PREMIXING DEVICE AND HOT-WATER SUPPLY APPARATUS

Abstract

A premixing device includes: a main pipe of a cylindrical shape, which is disposed so as to surround an air passage and has a fuel chamber of an annular shape, which is formed inside a pipe wall; a butterfly valve having an air inlet hole and rotatably disposed so as to be located within the air passage; at least one support part which internally has a fuel passage communicating with the fuel chamber and extends radially inward from an inner wall surface of the main pipe so as to be located within the air passage downstream of the butterfly valve; and a venturi ring supported by the at least one support part so as to be located within the air passage downstream of the butterfly valve. The fuel passage has an outlet opening into a space of the air passage on an inner circumferential side of the venturi ring.

Claims

1. A premixing device, comprising: a main pipe of a cylindrical shape, which is disposed so as to surround an air passage and has a fuel chamber of an annular shape, which is formed inside a pipe wall; a butterfly valve having an air inlet hole and rotatably disposed so as to be located within the air passage; at least one support part which internally has a fuel passage communicating with the fuel chamber and extends radially inward from an inner wall surface of the main pipe so as to be located within the air passage downstream of the butterfly valve; and a venturi ring supported by the at least one support part so as to be located within the air passage downstream of the butterfly valve, the fuel passage having an outlet opening into a space of the air passage on an inner circumferential side of the venturi ring.

2. The premixing device according to claim 1, wherein the venturi ring is arranged within the air passage so as to be concentric with the air inlet hole of the butterfly valve in a fully closed state.

3. The premixing device according to claim 1, wherein the venturi ring is supported by a pair of support parts as the at least one support part, and the pair of support parts are disposed on opposite sides of the venturi ring within the air passage so as to extend along a rotational axis of the butterfly valve.

4. The premixing device according to claim 3, wherein each of the support parts has a first width along a pipe axial direction of the main pipe, which is greater than a second width along a direction perpendicular to the pipe axial direction.

5. The premixing device according to claim 4, wherein a ratio of the second width of each of the support parts to a maximum thickness of the butterfly valve is at least 0.8 and at most 1.2.

6. The premixing device according to claim 1, wherein the venturi ring has an inner circumferential surface into which the outlet of the fuel passage opens.

7. The premixing device according to claim 6, wherein the inner circumferential surface of the venturi ring includes: a first tapered portion in which an inner diameter of the venturi ring decreases toward downstream; a first throat portion located downstream of the first tapered portion and disposed in a region into which the outlet of the fuel passage opens; and a first enlarging diameter portion in which the inner diameter of the venturi ring expands toward downstream, the first enlarging diameter portion being located downstream of the first throat portion.

8. The premixing device according to claim 7, wherein the inner wall surface of the main pipe includes: a second tapered portion in which an inner diameter of the main pipe decreases toward downstream, the second tapered portion being located downstream of an upstream end of the venturi ring; a second throat portion located downstream of the second tapered portion and disposed at a position corresponding to a downstream end of the venturi ring in a pipe axial direction of the main pipe; and a second enlarging diameter portion in which the inner diameter of the main pipe expands toward downstream, the second enlarging diameter portion being located downstream of the second throat portion.

9. A hot-water supply apparatus, comprising: the premixing device according to claim 1 for generating an air-fuel mixture of fuel and combustion air; a burner for burning the fuel contained in the air-fuel mixture from the premixing device; and a heater for generating hot water by utilizing potential heat of combustion gas generated by burning the fuel in the burner.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0011] FIG. 1 is a diagram showing the schematic configuration of a hot-water supply apparatus according to an embodiment.

[0012] FIG. 2 is a cross-sectional view of a premixing unit of a premixing device according to an embodiment, and shows a state of a low flow rate region.

[0013] FIG. 3 is a cross-sectional view of the premixing unit taken along line A-A of FIG. 2.

[0014] FIG. 4 is a perspective cross-sectional view of the premixing unit corresponding to FIG. 2.

[0015] FIG. 5 is a perspective cross-sectional view of the premixing unit corresponding to FIG. 3.

[0016] FIG. 6 is a cross-sectional view of the premixing unit of the premixing device according to an embodiment, and shows a state of a high flow rate region.

[0017] FIG. 7 is a cross-sectional view of the premixing unit taken along line B-B of FIG. 6.

[0018] FIG. 8 is a perspective cross-sectional view of the premixing unit corresponding to FIG.

[0019] FIG. 9 is a perspective cross-sectional view of the premixing unit corresponding to FIG. 7.

DETAILED DESCRIPTION

[0020] Some embodiments of the present invention will be described below with reference to the accompanying drawings. It is intended, however, that unless particularly identified, dimensions, materials, shapes, relative positions and the like of components described or shown in the drawings as the embodiments shall be interpreted as illustrative only and not intended to limit the scope of the present invention.

[0021] First, a hot-water supply apparatus as an application example of a premixing device according to some embodiments will be described with reference to FIG. 1.

