JPH10121110A - Boiling heat-transfer member and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a boiling heat-transfer member having a structure to further increase heat-transfer efficiency and its production method. SOLUTION: This boiling heat-transfer member has a metallic porous body obtained by compressing an open-cell metallic sintered compact in the thickness direction on its surface. The powder of metal or metallic alloy is deposited on the surface of the skeleton of a three-dimensional reticular structure as a substrate. The three-dimensional reticular structure coated with the powder is laminated on the surface of a member 130, then heated and burned off. The metal or metallic alloy is sintered to obtain an open-cell metallic sintered compact 110 which is fused to and integrated with the member surface. The formed metallic sintered compact is compressed in the thickness direction to form a metallic porous body 120 having a specified thickness, and a boiling heat- transfer member 100 is produced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat transfer member such as a heat transfer tube or a heat transfer plate for heat exchange used in various industrial fields. The present invention relates to a heat transfer member such as a heat transfer tube or a heat transfer plate capable of improving heat transfer efficiency and a method of manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, heat exchangers and heat exchangers for liquid-liquid, liquid-gas, gas-gas and the like are generally made of a heat transfer tube or a heat transfer plate using a copper material having good heat conductivity. Is used. The amount of heat exchange is said to be proportional to the temperature difference between each heat medium, the heat transfer coefficient, and the heat transfer area. In recent years, heat exchangers have been reduced in size and improved in performance due to demands for energy saving and space saving. In order to achieve miniaturization and high performance, not only use a material with high thermal conductivity, but also provide fins and grooves on the tube surface and plate surface to increase the heat transfer area and further improve the fin structure. By devising, a turbulent flow is generated on the heat transfer surface to increase the heat transfer coefficient.

Further, in order to improve the performance of a heat exchanger particularly involving boiling, it is necessary to devise a heat transfer surface structure. In order to promote the heat transfer of boiling, a large number of vapor nuclei are present, and a surface structure in which the trapped vapor nuclei are difficult to escape is suitable. To promote this boiling heat transfer, the surface of the heat transfer surface can be roughened,
In Japanese Patent Publication No. 63-16037, a cavity having a groove or a narrow opening is provided on the heat transfer surface by machining. Further, Japanese Patent Publication No. Sho 62-42699 and
In JP-A-110597, there is also disclosed a technique for achieving compactness and high performance by adding a porous body or a foamed body of copper or copper alloy to the above-mentioned effects by integrally molding or applying the same.

[0004]

[Problems to be Solved by the Invention] JP-B-63-1603
No. 7 provides a boiling heat transfer tube, which has a structure in which a microcavity is provided under the epidermis on the heat transfer surface and a micropore is formed in a skin covering the cavity. This boiling heat transfer tube is one-fifth to one-tenth that of a smooth tube for transmitting the same heat flux.
Although the superheat degree may be sufficient, the heat exchanger can be downsized and the performance thereof can be improved, but there is a problem that the manufacturing cost is high. JP-B-62-42699 and JP-A-4-110
No. 597 discloses that a porous body made of copper or a copper alloy or a foamed body is integrally formed or adhered so that a pipe for transferring a heat medium and a foamed body are bonded or adhered to each other. Take the method of injecting and solidifying the molten metal into the mold,
The latter requires a means such as crimping, brazing, plating and the like, and involves a problem that the manufacturing cost is increased beyond simply increasing the required area, and that the manufacturing process and equipment costs are increased. Furthermore, these techniques cannot integrally form the inside and outside of the heat transfer tube at the same time, so that the originally intended effect cannot be obtained, and the porous body or the foam to be adhered is a continuous void having the same diameter, and a certain turbulent flow effect can be obtained. But you can't get a bigger effect.

[0005] Further, when these metal porous bodies are used for promoting heat transfer in a boiling heat exchanger, the boiling heat transfer coefficient greatly depends on the thickness and pore diameter of the porous body. That is, if the porous body is thin and the pore diameter is large, bubbles cannot be retained, so that the nucleate boiling phenomenon is not observed and the effect of promoting heat transfer cannot be obtained. Conversely, if the porous body is thick and the pore diameter is small, the bubbles are difficult to separate, and the heat transfer coefficient decreases, the temperature of the heat transfer surface becomes extremely high, and melting may occur, as in the film boiling phenomenon. Tokiko Sho 62-426
According to the methods disclosed in Japanese Patent Application Laid-Open No. 99-1992 and Japanese Patent Application Laid-Open No. 4-110597, it is difficult to provide a metal porous body having a uniform thickness and a uniform hole diameter on a heat transfer surface. The effect of heat promotion is not obtained, or a melting accident occurs due to a partial rise in temperature. The present invention is intended to solve such a problem, and provides a heat transfer member such as a heat transfer tube or a heat transfer plate having a structure capable of further improving heat transfer efficiency, particularly boiling heat transfer efficiency, and a method of manufacturing the same. To provide.

