JPS63210514A - Improved fluid heating device - Google Patents

Abstract

PURPOSE:To transfer combustion heat effectively, miniaturize the whole of a device and prevent a combustion means from deforming, breaking and backfiring, by a method wherein a first heat transfer tube group is constituted so that heat transfer tubes are arranged in a plurality of stages with respect to the flow direction of combustion gas while at least a part of the heat transfer tubes in a stage, not the lowest, is located at the upstream side of a gap between the heat transfer tubes in the most downstream stage. CONSTITUTION:The mixture of air and fuel, which is formed in a mixing chamber 23, is supplied into a combustion chamber 24 through the flame ports of a burner plate 27 and becomes high-temperature combustion gas. The combustion gas passes through a gap between the heat transfer tubes 13a of a first heat transfer tube group 13 and heats a radiator 14 so as to become white-hot while keeping the high temperature. In this case, the radiator 14 is kept in the high temperature and heats the first heat transfer tube group 13 principally by radiation. The radiation heat passes through the gap between the heat transfer tubes 13a and is projected toward the burner plate 27, however, is intercepted by the heat transfer tubes 13b, located at the upstream of the gap; thereby, the radiation heat, projected against the burner plate 27, is reduced remarkably. When a projection area ratio is 0%, substantially no heat is directly radiated to the burner plate 27. Accordingly, the burner plate 27 may be prevented from being damaged by fusion due to radiation heat, thermally deforming, cracking under heat stress, and backfiring when used for a long period of time.

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, fuel is combusted in a combustion chamber downstream of a burner, and then the combustion gas is passed between a group of heat transfer tubes. It was designed to heat fluids such as water flowing inside a group of heat transfer tubes, mainly by using convective heat transfer.

In recent years, in order to make these fluid heating devices as compact as possible, the combustion chamber has been made as small as possible, and
This tends to increase the amount of heat transferred per unit volume of the heat exchange section.

Therefore, the inventors of the present invention previously applied for patent application No. 60-223980.
proposed a fluid heating device as shown in FIGS. 7 and 8. In this fluid heating device 10, a combustion means 12 such as a burner is disposed in the lower part of the casing 11, and a first heat exchanger tube group 1 is arranged in the upper part of the combustion means 12 in order from the bottom.
3. Breathable radiator 14 and second heat exchanger tube group 15r
8 are arranged. In the heat exchanger tube group 13 of the confectionery, a plurality of heat exchanger tubes are arranged in a row at predetermined intervals, and a fluid to be heated such as water flows through the first heat exchanger tube group 13 and the second heat exchanger tube group 15. It is now possible to

Then, the fuel gas ejected from the nozzle of the combustion means 12 forms a flame and burns. This combustion gas not only heats the first heat exchanger tube group 13 but also passes through the gaps between the heat exchanger tubes of the first heat exchanger tube group 13 and heats the radiator 14 . This heated radiator 14 mainly transfers radiant heat to the first heat exchanger tube group 1.
3, and the first heat exchanger tube group 13 is heated by both convective heat transfer by the combustion gas and radiant heat transfer from the radiator 14. Further, the second heat transfer tube group 15 is also heated by convection heat transfer by the combustion gas and radiant heat from the radiator 14 . In this way, the fluid to be heated flowing through the first heat exchanger tube group 13 and the second heat exchanger tube group 15 is heated.

According to the fluid heating device 10 described above, the radiant heat from the radiator 14 is transmitted not only to the first heat exchanger tube group 13 but also to the second heat exchanger tube group 1.
5 can also be irradiated and the combustion heat can be used effectively,
Since the first heat transfer tube group 13P8 is located close to the combustion means 12, the distance between the combustion chambers can be significantly reduced, and the entire device can be made compact. Even if incomplete combustion products occur,
Since it is oxidized when passing through the radiator 14 kept at a high temperature, the discharge of incomplete combustion products can be suppressed.

However, in the fluid heating device 10 described above, the first heat exchanger tube group 13 interposed between the combustion means 12 and the radiator 14
When the interval between the heat transfer tubes is wider than the tube outer diameter, a large amount of radiant heat from the radiator 14 passes between the heat transfer tubes of the first heat transfer tube group 13 and reaches the combustion means 12. Therefore, it has been found that even the combustion means 12 is heated by this radiant heat.