[0022] FIG. 1 is a diagram showing the schematic configuration of the hot-water supply apparatus according to an embodiment.

[0023] In some embodiments, as shown in FIG. 1, a hot-water supply apparatus 100 includes a fuel supply system 110, an air supply system 120, a premixing device 1 that generates an air-fuel mixture of fuel and combustion air, a burner 130 that burns the fuel contained in the air-fuel mixture, and a heater 140 for generating hot water.

[0024] The fuel supply system 110 is connected to a fuel supply port 2 of the premixing device 1 to supply fuel (fuel gas) to the premixing device 1.

[0025] The fuel supply system 110 includes a fuel supply line 112 and a fuel flow control valve 114 disposed in the fuel supply line 112. The fuel flow control valve 114 controls the flow rate of the fuel supplied to the premixing device 1 via the fuel supply line 112. In the exemplary embodiment shown in FIG. 1, the fuel supply system 110 includes a gas pressure regulator 116 disposed upstream of the fuel flow control valve 114 in the fuel supply line 112. The gas pressure regulator 116 maintains a supply pressure of the fuel gas to the premixing device 1 at a constant level. The gas pressure regulator 116 may be, for example, a zero governor for absorbing fluctuations in gas supply pressure in the fuel supply line 112 and supplying the fuel to the premixing device 1 at a gas pressure substantially equal to atmospheric pressure.

[0026] The air supply system 120 is connected to an air supply port 4 of the premixing device 1 to supply the combustion air to the premixing device 1.

[0027] The air supply system 120 includes an air supply line 122 and an air flow control valve 124 disposed in the air supply line 122. The air flow control valve 124 controls the flow rate of the combustion air supplied to the premixing device 1 via the air supply line 122.

[0028] Although FIG. 1 shows the fuel supply system 110 and the air supply system 120 separately from the premixing device 1, a part of the fuel supply system 110 or the air supply system 120 may be incorporated inside the premixing device 1.

[0029] For example, the fuel flow control valve 114 or the gas pressure regulator 116 of the fuel supply system 110 may be disposed in a fuel flow passage within the premixing device 1. Further, the air flow control valve 124 of the air supply system 120 may be disposed in an air flow passage within the premixing device 1.

[0030] The premixing device 1 includes a premixing unit 6 having the fuel supply port 2 and the air supply port 4, and a suction fan 8 disposed downstream of the premixing unit 6.

[0031] The premixing unit 6 which is a main part of the premixing device 1 mixes the fuel taken in from the fuel supply port 2 with the combustion air taken in from the air supply port 4 when an outlet of the premixing unit 6 becomes negative pressure due to drive of the suction fan 8, thereby generating the air-fuel mixture.

[0032] When the premixing device 1 is operated in a high flow rate region, a fluid can be agitated as it passes through the suction fan 8 on the downstream side of the premixing unit 6, and therefore it is unnecessary to complete premixing of the fuel and the combustion air in the premixing unit 6. In contrast, when the premixing device 1 is operated in the low flow rate region, the agitation of the fuel and the combustion air in the suction fan 8 cannot be expected very much, and it is necessary to sufficiently premix the fuel and the combustion air in the premixing unit 6. The premixing unit 6 that can promote premixing in the low flow rate region will be described in detail later.

[0033] A burner 130 is disposed downstream of the premixing device 1. The burner 130 burns the fuel contained in the air-fuel mixture generated in the premixing device 1 to generate high-temperature combustion gas. At this time, the combustion air contained in the air-fuel mixture is consumed as an oxidizing agent necessary for combustion reaction.

[0034] Potential heat of the combustion gas generated by the burner 130 is utilized to generate hot water in the heater 140. The heater 140 heats water by utilizing the potential heat of the combustion gas generated by the burner 130 to generate hot water.

[0035] In the exemplary embodiment shown in FIG. 1, the heater 140 is a heat exchanger 140A that exchanges heat between water flowing inside a heat transfer tube and combustion gas flowing outside the heat transfer tube. The heat exchanger 140A as the heater 140 generates hot water by directly using the potential heat of the combustion gas. The heat exchanger 140A is connected to an inlet line 142 communicating with an inlet side of the heat transfer tube and an outlet line 144 communicating with an outlet side of the heat transfer tube. Water is supplied from the inlet line 142 to the heat transfer tube of the heat exchanger 140A. The water supplied from the inlet line 142 is heated by the heat exchange with the combustion gas flowing outside the heat transfer tube and becomes hot water while flowing in the heat transfer tube, and flows out of the outlet line 144.

[0036] In another embodiment, the heater 140 is a heat exchanger that exchanges heat between water and a heat medium heated by heat exchange with the combustion gas. In this case, the heater 140 generates hot water by indirectly using the potential heat of the combustion gas.

[0037] The combustion gas having passed through the heater 140 is discharged as combustion exhaust gas via an exhaust gas passage 150.

