Electric heater and water pipe for electric boiler

Abstract

To suppress degradation of the performance of an electric heater.SOLUTION: An electric heater 7A includes: a pipe 23; a heat generation wire 25 arranged in the pipe 23; a terminal 26 arranged in one end part of the pipe 23 and connected to the heat generation wire 25; and a cover 29 connected to the other end of the pipe 23 by a welded part 28. The distance L between the heat generation wire 25 and the welded part 28 in the axial direction of the pipe 23 is set so that heat propagated from the heat generation wire 25 to the welded part 28 through at least a part of the pipe 23 is suppressed.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The technology disclosed herein relates to water tubes for electric heaters and electric boilers. [Background technology]

[0002] 2. Description of the Related Art In the technical field relating to electric heaters, an electric heater used in an electric boiler, such as that disclosed in Patent Document 1, is known. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2010-169356 A Summary of the Invention [Problem to be solved by the invention]

[0004] The electric heater includes a pipe and a heating wire disposed inside the pipe. If the electric heater has a welded portion, the heat of the heating wire may deteriorate the welded portion. The deterioration of the welded portion may result in a decrease in the performance of the electric heater.

[0005] The technique disclosed in this specification aims to suppress deterioration in the performance of an electric heater. [Means for solving the problem]

[0006] This specification discloses an electric heater including a pipe, a heating wire disposed inside the pipe, a terminal disposed at one end of the pipe and connected to the heating wire, and a cover connected to the other end of the pipe via a welded portion. In the axial direction of the pipe, the distance between the heating wire and the welded portion is determined so as to suppress heat transfer from the heating wire to the welded portion via at least a part of the pipe. Effect of the Invention

[0007] According to the technique disclosed in this specification, the deterioration of the performance of the electric heater is suppressed. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a front view showing a schematic diagram of an electric boiler according to a first embodiment. [Diagram 2] FIG. 2 is a side view diagrammatically illustrating the electric boiler according to the first embodiment. [Diagram 3] FIG. 3 is a cross-sectional view showing the heater device according to the first embodiment. [Figure 4] FIG. 4 is a cross-sectional view showing an electric heater according to the second embodiment. [Diagram 5] FIG. 5 is a cross-sectional view showing an electric heater according to the third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings, but the present disclosure is not limited to the embodiment. The components of the embodiments described below can be appropriately combined. In addition, some components may not be used.

[0010] In the embodiment, a three-dimensional orthogonal coordinate system is defined, and the positional relationship of each part will be described with reference to the three-dimensional orthogonal coordinate system. The direction parallel to the X-axis in a horizontal plane is defined as the X-axis direction. The direction parallel to the Y-axis in a horizontal plane perpendicular to the X-axis is defined as the Y-axis direction. The direction parallel to the Z-axis perpendicular to the horizontal plane is defined as the Z-axis direction. The Z-axis direction is the up-down direction. The +Z side is the upper side, and the -Z side is the lower side.

[0011] [First embodiment] A first embodiment will be described.

[0012] <Electric boiler> Fig. 1 is a front view showing an electric boiler 1 according to the present embodiment. Fig. 2 is a side view showing an electric boiler 1 according to the present embodiment. Fig. 1 and Fig. 2 each show a part of the electric boiler 1 in cross section.

[0013] As shown in Figures 1 and 2, the electric boiler 1 comprises a water supply device 2, a lower header 3 connected to the water supply device 2, a plurality of water tubes 4 connected to the lower header 3, a plurality of riser pipes 5 connected to each of the plurality of water tubes 4, an upper header 6 connected to the riser pipes 5, a heater device 8 including an electric heater 7A arranged inside the water tubes 4, and a water level detection device 9 for detecting the water level of the water tubes 4.

