JP3405679B2 - Heat exchanger - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat exchanger using a heat exchanger tube for a heat exchanger used in a high temperature waste heat utilization system in an incineration / power plant or the like. [0002] In order to effectively use the thermal energy of high-temperature waste gas generated in incineration and power generation plants and increase the energy efficiency of the entire plant, the generated high-temperature gas such as waste gas passes through the partition wall. Therefore, heat exchangers of a type that heats a low temperature gas to be heated have been used. Specifically, a general method is to arrange a heat transfer tube as a partition in a space where high-temperature gas is generated or passes, and to feed the heated gas into the tube and heat the heated gas by heat transfer. It is. Conventionally, metals have been used for heat transfer tubes in heat exchange systems at a relatively low temperature.
In addition to the high temperature of 000 ° C. or higher, the gas itself is highly corrosive, so it is not suitable for metals, and ceramics are beginning to be used instead. However, in order to increase the heat transfer efficiency of the heat exchanger tube for heat exchanger, it was necessary to use a heat transfer tube with a very high tube length / thickness ratio. . However, even if the wall thickness is reduced, there is a limit in terms of corrosion resistance and strength, so in reality, the heat transfer tube is lengthened to lengthen the gas flow path. Alternatively, a method of increasing the number of heat transfer tubes by reducing the supply speed of the fluid to be heated has been considered, but in any case, a space for that is required, which hinders the space saving of the equipment. Furthermore, if the ratio of the length / thickness of the heat transfer tube is very high, the mechanical strength and creep resistance are low, so that the handling property is poor and there is a problem that the heat transfer tube is deformed by long-term use. Also, the heat transfer tube has a one-side sealed shape, an inner tube is inserted into the heat transfer tube, and a heated gas is supplied to the heat transfer tube sealing portion through the inner tube, while passing through the gap between the inner tube and the heat transfer tube. In the heat transfer tube for a heat exchanger to be heated, the outer side is a high temperature of 1000 ° C. or higher at the sealing part, and a low-temperature heated gas is blown from the inner side. There was also a problem of being easily damaged. The present invention provides a heat exchanger for performing heat exchange inside and outside, wherein a heat transfer tube adapted to perform heat exchange inside and outside is formed of ceramics,
A plurality of fins are integrally formed on the inner surface, a curved sealing portion that is smoothly continuous with the side surface is formed on one side, and a hollow portion that does not have fins is formed in the central portion of the inner surface of the sealing portion. The inner tube whose both ends are open is inserted into the inside of this heat transfer tube, the heated gas is supplied to the sealing portion of the heat transfer tube through the inner tube, and heated through the gap between the inner tube and the heat transfer tube. It is characterized by. As a result, the surface area of the inner surface of the heat transfer tube can be increased, so that the heat transfer efficiency can be increased. For this reason
Compared to conventional heat transfer tubes, the tube length / thickness ratio can be reduced, and the length of the ceramic tube can be substantially shortened, contributing to space saving. DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings. A heat transfer tube 1 shown in FIG. 1 is a comparative example of the present invention. It is a cylindrical body made of ceramics, and a large number of fins 2 are integrally formed on its inner surface. If the outer surface of the heat transfer tube 1 is exposed to a high-temperature gas and the gas to be heated is allowed to pass inside, heat exchange can be performed through the heat transfer tube 1 to heat the gas to be heated. At this time, since the fins 2 are provided, the heat transfer area can be increased and the thermal efficiency can be increased. As an embodiment of the present invention, as shown in FIGS. 2 and 3, it is also possible to form a curved sealing portion 1a smoothly and continuously on the side surface on one side of the heat transfer tube 1. FIG.
When this heat transfer tube 1 is used, as shown in FIG. 3, the inner tube 4 is inserted inside, and the heated gas is supplied to the sealing portion 1a of the heat transfer tube 1 through the inner tube 4, and the inner tube 4 and the heat transfer tube are supplied. It is set as the system heated while passing the space | gap of 1. Here, if the number of the fins 2 is one, not only a sufficient effect of improving the heat transfer characteristics cannot be expected, but also the heat transfer tube 1
The weight balance in the axial direction cannot be achieved. Conversely, if the number of fins 2 is too large, it will result in an increase in the weight of the tube, and the air gap inside the heat transfer tube 1 will become narrower and the flow velocity will become too fast.
We cannot expect sufficient heat transfer characteristics. For this reason, the number of fins 2 is preferably between 6 and 24. The thickness of the fin 2 is preferably equal to or less than the thickness of the heat transfer tube 1, and the height of the fin 2 is preferably equal to or greater than the thickness of the fin 2 so as not to contact other fins 2 and the inner tube 4. . This is because if the fins 2 are too thick, the thermal shock characteristics deteriorate, and conversely if they are too thin, the strength cannot be maintained. Also,
If the height of the fin 2 is too low, it is difficult to improve the heat transfer efficiency, and if it is too high, the fin 2 comes into contact with other members. By forming the fins 2 in this manner, the mechanical strength per unit length of the heat transfer tube 1 itself can be improved, and the length of the heat transfer tube 1 can be shortened as described above. 1 handling property and creep resistance can be improved. Preferably, the fin 2 gradually becomes thinner toward the tip, and the connection portion 2 to the inner surface of the heat transfer tube 1 is obtained.