[0038] Next, the premixing device 1 according to some embodiments will be described with reference to FIGS. 2 to 9.

[0039] FIG. 2 is a cross-sectional view of the premixing unit of the premixing device according to an embodiment. FIG. 3 is a cross-sectional view of the premixing unit taken along line A-A of FIG. 2. FIGS. 4 and 5 are each a perspective cross-sectional view of the premixing unit shown in FIG. 2, FIG. 4 shows a cross section corresponding to FIG. 2, and FIG. 5 shows a cross section corresponding to FIG. 3. FIGS. 2 to 5 each show a state of the premixing unit when the premixing device is operated at a minimum flow rate.

[0040] FIG. 6 is a cross-sectional view of the premixing unit of the premixing device according to an embodiment. FIG. 7 is a cross-sectional view of the premixing unit taken along line B-B of FIG. 6. FIGS. 8 and 9 are each a perspective cross-sectional view of the premixing unit shown in FIG. 6, FIG. 8 shows a cross section corresponding to FIG. 6, and FIG. 9 shows a cross section corresponding to FIG. 7. FIGS. 6 to 9 each show a state of the premixing unit when the premixing device is operated at a maximum flow rate.

[0041] In some embodiments, as shown in FIGS. 2 to 9, the premixing unit 6 includes a cylindrical main pipe 10 surrounding an air passage 11, a butterfly valve 30 located within the air passage 11, a support part 40 extending radially inward from an inner wall surface 12 of the main pipe 10, and a venturi ring 60 supported by the support part 40.

[0042] In the present specification, when referring to arrangement of each part of the premixing unit 6 in a pipe axial direction of the main pipe 10, the arrangement may be expressed as upstream or downstream in the pipe axial direction of the main pipe 10. The term upstream or downstream here means upstream or downstream of a flow direction of the air passage 11.

[0043] The main pipe 10 has the inner wall surface 12 defining the air passage 11. A contour of the air passage 11 is a circle in a cross section taken along a direction perpendicular to the pipe axial direction of the main pipe 10. The air passage 11 has a circular shape centered on a central axis of the main pipe 10 in a cross section perpendicular to the pipe axial direction of the main pipe 10.

[0044] In the embodiments shown in FIGS. 2 to 9, the main pipe 10 has the air supply port 4 at an upstream end of the air passage 11. The combustion air flowing into the air passage 11 from the air supply port 4 flows along the pipe axial direction of the main pipe 10 and reaches a mixture outlet 5 located at a downstream end of the air passage 11. The air-fuel mixture flowing out of the mixture outlet 5 is guided to the suction fan 8 (see FIG. 1) on the downstream side of the premixing unit 6.

[0045] In the exemplary embodiments shown in FIGS. 2 to 9, the main pipe 10 is a cylindrical pipe extending along the pipe axial direction, and the air passage 11 formed inside the main pipe 10 extends linearly along the pipe axial direction. In another embodiment, the main pipe 10 has a bent portion or a curved portion upstream of the butterfly valve 30 or downstream of the venturi ring 60.

[0046] In some embodiments, as shown in FIGS. 2 to 9, the inner wall surface 12 of the main pipe 10 includes, downstream of an upstream end of the venturi ring 60, a second tapered portion 12A narrowing the air passage 11, a second throat portion 12B where the air passage 11 is most narrowed, and a second enlarging diameter portion 12C widening the air passage 11 toward the mixture outlet 5.

[0047] The second tapered portion 12A is located downstream of the upstream end of the venturi ring 60. An inner diameter of the main pipe 10 decreases toward downstream in a range in the pipe axial direction, which corresponds to the second tapered portion 12A. The second throat portion 12B is located downstream of the second tapered portion 12A. The second throat portion 12B is disposed in a range including a downstream end of the venturi ring 60 in the pipe axial direction. In other words, the downstream end of the venturi ring 60 is located within a range in the pipe axial direction, which corresponds to the second throat portion 12B. The inner diameter of the main pipe 10 is maintained approximately constant near a minimum diameter in the range in the pipe axial direction, which corresponds to the second throat portion 12B. The second enlarging diameter portion 12C is located downstream of the second throat portion 12B. The inner diameter of the main pipe 10 increases toward downstream in a range in the pipe axial direction, which corresponds to the second enlarging diameter portion 12C.

[0048] In FIGS. 2 to 9, for the sake of descriptive convenience, the change in inner diameter of the main pipe 10 in the second tapered portion 12A, the second throat portion 12B, and the second enlarging diameter portion 12C is emphasized.

[0049] In contrast to the embodiments shown in FIGS. 2 to 9, in some other embodiments, the inner wall surface 12 of the main pipe 10 has a substantially constant inner diameter over the entire range in the pipe axial direction of the main pipe 10 from the air supply port 4 to the mixture outlet 5.