[0014] The water supply device 2 supplies water to the water pipes 4 via the lower header 3. The water supply device 2 has a water supply pipe 10 connected to the lower header 3, a water supply pump 11 arranged on the water supply pipe 10, and a water supply valve 12 arranged on the water supply pipe 10. When the water supply pump 11 is operated, water is supplied to the lower header 3 via the water supply pipe 10. When water is supplied to the lower header 3, water is supplied to the water pipes 4.

[0015] The lower header 3 contains water supplied from the water supply device 2. The lower header 3 is connected to the lower ends of the water pipes 4. The lower header 3 distributes the water supplied from the water supply device 2 to each of the multiple water pipes 4. The water supplied from the water supply device 2 to the lower header 3 is supplied to each of the multiple water pipes 4. A drain pipe 13 is connected to the lower part of the lower header 3. A drain valve 14 is disposed on the drain pipe 13. When the drain valve 14 opens, at least a portion of the water contained in the lower header 3 is discharged through the drain pipe 13.

[0016] The water pipe 4 distributes water from the lower header 3. The water pipe 4 is a cylindrical member having a water flow path. The water pipe 4 is arranged so that its central axis is parallel to the Z-axis. The lower end of the water pipe 4 is connected to the upper part of the lower header 3. Multiple water pipes 4 are arranged at intervals in the X-axis direction. Each of the multiple water pipes 4 is connected to the lower header 3.

[0017] The electric heater 7A is disposed inside the water tube 4. The electric heater 7A is a rod-shaped member. The electric heater 7A is disposed so that the central axis of the electric heater 7A is parallel to the Z-axis. The surface of the electric heater 7A faces the inner surface of the water tube 4 across a gap. Water from the lower header 3 is supplied between the inner surface of the water tube 4 and the surface of the electric heater 7A. The electric heater 7A is immersed in water inside the water tube 4. The surface of the electric heater 7A comes into contact with the water supplied inside the water tube 4. The contact between the surface of the electric heater 7A and the water heats the water and generates steam.

[0018] The riser pipe 5 circulates the steam generated in the water pipes 4. The riser pipe 5 is a cylindrical member having a steam flow path. The riser pipe 5 connects the water pipes 4 and the upper header 6. The steam generated in the water pipes 4 is supplied to the upper header 6 through the riser pipe 5. The lower end of the riser pipe 5 is connected to the upper end of the water pipe 4. The upper end of the riser pipe 5 is connected to the lower part of the upper header 6. A plurality of riser pipes 5 are provided so as to be connected to each of the plurality of water pipes 4. Each of the plurality of riser pipes 5 is connected to the upper header 6.

[0019] As shown in Figure 2, in the Y-axis direction, the positions of the lower header 3 and water pipes 4 are different from the position of the upper header 6. A part of the riser pipe 5 is bent. The lower end of the riser pipe 5 is connected to the -Y side surface of the upper part of the water pipe 4. The upper end of the riser pipe 5 is connected to the lower part of the upper header 6.

[0020] The upper header 6 receives the steam supplied from the riser pipes 5. The upper header 6 communicates with the upper ends of the water pipes 4 via the riser pipes 5. The upper header 6 collects the steam supplied from each of the multiple riser pipes 5. A steam pipe 15 is connected to the top of the upper header 6. A steam valve 16 is disposed on the steam pipe 15. When the steam valve 16 opens, at least a portion of the steam received in the upper header 6 is discharged via the steam pipe 15.

