Heat exchanger inner pipe, double pipe heat exchanger, and double pipe connection structure

Abstract

To provide an inner pipe for a heat exchanger, a double pipe type heat exchanger, and a double pipe connection structure capable of improving heat exchange efficiency.SOLUTION: A first flat portion 4 that is flat in a first direction perpendicular to a pipe axis direction, a second flat portion 5 that is flat in a second direction perpendicular to the pipe axis direction and having a predetermined angle with respect to the first direction when viewed in the pipe axis direction, and a connecting portion 6 that connects the first flat portion 4 and the second flat portion 5, the double-pipe heat-exchanger 1 includes the heat-exchanger inner pipe 2 and the outer pipe 3 into which the heat-exchanger inner pipe 2 is inserted, and the double-pipe connecting structure includes the inner and outer pipes 2, 3 and the connecting member 13. The heat-exchanger inner pipe 2 includes the connecting portion 6 having the projecting surface 6a having a substantially triangular shape when viewed in the pipe axis direction, the projecting surface inner wall being formed of a curved surface connecting both vertices of the long axis of the first flat portion 4 and each vertex of the long axis of the second flat portion 5 adjacent to the first flat portion 4.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to an inner pipe for a heat exchanger, a double-pipe heat exchanger, and a double-pipe connection structure. [Background technology]

[0002] A double-pipe heat exchanger used in a bath heater that reheats bathwater may have an inner pipe inserted into an outer pipe, and for example, bathwater from a bathtub is circulated in the space between the inner surface of the outer pipe and the outer surface of the inner pipe, while heating water heated by a heat source is passed through the inner pipe, thereby exchanging heat between the bathwater and the heating water. An example of a double-pipe heat exchanger is shown in Patent Document 1 below.

[0003] The heat exchanger (continuous cooling device) disclosed in Patent Document 1 is configured to cool a fluid food material by passing the fluid food material through a heat transfer tube 1 (inner tube) and passing a cooling medium through a cooling medium passage 13 formed between the outer wall of the heat transfer tube 1 and the inner peripheral wall of an outer tube 7. The heat transfer tube 1 is composed of a plurality of unit heat transfer tube sections 1A-1N. Each unit heat transfer tube section 1A-1N is formed so that the cross section perpendicular to the longitudinal direction is flattened. The long diameter direction DL of each unit heat transfer tube section 1A-1N is arranged so that adjacent ones form an angle of 90 degrees. The unit heat transfer tube sections 1A-1N are connected via a throttle tube section 15 (see, particularly, paragraphs 0027-0029 and Figures 1-4 of Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-296091 Summary of the Invention [Problem to be solved by the invention]

[0005] In the heat exchanger (continuous cooling device) disclosed in Patent Document 1, as shown in Figure 2 of this document, the unit heat transfer pipe sections 1A-1N are arranged in a cross shape when viewed in the pipe axis direction, and most of the cooling medium flowing through the cooling medium passage 13 passes directly downstream through the cross-shaped gaps formed by the unit heat transfer pipe sections 1A-1N without exchanging heat with the unit heat transfer pipe sections 1A-1N, making it difficult to achieve high heat exchange efficiency. Also, the inner and outer pipes are joined by joints such as brazing or welding, but forming joints in the flow paths of a double-pipe heat exchanger presents the problem of the joints being susceptible to corrosion in corrosive environments such as high temperatures and turbulent flow.

[0006] Therefore, an object of the present invention is to provide an inner pipe for a heat exchanger and a double-pipe heat exchanger that can achieve high heat exchange efficiency, as well as a double-pipe connection structure that is less susceptible to corrosion at the joints of the double pipes. [Means for solving the problem]

[0007] In order to solve the above problems, the present invention provides: a first flat portion that is flat in a first direction perpendicular to the tube axis direction; a second flat portion that is flat in a second direction that is perpendicular to the tube axis direction and forms a predetermined angle with respect to the first direction when viewed in the tube axis direction; a connecting portion that connects the first flat portion and the second flat portion; are formed in line in the tube axial direction, The connecting portion is formed of curved surfaces connecting both vertices of the long axis of the first flat portion and each vertex of the long axis of the second flat portion adjacent to the first flat portion, and has a protruding surface that is approximately triangular when viewed in the direction of the pipe axis (first configuration).

[0008] In this way, the fluid (heat medium) flowing along the surface of the first flat portion flows along the protruding surface of the connection portion toward the second flat portion, which is flattened in a different direction from the first flat portion, and since the protruding surface protrudes into the gap between the inner pipe and the outer pipe when viewed in the pipe axis direction, the heat exchange efficiency between the heat medium and the fluid can be improved.

[0009] In the first configuration, it is preferable that the first flat portion and the second flat portion are arranged symmetrically with respect to a vertical line when viewed in the tube axial direction, and a continuous flow path is formed along a horizontal plane in the first flat portion, the connecting portion, and the inner bottom portion of the second flat portion (second configuration). In this way, almost no fluid remains inside the inner tube after draining from the inner tube, preventing problems caused by the remaining fluid freezing.

[0010] In the second configuration, it is preferable that the height difference between the inner bottom of the first flat portion, the inner bottom of the connecting portion, and the inner bottom of the second flat portion and the horizontal plane is within a range of 0% to 20% of the length of the major axis of the first flat portion (third configuration). In this way, the first flat portion, the connecting portion, and the inner bottom of the second flat portion become nearly flat, thereby improving the drainage efficiency during drainage.