For this reason, the combustion means 12 causes heat loss @ in the part that receives direct radiation from the radiant heat, or a large temperature difference occurs between the part that receives direct radiation and the part that does not. There is also a large temperature difference between the front and back surfaces, which can lead to deformation and damage to the combustion means 12, and even lead to dangerous backfires if the combustion means 12 is a premix burner. .

"Objective of the Invention" The object of the present invention is to solve the above-mentioned problems, to effectively transfer combustion heat, to downsize the entire device, and to reduce the high temperature overheating of the combustion means by radiant heat. An object of the present invention is to provide a fluid heating device capable of suppressing the occurrence of a large temperature difference within a combustion means and preventing deformation, damage, and backfire of the combustion means.

[Structure of the Invention J The fluid heating device according to the present invention includes a combustion means, a first heat exchanger tube group arranged in multiple stages adjacent to and downstream of the combustion means, and a ventilable portion adjacent to and downstream of the first heat exchanger tube group. and a second heat exchanger tube group disposed close to and downstream of the radiator, and the first It is characterized in that at least a part of the heat exchanger tubes constituting the non-downstream stage of the heat exchanger tube group is positioned.

In the present invention, the fuel includes city gas, propane gas,
Gaseous fuels such as natural gas or vaporized liquid fuels such as kerosene can be used.

Combustion means include a diffusion combustion type burner that supplies combustion air and fuel separately to the combustion chamber, or a premix combustion type burner that supplies combustion air and fuel to the combustion chamber after mixing them in a predetermined ratio. etc. are used. A planar burner is suitable as the premix combustion type burner.

The first heat exchanger tube group consisting of a plurality of heat exchanger tubes is arranged in multiple stages in the combustion gas flow direction, and is generally provided downstream of the combustion means and close to the combustion means.

The upstream edge of the most upstream heat transfer tube of the first heat transfer tube group is placed, for example, in the flame formed by the combustion means or in a position close to the tip of the flame. Specifically, the distance between the fuel gas discharge port of the combustion means (for example, the tip of the burner) and the upstream edge of the heat transfer tube 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 upstream edge of the heat exchanger tube is placed near the tip of the flame.

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.
The effects of the present invention may not be fully obtained, or the gas thickness will increase, increasing radiant heat input from the high-temperature combustion gas to the burner, which may cause damage to the burner and flashback.

A radiator is arranged adjacent to and downstream of the -th heat exchanger tube group. The radiant is a combustion gas or a gas. The generated heat energy is converted into strong radiant energy, and the radiant heat is applied mainly to the first heat exchanger tube group, and more generally to the second heat exchanger tube group. Both heat transfer tube groups are heated by radiant heat transfer from the radiator and convection heat transfer from the high temperature combustion gas, and the fluid flowing inside them is efficiently heated.

The radiator is preferably made of ceramics such as silicon carbide, enriched silicon, aluminum nitride, cordierite, mullite, lithium aluminum silicate, aluminum titanate, etc., in order to generate effective radiant heat at high temperatures. Ceramics with high strength and high thermal conductivity, such as silicon carbide, silicon nitride, and aluminum nitride, are preferred. Fully flexible materials such as heat-resistant steel may also be used depending on temperature conditions.

The radiator is designed so that the combustion gas that has passed through the first heat transfer tube group comes into contact with the radiator and can flow roughly downstream, that is, to allow ventilation of the combustion gas. It will be done.

A preferred example of such an arrangement is one in which a large number of rod-shaped or elongated plate-shaped radiators are arranged parallel to each other with slits formed between them. At this time, it is preferable that the elongated direction of the rod-shaped or elongated plate-shaped radiator is orthogonal to the flow direction of the combustion gas, but it may be oblique. In this case, the radiator itself may be non-breathable or breathable.

A more preferable way to install the radiator is to use, for example, a flat plate-shaped ventilation/injection radiator. The breathable radiator is
A plate-shaped body in which gas flows through both sides and the flow paths are uniformly distributed as a whole, typically honeycomb bodies, three-dimensional nets, open-cell foams, network laminates, etc. can be mentioned. Such a ventilation radiator is arranged, for example, so as to cross the entire length of the combustion gas flow path, so that the combustion gas passes from the upstream side through the inside of the ventilation radiator and flows downstream. Vent on the side.

