JPS63207911A - Fluid heating device - Google Patents

Abstract

PURPOSE:To effectively transfer combustion heat without burning a fire combustion means and a heat exchange part so as to prevent incomplete combustion by providing block-shaped or column-shaped radiators disposed in a gas- permeable manner between heat transfer tubes of a first heat transfer tube group and/or at the downstream in the vicinity thereof and a second transfer tube group disposed at the downstream in the vicinity of the radiators. CONSTITUTION:Block-shaped or column-shaped radiation elements are disposed between heat transfer tubes of a first heat transfer tube group and/or at the downstream in the vicinity thereof in a combustion gas permeable manner. Each of the block-shaped or column-shaped radiators are preferably made from a heat-resisting material such as silicon carbide, silicon nitride, ceramics such as cordierite or the like, or heat-resisting steel. The second heat transfer tube group is disposed at the downstream in the vicinity of heat transfer tube group 21. The block-shaped radiation element 20 emits radiant heat to both the first heat transfer group 19 and the second heat transfer group 21 disposed in a zigzag manner. The radiator 20 has a configuration of a spherical body, a cubic body, a rectangular parallelpiped, or a shape analogous thereto such as a golf ball or a Rugby ball.

Description

DETAILED DESCRIPTION OF THE INVENTION TECHNICAL FIELD The present invention relates to a fluid heating device used in water heaters, bathtubs, hot water boilers, and the like.

"Prior Art and its Problems" Conventionally, in fluid heating devices such as water heaters, bathtubs, and hot water boilers, after increasing the fuel to vAm in the combustion chamber downstream of the burner, the combustion gas is transferred between a group of heat transfer tubes. It was designed to heat a fluid such as water flowing inside a group of heat exchanger tubes, mainly by using confrontational heat transfer.

In recent years, in order to make these fluid heating devices as compact as possible, there has been a trend to reduce the size of the combustion chamber as much as possible and to increase the amount of heat transferred per unit volume of the heat exchange section.

By the way, if you simply downsize the combustion chamber, it will burn! The flame extends to the heat exchanger without completing the combustion reaction inside the tube, and as a result, the fuel in the middle of the combustion reaction comes into contact with the wall of the heat exchanger tube and the flame is cooled, stopping the combustion reaction and causing incomplete combustion. Combustion could occur. This not only results in a loss of fuel, but also generates carbon oxide, soot, aldehyde, etc., which has an adverse effect on the human body.

In addition, if the combustion chamber is downsized and integrated with the heat exchange section, if unburned fuel components are deposited on the surface of the heat exchanger tube, the heat exchanger tube may be overheated and damaged, and the mixture of combustion gases in the combustion chamber may be disrupted. When the temperature distribution worsens, the temperature distribution tends to widen, and the heat transfer load increases locally, which can also damage the heat transfer tubes.

For this reason, there is a limit to the miniaturization of the combustion chamber; for example, in currently commercially available gas water heaters, the size ratio between the combustion chamber and the heat exchanger is about 2:1, and the size difference between the burner tip and the downstream The distance from the heat exchanger tube is 20 to 30 cm, and the temperature is 1!
ff load is 5x 10' kcal/m3/hr
It was suppressed to a certain extent. It has become difficult to make the combustion chamber any smaller and bring the heat exchanger closer to the flame because this may accelerate damage to the heat exchanger tubes or increase the generation of CO.

As long as convection heat transfer is used, in order to increase the amount of heat transferred per unit volume of the heat exchange section, the distance between plate fins should be narrowed and the number of plate fins should be increased to increase the heat transfer area per unit volume. Measures can be taken to increase the heat transfer coefficient by increasing the flow rate of the combustion gas, or by increasing the temperature of the combustion gas flowing into the heat exchanger to increase the temperature difference between the heating side and the heated side. It becomes necessary.

However, in order to prevent clogging between the plate fins, the lower limit of the plate fin interval is about 2.6 mm. In order to suppress pressure loss, the upper limit of the combustion gas flow velocity is about 10 m/s. Roughly speaking, if the temperature of the combustion gas flowing into the heat exchange section is increased, the temperature at the tip of the plate fin will rise, causing problems with heat resistance and durability, so the upper limit of the combustion gas inflow temperature is about 1000℃. . Thus, there has been a limit to the miniaturization of the heat exchange section.