[0050] The main pipe 10 includes an annular fuel chamber 20 formed inside a pipe wall of the main pipe 10.

[0051] The fuel chamber 20 is an annular space for receiving the fuel gas from the fuel supply port 2. The fuel chamber 20 is disposed on an outer circumferential side of the air passage 11 so that at least a part of the fuel chamber 20 is located downstream of the butterfly valve 30 in the pipe axial direction. The fuel chamber 20 may be disposed around the entire circumference of the main pipe 10 or may be disposed in a partial range of the main pipe 10 in the circumferential direction.

[0052] In some embodiments, as shown in FIGS. 2 to 9, the main pipe 10 includes a fuel inlet pipe portion 14 protruding radially outward from an outer circumferential surface of the main pipe 10. The fuel inlet pipe portion 14 forms the fuel supply port 2. An inner flow passage of the fuel inlet pipe portion 14 communicates with the fuel chamber 20. The fuel gas from the fuel supply port 2 flows into the fuel chamber 20 via the fuel inlet pipe portion 14, and then flows out to the air passage 11 via a fuel passage 50 which will be described later.

[0053] From the viewpoint of ensuring that the fuel gas introduced from the fuel inlet pipe portion 14 is appropriately distributed to the fuel chamber 20, the fuel inlet pipe portion 14 may be disposed at a position that does not overlap a connection portion between the fuel chamber 20 and the fuel passage 50 in the pipe axial direction of the main pipe 10. In the exemplary embodiments shown in FIGS. 2 to 9, the fuel inlet pipe portion 14 is disposed downstream of the connection portion between the fuel chamber 20 and the fuel passage 50 in the pipe axial direction of the main pipe 10. Therefore, the fuel gas passing through the fuel inlet pipe portion 14 radially inward flows in the circumferential direction within the annular fuel chamber 20, and then flows from the fuel chamber 20 into the fuel passage 50.

[0054] In some embodiments, the fuel chamber 20 is formed between at least a plurality of parts that form the main pipe 10.

[0055] In the embodiments shown in FIGS. 2 to 9, the main pipe 10 is formed of a first part 210 having the fuel supply port 2 and the air supply port 4, and a second part 220 fitted to the first part 210. Specifically, the first part 210 is a pipe part forming an outer shape of the main pipe 10 over the entire length of the main pipe 10 and has, downstream in the pipe axial direction of the first part 210, a first recess 212 for receiving the second part 220. The second part 220 has a second recess 222 formed around the entire circumference on an outer circumferential surface of the second part 220. When the second part 220 is fitted to the first recess 212 of the first part 210, the annular fuel chamber 20 is formed between an inner circumferential surface of a portion of the first part 210, in which the first recess 212 is formed, and an outer circumferential surface of a portion of the second part 220, in which the second recess 222 is formed. A pair of seal rings 224 are disposed on both sides of the fuel chamber 20 in the pipe axial direction of the main pipe 10, and these seal rings 224 seal a gap between the first part 210 and the second part 220. The second part 220 is integrally provided with the venturi ring 60 and the support part 40 which will be described later.

[0056] In contrast to the embodiments shown in FIGS. 2 to 9, in some other embodiments, the main pipe 10 having the fuel chamber 20 inside the pipe wall is molded as a single piece by three-dimensional additive manufacturing.

[0057] The butterfly valve 30 is attached to the main pipe 10 so as to be located within the air passage 11. A rotational axis X (see FIGS. 4 and 8) of the butterfly valve 30 extends along the direction perpendicular to the pipe axial direction of the main pipe 10. The butterfly valve 30 is rotatable around the rotational axis X.

[0058] The butterfly valve 30 has an air inlet hole 31. The air inlet hole 31 is disposed on the rotational axis X. In other words, the rotational axis X of the butterfly valve 30 passes through the air inlet hole 31.

[0059] The air inlet hole 31 is disposed in a central region of the butterfly valve 30, as shown in FIGS. 6 and 8. The air inlet hole 31 may be a circular hole concentric with the butterfly valve 30.

[0060] As shown in FIGS. 2 to 5, in a fully closed state of the butterfly valve 30, the air inlet hole 31 is located in the central region of the air passage 11 in the cross section perpendicular to the pipe axial direction of the main pipe 10. Therefore, a flow within the air passage 11, which is throttled by the butterfly valve 30 in the fully closed state, biasedly flows to the central region of the air passage 11, in which the air inlet hole 31 is present.

[0061] In the exemplary embodiments shown in FIGS. 2 to 5, the air inlet hole 31 of the butterfly valve 30 in the fully closed state is concentric with the circular air passage 11 and is circular with its center on the central axis of the main pipe 10, in the cross section perpendicular to the pipe axial direction of the main pipe 10.

[0062] In contrast, in a fully open state of the butterfly valve 30, as shown in FIGS. 6 to 9, the butterfly valve 30 extends along the pipe axial direction of the main pipe 10 and a plane including the rotational axis X, air flows so as to pass through a side of the butterfly valve 30 within the air passage 11, and there is substantially no air flow passing through the air inlet hole 31.

