JPH0457936B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD The present invention relates to a device for heating a fluid used in water heaters, bathtubs, hot water boilers, and the like. "Prior art and its problems" Conventional fluid heating devices used in water heaters, bathtubs, hot water boilers, etc. have a combustion means such as a burner placed at one end of the casing, and the inside of the casing is is a combustion chamber and a flow path for combustion gas, and heat transfer tubes are arranged in a multi-stage structure along the flow path of combustion gas, and the heat transfer tubes are heated by contact with the combustion gas, so-called convection heat transfer. It was made using In response to this, there is a special fluid heating device that heats the fluid flowing inside the heat transfer tube by downsizing the combustion chamber and effectively utilizing combustion heat, and using radiant heat transfer in addition to convective heat transfer. No. 60-223980 (Unexamined Japanese Patent Publication No.
62-84258) by the present applicant. This fluid heating device is constructed by sequentially arranging a first heat exchanger tube, an air-permeable radiator, and a second heat exchanger tube in the flow direction of the combustion gas formed by the combustion means. In this fluid heating device, the heat transfer tube is irradiated with the radiant heat of the radiant that becomes incandescent due to the combustion gas, and the heat transfer tube is efficiently heated by convective heat transfer from the combustion gas and radiation heat transfer from the radiant. be done. In addition, when the first heat transfer tube is placed close to the combustion means, incompletely combusted components such as CO are generated due to the sudden temperature drop, but these incompletely combusted components are completely combusted when they pass through the high-temperature radiator. , the first heat exchanger tube can be placed close to the combustion means, thereby making it possible to make the device more compact. By the way, in order to further improve the heat transfer efficiency in the above fluid heating device, it is possible to provide fins on the outer periphery of the heat transfer tube to increase the contact area with the combustion gas and improve convective heat transfer. desired. However, if fins are provided around the outer periphery of the heat transfer tube, the fins may become overheated and thermally deformed, or the fins may lower the temperature of the gas, causing CO
There is a possibility that incompletely combusted components such as fins may increase, and the manner in which the fins should be provided has become an important issue. ``Object of the Invention'' The object of the present invention is to provide a fluid heating device in which a first heat transfer tube, a ventilated radiator, and a second heat transfer tube are sequentially arranged in the flow direction of combustion gas. By providing the fins in a predetermined manner, the purpose is to improve heat transfer efficiency without causing thermal deformation or thermal damage to the fins, and without causing an increase in incomplete combustion components due to the fins. "Structure of the Invention" A device for heating a fluid according to the present invention includes a first heat exchanger tube, a ventilated radiator, and a second heat exchanger tube arranged in this order in the flow direction of the combustion gas formed by the combustion means. In the apparatus for heating a fluid, the first heat exchanger tube is composed of a finch tube having a fin height of about 3 mm or less and a spacing between the fins being equal to or less than the height of the fins, and the second heat exchanger tube teeth,
It is characterized by being composed of a finch tube with a fin height of more than about 3 mm. In the present invention, the first heat transfer tube is sandwiched between the combustion means and the radiant, and is directly exposed to high-temperature (for example, 1500 to 1600°C) combustion gas from the combustion means, and is exposed to intense heat from the radiant. exposed to radiant heat.
In terms of heat transfer efficiency, it is generally desirable to have fins with fins and a high fin height. However, if the fin height is too high, the fins will be Due to the heat transfer resistance, the heat received by the fluid in the pipe cannot keep up, and the outer peripheral edge of the fin becomes overheated, eventually leading to thermal deformation. Therefore, in the present invention, thermal deformation of the fins is prevented by setting the fin height of the first heat transfer tube to 3 mm or less. In addition, it is more preferable that the fin height of the first heat exchanger tube be 2 mm or less. In addition, if a fin tube with a fin height of, for example, 5 mm or more is used for the first heat transfer tube,
The amount of combustion gas that contacts the low-temperature fins and rapidly decreases in temperature increases, and the CO concentration due to incomplete combustion increases in the combustion gas flowing through the first heat transfer tube region.