If a curved surface having a curvature radius of 0.3 to 3 mm is formed on the tip end 2a of b or the fin 2, it is possible to prevent an increase in weight and a decrease in thermal shock resistance, and to reduce the strength reduction factor. Further, in the heat transfer tube 1 having the structure shown in FIGS. 2 and 3, a hollow portion 3 where the fins 2 do not exist is formed at the center of the inner surface of the sealing portion 1a which is an intersection of the fins 2. Thereby, at the time of use as a heat exchanger, it becomes difficult for the air of the hollow part 3 to flow, and this part is the heat transfer tube 1.
It becomes a temperature boundary layer between the external high-temperature gas and the heated gas supplied from the inner tube 4, and the heated gas can be prevented from directly hitting the sealing portion 1a. As a result, the thermal stress on the inner and outer surfaces of the heat transfer tube 1 can be relaxed, and the life can be extended. As the ceramics forming the heat transfer tube 1, various ceramics such as silicon carbide and silicon nitride can be used, and silicon carbide ceramics are particularly preferable. This silicon carbide ceramic is 90
The main component is silicon carbide (SiC) of wt% or more, and B, C, etc. are included as sintering aids. Such silicon carbide ceramics have excellent properties such as thermal conductivity of 50 W / m · K or more and thermal shock resistance ΔT of 300 ° C. or more.
It is optimal as a material for the heat transfer tube 1. Further, the heat transfer tube 1 of the present invention is integrally molded by using the above-mentioned ceramic raw material so as to have the shape shown in FIGS. 1 and 2 by extrusion molding, and the obtained molded body is 1900 to 1900 in a vacuum atmosphere. It can be obtained by firing at 2300 ° C. If it does in this way, the heat exchanger tube 1 provided with the fin 2 integrally can be obtained easily. EXAMPLES Specific examples of the present invention will be described. First, a binder is added to a ceramic raw material powder having a composition containing SiC as a main component and containing B, C, etc. to form a clay. After kneading this well, it is molded by an extruder using a mold having a desired cross-sectional shape. The mold is composed of three dies: a core pin, and a die head. The tip of the core pin has a hemispherical shape or a smooth curved surface similar to the semispherical surface to form the inner shape of the sealed portion of the heat transfer tube molded body, and fins are formed on the molded body on the surface. It has a shape with deep grooves. The die is circular so that the outer surface of the heat transfer tube molded body is formed, and the inner surface of the die head is a hemispherical surface or a smooth curved surface similar to it to form the outer surface of the sealed portion of the heat transfer tube molded body. Yes. At the start of extrusion molding, the die head is fixed to the die, and the compact is filled between the die, the die head, and the core pin. Thereafter, the die head is removed and extrusion molding is performed to obtain a heat transfer tube molded body having fins 2 on the inner surface and sealed on one side as shown in FIG. The molded body obtained by the above method was sufficiently dried and then fired under optimum conditions to obtain a sintered body. Example 1 A one-side sealed heat transfer tube 1 having an outer diameter of 72 mm, an inner diameter of 64 mm, and lengths of 1100 mm and 800 mm, in which a plurality of fins having a height of 12 mm were formed inside, was produced by the above-described manufacturing method. Then, the heat transfer tube 1 was inserted into a test apparatus as shown in FIG. 4 from the sealing end to a position where the effective length shown in Table 1 was reached. Here, the effective length indicates that the heat transfer tube 1 can contribute to heat exchange. Further, the inner tube 4 having both an outer diameter of 36 mm and an inner diameter of 30 mm and being open at both ends was inserted into the heat transfer tube 1 until the distance from the sealed end of the heat transfer tube 1 to the end surface of the inner tube 4 was 100 mm. The inside of the test apparatus was heated to 1200 ° C., and air heated to 200 ° C. was supplied into the inner tube 4. And in Table 1, No. 1 on the open end side with 1 heat transfer tube 1
The flow rate of air to be supplied was adjusted so as to be 00 ° C., and the other heat transfer tubes 1 were fixed so that evaluation could be performed with a constant flow rate.
The arrows in FIG. 4 indicate the direction of air flow. Then, the air temperature obtained under the condition that the effective length of the heat transfer tube 1 and the number of fins were changed as shown in Table 1 at a constant flow rate was measured. As shown in Table 1, it was confirmed that the formation of the fins 2 can increase the air temperature and increase the heat exchange efficiency. For example, no. 1 and No. 7 was compared, it was possible to obtain a fluid having an effective length of about 70% and a temperature equal to or higher than that of a heat transfer tube without fins by forming 12 fins. On the contrary, in the heat transfer tube 1 in which 24 fins 2 are formed, the flow rate of the gas to be heated becomes too fast due to the decrease in the gap between the heat transfer tube 1 and the inner tube 4, and the heat transfer due to the increase in the surface area of the heat transfer tube. It seems that the improvement effect could not catch up and the obtained air temperature was lower than the heat transfer tube 1 having 12 fins. [Table 1] Experimental Example 2 The above heat transfer tube 1 was dropped freely on the concrete from a height of 0.5 m to confirm the presence or absence of breakage. The results are shown in Table 2. The number of tests is 7, and No in the table is N in Experimental Example 1.
