METHOD OF MANUFACTURING A HEAT EXCHANGER

Abstract: A pin-fin type heat exchanger (1) comprising a plurality of wire-like heat conductive elements (3) arranged in parallel and spaced from each other, and formed into a corrugated shape, and a method of manufacturing the same by making a corrugated sheet including the wire-­ like heat conductive elements and a temporary fixing material and removing the temporary fixing material after the heat conductive element is joined to a pipe (2) through which fluid passes.

Description: The present invention relates to a method of manufacturing a pin-fin type heat exchanger according to the preamble of claim 1. Such a method is disclosed in US-A-4,259,771 which describes an apparatus for producing a wire fin tube for heat transfer which comprises fin-forming means for shaping a plurality of wires to a wavy shape, means for guiding the wavy wires in an upstanding state including guide plates spaced apart a selected distance; means for feeding a revolving tube in a crossing direction to the wavy wires so that the wires can be wound on the tube; means for controlling the operative speed relation of the fin-forming means and the tube feeding means so that the wavy wires may be helically wound on the tube under a moderate tension so as to maintain the upstanding state and the same pitch as the distance of the guiding means; and means for welding the wire fins to the tube. In order to ensure that the wavy wires helically wound around the tube are maintained in their upstanding state without collapsing a tension sufficient to stand the wire fins upright on the tube is exerted to the fins and the root bottom portions of the wavy wires are resiliently in contact with the surface of the tube. Because the wavy wires are only kept in an radially upright state by the resiliently contact with the surface of the tube problems arise in case the thickness of the wires is reduced or the height of the waves is increased. Additional problems arise if the wires shall be fixed to a flat tube instead of a circular tube. An object of the present invention is to provide a method of manufacturing a pin-fin type heat exchanger having wire like corrugated pin-fins as heat conductive elements according to the preamble of claim 1 wherein the corrugated elements can be exactly fixed onto a pipe of circular cross-section or of another cross-section like in case of a flat-pipe in the desired positions. The method according to the invention is characterized by the features of claim 1. Further particulars of the invention are indicated in the subclaims. The present invention will now be described in detail with reference to the accompanying drawings, wherein Fig. 1 is a perspective view illustrating a part of an example of a corrugated sheet used to manufacture a pin-fin type heat exchanger in accordance with the present invention; Fig. 2 is a front view schematically illustrating an apparatus for manufacturing a sheet composed of a plurality of wire-like heat conductive elements and a temporary fixing material; Fig. 3 is a plan view illustrating a sheet in which a plurality of wire-like heat conductive elements are fixed by another plurality of wire-like heat conductive elements arranged in a direction perpendicular to the former elements; Fig. 4 is a perspective view illustrating an example of the corrugated sheet used to make the pin-fin type heat-exchanger in accordance with the present invention; Fig. 5 is a perspective view illustrating an example of a piece cut from the corrugated sheet illustrating in Fig. 4; Fig. 6 is a front view illustrating a piece of the corrugated sheet from which the temporary fixing material on a curved top of the sheet has been removed; Fig. 7 is a perspective view explaining an application of a solder on a surface of a pipe; Fig. 8 is a perspective view illustrating a winding of the corrugated sheet on the surface of the pipe; Fig. 9 is a perspective view illustrating an example of a fin-pipe assembly; Fig. 10 is a perspective view explaining a procedure of removing the temporary fixing material from the fin-pipe assembly; Fig. 11(A) is a longitudinal sectional view of the fin-pipe assembly from which the temporary fixing material has been completely removed; Fig. 11(B) is a traverse sectional view of the pipe-fin assembly corresponding to Fig. 11(A); Fig. 12 is a perspective view illustrating an embodiment of the pin-fin type heat exchanger made of the pipe-fin assembly illustrated in Fig. 11(A); Fig. 13(A) is a front view illustrating a flat pipe used in another embodiment of the pin-fin type heat exchanger manufactured in accordance with the present