This flows downstream without being sufficiently oxidized, resulting in an increase in the amount of CO in the exhaust gas. However, by setting the fin height of the first heat transfer tube to 3 mm or less, the temperature of the combustion gas flowing through the first heat transfer tube region is maintained sufficiently high, and as a result, the amount of CO in the exhaust gas is almost eliminated. Further, the distance between adjacent fins at the outer peripheral edge of the fins of the first heat exchanger tube (the distance excluding the wall thickness of the fins) is set to be equal to or less than the fin height. Thereby, the radiant heat from the radiator can be efficiently received. That is, although the radiant heat from the radiator is irradiated onto the outer circumferential surface of the heat exchanger tube body and both side surfaces of the fins, not all of the heat is received as is, and a considerable portion is diffusely reflected. However, if the spacing between the fins is set below the fin height as described above, most of the diffusely reflected radiant heat is captured again by the nearby fin surfaces and the outer peripheral surface of the heat exchanger tube body, resulting in the radiation emitted from the radiator as a whole. Most of it comes to be absorbed into this first heat exchanger tube. On the other hand, by passing through the radiator placement area,
Although the temperature of the combustion gas decreases by 100 to 150°C, it is still sufficiently high (for example, 600 to 900°C). In order to efficiently recover heat, in the present invention, the second heat transfer tube is provided with fins, and the height of the fins is more than 3 mm, preferably 5 mm or more. However, although the temperature in the second heat transfer tube area is lower than that in the first heat transfer tube area, the temperature is still quite high, so there is a risk of overheating of the outer peripheral edges of the fins and even thermal deformation. . For this reason, the fin height of the second heat exchanger tube is preferably 20 mm or less. In addition, in a more preferable embodiment of the present invention,
In the second heat exchanger tube, the fin height on the side closest to the radiator is 5 to 10 mm, and the fin height on the side furthest from the radiator is 10 to 20 mm. The material of both the first and second heat transfer tubes is a metal material such as copper or stainless steel, and copper is particularly preferable because it is inexpensive and has good heat conductivity. In the present invention, a combustion means such as a burner is generally disposed at the end of the casing on the upstream side of the combustion gas flow path, resulting in an overall compact fluid heating device. As the burner, a diffuse combustion type or the like can be used, but it is more preferable to use a premix burner in which combustion air and combustion gas are mixed in advance, and this mixed gas is ejected from a burner plate and combusted. A high surface load and a high combustion chamber load are achieved. Although there may be only one first heat exchanger tube and only one second heat exchanger tube, it is generally preferable that a plurality of each constitute a heat exchanger tube group. The first heat exchanger tube group and the second heat exchanger tube group may each be divided into a plurality of tubes to form a plurality of independent flow paths. It is preferable to use one that forms connected flow paths. In this case, the heat exchanger tubes are not only placed inside the casing so as to be in contact with the combustion gas, but some heat exchanger tubes are also placed so as to contact the casing from the outside to perform heat exchange from the outer wall of the casing. At the same time, the casing may be cooled. Further, as the radiator, ceramics such as silicon carbide, silicon nitride, aluminum nitride, cordierite, mullite, lithium aluminum silicate, aluminum titanate, etc. are preferable in order to generate effective radiant heat at high temperatures. Such a radiator has good air permeability in order not to obstruct the flow of combustion gas and to ensure a wide contact area with the combustion gas. Specifically, examples include those in which the radiator itself has air permeability, such as honeycomb bodies, three-dimensional mesh bodies, open-cell foam bodies, mesh laminates, flexible woven fabric bodies, etc. Among these, plate-shaped bodies in particular A honeycomb body is preferred. A plate-shaped honeycomb body has a large number of parallel cells penetrating the plate surface from the front and back, and the cell shape is as follows.
