Inner fin and manufacturing method of the same

Abstract: An inner fin (5), which is formed of a thin plate of an aluminum alloy having a corrugated section in a widthwise direction, includes a plurality of crest surfaces (7) extending parallel in a lengthwise direction, and a plurality of trough surfaces (6) extending parallel in the lengthwise direction. The crest surfaces and the trough surfaces are connected together by inclined surfaces (8). The crest surfaces are provided with concavities (10-13,20-23), which are shifted form each other in the lengthwise direction so that the concavities formed in the adjacent crest surfaces (7) are not aligned on the same line in the widthwise direction. The inner fin inserted into the tube partitions the passages which communicate with each other through the concavities.

Description: The present invention relates to an inner fin for a heat exchanger, and in particular, to an inner fin fixedly inserted into a heat exchange tube and a manufacturing method of the same. JP-A-01 098 896 discloses an inner fin which is insertable into the heat exchanger tube having first and second inner walls extending parallel to each other in lengthwise direction. A plurality of crest surfaces extending parallel in the lengthwise direction and a plurality of trough surfaces formed between the adjacent crest surfaces and extending parallel in the lengthwise direction are provided, wherein inclined surfaces extending between the crest surfaces and the trough surfaces. JP-A-01 011 022 discloses a forming method for a corrugated fin comprising two forming rollers having grooves extending in axial direction of the rollers. The inner fin inserted into the heat exchanger tube in the prior art is formed of a thin plate, which can be inserted into an insertion aperture of the tube, and has a corrugated section in a widthwise direction. For example, as shown in Figure 12, a tube 1 having a fluid passage of a flat section accommodates an inner fin 2 formed of a thin corrugated plate, which has parallel crests and troughs having a height of h₀ and extending in a lengthwise direction of the tube. Figure 12 shows the inner fin 2 partially drawn out from the tube 1, but in a practical state, the inner fin 2 is completely inserted into the tube 1, and the crest surfaces 2a of the inner fin 2 is brazed to an inner wall of the tube 1. Passages for cooling medium are defined by inclined surfaces 2c, which extend between the crest surfaces 2a and the trough surfaces 2b, and the inner wall of the tube. These passages extend in the lengthwise direction of the tube and are partitioned from each other by the inner fin. According to the inner fin thus formed for the heat exchanger, the passages formed between the inner wall of the tube and the surfaces of the inner fin may be clogged with contaminant such as dust and/or residue (e.g., flux residue generated in a manufacturing step) in the cooling medium flowing in the passages. If one or some passages are clogged, a total flow of the cooling medium flowing through the tube 1 decreases, and thus a heat exchanger performance decreases correspondingly to the reduction of the volume of the heat exchange medium. An object of the present invention is to provide an inner fin, which can minimize reduction of the total flow of fluid in a tube and thus can prevent reduction of the heat exchanger performance even in such a case that passages partitioned by the inner fin are partially clogged, and to provide a manufacturing method of the same. Another object of the invention is to provide a manufacturing method for forming the foregoing inner fin by a simple manner. The inner fin of the present invention as defined in claim 1 has a corrugated section in a widthwise direction, and has concavities which are formed in the crest surfaces and are spaced from the first or second inner wall of the tube into which the inner fin is inserted. In a manufacturing method of an inner fin according to the invention, a thin plate is transported and formed by rotation and pressing of first and second forming rollers, and, in the forming operation, the plate is formed into a corrugated configuration in an axial direction of the rollers and simultaneously is formed to have concavities in crest surfaces of the corrugated plate. The invention further provides a forming apparatus for an inner fin having a pair of forming rollers for forming the inner fin, wherein the rollers have a plurality of parallel grooves formed in peripheral surfaces of the rollers, a plurality of parallel projections formed between the adjacent grooves, and a plurality of concavities formed in the projections. According to the inner fin of the invention, even if one or some of the passages, which are defined in the tube by the partitions, i.e., inner fin, are clogged due for some reason, the fluid in the clogged passage(s) flows through the concavities into the adjacent passage(s). Therefore, the fluid in the clogged passage(s) is avoided from being completely stopped, so that the reduction of the total flow can be minimized and the reduction of the heat exchanger performance can be suppressed. According to the manufacturing method of the invention, the concavities is formed simultaneously with making