invention; Fig. 13(B) is a sectional view taken along the line I and I'; Fig. 14 is a perspective view illustrating an example of a piece of the corrugated sheet used to make another embodiment of the pin-fin type heat exchanger; Fig. 15 is a perspective view explaining an application of a solder on a surface of a flat pipe; Fig. 16 is a perspective view illustrating a method of making a plurality of pipe-fin assemblies to a piling body; Fig. 17 is a perspective view illustrating another method of making a plurality of pipe-fin assemblies to another piling body; Fig. 18 is a perspective view illustrating a relationship between the piling body illustrated in Fig. 27 and a header; An example of a corrugated sheet used to manufacture a pin-fin type heat exchanger, described in detail later, is illustrated in Fig. 1. As shown in Fig. 1, five wire-like heat conductive elements 3a, 3b, 3c, 3d and 3e are arranged in a corrugated shape in the sheet 22a. The five heat conductive materials 3a, 3b, 3c, 3d and 3e are embedded while spaced from each other into a temporary fixing material, e.g., a plastic sheet 11. In the present application, a distance between two adjacent heat conductive elements is defined as Z₂ , as shown in Fig. 1. Each heat conductive element is bent into a corrugated shape and a distance between a center point of a curved top 4 of a heat conductive element and a center point of an adjacent curved top 4 of the same element, i.e., a distance between two adjacent parallel portions 5a and 5b of the heat conductive elements 3a, is defined as Z₁ , as shown in Fig. 1. The density Y₁ of the heat conductive elements expressed as a number of elements per mm in a lengthwise direction of the heat conductive elements is calculated from the value Z₁ and the density Y₂ of the heat conductive elements expressed as a number of elements per mm in a direction perpendicular to the lengthwise direction of the heat conductive element is calculated from the value Z₂. The symbol Y used in the above equation is defined as a mean value of Y₁ and Y₂. Preferably, Y₁ and Y₂ represent 0.2 per mm to 10 per mm, respectively, under conditions satisfying the above equations. Preferably, the size of the wire-like heat conductive element and the density of the plurality of wire-like heat conductive element satisfies the following equation. 0.25 ≦ X ≦ 2.5 0.5 ≦ XY ≦ 2.5 Wherein, X stands for a circumferential length of the wire-like heat conductive element and is expressed as mm, and Y stands for a density of the wire-like heat conductive elements on the pipe and is expressed as a number per mm. When X is less than 0.25, the diameter of the wire-like heat conductive element is too small, and the mechanical properties of the heat conductive elements are correspondingly reduced, and thus the processing efficiency at the time of manufacture of the heat exchanger is lowered. Namely, the production efficiency of the heat exchanger is lowered. When X is more than 2.5, the diameter of the wire-like heat conductive element is too large, which reduces the number of heat conductive elements that can be arranged on an unit length of the pipe, and thus a problem arises in that the efficiency of the pin-type heat exchanger is lowered. When XY is less than 0.5, the total surface area of the wire-like heat conductive elements is too small, and thus it is impossible to obtain a high heat transfer efficiency. When XY is more than 2.5, although a wire-like heat conductive element having a large surface area can be used, since the distances between the heat conductive elements arranged in parallel, i.e, the distances Z₁ and Z₂ in Fig. 1, become too small, the pressure loss of the outside fluid is increased. An example of an apparatus for manufacturing a sheet composed of a plurality of wire-like heat conductive elements and a temporary fixing material is illustrated in Fig. 2. A plurality of packages of wire-like heat conductive elements 3 are arranged in a creel 13. Each heat conductive element 3 is withdrawn from the packages by a pair of heated press rolls 14 and 14', the heat conductive element 3 is passed through an eyelet plate 15, a front reed 16, and a tensioning bar 17 to apply an uniform tension to each heat conductive elements 3, and then the heat conductive elements 3 are arranged in a state in which substantially the same pitch is fixed between adjacent heat conductive elements by a guide roller 18 having a plurality of grooves and an arranging reed 19. A sheet 11 of a soluble resin is withdrawn from a sheet roll 11', and supplied through two guide rolls 20 and 21 to the pair of heated press rolls 14 and 14'. The sheet 11 and