JPS62142995A - Heat transfer pipe with inner surface spiral groove - Google Patents

Abstract

PURPOSE:To provide a high functional heat transfer pipe excellent in the evaporation function without increasing the pipe working cost and the like but with little effect of a plug expanding operation, by forming a fin configuration having a small vertical angle into a trapezoidal shape having a small tip end width, and suitably selecting the dimension on the tip end side and the dimensional ranges of the vertical angle, groove area and the like. CONSTITUTION:A spiral groove 2 having a substantially U-shape in section is provided in the inner surface of a pipe 1. The relationship (Hf/Di) between the depth (Hf) of the groove 2 and the minimum diameter (Di) of the pipe is selected to 0.02-0.03; a helix angle (beta) with respect to the tubular axis of the groove 2 to 7-30 deg.; the relationship (S/Hf) between the shaft rectangular sectional area (S) and the groove depth (Hf) to 0.25-0.40; the vertical angle in the groove rectangular section of a trapezoidal fin 3 having a small vertical angle and positioned between grooves to 25 deg.-50 deg.; the length of a flat portion on the fin tip end to 0.02-0.10mm; and the radius at each of the corner parts on both sides at the fin tip end is set to 0.2mm or less. The configuration of the fin 3 becomes beforehand close to that after the plug expanding operation upon assembling the heat exchanger, and the heat transfer ratio is improved without increasing the manufacture cost.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applicable to applications in which the fluid in the pipes transferred by pump means undergoes a phase change in a heat exchanger such as an air conditioner, a refrigerator, or a boiler. The present invention relates to the improvement of a suitable internally grooved heat exchanger tube (hereinafter referred to as "internally grooved tube").

[Prior art and its problems 1 An internally grooved tube is a metal tube such as a steel tube with a large number of spiral grooves provided on its inner surface. Since the specifications of the groove portion of this internally grooved tube have a profound effect not only on the heat transfer characteristics of the grooved tube but also on its manufacturing cost, various specifications have been proposed in the past.

Among these, a groove having a generally U-shaped cross section separated by fins having a triangular cross section with a relatively small apex angle is used as it is practical. However, one drawback of this internally grooved tube is that the tips of the triangular fins with small apex angles formed on the inside are easily deformed during plug expansion work when assembling the heat exchanger. In the case of copper, the generation of copper powder could have a serious impact on the frozen 1 day cycle. This metal powder is caught between the fine fins and is difficult to remove with normal cleaning operations, necessitating repeated and complicated cleaning operations.

[Object of the Invention] The object of the present invention is to provide a high-performance internally grooved tube with higher evaporation performance while reducing the drawbacks of the prior art described above and minimizing an increase in manufacturing costs. be.

[Summary of the Invention] The gist of the present invention is to make the fin shape with a small apex angle into a trapezoid with a small tip width, and to find a more effective size range for the size of the tip side, the apex angle, the groove area, etc. This is due to the selection.

That is, the present invention provides grooves ff for the minimum inner diameter (Di) of the tube.
(Hf) (7) Ratio (Hf/Di) is 0.02 to 0.0
3. The helix angle of the groove with respect to the tube axis is 7° to 30°, and the ratio (S/Hf) of the axis-perpendicular cross-sectional area (S) of each groove to the groove depth H[) is 0.25 to 0.40. A certain number of grooves have a substantially U-shaped cross section, and the fins located in the grooves have an apex angle of 30° to 50° in a cross section perpendicular to the grooves, and a flat length of 0.02 to 0.5° at the tip. It is characterized by a trapezoidal cross section with a radius of 0°02s or less at the corners on both sides of the tip.

Next, we will discuss the significance of each numerical value.

(1) Regarding the influence of full depth Groove depth (H = fin height) has a large influence on heat transfer performance in terms of increasing the inner surface area, promoting turbulence in the internal fluid, and the like.

Comparing the heat transfer coefficient and pressure loss with a smooth tube using the ratio of the groove depth H (= fin height) to the minimum inner diameter of the tube (Di),
When the value of Hf/Dt is gradually increased from zero, the heat transfer coefficient increases, but the increase is limited to Hf/Di = 0.
It becomes slow from around 0.02 to 0.03. On the other hand, the pressure loss shows a tendency to increase rapidly from around Hf/Di = 0.03.

Therefore, in order to obtain the highest possible heat transfer performance within a range where the pressure loss is not much different from that of a smooth pipe, the depth of the vortex (Hf) is the ratio of the minimum inner diameter (Di) of the pipe to H170i = 0,
It is desirable to set it as the range of 02-0.03.

(2) Regarding the influence of the groove torsion angle Based on the experimental results conducted under the most commonly used conditions, looking at the relationship between the groove torsion angle and the heat transfer coefficient ratio, it is found that during evaporation, the tube axis of the groove There is a slight peak in the torsion angle between 7° and 20°, and the performance tends to gradually increase as the torsion angle increases during rhombus contraction.