[0011] In the first to third configurations, it is preferable to use a configuration (fourth configuration) in which the first flat portion and the second flat portion are formed on a tube having a groove formed on the surface along the circumferential direction. In this configuration, springback is less likely to occur during processing of the first flat portion and the second flat portion, making it possible to smoothly process both flat portions and stabilize the processed dimensions. Furthermore, forming the groove can suppress buckling of the tube during bending.

[0012] Furthermore, in this invention, a double-pipe heat exchanger can be configured (fifth configuration) having an inner heat exchanger pipe according to any one of the first to fourth configurations and an outer pipe into which the inner heat exchanger pipe is inserted. In this way, it is possible to improve the efficiency of heat exchange between, for example, high-temperature heating water flowing inside the inner pipe and bath water flowing in the space between the inner surface of the outer pipe and the outer surface of the inner pipe.

[0013] In addition, in this invention, an inner tube for a heat exchanger; an outer tube into which the inner tube for a heat exchanger is inserted with both ends thereof protruding; a connecting member provided at an end of the outer pipe, the connecting member forming a space between the outer surface of the inner pipe and the outer pipe, the connecting member being continuous with a space formed between the outer surface of the inner pipe and the inner surface of the outer pipe; In a sixth configuration, a double-pipe connection structure can be provided in which a first fluid flows in the heat exchanger inner pipe and a second fluid flows in the space formed between the outer surface of the heat exchanger inner pipe and the inner surface of the outer pipe. In this way, heat can be exchanged smoothly between the fluids flowing in the heat exchanger inner pipe and the space.

[0014] In the sixth configuration, it is preferable that an extension pipe is connected to the end of the heat exchanger inner pipe, and the joint between the heat exchanger inner pipe and the extension pipe is formed in an axial position that does not overlap with the axial position of the space inlet or space outlet formed in the connecting member (seventh configuration). In this way, the joint (brazed part, welded part, soldered part, etc.) is outside the corrosive environment area where turbulence occurs and the temperature becomes high due to the inflow or outflow of high-temperature fluid, and corrosion of the joint can be prevented as much as possible.

[0015] In the sixth configuration, it is preferable that the joints between the inner pipe for heat exchanger, the outer pipe, and the connecting member are formed outside the flow path of the first fluid or the second fluid, whichever is hotter (eighth configuration). This prevents corrosion of the joints due to the high-temperature fluid, thereby improving the reliability. [Effects of the Invention]

[0016] According to the above-described configuration of the present invention, the heat exchange efficiency of the heat exchanger can be improved. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a partially cutaway front view showing one embodiment of a double-pipe heat exchanger according to the present invention; [Figure 2] Front view of the inner tube for the heat exchanger used in the double-pipe heat exchanger shown in Figure 1 [Figure 3] FIG. 3 is an enlarged perspective view showing the heat exchanger inner tube shown in FIG. 2 rotated 45 degrees around the tube axis. [Figure 4] FIG. 4 is a cross-sectional view showing the state in which the inner tube for a heat exchanger shown in FIG. 3 is inserted into the outer tube. [Figure 5] FIG. 3 is a front view showing another example of the inner tube for a heat exchanger shown in FIG. 2. [Figure 6] FIG. 2 is a perspective view showing a bent portion of the double-pipe heat exchanger shown in FIG. 1. [Figure 7] FIG. 7 is a cross-sectional view showing another example of the bent portion shown in FIG. [Figure 8] FIG. 7 is a partially cutaway perspective view showing yet another example of the bent portion shown in FIG. 6 . [Figure 9] 2A and 2B are front views schematically showing the steps of bending the double-pipe heat exchanger shown in FIG. 1, in which (a) shows the outer pipe, (b) shows the state in which the inner pipe for the heat exchanger is inserted into the outer pipe, (c) shows the state after bending, and (d) shows the state in which the end of the outer pipe has been subjected to diameter reduction. [Figure 10] This shows a first example of the connection structure between the inner and outer pipes at both ends of a double-pipe heat exchanger. (a) is a cross-sectional view, and (b) is an enlarged cross-sectional view of a portion before processing. [Figure 11] An enlarged cross-sectional view of the heating water inlet side of the connection structure shown in FIG. 10(a). [Figure 12] An enlarged cross-sectional view of the heating water outlet side of the connection structure shown in Figure 10(a) [Figure 13] A second example of the connection structure between the inner and outer pipes at both ends of a double-pipe heat exchanger is shown. (a) is a cross-sectional view, and (b) is an enlarged cross-sectional view of a portion before processing. [Figure 14] An enlarged cross-sectional view of the heating water inlet side showing a modified example of the connection structure between the inner pipe and the outer pipe. [Figure 15] An enlarged cross-sectional view of the heating water outlet side showing a modified example of the connection structure between the inner pipe and the outer pipe [Figure 16] 3 is a front view showing another application of the inner tube for the heat exchanger shown in FIG. 2. [Figure 17] Cross-sectional view taken along line XVII-XVII in Figure 16 [Figure 18]Cross-sectional view showing another example of a double-pipe heat exchanger [Figure 19] Cross-sectional view showing yet another example of a double-pipe heat exchanger DETAILED DESCRIPTION OF THE INVENTION

[0018] An embodiment of a double-pipe heat exchanger 1 according to the present invention will be described with reference to the drawings. This double-pipe heat exchanger 1 is a bath heater that reheats bathwater, and as shown in Figure 1, it has a heat exchanger inner pipe 2 (hereinafter referred to as the inner pipe 2) and an outer pipe 3 into which the inner pipe 2 is inserted. Note that this double-pipe heat exchanger 1 can also be used for purposes other than a bath heater.

