Premixing Device and Hot-Water Supply Apparatus

The present disclosure relates to a premixing device and a hot-water supply apparatus.

Conventionally, a e a venturi-shaped air passage, and fuel gas and combustion air are sucked in by a fan located downstream, thereby achieving premixing of fuel and air.

For example, Patent Document 1 describes a premixing device in which fuel gas is caused to flow out of a gap disposed in a venturi portion and the fuel gas is mixed with an air flow.

In the premixing device described in Patent Document 1, the amount of air flowing in the venturi portion can be adjusted by a butterfly valve.

Patent Document 1: JP2017-36889A

However, for example, in the conventional premixing device described in Patent Document 1, when a rotation speed of a fan is minimized and the butterfly valve is closed (i.e., when the premixing device is operated in a low flow rate region), momentum imparted to the fuel and the air by the fan is limited, and agitation of the fuel and the air in the fan cannot be expected.

Consequently, the fuel and the air reach a burner without being sufficiently premixed, which may impair combustion stability of the burner.

In view of the above, an object of at least some embodiments of the present invention is to provide a premixing device that can promote premixing of air and fuel in a low flow rate region.

A premixing device according to at least some embodiments of the present invention, 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.

According to at least some embodiments of the present invention, in the low flow rate region where premixing is likely to be insufficient, the air that has passed through the air inlet hole of the butterfly valve is biased toward the central portion of the air passage and premixing can be promoted by utilizing the vortex caused by the difference in flow velocity of the air flow on the downstream side of the venturi ring.

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.

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

is a diagram showing the schematic configuration of the hot-water supply apparatus according to an embodiment.

In some embodiments, as shown in, a hot-water supply apparatusincludes a fuel supply system, an air supply system, a premixing devicethat generates an air-fuel mixture of fuel and combustion air, a burnerthat burns the fuel contained in the air-fuel mixture, and a heaterfor generating hot water.

The fuel supply systemis connected to a fuel supply portof the premixing deviceto supply fuel (fuel gas) to the premixing device.

The fuel supply systemincludes a fuel supply lineand a fuel flow control valvedisposed in the fuel supply line. The fuel flow control valvecontrols the flow rate of the fuel supplied to the premixing devicevia the fuel supply line. In the exemplary embodiment shown in, the fuel supply systemincludes a gas pressure regulatordisposed upstream of the fuel flow control valvein the fuel supply line. The gas pressure regulatormaintains a supply pressure of the fuel gas to the premixing deviceat a constant level. The gas pressure regulatormay be, for example, a zero governor for absorbing fluctuations in gas supply pressure in the fuel supply lineand supplying the fuel to the premixing deviceat a gas pressure substantially equal to atmospheric pressure.

The air supply systemis connected to an air supply portof the premixing deviceto supply the combustion air to the premixing device.

The air supply systemincludes an air supply lineand an air flow control valvedisposed in the air supply line. The air flow control valvecontrols the flow rate of the combustion air supplied to the premixing devicevia the air supply line.

Althoughshows the fuel supply systemand the air supply systemseparately from the premixing device, a part of the fuel supply systemor the air supply systemmay be incorporated inside the premixing device.

For example, the fuel flow control valveor the gas pressure regulatorof the fuel supply systemmay be disposed in a fuel flow passage within the premixing device. Further, the air flow control valveof the air supply systemmay be disposed in an air flow passage within the premixing device.

The premixing deviceincludes a premixing unithaving the fuel supply portand the air supply port, and a suction fandisposed downstream of the premixing unit.

The premixing unitwhich is a main part of the premixing devicemixes the fuel taken in from the fuel supply portwith the combustion air taken in from the air supply portwhen an outlet of the premixing unitbecomes negative pressure due to drive of the suction fan, thereby generating the air-fuel mixture.

When the premixing deviceis operated in a high flow rate region, a fluid can be agitated as it passes through the suction fanon the downstream side of the premixing unit, and therefore it is unnecessary to complete premixing of the fuel and the combustion air in the premixing unit. In contrast, when the premixing deviceis operated in the low flow rate region, the agitation of the fuel and the combustion air in the suction fancannot be expected very much, and it is necessary to sufficiently premix the fuel and the combustion air in the premixing unit. The premixing unitthat can promote premixing in the low flow rate region will be described in detail later.

