JPH0424320Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a heat exchange tube used as a heat radiation tube in, for example, a radiation tube heating furnace.

[Conventional technology]

Conventionally, this type of heat exchange tube is made of chromium-nickel alloy heat-resistant steel (HK,
It is generally formed by HH, etc.). It is also being considered to use a dense silicon carbide-based material as a material that can ensure strength at high temperatures in a reducing atmosphere.

[Problem that the invention attempts to solve]

However, heat exchange tubes made of the above-mentioned chromium-nickel alloy heat-resistant steel begin to show deformation and deflection due to a decrease in strength at temperatures of 900°C or higher;
There was a problem in that it progressed rapidly at temperatures above. In addition, those using the above-mentioned heat-resistant steel have the problem that carburization occurs in a reducing atmosphere containing carbon or carbon monoxide, and it is even more difficult to use them in a weakly oxidizing atmosphere. Furthermore, due to problems such as strength and oxidation resistance, there was also the problem that the heat exchange tube itself had to be thick. Furthermore, the above-mentioned heat-resistant steel cannot ensure a sufficient heat transfer area unless fins or the like are provided to increase the surface area, and an increase in size is unavoidable.

On the other hand, heat exchange tubes made of silicon carbide-based materials maintain high strength even in high-temperature regions with excellent heat resistance. However, like the heat-resistant steel mentioned above, dense silicon carbide-based materials have a small heat transfer area, and once sintered, it is extremely difficult to cut them, making it difficult to obtain the desired shape. There were also problems.

The present invention was developed in view of the above-mentioned circumstances.
Our objective is to provide a heat exchange tube that can be used for long periods of time in high-temperature areas such as 100%, and can also be used in weakly acidic atmospheres, and that is thin and lightweight by taking advantage of its high mechanical strength. There is.

Another object of the present invention is to provide a heat exchange tube that can secure a large heat transfer area without providing any fins or the like, and can also be machined.

Still another object of the present invention is to provide a heat exchange tube equipped with a combustion catalyst and capable of efficiently carrying out a combustion reaction.

[Means to solve the problem]

In order to achieve the above object, the heat exchange tube according to the present invention includes a cylindrical dense ceramic layer made of silicon carbide or having a thermal conductivity equivalent to silicon carbide, and a cylindrical porous ceramic layer made of the same material as this dense ceramic. It is characterized by a multilayer structure that is fitted together.

Further, in such a heat exchange tube, it is more desirable that at least one of the outer circumferential surface and the inner circumferential surface is formed of a porous ceramic layer.

Further, a combustion catalyst can be supported on the surface of the porous ceramic layer forming the outer peripheral surface or the inner peripheral surface.

[Effect]

As mentioned above, the heat exchange tube, which is made of the same material but with different properties, is made of silicon carbide or a material with high thermal conductivity equivalent to silicon carbide.
Even at high temperatures of 1500℃, there is almost no decrease in strength and no deformation or bending occurs. Furthermore, it exhibits oxidation resistance superior to heat-resistant steel even in an oxidizing atmosphere. Furthermore, since the dense ceramics and the porous ceramics are made of the same material, they will not separate from each other or destroy each other due to differences in thermal expansion.

Furthermore, if at least one of the outer circumferential surface or the inner circumferential surface is formed of a porous ceramic layer, the porous ceramic has a large surface area (heat transfer area), which improves heat transfer efficiency, and the porous ceramic layer has a large surface area (heat transfer area). The ability to perform cutting facilitates mechanical processing of joints and the like.

Furthermore, if a combustion catalyst is supported on the porous ceramic layer forming the outer peripheral surface or the inner peripheral surface, it can be used as a combustion tube type heat exchange tube.

〔Example〕

Hereinafter, the present invention will be explained based on illustrated embodiments.

FIG. 1 is a longitudinal cross-sectional view of a heat exchange tube according to the present invention, which includes a cylindrical outer layer 1 made of a dense silicon carbide sintered body and a porous silicon carbide sintered body. Similarly cylindrical inner layer 2
It has a two-layer structure made by fitting together.

Here, the dense silicon carbide sintered body forming the outer peripheral layer 1 has a dense density of 3.05 g/cm ³ or more and has no air permeability. On the other hand, the porous silicon carbide sintered body forming the inner peripheral layer 2 has a pore diameter of 0.01 to
It is equipped with fine pores that are arbitrarily controlled in the range of 500 μm, thereby having a relatively small density of 1 to 2 g/cm ³ and a large specific surface area of 0.1 to 10 m ² /g, It is also breathable. The heat exchange tube, which has a two-layer structure of outer layer 1 and inner layer 2, has a total length of, for example, 120 mm, an inner diameter of 18 mm, and an outer diameter of
24mm, one side thickness 3mm. In this case, the thickness of one side of each layer is 1 to 1.5 mm.

In the heat exchange tube configured as described above, the outer peripheral layer 1 and the inner peripheral layer 2 are made of the same material, so gaps are created between each layer due to the difference in thermal expansion, reducing the originally high thermal conductivity. There is no storage, and conversely, one layer does not press on the other layer and destroy it.

