Fiber member and heat exchanger having fiber member

Abstract

To provide a heat exchanger capable of further improving a heat exchange efficiency which has not been sufficiently achieved by a conventional method, the heat exchange efficiency required to be high due to a steep rise of resource costs due to a global situation or a carbon neutral trend as a measure against global warming these days.SOLUTION: A fiber member is formed by entangled fibers. A surface of each of the fibers is coated with a material having higher heat conductivity than the fibers. If an apparent volume of the fiber member is Vm and a pore volume of the fiber member is Vp, porosity Pr (Pr=Vp / Vm×100) is 60% or more. A heat exchange efficiency can be improved by using the fiber member.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a fibrous member and a heat exchanger including the fibrous member. [Background technology]

[0002] Heat exchangers, which use the temperature difference between two fluids to exchange heat, are widely used and are used in products such as air conditioning equipment and water heaters. Heat exchangers are known to be devices that can heat and cool efficiently due to their principle. The mainstream form of heat exchanger uses a method in which a refrigerant flows through a heat transfer tube and exchanges heat with a fluid outside the heat transfer tube.

[0003] Patent document 1 discloses that in order to improve the heat exchange performance of such a heat exchanger, continuous spiral recesses are formed on the outer surface of the pipe, and continuous spiral protrusions are formed on the inner surface of the pipe. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-270755 Summary of the Invention [Problem to be solved by the invention]

[0005] However, due to the recent trend toward carbon neutrality as a measure against global warming and the rising cost of resources due to the global situation, higher heat exchange efficiency is required for heat exchangers, and the method disclosed in Patent Document 1 cannot be said to be sufficient, so further improvement in heat exchange efficiency is required.

[0006] The present invention has been made in view of the above problems, and has an object to provide a fibrous member capable of improving heat exchange efficiency. [Means for solving the problem]

[0007] In order to achieve the above-mentioned object, the fiber component of the present invention is a fiber component in which fibers are intertwined, the surface of the fibers is coated with a material having a higher thermal conductivity than the fibers, and when the apparent volume of the fiber component is Vm and the void volume of the fiber component is Vp, the void ratio Pr (Pr = Vp / Vm × 100) is 60% or more. [Effects of the Invention]

[0008] By providing the fiber member in this manner, it is possible to provide a fiber member capable of improving heat exchange efficiency. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 2 is a schematic diagram of a heat transfer tube unit of the heat exchanger. [Figure 2] FIG. 4 is a schematic view of a fibrous member disposed inside a heat transfer tube unit. [Figure 3] 1(a) is an enlarged view of a fiber 2 constituting the fiber material 1. FIG. [Figure 4] 1 is an example of an ALD apparatus for coating a fiber 2 with a material 3. [Figure 5] This is a variation of the method of coating the fiber 2 with the material 3. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. The embodiment described below is one embodiment of the invention, and the embodiment is not limited to this. In the following description and drawings, common components are designated by common reference numerals.

[0011] FIG. 1 is a schematic diagram of a heat transfer tube unit 100 of a heat exchanger according to this embodiment. The heat transfer tubes 4 are tubes made of copper, aluminum, or the like, through which a refrigerant 50 flows, and heat exchange fins 40 are welded to their outer periphery. The refrigerant 50 can be, for example, an HFC (hydrofluorocarbon) or water. Heat is exchanged by being transferred from the refrigerant 50 to the heat transfer tubes 4, the heat exchange fins 40, and the external fluid 60, and the heat transfer tube unit 100 functions as a heat exchanger. Note that FIG. 1 does not include a mechanism for compressing and expanding the refrigerant 50 to heat or cool it, nor does it include a pump for transporting the refrigerant 50.

[0012] In this embodiment, the heat exchange efficiency between the heat transfer tube 4 and the refrigerant 50 is improved by inserting a fibrous member 1, as described below, into the heat transfer tube 4 so as to be in contact with the inner wall of the heat transfer tube 4. In the example of FIG. 1, three fibrous members 1 are arranged inside the heat transfer tube 4, but the number and positions of the fibrous members 1 are not limited to this, and they can be arranged as appropriate depending on the desired degree of thermal efficiency.