Square, rectangle, hexagon, etc. can be selected as appropriate. Further, the plate-shaped honeycomb plate may be formed by laminating a large number of corrugated plates or a large number of corrugated plates and flat plates. Furthermore, even if the radiator itself does not have air permeability, the individual radiators may be arranged at predetermined intervals from each other to form a radiator that is breathable as a whole. As such,
Examples include a structure in which a large number of ceramic rod-shaped bodies are arranged parallel to each other in a staggered manner, or a structure in which a large number of narrow ceramic plates are arranged in a louver shape. Embodiments of the Invention In the following, embodiments of a device for heating a fluid according to the present invention will be described. 1 and 2 show a first embodiment of the device of the invention. Device 11 for heating this fluid
has a casing 12 whose upper part is connected to an exhaust port (not shown), and inside this casing 12, with a burner plate 13 disposed below as a boundary, a mixing chamber 14 is located on the lower side, and a combustion chamber 15 is located on the upper side. It is configured as. The burner plate 13 is
The casing 12 is formed into a planar shape with a large number of flame holes in the vertical direction, and a premixture made of combustion gas and air in the mixing chamber 14 is ejected from the flame holes to form a planar flame. Note that a fan for supplying combustion air to the premixing chamber 14, a combustion gas nozzle for supplying fuel gas, and ignition means for forming a flame are provided, but these are omitted in FIG. Then, after the premixture is ejected from the burner plate 13 to form a flame, the generated combustion gas flows from the lower side of the combustion chamber 15 to the upper side. Near the upper part of the burner plate 13, a plurality of first heat exchanger tubes 16 are horizontally arranged in parallel with each other. The first heat transfer tube 16 efficiently recovers convection heat of the combustion gas and radiant heat from the radiator 18. The first heat exchanger tubes 16 are arranged in one or more stages (in this embodiment, two stages) in the vertical direction, and in the case of multiple stages, the upper and lower heat exchanger tubes 16 are arranged, for example, in a staggered arrangement so that they do not overlap as much as possible. is preferred. Among the first heat exchanger tubes 16,
Burner plate 13 from the lower edge of the lowest heat exchanger tube
The distance to the top surface is 100 mm or less, preferably 5 to 50 mm.
It is assumed to be mm. In this embodiment, the first heat exchanger tube 16 is comprised of a loaf inch tube. That is, as shown in FIG. 2, a large number of loaf-ins 17 having a trapezoidal or square cross section are formed at a predetermined pitch P on the outer periphery of the first heat exchanger tube 16. It is preferable that the distance A (distance obtained by subtracting the thickness of the peripheral edge from the pitch P) at the outer peripheral edge of the loaf-in 17 is equal to the height H ₀ of the fin or less than or equal to the height H ₀ . In this embodiment, the height H ₀ is 1.5 mm and the interval A is 1.0 mm. In addition, the longitudinal ends of the loaf inches have a height
It becomes a thick straight pipe part C via a gradual part B where H ₀ gradually decreases, and is connected to the casing 12 at this thick straight pipe part C. In addition, in the present invention, the fin height H ₀ is not intended to be a value at such a gradual part B or a thick straight pipe part C. A radiator 18 is arranged above the first heat exchanger tube 16 . The radiator 18 has ventilation so that the combustion gas can flow through the radiator 18 to the downstream side, and covers almost the entire cross section of the combustion gas flow path. In this embodiment, the radiator 18 is composed of a honeycomb plate made of ceramics, but other materials such as a three-dimensional net, an open-cell foam, a laminate of nets, etc. can also be used. This radiator 18 allows the first heat exchanger tube 1
6 receives radiant heat as well as convection heat of the combustion gas. Further above the radiator 18, a plurality of second heat transfer tubes 19 are arranged. This second heat transfer tube 19 effectively recovers the heat of the combustion gas whose temperature has slightly decreased after passing through the radiator 18. In this embodiment, a plurality of parallel plate fins 20 are provided. A plate finch tube with heat transfer tubes passing through it is used. plate fin 20
The peripheral edges of the heat transfer tubes are cut out from each heat transfer tube in a substantially concentric manner so that the height of the fins is the same, and a smooth valley is formed. and,
Fin height of the lower peripheral edge closest to the radiator 18
_H1 is 5 to 10 mm, and the fin height _H2 of the upper peripheral edge furthest from the radiator 18 is 10 to 20 mm.