Corresponds to o. Note that the number of fractures at a level that cannot be completely used as a heat transfer tube was investigated, excluding micro damage such as chipping of the end face. As shown in Table 2, the results No. 1 heat transfer tube and No. 1 The heat transfer tube of 7 shows the same heat transfer performance in Experimental Example 1, but compared to the former having destroyed six,
The latter has decreased to three. It seems that the overall length can be shortened by forming the fins, and that the fins themselves have increased the strength of the heat transfer tubes, which has led to improved handling. [Table 2] Experimental Example 3 A heat transfer tube having the same material and dimensions as described above and having 12 fins with a height of 12 mm formed inside was opened. Then, 50% from both ends in a reducing atmosphere firing furnace.
It supported in the position of mm and heat-processed 1400 degreeC * 100 hours. The amount of warpage deformation after heat treatment was measured for each two pieces, and the average was obtained. As shown in Table 3, it was confirmed that the creep resistance was improved by forming the fins. [Table 3] Experimental Example 4 Using the same heat transfer tube as in Experimental Example 1, it was inserted into a test apparatus as shown in FIG. 4, and an inner tube having an outer diameter of 36 mm and an inner diameter of 30 mm was inserted into the inner tube from the heat transfer tube sealing end. The distance to the end face is 50mm
Inserted to the position. Thereafter, the inside of the test apparatus is heated to 1400 ° C.,
A thermal cycle test for intermittently supplying room temperature air from the inner tube was conducted for 60 minutes, and the number of heat transfer tubes in which breakage such as cracks occurred among the number of tests was investigated. As shown in Table 4, the heat transfer tubes with fins formed thereon were not formed. The number of breaks is less than that of 1 heat transfer tube. Since the center part of the sealing end, which is the intersection of fins, is hollowed out, a temperature boundary layer is created around the hollowed part inside the sealed part and around the intersecting part, and the thermal stress on the inner and outer surfaces is alleviated and the life is improved. I found out that [Table 4] Experimental Example 5 With a plurality of ceramics shown in Table 5, a height of 12
A single-side sealed heat transfer tube similar to Experimental Example 1 in which 12 mm fins were formed was produced. Then, the heat transfer tube was inserted into a test apparatus as shown in FIG. 4, and the inner tube was further inserted inside the heat transfer tube in the same manner as in Experimental Example 1. Then, the inside of the test apparatus was heated to 1200 ° C., and air heated to 200 ° C. was supplied into the inner tube.
No. in Table 1 The flow rate of air to be supplied was adjusted to 500 ° C. at the open end side of the heat transfer tube in one silicon carbide heat transfer tube, and the other heat transfer tubes were fixed so that evaluation could be performed with a constant flow rate. And the temperature of the air obtained with the heat exchanger tube of each material was measured. Table 5 shows the results. At the same time, the measurement results of thermal conductivity and thermal shock resistance of each material are also shown. Among the materials evaluated this time, thermal conductivity silicon carbide showed the highest air temperature. Alumina and zirconia could not be measured because the tube was broken. In this experiment, it was found that silicon carbide is the most excellent heat transfer tube material. [Table 5] As described above, by forming fins inside the heat transfer tube, heat transfer characteristics can be improved and space saving can be promoted. Furthermore, since the creep resistance and handling properties can be improved, the life can be extended. Further, in the heat transfer tube sealed on one side, the sealing end portion is curved, and the central portion of the inner surface of the sealing portion which is the intersection of the fins is hollowed out, so that the sealing portion is damaged by thermal shock. Can be suppressed.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view showing a comparative example of a heat transfer tube used in a heat exchanger of the present invention. FIG. 2 is a cross-sectional view showing a heat transfer tube used for heat exchange according to the present invention. FIG. 3 is a view showing a heat exchanger using the heat transfer tube of FIG. 2; FIG. 4 is a schematic view of a test apparatus used in an experimental example. [Explanation of Symbols] 1: Heat transfer tube 2: Fin 3: Hollow section 4: Inner tube

──────────────────────────────────────────────────── ─── Continued on the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) F28D 7/12 F28F 1/40 F28F 21/04

Claims (1)

(57) [Claims] [Claim 1] A heat transfer tube that exchanges heat inside and outside is formed of ceramics, and a plurality of fins are integrally formed on the inner surface thereof , and a side surface and a smooth surface are formed on one side. Continuous songs
Forms a planar sealing part and the center of the inner surface of the sealing part
This part has a hollow part without fins, and this heat transfer tube
Insert an inner pipe with both ends open into the inside of the
Supply the heated gas to the sealed part of the heat transfer tube.
A heat exchanger characterized by heating through a gap.