the plurality of the heat conductive elements 3 are piled together and pressed under heating by the pair of heated press rolls 14 and 14', and then united by embedding the heat conductive elements 3 in the sheet 11. The united sheet 22 composed of the soluble resin sheet 11 and the heat conductive elements 3, i.e., an anisotropic heat conductive sheet, can be obtained by applying two soluble resin sheets to the heat conductive elements 3 from both sides thereof and then pressing under heating. Further, a part of the cross section of each heat conductive element 3 may be embedded in the soluble resin sheet 11. The united sheet 22 is wound, through a pair of delivery rollers 23 and 23', onto a winding roll 24. Various sheets of a substance capable of being dissolved, decomposed or burnt by a heat, chemicals or the like can be used. For example, a sheet of a cellulose group, a polyester group, or a cellulose derivative, a sheet of the cellulose derivative, and a cellulose pulp or the like, can be used. A sheet manufactured by coating or laminating a polyvinyl alcohol on a sheet formed from a mixture of a carboxymethyl cellulose and the cellulose pulp also can be used. Further, it is possible to optionally combine the above-mentioned sheets. Note, a sheet made of the cellulose pulp is most preferable, due to the easy processing thereof. A width and a thickness of the soluble sheet can be optionally selected, but a sheet having a width of between 0.5 m and 1.5 m and a thickness of between 10 µm and 200 µm is preferable, due to the easy processing thereof. Although the wire-like heat conductive elements 3 are embedded in the soluble sheet 11 under the heat and pressing conditions described on the basis of Fig. 13, these elements 3 also can be fixed by coating an adhesive capable of being dissolved, decomposed or burnt by heat, chemicals or the like on the soluble sheet. Various adhesives, for example, a polyvinyl alcohol group, a polyester group, an ethylene·vinyl acetate group, a protein group, a cellulose derivative group or the like can be used. Further, the fixing of the plurality of wire-like heat conductive elements 3 arranged in parallel and spaced from each other can be carried out without using the soluble sheet, as shown in Fig. 3. Namely, first the plurality of the wire-like heat conductive elements 3 is withdrawn in a direction of an arrow 25, and other wire-like elements 26 consisting of a yarn having a thermoplastic property or a thermoadhesive property are piled in a direction perpendicular to the direction of the arrow 25 on the plurality of the wire-like heat conductive element 3, and then fixed at each cross point 27. Next, the plurality of the wire-like heat conductive elements fixed in parallel and spaced from each other are molded into a corrugated shape by a corrugate molding machine generally used to mold a corrugated fin of a conventional corrugated plate-fin type heat exchanger, or by a pleat molding machine commercially supplied for making pleated textile goods. For example, when using the corrugate molding machine, the plurality of the wire-like heat conductive elements fixed in parallel and spaced from each other are compression molded in a corrugated shape by a pair of corrugate press plates, and when a diameter of the wire-like heat conductive element is thin, e.g., 200 µm, an accordion type pleat molding machine may be used. The obtained wire-like heat conductive elements 22a having the corrugated shape (hereinafter, referred to as a corrugated and united body) are illustrated in Fig. 4. Although the densities Y₁ and Y₂ are the same in all portions of the corrugated and united body 22a illustrated in Fig. 4, if necessary, the density Y₁ and Y₂ may be partially changed in the corrugated and united body 22a according to the application of the heat exchanger. When manufacturing the heat exchanger the corrugated and united body 22a is cut along a lengthwise direction thereof, i.e., along the line 25 in Fig. 4, to produce a tape-like corrugated and united body 27 having a width W as shown in Fig. 4. The heat exchanger can be obtained by spirally winding the tape-like corrugated and united body 27 around a circumferential surface of a pipe 2 as shown in Fig. 8. If necessary, the tape-like corrugated and united body 27 is further cut along a direction perpendicular to the lengthwise direction of the corrugated and united body 22a, i.e., along the line 26 in Fig. 4, to provide a corrugated and united body unit 27a having a width W and a length G as shown in Fig. 4. In this case the length G is determined such that the length G corresponds to a length of the circumferential