JPS63254348A - 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 exchanger tube group 1 permeable radiator and a second heat exchanger tube group are sequentially arranged downstream of the 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 upstream of the first heat exchanger tube group through the gap. It also emits powerful radiant heat.

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.

In this way, there are parts of the burner plate that are strongly radiantly heated by the radiator and parts that are radiantly cooled from the first heat exchanger tube group, creating a complex and sharp distribution of thermal stress within the burner plate surface. , / This causes a large stress concentration near the flame hole of the Kuna plate, and as a result, cracks and damage begin to occur near the flame hole.

``Object of the Invention'' The present invention aims to prevent the occurrence of the above-mentioned thermal stress distribution in a burner plate, or to alleviate the thermal stress distribution, and to improve the heat transfer efficiency to a group of heat transfer tubes. The aim is to provide equipment.

"Summary of the Invention" The fluid heating device of the present invention includes a burner plate that is planar as a whole, a group of heat transfer tubes arranged adjacent to and downstream of the burner plate, and a radiation tube provided in a gap between the group of heat transfer tubes so as to be ventilated. The burner plate is characterized in that the downstream surface of the burner plate is provided with a surface that is inclined with respect to the overall surface.

"Operation" The radiation from the radiator is most intensely irradiated in the normal direction of the burner plate, which has a planar shape as a whole, that is, in the direction perpendicular to the entire surface of the burner plate. A part of the radiation irradiated to the burner plate is re-radiated from the burner plate, but at this time, if the downstream surface of the burner plate is parallel to the overall surface like a conventional burner plate, this re-radiation The wire is also returned to its original position on the radiator, and heat is exchanged between the radiator and the burner plate, resulting in local overheating of the burner plate.

On the other hand, if the downstream surface of the burner plate is provided with a surface that is inclined with respect to the overall surface, as in the present invention, first of all, the strongest radiation from the radiator occurs on the inclined surface of the burner plate. It can be received as radiant heat that is relaxed compared to vertical surfaces.

Second, some of the radiant heat received by the burner plate is radiated as radiation from the burner plate, but the direction of radiation is not to the original position of the radiator, but according to the inclination angle of the downstream surface of the burner plate. It is strongly returned in the biased direction.

Therefore, the radiation from the radiator and the burner plate do not reciprocate between a specific position of the radiator and a specific position of the burner plate, preventing local overheating of the burner plate. .

Thirdly, the heat transfer tube group is generally located in the direction where the radiation from the burner plate is strong, and the back side of the heat transfer tube group, which is not directly irradiated with the radiation from the radiator, can be irradiated and heated by the radiation from the burner plate. becomes. Therefore, the group of heat transfer tubes located between the radiator and the burner plate receives radiant heating evenly from both sides, which not only improves the efficiency of radiant heat transfer, but also alleviates the thermal stress acting on the group of heat transfer tubes. Along with this, radiation cooling from the heat transfer tube group to the burner plate is also relaxed.

For the burner plate, the degree of local heating and local cooling is greatly reduced, which can lead to cracks and damage to the burner plate.
Alternatively, the occurrence of thermal damage can be suppressed or prevented.

"Specific Embodiments of the Invention" The burner plate only needs to have a planar shape as a whole,
A flat burner plate is preferably used, but it may also be a curved surface with a large curve as a whole. In this case, the burner plate has a high surface that may be convex or concave toward the downstream direction of the combustion gas. Although a premixed burner plate is desirable to achieve high combustion chamber loads,
A diffuse combustion type burner plate can also be used.

The material of the burner plate is cordierite, alumina,
It can be made of mullite, various types of ceramics, or metal materials such as stainless steel. Alternatively, it may be formed by laminating the same or different materials.

The inclined surface provided on the downstream surface of the burner plate may have a constant maximum inclination angle with respect to the entire surface of the burner plate and a constant direction indicating the maximum inclination angle, but generally at least either the maximum inclination angle or the direction thereof is constant. It is considered preferable not to do so.