[0019] The inner pipe 2 is a tubular member made of stainless steel, and as shown in Figures 2 and 3, a first flat portion 4, a second flat portion 5, and a connection portion 6 are formed side by side in the pipe axial direction. One end of the inner pipe 2 (right side in Figure 1) is an inner pipe inlet 7 (hereinafter referred to as the heating water inlet and given the same reference number as the inner pipe inlet 7), and the other end (left side in Figure 1) is an inner pipe outlet 8 (hereinafter referred to as the heating water outlet and given the same reference number as the inner pipe outlet 8), and branch pipes (not shown) are connected to these inlets and outlets 7, 8, respectively.

[0020] The first flat portion 4 is a member that is flat (has a substantially elliptical cross section) in a first direction perpendicular to the tube axis direction, and is formed by clamping the inner tube 2 from both radial sides by a predetermined width in the tube axis direction with a clamping jig. The second flat portion 5 is a member that is flat (has a substantially elliptical cross section) in a second direction that is perpendicular to the tube axis direction and that forms a predetermined angle with the first direction as viewed in the tube axis direction, and is formed, similarly to the first flat portion 4, by clamping the inner tube 2 from both radial sides by a predetermined width in the tube axis direction with a clamping jig. In this embodiment, the angle between the first direction and the second direction is 90 degrees, and the first flat portion 4 and the second flat portion 5 are flattened in a state where they are rotated 90 degrees relative to each other around the tube axis. The angle between the first direction and the second direction can be changed as needed (for example, to 60 degrees).

[0021] The connecting portion 6 is a portion that connects the first flat portion 4 and the second flat portion 5, and is formed as the two flat portions 4, 5 are formed. As shown in Fig. 4, the connecting portion 6 is formed with a protruding surface 6a that is approximately triangular in shape when viewed in the tube axis direction, and is made up of curved surfaces that connect both vertices of the long axis of the first flat portion 4 and each vertex of the long axis of the second flat portion 5 adjacent to the first flat portion 4. The shape of the protruding surface 6a varies depending on the flatness of the first flat portion 4 and the second flat portion 5, the axial distance between the two flat portions 4, 5, the diameter of the inner tube 2, and other factors, but the shape when viewed in the tube axis direction is generally as shown in Fig. 4.

[0022] In this embodiment, the inner pipe 2 is formed by a process in which the first flat portion 4 is formed using a clamping jig having an axial width of approximately 10 mm that radially clamps the inner pipe 2, then the inner pipe 2 is rotated 90 degrees about the pipe axis and the clamping jig is moved 20 mm in the axial direction to form the second flat portion 5, and the inner pipe 2 is further rotated 90 degrees about the pipe axis and the clamping jig is moved 20 mm in the axial direction to form the first flat portion 4. This process continuously forms the first flat portion 4, the connecting portion 6, and the second flat portion 5, each having an axial width of 10 mm. Note that these processing dimensions are merely an example, and the axial width of the clamping jig used and the axial movement distance of the clamping jig can be appropriately changed depending on the diameter of the inner pipe 2, the application, etc.

[0023] 4, the first flat portion 4 and the second flat portion 5 formed along the horizontal pipe axis direction are arranged with their respective long axes inclined at the same angle (45 degrees in this embodiment) relative to the horizontal plane in the horizontally arranged portion of the double-pipe heat exchanger 1. In this case, a continuous flow path is formed along the horizontal plane in the inner bottom portions of the first flat portion 4, the connecting portion 6, and the second flat portion 5 (the region surrounded by a dashed square in FIG. 4).

[0024] The inner bottom of the first flat portion 4, the inner bottom of the connecting portion 6, and the inner bottom of the second flat portion 5 are all nearly flat with almost no difference in height from a common horizontal plane. The flattening process of the inner pipe 2 is performed so that this difference in height is within a range of 0% to 20% of the length of the major axis of the first flat portion 4, preferably within a range of 0% to 15%, and more preferably within a range of 0% to 10%.

[0025] The outer pipe 3 is a tubular member made of stainless steel, just like the inner pipe 2. As shown in Figure 1, reduced diameter sections 9 are formed at both ends of the outer pipe 3. The inner pipe 2 and reduced diameter section 9 (outer pipe 3) are joined by an appropriate joining method such as laser welding, TIG welding, or brazing, ensuring watertightness between the inner and outer pipes 2 and 3. A space inlet 10 (hereinafter referred to as the bath water inlet and designated by the same reference numeral as the space inlet 10) is formed near the other end (left side of Figure 1) of the outer pipe 3, and a space outlet 11 (hereinafter referred to as the bath water outlet and designated by the same reference numeral as the space outlet 11) is formed near one end (right side of Figure 1). Branch pipes (not shown) are connected to these inlets 10 and 11, respectively.