surface of the pipe 2. The corrugated and united body unit 27a is illustrated in Fig. 5. The heat exchanger can be obtained by joining each corrugated and united body unit 27a to the circumferential surface of the pipe 2. Before joining the corrugated and united body to the surface of the pipe, it is necessary to remove the temporary fixing material, e.g., a soluble resin covering curved tops of the wire-like heat conductive elements, to expose the surface of heat conductive element. Figure 6 illustrates an example of a corrugated and united body 28 to be used for a heat exchanger, from which the soluble resin 11 covering both curved tops 4 of the wire-like heat conductive material 3 has been removed by Δh₁. The value of Δh₁ may be between 0 and 1 mm. This resin removing treatment may be applied to the corrugated and united body before or after cutting same. The process of joining the corrugated and united body to the pipe will now be described. First, the joining process in a manufacture of a heat exchanger having pipes 2 of a cylindrical shape will be described. As shown in Fig. 7, a circumferential surface of a pipe 2 is applied with a solder 10 to produce a soldering pipe 29. The solder applying treatment may be performed by any known method, e.g., a coating method, a dipping method or a vapor deposition method. The solder is optionally selected according to a material constituting the pipe and a material of the wire-like heat conductive element. For example, when the pipe and the wire-like heat conductive element are manufactured from copper, a solder composed mainly of lead and tin may be used. If necessary, a resin having a high heat conductivity may be used. The coating of solder may be applied to the curved tops 4 exposed from the resin 11 or to both portions, i.e., the pipe 2 and the curved tops 4. As shown in Fig. 8, the tape-like corrugated and united body 27, the curved tops of which at a side opposite to the circumferential surface of the pipe 2 are exposed, is spirally wound on the pipe 2. The thus obtained wound body 30 is placed for e.g., 30 min, into an oven (not shown) at a temperature of e.g., 165°C, to firmly braze together the circumferential surface of the pipe 2 and the curved tops 4 of the corrugated and united body, to thereby produce a pipe fin assembly 31 as shown in Fig. 9. Since the temporary fixing material, i.e., the soluble resin 11, still remains in spaces between the wire-like heat conductive elements 3 in the fin-pipe assembly 31, the soluble resin 11 is removed by using the apparatus illustrated, for example, in Fig. 10. Namely, the fin-pipe assembly 31 is placed on a moving belt 32 and hot water 33 at a temperature of about 100°C is poured over the fin-pipe assembly 31 to completely remove the soluble resin 11 from the spaces. As shown in Fig. 11(A) and 11(B), when the resin is completely removed from the spaces, an exposed fin-pipe assembly 34 is obtained. The resin may be removed by dipping the fin-pipe assembly 31 into a vessel holding hot water. It is preferable to apply a surface treatment to the exposed fin-pipe assembly 34 to provide a hydrophilicity to the exposed fin-pipe assembly 34 or to increase a corrosion resistance of the exposed fin-pipe assembly 34. For example, when aluminum is used as a material of the pipe 2 and the wire-like heat conductive elements 3, a film having a good corrosion resistance may be formed on the surface of the exposed fin-pipe assembly 34 by treating same with a chemical, e.g., a chromate, a phosphate or the like, and then covering the film with another film of an organic substance or an inorganic substance by applying an inorganic substance, such as fine particles of a silicate, a silica or the like, or an organic substances, such as a polyvinyl alcohol, an acrylic group resin or the like, to provide a hydrophilicity. An embodiment of the heat exchanger 37 manufactured by bending the exposed fin-pipe assembly 34 into a S-like shape, and connecting an inlet 35 of a pipe-side fluid and an outlet 36 of the pipe-side fluid to the ends of the pipe 2 of the exposed fin-pipe assembly 34 is illustrated in Fig. 12. The joining process in a manufacture of a heat exchanger having flat pipes will be described hereafter. First, a flat pipe 12 having a size and a shape illustrated in Fig. 13(A) and 13(B) is prepared. In the drawings, J denotes a length of the pipe 12a, K a width of the pipe, L a thickness of the pipe, and M a thickness of metal plate constituting the pipe 12a. Although the flat pipe 12a in which opposite portions 12c and 12d in a sectional view are parallel is illustrated in Fig. 13(B), a pipe having an elliptic