Among such breathable radiators, a honeycomb plate made of ceramics is particularly suitable.
(It has a large number of parallel cells passing through it, and the cell shape can be selected as appropriate, such as square, rectangle, or hexagon.) Honeycomb board is also formed by laminating a large number of corrugated sheets or corrugated sheets and flat sheets. It could be something like this.

The second heat exchanger tube group is arranged adjacent to and downstream of the radiator. The combustion gas flowing into the second heat exchanger tube group area is 1F where the first heat exchanger tube group and radiator are located! Due to the heat exchange during passing through t, its temperature begins to decrease. Therefore, it is preferable that the second heat transfer tube group has fins on its outer surface to improve convective heat transfer.

Moreover, in order to make contact with the combustion gas evenly, the second heat exchanger tube group can also have heat exchanger tubes arranged in a staggered manner.

The material of the heat exchanger tubes in the first and second heat exchanger tube groups shall be metals such as copper, aluminum, aluminum alloy, stainless steel, or ceramics with excellent thermal conductivity and corrosion resistance such as silicon carbide and silicon nitride. Preferably,
In particular, reaction sintered silicon carbide, which has high thermal conductivity, low coefficient of linear expansion, high strength, and excellent formability, or copper, which is a highly thermally conductive material, is most preferred.

By the way, if the first heat exchanger tube group is arranged in a single stage between the radiator and the combustion means and it is intended to reduce the direct radiation of radiant heat from the radiator to the combustion means, the first heat exchanger tube group The gap between each heat transfer tube must be made small, or the pressure drop when the combustion gas passes through this gap becomes large.
It is restricted by the zero-shaped tube that connects the tube ends of the heat exchanger tubes. Therefore, in the present invention, the first heat exchanger tube group is arranged in multiple stages, and at least a portion of the heat exchanger tubes that constitute the non-downstream stage is located upstream of the gap between the heat exchanger tubes that constitute the most downstream stage. is located.

However, from the viewpoint of reducing the direct radiant heat from the radiator to the combustion means, it is possible to substantially reduce the direct radiant heat by using the staggered arrangement described below, but this is not essential. The sum of the projected areas of the radiators projected by the projection line perpendicular to the downstream surface of the combustion means through the gaps between the heat exchanger tubes constituting the first heat exchanger tube group, or the ratio to the area of the downstream surface of the combustion means (hereinafter referred to as projected area ratio) t40
% or less, particularly preferably 35% or less.

A typical preferable example of such a heat transfer tube arrangement is one in which a group of parallel heat transfer tubes are arranged at equal intervals in the same direction on the upstream and downstream sides and with even phase. A so-called staggered arrangement in which the upstream heat exchanger tubes are positioned upstream of the central portion of the gap between the heat tubes is particularly preferred.

Another preferable arrangement is to arrange a group of parallel, equally spaced heat exchanger tubes so that the upstream and downstream sides run in different directions.

For example, it is also good to arrange two spiral heat exchanger tubes with the positions M shifted between the upstream side and the downstream side.

If each heat exchanger tube is arranged in this way, each heat exchanger tube will
Since the amount of radiant heat from the radiator increases, the amount of radiant heat directly reaching the combustion means decreases. Therefore, high-temperature overheating of the combustion means due to radiant heat and the occurrence of large temperature differences within the combustion means due to this are suppressed, and thermal deformation of the combustion means,
Breakage and backfire are prevented. In addition, the radiant heat irradiated from the radiator to the heat transfer tube in the M contact direction also increases, improving heat transfer efficiency. In addition, the gap between the heat exchanger tubes does not need to be so small,
There is no pressure drop when the combustion gas passes through, and there are no restrictions when connecting the tube ends.Furthermore, since the fluid to be heated flows inside, the heat exchanger tubes do not suffer thermal damage.

In particular, when the above-mentioned staggered arrangement is used and the tube spacing in each of the upstream and downstream stages is less than or equal to the outer diameter of the tubes, the projected area ratio is 0%, that is, when the tubes are arranged perpendicularly to the downstream surface of the combustion means. Direct radiation can be eliminated. In this way, when the projected area ratio is 0%, the combustion gas can pass through the gap between the heat transfer tubes with low pressure loss, and most of the radiant heat from the radiator is absorbed by the first group of heat transfer tubes. does not reach the combustion means.

