Heat exchanger coil fin structure

Abstract

To improve heat exchange efficiency by installing a long slit to a fin of a coil of a heat exchanger while preventing flexure from occurring in the slit.SOLUTION: The present invention discloses a slit fin structure, where a slit fin installed to a coil of a heat exchanger enlarges a distance more than a distance between main pipes adjacent in a direction of stages of the main pipes of coils and a coil is provided with a rib for increasing longitudinal rigidity in a slit with a distance that is larger than at least a distance between main pipes, where the coil is provided with the rib that has a cross-sectional V shape, a cross-sectional circular arc-shape, or a cross-sectional trapezoidal shape.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to a fin structure of a heat exchanger coil, and more particularly to a fin structure of a heat exchanger that improves heat exchange performance. [Background technology]

[0002] As shown in Fig. 1, a conventional heat exchanger coil (so-called fin and tube) has fins attached to the main tube of the coil, with raised slits cut into the fin surface to enhance heat exchange performance. As shown in Patent Document 1, for example, these slit fins have several parallel slits cut shorter than the distance between the main tubes of the coil, with gaps between the slits and the fin material formed on the fin surface to allow air to pass through. The slits are usually formed in parallel and continuously in the row direction (longitudinal direction) of the main tube of the coil and in multiple row directions (lateral direction) of the left and right main tubes of the coil. Heat is exchanged by air passing through the slit surfaces and gaps. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Design Registration No. 1137226 Summary of the Invention [Problem to be solved by the invention]

[0004] In conventional fin-and-tube heat exchangers consisting of coils and fins, slits are cut into the fin surface to improve heat exchange performance. These slits are formed on the fin surface between the main pipes through which air passes, and the fins are stacked with these slits formed continuously in the row direction (longitudinal direction) and row direction (left and right direction). These slit fins function as heat transfer plates that transfer the heat of the heat medium flowing inside the main pipe to the air, and the leading edge of the slits (raised cuts) on the fin surface of the slit fins updates the thermal boundary layer, suppressing the development of the thermal boundary layer and improving the heat transfer coefficient (leading edge effect).As a result, the longer the slit length (the longer the slit leading edge), the higher the heat transfer coefficient can be.When slits are placed between the main pipes of the coil, increasing the slit length brings the slit leading edge, which has a high heat transfer coefficient, closer to the main pipe, which also leads to further improvement of the heat transfer coefficient. For this reason, in slit fins, the longer the slit (the longer the leading edge of the slit), the higher the heat transfer coefficient can be; however, the longer the slit, the more residual stress after slit forming (press forming) occurs, which causes the slit to deflect, which is an obstacle to improving performance by increasing the slit length.

[0005] When slits are placed in the fins between the main pipes of the coil in this way, increasing the slit length brings the leading edge of the slit, which has a high heat transfer coefficient, closer to the main pipe, further improving the heat transfer coefficient. However, the thickness of the slit fins used in the main pipes of the coil is usually very thin, ranging from 0.1 to 0.2 mm. Therefore, when the slit length is increased, deflection occurs as shown in Figure 6. As air moves along the slit fin, the deflection narrows the gap formed by the slit, restricting the movement of air and resulting in reduced heat exchange efficiency.

[0006] This invention aims to solve the inconvenience of making the slits as long as possible to increase the heat exchange efficiency of the slit fins mentioned above, and aims to improve the heat exchange efficiency by preventing the deflection of the slits that occurs when long slits are provided in the fins of the heat exchanger coil. [Means for solving the problem]

[0007] In order to achieve the above object, the slit fin structure is such that the slit fins provided on the coil of a heat exchanger are larger than the distance between adjacent main pipes in the direction of the number of stages of the coil's main pipes, and the slits are at least larger than the distance between the main pipes, and the slit fin structure is such that ribs are provided to increase longitudinal rigidity, and the ribs may have a V-shaped cross section (or groove), an arc-shaped cross section (or groove), or a trapezoidal cross section (or groove), and in short, they may have increased rigidity. [Effects of the Invention]