To explain this using a specific example, in a burner plate in which a protruding or grooved line having a symmetrical sawtooth cross section with an inclination angle of 30 degrees is provided on the downstream surface of the burner plate, the maximum inclination angle and the direction in which it is shown are constant. For burner plates with semicircular or semicylindrical protrusions or grooves on the downstream surface, the maximum inclination angle is not constant along the circumference of the semicircle, but the direction of the maximum inclination angle is the protrusion or groove. It is constant perpendicular to the running direction of the groove. When a conical protrusion or a concave hole with a constant base angle is provided on the downstream surface of the burner plate, the maximum inclination angle is constant, but the direction showing the maximum inclination angle can change 380 degrees around the apex of the cone.

If the maximum inclination angle or its direction is not constant as described above, the direction of the radiation from the burner plate will vary even if the radiation is incident almost parallel.

Localized heating by radiation from the burner plate on the back side of the heat exchanger tube or radiation cooling of the burner plate from the heat exchanger tube can be avoided.

The repeating units such as protrusions, grooves, protrusions, or recesses provided on the downstream surface of the burner plate should generally have a pitch that is equal to or less than the pitch of the heat exchanger tubes located downstream, and should be several minutes smaller than the pitch of the heat exchanger tubes located downstream. It is particularly preferable that the arrangement direction is about 1 degree, but it may be about a few tenths of an inch.Also, the direction in which these protrusions, grooves, protrusions, or holes are arranged does not have to be limited to one direction, but is orthogonal within the entire surface of the burner plate. They may be arranged along two directions, or three directions forming an angle of 60 degrees, etc.
It goes without saying that the arrangement direction is not limited to a straight line, but may be curved, and these arrangement directions and the running direction of the heat exchanger tubes may be parallel or perpendicular, but are not limited to this. You can choose as appropriate.

A preferred embodiment of providing an inclined surface on the downstream surface of the burner plate is to arrange a net-like body such as a wire mesh on the downstream surface of a plate-shaped burner plate main body having a through hole. 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 arranging a planar body having an inclined surface such as a net-like body on the downstream surface of the burner plate main body, it is recommended to integrate the burner plate main body and the planar body by an appropriate method such as adhesion, welding, or welding. It will be done.

However, it is not necessary to integrate the two; for example, a planar body may be suspended downstream of the flat burner plate body, which is very close to but separate from the heat transfer tube. At the same time, care must be taken to ensure that the burner plate body and the planar body are not too far apart and the flame becomes unstable.

In order to form an inclined surface on the downstream surface of the burner plate, in addition to the above, it is also possible to make the burner plate into a corrugated plate shape, or to spray a lump or a fibrous material onto the downstream surface of the burner 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 rod-shaped bodies are arranged perpendicularly to the flow direction of the combustion gas with a predetermined ventilation gap, and
Examples include those arranged so as to form a planar shape as a whole, and those arranged in a louver shape with a large number of narrow ceramic plates.

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 lO shown in FIGS. 1 and 2 is entirely surrounded by a casing 11 whose L side is connected to an exhaust port (not shown), and a fan is provided below the casing 11 via a mixing chamber 12. A casing 13 is 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.

A burner plate 18 having a generally planar shape is horizontally suspended at the upper edge of the mixing chamber 12 to partition the mixing chamber 12 and the combustion chamber 25 . Burner Brake) 1B is made of cordierite ceramics and has many flame holes penetrating between the upper and lower surfaces.

The lower surface of the burner plate 16 is planar, and the upper surface of the burner plate 1B has a large number of conical projections 17 and thus has a large number of inclined surfaces. Although the arrangement of the flame holes and the arrangement of the conical projections 17 may correspond,
Generally, it is preferable to change the pitch of the arrangement of the flame holes and the pitch of the arrangement of the conical projections 17 so that the two arrangements do not correspond.