[0026] In this embodiment, the direction in which heating water (a first fluid) flows inside the inner pipe 2 is opposite to the direction in which bath water (a second fluid) flows through the space between the outer surface of the inner pipe 2 and the inner surface of the outer pipe 3. As the heating water and bath water flow through the double-pipe heat exchanger 1, heat exchange occurs between the relatively high-temperature heating water and the relatively low-temperature bath water, heating the bath water. The flow directions of the heating water and bath water can be the same as long as a predetermined heat exchange efficiency is ensured. The inner pipe 2 and the outer pipe 3 can also be made of a material other than stainless steel (e.g., copper). Alternatively, the bath water can flow inside the inner pipe 2, and the heating water can flow in the space between the outer surface of the inner pipe 2 and the inner surface of the outer pipe 3. In this embodiment, both the first and second fluids are water, but both fluids can also be liquids other than water or gases.

[0027] The gap between the major axis side ends of the first flat portion 4 and the second flat portion 5 formed on the inner pipe 2 and the inner surface of the outer pipe 3 is relatively small, ensuring a predetermined degree of concentricity between the inner pipe 2 and the outer pipe 3. The diameters of the inner and outer pipes 2 and 3 are determined and the inner pipe 2 is flattened so that the ratio of the major axis length do of the first flat portion 4 or the second flat portion 5 of the inner pipe 2 to the inner diameter Di of the outer pipe 3 is within the range of 0.8≦do / Di≦0.99, preferably within the range of 0.85≦do / Di≦0.99, and more preferably within the range of 0.9≦do / Di≦0.99.

[0028] As shown in FIG. 5, the first flat portion 4, the second flat portion 5, and the connecting portion 6 can be formed on a pipe (inner pipe 2) that has been previously corrugated to form grooves along the circumferential direction. This prevents the inner pipe 2 from buckling when bending the unprocessed inner pipe 2 or the inner pipe 2 with the flat portions 4 and 5 formed thereon. Furthermore, the corrugation process increases the surface area of ​​the inner pipe 2, thereby improving heat exchange efficiency. Furthermore, the corrugation process reduces the risk of springback during processing of the first flat portion 4 and the second flat portion 5, allowing for smooth processing of the flat portions 4 and 5 and stabilizing the processed dimensions. Instead of corrugating, multiple grooves with a common axis can be formed on the surface of the pipe (inner pipe 2).

[0029] In the double-pipe heat exchanger 1 described above, the bent portion 12 is formed by bending the inner and outer pipes 2 and 3 at a predetermined location. Because high heat exchange efficiency is achieved at the bent portion 12 by agitating the water flow, the requirement for concentricity between the inner pipe 2 and the outer pipe 3 is not particularly high. However, as shown in FIG. 6 , for example, a region without the first flat portion 4 or the second flat portion 5 can be provided in the inner pipe 2 corresponding to the area that will become the bent portion 12 after bending, and the first flat portion 4 or the second flat portion 5 can be formed in the inner pipe 2 corresponding to the position that will become the straight pipe portion of the outer pipe 3 adjacent to the bent portion 12 before bending. In this case, the inner pipe 2 (the first flat portion 4 and / or the second flat portion 5) is supported by the inner surface of the straight pipe portion of the outer pipe 3 adjacent to the bent portion 12. Therefore, the inner pipe 2 is less likely to be biased inward in the bending direction at the bent portion 12, ensuring concentricity between the inner pipe 2 and the outer pipe 3. From the viewpoint of reducing water flow resistance, it is better for the length of the area in the axial direction of the inner pipe 2 where the flattened portions 4 and 5 are formed to be shorter relative to the length of the inner pipe 2, but this length in the axial direction is often set within the range of 40% to 60% of the entire length of the inner pipe 2.

[0030] Furthermore, when forming the bent portion 12, as shown in Fig. 7, the bending process can be performed after forming a first flat portion 4 or a second flat portion 5 in the inner pipe 2, whose major axis is included in the bent surface including the bent portion 12, in accordance with the range that will become the bent portion 12 after bending. At this time, the inner pipe 2 (first flat portion 4 or second flat portion 5) is supported by the inner surface of the bent portion 12 of the outer pipe 3. Therefore, the inner pipe 2 is less likely to be biased inward in the bending direction at the bent portion 12, ensuring coaxiality between the inner pipe 2 and the outer pipe 3 and preventing buckling of the inner pipe 2 at the bent portion 12. Note that Fig. 7 shows a configuration in which the first flat portion 4 is formed in only one location at the bent portion 12, but depending on the radius of curvature of the bent portion 12, the first flat portion 4 can also be formed in multiple locations.

[0031] Furthermore, when forming the bent portion 12, as shown in Figure 8, bending can be performed while deforming the cross-sectional shape of the outer pipe 3 with the inner pipe 2 inserted into a triangular shape with an apex pointing inward at the bent portion 12. At this time, the inner diameter of the outer pipe 3 narrows toward the inner apex of the bent portion 12, making it difficult for the inner pipe 2 to shift inward within the outer pipe 3 at the bent portion 12. This ensures concentricity between the inner pipe 2 and the outer pipe 3 and also exerts an effect of suppressing buckling at the portion of the outer pipe 3 inside the bent portion 12. When forming the bent portion 12, a notch can be formed on the inner surface of the portion of the outer pipe 3 that will become the bent portion 12, which will serve as a starting point for bending.