[0008] The present invention has a slit fin structure in which the slit fins provided on the coil of a heat exchanger are longer than the distance between adjacent main pipes in the row direction. Therefore, unlike conventional slits which are shorter than the distance between the main pipes of the coil, the length of the slit in the longitudinal direction is longer than the distance between the main pipes (Figure 4: X2×2), and since the longer slits contribute to heat exchange by the same amount, heat exchange efficiency is improved. Furthermore, since slits that are larger than the distance between adjacent main pipes will bend if the top surface of the slit is flat, providing ribs on the top surface of the slit increases rigidity and reduces bending. The rib shape is a V-shaped (or groove) cross section, an arc-shaped (or groove) cross section, or a trapezoidal (or groove) cross section, and although it is easy to process, it produces a remarkable effect. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a perspective view of the overall appearance of a heat exchanger according to a first embodiment; [Figure 2] FIG. 2 is a perspective view of an enlarged portion of the slit fin of FIG. 1; [Figure 3] Figure 3 is a front cross-sectional view showing the relationship between the main pipe and the slit fins. [Figure 4] 3 , a plan view of the slit; [Figure 5] Fig. 5(a) is a plan view of the long-side slit in Fig. 4, Fig. 5(b) is a side view of Fig. 5(a), [Figure 6] A side view of the slit fin with the top surface of the slit flat and deflected. [Figure 7]Fig. 7(a) is a plan view of a slit surface with a V-shaped cross-section rib, Fig. 7(b) is a cross-sectional side view thereof, Fig. 7(c) is a front view thereof, [Figure 8] FIG. 8(a) is a plan view of a rib having an arc-shaped cross section on the surface of a slit, FIG. 8(b) is a cross-sectional side view thereof, FIG. 8(c) is a front view thereof, and FIG. 8(d) is a perspective view thereof. [Figure 9] FIG. 9(a) is a plan view of a rib having a trapezoidal cross section on the surface of a slit, FIG. 9(b) is a cross-sectional side view thereof, FIG. 9(c) is a front view thereof, and FIG. 9(d) is a perspective view thereof. [Figure 10] Bar graph showing the amount of deflection for a flat surface with a slit width of 2.7 mm and for each rib shape. [Figure 11] These are analytical results showing the relationship between the pressure loss ratio and heat exchange rate of a V-shaped cross-section rib when the pressure loss and heat exchange efficiency of a conventional fin without ribs are taken as the reference (100%). DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention provides a slit fin structure in which slit fins are provided on the coils of a heat exchanger and are larger than the distance between adjacent main pipes in the row direction, thereby improving the heat exchange performance of the heat exchanger, and further provides that the cross-sectional shape of the slits between the main pipes in the row direction, which are longer than at least the distance between the main pipes, is not simply flat, but has ribs to suppress deflection of the slits in order to increase rigidity. [Example]

[0011] An embodiment of the present invention will be described with reference to the drawings. First, we will explain slit fin 321 (X4+X3 or X1+X2 in Fig. 4) which is longer than the slits of ordinary slit fins in heat exchangers to increase the heat exchange rate. In Fig. 3 to Fig. 5, and particularly Fig. 4, the part inside the two-dot chain line is the cut-up part (X1 in Fig. 4) of the conventional, ordinary, short short-side slit 322, but the premise of the present invention is that the diagonal line part (X2 in Fig. 4) outside the two-dot chain line in Fig. 4 is the longer-than-ordinary part (X2 or X3) of the long-side slit 321. Incidentally, the fin material itself of the fins 3 of the heat exchanger coil 2 is thin, having a thickness of 0.1 mm to 0.2 mm, but in this embodiment it is 0.15 mm, the slit length is approximately 31 mm, and the fin pitch (FP) is 2 mm to 4 mm. Therefore, when processing into this slit shape, the longer the slit length (the longer the slit leading edge), the higher the heat transfer coefficient can be. However, the longer the slit length, the more residual stress after slit forming (press forming) will cause the slit to develop a ``deflection'' 3212 as shown in Figure 6, which is an obstacle to improving performance by increasing the length of the long side slit 321. Therefore, by making the cross-sectional shape of the cut slit not simply a flat surface 40 but a shape with ribs to increase rigidity, the rigidity in the longitudinal direction of the rib is increased and the "deflection 3212" is suppressed, and the slit shape in Figure 7 was created with a V-shaped groove rib, Figure 8 with a circular groove rib, and Figure 9 with a trapezoidal groove rib, and analyzed.

[0012] [Rib Shape] The shape of the rib 4 will be described with reference to FIGS. In FIG. 6, the surface of the long side slit 321 of the slit fin 32 is flat 40 without ribs 4, but as will be described later, the long side slit 321 often has a "deflection 3212". In FIG. 7, a rib 41 having a V-shaped cross section is provided on the surface of the long side slit 321 as shown in FIG. 7(b). In Figure 8, as shown in Figure 8(b), a rib 42 with an arc-shaped cross section is provided on the surface of the long side slit 321. Depending on the dimensions, the arc shape can become almost the same as a V-shaped cross section, so as shown in Figure 8(b), the depth of the arc rib of the fin 3 itself is 0.26 mm, the radius of curvature R is 1.65 mm, and the gap (height) between the fin 3 and the slit surface 3211 is 1.3 mm, making the shape clearly recognizable as an arc. 9(b), a rib 43 having a trapezoidal cross section is provided on the surface of the long-side slit 321. Depending on the dimensions, the trapezoidal shape can be almost the same as an arc-shaped cross section or a V-shaped cross section, so as shown in FIG. 9(b), the depth of the trapezoid is 0.2 mm, the width on the left and right sides is 1.2 mm at the base and 1.6 mm at the top, and the gap (height) between the fin 3 and the slit surface 3211 is 1.3 mm, making the trapezoid shape clearly recognizable.