The present inventors previously disclosed in Japanese Patent Application No. 60-223980 that a first heat exchanger tube group and then a second heat exchanger tube group were provided downstream of a burner, etc., and the first heat exchanger tube group and the second heat exchanger tube group were We have proposed a fluid heating bag M in which a breathable radiator is placed between the groups. Since this fluid heating device uses a ceramic honeycomb flat plate as the radiator, the radiator may not have sufficient strength, or a considerable temperature difference may occur within the plane of the radiator, leading to damage. Ta.

"Objective of the Invention" An object of the present invention is to solve the problems of the prior art described above, to effectively transfer combustion heat without burning out the combustion means and the heat exchange part, and to suppress incomplete combustion. The object of the present invention is to provide a fluid-heated snow making device that can reduce the size of the entire device.

"Structure of the Invention" The fluid heating device according to the present invention includes a combustion means, a first heat exchanger tube group arranged in the vicinity downstream of the combustion means (between the first heat exchanger tube group and/or the first heat exchanger tube group and/or adjacent downstream of the combustion means). It is characterized by comprising a block-like or columnar radiator arranged to allow ventilation, and a second group of heat exchanger tubes arranged close to and downstream of the radiator.

In a preferred embodiment of the invention, the radiator is made of ceramics.

In another preferred embodiment of the present invention, the radiator is placed on the first group of heat exchanger tubes.

In the present invention, the combustion means uses gaseous fuel such as city gas, propane gas, and natural gas, or vaporized liquid fuel such as kerosene, and the combustion air and fuel are separately sent to the combustion chamber. A diffusion combustion type burner is used, or a premix combustion type burner is used, in which combustion air and the above-mentioned fuel are mixed in advance at a required ratio and then supplied to the combustion chamber.

The first heat exchanger tube group is preferably arranged in multiple stages, particularly in a staggered manner, and is generally provided downstream of and close to the combustion means.

The upstream edge of the heat exchanger tube (the most upstream heat exchanger tube when there are multiple stages) constituting the first heat exchanger tube group is placed, for example, in the flame formed by the combustion means or at a position close to the tip of the flame. Ru. Specifically, the fuel gas discharge port of the combustion means (
For example, the distance between the burner tip) and the upstream edge of the heat transfer tube described above is preferably 5 to 50 mm. In other words,
The length of the flame varies depending on the design of the combustion means, but is generally about 5 to 50 mm, so the most upstream heat exchanger tube in the first heat exchanger tube group is ultimately placed near the tip of the flame. become.

If the first heat transfer tube group is placed at a position farther from the combustion means than the above position, the temperature of the combustion gas will decrease due to heat loss or cooling pipes in the casing surrounding the combustion chamber.
There is a possibility that the effects of the present invention cannot be sufficiently obtained, or the gas thickness increases and the radiant heat input from the high temperature combustion gas to the burner increases, leading to damage to the burner and backfire. The first heat transfer tube group is closest to the combustion means and is exposed to high-temperature combustion gas, but is cooled by fluid such as water flowing inside, so thermal damage is prevented.

The first group of heat transfer tubes has fins on the outer surface (although it is preferable to do so without fins), since the surrounding combustion gas temperature is high and the heat transfer coefficient is also high due to radiation heat transfer from the radiator, which will be described later. From the viewpoint of increasing the amount of heat, it is also possible to use a so-called lo-fin type having fins with a height of 2 mm or less, for example.

Between the first heat exchanger tube group and/or adjacent downstream,
A block or columnar radiator is arranged to allow ventilation of combustion gases. In this way, in the present invention, a lump or columnar body, which has a simpler shape than a ceramic honeycomb plate or a porous ceramic plate, is used as the radiator, making it easier to manufacture the radiator and select the shape.
It also has the advantage that it can be used in any of the fluid heating devices with various heating temperature conditions, heating amounts, etc. In addition, since it has a simple shape, press molded bodies or ceramic hot press sintered bodies can be used, and as a result, it is possible to heat the radiator to a high temperature of 100 to 1300 degrees Celsius, which allows radiation to be transmitted. The amount of heat can be significantly increased.

