JPS63254349A - Improved fluid heating device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

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 the above-mentioned fluid heating device, after fuel is combusted in a combustion chamber downstream of a burner, combustion gas is guided between a group of heat transfer tubes, and mainly convection heat is generated. Conduction was used to heat fluids such as water flowing inside heat transfer tubes.

In recent years, in order to make these fluid heating devices as compact as possible, there has been a demand to reduce the size of the combustion chamber as much as possible and to increase the amount of heat transferred per unit volume of the heat exchange section that follows it.

Therefore, the present inventors previously proposed, in Japanese Patent Application No. 80-223980, a fluid heating device in which a first heat transfer tube group, an air permeable radiator, and a second heat transfer tube group are sequentially arranged downstream of a combustion means. did. This heating device achieved extremely high heat transfer efficiency by also using radiant heat transfer from a high-temperature solid radiator, compared to previous technology that focused on convective heat transfer from combustion gas. This greatly contributed to making the entire heating device more compact.

However, in such fluid heating devices using radiators, severe thermal conditions are also imposed on combustion means such as burner plates. In other words, the radiator heated to a high temperature by the combustion gas not only irradiates the first heat exchanger tube group with strong radiant heat, but also irradiates the combustion means such as the burner plate located in the L flow through the gap of the second heat exchanger tube group. Similarly, it is irradiated with powerful radiant heat to overheat it.

Moreover, the part of the downstream surface of the burner plate that is in the shadow of the first heat exchanger tube group is not irradiated with radiant heat from the radiator, and the cold heated fluid flows inside the tubes of the first heat exchanger tube group. Therefore, radiation cooling is performed by the first heat exchanger tube group.

The burner plate coexists with a part that is strongly radiated heated by the radiator and a part that is cooled by radiation from the first heat exchanger tube group, and a complex and sharp thermal stress distribution occurs within the burner plate surface. This causes thermal deformation and damage to the burner plate.

``Object of the Invention'' The present invention aims to prevent overheating of a burner plate, prevent the generation of an excessive thermal stress distribution as described above, and further improve the efficiency of heat transfer to a group of heat transfer tubes. The present invention is intended to provide a fluid heating device.

"Summary of the Invention" A fluid heating device according to the present invention includes a burner plate, a group of heat transfer tubes disposed adjacent to and downstream of the burner plate, and a radiator provided in a gap between the group of heat transfer tubes so as to be ventilated, The downstream surface of the burner plate is characterized by a glossy surface.

"Function" The radiation from the radiator is irradiated onto the birch plate through the gap between the heat exchanger tubes, but in the present invention.

The downstream surface of the burner plate should be a glossy surface, especially one with an emissivity of 0.
Since the burner plate has a glossy surface of 3 or less, most of the radiation irradiated onto the burner plate is reflected. Therefore, only a small amount of the applied radiation contributes to the heating of the burner plate, and overheating of the burner plate is prevented.

In particular, when a premix burner is employed, overheating of the burner plate causes dangerous backfire, but according to the present invention, such a situation can be prevented.

Further, although the radiation from the radiator is most strongly irradiated in the normal direction to the entire surface of the burner plate, the radiation radiated obliquely to the entire surface of the burner plate cannot be ignored. According to the present invention, most of the obliquely irradiated radiation is reflected by the glossy surface, and a group of heat transfer tubes is generally located in the direction of this reflected line, so that the radiation from the radiator is not directly irradiated. The back surface of the heat transfer tube can be irradiated and heated by the reflected beam from the burner plate.

Therefore, the heat exchanger tube located between the radiator and the burner plate receives radiant heating evenly from both the upstream and downstream sides, which not only improves the radiant heat transfer efficiency but also causes thermal stress that acts on the heat exchanger tube. As the radiation cooling from the heat transfer tubes to the burner plate is also relaxed, the degree of local heating and local cooling of the burner plate is greatly reduced, which can lead to cracks, breakage, or thermal damage to the burner plate. can be prevented from occurring.