[0013] As shown in Figure 1, by placing the fibrous material 1 inside the heat exchanger so that it is in contact with the inner wall, it is possible for the refrigerant inside the heat transfer tube and the fibrous material 1 to come into contact over a wide surface area, improving heat exchange efficiency. The fibrous material 1 is composed of fibers 2, and by ensuring that the porosity is above a certain value, pressure loss due to the fibrous material 1 can be reduced. Furthermore, by coating the fibers 2 that make up the fibrous material 1 with a material 3 that has a higher thermal conductivity than the fibers, heat exchange efficiency can be increased without placing any restrictions on the material of the fibers 2.

[0014] 2 is a schematic diagram of a fibrous member 1 disposed inside a heat transfer tube unit. The fibrous member 1 is composed of countless fibers 2 irregularly entangled. To improve thermal efficiency, it is important that the fibrous member 1 disposed inside the heat transfer tube 4 has a surface area sufficient for heat exchange and can sufficiently reduce the pressure loss when the refrigerant 50 flows through it. For this reason, it is preferable that the porosity Pr of the fibrous member 1 is 60% or more, and a porosity Pr of 80% or more is even more preferable in terms of pressure loss.

[0015] The porosity Pr can be defined as the ratio of the apparent volume Vm obtained from the outline of the fiber material 1 (in other words, the volume of an object when the outline of the fiber material 1 is the outer shape) to the void volume Vp of the fiber material 1, and is expressed by the following equation (1). Porosity Pr=Vp / Vm×100…Equation (1)

[0016] When the fibrous member 1 is inserted into a heat transfer tube 4, it is desirable that the porosity Pr be 60% or more when the fibrous member 1 is disposed inside the heat transfer tube 4. The surface area for heat exchange of the fibrous member 1 can be increased by increasing the thickness of the fibrous member 1 in the direction of refrigerant flow inside the heat transfer tube 4. The thickness is preferably 1 mm or more, more preferably 2 mm or more, but is preferably less than 50 mm for ease of placement.

[0017] 3(a) is an enlarged view of a fiber 2 constituting the fiber material 1, and FIG. 3(b) is a cross-sectional view of the fiber 2 in (a), showing the longitudinal cross section A-A' and the radial cross section B-B' shown in FIG. 3(a). Although not shown in FIG. 2, the entire surface of the fiber 2 is covered with material 3. In the example of FIG. 3, the fiber 2 is depicted as a straight line for convenience, but in reality it has a shape that combines curvatures.

[0018] The material for the fiber 2 can be appropriately selected from carbon fiber, glass fiber, resin fibers such as polyester, and natural fibers such as cellulose nanofibers. The smaller the fiber diameter of the fiber 2, the greater the specific surface area of ​​the fiber member 1. Furthermore, a smaller fiber diameter is advantageous in terms of pressure loss. Therefore, the fiber diameter of the fiber 2 is preferably 1000 nm or less, and more preferably 200 nm or less. Although fibers with diameters of 1000 nm or more may be mixed in due to manufacturing difficulties, the desired effect can be achieved as long as the fibers 2 present in the fiber member 1 are not mixed in so much that the average diameter of the fibers 2 exceeds 1000 nm. In other words, the fiber member 1 is preferably made of fibers with an average diameter of 1000 nm or less, and more preferably an average diameter of 200 nm or less. On the other hand, since strength can be improved by intentionally mixing in a small amount of fibers with a larger diameter, it is also preferable to mix fibers with a larger diameter into the fiber member 1 as long as the average diameter does not exceed the above average diameter.

[0019] The material 3 covering the fibers 2 is selected to have a higher thermal conductivity than the fibers 2. Examples of the material 3 include metals, oxides, or both, and more specific examples include Al, Cu, Ag, Au, and HfO2, either alone or in combination.