[0006]

SUMMARY OF THE INVENTION The present invention relates to a boiling heat transfer member having a metal porous body obtained by compressing a metal sintered body having continuous pores in the thickness direction on the surface of the member. Can be produced by including the following steps. (A) a step of depositing a metal or metal alloy powder on the skeleton surface of a three-dimensional network structure serving as a base; and (b) a member comprising a three-dimensional network structure coated with a metal or metal alloy powder. (C) sintering a metal or metal alloy to obtain a continuous-pored metal sintered body, and heat-sealing and integrating the surface of the member. And (d) compressing the formed metal sintered body in the thickness direction to form a metal porous body having a predetermined thickness. Then, in the step (d), the method is a method for manufacturing a boiling heat transfer member in which a metal sintered body is compressed by a press machine into a metal porous body.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS When a metal sintered body is formed using a metal or a metal alloy having a high thermal conductivity, the thermal conductivity is reduced even though a material having a high thermal conductivity is used. This is because when the porosity is 80% or more, the thermal conductivity of air becomes dominant, so that the overall thermal conductivity becomes small. In the present invention, when the thickness of the metal sintered body is used with respect to the initial value obtained by sintering, or by pre-compression to reduce the porosity, the heat conductivity is high, and Is a boiling heat transfer member in which trapped steam nuclei are difficult to escape. In the present invention, the porosity of the metal sintered body is preferably set to 80 to 98%. If the porosity is less than 80%, a large amount of the metal or metal alloy powder is applied to the skeleton surface of the three-dimensional network structure serving as the base. However, it is difficult to form a uniform metal sintered body because of unevenness in the adhesion. On the other hand, if the porosity exceeds 98%, the amount of the metal or metal alloy powder to be applied is small and the powder cannot be sintered, or the obtained metal sintered body becomes brittle, resulting in poor handling. The porosity of the metal sintered body is more preferably 85 to 96%.

[0008] The thickness of the metal sintered body is preferably 1 to 5 mm, and if it is less than 1 mm, it is difficult to form a substrate having a three-dimensional network structure for forming the metal sintered body,
This is because it becomes difficult to compress. On the other hand, if it exceeds 5 mm, it becomes difficult to uniformly apply the metal or metal alloy powder even to the inside of the substrate having the three-dimensional network structure. The thickness of the metal sintered body is more preferably 2 to 4 mm.

The members used in the present invention can be used without any particular limitation as long as they are used in ordinary heat exchangers.
Generally, it is a member having a structure having an enlarged heat transfer surface such as a tube shape, a plate shape, a plate-and-fin shape, a fin-and-tube shape, and the like. These members are made of a metal or alloy such as stainless steel, iron, copper, aluminum, nickel, and the like. A metal sintered body is formed on these metal members once and compressed, or after they are assembled and compressed, It can also be a porous body. For example, in the case of a fin-and-tube type plate fin-and-tube, when a metal porous body is formed only on a plate, a metal porous body is formed on one or both sides of the plate, and a tube (tube) is inserted. Drill holes in the locations, insert tubes, align and weld. When a porous body is formed in a tube, a hole is made in a plate where a tube with a porous body is to be inserted, and the tube is inserted and welded. When the porous body is formed on both the plate and the tube, the formed members are combined and welded. The sintering of a metal sintered body on a member is performed by laminating a metal or metal alloy powder adhered to the skeleton surface of a three-dimensional network structure serving as a substrate on the member surface and heating the three-dimensional network structure. Is formed by sintering at the same time as sintering by removing by burning. For this purpose, select and use a combination of members so that the metal or metal alloy sinters and maintain adhesion, roughen the member, or plating or clad so that it can be sintered with the metal or metal alloy. .

In the metal sintered body obtained by the present invention, the thickness of the metal sintered body is reduced to less than 1/2 of the initial value obtained by sintering, because of its high thermal conductivity and a large number of steam cores. It is preferred because the presence and trapped vapor nuclei are difficult to escape. As a method of compression, it is preferable to use a metal sintered compact by compressing it with a press. This is because compression can be performed uniformly. This is effective when the porosity of the metal sintered body is high or when the thickness is large. When the metal porous body is not planar,
A jig according to the shape is made, attached to a press and compressed.

