JPH0739880B2 - 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, fluid heating devices such as water heaters, bath kettles, and hot water boilers have combustion means such as burners, and after burning fuel in the combustion chamber, the combustion gas is transferred. It was designed to lead to the heat pipe group and heat fluid such as water flowing inside the heat transfer pipe group.

In recent years, in these fluid heating devices, in order to make it as compact as possible, the combustion chamber is made as small as possible,
There is a tendency to have a structure in which the combustion chamber and the heat exchange section are integrated.

However, when the size of the combustion chamber is reduced in this way, incomplete combustion may occur due to the contact of the fuel during combustion with the wall of the heat transfer tube (that is, cooling of the flame). This results in not only fuel loss but also CO, soot, aldehyde, etc., which adversely affects the human body.

Also, if the wall of the combustion chamber is a heat transfer surface like a boiler, or if the heat transfer tube is close to the flame, unburned fuel adheres to the heat transfer surface and the heat transfer surface becomes overheated and damaged. In addition, because of poor mixing of the combustion gas in the combustion chamber, the heat transfer load is locally increased, which may also damage the heat transfer surface.

Therefore, there is a limit to downsizing of the combustion chamber, for example, in the gas water heaters currently on the market, the size of the combustion chamber and the heat exchange section is about 2: 1 and the burner tip and The distance from the lower heat transfer tube is 200-300 mm. It has been difficult to reduce the size of the combustion chamber further and bring the heat exchange section closer to the flame because the heat transfer tube is damaged more quickly and CO generation is increased.

"Object of the Invention" The object of the present invention is to solve the above-mentioned problems of the prior art, prevent incomplete combustion, do not damage the heat transfer tube, etc., and have a high efficiency of fluid heating with less heat loss. To provide.

"Structure of the Invention" A fluid heating apparatus according to the present invention includes a burner, a first heat transfer tube group arranged in the vicinity of a downstream side of a flow of combustion gas of the burner, and a combustion of the first heat transfer tube group. A gas-permeable radiant body is disposed adjacent to the downstream side of the gas flow, and a second heat transfer tube group is further disposed adjacent to the downstream side of the combustion gas flow of the radiant body. It is characterized by

In the present invention, as the burner, those which use propane gas, natural gas, petroleum, etc. as a fuel and vaporize and burn these fuels are preferably used. Particularly preferably, a gas burner is used. A plurality of gas burners are arranged as needed.

The first heat transfer tube group is arranged on the downstream side of the flow of the combustion gas with respect to the burner, in a position close to the burner, that is, in a flame formed by the burner or a position close to the tip of the flame. In this case, the distance between the fuel gas discharge port of the burner and the first heat transfer tube group is preferably within 100 mm. In other words, the length of the flame varies depending on the burner design, but is generally about 50 mm or less,
After all, the first heat transfer tube group is arranged within about 50 mm from the vicinity of the tip of the flame. When the first heat transfer tube group is arranged at a position distant from the above, heat loss becomes large and the effect of the present invention cannot be sufficiently obtained. Although the first heat transfer tube group is closest to the burner, it is cooled by a fluid such as water flowing inside, so that heat damage is prevented.
In order to prevent thermal damage due to partial overheating, the first heat transfer tube group preferably has no fins on the outer surface,
You may attach a fin with a small heat transfer area increase rate.

The breathable radiator is disposed adjacent to the first heat transfer tube group and apart from the burner. The breathable radiant body is not particularly limited, but for example, a ceramic honeycomb body or the like is suitable because of its lightness, low ventilation resistance, and high effective emissivity. Further, a ceramics Schwank burner plate, a ceramics three-dimensional mesh body or the like can be adopted. As ceramics, alumina, zirconia, mullite, spodumene, cordierite, aluminum titanate, lithium aluminum titanate, silicon carbide, silicon nitride and the like can be used. Breathable radiator
When the combustion gas passes, it becomes incandescent and radiates heat to the first heat transfer tube group and the second heat transfer tube group. in this case,
Without the first heat transfer tube group, the radiant heat is directly applied to the burner and the burner is overheated, which is not preferable. Incomplete combustion products such as CO are generated by providing the first heat transfer tube group close to the burner, but these incomplete combustion products are radiated when they pass through the permeable radiator. It burns completely under the heat of. In this case, when the radiator is ceramics, the catalytic action of the ceramics itself promotes complete combustion of incomplete combustion products. Further, a catalyst such as an oxidation catalyst may be supported on the radiator to promote the combustion of the incomplete combustion products. It goes without saying that the fluid flowing inside the first heat transfer tube group is heated by heating the first heat transfer tube group.