The downstream surface of the burner plate is preferably a glossy surface having many irregularities. As mentioned above, the radiation from the radiator is most strongly irradiated in the direction normal to the entire surface of the burner plate, but if the downstream surface of the burner plate is flat, this strong radiation is directed toward the original radiator. It is reflected and eventually travels back and forth through uJl between the radiator and the burner plate, eventually leading to local heating of the burner plate.

On the other hand, if the downstream surface of the burner plate has many irregularities, the direction of reflection is not returned to the original position of the radiator, but in a direction biased according to the irregularities of the downstream surface of the burner plate. Therefore, the radiation from the radiator and the reflected ray from the burner plate do not reciprocate between the specific position of the radiator and the specific position of the burner plate, and local heating of the burner plate is prevented. It goes without saying that this reflected line also contributes to heating from the back side of the heat exchanger tube.

"Specific Embodiments of the Invention" As the burner plate, a flat burner plate is preferably employed, but it may also have a thick curved surface as a whole. In order to achieve a high burner plate surface load and a high combustion chamber load, a premix type burner plate is desirable, but a diffuse combustion type burner plate can also be adopted.

The material of the burner plate is preferably a metal material such as carbon steel or stainless steel. Use chromium or nickel to make the downstream surface of the burner plate shiny.

Stainless steels, especially cold-rolled or cold-drawn stainless steels, which are preferably plated with zinc or the like or polished with a puff surface finish, can meet the required surface conditions without special surface treatment. Many have a glossy surface.

Burner plates made of various ceramics such as cordierite, alumina, and mullite generally do not have luster as they are, but it is possible to use burner plates that have the downstream surface fully curved to achieve the required gloss. .

By providing protrusions, four stripes, protrusions, or recessed holes at appropriate intervals on the downstream surface of the burner plate, a large number of unevenness can be formed on the downstream surface of the burner plate. The position, shape, arrangement direction, etc. of these protrusions, grooves, protrusions, or holes are designed so that even if the radiation is incident almost parallel, the direction of the reflected line from the burner plate will change in various ways. It is better to In this way, localized heating due to reflected rays from the burner plate on the back surface of the heat exchanger tube can be avoided.

A preferred embodiment of providing unevenness on the downstream surface of the burner plate is 1.
On the downstream surface of the plate-shaped burner plate body having a through hole,
A net-like body such as a wire gauze made of a metal material, for example cold-drawn stainless steel, with the required glossy surface is provided.

In such a network, the strands have a circular cross section, the strands run in a wavy manner along the running direction, and the strands run in multiple directions, resulting in an extremely varied slope surface. A downstream surface of the burner plate can be formed.

When disposing a planar body such as a net-like body on the downstream surface of the burner plate main body, the burner plate main body and the planar body may be integrated by an appropriate method such as adhesion, welding, or welding. However, the integration of the two is not essential;
For example, a planar body may be suspended downstream of the flat burner plate body, which is very close to it but is far away from it. In this case, the planar body is positioned upstream of the heat exchanger tubes and Care must be taken to ensure that the flame does not become unstable due to the distance between the plate body and the planar body. In addition to the above, in order to form unevenness on the downstream surface of the burner plate,
It is also possible to make the burner plate shaped like a corrugated plate.

A suitable radiator in the present invention is one in which the radiator itself has air permeability. A typical example of such a breathable radiator is a ceramic honeycomb plate having a large number of parallel cells penetrating the front and back sides of the plate. In this case, the cell cross-sectional shape can be selected as appropriate, such as square, hexagon, or triangle.
Furthermore, it may be formed by laminating a large number of corrugated plates or a large number of corrugated plates and flat plates.Such a honeycomb plate is preferable because it has low ventilation resistance and excellent mechanical strength.

Other examples of air-permeable radiators include three-dimensional ceramic nets, open-cell foams, laminates of nets, and sintered metal bodies commercially available under trade names such as "Cerafoam."

Furthermore, it is not necessary to limit the material to a rigid material, and a flexible woven material, a flexible knitted material, etc. having the required heat resistance may be used.