Next, a method of manufacturing the boiling heat transfer member will be described. The method for manufacturing the boiling heat transfer member includes the following manufacturing steps. (A) a step of depositing a metal or metal alloy powder on the skeleton surface of a three-dimensional network structure serving as a base; and (b) a member comprising a three-dimensional network structure coated with a metal or metal alloy powder. (C) sintering a metal or metal alloy to obtain a continuous-pored metal sintered body, and heat-sealing and integrating the surface of the member. And (d) compressing the formed metal sintered body in the thickness direction to form a metal porous body having a predetermined thickness.

The three-dimensional network structure serving as a substrate is a foamable resin having an open-cell structure such as urethane foam, or a nonwoven fabric or a woven fabric made of, for example, a resin which is burned off by heating. Although it is appropriately selected according to the purpose, it is preferable that the thickness finally becomes 1 to 5 mm. The porosity of the metal sintered body is 85 to 96% and the thickness is 1 to 5
In order to make the three-dimensional network structure as mm, it is preferable that the porosity of the three-dimensional network structure serving as the substrate is 85% or more and the thickness is 1 mm or more. This is because the metal or metal alloy powder is applied to the skeleton surface of the three-dimensional network structure, so that the porosity and thickness of the three-dimensional network structure are reflected on the porosity and thickness of the metal sintered body. However, because of the sintering, the metal or metal alloy is fused and shrunk, so that the porosity and thickness of the obtained metal sintered body become smaller than the porosity and thickness of the three-dimensional network structure used. Considering this, select a three-dimensional network structure with a larger porosity and a larger thickness than the target porosity. The porosity of the three-dimensional network structure can be easily obtained by changing the expansion ratio. Here, the porosity is synonymous with the expansion ratio of the plastic foam, and is a value obtained by dividing the density of the unfoamed metal or metal alloy material by the apparent density of the metal sintered body or metal porous body after molding. It is.

It is preferable that the skeleton surface of the three-dimensional network structure serving as the substrate is provided with tackiness in order to facilitate adhesion of the powder and prevent peeling. The tackiness is provided by applying an acrylic or rubber-based adhesive solution or an adhesive resin solution such as a phenol resin, an epoxy resin, or a furan resin to the three-dimensional network structure. When the substrate is a resin, it is also possible to impart tackiness to the substrate itself by plasma treatment or the like. After preferably imparting tackiness to the skeleton surface of the substrate, the powder is applied to the skeleton surface by a method such as rocking the substrate in the powder or spraying the powder on the substrate. Thereby, the powder in a dry state can be directly adhered to the surface of the substrate. After the powder is applied, the step of applying the powder by further imparting adhesiveness may be repeated. The particle size of the powder may be within a range in which the powder can be adhered to the surface of the substrate, and is generally preferably in the range of 0.01 to 100 μm. The shape of the powder is not particularly limited, and if the particle size distribution is such that small particles can fill gaps between large particles, the distribution can be advantageous for subsequent sintering. The powder may be mixed with another metal or metal alloy in the same powder or as another powder depending on the purpose.

The metal or metal alloy used in the present invention includes metal powders such as gold, silver, copper, nickel, aluminum, titanium, chromium, zinc, tin, manganese, tungsten, cobalt and the like, and the metal and other elements. , For example, oxides, sulfides, and halides, and alloys of the metal with other metals. These powders can be three-dimensionally applied to members such as the inner and outer surfaces of metal plates and metal tubes by utilizing the property of being easily sintered alone or as a mixture by heating in an inert or reducing atmosphere. A heat transfer tube or a heat transfer plate to which a metal sintered body having a network structure is integrally adhered is obtained, and the metal porous body is not only a single hole diameter but also a plurality of layers of metal porous bodies having different hole diameters. Can also.

