JPS63207910A - Fluid heater with radiation cloth - Google Patents

Abstract

PURPOSE:To effectively transmit combustion heat without burning a fire combustion means and a heat exchanging part thereby to suppress incomplete combustion by providing a second heat transfer tube group at the downstream in the vicinity of a gas-permeable radiation cloth disposed by deflecting the same in a wave form at the downstream in the vicinity of a heat transfer tube of a first heat transfer tube group. CONSTITUTION:A gas-permeable radiation cloth 20 is disposed along heat transfer tubes arranged in a zigzag manner in a first heat transfer tube group 19. The radiation cloth 20 is held by flanges of an upper casing 12a and a lower casing 12b, and is disposed by being deflected in a wave form so that it is placed alternately on the upper stage heat transfer tubes and the lower stage heat transfer tubes of the first heat transfer tube group 19. The radiation cloth 20 radiates radiation heat to both the first heat transfer tube group 19 and a second heat transfer tube group 21. A heat conduction by a direct contact with fins is carried out from the radiation cloth to the first heat transfer group. For this reason, the temperature at this part slightly lowers. However, since in the vicinity of this part a high-temperature gas flows therein through gaps between fins, and passes through the radiation cloth, this part is heated to a high temperature, a strong radiation emitted from this part to the heat transfer tubes.

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 transferred 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.

By the way, if the mm chamber is simply downsized, the flame will extend to the heat exchange part 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 wall of the heat transfer tube and the flame will be cooled. As a result, the combustion reaction stopped and incomplete combustion occurred.This not only resulted in a loss of fuel, but also produced carbon oxides, soot, aldehydes, etc., which had a negative impact on the human body. This results in #.

In addition, if the combustion chamber is downsized and integrated with the heat exchange section, if unburned fuel components adhere to and accumulate on the surface of the heat transfer tube, the heat transfer tube may be overheated and damaged, or the combustion gas in the combustion chamber may not mix well. As a result, the temperature distribution tends to become large, 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 gas water heaters currently on the market, the size difference between the combustion chamber and the heat exchanger is approximately 2 = 1, and the size difference between the burner tip 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 Io' kcal/m 3 /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.

As long as convective heat transfer is used, in order to increase the amount of heat transferred per unit volume of the heat exchanger, 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 such as increasing the heat transfer rate by increasing the flow rate of the combustion gas, or 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. Is required.

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℃. be. Thus, there was 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 A fluid heating device is proposed in which a breathable radiator is placed between the groups. Since this fluid heating device employs a rigid body as the breathable radiator, large thermal stress is generated during use, which may pose a problem in the durability of the breathable radiator.

"Objective of the Invention" The 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 exchanger, and to suppress incomplete combustion. To provide a fluid heating device MIFr that can reduce the size of the entire device.

"Structure of the Invention J The fluid heating device according to the present invention includes a combustion means, a first heat exchanger tube group disposed adjacently downstream of the combustion means, and adjacently downstream of at least one heat exchanger tube of the first heat exchanger tube group. It is characterized by comprising an air-permeable radiation cloth arranged in a wave-like manner, and a second group of heat exchanger tubes arranged adjacent to and downstream of the radiation cloth.

In a preferred embodiment of the present invention, the radiation source is made of ceramic fiber.

In another preferred embodiment of the present invention, the radiation cloth is placed on the first heat exchanger tube group.

In still another preferred aspect of the present invention, the first heat exchanger tube group is arranged in multiple stages, and the radiation cross is connected to a downstream heat exchanger tube of the first heat exchanger tube group and a non-most downstream heat exchanger tube. They are in contact with the heat exchanger tubes of the stages alternately.

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 fuel as described above 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 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 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 is preferably one without fins on the outer surface because the temperature of the surrounding combustion gas is high and the heat transfer coefficient is also high due to the radiant heat transfer from the radiant cloth described in detail. From the viewpoint of increasing area, it is also possible to use a so-called lo-fin type having fins with a height of 2 mm or less, for example.

Adjacent downstream of at least one heat exchanger tube of the first heat exchanger tube group, a breathable radiant cloth is arranged in a wavy manner, for example, so as to cover the staggered heat exchanger tubes. With a rigid breathable radiator, problems such as vibration (change in posture, misalignment, falling off, or damage) may occur during transportation of the manufactured fluid heating device.

In contrast, with radiant cloth, the planar shape can be changed freely, making it easy to arrange the tubes in a shape that can effectively radiate radiant heat to each heat transfer tube in the first heat transfer tube group. In addition, by utilizing the uneven shape of a single piece of radiation cloth, it can be placed in a stable position without the need for special parts.

