JP4671404B2 - Finned tube heat exchanger - Google Patents

Description

  The present invention relates to a finned tube heat exchanger.

  In general, a finned tube heat exchanger used in an outdoor unit such as a heat pump includes a plurality of plate-like fins arranged in parallel at predetermined intervals, and heat transfer tubes inserted at right angles to these fins. Configured. For example, the fin is provided with a plurality of slit surfaces cut and raised at a predetermined angle along the direction of airflow, with the direction perpendicular to the air inflow direction being the longitudinal direction. By doing in this way, heat transfer efficiency is accelerated | stimulated and heat exchange capability can be increased.

  However, once frost formation has occurred on the fin surface, clogging is likely to occur between the slits of adjacent fins and the like, and the ventilation resistance increases and the heat exchange capability decreases. For this reason, a method is known in which the refrigerant temperature in the heat transfer tube is lowered to suppress the reduction in heat exchange capacity during frost formation. However, when the refrigerant temperature is lowered, the power source on the refrigerant side, that is, the compressor Power consumption increases and driving efficiency decreases.

  On the other hand, a method of adopting a fin having a shape close to a plate fin with few slits and the like can be considered, but such a fin has a lower heat transfer coefficient than a fin having many slits, for example. In order to maintain the same performance as a fin with many slits, the heat transfer area must be increased, which is disadvantageous in terms of space saving of the housing and reduction of the fin material.

  Therefore, in order to suppress an increase in ventilation resistance during frosting while maintaining a high heat transfer coefficient, for example, slit surfaces are alternately cut up and down with respect to the fins, and slits are formed along the air flow direction. There has been disclosed a fin tube heat exchanger in which the number of cuts is increased and arranged in order to cause uniform frost formation on the entire fin (see, for example, Patent Document 1).

Japanese Patent Laid-Open No. 10-332162

  However, since the frosting state of the fin differs depending on the air inflow conditions, etc., as shown in Patent Document 1, the frosting state is predicted and the slit is formed to uniformly frost on the entire surface of the fin under any conditions. It is extremely difficult to select the arrangement and shape.

  Further, as in Patent Document 1, it is not preferable in terms of manufacturing fins to arrange the slits asymmetrically with respect to the fins. That is, in general, fins are formed by pressing dozens of thin aluminum strips together with a metal mold, and then separating and laminating them to penetrate the heat transfer tubes. For this reason, if the fin shape is asymmetric, the fin is distorted during the molding process, which makes it difficult to incorporate the heat transfer tube. In addition, since the air inflow direction is uniquely determined along with the asymmetry of the fin shape, there is a problem that the direction is limited when the heat exchanger is incorporated in a housing such as an air conditioner.

  This invention makes it a subject to implement | achieve the fin tube type heat exchanger which can suppress the increase in the ventilation resistance at the time of frost formation while being able to obtain a high heat transfer rate.

In order to solve the above problems, the present invention provides a plurality of plate-like fins arranged in parallel with each other at set intervals, a heat transfer tube penetrating these fins, and a planar shape formed by cutting the fins. In a finned tube heat exchanger that includes a plurality of slit surfaces and performs heat exchange between the air flowing between the fins and the refrigerant flowing in the heat transfer tubes, the slit surfaces extend in the direction intersecting the air flow. as the direction, the height of the slit surface is arranged in a staircase pattern from the upstream side to the downstream side of the fin, are formed in a chevron shape in cross section in the widthwise direction of the slit, the apex of the mound are positioned by rotating tilted axis becomes, the upstream end of the fin, have a rectifying surface formed by bending so as to guide the flows into the flow are formed between the slit plane adjacent fins path air, this flow path is M-shaped formed by formed Jo or W shape And wherein the door.

According to this, the air which passed the rectification | straightening surface is guide | induced into the flow path formed between fins, the flow direction is bent. The flow path is provided so that the height of the slit surface changes stepwise from the upstream side to the downstream side of the fin, that is, is inclined with respect to the planar direction of the fin. For this reason, while the distance through which air flows becomes long, the one part branches off from the clearance gap of the adjacent slit surface. That is, since the transmission area is increased during non-frosting, a high heat transfer rate can be obtained, and during frosting, even if the stepped portion is clogged between adjacent slits, Since the flow path through which the main flow flows is secured, an increase in ventilation resistance can be suppressed. In addition, since the slit surface is formed in a mountain-shaped cross section in the short direction of the slit, a vortex flow is generated in the mountain-shaped concave portion even if the ventilation resistance is slightly increased, and the convex portion is predetermined with respect to the air flow. Therefore, the temperature boundary layer becomes thinner and the heat transfer coefficient is promoted. Furthermore, since the slit surface is rotationally inclined with respect to the peak of the mountain shape, the ventilation resistance is further reduced.

