Furthermore, compared with the case of the circular shape, the waste heat reduction ratio is increased by about 10% when the opening cross-section of the pipeline 1 is elliptical.

[0183] Here, this application claims priority, and the entire contents of Japanese Patent Application No. 2020-028033 (filed on February 21, 2020) are incorporated herein by reference and made part of this disclosure. Here, a limited number of embodiments have been described, but the scope of the claims is not limited thereto, and modifications based on the above-described disclosed embodiments will be obvious to those skilled in the art.

[0184] Explanation of reference numerals in the attached figures

[0185] 1. Piping

[0186] 1a inner wall surface

[0187] 2A Gas Generating Unit

[0188] 3 Furnace wall

[0189] 4. Heat transfer enhancer

[0190] 41 Main body

[0191] 42. Protrusion

[0192] 42a First protrusion

[0193] 42b Second protrusion

[0194] 100 radiant tube

[0195] R swirling flow

[0196] ΔL gap

Claims

1. A radiant tube having a tube line to be heated by a fluid gas flowing in the tube line, and one or more heat transfer promoting bodies arranged in the tube line along the axis of the tube line, characterized in that, the heat transfer promoting body has a main body portion arranged on the center side of the tube line, and a plurality of protrusion portions protruding from the main body portion toward the inner wall surface of the tube line, the plurality of protrusion portions are formed on the outer periphery of the main body portion in a manner arranged along the circumferential direction of the tube line, the plurality of protrusion portions are composed of a plurality of first protrusion portions and other second protrusion portions, the leading end portions of the first protrusion portions are opposed to the tube line inner wall surface with a gap ΔL, the second protrusion portions are longer than the first protrusion portions, the number of the first protrusion portions is set to be larger than the number of the second protrusion portions, in a case where the percentage of the ratio (ΔL / Dt) of the gap ΔL to the equivalent diameter Dt of the tube line portion of the tube line in which the heat transfer promoting body is arranged is set as x [%], the following equation (1) is satisfied, 0.3%<x<7% ···（1）。 2. The radiant tube of claim 1, wherein, the leading end of the second protrusion portion is in abutment with the tube line inner wall surface.

3. The radiant tube according to claim 1 or 2, characterized in that the heat transfer promoting body is arranged such that the center of gravity of the heat transfer promoting body coincides with the center of the opening cross section of the tube line.

4. The radiant tube according to any one of claims 1 to 3, characterized in that the cross sectional shape of each of the protrusion portions is such that the width along the circumferential direction of the tube line becomes smaller as it is farther from the main body portion along the radial direction of the tube line, and a space in which the distance between the two adjacent protrusion portions becomes wider as it is farther from the main body portion is formed between the two adjacent protrusion portions in the circumferential direction of the tube line.

5. The radiant tube according to any one of claims 1 to 4, characterized in that the leading end portion shape of the protrusion portion is a chamfered shape or a curved surface shape.

6. The radiant tube according to any one of claims 1 to 5, characterized in that the inside of the heat transfer promoting body is a hollow, which is a shape in which the surface opposed to the moving direction of the fluid flowing in the tube line is closed.

7. The radiant tube according to any one of claims 1 to 6, characterized in that the opening cross section of the tube line portion in which the heat transfer promoting body is arranged is an ellipse.

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