The breathable radiant cloth is preferably woven from a heat-resistant material, such as ceramic fibers such as silicon carbide, enriched silicon, aluminosilicate, and zirconia, so as to generate effective radiant heat at high temperatures.

In addition, the weave density, thickness, etc. of the cloth are appropriately selected to ensure the required ventilation so that the ventilation resistance when the combustion gas passes through the radiant cloth does not become excessive.

The radiant cloth converts the thermal energy of the combustion gas into strong radiant energy, and irradiates mainly the first heat transfer tube group with the radiant heat, regardless of the flow of the combustion gas. Due to the radiant heat transfer of this radiant cross and the convective heat transfer by the combustion gas,
The first heat exchanger tube group is heated, and the fluid flowing therein is heated. Furthermore, since the radiant cloth is heated to a high temperature, it promotes the oxidation reaction of unburned components such as CO1HC contained in the combustion gas, and exerts a kind of catalytic effect.

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

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 fi silicon carbide, which has excellent moldability, or copper, which is a highly thermally conductive material.

In the case of the present invention, by bringing 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. Also,
Depending on the conditions, the fluid to be heated, such as water, may locally boil, and the heat transfer may be affected by the generated steam, resulting in local (very high) temperatures. If the heat exchanger tube is made of poor metal, it will be heated and violently oxidized, and in extreme cases, it may melt. Therefore, it is desirable to select the material, layout, usage conditions, etc. appropriately. Ceramic is particularly preferred for heat exchanger tubes in high-temperature sections because it provides sufficient heat resistance.Also, when it is desired to recover not only sensible heat but also latent heat from the combustion gas, low-temperature Nitric acid may be generated in the heat exchanger (natural gas itself is clean, but nitrogen generated from high-temperature combustion
(Ox combines with moisture condensed on the surface of the heat exchanger tube at a low temperature to form nitric acid.) From this point of view as well, it is particularly preferable that the low-temperature heat exchange section be made of corrosion-resistant ceramics.

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 M11 shown in FIG. 1 is entirely surrounded by a casing 12 whose upper part is connected to an exhaust port (not shown).
The casing 12 includes a fan casing 13, a mixing chamber 14, and a combustion chamber 15 that communicate with each other, and is divided into an upper casing 12a and a lower casing +2b.

A fan 16 is incorporated into the fan cage jig 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). Therefore, fan 1
6 and 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.

A surface burner plate 18 as a combustion means is arranged at the boundary between the mixing chamber 14 and the combustion chamber 15. 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 at a position in the casing 12 close to the surface burner plate 18 . 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 mm.

The smaller the outer diameter of the heat transfer tube, the larger the ratio of the outer surface area of the heat transfer tube per unit volume of fluid flowing inside the tube, increasing the amount of radiant heat received. However, on the other hand, the number of required heat transfer tubes also increases, and the inside In consideration of the efficiency of the fluid heating device of the present invention, the above dimension range is preferable for water heaters and the like.

It is preferable that the arrangement spacing of the heat exchanger tubes is 6 to 30 mm, which is approximately the same as the outer diameter of the heat exchanger tubes.If this spacing is too small, not only will the pressure loss increase when the combustion gas passes, The bending radius of the radiant cloth becomes small, making it more likely to be damaged.

The distance Ha 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.

In the first heat exchanger tube group 19, an air-permeable radiation cloth 20 is arranged along each of the staggered heat exchanger tubes. This radiation cross 20 is held by the flanges of the upper casing 12a and the lower casing +2b, and is placed alternately ff12 on the upper and lower heat exchanger tubes of the first heat exchanger tube group 19.
The heat exchanger tubes are arranged in a wave-like manner, and radiant heat is applied to both the first heat exchanger tube group 19 and the second heat exchanger tube group 21, which will be described later.

The radiation cross 20 may be held by bringing the first and second heat exchanger tube groups close together and sandwiching them between them, or by fixing the ends with bolts that pass through the casing.
This prevents the radiation cross 20 from being lifted up by the gas flow, and consists of a ceramic arm protruding from the casing 12. The holding tool 23 is not essential.

In order to fix the radiation cloth 20, instead of placing the radiation cloth 20 on the lower heat exchanger tube in FIG. 1, it is passed around the lower edge of the lower heat exchanger tube and turned upward. It can also be proposed (see FIG. 2), in which case the radiant cross 20 is connected to the surface burner plate 18.
In order to increase the amount of radiant heat input into the tube, it is advisable to place at least one more stage of heat exchanger tubes roughly below.