This block-shaped or columnar radiator is made of heat-resistant material, such as silicon carbide, to generate effective radiant heat at high temperatures.
Ceramics such as silicon nitride and cordierite, or heat-resistant steel are preferred.

The block-like or columnar radiator converts the thermal energy of the combustion gas into strong radiant energy, and mainly irradiates the first heat exchanger tube group with the radiant heat, regardless of the flow of the combustion gas. The first heat transfer tube group is heated by the radiant heat transfer from the radiator and the convective heat transfer by the combustion gas, and the fluid flowing therein is heated. In general, since the radiator is heated to a high temperature, the CO1 contained in the combustion gas
It promotes the oxidation reaction of unburned components such as IC and exerts a kind of catalytic effect.

The second heat exchanger tube group is arranged adjacent to and downstream of the radiator. This second heat transfer tube group is also heated by convective heat transfer from the combustion gas and radiant heat transfer from the radiant, and the fluid flowing inside it is heated. In order to improve heat transfer efficiency, the second heat transfer tube group preferably has fins on the outer surface.In order to ensure that the combustion gases come into contact with each other evenly, the second heat transfer tube group has heat transfer tubes arranged in a staggered manner. They can also be arranged in a shape.

The heat exchanger tubes of the first and second heat exchanger tube groups are made of materials with excellent thermal conductivity and corrosion resistance, such as copper, stainless steel, aluminum, aluminum alloy, titanium, titanium alloy, silicon carbide, and silicon nitride. It is preferable that, in particular,
It has high thermal conductivity, high emissivity, low coefficient of linear expansion, and high strength.
Most preferred are reactive sintered silicon carbide, which has excellent formability, or copper, which is a highly thermally conductive material.

In the case of the present invention, by placing the first heat exchanger tube close to the combustion means, it is conceivable that the first and second heat exchanger tube groups receive a large heat transfer load and become locally high temperature. Furthermore, depending on the conditions, it is possible that the fluid to be heated, such as water, may locally boil and the generated steam may cause heat transfer, resulting in a locally extremely high temperature. therefore,
If the heat transfer tube is made of metal with poor heat resistance, the heat transfer tube will be heated and violently oxidized, and in extreme cases, it may melt, so it is desirable to select the material, layout, usage conditions, etc. appropriately. In this respect, ceramics are particularly preferable for heat exchanger tubes in high-temperature parts because sufficient heat resistance can be obtained. Additionally, when attempting to recover not only the sensible heat but also the latent heat of the combustion gas, nitric acid may be generated in the low-temperature heat exchanger (natural gas itself is clean, but the high-temperature NOX generated by combustion
(condensed with moisture condensed on the surface of the heat exchanger tube to form nitric acid); from this point of view as well, it is preferable that the low-temperature heat exchange section be made of ceramic, which has corrosion resistance.

For the same reason, the material of the fins provided on the outer surface of the heat exchanger tube in the high temperature section or the low temperature section is also preferably ceramic.

"Embodiments of the Invention" Examples of the fluid heating device according to the present invention will be described below with reference to the drawings.

The fluid heating device 11 shown in FIG. 1 is entirely surrounded by a casing 12 whose upper part is connected to an exhaust port (not shown).
The cage jig 12 includes a fan casing 13, a mixing chamber 14, and a combustion chamber 15 that communicate with each other.

A fan 16 is incorporated in the fan casing 13,
A fuel gas nozzle 17 is disposed at the discharge portion of the fan 16. Fuel gas is introduced into the fuel gas nozzle 17 from a gas supply source (not shown). Accordingly, the air flow from the fan 16 and the fuel gas from the fuel gas nozzle 17 are supplied from the fan casing 13 to the mixing chamber 14 to create a premixed mixture of fuel gas and air.

