JPH0195254A - Fluid heating apparatus with heat transfer promoter - Google Patents

Abstract

PURPOSE:To prevent a plate fin from receiving thermal damage due to partial overheating, and to increase the efficiency of heat transfer, by disposing a heat transfer promoter in a specified position in a flow passage of combustion gas on the plate fin. CONSTITUTION:A combustion gas 'G' flows upward in a can body 12, contacting to a plate fin 17 and heat transfer pipes 18, heating fluid to be heated, flowing through the heat transfer pipes 18. In the plate fin 17, the bottom edge on the upstream side of flowing combustion gas 'G' gets the highest temperature. But even in the edge part, the rise in temperature in parts 'A' which are close to the heat transfer pipes 18 is suppressed to some extent since the parts 'A' are cooled by the fluid to be heated. A heat transfer promoter 22 is disposed so as to be contacted to the parts 'B' on the upstream side which are between the heat transfer pipe 18, so that the flowing direction of combustion gas 'G' is changed by the heat transfer promoter 22 as shown by arrow signs 'F', flowing into the parts 'B' after the temperature in the combustion gas is a little decreased by exchanging heat with heat in the parts 'A'. As a result, the parts 'B' are prevented from being partially overheated.

Description

DETAILED DESCRIPTION OF THE INVENTION TECHNICAL FIELD The present invention relates to a fluid heating device applied to, for example, water heaters, bathtubs, hot water boilers, and the like.

"Prior Art and its Problems" Conventionally, the above-mentioned fluid heating device includes a combustion means such as a burner, a can body forming a passage for combustion gas formed by the combustion means, and a can body. Those equipped with multiple rows of heat exchanger tubes arranged inside are used. In this case, a finned heat exchanger tube is used as the heat exchanger tube in order to increase the heat exchange efficiency by increasing the contact area with the combustion gas as much as possible. Among these, heat exchanger tubes with plate fins, in which heat exchanger tubes are arranged in a plurality of rows passing through a large number of plate fins arranged substantially in parallel, are often adopted.

Plate fins are generally made of thin metal plates for reasons such as ease of manufacture, but they have the problem of being thermally damaged if they come into contact with the combustion gas flow and reach extremely high temperatures. Furthermore, even when a ceramic plate is used as the plate fin, it may be damaged due to localized overheating or rapid temperature changes. In this case, the portion of the plate fin that reaches the highest temperature is the edge portion located most upstream with respect to the combustion gas flow, and is the portion between the heat transfer tubes located most upstream.

That is, as shown in FIG. 6, a large number of plate fins 17 are arranged substantially parallel to each other along the flow of combustion gas G, and the plate fins 17 are arranged so as to pass through these plate fins 17 and cross the flow of combustion gas G. Heat exchanger tubes 18 are arranged in multiple rows. The upstream end edge of the plate fin 17 with respect to the flow of the combustion gas G, when viewed along the flow direction of the combustion gas G, is a portion that overlaps with the heat exchanger tube 1 and the heat exchanger tube 18.
A portion B located between the two is formed.

Since a fluid to be heated, such as water, is flowing inside the heat exchanger tubes 18, the heat exchanger tubes 18 have the function of removing heat from the plate fins 17 located on the outer periphery of the heat exchanger tubes 18 and cooling them. . Naturally, this cooling effect on the plate fins 17 is weaker in the portions away from the heat exchanger tubes.

In the plate fin 17, the highest temperature part is
The part that comes into contact with the combustion gas G first, that is, the combustion gas G
Of these, the part A is close to the heat exchanger tube 18 and is thus cooled, whereas the part 8 is away from the heat exchanger tube 18 and is cooled by this. Therefore, the cooling effect of the heat exchanger tubes 18 is weakened. For this reason, the portion 8 of the plate fin 17 is likely to be locally overheated and prone to thermal damage.

[Object of the Invention] An object of the present invention is to prevent heat damage to the plate fins due to local overheating and to improve heat transfer efficiency in a fluid heating device having a heat transfer tube with plate fins.

"Structure of the Invention" The present invention comprises a large number of plate fins arranged substantially parallel to each other along a heated gas flow, and heat transfer tubes arranged in multiple rows to pass through these plate fins and cross the heated gas flow. In the fluid heating device, the space between the heat transfer tubes is located upstream of the plate fin with respect to the heated gas flow and is located most upstream when viewed along the heated gas flow. It is characterized in that a rod-shaped, tubular or plate-shaped heat transfer accelerator is arranged so as to be located at .