The radiation cloth 20 has a large temperature distribution between the part that is in contact with the heat transfer tube and the part that is not in contact with it, and a large temperature change is given when the fluid heating device is ignited and stopped.
It is made of ceramic fiber that has excellent heat resistance, thermal shock resistance, and thermal conductivity.

Note that it is not essential that the radiation cloth 20 be in contact with the heat exchanger tubes; for example, in FIG. , or by supporting the radiation cross 20 with an appropriate support, the upper edge of the upper heat exchanger tube 19 and the radiation cross 2
The peak of 0 may be separated.

Roughly downstream of the radiation cross 20, a second heat exchanger tube group 21 is arranged close to the radiation cross 2°.

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 exchanger tubes that penetrate 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 in order to make it easier for air bubbles to escape when the heated fluid boils, The outlet side may be inclined 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, 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
9 and the second heat exchanger tube group 21, respectively, but preferably both lWl are flowed in series. 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 to flow countercurrently to the flow of combustion gas. On the other hand, in order to prevent local boiling within the tubes, it is preferable to connect them in the opposite direction so that the flow is parallel to the flow of combustion gas. Usually, the heat exchanger tubes are connected in series, but it is also possible to make an appropriate selection, such as connecting the heat exchanger tubes of the same stage in parallel and then connecting the heat exchanger tubes of different stages in series.

The operation of the device of 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 to form a premixed mixture. 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 amount of unburned components generated, the air ratio should be around 1.1 to 1.4. It is preferable to set the combustion gas to 1500 ~
The temperature reaches a high temperature of 1650°C, and the combustion gas is guided to the first heat exchanger tube group 19 arranged in the combustion chamber 15, and a part of the thermal energy possessed by the combustion gas is transferred to the first heat exchanger tube group 1 by convection heat transfer.
It is transmitted to the fluid such as water flowing inside the heat transfer tube 9. Roughly, the combustion gas flows through the radiant cloth 20 while remaining at a high temperature, and the radiant cloth 20 is also heated to become incandescent.

In the part where the radiation cross contacts the first heat exchanger tube group, direct contact heat conduction from the radiation cross to the first heat exchanger tube and the fins occurs, so the temperature in this part decreases slightly, but the temperature in the vicinity In this case, high-temperature gas flows in from the gap between the fins, passes through the radiation cross, is heated to a high temperature, and strong radiation is emitted from this part to the heat transfer tube.

Figures 3 and 4 explain this and show the relationship between the radiation cloth 20 placed on the fins 19a of the heat exchanger tubes of the first heat exchanger tube group 19, the flow of high temperature gas, and the radiation. ing. In Figures 3 and 4, white arrows indicate the flow of high-temperature gas, wavy arrows indicate radiation, and solid arrows indicate direct contact heat conduction. Almost no radiation leaks out, and almost perfect radiant heat transfer occurs.

Therefore, it is preferable to bend the radiation cloth 20 as much as possible and arrange it so as to wrap around the heat exchanger tubes.However, if the heat exchanger tubes of the first heat exchanger tube group 19 are not equipped with fins, the radiation cloth 20 should be bent as much as possible to wrap around the heat exchanger tubes. Because it plays a role like
It is preferable to make the contact area between the radiation cloth and the heat transfer tube as small as possible.

The radiation cloth 20 is maintained at a high temperature of 800 to 1200° C., and radiantly heats almost the entire first heat exchanger tube group 19. From the perspective of radiant heat transfer, it is preferable to raise the temperature of the radiant cloth as much as possible, but when considering temperature changes during ignition and stopping, and temperature distribution at various parts of the radiant cloth, the above-mentioned It is preferable to use the radiant heat within a temperature range. In this case, radiant heat is also irradiated in the direction of the surface burner plate 18, but a considerable amount is used by the lower heat exchanger tubes of the first heat exchanger tube group 19. Therefore, the surface burner plate 18 is not burned out by this radiant heat.

While the combustion gas passes through the first heat exchanger tube group 19 and the radiation cloth 20, its temperature decreases to 600 to 800°C by heat exchange with the fluid flowing inside the heat exchanger tubes, and then the combustion gas passes through the second heat exchanger tube group 21. The heat energy is transferred back to the fluid flowing inside. The second heat transfer tube group 21 is also irradiated with the radiant heat from the radiant oxygen 20 .

Thus, the fluid such as water inside the second heat exchanger tube group 21 is
It reaches a temperature of 40 to 80°C and is led out of the container.

