JPH0810046B2 - Improved fluid heating device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a fluid heating device used in a water heater, a bathtub, a hot water boiler, or the like.

"Prior art and its problems" Conventionally, in a fluid heating device such as a water heater, a bath kettle, and a hot water boiler, after burning fuel in a combustion chamber downstream of a burner, combustion gas is transferred between the heat transfer tube groups. It was designed to heat the fluid such as water flowing inside the heat transfer tube group mainly by using convective heat transfer.

In recent years, in order to make these fluid heating devices as compact as possible, there is a tendency to make the combustion chamber as small as possible and to increase the amount of heat transfer per unit volume of the heat exchange section.

Therefore, the present inventors previously proposed a fluid heating device as shown in FIGS. 7 and 8 in Japanese Patent Application No. 60-223980. In this fluid heating device 10, a combustion means 12 such as a burner is arranged in the lower part of the casing 11, and the combustion means 12
A first heat transfer tube group 13, a breathable radiator 14, and a second heat transfer tube group 15 are arranged in this order from the bottom on the above. In the first heat transfer tube group 13, a plurality of heat transfer tubes are arranged in a row at a predetermined interval, and a heated fluid such as water flows through the first heat transfer tube group 13 and the second heat transfer tube group 15. It is supposed to be.

Then, the fuel gas ejected from the nozzle of the combustion means 12 forms a flame and burns. The combustion gas heats the first heat transfer tube group 13 and also passes through the gaps between the heat transfer tubes of the first heat transfer tube group 13 to heat the radiator 14 as well. The heated radiant body 14 mainly radiates radiant heat to the first heat transfer tube group 13, and the first heat transfer tube group 13 is heated by both convective heat transfer by combustion gas and radiant heat transfer from the radiant body 14. To be done. The second heat transfer tube group 15 is also heated by the convective heat transfer by the combustion gas and the radiant heat from the radiator 14. Thus, the heated fluid flowing in the first heat transfer tube group 13 and the second heat transfer tube group 15 is heated.

According to the fluid heating device 10 described above, the radiant heat from the radiator 14 is applied not only to the first heat transfer tube group 13 but also to the second heat transfer tube group 15 and the combustion heat can be effectively used. Since one heat transfer tube group 13 is placed close to the combustion means 12, the combustion space can be greatly reduced and the entire apparatus can be made compact.
Further, even if the incomplete combustion product is generated, it is oxidized when passing through the radiator 14 which is kept at a high temperature, so that the discharge of the incomplete combustion product can be suppressed.

However, in the above fluid heating device 10, the combustion means
When the distance between the heat transfer tubes of the first heat transfer tube group 13 interposed between the heat transfer tubes 12 and the radiator 14 is wider than the outer diameter of the tube, the radiator 14
It was found that a large amount of radiant heat from the heat transfer tubes passed between the heat transfer tubes of the first heat transfer tube group 13 and reached the combustion means 12, so that the combustion means 12 was also heated by this radiant heat.

For this reason, the combustion means 12 causes thermal damage to the portion directly exposed to the radiant heat, or causes a large temperature difference between the portion that is directly exposed to the radiant heat and the portion that is not directly exposed to the surface. And a large temperature difference between the back surface and the back surface, which in turn deforms or damages the combustion means 12,
Furthermore, if the combustion means 12 is a premixed burner, it will cause a dangerous situation of flashback.

"Object of the Invention" The object of the present invention is to solve the above-mentioned problems, to effectively transfer the heat of combustion, to reduce the size of the entire apparatus, and to prevent the high-temperature overheating of the combustion means by radiant heat and It is an object of the present invention to provide a fluid heating device capable of suppressing the occurrence of a large temperature difference in the combustion means and preventing the combustion means from being deformed, damaged or flashback.

[Configuration of the Invention] The fluid heating device according to the present invention enables ventilation to the combustion means, the first heat transfer tube group arranged in a plurality of stages in the vicinity of the combustion means, and the vicinity of the first heat transfer tube group in the downstream side. A radiant body provided and a second heat transfer tube group arranged in the vicinity of the radiant body and a second heat transfer tube group, and the first heat transfer tube upstream of the gap of the heat transfer tube forming the most downstream stage of the first heat transfer tube group. It is characterized in that at least a part of the heat transfer tubes forming the non-downstream stage of the heat transfer tube group is positioned.