[0032] If the inner pipe 2 and the outer pipe 3 were entirely made of stainless steel, the poor workability and weldability of stainless steel could hinder the formation of the bent section 12 and the welding of the branch pipes. Therefore, by replacing some of the stainless steel pipes with copper pipes, which have excellent workability and weldability, it becomes easier to form the bent section 12 and weld the branch pipes. For example, the process of fabricating a U-shaped double-pipe heat exchanger 1 from a straight pipe will be described with reference to Figures 9(a) to 9(d).

[0033] First, as shown in FIG. 9(a), the material of the portion of the outer pipe 3 corresponding to the bent portion 12 and both ends of the outer pipe 3 to which the branch pipes are welded is replaced from stainless steel to copper. The stainless steel pipe and the copper pipe can be connected by known techniques such as brazing (e.g., copper tin solder), laser welding, or TIG welding. One end of the outer pipe 3 (the left end in FIG. 9(a)) is formed with a reduced diameter portion 9 whose diameter is reduced to match the outer diameter of the inner pipe 2. Since both ends of the outer pipe 3 only need to be weldable, instead of replacing the material of the both ends from stainless steel to copper, a copper plating layer can be formed on the surface of the stainless steel.

[0034] Next, as shown in Figure 9(b), the inner pipe 2, which has pre-formed flattened portions 4 and 5 as shown in Figure 2 etc., is inserted into the outer pipe 3, and the inner pipe 2 and the outer pipe 3 are brazed at the reduced diameter portion 9, and connected by a known method such as laser welding or TIG welding. The material of the portion of the inner pipe 2 corresponding to the bent portion 12 has been changed from stainless steel to copper, as with the outer pipe 3. Note that instead of changing the material from stainless steel to copper, a copper plating layer can also be formed on the surface of the stainless steel.

[0035] Furthermore, as shown in Figure 9(c), bending is performed at predetermined positions to form the double-pipe heat exchanger 1 into a U-shape. Note that the workability of the bent portion 12 can be improved by corrugating the stainless steel pipe while leaving the material of the bent portion 12 as stainless steel. Finally, as shown in Figure 9(d), a reduced diameter portion 9 is formed at the other end side of the outer pipe 3 (the lower right end side of Figure 9(d)), and a branch pipe (not shown) is then brazed to it.

[0036] The inner pipe 2 employed in the above-described double-pipe heat exchanger 1 has a connecting portion 6 having a protruding surface 6a that is approximately triangular when viewed in the pipe axial direction, the protruding surface 6a being made up of curved surfaces connecting both vertices of the long axis of the first flat portion 4 and each vertex of the long axis of the second flat portion 5 adjacent to the first flat portion 4. Therefore, a fluid (bathwater in this case) flowing axially toward the protruding surface 6a (toward the back of the drawing in FIG. 4) flows along the surface of this protruding surface 6a (see the outline arrow in FIG. 4) from circled portion A toward portion B. In this way, the fluid moves and flows within the cross section shown in FIG. 4, thereby improving the heat exchange efficiency between the heat transfer medium and the fluid.

[0037] Furthermore, the fluid flowing through portion B in FIG. 4, where contact with the inner pipe 2 is relatively unlikely, moves circumferentially (clockwise in FIG. 4) along the protruding surface 6a of the connecting portion 6 (6A), making it more likely to come into contact with the protruding surface 6a of the next connecting portion 6 (6B) (see FIG. 3). This further improves the heat exchange efficiency between the heat transfer medium and the fluid. In addition, because the flat portions 4, 5 of the inner pipe 2 are smoothly connected by the connecting portions 6, pressure loss of the fluid (heat transfer medium) flowing within the inner pipe 2 can be minimized. Furthermore, temperature unevenness of the fluid that occurs within the flat portions 4, 5 can be eliminated when the fluid passes through the connecting portions 6, further improving the heat exchange efficiency in the flat portions 4, 5.

[0038] Furthermore, when installing a double-pipe heat exchanger 1 employing the inner pipe 2, the first flat portion 4 and the second flat portion 5 are arranged symmetrically with respect to a vertical line when viewed in the pipe axis direction. Continuous flow paths are formed along a horizontal plane in the inner bottoms of the first flat portion 4, the connecting portion 6, and the second flat portion 5. This ensures that almost no fluid remains inside the inner pipe 2 after draining, preventing problems caused by the remaining fluid freezing. In particular, high drainage efficiency can be achieved by setting the height difference between the inner bottoms of the first flat portion 4, the connecting portion 6, and the second flat portion 5 and the horizontal plane within a range of 0% to 20% of the length of the major axis of the first flat portion 4. Furthermore, drainage efficiency can be further improved by tilting the pipe axis direction of the double-pipe heat exchanger 1 from the horizontal plane.

[0039] Furthermore, in the above-mentioned double-pipe heat exchanger 1, the ratio of the length do of the major axis of the first flat portion 4 or the second flat portion 5 of the inner pipe 2 to the inner diameter Di of the outer pipe 3 is set within the range of 0.8≦do / Di≦0.99, so that the bathwater flowing through the space between the outer surface of the inner pipe 2 and the inner surface of the outer pipe 3 can be efficiently brought into contact with the surface of the inner pipe 2, and further improvement in heat exchange efficiency can be expected.