[0013] The deflection was analyzed for the flat surface 40 on which these were formed, the V-shaped groove 41, the circular-hole arc-shaped groove (rib) 42, and the trapezoidal rib groove 43 (rib) with a slit width of 2.7 mm and a long-side slit 321 with a length of approximately 31 mm. The results are explained using the bar graph in Figure 10. [Graph 1] in Figure 10 shows the long side slits 321, from left to right: slit 40 without rib 4, rib 41 with a V-shaped cross section, rib 42 with an arc-shaped cross section, and rib 43 with a trapezoidal cross section.The amount of deflection of these long side slits with ribs 4 was analyzed, and the ratio to the deflected part 3212 on the surface of flat 40 without ribs was calculated and plotted as a bar graph. The analysis results show that when the deflection of the flat surface is 0%, and despite the thickness of the fin 3 itself being as thin as 0.15 mm, the rib 41 with a V-shaped cross section deflects only -34%, the rib 42 with a circular arc cross section deflects only -39%, and the rib 43 with a trapezoidal cross section deflects only -48%. In other words, while a considerable degree of rigidity is obtained overall, the rigidity increases in the order of the rib 43 with a V-shaped cross section, the rib 42 with a circular arc cross section, and the rib 41 with a trapezoidal cross section.

[0014] Next, the effect of the embodiment of the present invention will be explained with reference to graph 2 in FIG. In graph 2 of Figure 11, point y1 represents the relationship between pressure loss and heat exchange efficiency for a conventional heat exchanger with flat slit surfaces and ribbed fins 40, with a fin mounting pitch (FP) of 3.4 mm. This point is taken as the reference point (100%). With V-shaped ribs 41 on the slit surfaces, point y2 represents a pressure loss ratio of 120% and a heat exchange efficiency of 128%, a 28% increase in heat exchange efficiency, but a 20% increase in pressure loss. To reduce pressure loss, the V-shaped ribs 41 on the slit surfaces are retained, but the fin mounting pitch is increased to 4.1 mm, resulting in point y3. At point y3, pressure loss is equivalent to that of fins 40 without ribs, while heat exchange efficiency is increased by 113%. In other words, adjusting the fin pitch with V-shaped ribs 41 on the slit surfaces increases heat exchange efficiency while maintaining pressure loss at the same level as the conventional method. Here, the overall effect of the embodiment of the present invention will be explained. The slit fins provided on the coil of the heat exchanger have a slit fin structure that is larger than the distance between adjacent main pipes in the row direction. Therefore, unlike conventional slits that are shorter than the distance between the main pipes of the coil, the length of the slits in the longitudinal direction is longer than the distance between the main pipes (Figure 4: X2×2). Since the longer slits participate in heat exchange by the same amount, the heat exchange efficiency is improved. Furthermore, since slits that are larger than the distance between adjacent main pipes will warp if the top surface of the slit is flat, providing ribs on the top surface of the slit increases rigidity and reduces warping, even though the fin material 3a is only 0.15 mm thin. The rib shape is a V-shaped (or groove) cross section, an arc-shaped (or groove) cross section, or a trapezoidal (or groove) cross section, so a remarkable effect can be obtained despite the simple processing, but of course other ribs may also be used, such as a combination of the cross sections mentioned above, or a wave-shaped cross section, and any shape of rib may be used as long as it increases rigidity. [Explanation of symbols]

[0015] 1...heat exchanger, 2. Coil, 21. Coil frame, 22··Header, 221··Cold and hot water inlet side header, 222··Cold and hot water outlet side header, 23··Cold and hot water inlet, 24··Cold and hot water outlet, 25··Main pipe, 26··U-bend, 3··Fin, 3a··Fin material, 31··Through hole for coil main pipe, 32··Slit fin, 321··Long side slit, 3211··Gap between slit surface and fin (height), 3212··Slit deflection part, 322··Short side slit, 33··Leg, 4·· Rib, 40·· No rib (flat surface), 41·· V-shaped cross section rib, 42··Circular cross-section rib, 43··Trapezoid cross-section rib

Claims

1. A fin structure for a heat exchanger coil, characterized in that the slit fins provided on the coil of a heat exchanger are larger than the distance between adjacent main pipes in the direction of the number of stages of the coil, and in that the slits are larger than at least the distance between the main pipes, flat portions are provided on both the left and right sides of the slit surface, and ribs with arc-shaped cross sections are provided in the center of the left and right sides of the slit surface to increase rigidity in the longitudinal direction, the slits with the arc-shaped ribs have a slit width of 2.7 mm and a slit height of 1.3 mm, and the rib with the arc-shaped cross section has a rib depth of 0.26 mm and a rib radius of curvature of 1.65 mm.

2. A fin structure for a heat exchanger coil, characterized in that the slit fins provided on the coil of a heat exchanger are larger than the distance between adjacent main pipes in the direction of the number of stages of the coil, and in that the slits are larger than at least the distance between the main pipes, flat portions are provided on both the left and right sides of the surface of the slit, and ribs with trapezoidal cross sections are provided in the center of the left and right sides of the surface of the slit to increase rigidity in the longitudinal direction, the slits in which the trapezoidal cross section ribs are provided have a slit width of 2.7 mm and a slit height of 1.3 mm, and the trapezoidal cross section ribs have a trapezoidal cross section depth of 0.2 mm, a base dimension of 1.2 mm, and an upper dimension of 1.6 mm.

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