[0020] The thickness of the material 3 is preferably between 0.5 nm and 100 nm to prevent the porosity of the fiber member 1 from decreasing due to the coating. Furthermore, it is preferable that the fibers 2 in the center of the fiber member 1 are coated uniformly, just like the fibers 2 in the outer periphery of the fiber member 1. The center of the fiber member 1 here refers to a region S that is similar in shape to the outline of the fiber member 1, occupies 10% of the apparent volume Vm of the fiber member 1, and is centered on the hypothetical center of gravity G when the specific gravity of the interior of the fiber member 1 is assumed to be constant. Furthermore, the composition of the material 3 preferably has a carbon atom (C) content near the surface of 1 at% to 25 at% (1.0 at% to 25 at%). C originates from the CH groups contained in the material 3. However, if the C content is greater than 25 at%, the hydrophilicity is insufficient, potentially resulting in poor heat exchange. The C content can be analyzed using XPS (X-ray photoelectron spectroscopy).

[0021] (Method of manufacturing the fiber member 1) The fiber member 1 may be manufactured by coating single fibers of the fibers 2 with the material 3 and then entangling the fibers 2 together, or by entangling the fibers 2 together before being covered with the material 3 and then coating them with the material 3. There are no particular limitations on the method for coating the fibers 2 with the material 3, and coating techniques such as known techniques such as wet coating, sputtering, vapor deposition, ion plating, chemical vapor deposition (CVD), and atomic layer deposition (ALD) can be selected. Examples of CVD methods include plasma CVD, which uses plasma, and thermal CVD, which uses heat.

[0022] From the viewpoint of stable production, it is preferable to entangle the fibers 2 before they are covered with the material 3 and then coat the fibers 2 with the material 3 using the ALD method.

[0023] The ALD method, as disclosed in, for example, Patent Document 2009-525406, is a method in which two or more types of source gases are alternately introduced and repeatedly exhausted, causing the source materials adsorbed on the surface of the film to react, thereby forming a thin film in atomic layer units.

[0024] 4 shows an example of an ALD apparatus 200 that performs the ALD method of coating a fiber 2 with a material 3. The ALD apparatus 200 has a metal vacuum chamber 201 connected to it, a vacuum pump 202 for evacuation, a precursor supply line 203, a reaction gas supply line 204, and a purge gas supply line 205. Each line connected to the chamber has a valve for adjusting the flow rate, but these are omitted from FIG.

[0025] The vacuum chamber 201 contains a holder 211 for holding a fiber material 210, which is made of intertwined fibers 2 to be coated with material 3, and multiple heaters 212 for heating the fiber material 210. The uncoated fiber material 210 is placed on the holder 211, and the vacuum chamber 201 is evacuated to approximately 1 Pa. The heater 212 is then turned on to heat the fiber material 210 to an appropriate temperature. The heating temperature can be adjusted depending on the precursor and reactive gas used, but is generally approximately 100 to 500°C. Once the fiber material 210 reaches the target temperature, reactive gas is introduced, and after the desired time, the gas introduction is stopped. Purge gas is then introduced for the desired time to remove unwanted precursors and decomposition gases. The reactive gas is then introduced for the desired time, resulting in a coating of the desired material 3 composition. Purge gas is then introduced to remove unwanted gases. This cycle is repeated to coat the fiber material 1 with material 3 until the desired film thickness is reached.

[0026] When coating fiber 2 with Cu as material 3, Cu(DMAP)2 can be used as the precursor and hydrazine as the reactive gas. Depending on the coating conditions, material 3 contains 1 to 20 atomic percent (at%) of C. C improves the adhesion of material 3 to fiber 2. While the exact reason is unknown, it is thought that the inclusion of C reduces the density of the coating, which in turn reduces internal stress.

[0027] After coating, the heater 212 is stopped heating, and after the vacuum chamber 201, the holder 211, and the coated fiber 2 have cooled sufficiently, the vacuum chamber 201 is opened to the atmosphere, and the fiber material 1 is removed.

[0028] The fibrous member 2 thus manufactured is placed inside the heat transfer tube 4 of the heat exchanger so as to be in contact with the inner wall of the heat transfer tube 4, thereby making it possible to improve the heat exchange efficiency.