[0063] In the exemplary embodiments shown in FIGS. 2 to 9, the butterfly valve 30 is driven by a motor 230 having an output shaft 232 penetrating the pipe wall of the main pipe 10. The butterfly valve 30 is attached to a tip of the output shaft 232 of the motor 230 by using a screw 234.

[0064] Seal rings 233 for sealing a gap between the output shaft 232 and the pipe wall are disposed in a portion where the output shaft 232 of the motor 230 penetrates the pipe wall of the main pipe 10.

[0065] In some embodiments, as shown in FIGS. 2 to 9, the butterfly valve 30 includes a central portion 32 disposed along the rotational axis X and a pair of side portions 34 gradually decreasing in thickness from the central portion 32. A thickness of the butterfly valve 30 becomes a maximum thickness t_max in the central portion 32 and becomes a minimum thickness t_min at an end of each of the side portions 34. Each of the side portions 34 decreases in thickness from the maximum thickness t_max to the minimum thickness t_min as it moves away from the central portion 32.

[0066] By adopting the butterfly valve 30 having the side portions 34 gradually decreasing in thickness, in the fully open state of the butterfly valve 30, the butterfly valve 30 becomes approximately streamlined within the air passage 11 as shown in FIGS. 7 and 9, and a resistance of the flow in the air passage 11 can be reduced.

[0067] At least one support part 40 (40A, 40B) is disposed downstream of the butterfly valve 30.

[0068] The support part 40 (40A, 40B) extends radially inward from the inner wall surface 12 of the main pipe 10 so as to be located within the air passage 11 downstream of the butterfly valve 30. The support part 40 (40A, 40B) has a hollow structure and internally has the fuel passage 50 communicating with the fuel chamber 20.

[0069] In some embodiments, as shown in FIGS. 4 and 8, a pair of support parts 40A, 40B each extend along the rotational axis X of the butterfly valve 30 within the air passage 11. The pair of support parts 40A and 40B are disposed on opposite sides of the venturi ring 60 which will be described later, within the air passage 11.

[0070] The pair of support parts 40A, 40B each include one end 42 connected to the inner wall surface 12 of the main pipe 10 and another end 44 connected to the venturi ring 60. The pair of support parts 40A, 40B each extend from the one end 42 to the another end 44 along the rotational axis X, in an annular space (an outer circumferential region of the air passage 11) between the inner wall surface 12 of the main pipe 10 and an outer circumferential surface of the venturi ring 60.

[0071] In some embodiments, each of the support parts 40 (40A, 40B) has a first width W1 (see FIGS. 2, 4, 6, and 8) along the pipe axial direction of the main pipe 10, which is greater than a second width W2 (see FIGS. 5 and 9) along the direction perpendicular to the pipe axial direction.

[0072] The first width W1 and the second width W2 of each of the support parts 40 (40A, 40B) may satisfy 2W1/W25.

[0073] Further, in some embodiments, the ratio of the second width W2 of each of the support parts 40 (40A, 40B) to the maximum thickness t_max of the butterfly valve 30 is at least 0.8 and at most 1.2.

[0074] As shown in FIGS. 2 to 9, the fuel passage 50 passes through the inside of each of the support parts 40 (40A, 40B) and extends along the radial direction of the main pipe 10.

[0075] The fuel passage 50 has an inlet 52 opening into the fuel chamber 20 and an outlet 54 opening into a space of the air passage 11 on an inner circumferential side of the venturi ring 60 (a central region 61 of the air passage 11). The fuel gas from the fuel chamber 20 flows out via the fuel passage 50 within the support part 40 to the space on the inner circumferential side of the venturi ring 60.

[0076] In some embodiments, the another end 44 of each of the support parts 40 (40A, 40B) is connected to the outer circumferential surface of the venturi ring 60, and the outlet 54 of the fuel passage 50 as an inner flow passage of each support part 40 opens into an inner circumferential surface 62 of the venturi ring 60.

[0077] In some other embodiments, the support part 40 (40A, 40B) penetrates the venturi ring 60 and extends to the space on the inner circumferential side of the venturi ring 60, and the outlet 54 of the fuel passage 50 opens into an outer surface of a portion of the support part 40, which protrudes on the inner circumferential side of the venturi ring 60. In this case as well, the outlet 54 of the fuel passage 50 opens into the space of the air passage 11 on the inner circumferential side of the venturi ring 60.

[0078] The venturi ring 60 is supported by at least the pair of support parts 40 (40A, 40B) so as to be located within the air passage 11 downstream of the butterfly valve 30.