[0021] The water level detector 9 detects the water level of the water tube 4. The water level refers to the position of the surface of the water in the Z-axis direction. The water level detector 9 has a detection container 17, a plurality of electrode rods 18 arranged inside the detection container 17, a lower connecting pipe 19 connecting the detection container 17 and the lower header 3, and an upper connecting pipe 20 connecting the detection container 17 and the upper header 6. In this embodiment, three electrode rods 18 are provided. It is to be noted that, for example, four or more electrode rods 18 may be provided. The upper end of the electrode rod 18 is held on the upper lid of the detection container 17 via an insulating material. The lower end of the electrode rod 18 is separated from the detection container 17. The positions of the lower ends of the plurality of electrode rods 18 in the Z-axis direction are different from each other. The detection container 17 is formed of a conductive material. The detection container 17 functions as a common electrode for the plurality of electrode rods 18. Water is contained in the detection container 17. The water level of the detection container 17 and the water level of the water tube 4 are substantially equal. When the water contained in the detection container 17 comes into contact with the lower end of the electrode rod 18, electricity is passed between the detection container 17 and the electrode rod 18 via the water. When a current flows through the electrode rod 18, the water level detection device 9 determines that the electrode rod 18 has come into contact with the water. The water level detection device 9 detects the water level of the detection container 17 based on the presence or absence of a current flowing through each of the multiple electrode rods 18. The water level detection device 9 can detect the water level of the water tube 4 by detecting the water level of the detection container 17.

[0022] <Heater device> Fig. 3 is a cross-sectional view showing the heater device 8 according to this embodiment. As shown in Fig. 1, Fig. 2, and Fig. 3, the heater device 8 has an electric heater 7A, a flange 21 supported on the upper end of the water pipe 4, and a connector 22 connected to a power source.

[0023] The electric heater 7A is disposed inside the water tube 4 for the electric boiler 1. The electric heater 7A is a sheathed heater. The electric heater 7A has a surface that faces the inner surface of the water tube 4 with a gap therebetween. The electric heater 7A is inserted into the inside of the water tube 4 from an opening at the upper end of the water tube 4. A flange 21 is fixed to the upper end of the water tube 4. The heater device 8 is detachable from the water tube 4.

[0024] As shown in FIG. 3, the electric heater 7A includes a pipe 23, a core 24 arranged inside the pipe 23, a heating wire 25 arranged inside the pipe 23, a terminal 26 arranged at the upper end of the pipe 23, an insulating material 27 arranged inside the pipe 23, and a cover 29 connected to the lower end of the pipe 23 via a welded portion 28.

[0025] The pipe 23 is made of a metal. The pipe 23 is made of a metal having high thermal conductivity. Examples of the metal that forms the pipe 23 include stainless steel (SUS), nickel (Ni), and copper (Cu). The pipe 23 has a straight shape. The pipe 23 is arranged such that the central axis of the pipe 23 is parallel to the Z-axis.

[0026] The core 24 is a cylindrical member. The core 24 is made of an insulating material such as ceramics. The core 24 is disposed so that the central axis of the core 24 is parallel to the Z-axis.

[0027] The heating wire 25 is a nichrome wire. The heating wire 25 is disposed around the core 24 inside the pipe 23. The heating wire 25 is wound around the core 24 in a coil shape.

[0028] The terminal 26 is connected to the heating wire 25. A pair of terminals 26 are provided. At least a portion of the terminal 26 is disposed at the upper end of the pipe 23. At least a portion of the terminal 26 is disposed inside the core 24. The terminal 26 is connected to a power source via the connector 22. When a current is supplied from the power source to the heating wire 25 via the terminal 26, the heating wire 25 generates heat. One terminal 26 is connected to the upper end of the heating wire 25. The other terminal 26 is connected to the lower end of the heating wire 25. A current input from the power source to one terminal 26 flows through the heating wire 25 and is then output from the other terminal 26.

[0029] The insulating material 27 is filled between the pipe 23 and the core 24 and between the pipe 23 and the heating wire 25. The insulating material 27 is made of an insulating material such as magnesium oxide (MgO). The insulating material 27 is in a powder form.

[0030] The opening at the upper end of the pipe is closed by a sealing member 30. The flange 21 is disposed at the upper end of the pipe .

[0031] The opening at the lower end of the pipe 23 is closed by the cover 29. The cover 29 is formed of a metal. The cover 29 is formed of a metal with high thermal conductivity. Examples of the metal forming the cover 29 include stainless steel (SUS), nickel (Ni), and copper (Cu). In this embodiment, the cover 29 is substantially disk-shaped. The cover 29 is fixed to the lower end of the pipe 23 by welding. A weld 28 is formed at the boundary between the lower end of the pipe 23 and the cover 29. The weld 28 includes a weld metal and the heat-affected zones of the pipe 23 and the cover 29.

