JPS63210513A - 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 deformation, breakage or backfire, by a method wherein the total sum of the projection areas of radiators, which are projected by projection lines, orthogonal to the downstream surface of the combustion means, through clearances of respective heat transfer tubes, which are constituting a first heat transfer tube group, is limited to a specified rate. CONSTITUTION:Premixed gas, consisting of fuel gas from a fuel gas nozzle 26 and air from a fan 25, is supplied to a combustion chamber 24 through the flame ports of a burner plate 27 and becomes high temperature combustion gas. The combustion gas passes through the clearances of the heat transfer tubes 13a of a first heat transfer tube group 13, flows through a radiator 14 while keeping the high temperature, and heats the radiating body 14 also so as to become white-hot. 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 is projected through the clearances of the first heat transfer tube group 13 toward the burner plate 27. Since the intervals (d) of arranged heat transfer tubes 13a are designed so as to be smaller than the outer diameter (a) of the tube to obtain the projection area ratio of 40% or less, a considerable amount of radiation heat is interfered by the heat transfer tube group 13, whereby the burner plate 27 may be prevented from breakage due to radiation heat even when the plate 27 is used for a long period of time.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field J 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 transferred between a group of heat transfer tubes. It was designed to heat a fluid such as water flowing inside a group of heat transfer tubes, mainly 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.

By the way, if the combustion chamber is simply downsized, the flame will extend to the heat exchanger without completing the combustion reaction within the combustion chamber, and as a result, the fuel in the middle of the combustion reaction will come into contact with the walls of the heat transfer tubes and the flame will be cooled down. This could cause the combustion reaction to stop, resulting in incomplete combustion. 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.

Also, combustion! If the heat exchanger is miniaturized and integrated with the heat exchanger, if unburned fuel components are deposited on the surface of the heat exchanger tube, the heat exchanger tube may be overheated and damaged. Mixing of the combustion gas in the i-boundary chamber deteriorates, and the temperature distribution tends to become large, and the heat transfer load increases locally, which may also damage the heat exchanger tubes.

For this reason, there is a limit to the miniaturization of the combustion chamber. For example, in currently commercially available gas water heaters, when comparing the size of the combustion chamber and the heat exchange section, it is approximately 2 = 1, and the size of the combustion chamber and the downstream The distance from the heat exchanger tubes was 20 to 30 cm, and the combustion chamber load was suppressed to about 5x + o' kcal/m3/hr or less. 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.

Therefore, the present inventors previously applied for patent application No. 6'O-22398.
0, proposed a fluid heating device as shown in FIGS. 5 and 6. In this fluid heating device 10, a combustion means 12 such as a burner is arranged in the lower part of the casing 11,
Above this combustion means 12, in order from the bottom, a first heat exchanger tube group 13, a breathable radiator 14, and a second heat exchanger tube group 15.
has been placed. The first heat exchanger tube group 13 has a plurality of heat exchanger tubes 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 was irradiated with 1. It is heated by both convective heat transfer by the sintering 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 to both the first heat exchanger tube group 13 and the second heat exchanger tube group 1.
5 can also be irradiated and the combustion heat can be used effectively,
Since the first heat exchanger tube group 13 is located close to the combustion means 12, the combustion space can be significantly reduced, and the entire apparatus can be made more compact. In general, even if the main products of incomplete combustion are generated, they are oxidized when passing through the radiator 14 kept at a high temperature, so that the discharge of incomplete combustion products can be suppressed.

However, in the fluid heating device M10 described above, the first heat transfer tube group 13 interposed between the combustion means 12 and the radiator 14 is
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 was found that even the combustion means 12 was heated by this radiant heat.

For this reason, the combustion means 12 may cause thermal damage to the parts that receive direct radiant heat, or a large temperature difference will occur between the parts that receive direct radiation and the parts that do not. There is also a large temperature difference between the front surface and the back surface, which can lead to deformation and damage to the combustion means 12, and furthermore, if the combustion means 12 is a premix burner, a dangerous situation of backfire may occur.

``Object of the invention j 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 and the accompanying An object of the present invention is to provide a fluid heating device that can suppress the occurrence of large temperature differences within combustion means and prevent deformation, damage, and backfire of the combustion means.

"Structure of the Invention" The fluid heating device according to the present invention includes a combustion means, a first heat exchanger tube group disposed adjacent to and downstream of the combustion means, and a ventilable structure provided adjacent to and downstream of the first heat exchanger tube group. comprising a radiator and a second group of heat exchanger tubes arranged adjacently downstream of the radiator, projected by a projection line perpendicular to the downstream surface of the combustion means through the gap of each heat exchanger tube constituting the first group of heat exchanger tubes. The total projected area of the radiators is 40% or less of the area of the downstream surface of the combustion means.