In addition, since it is made of only silicon carbide, it has a resistance of about 800 to
It does not deform or bend even when used at high temperatures of 1500°C for long periods of time, and exhibits higher oxidation resistance than heat-resistant steel even in oxidizing atmospheres.

Furthermore, by forming the inner peripheral layer 2 from a porous silicon carbide sintered body, heat can be transferred extremely efficiently to or from the fluid passing through the heat exchange tube by utilizing a large surface area. be able to. Furthermore, since the porous silicon carbide sintered body is machinable, processing such as forming a joint part such as a female thread on the inner peripheral layer 2 and adjusting the inner diameter size can be relatively easily performed by cutting. can.

FIG. 3 shows a three-layer structure in which a cylindrical intermediate layer 12 made of a dense silicon carbide sintered body is fitted between a cylindrical outer layer 11 and an inner circumferential layer 13 made of a porous silicon carbide sintered body. The structure shows a heat exchange tube.
Even with this three-layer structure, there will be no gaps between the layers or destruction of the layers due to differences in thermal expansion. In addition, if both the inner and outer circumferential sides are formed of porous silicon carbide sintered bodies, the heat transfer efficiency will be further improved, and it will be possible to cut not only the inner circumferential surface but also the outer circumferential surface. I can do it.

As shown in FIG. 4, the heat exchange tube according to the present invention has an outer peripheral layer 2 made of a dense silicon carbide sintered body.
A three-layer structure may be adopted in which an intermediate layer 22 made of a porous silicon carbide sintered body is superimposed and fitted between the intermediate layer 1 and the inner peripheral layer 23.

The heat exchange tubes in Figure 5 are similar to those in Figures 1 and 2.
Similar to the heat exchange tube shown in the figure, an outer circumferential layer 1 made of a dense silicon carbide sintered body and an inner circumferential layer 2 made of a porous silicon carbide sintered body are fitted, and the porous silicon carbide sintered body is A combustion catalyst 4 made of platinum, palladium, nickel, etc. is supported on the surface of the inner peripheral layer 2 by utilizing its large surface area. In this way, by forming the inner peripheral layer 2 from a porous silicon carbide sintered body, the combustion catalyst 4 can be supported on the inner peripheral surface, and as described above, the outer peripheral layer 1 and the inner peripheral layer 2 Since the tube body made of the above does not undergo deformation or deflection even in extremely high temperature ranges, it can be used as a combustion tube type heat exchange tube for producing various combustion products.

In the above embodiment, a silicon carbide sintered body is used to form the dense ceramic layer and the porous ceramic layer, but silicon nitride, alumina, aluminum nitride, which has a thermal conductivity equivalent to silicon carbide, The dense ceramic layer and the porous ceramic layer may be formed of ceramics such as sialon or a composite thereof containing silicon carbide.

Furthermore, the multilayer structure consisting of a dense ceramic layer and a porous ceramic layer may be made of four or more layers as necessary, and it is also possible to arbitrarily select whether the inner circumferential surface and the outer circumferential surface are formed of dense or porous ceramic layers. can.

[Effect of idea]

According to the first aspect, high thermal conductivity can be ensured even in a high temperature range of approximately 800 to 1500° C., and the device can be used for a long period of time, so that it can be used for a wide range of purposes. Moreover, since precise dimensional adjustment is possible by cutting the porous ceramic layer, a multilayer structure with no gaps between the layers can be obtained. Moreover, since each layer has a thin wall thickness, the heat exchange tube is lightweight.

According to the second aspect, since the porous ceramic layer is exposed on the surface, it is possible to easily form the joint portion etc. by cutting.

According to claim 3, a combustion type heat exchange tube that efficiently performs a combustion reaction is obtained.

[Brief explanation of the drawing]

Fig. 1 is a longitudinal cross-sectional view of a heat exchange tube, Fig. 2 is a - cross-sectional view of Fig. 1, Fig. 3 is a cross-sectional view of another heat exchange tube, and Fig. 4 is a cross-sectional view of yet another heat exchange tube. , FIG. 5 is a cross-sectional view of yet another heat exchange tube. 1... Outer layer (dense ceramic layer), 2...
...Inner circumferential layer (porous ceramic layer), 11... Outer circumferential layer (porous ceramic layer), 12... Intermediate layer (dense ceramic layer), 13... Inner circumferential layer (porous ceramic layer), 21... ... Outer peripheral layer (dense ceramic layer), 22 ... Intermediate layer (porous ceramic layer), 23 ... Inner peripheral layer (dense ceramic layer), 4 ... Combustion catalyst.

Claims (1)

[Scope of Claim for Utility Model Registration] (1) In a heat exchange tube that transfers heat inside and outside the tube, a cylindrical dense ceramic layer of silicon carbide or having a thermal conductivity equivalent to silicon carbide, and a layer made of the same material as this dense ceramic. A heat exchange tube characterized in that it has a multilayer structure by fitting cylindrical porous ceramic layers. (2) The heat exchange tube according to claim 1, wherein at least one of the outer peripheral surface and the inner peripheral surface is formed of a porous ceramic layer. (3) The heat exchange tube according to claim 2, wherein the porous ceramic layer forming the outer peripheral surface or the inner peripheral surface supports a combustion catalyst.