[0032] <Operation> Next, the operation of the heater device 8 will be described. With the electric heater 7A immersed in water inside the water tube 4, a current is supplied from a power source to the heating wire 25 via one terminal 26. As a result of the current being supplied to the heating wire 25, the heating wire 25 is heated, for example, to about 500°C. As the heating wire 25 is heated, the water inside the water tube 4 is heated and steam is generated. The temperature of the water (steam) inside the water tube 4 rises to, for example, about 180°C.

[0033] If the temperature of the welded portion 28 rises excessively while the welded portion 28 is immersed in the water inside the water pipe 4, the welded portion 28 may deteriorate. If the heat of the heating wire 25 is transferred to the welded portion 28 via at least a part of the pipe 23 while the welded portion 28 is immersed in water, cracks or corrosion may occur in the welded portion 28. If the temperature of the welded portion 28 rises to, for example, approximately 500°C due to the heat of the heating wire 25 while the welded portion 28 is immersed in water, cracks or corrosion may occur in the welded portion 28.

[0034] In this embodiment, the distance L between the heating wire 25 and the welded portion 28 in the Z-axis direction, which is the axial direction of the pipe 23, is determined so as to suppress heat transfer from the heating wire 25 to the welded portion 28 via at least a part of the pipe 23. In other words, the distance L is determined so as to prevent cracks or corrosion from occurring in the welded portion 28 when the heating wire 25 generates heat while the welded portion 28 is immersed in the water of the water pipe 4.

[0035] Distance L is determined so that even if the temperature of heating wire 25 rises to about 500° C., the temperature of welded portion 28 does not rise to about 500° C. Distance L is determined so that even if the temperature of heating wire 25 rises to about 500° C., the temperature of welded portion 28 becomes approximately the same as the temperature of the surrounding water (about 180° C.).

[0036] In this embodiment, the distance L is four or more times the outer diameter D of the pipe 23. For example, when the outer diameter D of the pipe 23 is 12 mm, the distance L may be 50 mm.

[0037] In this embodiment, the position of the lower end of the core 24 and the position of the lower end of the heating wire 25 are substantially equal in the Z-axis direction. An insulating material 27 is filled inside the pipe 23 between the lower end of the core 24 and the cover 29. Note that a member other than the insulating material 27 may be disposed inside the pipe 23 between the lower end of the core 24 and the cover 29. The lower end of the core 24 may protrude downward from the lower end of the heating wire 25 so that the lower end of the core 24 contacts the upper surface of the cover 29.

[0038] <Effects> As described above, according to this embodiment, the distance L between the lower end of the heating wire 25 and the welded portion 28 is determined so as to suppress the heat transferred from the heating wire 25 to the welded portion 28 through at least a part of the pipe 23. In this embodiment, the distance L is four times or more the outer diameter D of the pipe 23. Since the heat of the heating wire 25 is not easily transferred to the welded portion 28, deterioration of the welded portion 28 caused by the heat of the heating wire 25 is suppressed. Even if the heating wire 25 generates heat while the welded portion 28 is immersed in water, the occurrence of cracks or corrosion in the welded portion 28 is suppressed. In addition, since the heat of the heating wire 25 is not easily transferred to the welded portion 28, the thermal stress acting on the welded portion 28 is alleviated. Since deterioration of the welded portion 28 is suppressed, the deterioration of the performance of the electric heater 7A is suppressed.

[0039] [Second embodiment] A second embodiment will be described below. In the following description, the same or equivalent components as those in the above-described embodiment are denoted by the same reference numerals, and the description of those components will be simplified or omitted.

