JP7789726B2 - Heat exchanger coil fin structure - Google Patents

Description

The present invention relates to a fin structure for a heat exchanger coil, and in particular to a fin structure for a heat exchanger that improves heat exchange performance.

As shown in Figure 1, conventional heat exchanger coils (so-called fin and tube) have fins attached to the main tubes 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 formed between the slits and the fin material on the fin surface to allow air to pass through. The slits are usually formed in parallel in the row direction (longitudinal direction) of the main tubes of the coil and in multiple row directions (left-right direction) of the left and right main tubes of the coil. Heat is exchanged as air passes through the slit surfaces and gaps.

Design Registration No. 1137226

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 column 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 edges of the slits (raised cuts) on the fin surface of the slit fins update the thermal boundary layer, suppressing its development 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, further improving 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 warp, which is an obstacle to improving performance by increasing the slit length.

When slits are placed in the fins between the main pipes of the coil, 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 typically very thin, ranging from 0.1 mm 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.

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 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.

To achieve the above objective, the slit fins provided on the coil of a heat exchanger have a slit fin structure that is 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, which are at least larger than the distance between the main pipes, have ribs that increase longitudinal rigidity.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 the key is to increase rigidity.

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 slits in the longitudinal direction is longer than the distance between the main pipes (Figure 4: X2 x 2). As the slits are involved in heat exchange by the increased length, the 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.

FIG. 1 is a perspective view of the overall appearance of a heat exchanger according to a first embodiment; FIG. 2 is a perspective view of an enlarged portion of the slit fin of FIG. 1; Figure 3 is a front cross-sectional view showing the relationship between the main pipe and the slit fins. 4 is a plan view of the slit of FIG. 3; 5(a) is a plan view of the long-side slit of FIG. 4, FIG. 5(b) is a side view of FIG. 5(a), A side view of the slit fin with the top surface of the slit flat and deflected. FIG. 7(a) is a plan view of a slit surface provided with a V-shaped cross-section rib, FIG. 7(b) is a cross-sectional side view thereof, and FIG. 7(c) is a front view thereof. FIG. 8(a) is a plan view of a slit surface provided with a rib having an arcuate cross section, 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. FIG. 9(a) is a plan view of a rib having a trapezoidal cross section provided 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. A bar graph showing the amount of deflection for a flat surface with a slit width of 2.7 mm and for each rib shape. 10 shows the results of an analysis 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%).

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

An embodiment of the present invention will be described with reference to the drawings.
First, we will explain the slit fin 321 (X4+X3 or X1+X2 in FIG. 4) that is longer than the slits of a normal slit fin of a heat exchanger in order to increase the heat exchange efficiency. In FIGS. 3 to 5, and particularly in FIG. 4, the inside of the two-dot chain line is the cut-up portion (X1 in FIG. 4) of the normal short short-side slit 322 of the conventional art. However, the premise of the present invention is that the diagonally shaded portion (X2 in FIG. 4) outside the two-dot chain line in FIG. 4 is the longer-than-normal portion (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 a problem that hinders performance improvement by increasing the length of the long side slit 321.
Therefore, by making the cross-sectional shape of the cut and raised slit not simply a flat surface 40 but a shape equipped 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 shapes of Figure 7 were created and analyzed using V-shaped groove ribs, Figure 8 circular groove ribs, and Figure 9 trapezoidal groove ribs.

[Rib Shape]
The shape of the rib 4 will be described with reference to FIGS.
In FIG. 6, the surfaces of the long side slits 321 of the slit fin 32 are flat 40 without ribs 4, but as will be described later, the long side slits 321 often have "flexed portions 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).
8(b), a rib 42 having 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 FIG. 8(b), the arc rib depth 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 arc shape clearly recognizable.
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 trapezoidal shape clearly recognizable.

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.
In [Graph 1] of Figure 10, the long side slits 321 are, from left to right, a slit 40 without a rib 4, a rib 41 with a V-shaped cross section, a rib 42 with an arc-shaped cross section, and a 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 portion 3212 on the surface of a flat 40 without a rib 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.

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 when a ribbed slit fin 40 is used on a conventional heat exchanger coil with a flat slit surface and a fin mounting pitch (FP) of 3.4 mm. If this point is taken as the reference point (100%), the pressure loss ratio is 120% and the heat exchange efficiency is 128% when the slit surface is fitted with V-shaped ribs 41. This results in a 28% increase in heat exchange efficiency, but also a 20% increase in pressure loss. Here, y3 represents the state where the slit surface is left with V-shaped ribs 41 but the fin mounting pitch is set to 4.1 mm to reduce pressure loss. It can be seen that in the y3 state, pressure loss is equivalent to that of a ribbed fin 40, while heat exchange efficiency alone can be increased to 113%. In other words, by adjusting the fin pitch with V-shaped ribs 41 on the slit surface, heat exchange efficiency can be increased while maintaining the same pressure loss as the conventional system.
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 x 2). Since the longer slits participate in 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 deflection, 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 be used, such as a combination of the above cross sections, or a wave-shaped cross section, as long as they increase rigidity.

1...Heat exchanger,
2... Coil, 21... Coil frame,
22...Header, 221...Cold and hot water inlet header, 222...Cold and hot water outlet 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 portion,
322... Short side slit, 33... Leg,
4. Rib, 40. No rib (flat surface), 41. V-shaped cross section rib,
42: Rib with arc-shaped cross section, 43: Rib with trapezoidal cross section

Claims (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 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 . 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 .