  In this case, it is preferable that the slit surfaces of adjacent fins are arranged at regular intervals from the upstream side to the downstream side of the fins. According to this, since the distribution of the slits can be made dense in the direction orthogonal to the direction of the air flow, the air flow branched by hitting the slits can be increased, and the heat transfer rate can be improved.

  Moreover, it is preferable that a slit surface is formed in a fixed level | step difference from the upstream of a fin to the downstream. According to this, for example, even during frost formation, the ventilation resistance of the air flowing through the flow path can be made as small as possible.

Moreover, it is preferable that the height of the slit surface is formed symmetrically on the upstream side and the downstream side of the fin. That is, the air flow is M -shaped or W-shaped in the short direction of the slit, so that the flow path formed in a staircase shape is symmetric between the upstream side and the downstream side, and the heat exchanger is limited on both sides Can be incorporated into the housing without any problem. Further, since the distortion of the fin itself can be suppressed during the molding of the fin, productivity can be improved. Further, the slit surface and the rectifying surface are preferably formed by lifting in the same direction with respect to the fin. According to this, productivity can be further improved.

  ADVANTAGE OF THE INVENTION According to this invention, while being able to obtain a high heat transfer rate, the fin tube type heat exchanger which can suppress the increase in the ventilation resistance at the time of frost formation is realizable.

(First embodiment)
Hereinafter, the finned tube heat exchanger according to the present invention will be described in detail with reference to the drawings. FIG. 1 is an enlarged plan view showing a main part of a finned tube heat exchanger according to the present invention, and FIG. 2 is a cross-sectional view taken along line AA of FIG. FIG. 3 is a perspective view showing the appearance of the finned tube heat exchanger according to the present invention. FIG. 4 is a diagram for explaining the air flow direction in FIG. 2.

  As shown in FIG. 3, the finned tube heat exchanger 2 of the present embodiment includes a plurality of plate-like fins 3 arranged in parallel at set intervals, and heat transfer tubes inserted orthogonally to these fins 3. 5 and is configured to exchange heat with the refrigerant flowing in the heat transfer tubes 5 by flowing air through the gaps between the fins 3. The fins 3 are arranged in, for example, two rows in the air flow direction, and the heat transfer tubes 5 are repeatedly bent in each row and penetrate the fins 3. Here, the fin 3 is made of a thin and long aluminum material, and includes a plurality of slit-like cut-and-raised portions (hereinafter referred to as slit 1 or slit surface 1) so that heat exchange efficiency is improved. .

  As shown in FIG. 1, a plurality of slits 1 are formed in the fin 3 with the direction intersecting the air flow direction as a longitudinal direction, and a slit group 7 is formed in the center of the fin 3. On the outside of the slit group 7, that is, on the upstream end and the downstream end of the fin 3, a rib surface 9 is formed so as to extend in the longitudinal direction of the fin 3 (vertical direction in FIG. 1). The rib surface 9 is formed wider than the slit surface 1 in the direction of air flow, and is formed by bending a cross section as will be described later. The collar 11 is formed by being raised along the peripheral edge of the heat transfer tube 11, and has a function of a support member that is in close contact with the heat transfer tube 11 and secures a distance between adjacent fins 3. The rib surface 9 is continuously formed in a direction orthogonal to the air flow without being cut off by the collar 11.

  Next, the configuration of the slit 1 formed in the fin 3 will be described in detail. The slit 1 cuts and raises the fin 3 in one direction to form a slit surface 1 parallel to the fin 3 and is continuously arranged along the air flow direction. As shown in FIG. 2, the height of the slit surface 1 is stepped along the direction of air flow, and the adjacent slit surfaces 1 are arranged so as not to have the same height. The slit surface 1 is formed with a certain level difference from the upstream side to the downstream side of the fin 3, and has a certain distance from the slit surface of the adjacent fin 3.