In the present invention, as the fuel, gas fuel such as city gas, propane gas, natural gas, or liquid fuel such as kerosene can be used. As the combustion means, a diffusion combustion type burner that supplies combustion air and fuel separately to the combustion chamber, or a premixed combustion type burner that mixes the combustion air and fuel in a required ratio in advance and then supplies the combustion chamber to the combustion chamber. Etc. are used. A planar burner is suitable as the premixed combustion type burner.

The first heat transfer tube group including a plurality of heat transfer tubes is arranged in a plurality of stages in the combustion gas flow direction, and is provided downstream of the combustion means as a whole and close to the combustion means.

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

When the first heat transfer tube group is arranged at a position distant from the above position with respect to the combustion means, the temperature of the combustion gas decreases due to heat loss or the cooling pipe of the casing surrounding the combustion chamber, and the effect of the present invention is obtained. There is a possibility that the burner may not be sufficiently obtained or that the radiant heat from the high temperature combustion gas to the burner may increase due to an increase in gas thickness, resulting in damage to the burner and flashback.

A radiator is arranged in the vicinity of the first heat transfer tube group and downstream thereof.
The radiant body converts the heat energy of the combustion gas into strong radiant energy, and mainly radiates radiant heat to the first heat transfer tube group and further to the second heat transfer tube group. Both the heat transfer tube groups are heated by the radiant heat transfer from the radiator and the convective heat transfer from the high temperature combustion gas, and the fluid flowing therein is efficiently heated.

The radiator is ceramics such as silicon carbide, silicon nitride, aluminum nitride, cordierite, mullite, lithium aluminum silicate, and aluminum titanate, which are suitable materials for generating effective radiant heat at high temperatures. Ceramics having high strength and high thermal conductivity, for example, ceramics such as silicon carbide, silicon nitride and aluminum nitride are preferable. A metal material such as heat resistant steel may also be used depending on the temperature conditions.

This radiant body is provided so that the combustion gas passing through the first heat transfer tube group region comes into contact with the radiant body and can flow further downstream, that is, the combustion gas can be aerated. .

A preferred example of such an arrangement is to arrange a large number of rod-shaped or elongated plate-shaped radiators parallel to each other and with slits formed between them. At this time,
The longitudinal direction of the rod-shaped or elongated plate-shaped radiator is preferably orthogonal to the combustion gas flow direction, but may be oblique.
In this case, the radiator itself may be non-breathable or breathable.

A more preferable method of providing the radiator is to use a breathable radiator having a flat plate shape, for example. Breathable radiator
The flow paths through which gas can flow between the two surfaces of the plate-like body are uniformly distributed as a whole, and typically, a honeycomb body, a three-dimensional mesh body, a communicating cell body, a mesh body laminate, etc. Is mentioned. Such a breathable radiator is arranged, for example, so as to traverse substantially the entire area of the combustion gas flow path, whereby the combustion gas passes through the inside of the breathable radiator and is vented to the downstream side. To do.

Of these breathable radiators, ceramic honeycomb plates are particularly suitable. This honeycomb plate has a large number of parallel cells that penetrate the front and back of the plate surface, and the cell shape can be appropriately selected from square, rectangular, hexagonal and the like. Further, the honeycomb plate may be formed by corrugated plates or by laminating a large number of corrugated plates and flat plates.

The second heat transfer tube group is arranged near and downstream of the radiator.
The combustion gas flowing into the second heat transfer tube group area is subjected to heat exchange when passing through the arrangement area of the first heat transfer tube group and the radiator,
The temperature has dropped. Therefore, it is preferable that the second heat transfer tube group has fins on the outer surface to improve convective heat transfer. Further, in order to make the combustion gases come into contact with each other evenly, the heat transfer tubes in the second heat transfer tube group may be arranged in a staggered manner.