The second heat transfer tube group is arranged adjacent to the radiator and further away from the burner. The second heat transfer tube group is heated by coming into contact with the combustion gas that has passed through the radiant body and receiving radiant heat from the radiant body. Then, the fluid flowing inside is heated by exchanging heat with the combustion gas. The second heat transfer tube group improves heat transfer efficiency,
Those having fins on the outer surface are preferable. Further, in order for the combustion gases to come into contact with each other on average, it is preferable that the heat transfer tubes in the second heat transfer tube group are arranged in a staggered manner.

The material of the heat transfer tubes of the first heat transfer tube group and the second heat transfer tube group is preferably a ceramic having excellent heat resistance and corrosion resistance such as silicon carbide and silicon nitride, and particularly high thermal conductivity and low wire Reactive sintered silicon carbide, which has an expansion coefficient, high strength, and excellent moldability, is most preferable. In the case of the present invention, since the first heat transfer tube group is brought close to the burner, the first and second heat transfer tube groups are subject to a large heat transfer load and are likely to locally become hot. Further, in some cases, the fluid to be heated such as water causes local boiling and thus the heat generated by the steam or the like is hindered so that the temperature locally becomes extremely high.
Therefore, if a metal with poor heat resistance is used, the heat transfer wall may be overheated and violently oxidized, and in extreme cases, it may be melted.Therefore, the specifications such as material, layout, and operating conditions should be selected appropriately. desirable. In this respect, when it is made of ceramics, sufficient heat resistance can be obtained. In addition, when trying to recover not only the sensible heat but also the latent heat of the combustion gas, nitric acid may be generated (natural gas itself is clean, but NOx is generated due to high temperature combustion, When this becomes low temperature, it is combined with water to form nitric acid. From this point as well, a ceramic having corrosion resistance is preferable. For the same reason, the material of the fins provided on the outer surface of the heat transfer tube is preferably ceramics, but metals such as copper and stainless steel can also be used.

"Embodiment of the Invention" FIGS. 1 and 2 show an embodiment of a fluid heating apparatus according to the present invention.

The fluid heating device 11 includes a casing 12 having an upper opening.
A burner 13 is arranged in the lower part of the casing 12 by being surrounded by. The burner 13 has a plurality of nozzles 14, and a fuel gas, for example, natural gas is ejected from the nozzles 14 to form a flame 15.

A first heat transfer tube group 16 is arranged above the burner 13. In the case of this embodiment, the heat transfer tubes of the first heat transfer tube group 16 are
The outer diameter is 5 to 20 mm, the wall thickness is 1 to 3 mm, the heat transfer tube arrangement interval is 10 to 20 mm, and the distance a from the tip of the nozzle 14 of the burner 13 is 10
It is within 0 mm. The heat transfer tubes of the first heat transfer tube group 16 may be ordinary cylindrical tubes or tubes having an elliptical cross section or the like.

An air permeable radiator 18 is arranged above the first heat transfer tube group 16. In this embodiment, as the radiator 18, a ceramic radiator as shown in FIG. 3 is used. This ceramic radiator is provided with a large number of ventilation holes that penetrate vertically through a grid-shaped partition wall, the wall thickness w is 0.1 to 2 mm, the open area ratio is 60% or more, and the height h is 2 to 2. 30
It is said to be mm. The shape of the ventilation holes of the ceramic radiator is not limited to the square shape as shown in FIG. 3, but may be a rectangular shape or a hexagonal shape as required. Further, it may be a ceramic radiator formed by laminating a plurality of corrugated plates or a plurality of corrugated plates and flat plates.

A second heat transfer tube group 19 is arranged further above the radiator 18. In this embodiment, each heat transfer tube of the second heat transfer tube group 19 is inserted through a common plate type fin 20,
They are arranged in parallel with each other and in a staggered pattern. The heat transfer tubes of the second heat transfer tube group 19 have an outer diameter of 5 to 20 mm and a wall thickness of 1 to 3 mm, and the heat transfer tubes are arranged at an interval of 15 to 50 mm.
The wall thickness of 20 is 0.1 to 1 mm, and the arrangement interval of the fins 20 is 1 to 10 mm. As the fins 20, a laminated body formed by laminating a large number of corrugated plates and flat plates alternately is used, and the heat transfer tubes may be inserted vertically with respect to the traveling direction of the ventilation path of the laminated body. Good.

The heat transfer tubes of the first and second heat transfer tube groups 16 and 19 are generally arranged horizontally, but on the inlet side of the fluid to be heated so that the bubbles easily escape when the fluid to be heated boils. You may incline so that an exit side may become an upper side compared.