  Between the slit surfaces 1 of the adjacent fins 3, a flow path space 13 through which air flows is formed. On the upstream side of the flow path space 13, a rib surface 9 is formed by being bent at a predetermined angle so as to guide the incoming air into the flow path space 13. In addition, a rib surface 9 that is bent at a predetermined angle is similarly formed on the downstream side of the flow path space 13. Here, the heights of the slit surface 1 and the rib surface 9 are preferably arranged symmetrically on the upstream side and the downstream side of the fin 3. In the present embodiment, the height of the slit surface 1 is inclined in a stepwise manner in one direction from the upstream side to the central portion of the fin 3 and is arranged in a stepwise manner in the other direction from the central portion to the downstream side. However, it is not limited to this arrangement.

  Next, the operation of this embodiment will be described. FIG. 4 is a diagram illustrating the flow of air flowing through the flow path space 13 of FIG. The air passing between the rib surfaces 9 is largely bent in the flow direction by the rectifying action of the rib surfaces 9 and is guided to the flow path space 13 formed between the fins 3. The flow path space 13 changes from the upstream side to the downstream side of the fin 3 in the direction in which the fins 3 are stacked as the height of the slit surface 1 changes. That is, the air flow forms an M-shaped flow as a whole as shown by the arrows in the figure. For this reason, a part of the main flow 15 of the air flow is branched from the gap of the step of the slit surface 1 to form the branch flow 17, and the leading edge effect of cutting the temperature boundary layer is increased.

  Further, as the air flow direction changes, the air flow distance becomes longer, so the number of air branches from the main flow 15 increases. Thereby, while a high heat transfer rate is obtained at the time of non-frosting, the fall of heat exchange capability can be controlled also at the time of frost formation. Furthermore, even when clogging due to frost occurs between adjacent slits 1 during frost formation, it is possible to secure a flow path through which the main air flow 15 passes, and thus increase in ventilation resistance can be suppressed. Alternatively, since the time until the gap between the fins 3 can be lengthened, the defrost cycle can be extended, which is advantageous in terms of comfort and energy efficiency.

  FIG. 6 is a diagram for explaining the difference in air flow path between the present embodiment and a comparative example, where (a) represents a comparative example, and (b) represents the finned tube heat exchanger of the present embodiment. . In the present embodiment, since the wide rib surfaces 9 are provided at both ends of the fin, an air rectifying action works to generate an M-shaped flow path through the flow path space 13. A branch flow (not shown) is formed. Thereby, in addition to high heat exchange efficiency, the ventilation resistance at the time of frost formation can be suppressed.

  On the other hand, in the case of the comparative example, it is similar to the present embodiment in that the height of the rib surface is arranged in a stepped manner, but there is no wide rib surface at both ends of the fin, and all the slit surfaces have the same width. It has become. That is, the air guided to the flow path space goes straight in the direction of the arrow without being rectified, and passes through the slit provided at the same height on the extension. For this reason, the air heat-exchanged in contact with the slit is repeatedly brought into contact with another fin on the downstream side, which causes a reduction in heat exchange efficiency. In addition, if frost formation occurs between adjacent slits, the air flow is hindered, so the ventilation resistance increases rapidly. On the other hand, in this embodiment, since the air once cooled or heated can be prevented from coming into contact with the slit 1 on the downstream side, a temperature difference from the air in contact with the slit 1 can be secured, The exchange amount can be increased.

  FIG. 7 is a diagram illustrating the air flow during frost formation in the present embodiment. As shown in the figure, a frost layer 19 is formed in the gap between adjacent slits 1. As described above, when frost forms in the gaps between the fins 3, first, clogging occurs in the narrow gaps between the adjacent slits 1. However, according to the present embodiment, the flow path space 13 can be reduced even during frost formation. Since it can leave, acceleration frost formation can be prevented and the temperature fall of the refrigerant | coolant which flows through the inside of the heat exchanger tube 5 can be suppressed. Furthermore, since the flow path space 13 at the time of frost formation is M-shaped, the heat transfer coefficient is higher than that of the linear type, which is advantageous in maintaining the ability at the time of frost formation.