[0040] 4 is a cross-sectional view showing an electric heater 7B according to this embodiment. The electric heater 7B according to this embodiment does not have a welded part. The electric heater 7B includes a pipe 230, a first core 241 and a second core 242 arranged inside the pipe 230, a first heating wire 251 and a second heating wire 252 arranged inside the pipe 230, an electric wire 31 connecting the first heating wire 251 and the second heating wire 252, and an insulating material 27 arranged inside the pipe 230.

[0041] The pipe 230 is made of a metal. The pipe 230 is made of a metal with high thermal conductivity. Examples of metals that form the pipe 230 include stainless steel (SUS), nickel (Ni), and copper (Cu). A part of the pipe 230 is bent. In this embodiment, the pipe 230 is formed by bending the center part of a straight pipe. The pipe 230 has a first straight part 231, a second straight part 232, and a bent part 233 that connects the lower end of the first straight part 231 and the lower end of the second straight part 232.

[0042] The first straight portion 231 is disposed so that its central axis is parallel to the Z-axis. The second straight portion 232 is disposed so that its central axis is parallel to the Z-axis. The first straight portion 231 and the second straight portion 232 are disposed in parallel. In the Z-axis direction, the position of the upper end of the first straight portion 231 and the position of the upper end of the second straight portion 232 are substantially the same. In the Z-axis direction, the position of the lower end of the first straight portion 231 and the position of the lower end of the second straight portion 232 are substantially the same. The bent portion 233 is in the shape of a circular arc with the center of the bent portion 233 bulging downward.

[0043] Each of the first core 241 and the second core 242 is a cylindrical member. Each of the first core 241 and the second core 242 is formed of an insulating material such as ceramics. The first core 241 is disposed inside the first straight portion 231. The second core 242 is disposed inside the second straight portion 232. No core (the first core 241 and the second core 242) is disposed inside the bent portion 233.

[0044] The length of the first core 241 and the length of the second core 242 are substantially the same. The thickness of the first core 241 and the thickness of the second core 242 are substantially the same. The first core 241 is disposed so that the central axis of the first core 241 and the Z axis are parallel. The second core 242 is disposed so that the central axis of the second core 242 and the Z axis are parallel. The first core 241 and the second core 242 are disposed in parallel. In the Z axis direction, the position of the upper end of the first core 241 and the position of the upper end of the second core 242 are substantially the same. In the Z axis direction, the position of the lower end of the first core 241 and the position of the lower end of the second core 242 are substantially the same.

[0045] Each of the first heating wire 251 and the second heating wire 252 is a nichrome wire. The first heating wire 251 is disposed inside the first straight portion 231. The first heating wire 251 is disposed around the first core 241 inside the first straight portion 231. The first heating wire 251 is wound in a coil shape around the first core 241. The second heating wire 252 is disposed inside the second straight portion 232. The second heating wire 252 is disposed around the second core 242 inside the second straight portion 232. The second heating wire 252 is wound in a coil shape around the second core 242.

[0046] The length of the first heating wire 251 is substantially the same as the length of the second heating wire 252. The thickness of the first heating wire 251 is substantially the same as the thickness of the second heating wire 252.

[0047] The electric wire 31 is disposed inside the bent portion 233. The electric wire 31 connects the lower end of the first heating wire 251 and the lower end of the second heating wire 252. The electric wire 31 is made of a conductive material. The electric wire 31 may be a nichrome wire or a copper wire.

[0048] The insulating material 27 is filled inside the pipe 230. The insulating material 27 is filled between the first straight portion 231 and the first core 241 and the first heating wire 251. The insulating material 27 is filled between the second straight portion 232 and the second core 242 and the second heating wire 252. The insulating material 27 is filled inside the bent portion 233.

[0049] In this embodiment, the electric heater 7B has a first terminal 261 disposed at an upper end of the first straight portion 231 and a second terminal 262 disposed at an upper end of the second straight portion 232. The first terminal 261 is connected to an upper end of the first heating wire 251. The second terminal 262 is connected to an upper end of the second heating wire 252.