the corrugated configuration having the crest and trough surfaces. The advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1(a) is a schematic perspective view showing an inner fin according to an embodiment of the invention, and Figure 1(b) is a cross section taken along line A-A in Figure 1(a); Figure 2(a) is a fragmentary schematic enlarged view at a compressed scale in the lengthwise direction of an inner fin, showing an inner fin according to an embodiment of the invention, with a certain part cut away, and Figure 2(b) is a cross section taken along line B-B in Figure 2(a); Figure 3 is a schematic perspective view showing an inner fin according to an embodiment of the invention, which is partially drawn from a heat exchanger tube; Figure 4 is a schematic cross section showing an inner fin according to an embodiment of the invention, which is inserted into a heat exchanger tube; Figure 5 is a characteristic diagram for comparing an embodiment of the invention with a conventional example for comparison with respect to a relationship between degrees of clogging and heat releasing performances; Figure 6 is a schematic perspective view showing a forming apparatus for manufacturing an inner fin according to an embodiment of the invention; Figure 7(a) is a front view showing an upper roller of a forming apparatus according to an embodiment of the invention, and Figure 7(b) is a side view thereof; Figure 8 is an enlarged front view of a portion indicated by "E" in Figure 7; Figure 9(a) is a front view showing a lower roller of a forming apparatus according to an embodiment of the invention, and Figure 9(b) is a side view thereof; Figure 10 is an enlarged front view showing a portion indicated by "F" in Figure 9; Figure 11 is a schematic cross section for showing formation of an inner roller by upper and lower rollers; and Figure 12 is a schematic perspective view showing an inner fin in the prior art, which is partially drawn out from a heat exchanger tube. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the invention will be described below with reference to the accompanying drawings. Figures 1 - 4 show an embodiment, in which an inner fin of the invention is applied to a heat exchanger tube used in an air conditioner for an automobile. As shown in Figure 1(a), an inner fin 5 is formed of a thin plate which extends in a lengthwise direction and has a corrugated section in a widthwise direction. The thin plate is made of aluminum or aluminum alloy. In a plan view, trough surfaces 6 and crest surfaces 7 are connected together by inclined surfaces 8, and the trough surface 6 and the crest surfaces 7 are located alternately in the widthwise direction. The illustrated crest surfaces 7 are four in number and extend parallel in the lengthwise direction in the top view, as shown in Figure 1. In Figure 1(b), the crest surfaces 7 are designated by "7a", "7b", "7c" on, the concavities 10, 11 and 12 represented by solid line hatching are formed in the front surface of the inner fin 5. Similarly, concavities 20, 21, 22 and 23 represented by dashed line hatching are formed in the parallel crest surfaces of the opposite surface, i.e., rear surface. Since these concavities 20, 21, 22 and 23 are located at the side opposite to the front surface, they form convexities formed in the trough surfaces when viewed from the front side. Assuming that each crest has a height of h and the plate has a thickness of d, as shown in Figure 2(b), the height of the concavities 10, 11, 12, 13, 20, 21, 22 and 23 is determined such that the concavity 12 has the height of h/2 if measured from a center of the thickness of the plate. In connection with the height of the crest, concave lengths h1 and h2 shown in Figure 2(b) are determined as follows. The length h1 allows the fluid to pass through the concavity 12 between adjacent passages C and D, which are formed by inserting the inner fin 5 into the tube 1. The length 12 of the concavities formed in the rear surface is determined to allow flow of the fluid through a passage E located at the same position as the concavity 12 in the rear surface. In Figure 2(a), a distance δ between the lengthwise adjacent concavities 10 may be appropriately determined in accordance with the condition of use. Also, the number of the concavities 10, which are formed in one crest surface (i.e., 7a) of the inner fin 5, as well as the lengthwise length 10 of one concavity 10 may be appropriately determined in accordance with the condition of use. The inner fin 5 thus formed is fixedly inserted into the tube having a flat and oblong aperture. For example, as shown in Figure 3, the inner fin 5 is inserted into the flat tube 1. For the sake of clarity, in Figure 3, the inner fin 5 is shown to be partially drawn out from the tube 1. The inner fin 5 completely inserted into the tube 1 is brazed thereto with non-corrosive flux, for instance, potassium aluminum fluoride. An Al-Si-alloy material is adopted as a brazing material. Figure 4 shows a plurality of parallel passages, which are defined by the inner wall 1a of the tube 1 and the inner fin 5 and extend in the lengthwise direction of the tube. The adjacent passages C and D are partitioned by the inner fin 5. The passages C and D formed at opposite