[0079] The venturi ring 60 is an annular body extending in the circumferential direction around the pipe axis of the main pipe 10. The space on the inner circumferential side of the venturi ring 60, which is defined by the inner circumferential surface 62 of the venturi ring 60, forms the central region 61 of the air passage 11 as a part of the air passage 11. The outlet 54 of the fuel passage 50 opens into the space of the air passage 11 (the central region 61 of the air passage 11) on the inner circumferential side of the venturi ring 60, as described above. A space on an outer circumferential side of the venturi ring 60 forms an outer circumferential region of the air passage 11. The above-described support part 40 (40A, 40B) is arranged in the space of the air passage 11 on the outer circumferential side of the venturi ring 60.

[0080] An inner diameter D_venturi at the upstream end of the venturi ring 60 is at least 0.8 and at most 1.2 times an inner diameter D_valve of the air inlet hole 31 of the butterfly valve 30.

[0081] In some embodiments, as shown in FIGS. 2 to 9, the inner circumferential surface 62 of the venturi ring 60 includes a first tapered portion 62A narrowing the central region 61 of the air passage 11, a first throat portion 62B where the central region 61 of the air passage 11 is most narrowed, and a first enlarging diameter portion 62C widening the central region 61 of the air passage 11 toward the downstream end of the venturi ring 60.

[0082] The first tapered portion 62A is located upstream of the venturi ring 60. An inner diameter of the venturi ring 60 decreases toward downstream in a range in the pipe axial direction, which corresponds to the first tapered portion 62A. The first throat portion 62B is located downstream of the first tapered portion 62A. The inner diameter of the venturi ring 60 is maintained approximately constant near a minimum diameter in the range in the pipe axial direction, which corresponds to the first throat portion 62B. The first enlarging diameter portion 62C is located downstream of the first throat portion 62B. The inner diameter of the venturi ring 60 increases toward downstream in a range in the pipe axial direction, which corresponds to the first enlarging diameter portion 62C.

[0083] In FIGS. 2 to 9, for the sake of descriptive convenience, the change in inner diameter of the venturi ring 60 in the first tapered portion 62A, the first throat portion 62B, and the first enlarging diameter portion 62C is emphasized.

[0084] In some embodiments, the first throat portion 62B is disposed in a region of the inner circumferential surface 62 of the venturi ring 60, into which the outlet 54 of the fuel passage 50 opens.

[0085] In the exemplary embodiments shown in FIGS. 2 to 9, the outlet 54 of the fuel passage 50 is disposed in, of the inner circumferential surface 62 of the venturi ring 60, a part of the first tapered portion 62A, the first throat portion 62B, and a part of the first enlarging diameter portion 62C. That is, in the pipe axial direction of the main pipe 10, an upstream end 54A of the outlet 54 of the fuel passage 50 is located within a region of the inner circumferential surface 62 of the venturi ring 60, which is occupied by the first tapered portion 62A, and a downstream end 54B of the outlet 54 of the fuel passage 50 is located within a region of the inner circumferential surface 62 of the venturi ring 60, which is occupied by the first enlarging diameter portion 62C.

[0086] In some other embodiments, at least either of the upstream end 54A or the downstream end 54B of the outlet 54 of the fuel passage 50 is located within a region of the inner circumferential surface 62 of the venturi ring 60, which is occupied by the first throat portion 62B, in the pipe axial direction of the main pipe 10.

[0087] In some embodiments, as shown in FIGS. 2 to 5, the venturi ring 60 is arranged within the air passage 11 so as to be concentric with the air inlet hole 31 of the butterfly valve 30 in the fully closed state. That is, when the butterfly valve 30 is in the fully closed state, a circle defined by the inner circumferential surface 62 of the venturi ring 60 is concentric with a circle defining the contour of the air inlet hole 31 of the butterfly valve 30, as viewed from the pipe axial direction of the main pipe 10.

[0088] Therefore, in a low flow rate region where the butterfly valve 30 is in the fully closed state or a state close thereto, air which is throttled by the air inlet hole 31 and has a relatively high flow rate flows to the space (the central region 61 of the air passage 11) on the inner circumferential side of the venturi ring 60.

[0089] From the viewpoint of effectively taking in the air flow that has passed through the air inlet hole 31 to the inner circumferential side of the venturi ring 60, in the fully closed state of the butterfly valve 30, a distance from the air inlet hole 31 to the upstream end of the venturi ring 60 in the pipe axial direction may be at least 1.5 and at most 4 times the diameter D_valve of the air inlet hole 31.

[0090] In the premixing device 1 including the premixing unit 6 of the above-described configuration, in the fully closed state of the butterfly valve 30, the air flow in the air passage 11 is throttled by the butterfly valve 30 and passes through the air inlet hole 31 of the butterfly valve 30 (see solid arrows in FIGS. 2 to 5). Consequently, downstream of the butterfly valve 30, the air flow in the air passage 11 is biased toward the center and passes through a space (the central region 61 of the air passage 11) inside the venturi ring 60 (see the solid arrows in FIGS. 2 to 5). Then, downstream of the venturi ring 60, a vortex V is generated as indicated by a dashed line, due to a difference in flow velocity between the center and the outer circumferential side of the air passage 11. As a result, the vortex V promotes premixing of the fuel and the combustion air downstream of the venturi ring 60.