In addition, since the temperature of the surrounding combustion gas is high and there is also radiant heat transfer from the radiator, the heat transfer coefficient is also high, so it is preferable that no fins be attached to the outer surface of each heat transfer tube in the first heat transfer tube group. However, it is also possible to use a fin with a fin height of about 2 mm or less, for example.

Incidentally, in the present invention, a group of heat exchanger tubes means that, for example, a cross section of several paddles of heat exchanger tubes is recognized in an appropriate cross section along the combustion gas flow direction. Therefore, each heat exchanger tube may be a different heat exchanger tube, or one heat exchanger tube may meander,
It may be arranged in a spiral or spiral shape, and cross sections at multiple locations can be recognized.

The combustion means is generally assumed to have a flat burner plate, but it may also have a curved surface as appropriate. Also, instead of a planar burner plate,
For example, a small cylindrical fuel outlet may be provided protruding into the rice field, and in this case, the combustion surface formed by this group of fuel outlets is the downstream surface of the combustion means in the present invention. For example, in the case of a small cylindrical fuel outlet in which the fuel outlet is sparsely protruded, the cross section of the small cylinder is the downstream face of the combustion means in the present invention.

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

A fluid heating device 20 according to an embodiment of the present invention shown in FIGS. 1 and 2 is entirely surrounded by a casing 21 connected to an exhaust port (not shown) above the fluid heating device 20. The chamber 23 and the combustion chamber 24 are connected to each other. Air and fuel gas are supplied to the mixing chamber 23 from below (not shown).
is supplied to create a mixture with a predetermined air ratio.

At the boundary between the mixing chamber 23 and the combustion chamber 24, a planar burner plate 27 made of cordierite ceramic is arranged as a combustion means. This burner plate 27 has a large number of flame ports, and the air-fuel mixture that has passed through the flame ports forms a planar flame on the downstream surface 27a of the burner plate 27. That is, in this embodiment, a premixed surface burner method is adopted.

Above the burner plate 27 in the casing 21, a plurality of heat exchanger tubes 13a and 13b are arranged in two stages and parallel to each other at equal intervals, forming a first heat exchanger tube group 13. ing. Each heat exchanger tube 13a.

+3b has an outer diameter a of 12 to 20 mm and a wall thickness of 0.6 to 2.
The distance d between the upper heat exchanger tubes 13a or the distance d between the lower heat exchanger tubes +3b is approximately 0.5 to 1.5 times the outer diameter a. Further, the heat exchanger tubes +3b are located upstream of the central portion ad between the heat exchanger tubes 13a, 13a, and are arranged in a so-called staggered arrangement. Note that when this d/a ratio is set to 1.0 or less, the projected area ratio becomes substantially 0%.

The distance from the downstream surface 27a of the burner plate to the lower edge of the heat exchanger tube +3b is 5 to 50 mm.

An air-permeable radiator 14 made of a ceramic honeycomb plate is arranged adjacent to and above the first heat exchanger tube group 13.
A second heat exchanger tube group 15 is arranged close to and above the radiator 14 . In this embodiment, the second heat exchanger tube group 15 is a plate fin tube consisting of a large number of parallel flat plates 28 and a plurality of parallel transverse heat exchanger tubes passing through the flat plates 28 orthogonally. However, for example, each heat exchanger tube may have a plurality of fins formed on its outer surface.

Note that the heat exchanger tubes in both heat exchanger tube groups 13 and 15 are generally arranged horizontally, or on the outlet side or above the inlet side of the heated fluid so that bubbles can easily escape when the heated fluid boils. It may be tilted as shown.

A fluid to be heated is flowed into the first heat exchanger tube group 13 and the second heat exchanger tube group 15. A liquid, especially water, is suitable as the fluid to be heated. This fluid to be heated is supplied to the first heat exchanger tube group 1
3 and the second heat exchanger tube group 15 independently, but preferably it is flowed in series between them. In this case, in order to increase the temperature efficiency, first the second heat exchanger tube group 1
5, and the fluid to be heated that exits there is then allowed to flow through the first heat exchanger tube group 13, thereby causing the fluid to flow countercurrently to the flow of the combustion gas. On the other hand, in order to prevent local disturbance within the pipe, it is preferable to connect in the opposite direction so that the flow is parallel to the flow of combustion gas.

Further, although each heat exchanger tube group is usually connected in series, series connection and parallel connection may be combined as appropriate.