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 11.4 mm, outer diameter 12.
7mm, fin height 1.6mm, fin outer diameter 15.9
5 mm copper loaf-in tubes are arranged horizontally in a staggered manner with an interval of 16 mm (pitch approximately 32 mm).

■Radiation Cloth 20: 15u SiC500 filament/yarn continuous fibers twisted and woven at 5 yarns/inch, arranged as shown in Figure 1.

■Second heat exchanger tube group 21: inner diameter of heat exchanger tubes 11, 5mm,
Copper tube with outer diameter 12.7mm and fin thickness 0.35m
Plate fin tube that combines m, fins and Sochi 2.7mm fins.

In addition, in the apparatus of the embodiment, the surface burner plate 18
The distance Ma from the end face to the lower edge of the fin of the lower heat exchanger tube of the first heat exchanger tube group 19 is 20 mm, and the distance Ma from the end face of the surface burner plate 18 to the lower edge of the fin of the second heat exchanger tube group 21 is 68 mm. And so.

In addition, in the apparatus of the control example, the first heat exchanger tube group 19 and the radiation cross 201Fr were not provided, and only the second heat exchanger tube group 21, which was the same as that used in the apparatus of the example, was installed at a distance of 200 Fr.
It was installed at a position of mm.

(Experimental results) Combustion space volume + heat exchange section volume Control example: Example = I: 0.28 Heat transfer area Control example: Example = 1.1.18 Heat received Control example: Example = I: 1.64 Exhaust CO concentration: Control example 80 ppm, Example 15 ppm
As can be seen from this result, in the apparatus of the example, by arranging the first heat exchanger tube group 19 and the radiation cross 20 in the above-mentioned relationship in the combustion chamber 15, the burner can be heated while keeping the CO concentration low. It was possible to significantly reduce the combustion space by placing the heat transfer tube close to the heat transfer tube, and by increasing the heat transfer area by only 18%, an increase in the amount of heat exchanged by 64% was obtained.

In addition, in the device of the example, the combustion chamber load is about 30% compared to the control example.
1.5 x 10' kcal/m 3/hr
It has become increasingly obsolete.

"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 radiation cross are performed simultaneously with respect to the first and second heat transfer tube groups. Heat can be used effectively. Furthermore, since the amount of radiant heat from the radiant cross is limited by the heat transfer tubes in the lower stage of the first heat transfer tube group, burning out of the combustion means due to the radiant heat is prevented. Furthermore, since the radiant cloth 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 radiant cloth, suppressing the amount of incomplete combustion products emitted. I can do it.

Furthermore, by configuring as in the present invention, it is possible to downsize the entire drawing. In addition, radiant cloth has great flexibility and excellent heat transfer, reducing thermal stress and
It is more advantageous than ceramic honeycomb in terms of thermal shock. Compared to rigid bodies such as ceramic honeycomb, it is also easier to position, as shown in the example, it can be easily gripped with a casing flange, etc., and this makes it difficult to change posture or fall off due to transportation or use. There is no need to worry about

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a fluid heating device according to the present invention, and FIG. 2 is a cross-sectional view of a main part of another fluid heating device according to the present invention. Figure 3 is an enlarged view of part 8 of Figure 1, Figure 4 is A-A of Figure 3.
It is a sectional view along the line. 11 is a fluid heating bag, 12 is a casing, 13 is a fan casing, 14 is a mixing chamber, 15 is a combustion chamber, 18 is a surface burner plate, 19 is a first heat exchanger tube group, 20 is a radiation cross, 21 is a second 22 is a fin.

Claims (1)

[Scope of Claims] 1. Combustion means, a first heat exchanger tube group disposed adjacently downstream of the combustion means, and a wave-like bending device adjacent to and downstream of at least one heat exchanger tube of the first heat exchanger tube group. 1. A fluid heating device comprising: an air-permeable radiant cloth disposed in the vicinity of the radiant cloth; and a second group of heat transfer tubes disposed adjacently downstream of the radiant cloth. 2. The fluid heating device according to claim 1, wherein the radiation cloth is made of ceramic fiber. 3. The fluid heating device according to claim 1 or 2, wherein the radiation cloth is placed on the first heat exchanger tube group. 4. In any one of claims 1 to 3, the first heat exchanger tube group is arranged in a plurality of stages, and the radiation cross is located at the top of the first heat exchanger tube group. A fluid heating device that alternately contacts downstream heat transfer tubes and non-downstream heat transfer tubes.