[0040] 10(a) shows a first example of a connection structure between the inner pipe 2 and the outer pipe 3 at both ends of a double-pipe heat exchanger 1. In the explanation of this connection structure, the first flat portion 4 and the second flat portion 5 are omitted. This connection structure can also be applied to a double-pipe heat exchanger 1 in which the first flat portion 4 and the second flat portion 5 are not formed.

[0041] This connection structure includes a stainless steel inner pipe 2 and a stainless steel outer pipe 3 into which the inner pipe 2 is inserted with both ends protruding. Copper connection members 13 are provided on both ends of the outer pipe 3. Copper extension pipes 14 are connected to the outer surface of both ends of the inner pipe 2. High-temperature heating water heated by a heat source flows from the extension pipe 14 (heating water inlet 7 (right side of FIG. 10(a))) connected to one end of the inner pipe 2 to the extension pipe 14 (heating water outlet 8 (left side of FIG. 10(a))) connected to the other end. Branch pipes (not shown) are connected to each extension pipe 14.

[0042] As shown in Figure 11, on the heating water inlet 7 side, connecting member 13 is arranged to straddle the outer surface of inner pipe 2 and the outer surface of outer pipe 3. A space is formed between the inner surface of connecting member 13 and the outer surface of inner pipe 2, which is continuous with the space formed between the outer surface of inner pipe 2 and the inner surface of outer pipe 3. A bath water outlet 11 is formed on the circumferential surface of connecting member 13 on the heating water inlet 7 side, and a branch pipe (not shown) is connected to this bath water outlet 11. Connecting member 13 and extension pipe 14 are arranged to be aligned in the axial direction.

[0043] On the heating water inlet 7 side, the outer surface of the inner pipe 2 and the connecting member 13, the outer surface of the outer pipe 3 and the connecting member 13, and the outer surface of the inner pipe 2 and the extension pipe 14 are all brazed with copper tin solder (melting point: approximately 1050°C) as a first brazing material. Brazing with the first brazing material is performed in a continuous furnace that is capable of brazing multiple straight double-pipe heat exchangers 1 at once. The brazed portions made of this copper tin solder are formed on the outer surfaces of the inner pipe 2 and the outer pipe 3, and are configured so that these brazed portions do not come into direct contact with the high-temperature heating water.

[0044] As shown in Figure 12, on the heating water outlet 8 side, the connecting member 13 is arranged to straddle the outer surface of the extension pipe 14 connected to the inner pipe 2 and the outer surface of the outer pipe 3. A space is formed between the inner surface of the connecting member 13 and the outer surface of the inner pipe 2, which is continuous with the space formed between the outer surface of the inner pipe 2 and the inner surface of the outer pipe 3. A bath water inlet 10 is formed on the circumferential surface of the connecting member 13 on the heating water outlet 8 side, and a branch pipe (not shown) is connected to this bath water inlet 10.

[0045] On the heating water outlet 8 side, the outer surface of the inner pipe 2 and the extension pipe 14, and the outer surface of the outer pipe 3 and the connecting member 13 are both brazed with copper-tin solder (melting point: 1050°C) as a first brazing material. Meanwhile, the outer surface of the extension pipe 14 and the connecting member 13 are brazed with phosphorus copper solder (melting point: approximately 750°C) as a second brazing material after the double-pipe heat exchanger 1 is bent into a predetermined shape. The brazed portion with copper-tin solder between the outer surface of the inner pipe 2 and the extension pipe 14 comes into contact with bath water, which is relatively colder than the heating water. The types of brazing materials described above are examples and can be changed. However, it is preferable to select a brazing material with a lower melting point than the first brazing material as the second brazing material. Alternatively, for example, TIG welding, which is performed at a higher temperature than copper-tin solder, can be used instead of brazing with copper-tin solder, and copper-tin solder can be used instead of phosphorus copper solder.

[0046] In this embodiment, the heating water flows inside the inner pipe 2, and the bath water flows in the space formed between the outer surface of the inner pipe 2 and the inner surface of the outer pipe 3, but it is also possible to have the bath water flow inside the inner pipe 2, and the heating water flow in the space formed between the outer surface of the inner pipe 2 and the inner surface of the outer pipe 3. Also, in this embodiment, the heating water and the bath water flow in opposite directions, but it is also possible to have the heating water and the bath water flow in the same direction.

[0047] A first example of the assembly procedure for the connection structure shown in Figure 10(a) will be described. First, the extension pipe 14 is brazed to the heating water outlet 8 side of the inner pipe 2, and then the inner pipe 2 is inserted into the outer pipe 3. Next, connection members 13, one end of which has been reduced in diameter, are connected to both ends of the outer pipe 3, and then the extension pipe 14 is connected to the heating water inlet 7 side of the inner pipe 2. Then, brazing is performed between the outer pipe 3 and both connection members 13, and between the inner pipe 2 on the heating water inlet 7 side and the extension pipe 14. Note that brazing between the inner pipe 2 on the heating water outlet 8 side and the extension pipe 14 can also be performed at the same time. In addition to brazing, laser welding, TIG welding, and other methods can be used to fasten the various parts.

[0048] As another example of the assembly procedure for the connection structure shown in Fig. 10(a), a cylindrical connection member 13 with one end having a fixed diameter may be provided in advance on the heating water inlet 7 side of the outer pipe 3, as shown in Fig. 10(b), and after the inner pipe 2 with an extension pipe 14 brazed to the heating water outlet 8 side is inserted into the outer pipe 3, the diameter of one end of this connection member 13 may be reduced to close this one end. Note that this assembly method is merely an example, and other assembly methods may be employed as long as the connection structure shown in Fig. 10(a) is ultimately obtained.