A burneris disposed downstream of the premixing device. The burnerburns the fuel contained in the air-fuel mixture generated in the premixing deviceto 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.

Potential heat of the combustion gas generated by the burneris utilized to generate hot water in the heater. The heaterheats water by utilizing the potential heat of the combustion gas generated by the burnerto generate hot water.

In the exemplary embodiment shown in, the heateris a heat exchangerA that exchanges heat between water flowing inside a heat transfer tube and combustion gas flowing outside the heat transfer tube. The heat exchangerA as the heatergenerates hot water by directly using the potential heat of the combustion gas. The heat exchangerA is connected to an inlet linecommunicating with an inlet side of the heat transfer tube and an outlet linecommunicating with an outlet side of the heat transfer tube. Water is supplied from the inlet lineto the heat transfer tube of the heat exchangerA. The water supplied from the inlet lineis 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.

In another embodiment, the heateris a heat exchanger that exchanges heat between water and a heat medium heated by heat exchange with the combustion gas. In this case, the heatergenerates hot water by indirectly using the potential heat of the combustion gas.

The combustion gas having passed through the heateris discharged as combustion exhaust gas via an exhaust gas passage.

Next, the premixing deviceaccording to some embodiments will be described with reference to.

is a cross-sectional view of the premixing unit of the premixing device according to an embodiment.is a cross-sectional view of the premixing unit taken along line A-A of.are each a perspective cross-sectional view of the premixing unit shown in,shows a cross section corresponding to, andshows a cross section corresponding to.each show a state of the premixing unit when the premixing device is operated at a minimum flow rate.

is a cross-sectional view of the premixing unit of the premixing device according to an embodiment.is a cross-sectional view of the premixing unit taken along line B-B of.are each a perspective cross-sectional view of the premixing unit shown in,shows a cross section corresponding to, andshows a cross section corresponding to.each show a state of the premixing unit when the premixing device is operated at a maximum flow rate.

In some embodiments, as shown in, the premixing unitincludes a cylindrical main pipesurrounding an air passage, a butterfly valvelocated within the air passage, a support partextending radially inward from an inner wall surfaceof the main pipe, and a venturi ringsupported by the support part.

In the present specification, when referring to arrangement of each part of the premixing unitin a pipe axial direction of the main pipe, the arrangement may be expressed as “upstream” or “downstream” in the pipe axial direction of the main pipe. The term “upstream” or “downstream” here means upstream or downstream of a flow direction of the air passage.

The main pipehas the inner wall surfacedefining the air passage. A contour of the air passageis a circle in a cross section taken along a direction perpendicular to the pipe axial direction of the main pipe. The air passagehas a circular shape centered on a central axis of the main pipein a cross section perpendicular to the pipe axial direction of the main pipe.

In the embodiments shown in, the main pipehas the air supply portat an upstream end of the air passage. The combustion air flowing into the air passagefrom the air supply portflows along the pipe axial direction of the main pipeand reaches a mixture outletlocated at a downstream end of the air passage. The air-fuel mixture flowing out of the mixture outletis guided to the suction fan(see) on the downstream side of the premixing unit.

In the exemplary embodiments shown in, the main pipeis a cylindrical pipe extending along the pipe axial direction, and the air passageformed inside the main pipeextends linearly along the pipe axial direction. In another embodiment, the main pipehas a bent portion or a curved portion upstream of the butterfly valveor downstream of the venturi ring.

In some embodiments, as shown in, the inner wall surfaceof the main pipeincludes, downstream of an upstream end of the venturi ring, a second tapered portionA narrowing the air passage, a second throat portionB where the air passageis most narrowed, and a second enlarging diameter portionC widening the air passagetoward the mixture outlet.