[0029] (Modification of the manufacturing method of the fiber material 1) In the method shown in Figure 4, the fiber member 2 is placed inside the ALD apparatus and coated with the material 3, but it is also possible to place the fiber member 2 inside the heat transfer tube 4 and coat the fiber 2 with the material 3 using the ALD method.

[0030] FIG. 5 shows the process of coating the material 3 on a heat transfer tube 4, with the heat transfer tube 4 being treated as the vacuum chamber of an ALD apparatus, with a fibrous member 210 made of intertwined fibers 2 to be coated with the material 3. In this case, the open end of the heat transfer tube 4 is connected to a vacuum flange 206. A vacuum flange 206A connected to a vacuum pump 202 for evacuation and a vacuum flange 206b connected to a precursor supply line 203, a reactant gas supply line 204, and a purge gas supply line 205 are connected to the heat transfer tube 4. The vacuum pump then draws a vacuum, and the heat transfer tube 4 and the fibrous member 210 are heated by a heater 212 located outside the heat transfer tube 4. The coating of the material 3 is then performed in the same manner as in the ALD apparatus shown in FIG. 4.

[0031] 5, the fiber member 1 and the heat transfer tube 4 are simultaneously coated with the material 3, and therefore the contact portion between the fiber member 1 and the heat transfer tube 4 is also coated with the material 3. By covering the contact portion with the material 3 in this way, the heat exchange efficiency can be further improved.

[0032] <Evaluation of Examples and Comparative Examples> EXAMPLES The present invention will be specifically described below with reference to examples and comparative examples, but the scope of the present invention is not limited to these examples.

[0033] The heat transfer tube 4 was a copper cylindrical tube with an outer diameter of 12 mm, an inner diameter of 10 mm, and a length of 1 m. Refrigerant 50, R32 (HFC-32) at 15°C, was circulated at a flow rate of 0.01 kg / min, and the amount of heat exchanged was evaluated. The temperature of the heat transfer tube at room temperature and at the start of the test was 25°C.

[0034] Example 1 Fiber 2, with an average fiber diameter of 900 nm, was coated with 100 nm of Cu as material 3 using the ALD method. Furthermore, composition analysis using X-ray photoelectron spectroscopy (XPS) revealed that the coated surface contained 5 atomic % of C. The fiber material 1 was placed inside heat transfer tube 4 so that its porosity was 60% and its thickness in the direction of refrigerant flow inside the heat transfer tube was 5 mm.

[0035] <Example 2> Fiber 2 with an average fiber diameter of 200 nm was coated with 100 nm of Cu as material 3 using the ALD method. The fiber material 1 was placed inside the heat transfer tube 4 so that the porosity of the fiber material 1 was 80% and the thickness of the fiber material 1 in the direction of the refrigerant flow inside the heat transfer tube was 5 mm.

[0036] <Comparative Example 1> A heat transfer tube 4 in which no fiber member 1 was disposed was prepared.

[0037] <Comparative Example 2> A fibrous material 210 (a fibrous material before being coated with material 3) made by intertwining fibers 2 with an average fiber diameter of 900 nm was used, and was placed inside a heat transfer tube 4 so that the porosity of the fibrous material 210 was 60% and the thickness of the fibrous material 210 in the direction of refrigerant flow inside the heat transfer tube was 5 mm.

[0038] The parameters and heat exchange efficiency are summarized in Table 1. Improvements in heat exchange efficiency were confirmed in Examples 1 and 2 compared to Comparative Example 1. On the other hand, no difference in heat exchange efficiency was observed between Comparative Example 1 and Comparative Example 2. In other words, the results of this investigation confirmed that the heat conversion efficiency can be improved by placing a fibrous member 1, the surface of which is coated with material 1, a substance with a higher thermal conductivity than fiber 2, inside a heat transfer tube 4. It was also confirmed that the heat conversion efficiency can be further improved by increasing the porosity of the fibrous member 1. In other words, by installing the fibrous member disclosed in the present invention in the heat transfer tube of a heat exchanger, the heat exchange efficiency can be improved, and it is expected that the energy consumption of heat exchange equipment, including air conditioning, can be reduced.