  FIG. 5 is an enlarged view of a portion B in FIG. A smaller step hs between adjacent slits 1 is advantageous in preventing the overlapping of the slit surfaces 1, but if it is too small, the air does not easily branch between the slits 1, and the leading edge effect is halved. Therefore, the step hs of the slit is preferably about 3 to 5 times the plate thickness of the fin 3. The slit step hs is preferably set at the same interval between all the slits 1. According to this, for example, even during frosting, the ventilation resistance of the air flowing through the flow path space 13 can be reduced.

  In addition, fins for fin-tube heat exchangers generally used in air conditioners and the like have a very thin plate thickness of about 0.1 mm. Therefore, the fins alone are weak in strength, and the fins 3 are stacked in an orderly manner to heat transfer tubes. 5 may be difficult to pass. For this reason, by disposing the rib surfaces 9 at both ends of the fin 3 without interruption, the rigidity of the fin 3 itself can be increased, the assemblability is improved, and the heat exchanger can be easily assembled. However, the height of the rib surface 9 (the level difference between the rib surface 9 and the adjacent slit surface, that is, hs) may be higher to increase the rigidity, but if it is too high, the air flow direction is greatly bent. Therefore, the ventilation resistance is amplified. For this reason, as shown in FIG. 5, it is preferable that the level | step difference hs of a slit is 20 to 30% of the fin pitch Pf (distance between the adjacent fins 3), for example.

  The rib surface 9 is preferably formed as wide as possible in the direction of air flow. Since the rib surfaces 9 are formed at both ends of the fin 3, the rib surfaces 9 are easily corroded under the influence of the air quality of the outside air. For this reason, when a slit, a looper, etc. are formed in both ends, there is a possibility of causing corrosion cracking, dropping off, etc., which is not preferable in terms of appearance. For this reason, the corrosion crack etc. can be suppressed by giving the rib surface 9 a predetermined width. In addition, since both ends of the fin 3 are farthest from the heat transfer tube 5, in general, a temperature change is likely to occur. However, the temperature difference can be reduced by forming the rib surface 9 of the present embodiment.

  Further, the height of the M-shaped (or W-shaped) air flow passing between the fins 3, that is, the height H of the fin 3 in the direction orthogonal to the air flow is also called a corrugated height, and is shown in FIG. As shown, for example, about 1.2 times the fin pitch Pf is suitable. This height H greatly affects not only the heat exchange performance during non-frosting but also the performance during frosting.

  FIG. 8 is a diagram illustrating the flow of air near the center of the fin 3 in FIG. Here, the direction of the airflow flowing through the gaps in the heat transfer tubes 5 is indicated by arrows. In the space sandwiched between the heat transfer tubes 5, as shown in the figure, a contracted air flow is generated and the flow velocity is increased, so that heat transfer is promoted. Therefore, the leading edge effect can be effectively utilized by arranging a large number of slits 1 at the center of such fins 3. Moreover, since the distance between the heat transfer tube 5 and the slit 1 is short, the temperature of the slit 1 hardly changes, and a high heat transfer rate can be realized.

  In the present embodiment, the slit surfaces 1 are arranged symmetrically on the upstream side and the downstream side of the fins 3. Therefore, it is not limited to the case where air flows in with one as an inlet, and the same effect can be exhibited even when air flows in with the other as an inlet. For this reason, for example, the heat exchanger can be incorporated into a housing such as an air conditioner without any restriction on the front and back.

  Further, in the step of punching and forming the fin 3 with a mold, when the slit surface 1 is an asymmetrical fin 3, residual stress is generated due to a partial difference in the elongation rate of the fin material. On the other hand, since the fin 3 according to the present embodiment is bilaterally symmetric, the residual stress is canceled and the curvature of the fin 3 is suppressed, so that the assemblability can be improved.

  FIGS. 9 (a) and 9 (b) correspond to the finned tube heat exchangers of FIGS. 6 (a) and 6 (b), respectively, and simulated temperature distribution and ventilation resistance when air was passed under the same conditions. Results are shown. In the figure, the shade of color represents the temperature distribution, and the darker the color, the lower the temperature. Here, air having a temperature of 2 ° C. and a wind speed of 1.5 m / s is supplied from the inlet side at one end (left side in the figure), and the air temperature and ventilation resistance at the outlet side at the other end are calculated. The fin is cooled to -5 ° C.