However, the outer peripheral edge of the plate fin 20 does not necessarily have to be formed into a smooth valley, and may be formed into a simple rectangular shape with a straight peripheral edge, for example. Note that in this embodiment, the first heat exchanger tube 16
The second heat exchanger tubes 19 are actually connected in series to constitute one flow path as a whole. Next, the operation of the fluid heating device 11 having the above configuration will be explained. The premixture produced in the mixing chamber 14 is ignited after passing through the flame hole of the burner plate 13 to form a flame, and is sent to the combustion chamber 15 as a high-temperature combustion gas of 1500 to 1600°C. This combustion gas is guided to the area where the first heat exchanger tube 16 is arranged, and a part of the thermal energy contained in the combustion gas is transferred by convective heat transfer to the fluid flowing inside the first heat exchanger tube 16, in particular, Transfers to liquids such as water. Furthermore, the combustion gas flows between the first heat exchanger tubes 16.
The light passes through the radiator 18 while remaining at a high temperature, and heats the radiator 18 as well, making it incandescent. Thereby, the radiator 18 is maintained at a high temperature of, for example, 1000 to 1200°C, and mainly radiates and heats the first heat exchanger tube 16. Therefore, the liquid such as water flowing in the first heat transfer tube 16 receives heat by both convective heat transfer by the combustion gas and radiant heat transfer by the radiator 18. In this case, the first heat exchanger tube 16 is the loaf-in 1
Since the loaf-in tube 7 has a height of 3 mm or less, in this embodiment 1.5 mm, the radiant heat from the radiator 18 is efficiently captured by the loaf-in tube 17, and the high-temperature combustion gas is Even when exposed to intense radiant heat, thermal deformation and thermal damage to the outer peripheral edge of the loaf-in 17 are prevented. Also,
By arranging the first heat exchanger tube 16 close to the burner plate 13, CO, etc. may be generated in the combustion chamber 15 due to incomplete combustion. This limits the amount of combustion gas that comes into contact with the fins and causes a sudden temperature drop, and the temperature drop occurs smoothly, which promotes oxidation of CO and prevents an increase in the amount of residual CO in the combustion gas.
Furthermore, the spacing A of the loaf ins 17 is set to the fin height.
By setting H to ₀ or less, radiant heat can be absorbed well and heat transfer efficiency can be increased. Then, while the combustion gas passes through the radiator 18 , its temperature decreases by about 100 to 150° C., and the combustion gas is guided to the region where the second heat transfer tube 19 is arranged. Second heat exchanger tube 19
Radiant heat is irradiated from the radiator 18 to the radiator 18, but since the temperature of the upper surface of the radiator 18 is correspondingly lower than the temperature of the lower surface, the radiant heat is irradiated from the radiator 18 to the first heat exchanger tube. Compared to the amount, and 50-70
% is irradiated onto the second heat exchanger tube. Therefore, in the second heat transfer tube 19, convective heat transfer is mainly performed through contact with the combustion gas. and,
The second heat exchanger tube 19 has plate fins 20 having a higher fin height than the fins 17 of the first heat exchanger tube 16.
Since it has a larger contact area with combustion gas, convection heat transfer is improved. Furthermore, since the temperature of the combustion gas is lowered, thermal deformation at the peripheral edge of the fin is prevented even if the height of the fin is high. In this embodiment, the fin height _H1 of the lower peripheral edge closest to the radiator 18 is 5 to 10 mm, and the fin height _H2 of the upper peripheral edge furthest from the radiator 18 is 10 to 20 mm. Therefore, convective heat transfer efficiency can be increased as much as possible while preventing thermal deformation and thermal damage of the fins. In this way, fluid such as water passes through the first heat exchanger tube 16 connected in series, and then passes through the second heat exchanger tube 19, receives thermal energy in each, and is heated to a predetermined temperature. taken out. A second embodiment of the invention is shown in FIG. In this embodiment, the second heat exchanger tube 19 is configured as a hyphen tube. That is, the second heat exchanger tube 19 has a large number of hyphens 21 on its outer periphery. This high fin 21 has different fin heights between the upper and lower heat transfer tubes, and the lower fin height H ₁ and the upper fin height H ₂ have a relationship of H ₁ <H ₂ . In this example, H ₁ is 5 to 10 mm, and H ₂ is 10 to 10 mm.