At the boundary between the mixing chamber 14 and the combustion chamber 15, a surface burner plate 18 is disposed as a combustion means. This surface burner plate 18 has porous holes, and the premixture that has passed through these holes forms a flame in a planar shape on the downstream side of the surface burner plate 18. Note that the ignition source necessary for starting is omitted from the illustration.

A first heat exchanger tube group 19 is arranged in a staggered manner in the vicinity of the surface burner plate 18 within the casing 12 . In this embodiment, each heat exchanger tube of the first heat exchanger tube group 19 has an outer diameter of 12 to 20 mm and a wall thickness of 0.6 to 2.0 mrn.

As the outer diameter of the heat transfer tube becomes smaller, the ratio of the outer surface area of the heat transfer tube per unit volume of the fluid flowing inside increases, and the amount of radiant heat received increases, but on the other hand, the number of required heat transfer tubes also increases, and the If boiling occurs within the pipe, the possibility of blockage of the flow path due to bubbles also increases. Considering the efficiency of the fluid heating device of the present invention, the above size range is preferable for water heaters and the like.

It is preferable that the heat exchanger tubes be arranged at intervals of 6 to 30 mm, which is approximately the same as the outer diameter of the heat exchanger tubes. If this interval is too small, the pressure drop when the combustion gas passes through will increase, or if heat transfer tubes are arranged in multiple stages, the amount of radiant heat from the radiator to the heat transfer tubes in the stage far away from the radiator will be insufficient. .

The distance a from the end surface of the surface burner plate 18 to the lowest heat exchanger tube is 5 to 50 mm. Note that the heat exchanger tubes of the first heat exchanger tube group 19 may be of a normal cylindrical shape or may be tubes having an elliptical cross section. Further, although a finless tube may be used, in order to utilize radiation more effectively, in this embodiment, a loaf-in type heat exchanger tube having fins of 2 mm or less is used.

A plurality of lump-shaped radiators 20 are placed between the tubes on the upper heat transfer tubes constituting the first heat transfer tube group 19@. This block-shaped radiator 20 irradiates radiant heat to both a first heat exchanger tube group 19 and a second heat exchanger tube group 21, which will be described later, which are arranged in a staggered manner. As the lump-like radiator 20, a sphere,
They may be cubes, rectangular parallelepipeds, or similar shapes such as golf balls or rugby balls, and also include small nodules with somewhat complex shapes such as konpeito, burr, and tetrabod shapes. Moreover, it is preferable to use ceramics for such a lump-like radiator 20.

Roughly downstream of the block-like radiator 20, a second heat transfer tube group 21 is arranged close to the radiator 20! has been done. In this embodiment, the second heat exchanger tube group 21 is composed of a large number of flat plate fins 22.
and a plurality of heat transfer tubes that pass through the fins 22 and are in thermal contact with them. The heat exchanger tubes are arranged perpendicularly to the plane of the fins 22 and remain parallel to each other. Moreover, the second heat exchanger tube group 21 can also be arranged in a staggered manner.

Each heat exchanger tube of the second heat exchanger tube group 21 has an outer diameter of 12 to 20 m.
m, the wall thickness is 0.6 to 2.0 mm, the arrangement interval of the heat exchanger tubes is 6 to 30 mm, and the wall thickness of the fins 22 is 0.3 to 1.5 mm.
mm, and the arrangement interval of the fins 22 is 2.6 to 6.0 mm.

The heat exchanger tubes of the first heat exchanger tube group 19 and the second heat exchanger tube group 21 are generally arranged horizontally, but the heat exchanger tubes of the first heat exchanger tube group 19 and the second heat exchanger tube group 21 are generally arranged horizontally. It may be inclined so that the outlet side is higher than the inlet side.

A fluid to be heated is flowed into the first heat exchanger tube group 19 and the second heat exchanger tube group 21. A liquid, particularly water, is suitable as the fluid to be heated. This fluid to be heated is supplied to the first heat exchanger tube group 1
Although the heat exchanger tubes 9 and the second heat exchanger tube group 21 may be flown independently, preferably they are flown in series between them. In this case, in order to increase the temperature efficiency, the fluid to be heated should first flow through the second heat exchanger tube group 21 and then flow through the first heat exchanger tube group 19, so that the fluid flows counter-currently to the flow of the combustion gas. is preferred.