cross section may be used in place of the flat pipe 12a. As shown in Fig. 14, a corrugated and united body unit 27a is prepared by cutting the corrugated and united body 22a illustrated in Fig. 4. In this case, a length J' and a width K' of the corrugated and united body unit 27a may be shorter than that of the corresponding portions of the pipe 12 illustrated in Figs. 13(A) and 13(B). The curved tops 4 at both sides of the corrugated and united body 27a are removed. Flat portions 12c and 12d of the flat pipe 12a are applied with a solder 10 to provide a soldering pipe 38 (Fig. 15 The solder may be applied in the same manner as described for Fig. 7. Figure 16 illustrates a method of assembling the corrugated and united body units 27a and the soldering pipes 38 to obtain a piling body 39 constituting a heat exchanger having headers 7 (see Fig. 18). As shown in Fig. 16, several corrugated and united body units 27a and several soldering pipes 38 are alternately piled by an implement 41 and are fixed to each other under a pressure of, for example, about 2 daN per cm², to produce a piling body 39. The piling body 39 is placed for, e.g., 30 min, in an oven at a temperature of, e.g., 165°C, (not shown) to firmly braze together the surface of the soldering pipe 38 and the curved tops 4 of the corrugated and unit body unit 27a, to thereby produce a fin-pipe assembly. A soluble resin 11 remaining in spaces between the wire-like heat conductive elements 3 in the fin-pipe assembly is removed in the same manner as described for Fig. 10. The thus obtained an exposed fin-pipe assembly 45 is connected to a header 7, as shown in Fig. 18, and the header is connected to both sides of the exposed fin-pipe assembly 45, and the headers and the exposed fin-pipe assembly 45 are brazed together by a solder. The header 7 includes several connecting pipes connecting adjacent flat pipes 12, an inlet of a pipe-side fluid, and an outlet of the pipe-side fluid. It is preferable to apply a surface treatment to the exposed fin-pipe assembly 45 to provide hydrophilicity thereto and to improve the corrosion resistance. The pressure used to obtain the piling body 39 depends on manufacturing conditions for the corrugated and united body unit 27a, e.g., the diameter of the wire-like heat conductive elements, the pitch of the heat conductive elements, the thickness and the material of the soluble resin sheet, or the like. Of course, the pressure must not be such that the corrugated and united body unit 27a is buckled by the pressure and temperature in the oven and the joining between the pipes and the curve tops of the wire-like heat conductive material is weak. Figure 17 illustrates a method of assembling the corrugated and united body units 27a and a soldering pipe having an S-like shape to obtain a piling body 40. When preparing the soldering pipe 42, preferably a distance h₂ between adjacent parallel portions of the soldering pipe 42 is smaller than the height h₁ of the corrugated and united body units 27a. The corrugated and united body units 27a are inserted into spaces between the adjacent parallel portions of the soldering pipe 42 having the S-like shape, and the units 27a and the pipe 42 are arranged in an implement 43. In that time, spacers 44 are inserted between the adjacent parallel portion of the soldering pipe 42 so that the distance h₂ becomes the distance h₁ after applying a pressure to the units 27a and the pipe 42. The piling body 40 is obtained by carrying out a heat treatment on the implement 43 with the units 27a and the pipe 42, similar to that described for Fig. 16. A heat exchanger using the flat pipe having the S-like shape can be obtained by connecting an inlet of a pipe-side fluid and an outlet of the pipe-side fluid to ends of the flat pipe. Since a fin of the heat exchanger in accordance with the present invention is formed by corrugating the wire-like heat conductive elements, a heat exchanger having a desired excellent heat transfer efficiency can be obtained by suitably determining the diameter of the wire-like heat conductive elements and the density thereof. Also, since the wire-like heat conductive element is used and the corrugating operation is used to make the corrugated and united body, it is possible to manufacture a fin having a precisely arranged density of the wire-like heat conductive elements. Further, since the fin includes the plurality of curved tops, a heat exchanger having the excellent heat transfer efficiency and less pressure loss can be obtained. Since in the method of manufacturing the heat exchanger in accordance with the present invention the corrugated and united body is