[0049] In the first example of the connection structure, no brazing is formed in the water channel on the heating water inlet 7 side through which high-temperature heating water flows (see FIG. 11), preventing the brazing from corroding due to the high-temperature heating water and improving reliability. Also, because a brazing material with a lower melting point than the first brazing material is used as the second brazing material, when brazing the connection member 13 and the extension pipe 14 with the second brazing material, the brazing material between the inner pipe 2 and the extension pipe 14, and between the outer pipe 3 and the connection member 13, which have already been brazed with the first brazing material, will not melt and come off. This allows the brazing work of each part to be carried out smoothly.

[0050] 13(a) shows a second example of the connection structure between the inner pipe 2 and the outer pipe 3 at both ends of the double-pipe heat exchanger 1. The connection structure of the second example shares the configuration on the heating water outlet 8 side with the connection structure of the first example, but differs from the above in the configuration on the heating water inlet 7 side. That is, in the first example, the connection member 13 on the heating water inlet 7 side is provided so as to straddle the outer surface of the inner pipe 2 and the outer surface of the outer pipe 3, whereas in the second example, the connection member 13 on the heating water inlet 7 side is provided so as to straddle the outer surface of the extension pipe 14 connected to the inner pipe 2 and the outer surface of the outer pipe 3. The outer surface of the outer pipe 3 is brazed to the connection member 13 with copper tin brazing (melting point: 1050°C) as a first brazing material, and the outer surface of the extension pipe 14 is brazed to the connection member 13 with phosphorus copper brazing (melting point: approximately 750°C) as a second brazing material.

[0051] An example of the assembly procedure for the connection structure shown in FIG. 13(a) will be described. First, extension pipes 14 are fixed to both ends of the inner pipe 2, and connection members 13 are fixed to both ends of the outer pipe 3 (both are fixed between dissimilar metals), and then the inner pipe 2 is inserted into the outer pipe 3. During this insertion, one end of one connection member 13 is cylindrical with a fixed diameter, as shown in FIG. 13(b). After the inner pipe 2 is inserted into the outer pipe 3, the diameter of one end of this connection member 13 is reduced to close this end. Furthermore, before bending, the diameter of one extension pipe 14 (the extension pipe 14 on the right side in FIG. 13(a)) is expanded to fix the one extension pipe 14 and the connection member 13 at that point so that they cannot move relative to each other in the axial direction. Then, after bending the double-pipe heat exchanger 1 into a predetermined shape, the connection member 13 and both extension pipes 14 are fixed by brazing or the like. In addition to brazing, laser welding, TIG welding, and other methods can be used to fix each part. It should be noted that this assembly means is merely an example, and other assembly means can be employed as long as the connection structure shown in FIG. 13(a) is ultimately obtained.

[0052] In the second example of the connection structure, the inner tube 2 and the outer tube 3 can be assembled after the dissimilar metals (stainless steel and copper) are fixed to each other by brazing or the like, thereby simplifying the assembly procedure.

[0053] Generally, when connecting a stainless steel pipe and a copper pipe, a copper pipe (here, extension pipe 14), which is relatively easy to process, is first socketed, and then the stainless steel pipe (here, inner pipe 2) is inserted and connected, as shown in Figure 12. In this case, the brazed and welded joints of both pipes 2 and 14 are located in the corrosive environment area, surrounded by the dashed line in Figure 12, where turbulence occurs as bathwater flows in and the temperature becomes high, which may accelerate corrosion. Therefore, for example, as shown in Figure 14, on the heating water inlet 7 side, a stainless steel pipe (inner pipe 2) is provided with a receiving nozzle and then a copper pipe (extension pipe 14) is inserted and connected, and as shown in Figure 15, on the heating water outlet 8 side, a stainless steel pipe (inner pipe 2) is provided with a receiving nozzle and then a copper pipe (extension pipe 14) is inserted and connected, so that the joint between the inner pipe 2 and the extension pipe 14 is formed in an axial position that does not overlap with the axial position of the bath water outlet 11 formed in the connecting member 13.This configuration places the joint outside the corrosive environment area where turbulence occurs and the temperature rises as high-temperature fluid flows in or out, thereby minimizing corrosion of this joint.

[0054] Although Fig. 1 and other figures illustrate an example of application of an inner pipe 2 having a first flat portion 4 and a second flat portion 5 to a double-pipe heat exchanger 1, as shown in Figs. 16 and 17, this inner pipe 2 can also be used alone as a heat exchanger (primary heat exchanger) for a gas water heater, etc. By tilting the first flat portion 4 and the second flat portion 5 of this inner pipe 2 at 45 degrees with respect to the horizontal, the combustion gas rising from the combustion section 15 moves in a zigzag pattern between adjacent inner pipes 2, i.e., the combustion gas rises along the surfaces of the inclined flat portions 4, 5, weaving its way between them, thereby efficiently exchanging heat between the combustion gas and the fluid (such as water) flowing inside the inner pipe 2. Although Figs. 16 and 17 show a configuration in which multiple inner pipes 2 are arranged horizontally and vertically, the inner pipe 2 can also be wound in a spiral pattern.