As mentioned above, the part of the plate fin that has the highest temperature ν is the edge located furthest upstream with respect to the flow of heated gas such as combustion gas, and when viewed along the flow of heated gas, This is the part between the heat transfer tubes located on the most upstream side, but in the present invention, the heat transfer promoter is placed upstream of this part, so high temperature heated gas does not directly flow into this part. , this part is prevented from overheating and thermal damage to the fins can be prevented.

Further, the heated gas causes turbulence when it hits the heat transfer promoter, and a part of the flow path is blocked by the heat transfer promoter, increasing the flow velocity. This turbulent flow with increased flow velocity comes into contact with the heat transfer tubes and plate fins located downstream of the heat transfer promoter and on both sides of the heat transfer promoter, thereby improving heat transfer efficiency. Roughly speaking, when the temperature of the heated gas is a high temperature of about 900 to 1300°C, the heat transfer accelerator becomes red hot and radiant heat transfer from the heat transfer accelerator is also performed effectively, so the heat transfer efficiency is roughly reduced. can be improved.

The fluid heating device to which the present invention is applied can be any device that has a heat exchanger tube with plate fins.For example, a combustion means, a can body forming a combustion space and a flow path for combustion gas, The exhaust duct for discharging gas to the outside, and a heat exchanger tube with plate fins arranged in the flow path of the combustion gas are employed. Also, along the flow path of the combustion gas, a first transmission tube made of a pair tube or a tube with loaf-in, a radiator made of a ceramic fiber molded body having ventilation holes, and a second heat transfer tube with play fins are arranged in order. It is also possible to adopt one in which .

Combustion methods include a diffusion combustion method in which fuel and air are supplied separately to the combustion chamber, and a premix combustion method in which fuel and air are mixed in advance in the desired ratio and passed through a burner plate to the combustion chamber. method etc. will be adopted. Alternatively, it may be of a type in which molten oil or the like is vaporized and burned. Therefore, natural gas, buoyant gas, molten oil, etc. are used as the fuel.

The heat exchanger tube with plate fins is usually made of metal such as copper, aluminum, and stainless steel, but it can also be made of ceramics such as silicon carbide and silicon nitride.

The plate fins are usually arranged in parallel along the flow direction of the heated gas at intervals of about 2.5 to 3.5 mm. The heat exchanger tubes are arranged in multiple rows through the plate fins, preferably perpendicular to the flow direction of the heated gas. It is preferable that the joint between the plate fin and the heat transfer tube be sufficiently joined by means such as brazing to reduce heat transfer resistance.

The rod-shaped, tubular or plate-shaped heat transfer promoter in the present invention is
Usually, it is made of a material with higher heat resistance than the material of the plate fin, and preferable examples include heat-resistant metals such as stainless steel and various ceramics. The heat transfer promoter preferably has a long and narrow shape that is continuous so as to cross the flow path of the heated gas and parallel to the extending heat transfer tube, but it does not necessarily have to be continuous in the longitudinal direction.

In a preferred embodiment of the present invention, the heat transfer promoter is disposed in contact with or in close proximity to the edge of the plate fin located upstream with respect to the heated gas flow. When the heat transfer promoter is located at a considerable distance from the upstream end tightening part of the plate fin,
The effect of the heat transfer promoter arrangement is difficult to reach the upstream end tightening portion of the plate fin.

Further, in a preferred embodiment of the present invention, the edge portion of the plate fin located on the upstream side with respect to the heated gas flow is located between the heat transfer tubes arranged furthest upstream when viewed along the heated gas flow. The heat transfer accelerator is arranged so as to fit into the concave notch.

By providing the above-mentioned notches in the edge portions of the plate fins, the portions of the edge portions of the plate fins that are prone to thermal damage can be brought closer to the heat transfer tubes, thereby increasing the cooling effect. By arranging the heat transfer promoter so as to fit into this notch, the effect of preventing heat damage to the plate fins by the heat transfer promoter can be further improved. Furthermore, since the heat transfer promoter is placed closer to the heat transfer tube, the effect of making the heated gas turbulent and increasing the flow velocity by the heat transfer promoter can be further enhanced, and the heat transfer efficiency can be further improved.