  According to this, the air temperature and the ventilation resistance on the outlet side are −4.17 ° C. and 13.35 Pa in the conventional configuration of (a), whereas in the present embodiment of (b), −4.36. The outlet temperature is lower than that of the conventional configuration, and the ventilation resistance is reduced. Further, as is clear from the arrows indicating the air flow, the air flows in the horizontal direction in the conventional configuration, so that the air repeatedly contacts the fins and reduces the heat exchange efficiency. Since the air bent at the surface forms an M-shaped air flow and at the same time a branch flow is formed, high heat exchange efficiency can be obtained.

  As described above, according to the present embodiment, by combining the rib surface 9 and the slit surface 1, for example, the air flow changes to an M shape, so that the heat transfer rate can be improved and frost formation is achieved. Even at times, an increase in ventilation resistance can be suppressed regardless of the frost layer distribution. In addition, it is possible to provide a finned tube heat exchanger having excellent fin processability.

  In the present embodiment, the rib surface 9 may be formed at least at the upstream end of the fin 3, but is preferably formed on both end surfaces in order to make the air flow smooth.

(Second Embodiment)
Next, another embodiment of the finned tube heat exchanger according to the present invention will be described. FIG. 10 is a diagram illustrating the flow of air passing through the flow path space in the present embodiment. In the present embodiment, as in the first embodiment, wide rib surfaces 21 are formed on both end surfaces of the fin 3. Inside the rib surface 21, the slit surfaces 1 are arranged stepwise from the upstream side to the downstream side of the fin 3. In the first embodiment, the height of the slit surface 1 is arranged symmetrically on the upstream side and the downstream side of the fins 3 so that the air flow is M-shaped, whereas in the present embodiment, the upstream side The slit surface 1 has an asymmetrical arrangement in which only one side is inclined from the side to the downstream side.

  According to the present embodiment, as in the first embodiment, the air rectified by the rib surface 21 is guided into the flow path space 23, and the branch flow 24 is generated from the linear main flow 22 as indicated by the arrows. . In this case, although the heat transfer rate is somewhat lower than that of the M-shaped air flow, the flow passage space 23 is ensured during frost formation, so that an increase in ventilation resistance can be suppressed.

(Third embodiment)
Next, as described with reference to FIG. 3, an example will be described in which a plurality of stacked fin groups are arranged in the air flow direction. FIG. 11 is an enlarged plan view showing a main part of the finned tube heat exchanger according to this embodiment, and FIG. 12 is a cross-sectional view taken along the line CC in FIG.

  In the present embodiment, as shown in the figure, the fins are arranged in two rows in the air flow direction, and the heat transfer tubes 5 are alternately arranged in a staggered pattern. FIG. 12 shows a cross-sectional shape of a fin formed by connecting two rows of fins, and does not have an M-shaped slit arrangement, but an M-shaped channel space is formed by stacking with other fins. 13 is formed.

  A rib surface 9 is formed on the upstream side and the downstream side of the collar 11, and a series of slit groups 7 are continuously formed in a stepped manner on the downstream side via the rib surface 9. A rib surface 9 is formed at the downstream end of the slit group 7. Here, the rising directions of the slit 1 and the rib are all the same as the rising direction of the collar. For this reason, it is excellent in productivity in the following points. That is, at the time of slit forming, the fins are usually moved sequentially in the mold and the fins as shown in the figure are formed through several steps, but the rising direction of the slit 1 is aligned with the same direction as the collar 11. Thus, the slit 1 can be smoothly moved in the mold without being caught. Further, it is not necessary to damage the fins 3 or to perform any special device on the mold.

(Fourth embodiment)
Next, a fourth embodiment of the finned tube heat exchanger according to the present invention will be described. FIG. 13 is a diagram illustrating the flow of air passing through the flow path space 28 in the present embodiment. The slit 26 of the present embodiment has a cross section in the short-side direction formed in a mountain shape, and other configurations are basically the same as those of the first embodiment.

  By arranging the slits 26 having a mountain-shaped cross section in this way, the ventilation resistance is somewhat increased. However, when the branch flow 32 is formed from the main air flow 30, the projections of the slits 26 against the air flow. While providing a predetermined angle, since a vortex | eddy_current arises in a recessed part, a temperature boundary layer becomes thin and can improve a heat transfer rate. Thereby, when air volume is ensured enough, it is preferable to form the slit surface 1 in a mountain shape.