sides of the concavity 12 in the inner fin 5 communicate with each other through the concavity, as indicated by arrow. Therefore, the cooling medium flowing through the passages C and D can flow into and from the passages D and C through the concavity 12. For example, when the passage C is clogged with contaminant, the fluid in the passage C can flow into the passage D through the concavity 12. Therefore, it is possible to prevent significant reduction of the flow in a case of the clogging of the passage C with the contaminant. The crest surfaces 7a, 7b, 7c and 7d are provided with the concavities, which correspond to the foregoing concavity 12 and are spaced by predetermined distances from each other in the lengthwise direction. Therefore, even if one of the passages is clogged, the fluid can flow from the clogged passage into the adjacent passages through the concavities 10, 11, 12, 13, 20, 21, 22 and/or 23. The crest surfaces 7 are brazed to the inner wall 1a of the tube 1. Figure 5 shows a relationship between the heat releasing performance and the degree of clogging of the tube, into which the foregoing inner fin is inserted, with the contaminant. The degree of clogging represents a sectional area of the clogged portion of the passage with respect to the sectional area of the passage across the tube. In the inner fin of the embodiment used in this experiment, the concavities, which are formed in the crest surfaces corresponding to the crest surfaces 7 shown in Figure 2(a) and 2(b), each have the lengthwise length l₀ of 10mm, and are spaced lengthwise by the distance δ of about 205mm. The concavities 12 each have the length h1 of about 0.3mm between the bottom of the concavities and the crest surfaces 7. In the conventional example for comparison, when the degree of clogging of the tube accommodating the inner fing is 25%, the heat releasing performance is reduced 3% as compared with the heat releasing performance corresponding to the degree of clogging of 0%. In contrast to this, according to the foregoing embodiment, when the degree of clogging is 25%, the heat releasing performnace is substantially equal to that corresponding to the degree of clogging of 0%. The reason for this can be considered as follows. According to the inner fin of the foregoing embodiment, the cooling medium in the clogged passage can flow to the adjacent passages through the concavities, and consequently, in the case that the degree of clogging is 25%, the heat releasing performance is improved about 3% as compared with the conventional inner fin. Figure 6 shows a forming apparatus for manufacturing the inner fin. The forming apparatus 30 includes a pair of forming rollers 31 and 32 for applying the roll forming to a band plate 34. The rollers 31 and 32 have corrugated peripheral surfaces. The band plate 34 which is transported in the direction indicated by arrow is formed in a corrugated shape by the rollers 31 and 32, whereby the inner fin is formed, and then is cut into predetermined lengths. In this manner, the foregoing inner fin 5 is manufactured relatively facilely by the roll forming. Figure 7-10 show the configurations of the rollers 31 and 32. The upper roller 31 shown in Figures 7 and 8 is provided at its central portion of its peripheral surface with ten parallel and circumferential grooves. The roller 31 is also provided with low crest portions 41, which have centers circumferentially spaced by 45 degrees from each other and are disposed in convex portions between the adjacent grooves 40. The low crest portions 41, which are eight in number, are disposed in such positions that the adjacent two portions 41 are circumferentially spaced by 45 degrees and are located at the different but adjacent convex portions. Similarly, as shown in Figures 9 and 10, the lower roller 32 is provided with circumferential and parallel protrusions 42 corresponding to the grooves 40 and is also provided with eight low crest portions 43, which are circumferentially spaced by 45 degrees and are shifted in the axial direction. The upper and lower rollers 31 and 32 form the forming roller pair, as shown in Figure 6. A driving force is transmitted to the upper and lower rollers 31 and 32 for driving them with the synchronized phase. An example of the manufacturing method of the inner fin will be described below. The band plate is roll-formed by the forming apparatus 30 into the corrugated plate, which is then cut into predetermined lengths. The cut piece, i.e., inner fin is inserted into the tube, and is subjected to alkaline degreasing and to cleaning by immersing it in the flux solution. Then, the tube and the inner fin are fitted together, and the crest surfaces of the inner fin are brazed to the inner wall of the tube, whereby the tube accommodating the inner fin is completed. According to the manufacturing method of the inner fin, a pair of the rollers simultaneously form the widthwise corrugated configuration and the concavities for forming the bypass passages. The manufacturing steps are remarkably simple. In the forming operation, for example, as shown in Figure 11, half-worked (half-formed) portions 50, of which height is nearly half the height of the crest portion, remain in an inner fin 53 formed by the upper