On the other hand, in order to prevent local boiling within the tube, it is preferable to connect the tube in the opposite direction so that the flow is parallel to the flow of combustion gas. In addition, although it is customary for each heat exchanger tube group to be connected in series, it is also possible to make an appropriate selection, such as connecting heat exchanger tubes in the same stage in parallel and then connecting different stages in series. .

The operation of the snowmaking according to the present invention will be explained below.

The fuel gas is injected into the outlet of the fan casing 13 by the fuel gas nozzle 17, and is sent to the mixing chamber 14 together with combustion air by the airflow from the fan 16, thereby forming a premixture. The premixture passes through the surface burner plate 18 and is supplied to the combustion chamber 15, where it is formed into a flame and becomes combustion gas.

In the case of premix combustion, in order to increase the combustion gas temperature, it is best to keep the air ratio as close to 1.0 as possible, but from the perspective of suppressing the generation of unburned components, the air ratio should be around 1.1 to 1.4. It is preferable to set it to . As a result, the combustion gas is 1500 ~
The combustion gas reaches a high temperature of 1650° C. and is guided to the first heat exchanger tube group 19 arranged in the combustion chamber 15, and a part of the thermal energy of the combustion gas is transferred to the first heat exchanger tube group 19 by convection heat transfer.
The heat is transferred to the fluid such as water flowing inside the heat transfer tube. Roughly, the combustion gas flows through the lumpy radiators 20 while remaining at a high temperature, and this radiator 201Fr is also heated and becomes incandescent.

The block-shaped radiator 20 is maintained at a high temperature of 1100 to 1300° C. and radiates substantially the entire first heat exchanger tube group 19 . From the perspective of radiant heat transfer, it is preferable to raise the temperature of the radiator as much as possible, but when considering temperature changes during ignition and stopping, and temperature distribution on the radiator, the above-mentioned It is preferable to use the radiant heat within the temperature range. In this case, the radiant heat is also irradiated in the direction of the surface burner plate 18, but a considerable amount is concentrated by the lower heat exchanger tubes of the first heat exchanger tube group 19. Therefore, the surface burner plate will not be burned out by this radiant heat.

While the combustion gas passes through the area where the first heat transfer tube group 19 and the radiator 20 are arranged, its temperature decreases to 800 to 1000°C by heat exchange with the fluid flowing inside the heat transfer tubes, and the temperature of the combustion gas decreases to 800 to 1000°C. It is guided to the heat tube group 21 and transfers heat energy again to the fluid flowing inside. The radiant heat from the radiator 20 is also irradiated to the second heat exchanger tube group 21 . Second heat exchanger tube group 21
Fluid such as water inside is heated to 40 to 80°C and led out of the device.

A performance evaluation experiment was conducted using the fluid heating device 11 of the above embodiment and a fluid heating device having a different configuration. The experimental conditions and results are as follows.

(Experimental conditions) ■Fuel: natural gas, air ratio 1.2 ■Heated fluid for two people Water at a water temperature of 20°C is first flowed through the first heat transfer tube group 19, and after leaving here, it is passed through the second heat transfer tube group 19. It flows into the heat tube group 21.

■First heat exchanger tube group 19: inner diameter 11, 4mm, outer diameter 12
．． 7mm, fin height 1.6mm, fin outer diameter 15.9
Five mm copper loaf-in tubes are arranged in a staggered manner with an interval of 16 mm (pitch approximately 32 mm).

■Radiator 20: 8 pressureless sintered SiC spheres each having a typical outer diameter of 20 mm are placed across the two upper heat exchanger tubes of the first heat exchanger tube 19, four each. @place,
The heat exchanger tubes 19 were arranged at approximately equal intervals with a pitch of about 44 mm in the running direction.

■Second heat transfer tube group 21: Copper tubes with inner diameter of heat transfer tubes of 11.5 mm and outer diameter of 12.7 mm, and fin thickness of 0.35 mm.
, a plate fin tube combined with a fin pitch of 2.7 mm.