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 burner that supplies combustion air and fuel separately to the combustion chamber, or a premix combustion burner that mixes combustion air and fuel in a predetermined ratio and then supplies the mixture to the combustion chamber. Burners 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 one or more stages in the combustion gas flow direction, and is provided as a whole 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 exchanger 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 5.
Since the distance is approximately 50 mm, the upstream edge of the heat exchanger tube described above will be placed near the tip of the flame.

If the first heat transfer tube group is arranged 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 sufficiently obtained, or the gas thickness may increase, increasing radiant heat input from the high-temperature combustion gas to the burner, leading to damage to the burner and backfire.

A radiator is arranged adjacent to and downstream of the first heat exchanger tube group. The radiator converts the thermal energy contained in the combustion gas into strong radiant energy, and irradiates the radiant heat mainly to the first heat exchanger tube group, and generally to the second heat exchanger tube group. Both heat transfer tube groups are heated by radiant heat transfer from the radiator and convective heat transfer from the high temperature combustion gas, and the fluid flowing inside the tube groups is efficiently heated.

In order to generate effective radiant heat at high temperatures, suitable materials for the radiator include ceramics such as silicon carbide, enriched silicon, aluminum nitride, cordierite, mullite, lithium aluminum silicate, and aluminum titanate, with particularly high heat resistance. , high strength, high thermal conductivity ceramics such as silicon carbide, enriched silicon, aluminum nitride, etc. are preferred. Depending on temperature conditions, metal materials such as heat-resistant steel may also be used.

The radiator is designed so that the combustion gas that has passed through the first heat exchanger 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 preferable example of such installation is to install a large number of rod-shaped or elongated plate-shaped radiators in parallel with each other and between them (
In this case, the rod-shaped or elongated plate-shaped radiator is preferably arranged such that its longitudinal direction is perpendicular to the flow direction of the combustion gas, or may be diagonal to the flow direction of the combustion gas. In this case, the radiator itself may be non-breathable or breathable.

A more preferable way to install the radiator is to use a breathable radiator, such as a flat plate. The ventilation/radiant body is
A plate-shaped body in which flow channels are uniformly distributed throughout so that gas can flow through the layers on both sides, and typically a honeycomb body, three-dimensional network, open-cell foam, or network laminate. Examples include. Such a breathable radiator is arranged, for example, so as to cross substantially the entire area of the combustion gas flow path, so that the combustion gas passes through the interior of the breathable radiator from the upstream side (already from the downstream side). ventilate.

Among such breathable radiators, ceramic honeycomb plates are particularly preferred. This honeycomb plate has a large number of parallel cells penetrating the front and back sides of the plate surface, and the cell shape can be appropriately selected from square, rectangular, hexagonal, etc. Further, the honeycomb plate may be formed by laminating a large number of corrugated plates or a large number of corrugated plates and flat plates.

The second heat exchanger tube group is arranged adjacent to and downstream of the radiator. The temperature of the combustion gas flowing into the second heat exchanger tube group area is lowered by heat exchange when passing through the first heat exchanger tube group and the radiator arrangement area. Therefore, it is preferable that the second heat transfer tube group has fins on its outer surface to improve convective heat transfer.

Furthermore, in order to ensure that the combustion gases come into contact with each other 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 must be metals such as copper, aluminum, aluminum alloy, and stainless steel, or ceramics with excellent thermal conductivity and corrosion resistance such as silicon carbide and silicon nitride. is preferable,
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.

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 of the heat exchanger tubes constituting the first heat exchanger tube group is the ratio (hereinafter referred to as , projected area ratio) is set to be 40% or less, particularly 35% or less.

If each heat exchanger tube is distributed in this way, each heat exchanger tube will
Since the amount of radiant heat that is blocked from the radiator increases, the amount of radiant heat that directly reaches the combustion means is reduced. 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 directly irradiated from the radiator to the heat transfer tube increases, improving heat transfer efficiency. By the way, the heat exchanger tubes do not suffer thermal damage because the fluid to be heated flows inside them.

The smaller the projected area ratio, the better; however, when the first heat exchanger tube group is arranged in one stage and each heat exchanger tube is cylindrical, it should be about 20% or more in order to allow the combustion gas to pass through the gaps between the heat exchanger tubes without any problem. It is preferable that

In addition, for example, by arranging a plurality of heat transfer tubes with concave sections in one row, sufficient gaps between the heat transfer tubes can be secured, and the projected area ratio can be reduced to 0% without having almost any effect on the combustion gas passage pressure drop VI. You can do up to. 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.