[0091] In contrast, in the fully open state of the butterfly valve 30, flows within the air passage 11 are substantially uniform (see solid arrows in FIGS. 6 to 9). Therefore, in contrast to the fully closed state of the butterfly valve 30, downstream of the venturi ring 60, substantially no vortex V caused by the difference in flow velocity is generated and a pressure loss in the main pipe 10 is reduced.

[0092] In particular, as in the exemplary embodiments shown in FIGS. 2 to 9, when the support part 40 (40A, 40B) extends along the rotational axis X of the butterfly valve 30, an increase in pressure loss in the support part 40 (40A, 40B) can be suppressed.

[0093] The characteristic configurations of the premixing device 1 and the hot-water supply apparatus 100 according to some embodiments described above are summarized as follows.

[0094] [1] A premixing device (1) according to at least some embodiments of the present invention, includes: a main pipe (10) of a cylindrical shape, which is disposed so as to surround an air passage (11) and has a fuel chamber (20) of an annular shape, which is formed inside a pipe wall; a butterfly valve (30) having an air inlet hole (31) and rotatably disposed so as to be located within the air passage (11); at least one support part (40) which internally has a fuel passage (50) communicating with the fuel chamber (20) and extends radially inward from an inner wall surface (12) of the main pipe (10) so as to be located within the air passage (11) downstream of the butterfly valve (30); and a venturi ring (60) supported by the at least one support part (40) so as to be located within the air passage (11) downstream of the butterfly valve (30). The fuel passage (50) has an outlet (54) opening into a space (61) of the air passage (11) on an inner circumferential side of the venturi ring (60).

[0095] According to the above configuration [1], in the low flow rate region where premixing is likely to be insufficient, by bringing the butterfly valve (30) into the fully closed state or the state close thereto, the air that has passed through the air inlet hole (31) is biased toward the central portion of the air passage (11) and premixing can be promoted by utilizing the vortex (V) caused by the difference in flow velocity of the flow on the downstream side of the venturi ring (60).

[0096] [2] In at least some embodiments, in the above configuration [1], the venturi ring (60) is arranged within the air passage (11) so as to be concentric with the air inlet hole (31) of the butterfly valve (30) in a fully closed state.

[0097] According to the above configuration [2], in the low flow rate region where the butterfly valve (30) is in the fully closed state or the state close thereto, the air which is throttled by the air inlet hole (31) and has the relatively high flow rate passes through the inner circumferential side of the venturi ring (60), a pressure in the space (61) on the inner circumferential side of the venturi ring (60) is effectively reduced, and the outflow of the fuel from the outlet (54) of the fuel passage (50) can be promoted.

[0098] [3] In at least some embodiments, in the above configuration [1] or [2], the venturi ring (60) is supported by a pair of support parts (40A, 40B) as the at least one support part (40), and the pair of support parts (40A, 40B) are disposed on opposite sides of the venturi ring (60) within the air passage (11) so as to extend along a rotational axis (X) of the butterfly valve (30).

[0099] According to the above configuration [3], in the high flow rate region where the butterfly valve (30) is fully open, when the air passage (11) is viewed from the upstream side, the butterfly valve (30) and the pair of support parts (40A, 40B) at least partially overlap, making it possible to suppress an increase in pressure loss due to the pair of support parts (40A, 40B).

[0100] [4] In at least some embodiments, in the above configuration [3], each of the support parts (40A, 40B) has a first width (W1) along a pipe axial direction of the main pipe (10), which is greater than a second width (W2) along a direction perpendicular to the pipe axial direction.

[0101] According to the above configuration [4], while ensuring a flow-passage cross-sectional area of the fuel passage (50) disposed inside the support part (40A, 40B), when the butterfly valve (30) is fully open, the overlap between the butterfly valve (30) and the support part (40A, 40B) is increased as viewed from the upstream side of the air passage (11), making it possible to suppress the increase in pressure loss due to the support part (40A, 40B) in the high flow rate region.

[0102] [5] In at least some embodiments, in the above configuration [4], a ratio of the second width (W2) of each of the support parts (40A, 40B) to a maximum thickness (t_max) of the butterfly valve (30) is at least 0.8 and at most 1.2.

[0103] According to the above configuration [5], in the high flow rate region where the butterfly valve (30) is substantially fully open, when the air passage (11) is viewed from the upstream side, most of each of the support parts (40A, 40B) overlaps the butterfly valve (30), making it possible to further suppress the increase in pressure loss due to the support part (40A, 40B).

[0104] [6] In at least some embodiments, in any of the above configurations [1] to [5], the venturi ring (60) has an inner circumferential surface (62) into which the outlet (54) of the fuel passage (50) opens.