A plurality of heat exchanger tubes 18 are suspended horizontally in parallel to each other above the burner plate 16 to form a first heat exchanger tube group 18 . On both sides of the first heat exchanger tube group 19, a plurality of heat exchanger tubes 20 are horizontally hung 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 19 and the second heat exchanger tube group 21, a honeycomb plate 22 made of silicon carbide ceramics 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 loaf-in type with a not so high fin height. Moreover, the plurality of heat exchanger tubes 20 located above the honeycomb plate 22 pass through a common flat plate fin 23, and constitute a plate fin tube as a whole. The outer shape of the flat plate fins 23 is formed into an arc shape so that the height of the fins from each heat exchanger tube 2° is approximately equal, and the spaces between adjacent arcs are formed into a smooth curve. Note that, instead of the flat fins 23 as in this embodiment, flat 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 18 and the heat exchanger tube group 21 are also connected in the same way in series, and the whole is made into a single flow path and the inside is water-filled. A low-temperature heated fluid such as

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.

A 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 1B, 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 /X honeycomb plate 22 and heats this honeycomb plate 22 as well, making it incandescent.

Radiation is emitted from the incandescent honeycomb plate 22 mainly in the upstream direction. As shown in Figure 3, this radiation! ! (indicated by arrows in the figure), the heat exchanger tube 18 receives strong radiant heating mainly from the downstream side. The radiation from the nicum plate 22 passes through the gap between the heat transfer tubes 18 and is strongly irradiated onto the burner plate 16 in a band-like manner, but a considerable portion of the radiant heat received from the inclined surface of the conical projection 17 is The heat exchanger tubes 18 are also radiantly heated from the upstream side by the radiation from the burner plate 16.

In this way, the heat exchanger tube 18 is heated evenly from almost its entire circumference, and since the downstream surface of the burner plate is parallel to the entire surface, the heating efficiency is improved compared to a case where the heat exchanger tube 18 is heated only from the downstream side, and the length of the heat exchanger tube is increased. This results in a reduction in heat and an increase in the heating temperature of the heated fluid.

Furthermore, the difference in thermal expansion acting on the heat exchanger tubes 18 is alleviated, improving the durability of the heat exchanger tubes 18 and the casing 11, and the temperature distribution of the burner plate 1B is also alleviated, so that cracks and
Breakage and thermal damage are prevented or suppressed.

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 region where the second heat exchanger tube group 21 is arranged 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. In this way, the first heat exchanger tube group 18 is taken out.

FIGS. 4, 5, and 6 show different embodiments of the present invention, and portions that are substantially the same as those in the previous embodiments are designated by the same reference numerals, and a description thereof will be omitted.

In the example shown in FIG. 4, the burner plate is composed of a flat burner plate main body lea made of stainless steel and a wire mesh 113b made of stainless steel spot-welded to the downstream surface thereof. A large number of flame holes are formed so as to pass through the burner plate body lea, 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 tea. For this reason, the downstream face of the burner plate is provided with a virtually random slope.

The example shown in FIG. 5 is the same as the example shown in FIG. 4, except that a plate-shaped ceramic three-dimensional mesh body 22a is used instead of the /X nicum plate 22 as the radiator.

In the example shown in FIG. 6, the burner plate 18c is made of a corrugated plate having a large number of flame holes, and as a radiator, a plurality of ceramic solid round rods 22b are arranged in two stages in a staggered manner.

"Effects of the Invention" As explained above, in the present invention, since the downstream surface of the burner plate is provided with a surface that is inclined with respect to the overall surface, the efficiency of heat transfer to the heat transfer tube is improved, and the local heating and The degree of local cooling is reduced, and the occurrence of cracks, breakage, thermal damage, etc. in the burner plate can be prevented or suppressed.

[Brief explanation of drawings]

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,
Figure 3 is an explanatory diagram showing the main parts of Figure 1 in an enlarged manner; Figure 4;
5 and 6 are sectional views of essential parts of different embodiments of the fluid heating device according to the present invention. 11: casing, lB: burner plate. 18.20: Heat exchanger tube, 22: Honeycomb plate.

Claims (1)

[Claims] 1. Equipped with a generally planar burner plate, a group of heat exchanger tubes disposed adjacent to and downstream of the burner plate, and a radiator provided in a gap between the group of heat exchanger tubes to allow ventilation, and a radiator is provided on the downstream surface of the burner plate. A fluid heating device characterized by having a surface inclined with respect to the entire surface.