The second tapered portionA is located downstream of the upstream end of the venturi ring. An inner diameter of the main pipedecreases toward downstream in a range in the pipe axial direction, which corresponds to the second tapered portionA. The second throat portionB is located downstream of the second tapered portionA. The second throat portionB is disposed in a range including a downstream end of the venturi ringin the pipe axial direction. In other words, the downstream end of the venturi ringis located within a range in the pipe axial direction, which corresponds to the second throat portionB. The inner diameter of the main pipeis maintained approximately constant near a minimum diameter in the range in the pipe axial direction, which corresponds to the second throat portionB. The second enlarging diameter portionC is located downstream of the second throat portionB. The inner diameter of the main pipeincreases toward downstream in a range in the pipe axial direction, which corresponds to the second enlarging diameter portionC.

In, for the sake of descriptive convenience, the change in inner diameter of the main pipein the second tapered portionA, the second throat portionB, and the second enlarging diameter portionC is emphasized.

In contrast to the embodiments shown in, in some other embodiments, the inner wall surfaceof the main pipehas a substantially constant inner diameter over the entire range in the pipe axial direction of the main pipefrom the air supply portto the mixture outlet.

The main pipeincludes an annular fuel chamberformed inside a pipe wall of the main pipe.

The fuel chamberis an annular space for receiving the fuel gas from the fuel supply port. The fuel chamberis disposed on an outer circumferential side of the air passageso that at least a part of the fuel chamberis located downstream of the butterfly valvein the pipe axial direction. The fuel chambermay be disposed around the entire circumference of the main pipeor may be disposed in a partial range of the main pipein the circumferential direction.

In some embodiments, as shown in, the main pipeincludes a fuel inlet pipe portionprotruding radially outward from an outer circumferential surface of the main pipe. The fuel inlet pipe portionforms the fuel supply port. An inner flow passage of the fuel inlet pipe portioncommunicates with the fuel chamber. The fuel gas from the fuel supply portflows into the fuel chambervia the fuel inlet pipe portion, and then flows out to the air passagevia a fuel passagewhich will be described later.

From the viewpoint of ensuring that the fuel gas introduced from the fuel inlet pipe portionis appropriately distributed to the fuel chamber, the fuel inlet pipe portionmay be disposed at a position that does not overlap a connection portion between the fuel chamberand the fuel passagein the pipe axial direction of the main pipe. In the exemplary embodiments shown in, the fuel inlet pipe portionis disposed downstream of the connection portion between the fuel chamberand the fuel passagein the pipe axial direction of the main pipe. Therefore, the fuel gas passing through the fuel inlet pipe portionradially inward flows in the circumferential direction within the annular fuel chamber, and then flows from the fuel chamberinto the fuel passage.

In some embodiments, the fuel chamberis formed between at least a plurality of parts that form the main pipe.

In the embodiments shown in, the main pipeis formed of a first parthaving the fuel supply portand the air supply port, and a second partfitted to the first part. Specifically, the first partis a pipe part forming an outer shape of the main pipeover the entire length of the main pipeand has, downstream in the pipe axial direction of the first part, a first recessfor receiving the second part. The second parthas a second recessformed around the entire circumference on an outer circumferential surface of the second part. When the second partis fitted to the first recessof the first part, the annular fuel chamberis formed between an inner circumferential surface of a portion of the first part, in which the first recessis formed, and an outer circumferential surface of a portion of the second part, in which the second recessis formed. A pair of seal ringsare disposed on both sides of the fuel chamberin the pipe axial direction of the main pipe, and these seal ringsseal a gap between the first partand the second part. The second partis integrally provided with the venturi ringand the support partwhich will be described later.

In contrast to the embodiments shown in, in some other embodiments, the main pipehaving the fuel chamberinside the pipe wall is molded as a single piece by three-dimensional additive manufacturing.

The butterfly valveis attached to the main pipeso as to be located within the air passage. A rotational axis X (see) of the butterfly valveextends along the direction perpendicular to the pipe axial direction of the main pipe. The butterfly valveis rotatable around the rotational axis X.

The butterfly valvehas an air inlet hole. The air inlet holeis disposed on the rotational axis X. In other words, the rotational axis X of the butterfly valvepasses through the air inlet hole.

The air inlet holeis disposed in a central region of the butterfly valve, as shown in. The air inlet holemay be a circular hole concentric with the butterfly valve.