and lower rollers 31 and 32. Therefore, camber such as deformation or warpage, which may generate in the inner fin 53, is absorbed by the half-worked portions 50, and thus is not generated. In comparison between thicknesses t1 and t2 of a worked portion 51 and the half-worked portion 50, the thickness t2 of the half-worked portion 50 is larger than the other. According to the experiment, when the thickness t1 of the worked portion 51 is 0.2mm, the thickness t2 of the half-worked portion 50 is 3mm. According to the structures in which the inner fin manufactured by the method described above is inserted into the heat exchanger tube, if one of the passages is clogged, the cooling medium in the clogged passage flows through the concavities to the adjacent passages, so that the total flow of the cooling medium in the passages is minimized, and thus the degree of reduction of the heat exchanger performance can be minimized. Generally, in the operation for inserting and joining the inner fin into the tube, such a disadvantage may generated that the flux due to the brazing, chip due to the cutting or the like clog the passage. Even if such disadvantage generates, the reduction of the heat exchanger performance can be minimized, because the concavities can minimize the reduction of the flow of the cooling medium in the embodiment. The embodiment has been described in connection with the inner fin and tube, of which configurations are schematically shown. However, the entire lengths of the tube and the inner fin fitted therein are not restricted. Also, the number of the concavities, wave-shaped grooves, the spaces between the concavities and others are not restricted to those of the illustrated embodiment. According to the heat exchanger tube accommodating the inner fin of the invention, as described hereinabove, even when one or some of the passages defined by the inner fin are clogged for some reason, the fluid in the clogged passage(s) flows through the concavities to the adjacent passages, so that the reduction of the total flow of the fluid is suppressed, and thus the reduction of the heat exchanger performance is minimized. Also, according to the manufacturing method of the inner fin of the invention, a pair of the rollers form the concavities, which form the bypass passages, simultaneously with the basic formation, so that the inner fin can be facilely manufactured in one manufacturing step. Further, according to the manufacturing method of the invention, the concavities, which form relatively low portions in the inner fin, are formed discontinuously in the lengthwise direction. Therefore, the camber such as deflection and warpage can be prevented in the forming operation, and thus dimensional accuracy of the inner fin is improved, resulting in easy insertion and assembly of the inner fin into the heat exchanger tube.

Claims: An inner fin (5) which is insertable into a heat exchanger tube (1) having first and second inner walls extending parallel to each other in a lengthwise direction, comprising: a plurality of crest surfaces (7) extending parallel in the lengthwise direction; a plurality of trough surfaces (6) formed between the adjacent crest surfaces and extending parallel in the lengthwise direction; and inclined surfaces (8) extending between said crest surfaces and said trough surfaces; characterised by concavities (10-13) which are formed in said crest surfaces (7) and are arranged at a distance from each other in the lengthwise direction, wherein the height of the concavities (10-13) corresponds to a part of the height of the crests. An inner fin according to claim 1, wherein said concavities (10-13) are shifted from each other in the lengthwise direction such that said concavities formed in the adjacent crest surfaces (7) are not aligned linearly in the widthwise direction. An inner fin according to claim 1, wherein said inner fin (5) and said tube (1) are made of an aluminum alloy. An inner fin according to claim 3, wherein said crest surfaces (7) are brazable to said inner walls with a non-corrosive flux. A manufacturing method of an inner fin (5), wherein a thin plate is transported and formed by rotation and pressing of first and second forming rollers (31,32), and in the forming operation, said plate is formed into a corrugated configuration in a normal direction to an axis of said rollers and simultaneously is formed to have concavities in crest surfaces (7) of said corrugated plate. A forming apparatus for an inner fin (5) including a pair of forming rollers (31,32) for forming said inner fin, comprising; a plurality of parallel grooves (40) formed in peripheral surfaces of said rollers; a plurality of parallel projections formed between the adjacent grooves; and a plurality of concavities (41) formed in said projections. A forming apparatus for an inner fin according to claim 6, wherein said concavities are shifted in an circumferential direction of said rollers such that said concavities are not aligned along a straight line in an axial direction of said rollers.

Inventors: OGAWA YUJI, OTSUKA HARUHIKO, OGAWA, YUJI, OTSUKA, HARUHIKO
Applicants: NIPPON DENSO CO, NIPPONDENSO CO., LTD.
Application year: 1992
Main classification: F28F3
IPC codes: F28F3, F28F1, B21D13, B23P15