A fluid to be heated is caused to flow in the first heat transfer tube group 16 and the second heat transfer tube group 19. A liquid, especially water, is suitable as the fluid to be heated. The fluid to be heated may be separately flown into the first heat transfer tube group 16 and the second heat transfer tube group 19, but is preferably flowed in series between both. In this case, in order to increase the temperature efficiency, it is preferable that the first heat transfer tube group 16 is first caused to flow through the second heat transfer tube group 19, and the heated fluid that has flowed out of the second heat transfer tube group 19 is then allowed to flow. On the other hand, in order to prevent local boiling in the tube, on the contrary, first flow to the first heat transfer tube group 16 and then the heated fluid exiting here to the second heat transfer tube group 19 Is preferred. When a plurality of heat transfer tubes are provided in the combustion gas flow direction in each heat transfer tube group, the combustion gas is allowed to flow from the upstream side to the downstream side in the first heat transfer tube group 16, In the second heat transfer tube group 19, the combustion gas may flow from the downstream stage to the upstream stage.

An experiment was conducted to evaluate the performance by using the fluid heating device 11 of the above-described embodiment and a fluid heating device having a different configuration. The experimental conditions and the experimental results are as follows.

(Experimental conditions) Fuel: Natural gas, excess air ratio 1.02 Fluid to be heated: Water with an inlet water temperature of 20 ° C. was first passed through the first heat transfer tube group 16 and then exited to the second heat transfer tube group 19. Flowing first heat transfer tube group 16: inner diameter 4.5 mm, outer diameter 7 mm, arrangement interval 12 mm,
A total of 10 arranged in a row, reaction-sintered silicon carbide radiator 18:20 cells / inch ² , honeycomb with a square cell cross section, height h20 mm in gas flow direction, mullite second heat transfer tube group 19: transfer inner diameter 8.5mm heat pipe, an outer diameter of 12 mm, the thickness of the fins 0.4 mm, 20 times the heat transfer area increasing rate due to the fins, reaction sintering silicon carbide, the outer surface reference heat transfer area 1.4 m ^2, the combustion gas flow direction dimension b85mm In the apparatus of the embodiment, the distance a from the tip of the nozzle 14 of the burner 13 to the first heat transfer tube group 16 is 50 mm,
The distance c from the tip of the nozzle 14 to the second heat transfer tube group 19 is 80
mm.

Further, in the apparatus of the comparative example, the first heat transfer tube group 16 and the radiator 18 are not provided, only the second heat transfer tube group 19 is provided as in the case of the apparatus of the example, and the nozzle of the burner 13 is provided. 14 The distance c from the tip to the second heat transfer tube group 19 was 250 mm.

(Experimental Results) The following table compares the performances of the device of the example and the device of the comparative example. The relative ratios are shown except for the concentration of CO emissions.

Further, when the flow of water was reduced, local boiling occurred in the uppermost heat transfer tube at the outlet water temperature of 72 ° C. in the control apparatus. On the other hand, in the device of the example, the outlet water temperature is 93 ° C.
For the first time, local boiling occurred in the uppermost heat transfer tube. The occurrence of local boiling was judged in the state where vibration was generated along with a loud noise.

As described above, in the apparatus of the embodiment, by providing the first heat transfer tube group 16 and the radiator 18, the burner 13 is brought close to the heat transfer tube while the CO concentration is kept low, and the combustion space is greatly reduced. can do. In addition, local boiling is less likely to occur, and the outlet water temperature can be significantly increased.

The reason why the device of the embodiment is less likely to cause local boiling is considered as follows. That is, the radiator 18 is heated by the combustion gas, and its temperature is made uniform by the heat transfer inside. It is considered that the radiant body 18 irradiates the second heat transfer tube group 19 with uniform radiant heat to uniformly heat the second heat transfer tube group 19. Further, the first heat transfer tube group 16 does not cause local boiling because the temperature of the tube wall is kept low because there is no fin on the outer surface, and the first heat transfer tube group 16 has strong convection due to the flame. It is considered that not only heat transfer but also radiant heat equivalent to this is received from the radiator 18.