[0050] Next, the operation of the electric heater 7B will be described. The electric heater 7B is disposed inside the water tube 4 so that the bent portion 233 is immersed in the water inside the water tube 4, and the upper end of the first straight portion 231 and the upper end of the second straight portion 232 are not immersed in the water inside the water tube 4. When the electric heater 7B is immersed in the water inside the water tube 4, a current is input from a power source to the first terminal 261. The current input to the first terminal 261 flows through the first heating wire 251, flows through the electric wire 31, and is then supplied to the second heating wire 252. The current supplied from the electric wire 31 to the second heating wire 252 flows through the second heating wire 252, and is then output from the second terminal 262. When a current is supplied to each of the first heating wire 251 and the second heating wire 252, the first heating wire 251 and the second heating wire 252 are heated, and the water inside the water tube 4 is heated and steam is generated.

[0051] As described above, in this embodiment, the electric heater 7B does not have a welded portion. Therefore, deterioration of the welded portion due to the heat of the first heating wire 251 and the second heating wire 252 does not occur. Therefore, deterioration of the performance of the electric heater 7B is suppressed.

[0052] [Third embodiment] A third embodiment will be described below. In the following description, the same or equivalent components as those in the above-described embodiment are denoted by the same reference numerals, and the description of those components will be simplified or omitted.

[0053] 5 is a cross-sectional view showing an electric heater 7C according to this embodiment. The electric heater 7C according to this embodiment is a modified example of the electric heater 7B according to the second embodiment described above. Like the electric heater 7B, the electric heater 7C does not have a welded portion. The electric heater 7C does not have the electric wire 31 described in the second embodiment described above.

[0054] The electric heater 7C includes a pipe 230, a first core 241 and a second core 242 arranged inside the pipe 230, a first heating wire 251 and a second heating wire 252 arranged inside the pipe 230, and an insulating material 27 arranged inside the pipe 230.

[0055] Pipe 230 has a first straight portion 231, a second straight portion 232, and a bent portion 233 connecting a lower end of first straight portion 231 and a lower end of second straight portion 232. Pipe 230 is formed by bending the center portion of a straight pipe.

[0056] The first core 241 is disposed inside the first straight portion 231. The second core 242 is disposed inside the second straight portion 232. No cores (the first core 241 and the second core 242) are disposed inside the bent portion 233.

[0057] The first heating wire 251 is disposed around the first core 241 on the inner side of the first straight portion 231. The second heating wire 252 is disposed around the second core 242 on the inner side of the second straight portion 232.

[0058] The insulating material 27 is filled inside the pipe 230. The insulating material 27 is filled between the first straight portion 231 and the first core 241 and the first heating wire 251. The insulating material 27 is filled between the second straight portion 232 and the second core 242 and the second heating wire 252. The insulating material 27 is filled inside the bent portion 233.

[0059] In this embodiment, the electric heater 7C has a pair of first terminals 261A, 261B arranged at the upper end of the first straight portion 231, and a pair of second terminals 262A, 262B arranged at the upper end of the second straight portion 232. The pair of first terminals 261A, 261B are connected to the first heating wire 251. The pair of second terminals 262A, 262B are connected to the second heating wire 252. The first terminal 261A is connected to the upper end of the first heating wire 251. The first terminal 261B is connected to the lower end of the first heating wire 251. The second terminal 262A is connected to the upper end of the second heating wire 252. The second terminal 262B is connected to the lower end of the second heating wire 252.

[0060] Next, the operation of the electric heater 7C will be described. The electric heater 7C is disposed inside the water tube 4 so that the bent portion 233 is immersed in the water inside the water tube 4, and the upper end of the first straight portion 231 and the upper end of the second straight portion 232 are not immersed in the water inside the water tube 4. With the electric heater 7C immersed in the water inside the water tube 4, a current is input from the power source to each of the first terminal 261A and the second terminal 262A.