The material of the heat transfer tubes of the first and second heat transfer tube groups is
Metals such as copper, aluminum, aluminum alloys and stainless steel, or ceramics such as silicon carbide and silicon nitride that have excellent thermal conductivity and corrosion resistance are preferable, and particularly have high thermal conductivity, low linear expansion coefficient, and high strength. Then
Most preferred is reaction-sintered silicon carbide which is also excellent in formability, or copper which is a high thermal conductivity material.

By the way, if the first heat transfer tube group is arranged in one stage between the radiant body and the combustion means and the direct radiation of the radiant heat from the radiant body to the combustion means is attempted to be reduced, the first heat transfer tube group is formed. However, the pressure loss when the combustion gas passes through this gap becomes large, and the U-shaped tube connecting the tube ends of the heat transfer tube is restricted. Therefore, in the present invention, the first heat transfer tube group is arranged in a plurality of stages, and at least a part of the heat transfer tubes forming the non-most downstream stage is provided upstream of the gap of the heat transfer tubes forming the most downstream stage. Is located.

From the viewpoint of reducing the direct radiant heat from the radiant body to the combustion means, it is possible to make the direct radiant heat substantially zero by the staggered arrangement described later, but this is not essential. The ratio of the sum of the projected areas of the radiators projected by the projection lines perpendicular to the downstream surface of the combustion means through the gaps of the heat transfer tubes forming the first heat transfer tube group to the area of the downstream surface of the combustion means (hereinafter, 40% of projection area ratio)
It is preferably below 35%.

A preferable typical example of such a heat transfer tube arrangement is one in which parallel and evenly spaced heat transfer tube groups are arranged in the same direction on the upstream side and the downstream side and with a phase shift, and above all, the heat transfer tube on the downstream side is arranged. The upstream heat transfer tube is located upstream of the central part of the gap of
The so-called staggered arrangement is particularly preferred.

Another preferred arrangement example is to arrange heat transfer tube groups at equal intervals in parallel so as to run in different directions on the upstream side and the downstream side.

Further, for example, two spiral heat transfer tubes may be arranged so that their positions are shifted on the upstream side and the downstream side.

When each heat transfer tube is arranged in this way, the amount of radiant heat from the radiant body is blocked by each heat transfer tube, so that the amount of radiant heat that reaches the combustion means directly decreases. Therefore, high temperature overheating of the combustion means due to radiant heat and generation of a large temperature difference in the combustion means due to this are suppressed, and thermal deformation, damage, and flashback of the combustion means are prevented. Further, the radiant heat directly radiated from the radiator to the heat transfer tube is also increased, and the heat transfer efficiency is improved. Further, it is not necessary to make the gap between the heat transfer tubes so small, neither is there a pressure loss through combustion gas, nor is there any restriction when connecting the tube ends. Since the fluid to be heated flows inside, the heat transfer tube is not damaged by heat.

In particular, when the staggered arrangement as described above is used, and the pipe spacing in each of the upstream stage and the downstream stage is equal to or smaller than the pipe outer diameter, the projected area ratio is 0%, that is, the direct irradiation is perpendicular to the downstream surface of the combustion means. It is possible to eliminate the emitted radiation. When the projected area ratio is 0% as described above, the combustion gas can pass through the gap between the heat transfer tubes with a low pressure loss, and most of the radiant heat from the radiator is blocked by the first heat transfer tube group. It does not reach the combustion means.

Since the temperature of the combustion gas in the surroundings is high and the heat transfer coefficient is higher due to the radiant heat transfer than the radiator, it is preferable that no fins are attached to the outer surface of each heat transfer tube of the first heat transfer tube group. However, for example, a fin with a fin height of about 2 mm or less can be used.

In the present invention, the term "heat transfer tube group" means that a plurality of heat transfer tube cross sections are recognized, for example, in an appropriate cross section along the combustion gas flow direction. Therefore, each heat transfer tube may be a different heat transfer tube, or one heat transfer tube meanders,
It may be arranged in a spiral shape or a spiral shape, and the cross-sections at a plurality of points may be recognized.