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

In this fluid heating device 11, a burner plate 13 is installed at the bottom of a can body 12, and a premixing chamber 14 is provided below the burner plate 13. A nozzle 15 is provided in the premixing chamber 14.
Fuel from the fan 16 and combustion air from the fan 16 are supplied,
Both are mixed in advance in the required ratio. This mixed gas is ejected into the can body 12 from the holes in the burner plate 13, and is ignited and combusted by an ignition means (not shown).The inside of the can body 12 has a combustion chamber and a flow path for combustion gas. The upper part of the can body 12 is connected to an exhaust duct (not shown).

In the combustion gas flow path of the can body 12, a large number of plate fins 17 are arranged substantially parallel to each other along the flow direction of the combustion gas.
and heat transfer tubes 1 arranged in multiple rows (four rows in the figure) so as to pass through the plate fins 17 and cross the combustion gas flow path.
A heat exchanger tube 19 with plate fins consisting of 8 is arranged. Note that the edge portion of the plate fin 17 on the upstream side of the combustion gas is formed so that the portion 8 located between the heat exchanger tubes 18 is notched in a concave shape, and the entire plate fin 17 has a corrugated shape.

Although the heat transfer tubes 18 are arranged in a plurality of rows, they are actually one continuous conduit in order to flow the fluid to be heated in series. Therefore, both ends of the heat transfer tube 18 protrude from the can body 12 and are connected by a U-shaped tube 21, as shown in FIG.

In this fluid heating device, a cylindrical stainless steel heat transfer promoter 22 is in contact with the edge of the plate fin 17 on the upstream side of the combustion gas, and the edge of the plate fin 17 is notched in a concave shape. The MM is arranged so that it partially enters the day. No fluid to be heated is flowed into this heat transfer promoter 22 .

In the above configuration, the fluid to be heated such as water is caused to flow in series through the continuous heat transfer tubes 18. In addition, the combustion gas G is
The plate fins 17 move upward inside the can body 12.
Then, it contacts the heat exchanger tube 18 and exchanges heat with the fluid to be heated flowing inside the heat exchanger tube 18 to heat the i-body to be heated.

The edge portion of the plate fin 17 on the upstream side of the flow of the combustion gas G has the highest temperature. Also in this end portion, the portion close to the heat exchanger tube 18 is cooled by the heated fluid such as water flowing through the heat exchanger tube 18, and the temperature rise therein is suppressed to some extent. However, since the portion 6 located between the heat exchanger tubes 18 is far from the heat exchanger tubes 18, the above-mentioned cooling effect is weak and tends to be locally overheated. However, in this device, since the heat transfer promoter 22 is placed in contact with the upstream side of the portion 8, the combustion gas G is moved through the flow path by the heat transfer promoter 22 as shown by the arrow F in FIG. After the temperature of the combustion gas decreased slightly through heat exchange with part A,
This prevents local overheating in the sun part. In this way, thermal damage due to local overheating of the plate fins 17 can be prevented.

On the other hand, the flow of the combustion gas G is changed by the heat transfer promoter 22 to generate turbulent flow, and this turbulent flow is transmitted to the heat transfer tubes 18 and the plates located downstream of the heat transfer promoter 22 and on both sides thereof. It actively hits parts other than the part 8 of the fin 17. Moreover, since a part of the flow path of the combustion gas G is blocked by the heat transfer promoter 22, the flow velocity of the combustion gas G is increased. For this reason,
Heat transfer from the combustion gas G to the fluid to be heated flowing within the heat transfer tube 18 is promoted, and the fluid can be heated more efficiently.

3, 4, and 5 show other embodiments of the heat transfer promoter 22, respectively.

That is, in the embodiment shown in FIG. 3, the heat transfer accelerator 22 has a cylindrical shape with a substantially triangular cross section, and is arranged so that the top of the triangle is in contact with eight concave notches at the end edge of the plate fin 17. l has been used. The base of the triangle faces upstream of the combustion gas flow, increasing the turbulence given to the combustion gas flow.

Furthermore, in this example, the entire heat transfer accelerator 22 is located on the downstream side of the plane connecting the protruding portions A of the plate fins 17, which is particularly effective in downsizing this fluid heating device.

In the embodiment shown in FIG. 4, the heat transfer accelerator 22 has a cylindrical shape with a substantially fan-shaped cross section, and is arranged so that the fan-shaped arcuate portion contacts the concave (8 cutout portions) of the end edge of the plate fin 17. In this example, since the top of the sector is oriented toward the upstream side of the combustion gas flow, there is an advantage that resistance to the combustion gas 6 is reduced.