Even if the radiator itself is non-breathable, it may be provided so that the combustion gas can pass through the vicinity of the radiator layer as a whole, particularly between both surfaces of the radiator layer. For example, a large number of ceramic rods are arranged at a predetermined ventilation gap so as to be perpendicular to the combustion gas flow direction and form a planar shape as a whole, or An example is one in which narrow plates are arranged in a louver shape.

Radiators can effectively generate radiant heat at high temperatures.
Preferred materials include silicon carbide, silicon nitride, aluminum nitride, cordierite, mullite, subodumene, and aluminum titanate. In particular, ceramics with high heat resistance, high strength, and high thermal conductivity, such as silicon carbide, silicon nitride, and aluminum nitride, are preferred. Ceramics are preferred. Depending on the temperature conditions, it may be made of a metal material such as heat-resistant steel.

"Embodiments of the Invention" The present invention will be described in detail below with reference to drawings of embodiments, but the present invention is not limited to the following embodiments.

The fluid heating device 10 shown in FIGS. 1 and 2 is entirely surrounded by a casing 11 whose upper part is connected to an exhaust port (not shown), and a fan casing is provided below the casing 11 via a mixing chamber 12. 13 are connected. The fan casing 13 is provided with a fan 14 for sending air and a nozzle 15 for supplying fuel gas.
A premixture of fuel gas and air is created within the tank.

An air plate 16 having a generally planar shape extends horizontally from the upper edge of the mixing chamber 12 to partition the mixing chamber 12 and the combustion chamber 25 . The burner plate 16 is made of a carbon steel flat plate, and has a large number of flame holes passing through its two lower surfaces. At least the upper surface of the burner plate 16 is nickel plated and then puff finished, with an emissivity of 0.10.
It is said to have a shiny surface.

Alternatively, the burner plate 1B may be constructed of a cold-rolled stainless steel flat plate having an emissivity of 0.28, for example. In this case, no plating treatment is required.

Above the burner plate 16, a plurality of heat exchanger tubes are suspended horizontally in parallel to each other to form a first heat exchanger tube group 19. Also above the first heat exchanger tube group 19, a plurality of heat exchanger tubes 20 are horizontally suspended parallel to each other and in a staggered cross-sectional arrangement to form a second heat exchanger tube group 21. In the gap between the first heat exchanger tube group 18 and the second heat exchanger tube group 21, a silicon carbide ceramic acid honeycomb plate 22 having a large number of cells penetrating between the front and back of the plate surface is horizontally suspended parallel to the burner plate 16. ing.

In this embodiment, the heat exchanger tubes 18 located between the burner plate 16 and the honeycomb plate 22 are of a pair tube type without fins on the outer periphery, but they may be of a finned tube type if necessary. It is best to use a lo-fin type with a not so high fin height.

In addition, a plurality of heat exchanger tubes 2 located above the honeycomb plate 22
0 passes through a common flat plate fin 23 and constitutes a plate fin tube as a whole. The outer shape of the flat plate fins 23 is formed into an arc shape such that the height of the fins from each heat transfer tube 20 is approximately equal, and the spaces between adjacent arcs are formed into a smooth curve. Note that, instead of the flat plate fins 23 as in this embodiment, flat plate fins having a simpler square cross section may be used, or each heat transfer tube 20 may be of a finned tube type having independent fins.

In the heat exchanger tube group 18, the heat exchanger tubes 18 are connected in series on the outside of the casing 11 by connecting tubes (not shown). Each heat exchanger tube 20 in the heat exchanger tube group 21 is connected in series in the same way, and furthermore, the heat exchanger tube group 19 and the heat exchanger tube group 21 are also connected in series in the same way, and the whole is made into a single flow path and the inside is water-filled. A low-temperature applied fluid such as 8 is flowed.

The material of these heat transfer tubes or fins is preferably copper, which has high thermal conductivity, but other metal materials such as aluminum, aluminum alloy, and stainless steel may also be used, and furthermore, reaction sintered silicon carbide is a typical material. Ceramics with high thermal conductivity and high corrosion resistance can also be used.

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

The premixture of fuel gas from the nozzle 15 and air from the fan 14 passes through the flame hole of the burner plate 16 and is supplied to the combustion chamber 25, forming a planar flame on the upper surface of the burner plate 16. This results in high-temperature combustion gas of 1,500 to 1,650°C.