It should be noted that as the combustion means, generally, a burner having a flat burner plate is assumed, but a curved curved surface may be used. Further, instead of the planar burner plate, for example, a small cylindrical fuel outlet may be densely provided so as to project. In this case, the combustion surface formed by this fuel outlet group is the combustion means referred to in the present invention. It is the downstream side. Further, for example, in a case where a small cylindrical fuel outlet is sparsely provided, the small cylindrical cross section is the downstream surface of the combustion means in the present invention.

[Examples 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 20 of one embodiment of the present invention shown in FIGS. 1 and 2 is wholly surrounded by a casing 21 whose upper part is connected to an exhaust port (not shown), and the casing 21 is mixed below the casing 21. The chamber 23 and the combustion chamber 24 are connected and configured.
Air and fuel gas are supplied to the mixing chamber 23 from below (not shown) 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 ceramics is arranged as a combustion means. The burner plate 27 has a large number of flame openings, and the air-fuel mixture that has passed through the flame openings forms a planar flame on the downstream surface 27a of the burner plate 27. That is,
In this embodiment, a premixing surface burner system is adopted.

Above the burner plate 27 in the casing 21, a plurality of heat transfer tubes 13a and 13b are arranged in two stages in parallel with each other in parallel and at equal intervals to form a first heat transfer tube group 13. ing. The outer diameter a of each heat transfer tube 13a, 13b is 12 to 20 mm,
The wall thickness is about 0.6 to 2.0 mm, and the distance d between the upper heat transfer tubes 13a or the distance d between the lower heat transfer tubes 13b is about 0.5 to 1.5 times the outer diameter a. In addition, the heat transfer tube 13
b is located upstream of the center of the space d between the heat transfer tubes 13a and 13b,
It is a so-called staggered arrangement. This d / a ratio is 1.0
In the following cases, the projected area ratio will be substantially 0%.

The distance b from the downstream surface 27a of the burner plate to the lower edge of the heat transfer tube 13b is 5 to 50 mm.

Above the first heat transfer tube group 13 is provided a breathable radiator 14 made of a ceramic honeycomb plate, and above the radiator 14 is provided a second heat transfer tube group 15. There is. In this embodiment, as the second heat transfer tube group 15, a plate fin tube including a large number of parallel flat plates 28 and a plurality of parallel transverse heat transfer tubes penetrating the flat plates 28 at right angles is used. For example, a plurality of fins may be formed on the outer surface of each heat transfer tube.

The heat transfer tubes of both heat transfer tube groups 13 and 15 are generally arranged horizontally, but the outlet side is higher than the inlet side of the heated fluid so that bubbles easily escape during boiling of the heated fluid. It may be inclined to.

A fluid to be heated is caused to flow in the first heat transfer tube group 13 and the second heat transfer tube group 15. A liquid, especially water, is suitable as the fluid to be heated. The heated fluid may flow independently into the first heat transfer tube group 13 and the second heat transfer tube group 15, but is preferably flowed in series between the two. In this case, in order to increase the temperature efficiency, the first heat transfer tube group 13 is made to flow through the second heat transfer tube group 15 first, and the heated fluid that has flowed out of the second heat transfer tube group 15 is then discharged.
It is preferable to flow the gas in a countercurrent to the flow of the combustion gas. On the other hand, in order to prevent local boiling in the tube, it is preferable that the connection is made in the opposite direction to make the flow parallel to the flow of the combustion gas.

Further, in each heat transfer tube group, all are usually connected in series, but series connection and parallel connection may be appropriately combined.

 The operation of the device of the present invention will be described below.

The air-fuel mixture formed in the mixing chamber 23 passes through the flame opening of the burner plate 27 and is supplied to the combustion chamber 24.
A planar flame is formed in the vicinity of the downstream surface 27a of the burner plate 27 and becomes a combustion gas having a high temperature of 1500 to 1650 ° C.

This combustion gas is guided to the first heat transfer tube group 13 and transfers a part of the heat energy of the combustion gas by convective heat transfer to the fluid flowing in the heat transfer tube 13a of the first heat transfer tube group 13. . Further, the combustion gas is the heat transfer tubes 13a of the first heat transfer tube group 13.
Through the gap, and flows in the radiator 14 at a high temperature, and the radiator 14 is also heated to be incandescent. Radiant body 14 at this time
Is maintained at a high temperature of 1000 to 1200 ° C. and mainly radiatively heats the first heat transfer tube group 13.