In the embodiment shown in FIG. 5, a solid round bar is used as the heat transfer accelerator 22, and is arranged so as to partially fit into the 8 concave notches at the end edge of the plate fin 17. There is. In this example, the heat transfer tubes 18 are arranged in a staggered manner in three stages, upper and lower, but the heat transfer promoter 22 is
The heat exchanger tube 18 is placed in the dark position of the heat transfer tube 18 on the most upstream stage with respect to the flow.

In the fluid heating device flfll as described above, natural gas is used as fuel, heat transfer tube 18, material: copper, tube diameter;
19.05 mm, heat transfer tube arrangement = 4 X-row, heat transfer tube pitch: 36 mm, plate fin 17, fin edge: 2.6 mm, heat transfer area: 0.75 r/
The distance M from the center of the heat transfer tube 18 to the upstream end line A of the plate fin 17 is 16.5 mm, and the distance from the upstream end edge B is I 9 , 5 mm.
As shown in FIG.
At was constructed, water was flowed in series in the heat transfer tube 18 to perform heat exchange, and the amount of heat exchanged, thermal efficiency, etc. were measured. In addition,
For comparison, a fluid heating device without the heat transfer accelerator 22 was also measured with the same flow rates of fuel, firing air, and tapping water temperature. The results are shown in the table below.

From the results in the table, by providing the heat transfer promoter 227&
Heat transfer promoter 22I! It can be seen that the amount of heat exchanged is considerably increased compared to the case where it is not provided. I think this is because the heat transfer promoter 22 causes turbulence in the flow of combustion gas, increasing the flow velocity toward the heat transfer tubes 18 and plate fins 17, and the radiation heat transfer of the heat transfer promoter 22 also contributes. In addition, when the plate fin is made of copper, it is required to keep its temperature at about 250°C or less to ensure its durability.When the heat transfer promoter 22 is provided as in this example, It can be seen that the temperature of eight portions of the plate fin 17 is reduced, local overheating of the plate fin 17 is prevented, and the durability of the plate fin 17 is also improved.

"Effects of the Invention" As explained above, according to the present invention, the heat exchanger tube is located upstream of the plate fin with respect to the heating gas flow and is the most upstream side when viewed along the flow direction of the heating gas. Since a rod-shaped, tubular, or plate-shaped heat transfer accelerator is arranged between them, the part of the upstream end line of the plate fin that is most likely to be heated becomes the downstream side of the heat transfer accelerator.
Heat damage to the plate fins due to local overheating can be prevented. In addition, the heat transfer promoter causes turbulence in the flow of the heated gas and partially blocks the heating girth flow path, increasing the flow rate of the combustion gas, thereby improving heat transfer efficiency. . Also, the heating gas temperature is 900℃.
At a high temperature of ~1300°C, radiation heat transfer from the heat transfer promoter also contributes to further improve heat transfer efficiency.

[Brief explanation of the drawing]

FIG. 1 is a front sectional view showing one embodiment of the fluid heating device according to the present invention, FIG. 2 is a sectional view taken along the line ■-■ in FIG. 1, and FIGS. FIG. 6 is a cross-sectional view showing other examples of the heat transfer promoter in the fluid heating device according to the invention, and FIG. 6 is a cross-sectional view for explaining the heating state of the plate fin when it comes into contact with combustion gas. In the figure, 11 is a fluid heating device, 12 is a can body, 13 is a burner plate, 14 is a premixing chamber, 17 is a plate fin, 1
8 is a heat exchanger tube, 19 is a heat exchanger tube with plate fins, and 22 is a heat transfer promoter.

Claims (3)

[Claims] (1) A fluid heating device having a large number of plate fins arranged substantially parallel to each other along a heated gas flow, and heat transfer tubes arranged in multiple rows so as to pass through these plate fins and cross the heated gas flow. , the rod-shaped heat exchanger tube is located upstream of the plate fin with respect to the heated gas flow and located between the heat transfer tubes disposed most upstream when viewed along the heated gas flow. , a fluid heating device characterized in that a tubular or plate-shaped heat transfer promoter is arranged. (2) According to claim 1, the heat transfer promoter is disposed in contact with or in close proximity to an edge of the plate fin located upstream with respect to the heated gas flow. heating device. (3) In claim 1 or 2, an edge portion of the plate fin located upstream with respect to the heated gas flow is the most upstream edge when viewed along the heated gas flow. A fluid heating device, wherein a portion located between the heat transfer tubes arranged on the side is formed so as to be cut out in a concave shape, and the heat transfer promoter is arranged so as to fit into the concave cutout portion. .