This combustion gas is guided to the area where the first heat exchanger tube group 18 is arranged, and heats the heat exchanger tubes 18 by convection heat transfer. The combustion gas whose temperature has decreased slightly flows through the honeycomb plate 22 and heats the honeycomb plate 22 as well, making it incandescent.

Radiation is emitted from the incandescent honeycomb plate 22 mainly in the upstream direction. Due to this radiation, the heat exchanger tube 18 receives strong radiant heating mainly from the downstream side. The radiation from the Nikum plate 22 passes through the gap between the heat exchanger tubes 18 and is strongly irradiated to the burner plate 16 in a roughly band-like manner.
A considerable portion of the received radiant heat is reflected by the glossy surface of the downstream surface of the burner plate 16, and the heat exchanger tube 18 is also radiantly heated from the upstream side by the reflected line from the burner plate 16.

In this way, the heat exchanger tube 18 is heated evenly from almost its entire circumference, improving heating efficiency, resulting in a reduction in the length of the heat exchanger tube and an increase in the heating temperature of the heated fluid.

Furthermore, the thermal expansion difference acting on the heat exchanger tubes 18 is alleviated, improving the durability of the heat exchanger tubes 18 and the casing 11, and the burner plate 1B is not overheated, and the burner plate 1
The temperature distribution within the plane of 6 is also relaxed, thereby preventing thermal damage due to local heating and backfire due to overheating.

The temperature of the combustion gas decreases by, for example, 100 to 150°C while passing through the honeycomb plate 22, but it still remains at a temperature of, for example, 800°C.
This gas passes through the arrangement area of the second heat exchanger tube group 21 and heats the heat exchanger tubes 20.

The heat exchanger tube 20 or the flat plate fin 23 is a honeycomb plate 22
It is also radiantly heated. Thus, within the first heat exchanger tube group 18,
Next, the fluid to be heated, such as water, that has flowed into the second heat transfer tube group 20 is taken out of the system as hot water at a temperature of, for example, 40 to 80°C.

FIGS. 3 and 4 show different embodiments of the present invention, and parts that are substantially the same as those in the previous embodiment are designated by the same reference numerals, and a description thereof will be omitted.

In the example shown in FIG. 3, the burner plate is composed of a flat burner plate main body lea made of cold-rolled stainless steel, and a wire mesh 18b made of cold-drawn stainless steel spot-welded to the downstream surface thereof. The emissivity of the wire mesh tab is 0.15. A large number of flame holes are formed so as to pass through the burner plate body 18a, and the wire pitch of the wire mesh 18b is selected so as not to match the flame hole pitch of the burner plate body 18a. Therefore, virtually random irregularities are formed on the downstream surface of the burner plate.

The example shown in FIG. 4 is the same as the example shown in FIG. 3, except that a plate-shaped ceramic three-dimensional mesh body 22a is used instead of the honeycomb plate 22 as the radiator.

"Effects of the Invention" As explained above, in the present invention, the downstream surface of the burner plate is made of a glossy surface, which improves the heat transfer efficiency to the heat transfer tube, eliminates overheating and local heating of the burner plate, and eliminates overheating and local heating of the burner plate. It can prevent heat damage and backfire.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of an embodiment of a fluid heating device according to the present invention, FIG. 2 is a sectional view taken along the line ■-■ in FIG. 1,
3 and 4 are sectional views of essential parts of different embodiments of the fluid heating device according to the present invention. 11: Casing, 16: Burner plate, 18.20
: Heat exchanger tube, 22: Honeycomb plate.

Claims (1)

[Claims] 1. A burner plate, a group of heat transfer tubes disposed adjacent to and downstream of the burner plate, and a radiator provided in a gap between the group of heat transfer tubes so as to be ventilated, and the downstream surface of the burner plate is A fluid heating device characterized by a glossy surface. 2. The fluid heating device according to claim 1, wherein the downstream surface is a glossy surface with an emissivity of 0.3 or less. 3. The fluid heating device according to claim 1 or 2, wherein the downstream surface is a glossy surface having many irregularities.