Note that in the present invention, a group of heat exchanger tubes means that a plurality of cross sections of heat exchanger tubes are recognized in an appropriate cross section along the combustion gas flow direction, for example. Therefore, each heat exchanger tube may be a different heat exchanger tube, or a single heat exchanger tube may be arranged in a meandering, spiral, or spiral shape, and cross sections at multiple points can be recognized. good.

The combustion means is generally assumed to have a planar burner plate, but it may also have a curved surface as appropriate, and instead of a planar burner plate,
For example, it may be one in which small cylindrical fuel outlets are closely protruded, 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. In cases where, for example, small cylindrical fuel outlets are loosely protruded, the cross section between the small circles is the downstream surface 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 FIG.
The entire body is surrounded by a casing 21 whose upper part is connected to an exhaust port (not shown), and the casing 21 is configured with a fan casing 22, a mixing chamber 23, and a combustion chamber 24 communicating with each other in this order from the bottom. A fan 25 is incorporated into the fan casing 22, and a fuel gas nozzle 26 is disposed at a discharge portion of the fan 25. Air flow from the fan 25 and fuel gas from the fuel gas nozzle 26 are supplied to the mixing chamber 23 through the fan casing 22 to create a mixture of fuel gas and air.

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. The 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 are arranged transversely parallel to each other at equal intervals to form a first heat exchanger tube group I3. In this case, the first heat exchanger tube group 13 is one stage, and each heat exchanger tube +38 has an outer diameter of 12 to 20 mm.
, wall thickness 0.6~2.0mm, arrangement interval d of heat exchanger tubes 6~
It is set to 10 mm. Therefore, the total area of the vertical projection projected onto the downstream surface 27a of the burner plate through the gap of each heat transfer tube of the radiator is 7d/(7d+7a)=d/( d+a) = 1
0/(1(D20)=0J3(d=IOn+n+
, when a = 20 mm), that is, 1540% or less. Also, the downstream surface 27a of the burner plate
The distance Mb from the lower edge of the heat exchanger tube 13a is 5 to 50 mm.

An air-permeable radiator 14 made of a ceramic honeycomb plate is arranged adjacent to and above each of the heat exchanger tube groups 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. For example, each heat transfer tube may have a plurality of fins formed on its outer surface.

Incidentally, the heat exchanger tubes in both heat exchanger tube groups 13 and 15 are generally arranged horizontally, but in order to make it easier for air bubbles to escape when the heated fluid boils, they are arranged so that the outlet side is higher than the inlet side of the heated fluid. It may be tilted to

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 the heat exchanger is flowed between the two in the 1 nose. In this case, in order to increase the temperature efficiency, the fluid to be heated is first flowed through the second heat exchanger tube group 15, and the heated fluid exiting there is then flowed through the first heat exchanger tube group 13, thereby controlling the flow of combustion gas. It is preferable to flow countercurrently. On the other hand, in order to prevent local cypress 'A' in the pipe, it is preferable to connect in the opposite direction so that the flow is parallel to the flow of combustion gas.

Moreover, within each heat exchanger tube group, all are usually connected in series, or series connection and parallel connection may be combined as appropriate.

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

Fuel gas from the fuel gas nozzle 26 and air from the fan 25 are sent to the mixing chamber 23 to form a premixture. The premixture passes through the flame port of the burner plate 27 and is supplied to the combustion chamber 24 to form a flame.
It becomes a high temperature combustion gas such as ℃.

This combustion gas is guided to the first heat exchanger tube group 13, and a part of the thermal energy contained in 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 speaking, the combustion gas passes through the gap between the heat exchanger tubes 13a of the first heat exchanger tube group I3, 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 transferred to the heat exchanger tubes 13a of the first heat exchanger tube group 13.
The light is also irradiated in the direction of the burner plate 27 through the gap, but since the arrangement interval d of the heat transfer tubes 13a is set smaller than the tube outer diameter a, and the projected area ratio is 40% or less, The amount of radiation heat is blocked by the heat transfer tube group 13. Therefore, the upstream side of the burner plate 27 is maintained at about 150° C. at most, and the in-plane hot water temperature difference at the downstream surface 27a is about 350° C. or less, so that it will not be damaged by radiant heat even when used for a long period of time.