A three-dimensional network structure serving as a base is coated with a metal or metal alloy powder on the skeleton surface, and is laminated on the surface of the member. At this time, the layers may be simply laminated, but powder may be applied to the member surface, or the member surface or the surface of the powder-coated three-dimensional network structure may be wetted with water, an organic solvent, a solution containing a metal salt, or the like. It is preferable to laminate the metal sintered body so that the obtained metal sintered body and the member have good adhesiveness. Any metal salt may be used as long as it dissolves in a liquid, but a metal salt that forms an oxide at a temperature near the temperature at which the resin substrate is decomposed and removed is preferred because of its large effect of improving strength. For this reason, salts such as nitrates, acetates, and formates that generate oxides at 500 ° C. or lower at which the general resin substrate decomposes are preferable. The kind of the metal salt may contain the same kind of metal ion as the powder, or may contain a different kind of metal ion. These are applied to a powder-coated three-dimensional network structure, wet the powder by dipping or spraying,
By drying and aggregating the powders, the strength can be maintained during heating and the strength of the obtained porous metal layer can be increased.

The heating of the powder-coated three-dimensional network structure laminated on the surface of the member is intended to remove the substrate and sinter the powder. As the heating conditions, the processing temperature, time, and atmosphere are appropriately selected depending on the properties of the substrate and the powder used. When the foamed resin is used for the base and the metal is used for the powder, it is preferable to change the atmosphere so that the burning of the base becomes an oxidizing atmosphere and the sintering of the metal powder becomes a reducing atmosphere. In the step (d), the step of compressing the formed metal sintered body in the thickness direction to form a metal porous body having a predetermined thickness is performed by using a press machine capable of controlling a moving distance, and using a press machine capable of controlling a moving distance. It can also be compressed at a compression rate.

[0017]

【Example】

(Embodiment 1) FIG. 1A shows a manufacturing process of a boiling heat transfer member of the present invention and an example of a boiling heat transfer member manufactured according to the present invention. As a substrate having a three-dimensional network structure, a polyurethane foam (Everlight SF, trade name, manufactured by Bridgestone Corporation) having a thickness of 3 mm was used. This polyurethane foam was immersed in an acrylic pressure-sensitive adhesive solution having the following resin content of 8% by weight, and an excess solution was removed through a roll to impart tackiness to the surface of the substrate skeleton. Acrylic copolymer HTR-600LB (trade name of Teikoku Chemical Industry Co., Ltd.) 50 parts by weight Acrylic copolymer Q-1851 (trade name of Nippon Carbide Industry Co., Ltd.) 50 parts by weight Crosslinking agent Coronate L (Japan 1 part by weight, manufactured by Polyurethane Industry Co., Ltd.) 1 part by weight Solvent: 1161.5 parts by weight This was further dried at 100 ° C. for 10 minutes to remove the solvent, and then the base was inserted into copper powder having an average particle diameter of 5 μm. It was applied by rocking. On the other hand, FIG. 1 (b), (c)
As shown in the figure, the external dimensions of the member 300 × 200 mm,
A copper plate 130 having a thickness of 3 mm was used, copper powder was adhered on one side thereof, and a polyurethane foam having copper powder adhered thereon was layered. Then, the substrate was heated and maintained at 500 ° C. for 10 minutes in an air atmosphere to decompose and remove the polyurethane foam as the substrate. Then, it was kept at 900 ° C. for 20 minutes in a reducing atmosphere in which a hydrogen gas was flowed. With this, the copper oxide is reduced, the copper powder is sintered, and a metal sintered body 110 having a shape obtained by transferring the three-dimensional network structure of the polyurethane foam, which is a three-dimensional copper network structure, is provided. A copper plate was obtained. The thickness of the metal sintered body 110 was 2 mm, and the porosity was 95%. The copper plate with the metal sintered body was placed on a press plate of a press machine, and the thickness 4
mm copper spacer is placed, and at room temperature, 10 kgf / c
Pressed at a pressure of m ² . The thickness of the metal sintered body 110 after pressing is 1 mm and the metal porous body 1 having a porosity of 48%.
20 was obtained. Unnecessary portions of the metal porous body were cut off with a cutter to obtain a boiling heat transfer plate 100. Table 1 shows the heat transfer measurement results of the boiling heat transfer plate obtained in the present invention.

(Comparative Example 1) A member in which the member with a metal sintered body was not pressed during the manufacturing process of Example 1 was used as Comparative Example 1.

Comparative Example 2 A comparative example 2 was made using only the members used in Example 1. Table 1 shows the heat transfer measurement results of the boiling heat transfer members of Comparative Examples 1 and 2 obtained by performing the measurement in the same manner as in Example 1. In the schematic diagrams shown in the items, the upper figure shows a plan view of the boiling heat transfer member, and the lower figure shows a sectional view of the boiling heat transfer member. The boiling heat transfer member of Comparative Example 1 which was not pressed had a boiling heat transfer coefficient about twice that of the smooth plate of Comparative Example 3, but in the compressed Example 1 of the present invention, about 3 times of the smooth plate. Twice the heat transfer coefficient. Further, since the porous metal body was formed uniformly on the surface of the member, the boiling heat transfer coefficient on the surface became uniform.