[0105] According to the above configuration [6], for example, compared to a case in which a protrusion protruding to the inside of the venturi ring (60) is provided in order to direct the outlet (54) of the fuel passage (50) toward downstream, it is easier to ensure the flow-passage cross-sectional area of the flow passage (61) on the inner circumferential side of the venturi ring (60) and the pressure loss can be reduced.

[0106] [7] In at least some embodiments, in the above configuration [6], the inner circumferential surface (62) of the venturi ring (60) includes: a first tapered portion (62A) in which an inner diameter of the venturi ring (60) decreases toward downstream; a first throat portion (62B) located downstream of the first tapered portion (62A) and disposed in a region into which the outlet (54) of the fuel passage (50) opens; and a first enlarging diameter portion (62C) in which the inner diameter of the venturi ring (60) expands toward downstream, the first enlarging diameter portion (62C) being located downstream of the first throat portion (62B).

[0107] According to the above configuration [7], the air that has flowed into the space (61) on the inner circumferential side of the venturi ring (60) is throttled in the first tapered portion (62A) and the flow velocity increases, reducing the pressure in the first throat portion (62B). Further, due to an effect of static pressure recovery in the first enlarging diameter portion (62C) on the downstream side of the first throat portion (62B), the pressure in the first throat portion (62B), which is based on the downstream end of the venturi ring (60), is further reduced. Thus, the venturi ring (60) including the first tapered portion (62A), the first throat portion (62B), and the first enlarging diameter portion (62C) can reduce the pressure in the first throat portion (62B) disposed in the region into which the outlet (54) of the fuel passage (50) opens, and promote the outflow of the fuel from the outlet (54) of the fuel passage (50).

[0108] [8] In at least some embodiments, in the above configuration [7], the inner wall surface (12) of the main pipe (10) includes: a second tapered portion (12A) in which an inner diameter of the main pipe (10) decreases toward downstream, the second tapered portion (12A) being located downstream of an upstream end of the venturi ring (60); a second throat portion (12B) located downstream of the second tapered portion (12A) and disposed at a position corresponding to a downstream end of the venturi ring (60); and a second enlarging diameter portion (12C) in which the inner diameter of the main pipe (10) expands toward downstream, the second enlarging diameter portion (12C) being located downstream of the second throat portion (12B).

[0109] According to the above configuration [8], at the high flow rate, the air flow flowing along the inner wall surface (12) of the main pipe (10) is throttled in the second tapered portion (12A) and the flow velocity increases, reducing the pressure in the second throat portion (12B). Further, due to an effect of static pressure recovery in the second enlarging diameter portion (12C) on the downstream side of the second throat portion (12B), the pressure in the second throat portion (12B), which is based on the downstream end of the second enlarging diameter portion (12C), is further reduced. Thus, a flow passage shape of the main pipe (10) including the second tapered portion (12A), the second throat portion (12B), and the second enlarging diameter portion (12C) reduces the pressure in the second throat portion (12B) disposed at the position corresponding to the downstream end of the venturi ring (60). Therefore, the pressure in the first throat portion (62B) disposed in the region of the inner circumferential surface (62) of the venturi ring (60), into which the outlet (54) of the fuel passage (50) opens, is further reduced by the effect of reduced pressure due to the flow passage shape of the main pipe (10), in addition to the effect of reduced pressure due to the shape of the inside of the venturi ring (60), which is described in the above [5]. Therefore, even if the amount of throttling in the second tapered portion (12A) of the inner wall surface (12) of the main pipe (10) is small, it is possible to cause a sufficient amount of fuel to flow out of the outlet (54) of the fuel passage (50), and the pressure loss can be suppressed by the decrease in amount of throttling in the second tapered portion (12A) of the main pipe (10).

[0110] [9] A hot-water supply apparatus according to at least some embodiments of the present invention, includes: the premixing device (1) according to any of the above [1] to [8] for generating an air-fuel mixture of fuel and combustion air; a burner (130) for burning the fuel contained in the air-fuel mixture from the premixing device (1); and a heater (140) for generating hot water by utilizing potential heat of combustion gas generated by burning the fuel in the burner (130).

[0111] When the hot-water supply apparatus is cold started, the amount of combustion required in the burner is relatively large until warm-up of the hot-water supply apparatus is completed, but once the warm-up is completed, the amount of combustion required in the burner decreases. Therefore, it is desirable for the premixing device for the hot-water supply apparatus to reliably perform premixing even in the low flow rate region where it is difficult to expect a mixing effect between fuel and air when passing through a fan, and to achieve stable combustion in the burner.

[0112] In this regard, according to the above configuration [9], as described in the above [1], even in the low flow rate region, since premixing can be promoted by utilizing the vortex (V) caused by the difference in flow velocity of the flow on the downstream side of the venturi ring (60), it is possible to achieve stable combustion in the burner (130).