It is set to 20mm. Also in this example, the radiator 18
It is possible to efficiently absorb the heat of the combustion gas whose temperature has been lowered by passing through the combustion gas. Other configurations are the first
Since this is similar to the embodiment, the explanation will be omitted. Experimental example In the apparatus shown in FIGS. 1 and 2, the first heat exchanger tube 16 was made without fins (No. 1),
The height of the fins 17 of the first heat exchanger tube 16 is 2 mm and the pitch is 2 mm (No. 2), the first heat exchanger tube 1
The first heat transfer tube 16 and the second heat transfer tube 19 were connected in series, and the first heat transfer tube 16 and the second heat transfer tube 19 were connected in series. The energy transferred to the water when water flowed from the heat tube 16 to the second heat transfer tube 19 was measured. The fins 20 of the second heat exchanger tube 19 have a fin height H ₁ at the lower peripheral edge closest to the radiator 18.
The fin height H ₂ of the upper edge periphery furthest from the radiator 18 was 20 mm. Moreover, both the first and second heat exchanger tubes are tubes made of copper. Further, the energy of the supplied gas is 29200 kcal/h, the flow rate of water is 20/m (1200/h), and the temperature of the inflow water is 15°C. The results are shown in Table 1.

[Table] From the results in Table 1, compared to No. 1 in which the first heat exchanger tube 16 had no fins, No. 2 in which the first heat exchanger tube 16 was provided with fins 17 of 2 mm or 4 mm in height, and No. 3 has an energy efficiency of about 72.6% to 76%.
It was found that the improvement was 3.4%. This efficiency increase corresponds to an approximately 5% saving effect based on gas consumption. In addition, after conducting a heating experiment for about 3 hours, the above No.
When we observed the state of thermal damage to the fins 17 of the first heat exchanger tube 16 for No. 2 and No. 3, we found that in the case of No. 3 with a fin height of 4 mm, the tip of the fin 17 was thermally damaged. Admitted. In addition, the combustion state of No. 3 seemed to be somewhat unstable. "Effects of the Invention" As explained above, according to the fluid heating device of the present invention, the fin height of the first heat exchanger tube is approximately 3 mm.
Since the height of the fins of the second heat transfer tube was set to exceed approximately 3 mm, convection heat transfer was improved without causing thermal deformation of the fins, thermal damage, or an increase in incomplete combustion components such as CO. Heat transfer efficiency can be increased.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an embodiment of a fluid heating device according to the present invention, and FIG. 2 is a partially cutaway front view of one of the first heat exchanger tubes 16 in FIG. 1. , FIG. 3 is a sectional view showing another embodiment of a device for heating a fluid according to the present invention. In the figure, 11 is a fluid heating device, 12 is a casing, 13 is a burner plate, 14 is a mixing chamber,
15 is a combustion chamber, 16 is a first heat exchanger tube, 17 is a loaf-in, 18 is a radiator, 19 is a second heat exchanger tube, 2
0 is a plate fin, and 21 is a hyphen.

Claims (1)

[Claims] 1. In the flow direction of the combustion gas formed by the combustion means, a first heat exchanger tube, a ventilated radiator,
In an apparatus for heating a fluid arranged in the order of second heat exchanger tubes, the first heat exchanger tubes have a fin height of about 3
Consisting of a metal fin fin whose width is less than mm and the interval between the fins is less than or equal to the height of the fins,
A device for heating a fluid, wherein the second heat transfer tube is constituted by a metal fin tube having a fin height of more than about 3 mm. 2. The device for heating a fluid according to claim 1, wherein the second heat exchanger tube has a fin height of about 20 mm or less.