  Furthermore, as shown in FIG. 14, each slit 26 may be arranged with the slit surface rotated and inclined with the peak of the mountain shape as an axis. Here, the relationship between the rotation angle of the mountain-shaped slit 26 and the air flow will be described. FIGS. 15A and 15B are diagrams for explaining the flow of air flowing around the mountain-shaped slit 23, that is, the flow of the branch flow 34. FIG. 15A shows the slit of FIG. 13, and FIG. 15B shows the slit of FIG. Yes. As shown in FIG. 15A, the air flow is separated around the mountain-shaped slit 26, which is a factor of the ventilation resistance. On the other hand, as shown in FIG. 15B, when the mountain-shaped slit 26 is rotated and tilted, separation of the air flow is suppressed, so that the ventilation resistance is reduced and the heat transfer coefficient is ensured. Can do.

  Therefore, as shown in FIG. 14, for example, by rotating the mountain-shaped slit 26 by a predetermined amount about the mountain-shaped apex so as to be symmetric between the upstream side and the downstream side, a high heat transfer coefficient is added. Thus, it is possible to provide a heat exchanger with low ventilation resistance even during frost formation.

It is a top view which expands and shows the principal part of the finned-tube heat exchanger which concerns on the 1st Embodiment of this invention. It is AA sectional drawing of FIG. It is a perspective view which shows the external appearance of the fin tube type heat exchanger which concerns on the 1st Embodiment of this invention. It is a figure explaining the flow of the air in the flow-path space of the cross section shown in FIG. It is an enlarged view of the B section of FIG. It is a figure explaining the difference of the air flow path of the 1st Embodiment of this invention, and a comparative example, (a) represents a comparative example, (b) represents the finned tube heat exchanger of this embodiment, respectively. Yes. It is a figure explaining the flow of the air at the time of frost formation of the cross section shown in FIG. It is a figure explaining the flow of the air near the center of the fin shown in FIG. It is a figure corresponding to each of Drawing 6 (a) and (b), and showing the result of having simulated about temperature distribution and ventilation resistance at the time of flowing air on the same conditions. It is a figure explaining the flow of the air which passes the flow-path space which concerns on the 2nd Embodiment of this invention. It is a top view which expands and shows the principal part of the finned-tube heat exchanger which concerns on the 3rd Embodiment of this invention. It is CC sectional drawing of FIG. It is a figure explaining the flow of the air which passes the flow-path space which concerns on the 4th Embodiment of this invention. It is the figure which arranged the slit surface in FIG. It is a figure explaining the airflow which flows through the transversal direction of the slit of FIG.13, 14, (a) represents the slit of FIG. 13, (b) represents the slit of FIG.

Explanation of symbols

1,26 Slit (Slit surface)
3 Fin 5 Heat Transfer Tube 7 Slit Group 9, 21 Rib Surface 13, 23, 28 Channel Space 15, 22, 30 Main Flow 17, 24, 32, 34 Branch Flow

Claims (5)

A plurality of plate-like fins arranged parallel to each other at set intervals, a heat transfer tube penetrating these fins, and a plurality of planar slit surfaces formed by cutting the fins, In the finned tube heat exchanger that performs heat exchange between the air flowing in between and the refrigerant flowing in the heat transfer tube,
The slit surface forms a direction intersecting the air flow as a longitudinal height of the slit surface is arranged in a staircase pattern from the upstream side to the downstream side of the fin, the cross-sectional mountain shape in the lateral direction of the slit And is arranged to rotate and tilt around the peak of the mountain shape,
An upstream end of said fin, have a rectifying surface formed by bending the incoming air to flow is formed between the slit surface of the fin adjacent channel to guide the flow path A finned tube heat exchanger, which is formed in an M shape or a W shape .   2. The finned tube heat exchanger according to claim 1, wherein slit surfaces of the adjacent fins are arranged at regular intervals from the upstream side to the downstream side of the fins.   3. The finned tube heat exchanger according to claim 1, wherein the slit surface is formed with a certain step from an upstream side to a downstream side of the fin. 4.   The fin tube heat exchanger according to any one of claims 1 to 3, wherein the height of the slit surface is symmetrical between the upstream side and the downstream side of the fin.   The fin tube heat exchanger according to claim 1, wherein the slit surface and the rectifying surface are formed by lifting in the same direction with respect to the fin.

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