Then, the combustion gas is transferred to the first heat exchanger tube group 13 and the radiator 14.
The temperature of the opening passing through the M range of 800 to 1000
°σ 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 applied to the second heat exchanger tube group 15 . 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 drawing.

An experiment was conducted to evaluate the radiant heat blocking performance and the like using the fluid heating device 20 of the above example and the fluid heating device of the control 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 an input temperature of 20°C is first flowed through the first heat transfer tube group 13, and after leaving here, the second Heat exchanger tube group I5
flow to.

■First heat exchanger tube group 13: inner diameter 17.4 mm, outer diameter 19.
Copper tubes having a diameter of 0 mm were arranged in a single layer parallel to each other and at regular intervals. In the device of the example, the arrangement interval d was 9.5 mm, the number of arrangement was 8, and the projected area ratio was 33%. In the device of the control example, the tube length was lengthened to make the heat transfer area equal to that of the device of the example (the vertical and horizontal dimensions of the radiator, burner plate, etc. were changed accordingly), and the arrangement spacing d was I 9n+m.
, the number of arrays was 6, and the projected area ratio was 50%.

■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 from the downstream surface 27a of the burner plate 27 to the lower edge of the ivy 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.

These conditions were the same for the apparatus of the example and the apparatus of the control example, except for (1), and the supply rates of fuel and heated fluid were also the same.

(Experimental results) Projected area ratio Control example 50%, Example 33% In-plane temperature difference of burner plate downstream surface 27a Control example 490'
C1 Example 210°C Total absorbed heat amount control example 1890 in first heat exchanger tube group 13
0 kcal/h (Example 21000 kcal/hr) As is clear from this result, the projected area ratio was 17% smaller than the control example, and the burner plate downstream surface 27
The in-plane temperature difference of a was reduced by about 280°C. Furthermore, the total amount of heat absorbed by the first heat exchanger tube group 13 increased by about 11% in the example compared to the control example. Generally speaking, in the control device, the burner plate had a crack.

FIGS. 2, 3, and 4 show different embodiments of the present invention.

In the embodiment shown in FIG. 2, a large number of solid round rods 14a made of enriched silicon sintered material are arranged in two stages, upper and lower, in a staggered manner to form the radiator 14. In the embodiment shown in FIG. 3, a radiator 14 is formed by arranging a large number of elongated plates +4b made of silicon nitride sintered body in a louver shape. Both the embodiments shown in FIGS. 2 and 3,
The ratio of the outer diameter a of heat exchanger tube +3a to the arrangement interval d is a:d=
3: I.

In the embodiment shown in FIG. 4, a plurality of hollow tubes +3b having a substantially doglegged cross-sectional shape are arranged between an air-permeable radiator 14 made of a ceramic honeycomb plate and a planar burner plate 27. The first heat exchanger tube group 13 has been formed. As can be seen from FIG. 4, the rightward convex portion 13c of the hollow tube +3b having a dogleg shape is located at the left end of another hollow tube +3b on the right side.
It is placed on the plane connecting 3d and I3d, and while ensuring a sufficient flow path for combustion gas, the adjacent hollow tubes +3b, +
The projected area ratio through the gap 3b is 0%.

Although the above embodiments have all been described for premix burners, they are equally effective for diffusion combustion burners.

"Effects of the Invention" As explained above, according to the present invention, the projection of the radiant is projected by the projection line perpendicular to the downstream surface of the combustion means through the gap of each heat exchanger tube constituting the first heat exchanger tube group. Since the total area is 40% or less of the area of the downstream surface of the combustion means, it is possible to effectively transfer combustion heat and downsize the entire device. Since it can be effectively blocked by one group of heat transfer tubes, heating of the combustion means to a high temperature due to radiant heat is suppressed, and it is also possible to prevent deformation and damage of the combustion means and backfire. In general, 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 a third embodiment of a fluid heating device according to the present invention, FIGS. 2, 3, and 4 are sectional views of essential parts of different embodiments of the present invention, and FIG. FIG. 6 is a cross-sectional view of the previously proposed fluid heating device, which is a cross-sectional view taken along the line Vl--Vl in FIG. 5. In the figure, 13 is a first heat exchanger tube group, 14 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. A combustion means, a first heat exchanger tube group disposed proximately downstream of the combustion means, a radiator disposed proximately downstream of the first heat exchanger tube group in a ventilable manner, and disposed proximately downstream of the radiator. 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 gap of each heat exchanger tube constituting the first heat exchanger tube group is the combustion A fluid heating device characterized in that the area is 40% or less of the downstream surface area of the means.