[0055] Furthermore, although the above description has been given of an example in which the inner pipe 2 of the double-pipe heat exchanger 1 is formed with the first flat portion 4 and the second flat portion 5, as shown in FIG. 18, the inner pipe 2 may be bent in a zigzag shape without forming any flat portions. This increases the heat exchange area per unit axial length, improving heat exchange efficiency. Furthermore, contact between the inner surfaces of the zigzag-bent inner pipe 2 and the outer pipe 3 also prevents the inner pipe 2 from shifting to one side inside the outer pipe 3. Note that FIG. 18 shows a configuration in which two inner pipes 2 are inserted inside the outer pipe 3 with their zigzags staggered, but a configuration in which a single zigzag-shaped inner pipe 2 is inserted into the outer pipe 3 is also possible.

[0056] 19, notch-shaped stepped portions 16 may be formed on the outer tube 3 at predetermined axial intervals from the upper or lower side of the outer tube 3 toward the inner tube 2, and the stepped portions 16 may be brought into contact with the outer periphery of the inner tube 2, thereby ensuring concentricity between the inner tube 2 and the outer tube 3. Note that the positions, number, and shapes of the stepped portions 16 shown in FIG. 19 are merely examples, and can be changed as appropriate (for example, the stepped portions 16 may be arranged at 90-degree intervals around the tube axis) as long as they have the same effect.

[0057] The embodiments disclosed herein are to be considered in all respects as illustrative and not restrictive. Therefore, the scope of the present invention is defined by the claims, not by the above description, and is intended to include the meaning equivalent to the claims and all modifications thereof.

[0058] In the above, a configuration is shown in which both first flat portions 4 and second flat portions 5 with different inclination directions are formed alternately on the inner tube 2 via the connecting portions 6, but as long as a predetermined heat exchange efficiency can be ensured, a configuration in which only the first flat portions 4 are formed can also be used. [Explanation of symbols]

[0059] 1 Double tube heat exchanger 2 Inner tube for heat exchanger (inner tube) 3 outer tube 4 First flat section 5 Second flat section 6(6A, 6B) Connection 6a Projecting surface 7 Inner pipe inlet (heating water inlet) 8 Inner pipe outlet (heating water outlet) 9 Reduced diameter part 10 Space entrance (bath water entrance) 11 Space outlet (bath water outlet) 12 Bend 13 Connecting member 14 Extension pipe 15 Combustion section 16-stage pressing section

Claims

1. a first flat portion (4) that is flat in a first direction perpendicular to the tube axis direction; a second flat portion (5) that is flat in a second direction perpendicular to the tube axis direction and that forms a predetermined angle with the first direction when viewed in the tube axis direction; a connecting portion (6) connecting the first flat portion (4) and the second flat portion (5); are formed in line in the tube axial direction, The connecting portion (6) has a protruding surface (6a) that is approximately triangular when viewed in the tube axis direction, the protruding surface (6a) being made of curved surfaces that connect both vertices of the long axis of the first flat portion (4) and each vertex of the long axis of the second flat portion (5) adjacent to the first flat portion (4).

2. 2. The heat exchanger inner pipe according to claim 1, wherein the first flat portion (4) and the second flat portion (5) are disposed symmetrically with respect to a vertical line when viewed in the tube axial direction, and a continuous flow path is formed along a horizontal plane at inner bottom portions of the first flat portion (4), the connecting portion (6), and the second flat portion (5).

3. 3. The heat exchanger inner pipe according to claim 2, wherein a difference in elevation of an inner bottom of the first flat portion (4), an inner bottom of the connection portion (6), and an inner bottom of the second flat portion (5) from the horizontal plane is within a range of 0% to 20% of the length of the major axis of the first flat portion (4).

4. 2. The heat exchanger inner pipe according to claim 1, wherein the first flat portion (4) and the second flat portion (5) are formed on a pipe body having a groove formed on the surface along the circumferential direction.

5. The heat exchanger inner tube (2) according to any one of claims 1 to 4, an outer pipe (3) into which the inner pipe (2) for the heat exchanger is inserted; A double-pipe heat exchanger having:

6. a heat exchanger inner tube (2); an outer pipe (3) into which the inner pipe (2) for the heat exchanger is inserted with both ends thereof protruding; a connecting member (13) provided at an end of the outer pipe (3) and forming a space between the outer surface of the heat exchanger inner pipe (2) and the outer surface of the heat exchanger inner pipe (2), the connecting member forming a space continuous with the space formed between the outer surface of the heat exchanger inner pipe (2) and the inner surface of the outer pipe (3); a first fluid flows in the inner pipe for a heat exchanger (2), and a second fluid flows in a space formed between the outer surface of the inner pipe for a heat exchanger (2) and the inner surface of the outer pipe (3).

7. 7. The double-pipe connection structure according to claim 6, wherein an extension pipe (14) is connected to an end of the heat exchanger inner pipe (2), and the joint between the heat exchanger inner pipe (2) and the extension pipe (14) is formed in an axial position that does not overlap with the axial position of the space inlet (10) or the space outlet (11) formed in the connecting member (13).

8. 7. The double pipe connection structure according to claim 6, wherein a joint between the heat exchanger inner pipe (2), the outer pipe (3), and the connecting member (13) is formed outside a flow path of the first fluid or the second fluid, whichever is hotter.

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