At this time, the radiant heat passes through the gap of the heat transfer tube 13a and is also radiated toward the burner plate 27, but is blocked by the heat transfer tube 13b located upstream of this gap and not only heats the heat transfer tube 13b, but also the burner. The radiant heat applied to the plate 27 is significantly reduced, and when the projected area ratio is 0%, the direct radiant heat to the burner plate 27 becomes substantially zero. Therefore, the burner plate 27 only receives a slight amount of radiant heat of gas from the flame, and the upstream side of the burner plate 27 is maintained at about 150 ° C. at the most, together with the cooling effect at the time of passage of the air-fuel mixture, and the downstream surface 27a is slightly smaller than this. Although it gets hot,
The in-plane temperature difference of the downstream surface 27a is about 350 ° C. or less, and it is possible to prevent melting, thermal deformation, thermal stress cracking, flashback, etc. of the burner plate 27 due to radiant heat even when used for a long period of time. Further, there is also an advantage that the pressure loss of passing the combustion gas can be made sufficiently low without making the cross-sectional outer shape of the heat transfer tube a special shape so that the distance between the heat transfer tubes 13a and 13b can be sufficiently reduced.

Then, the combustion gas, while passing through the arrangement area of the first heat transfer tube group 13 and the radiator 14, its temperature is lowered to 800 ~ 1000 ℃, is guided to the second heat transfer tube group 15, the inside Transfers thermal energy back to the flowing fluid. Further, the radiant heat from the radiator 14 is also applied to the second heat transfer tube group 15. Thus, the fluid inside the second heat transfer tube group 15 becomes hot water at 40 ° C. to 80 ° C., for example, and is drawn out of the apparatus.

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

(Experimental conditions) Fuel: Natural gas, air ratio 1.2 Heated fluid: Water with an inlet temperature of 20 ° C is first passed through the first heat transfer tube group 13, and then exits and then passed through the second heat transfer tube group 15. .

Radiator 14: A thickness of 5 mm, a number of cells of 200 / in ² , and a honeycomb plate made of pressureless sintered silicon carbide having a square cell cross section are arranged above the first heat transfer tube group 13.

Second heat transfer tube group 15: Heat transfer tube inner diameter 17.4 mm, outer diameter 19.0 m
m copper tube and fin thickness 0.35mm, fin pitch 2.7mm
Plate fin tube combined with the copper fin of.

Burner plate 27: 10 mm thick cordierite ceramic burner plate 27 from the downstream surface 27a to the first heat transfer tube group 1
The distance b to the lower edge of 3 is 30 mm, and the distance c from the downstream surface 27a of the burner plate 27 to the lower edge of the fin of the second heat transfer tube group 15
Is 57 mm.

These are the same as those in the examples and the control examples, and the fuel,
The water supply rate was also the same.

First heat transfer tube group 13: Eight copper tubes with an inner diameter of 17.4 mm and an outer diameter of 19.0 mm are arranged in two rows, four in each row. The distance d in each step is 19 mm. In the embodiment, the two-stage zigzag arrangement is used, and in the control example, the two-stage square arrangement (that is, the upper heat transfer tube is arranged directly above the lower heat transfer tube).

(Experimental results) Projected area ratio Control example 50%, Example 0% Average temperature of burner plate 27 Control example 150-160 ° C, Example
70-80 ° C. Total absorbed heat of the first heat transfer tube group 13 Control example 13800 kcal / hr, Example 14700 kcal / hr Furthermore, in the control apparatus, the burner plate was missing at the flame mouth.