[0061] A current input to one of the first terminals 261A flows through the first heating wire 251 and is then output from the other of the first terminals 261B. A current input to one of the second terminals 262A flows through the second heating wire 252 and is then output from the other of the second terminals 262B. When a current is supplied to each of the first heating wire 251 and the second heating wire 252, the first heating wire 251 and the second heating wire 252 are heated, and the water inside the water tube 4 is heated and steam is generated.

[0062] As described above, in this embodiment, the electric heater 7C does not have a welded portion. Therefore, deterioration of the welded portion due to the heat of the first heating wire 251 and the second heating wire 252 does not occur. Therefore, deterioration of the performance of the electric heater 7C is suppressed.

[0063] [Contribution to the United Nations-led Sustainable Development Goals (SDGs)] This disclosure includes matters that contribute to achieving Goal 12 "Responsible consumption and production" and Goal 13 "Take urgent action to combat climate change" of the Sustainable Development Goals (SDGs). [Explanation of symbols]

[0064] 1...electric boiler, 2...feedwater device, 3...lower header, 4...water pipe, 5...rising pipe, 6...upper header, 7A...electric heater, 7B...electric heater, 7C...electric heater, 8...heater device, 9...water level detection device, 10...feedwater pipe, 11...feedwater pump, 12...feedwater valve, 13...drain pipe, 14...drain valve, 15...steam pipe, 16...steam valve, 17...detection vessel, 18...electrode rod, 19...lower connecting pipe, 20...upper connecting pipe, 21...flange, 22...connector, 23...pipe, 24...connector A, 25...heating wire, 26...terminal, 27...insulating material, 28...welded portion, 29...cover, 30...sealing member, 31...electric wire, 230...pipe, 231...first straight portion, 232...second straight portion, 233...bent portion, 241...first core, 242...second core, 251...first heating wire, 252...second heating wire, 261...first terminal, 261A...first terminal, 261B...first terminal, 262...second terminal, 262A...second terminal, 262B...second terminal, D...outer diameter, L...distance.

Claims

1. Pipes and A heating wire disposed inside the pipe; a terminal disposed at one end of the pipe and connected to the heating wire; a cover connected to the other end of the pipe via a welded portion; In the axial direction of the pipe, a distance between the heating wire and the welded portion is determined so as to suppress heat transfer from the heating wire to the welded portion through at least a part of the pipe. Electric heater.

2. The distance is determined so that cracks or corrosion do not occur in the welded portion when the heating wire generates heat in a state where the welded portion is immersed in water.

2. The electric heater according to claim 1.

3. The distance is equal to or greater than four times the outer diameter of the pipe.

2. The electric heater according to claim 1.

4. a pipe having a first straight portion, a second straight portion, and a bent portion connecting one end of the first straight portion and one end of the second straight portion; a first heating wire disposed inside the first straight portion; A second heating wire is disposed inside the second straight portion. Electric heater.

5. a first core disposed inside the first straight portion; a second core disposed inside the second straight portion, the first heating wire is disposed around the first core, The second heating wire is disposed around the second core.

5. The electric heater according to claim 4.

6. a first terminal disposed at the other end of the first straight portion and connected to the first heating wire; a second terminal disposed at the other end of the second straight portion and connected to the second heating wire; an electric wire disposed inside the bent portion and connecting the first heating wire and the second heating wire; A current input to the first terminal flows through the first heating wire, the electric wire, and the second heating wire, and is then output from the second terminal.

6. The electric heater according to claim 5.

7. a pair of first terminals disposed at the other end of the first straight portion and connected to the first heating wire; a pair of second terminals disposed at the other end of the second straight portion and connected to the second heating wire; A current input to one of the first terminals flows through the first heating wire and is then output from the other first terminal, A current input to one of the second terminals flows through the second heating wire and is then output from the other second terminal.

5. The electric heater according to claim 4.

8. 5. The electric heater according to claim 4, wherein the bent portion is immersed in water, and the electric heater is disposed inside so that the other end of the first straight portion and the other end of the second straight portion are not immersed in water. Water tubes for electric boilers.

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