[0039] [Table 1]

[0040] <Summary of the embodiment> The disclosure of the present specification includes at least the following configurations.

[0041] (Item 1) A fiber member in which fibers are intertwined, The surface of the fiber is coated with a material having a higher thermal conductivity than the fiber; A fiber member characterized in that, when the apparent volume of the fiber member is Vm and the void volume of the fiber member is Vp, the void ratio Pr (Pr=Vp / Vm×100) is 60% or more.

[0042] (Item 2) 2. The fiber member according to item 1, wherein the material includes at least one of Al, Cu, Ag, Au, and HfO2.

[0043] (Item 3) 3. The fiber member according to item 1 or 2, wherein the material contains carbon atoms in an amount of 1 at % or more and 25 at % or less.

[0044] (Item 4) 4. The fiber member according to any one of items 1 to 3, wherein the material of the fiber member has an average diameter of 1000 nm or less.

[0045] (Item 5) A heat transfer tube in which the fibrous member according to any one of items 1 to 4 is disposed inside and heat exchange is performed by flowing a refrigerant through the inside.

[0046] (Item 6) 6. The heat transfer tube according to item 5, wherein the thickness of the fibrous member is 1 mm or more in the direction in which the refrigerant flows inside the heat transfer tube.

[0047] (Item 7) 7. The heat transfer tube according to item 5 or 6, wherein an inner wall of the heat transfer tube is in contact with the fiber member.

[0048] (Item 8) 8. The heat transfer tube according to any one of items 5 to 7, wherein the inner wall of the heat transfer tube is covered with the same material as the material.

[0049] (Item 9) A method for manufacturing a fiber member to be disposed inside a heat transfer tube that performs heat exchange by flowing a refrigerant, coating a surface of the fiber with a material having a higher thermal conductivity than the fiber; intertwining the fibers to provide a fibrous member; A manufacturing method comprising the steps of:

[0050] (Item 10) 10. The manufacturing method according to item 9, wherein the covering step is performed after the step of providing the fiber member.

[0051] (Item 11) 11. The method according to item 9 or 10, wherein the coating step is performed using an atomic layer deposition method.

Claims

1. A fiber member in which fibers are intertwined, The surface of the fiber is coated with a material having a higher thermal conductivity than the fiber; A fibrous member characterized in that, when the apparent volume of the fibrous member is Vm and the void volume of the fibrous member is Vp, the void ratio Pr (Pr = Vp / Vm x 100) is 60% or more.

2. The fiber member according to claim 1 , wherein the material includes at least one of Al, Cu, Ag, Au, and HfO 2 .

3. 2. The fiber member according to claim 1, wherein the material contains carbon atoms in an amount of 1 at % or more and 25 at % or less.

4. 2. The fiber member according to claim 1, wherein the material of the fiber member has an average diameter of 1000 nm or less.

5. A heat transfer tube in which the fibrous member according to claim 1 is disposed inside and a refrigerant is passed through the inside to perform heat exchange.

6. 6. The heat transfer tube according to claim 5, wherein the thickness of the fibrous member is 1 mm or more in the direction in which the refrigerant flows inside the heat transfer tube.

7. The heat transfer tube according to claim 5 , wherein an inner wall of the heat transfer tube is in contact with the fiber member.

8. 6. The heat transfer tube according to claim 5, wherein the inner wall of the heat transfer tube is coated with the same material as the material.

9. A method for manufacturing a fiber member to be disposed inside a heat transfer tube that performs heat exchange by flowing a refrigerant, coating a surface of the fiber with a material having a higher thermal conductivity than the fiber; intertwining the fibers to provide a fibrous member; A manufacturing method comprising the steps of:

10. The manufacturing method according to claim 9, wherein the covering step is performed after the fibrous member providing step.

11. The method according to claim 9 , wherein the coating step uses atomic layer deposition.

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