During the experiment, the second heat transfer tube group 19 receives strong radiant heat from the radiant body 18, and the tips of the fins 20 are colored azuki-colored,
It is estimated that the temperature was above 650 ° C. Although the reaction sintered silicon carbide was used as the material of the second heat transfer tube group 19,
Reactively sintered silicon carbide has a thermal conductivity of 170 kcal / m ² h at room temperature.
50kcal / m ² h ℃ at ℃ and 1000 ℃ is very large, and if the heat conductivity is 20kcal / m ² h ℃ at most, if the heat-resistant alloy is used, the tip of the fin 20 is 850 ℃ or more. It is estimated to be. Further, the first heat transfer tube group 16 has relatively low temperature water flowing therein, but since it is close to the flame, it locally becomes considerably hot. Therefore, under such usage conditions, the heat-resistant alloy may not be able to withstand long-term use, and it is preferable to set more appropriate specifications. By using the reaction-sintered silicon carbide for the first and second heat transfer tube groups 16 and 19, corrosion resistance to nitric acid accompanying NOx generation can also be obtained.

4 and 5 show another embodiment of the fluid heating apparatus according to the present invention. In this fluid heating device 11,
An upper portion of the casing 20 is closed and an exhaust port 21 is formed in the lower portion. Then, the burner 13, the first heat transfer tube group 16, the radiator 18, and the second heat transfer tube group 19 are sequentially arranged in the casing 20 from the upper side to the lower side. Further, a tray 22 for the condensed water is arranged at the bottom of the casing 20. Therefore, in this device 11, the combustion gas flows downward and the condensed water flows downward. This device 11 is suitable for a type that also recovers latent heat in combustion gas.

Further, in the embodiment shown in FIGS. 1 and 4, it is also preferable to dispose a finless heat transfer tube group between the air permeable radiator 18 and the second heat transfer tube group 19 having fins.
Thereby, the temperature difference between the high temperature portion side and the low temperature portion side of the second heat transfer tube group 19 including the fins can be reduced. Furthermore, a finless heat transfer tube group, a breathable radiator, a finless heat transfer tube group, a breathable radiator, and a finned heat transfer tube group may be arranged in this order from the burner side.

[Advantages of the Invention] As described above, according to the present invention, the first heat transfer tube group, the breathable radiator, and the second heat transfer tube group are sequentially arranged from the position close to the burner. Radiant heat is radiated from the radiant radiator to the first heat transfer tube group and the second heat transfer tube group,
The combustion heat can be effectively used. Further, even if incomplete combustion products are generated by bringing the first heat transfer tube group close to the burner, they are completely combusted when passing through the radiator, so that the generation of incomplete combustion products is extremely reduced. be able to. Further, the first heat transfer tube group can be brought close to the burner to significantly reduce the combustion space, and the device can be made compact.

[Brief description of drawings]

FIG. 1 is a front sectional view showing an embodiment of a fluid heating apparatus according to the present invention, FIG. 2 is a sectional view taken along line II-II in FIG. 1, and FIG. 3 is a radiator used in the apparatus. FIG. 4 is a front sectional view showing another embodiment of the fluid heating apparatus according to the present invention, and FIG. 5 is a sectional view taken along the line VV of FIG. In the figure, 11 is a fluid heating device, 12 is a casing, 13 is a burner, 14 is a nozzle, 15 is a flame, 16 is a first heat transfer tube group, 18 is a breathable radiator, 19 is a second heat transfer tube group. , 20 are fins.

Front page continued (72) Inventor Tetsuo Takehara 2-1-2 Marunouchi, Chiyoda-ku, Tokyo Inside Asahi Glass Co., Ltd. (72) Inventor Hiroshi Maeno 6 (72) Inventor, Umei, Ibo-cho, Takasago, Hyogo Prefecture (72) Kozo Sakurai 22-22, 5 Nagakura-cho, Totsuka-ku, Yokohama-shi, Kanagawa (72) Inventor Yoshihiro Sugano 3-114 Umeda, Kasukabe-shi, Saitama (72) Inventor Daisuke Koshimizu 1-3-25-25 Kisiya, Tsurumi-ku, Yokohama-shi, Kanagawa ) Reference JP-A-61-225542 (JP, A)

Claims (4)

[Claims] 1. A burner, a first heat transfer tube group arranged in proximity to a downstream side of a combustion gas flow of the burner, and a downstream side of a combustion gas flow of the first heat transfer tube group. And a second heat transfer tube group disposed adjacent to the downstream side of the combustion gas flow of the radiant body. . 2. The fluid heating device according to claim 1, wherein each of the first heat transfer tube group, the air-permeable radiator and the second heat transfer tube group is made of ceramics. 3. The first heat transfer tube group according to claim 1 or 2, wherein the first heat transfer tube group is a tube without fins on the outer surface,
The fluid heating device in which the second heat transfer tube group is a tube having fins on the outer surface. 4. The fluid heating according to any one of claims 1 to 3, wherein the first heat transfer tube group is arranged within a range of 100 mm from a fuel gas discharge port of the burner. apparatus.