In addition, in the apparatus of the embodiment, the surface burner plate 18
The distance Ha from the end face of the first heat exchanger tube group 19 to the lower edge of the fins of the lower heat exchanger tubes is 20 mm, and the distance ub from the end face of the surface burner plate 18 to the lower edge of the fins of the second heat exchanger tube group 21.
was set to 83 mm.

In addition, in the control example device, a pressureless sintered SiC honeycomb plate with 200 cells/in2 and a thickness of 5 mm is arranged as a radiator instead of the bulk radiator 20 described above, and the temperature of the radiator is controlled. In order to lower the temperature by about 100°C, the number of heat exchanger tubes constituting the first heat exchanger tube group 19 was set to seven. Further, the heat transfer area of the second heat transfer tube 21 was adjusted so that the amount of heat supplied and the amount of heat exchanged were the same between the example and the control example.

(Experimental results) Combustion space volume + heat exchanger volume Control example: Example = 1.0.74 Heat transfer area Control example: Example = I: 1.03 Radiant temperature Control example 1140°C, Example + 250"
C discharge CO concentration Control example 15 ppm, Example 10
ppm As can be seen from this result, the volume of the heat exchanger required to obtain the same amount of heat exchanged could be made much more compact in the case of the block-shaped radiator than in the case of the honeycomb plate. By making this a lumpy radiator, the temperature of the radiator can be reduced by approximately 1
This is because the temperature could be set 00°C higher. If the honeycomb plate radiator used in the control example is used as is in the device of the example, cracks will occur in the honeycomb plate radiator.

Another embodiment of the invention is shown in FIG. In this embodiment, on the upper heat exchanger tube of the first heat exchanger tube group 19,
The columnar radiators 23 of the number of tanks intersect with the running direction of the first heat exchanger tube group 19 and are spaced at equal intervals. In this embodiment, a half-split cylinder 24 is used as the columnar radiator 23. A large number of through holes 25 are bored in the half-split cylinder 24, and high temperature combustion gas heats the half-split cylinder 24 while passing through the through-holes 24. The incandescent half-split cylinder body 24 mainly radiates and heats the first heat exchanger tube group 19 and also heats the second heat exchanger tube group 21 as well.

In addition to the half-split cylinder 24 described above, the columnar radiator 23 can also be formed, for example, in a polygonal, half-moon, or other appropriate cross-sectional shape. In addition, in FIG. 2, a columnar radiator 23
was placed on the upper heat exchanger tube of the first heat exchanger tube group 19,
It may be placed on the lower heat exchanger tube. Other configurations and operations are similar to those in the first embodiment, so their explanations will be omitted.

"Effects of the Invention" As explained above, according to the present invention, convective heat transfer by the combustion gas and radiant heat transfer by the radiator are simultaneously performed with respect to the first and second heat exchanger tube groups, and, Since a radiator with a relatively simple shape is used, a high-strength ceramic body can be used. As a result, the temperature of the radiator can be raised and the amount of radiant heat transferred can be increased, so combustion heat can be effectively utilized. Moreover, since a considerable amount of the radiant heat from the radiator is blocked by the first heat transfer tube group, burning out of the combustion means due to the radiant heat is prevented. In general, since the radiator is kept at a high temperature, even if incomplete combustion products are generated in the combustion chamber, the oxidation reaction is promoted by this high temperature radiator, suppressing the amount of incomplete combustion products emitted. can do. Furthermore, the entire device can be made smaller.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a first embodiment of a fluid heating device according to the present invention, and FIG. 2 is a perspective view of essential parts of a fluid heating device according to a second embodiment of the present invention.

Claims (1)

[Scope of Claims] 1. Combustion means, a first heat exchanger tube group disposed proximately downstream of the combustion means, and a block-like structure disposed so as to be ventilated between and/or proximally downstream of the first heat exchanger tube group. Alternatively, a fluid heating device comprising a columnar radiator and a second heat transfer tube group disposed adjacent to and downstream of the radiator. 2. The fluid heating device according to claim 1, wherein the radiator is made of ceramics. 3. A fluid heating device according to claim 1 or 2, wherein the radiator is placed on the first heat exchanger tube group.