joined to the pipe instead of fixing each pin on a surface of a pipe as a conventional heat exchanger, it is possible to easily manufacture the heat exchanger having an excellent heat transfer efficiency. Examples: The present invention will be explained further by means of examples: An united sheet is manufactured from a plurality of wire-like heat conductive elements and a sheet of soluble resin by an apparatus illustrated in Fig. 2, a corrugated and united body is manufactured by corrugating the united sheet, and curved tops of the wire-like heat conductive elements in the corrugated and united body are exposed by removing the soluble resin on the curved tops. The manufacturing conditions when making the corrugated and united body are as follows Wire-like heat conductive element Shape in Cross Section: Circular Diameter: 200 µm Material: Copper Number of bobbins of wire-like element: 500 Feeding of Wire-like element: Withdrawing in direction perpendicular to bobbin axis while rotating bobbin Running speed of wire-like element: 1 m/min Reed: 25.4 pieces per 25.4 mm, i.e., pitch of reed: 1 mm Soluble resin sheet: Polyvinyl alcohol film supplied from Soko seiren Co., Ltd, thickness: 200 µm Heated press roller Temperature: 200°C Press: 20 daN/cm Corrugating machine: Accordion pleat machine supplied from Toyo Kokisha Height of corrugation: 8 mm Example 1 To manufacture a heat exchanger having a structure similar to that illustrated in Fig. 12, a circular pipe having a diameter of 7.94 mm and produced from a copper plate having a thickness of 0.30 mm was prepared. A tape-like corrugated and united body was wound around the circular pipe as shown in Fig. 8 and placed in an oven to braze the tape-like corrugated and united body to the circular pipe to produce a fin-pipe assembly. The soluble resin in the fin-pipe assembly was removed, and an inlet and an outlet of a pipe-side fluid are provided at both ends of the circular pipe, whereby a heat exchanger similar to the heat exchanger illustrated in Fig. 12 was obtained. Example 2 To manufacture a heat exchanger having a structure similar to that illustrated in Fig. 18, several corrugated and united body units were arranged in spaces between adjacent flat pipes having a minor axis of 5 mm and a major axis of 12.7 mm in cross section and made of a copper plate having a thickness of 0.65 mm, respectively, by a jig illustrated in Fig. 16, and placed in an oven to braze the corrugated and united body units to the flat pipes to produce a fin-pipe assembly. The soluble resin in the fin-pipe assembly was removed, and a header including an inlet and an outlet of a pipe-side fluid was provided at both ends of the flat pipes, respectively.

Claims: A method of manufacturing a pin-fin type heat exchanger having corrugated wire-like pin-fins as heat conductive elements, wherein curved tops of the corrugated wire-like heat conductive elements are joined at least at one side of the corrugated elements (3) to a pipe (12a), comprising a step of arranging a plurality of wire-like heat conductive elements (3) in parallel and spaced from each other, characterized by a step of temporarily fixing the plurality of wire-like conductive elements (3) in an arrangement such that they form a sheet (22) constituted of the wire-like heat conductive elements (3) and a temporary fixing material (11), a step of shaping the sheet (22) in a corrugated sheet (22a, 27), a step of joining curved tops of the corrugated sheet (22a, 27a) to a pipe (12a), and a step of removing the temporary fixing material (11). A method according to claim 1, wherein said temporary fixing material is a resin. A method according to claim 2, wherein said resin is a soluble resin. A method according to claim 3, wherein said soluble resin is a substance capable of being melted by heat. A method according to claim 3, wherein said soluble resin is a substance capable of being decomposed by heat. A method according to claim 3, wherein said soluble resin is a substance capable of being burnt by heat. A method according to claim 3, wherein said soluble resin is a substance capable of being dissolved by a chemical. A method according to claim 3, wherein said soluble resin is a substance capable of being decomposed by a chemical. A method according to any of claims 2 to 8, said method further including a step of removing the resin of the wire-like heat conductive material on the curved tops applied on at least a side of the corrugated sheet.

Inventors: ISHIDA, MINORU, ISOBE, TOSHIO
Applicants: ASAHI KASEI KOGYO KABUSHIKI KAISHA
Application year: 1989
Main classification: F28F1
IPC codes: B21C37, F28F1, B23P15, F28D1