In the embodiment shown in FIGS. 3 and 4, a large number of elongated silicon nitride sintered plates 14a are arranged in a louver shape to form the radiator 14. The first heat transfer tube group 13 is the upper heat transfer tube 13c
And the heat transfer tube 13d in the lower stage.The heat transfer tubes 13c and 13d are arranged in parallel and at equal intervals, and the traveling direction of the heat transfer tube 13c and the traveling direction of the heat transfer tube 13d are arranged orthogonally to each other. ing. In this case, the heat transfer tube outer diameter a and the heat transfer tube interval d
Since the ratio of d / a is 3/4, the projected area ratio is about 43% only in the upper or lower stage, but the projected area ratio as a whole is about 18%.

In the embodiment shown in FIGS. 5 and 6, a large number of solid round rods 14b made of a silicon nitride sintered body are arranged in two stairs in a zigzag pattern to form the radiator 14. The first heat transfer tube group 13 is configured by arranging two spiral heat transfer tubes 13e and 13f in upper and lower two stages. As can be seen from FIG. 6, when viewed from the up and down direction, the heat transfer tubes 13e Since 13f and 13f are arranged with a phase shift of half pitch in each of the width direction and the depth direction, the projected area ratio is significantly reduced as compared with the case where the phase is not shifted. In FIG. 6, the heat transfer tubes 13e and 13f are hatched for the sake of easy viewing of the drawing.

In each of the above embodiments, the first heat transfer tube group is composed of two upper and lower stages, but three or more stages may be used.
Further, a diffusion combustion type burner can be adopted instead of the premix type burner. Furthermore, instead of sequentially arranging the heat transfer tubes and the radiators above the burner plate, they may be sequentially arranged below and to the side.

[Advantages of the Invention] As described above, according to the present invention, the first heat transfer tube group is arranged in a plurality of stages in the combustion gas flow direction, and the gap between the heat transfer tubes in the most downstream stage among them is arranged. Since at least a part of the non-downstream stage heat transfer tube is located upstream of, the effective transfer of the radiant heat from the radiator to the first heat transfer tube and the miniaturization of the entire device can be achieved. Since the radiant heat from the radiant body is blocked by the first heat transfer tube group and the direct radiant heat reaching the combustion means is substantially or almost completely eliminated, the combustion means is kept at a low temperature. Therefore, it is possible to prevent melting, thermal deformation, damage, and backfire of the combustion means. Further, when the present invention is applied to a gas water heater or the like, there is no occurrence of trouble such as after-boiling immediately after the water heater is used, which is caused by heat storage in the combustion means such as a burner plate.

[Brief description of drawings]

1 is a sectional view of an embodiment of the fluid heating apparatus of the present invention, FIG. 2 is a sectional view taken along the line II-II of FIG. 1, and FIGS. 3 and 5 are the radiator and the radiator in FIG. Cross-sectional views of the radiator and the first heat transfer tube group part of different embodiments of the fluid heating apparatus of the present invention having different first heat transfer tube group parts, and FIG. 4 is a line IV-IV of FIG. A sectional view along the line, and Fig. 6 is VI of Fig. 5.
-VI is a cross-sectional view taken along line VI, FIG. 7 is a cross-sectional view of the previously proposed fluid heating device, and FIG. 8 is a cross-sectional view taken along line VIII-VIII in FIG. 13 is a first heat transfer tube group, 13a to 13f are heat transfer tubes, 14 is a radiator, 15 is a second heat transfer tube group, 20 is a fluid heating device, and 27 is a burner plate.

(72) Inventor Yoshimasa Arai 4-29-16 Mitsuwadai, Chiba City, Chiba Prefecture (72) Kozo Sakurai 5-22 Nagakuracho, Sakae Ward, Yokohama City, Kanagawa Prefecture

Claims (1)

[Claims] Claim: What is claimed is: 1. Combustion means, a first heat transfer tube group arranged in a plurality of stages in the vicinity of the vicinity of the combustion means, a radiant body provided in the vicinity of the first heat transfer tube in the vicinity of the first heat transfer tube so that ventilation is possible, and radiation. A second heat transfer tube group arranged in the vicinity of the downstream of the body, and a non-downstream stage of the first heat transfer tube group is provided upstream of the gap of the heat transfer tubes forming the most downstream stage of the first heat transfer tube group. A fluid heating device characterized in that at least a part of a heat transfer tube constituting the above is positioned.