[0020]

[Table 1]

(Embodiment 2) As shown in FIG.
mm, 1.8mm thick, 300mm long copper tube surface,
Copper powder was mixed with the adhesive solution used in Example 1, and applied and dried. Further, an adhesive was applied in the same manner as in Example 1,
A long polyurethane foam having a width of 15 mm and a thickness of 3 mm to which copper powder was adhered was prepared, wound around a copper tube surface coated with an adhesive, and decomposed and removed of the polyurethane foam as a substrate in the same manner as in Example 1. A metal sintered body was formed.
The thickness of the obtained metal sintered body was about 2 mm, and the porosity was 94 mm.
%Met. Remove 10mm from the end of the copper tube of the metal sintered body with a cutter, put it between two rolls rotating in the opposite direction, and rotate the copper tube with the metal sintered body with another vertically movable roll. The resulting mixture was compressed to obtain a porous metal body having a thickness of 1 mm, and a boiling heat transfer tube was obtained. In addition to those shown in Examples 1 and 2, the surface on which the metal porous body is formed may be both surfaces of the plate depending on the application. In the case of a pipe, the surface on which the metal porous body is formed may be either the inner wall or the outer wall of the pipe, or both.

Example 3 The boiling heat transfer member obtained in Example 1 was immersed in the following blackening treatment solution at 95 ° C. for 2 minutes to oxidize copper to obtain copper oxide. Sodium chlorite 30 g / l Sodium hydroxide 15 g / l Trisodium phosphate 12 g / l The heat transfer member obtained in Example 1 may be easily oxidized depending on use conditions. Therefore, by oxidizing in advance, a heat transfer member having stable characteristics can be obtained. In addition, oxidation can be performed using a solution of peroxoammonium, potassium permanganate, sodium perchlorate, or the like.
Further, when a hydrophilic paint containing silicon dioxide is coated against corrosion, the heat transfer performance is improved by improving the wettability, and the heat transfer performance can be maintained for a long period of time, as in the case of the oxidation treatment.

[0023]

According to the present invention, the metal sintered body on the surface of the heat transfer member is compressed in the thickness direction to be a metal porous body, and a hole having a smaller diameter than the metal sintered body can be formed. At the time of generation, the bubbles are hardly detached, and the nucleate boiling phenomenon is maintained. Therefore, the boiling heat transfer coefficient increases, and the heat exchanger can be reduced in size and improved in performance. In the present invention, by controlling the amount of compression, an arbitrary boiling transmissivity can be obtained, and the heat transfer design of the heat exchanger becomes easy. In terms of manufacturing,
A heat transfer member excellent in boiling heat transfer can be obtained without complicated machining, and the bonding between the heat transfer member and the porous metal body is performed during the sintering step, so that the heat transfer member can be manufactured at low cost.

[Brief description of the drawings]

FIG. 1A is a view showing each step for explaining one embodiment of the present invention, FIG. 1B is a plan view of a boiling heat transfer member manufactured by the present manufacturing method, and FIG. Is an aa cross-sectional view thereof.

FIG. 2 (a) is a plan view of a boiling heat transfer tube of the present invention,
(B) is the aa sectional view.

[Explanation of symbols]

 100. Boiling heat transfer member 110. Metal sintered body 120. Metal porous body 130. Element

Claims (3)

[Claims] 1. A boiling heat transfer member comprising a metal porous body obtained by compressing a metal sintered body having continuous pores in a thickness direction on a member surface. 2. A method for producing a boiling heat transfer member, comprising the following steps. (A) a step of depositing a metal or metal alloy powder on the skeleton surface of a three-dimensional network structure serving as a base; and (b) a member comprising a three-dimensional network structure coated with a metal or metal alloy powder. (C) sintering a metal or metal alloy to obtain a continuous-pored metal sintered body, and heat-sealing and integrating the surface of the member. And (d) compressing the formed metal sintered body in the thickness direction to form a metal porous body having a predetermined thickness. 3. In the step (d) according to claim 2,
A method for producing a boiling heat transfer member in which a sintered metal body is compressed by a press to form a porous metal body.