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

A mixture of air and fuel gas formed in the mixing chamber 23 (well,
It passes through the flame port of the burner plate 27 and is supplied to the combustion chamber 24, forming a planar flame near the downstream surface 27a of the burner plate 27, and becomes a high-temperature combustion gas of 1500 to 1650°C.

This combustion gas is guided to the first heat exchanger tube group 13, and a part of the thermal energy of the combustion gas is transferred to the fluid flowing inside the heat exchanger tubes 13a of the first heat exchanger tube group 13 by convection heat transfer. . Roughly, the combustion gas passes through the gap between the heat transfer tubes 13a of the first heat transfer tube group 13, flows inside the radiator 14 while remaining at a high temperature, and also heats the radiator 14, causing it to become incandescent. At this time, the radiator 14 is maintained at a high temperature of 1000 to 1200°C, and mainly radiates and heats the first heat exchanger tube group 13.

At this time, the radiant heat is also irradiated toward the burner plate 27 through the gap between the heat exchanger tubes 13a, but it is blocked by the heat exchanger tube +3b located upstream of this gap.
In addition to heating the burner plate 27, the radiant heat irradiated to the burner plate 27 is significantly reduced, and when the projected area ratio is 0%, the direct radiant heat irradiated to the burner plate 27 becomes substantially zero. Therefore, the burner plate 27 receives only a small amount of gas radiant heat from the flame, and combined with the cooling effect when the air-fuel mixture passes through, the upstream side of the burner plate 27 is kept at about 150°C, and the downstream side 27a is kept at about 150°C. Although the temperature is slightly higher than this, the temperature difference between the solid and hot water at the downstream surface 27a is 350.
℃ or less, and even if used for a long time, radiant heat (damage to the burner plate 27, thermal deformation, thermal stress cracking, etc.)
This will prevent backfires and the like.

Further, there is an advantage that the interval between the heat exchanger tubes 13a and +3b can be set so that the combustion gas passage pressure loss can be made sufficiently low without making the cross-sectional shape of the heat exchanger tubes a special shape.

Then, the combustion gas is transferred to the first heat exchanger tube group 13 and the radiator 14.
While passing through the placement area, the temperature increases from 800 to 1000
°C and is led to the second heat transfer tube group 15, where the heat energy is transferred again to the fluid flowing inside. In general, the radiant heat from the radiator 14 is also irradiated to the second heat exchanger tube group 15. Thus, the fluid inside the second heat exchanger tube group 15 becomes, for example, hot water at a temperature of 40° C. to 80° C. and is led out of the apparatus.

An experiment was conducted to evaluate the radiant heat blocking performance, etc. using the fluid heating device 20 of the above example and the fluid heating device of the comparative example. The experimental conditions and experimental results are as follows.

(Experimental conditions) ■Fuel/natural gas, air ratio 1,2 ■Fluid to be heated Water with a population temperature of 20°C is first flowed through the first heat exchanger tube group 13, and then the heat exchanger tubes exiting from this, the second heat exchanger tube Transfer to group 15.

■Radiator 14: plate thickness 5mm, number of cells 200/in2,
A pressureless sintered silicon carbide honeycomb plate with a square cell cross section is placed above the first heat exchanger tube group 13.

■Second heat transfer tube group 15: Copper tubes with inner diameter of heat transfer tubes of 17.4 mm and outer diameter of 19.0 mm, and fin thickness of 0.35 mm.
, plate fin tube combined with copper fins with a fin pitch of 2.7 mm.

■Burner plate 27: made of cordierite ceramics with a plate thickness of 10 mm ■The distance ub from the downstream surface 27a of the burner plate 27 to the lower edge of the first heat exchanger tube group 13 is 30 mm, and from the downstream surface 27a of the burner plate 27 to the second The distance Mc to the lower edge of the fin of the heat exchanger tube group 15 is 57 mm.

Items (1) to (2) were the same for both the example and the control example, and the fuel and water supply rates were also the same.

■First heat exchanger tube group 13. Inner diameter 17.4mm, outer diameter 19.
Eight copper tubes of 0 mm are arranged in two stages, four on each stage, top and bottom, and the interval d in each stage is I 9 mm. In the example, the two-stage staggered arrangement is used, and in the control example, the two-stage square arrangement (i.e., the lower row Place the upper heat transfer tube directly above the heat transfer tube (M).

(Experimental results) Projected area ratio Control example 50%, Example 0% Average temperature of burner plate 27 Control example 150 to 160°C, Example 70 to 80°C Linear absorption heat amount control example of first heat exchanger tube group 13 13800 kcal/ hr, tiger example 14700k
Cal/hr In contrast, in the snowmaking control example, the flame opening of the burner plate was missing.

In the embodiments shown in FIGS. 3 and 4, a large number of elongated plates 14a made of a silicon nitride sintered body are arranged in a louver shape to serve as the radiator 14. The first heat exchanger tube group 13 is composed of an upper heat exchanger tube 13c and a lower heat exchanger tube +3d.
The heat exchanger tubes c and heat exchanger tubes +3d are arranged parallel to each other at equal intervals, and the running direction of the heat exchanger tubes 13c and the running direction of the heat exchanger tubes +3d are orthogonal to each other. In this case, the ratio of the heat exchanger tube outer diameter a to the heat exchanger tube interval d is d/a = 3/4, so the projected area ratio of only the upper or lower stage is approximately 4.
3%, but the overall projected area ratio is about 18%.

In the embodiments shown in FIGS. 5 and 6, a large number of solid round bars +4b made of enriched silicon sintered material are arranged in two stages, upper and lower, in a staggered manner to form the radiator 14. The first heat exchanger tube group 13 has two
It is constructed by arranging spiral heat exchanger tubes 13e and 13f in two stages, upper and lower, and as can be seen from FIG.
Since the phases are shifted by half a pitch in each depth direction, the projected area ratio is significantly reduced compared to the case where the phases are not shifted. In addition, in FIG. 6, each heat exchanger tube 13e.

+3f is hatched for ease of viewing the drawing.

In the above embodiments, the first heat exchanger tube group is configured in two stages, upper and lower, but even if there are three or more stages, it will not be too difficult, and a diffusion combustion type burner is also used instead of a premix type burner. can. In other words, instead of sequentially arranging the heat exchanger tubes and radiators above the burner plate, they may be sequentially arranged below or to the sides.

"Effects of the Invention" As explained above, according to the present invention, the first heat exchanger tube group is arranged in multiple stages in the combustion gas flow direction,
In addition, at least a part of the non-downstream heat transfer tubes is located upstream of the gap between the heat transfer tubes at the most downstream stage, so that the radiant heat from the radiator is effectively transferred to the first heat transfer tube. In addition to reducing heat and the overall size of the device, the first group of heat transfer tubes blocks the radiant heat from the radiator, and direct radiant heat reaching the combustion means is largely or almost completely eliminated.
The combustion means is kept at a low temperature. Therefore, it is possible to prevent melting, thermal deformation, damage, etc. of the combustion means and backfire. Furthermore, when the present invention is applied to a gas water heater or the like, troubles such as after-boiling immediately after the water heater is used, which are caused by heat accumulation in combustion means such as burner plates, do not occur.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of an embodiment of the fluid heating device of the present invention, FIG. 2 is a sectional view taken along the line II-H in FIG. 1, and FIGS. 3 and 5 are the radiator and Cross-sectional views of the radiator and the first heat exchanger tube group portion of different embodiments of the fluid heating device of the present invention in which the first heat exchanger tube group portion is different, FIG. 4 is taken along the line ■-rV in FIG. A sectional view along the line, Figure 6 is the 5th
FIG. 7 is a sectional view of the previously proposed fluid heating device, and FIG. 8 is a sectional view taken along line 4--2 in FIG. 7. 13 is the first heat exchanger tube group, 13a to +3f are heat exchanger tubes, 14
15 is a radiator, 15 is a second heat exchanger tube group, 20 is a fluid heating device, and 27 is a burner plate.

Claims (1)

[Claims] 1. Combustion means, a first heat exchanger tube group arranged in multiple stages adjacently downstream of the combustion means, a radiator provided so as to be ventilated adjacently downstream of the first heat exchanger tube group, and proximity of the radiator. and a second heat exchanger tube group arranged downstream, and a non-downstream stage of the first heat exchanger tube group is provided upstream of the gap between the heat exchanger tubes that constitute the most downstream stage of the first heat exchanger tube group. A fluid heating device characterized by having at least a portion of a heat transfer tube positioned therein.