However, considering that this increase in the helix angle reduces the workability during tube manufacturing, it is preferable that the helix angle of the groove with respect to the tube axis is kept within a range of about 7° to 30°. Moreover, within this range, there is not much difference in evaporation and condensation performance, so it can also be applied to heat pump types that require a balance between both performances.

(3) Regarding the influence of groove cross-sectional area When the depth is constant, the behavior of the liquid film on the inner wall of the pipe (groove) becomes a major influencing factor on performance. In other words, if we look at the relationship between the cross-sectional area of the groove and the refrigerant flow rate by changing the groove width while keeping the groove depth constant, we can see that when the groove width is increased, the groove area becomes too large, the liquid film becomes thin, and the fins become thinner. The dry part of the tip no longer contributes to evaporation. Furthermore, if the width of the groove is made small, the groove area becomes too small, and the absolute amount b) of the liquid to be scooped up in the groove becomes insufficient relative to the amount of heating, resulting in a decrease in evaporation performance. On the other hand, regarding condensation, it is desirable to have as many dry areas as possible, as in the former case, but in the former case, the total surface area decreases significantly as the groove pitch increases, which tends to reduce both evaporation and condensation performance. becomes.

Therefore, there should be an optimal groove cross-sectional area value that balances the liquid film behavior and the inner surface area.

Therefore, as shown in Fig. 7, the influence of the cross-sectional area of the groove was examined by changing the pitch while keeping the cross-sectional shape of the fin constant. As a result, the evaporation performance was determined by
) has a peak around 0.3 (S/l-1f),
Compared to the rapid performance drop above this value, the performance drop below 0.3 is gradual. On the other hand, the condensing performance increases as the value of S/Hf decreases.

Looking at the trends in both of these performances, it seems that the smaller S/H[ is, the more stable the performance is, but the smaller S/Hf is due to the increase in the number of fins per unit length. It must also be remembered that the weight (hereinafter referred to as a motorcycle) increases considerably. Therefore, when considering performance and unit weight comprehensively, the groove cross-sectional area (S) is S/H in relation to the groove depth (Hf).
It is desirable that the value of f is in the range of 0.25 to 0.4.

(4) Shadow of fin shape! In general, triangular fins have a more or less rounded tip. This is because, considering practicalities such as manufacturing a grooved processing tool and maintaining processing viscosity, it is inevitable that the tips of the fins have a rounded shape. Moreover, the roundness of the fin tip increases as the fin apex angle decreases. Under typical specification conditions in which an internally grooved tube is used, the radius of the fin tip is 0.03 to 0.05 m.

When this internally grooved tube is expanded by about 6% from the normal tube outside diameter during plug expansion work when assembling a heat exchanger, the amount of decrease in groove depth (fin height) is approximately 0.02 mm, and as a result, The fins are trapezoidal with a flat section at the tip.

Therefore, if the fin shape is made trapezoidal in advance with this in mind, the surface pressure and amount of deformation at the tip of the fin can be reduced, and the rate at which metal powder is generated can be greatly reduced.

In this case, the length of the flat portion of the fin tip must be 0.02 mIR or more, but an excessive increase in the width of the fin tip naturally leads to an increase in unit weight, so the upper limit is preferably about 0.1 s. Also, ensure that the tip corner is flat,
Considering the flow of internal fluid, etc., the radius is 0.02 rN.
It is desirable that it be R or less.

In the results of experiments conducted under typical conditions in which an internally grooved tube is used, the fin tip width is 0.06 mm, and the fin 714 angle is changed, the fin apex angle (
When α) is in the range of 25° to 50°, the evaporative heat transfer coefficient is improved more than the difference in surface area. This seems to be because the fin shape maintains the flow rate of the refrigerant liquid flowing in the grooves, or because stirring has an effect of promoting heat transfer.

[Embodiments of the Invention] Examples of the present invention will be described below with reference to FIGS. 1 to 8.

As shown in FIGS. 1 and 2, a spiral groove 2 with a substantially U-shaped cross section is provided on the inner surface of the tube 1, and the depth of the groove is Hr).
The relationship (Hf/Di) with the minimum inner diameter (Di) of the pipe is 0.02 to 0.03, the torsion angle (β) of groove 2 with respect to the pipe axis is 7 to 30°, and the axis perpendicularity of each groove Cross-sectional area (S
) to the groove depth If) and (7) r%l(M (S/l-1f
) Te 0.25 to 0.40, the apex angle in the cross section perpendicular to the groove of the trapezoidal fin 3 with a small apex angle located at each position is 25° to 5
0°, the length of the flat end of the fin tip is 0.02 to 0.10 m
, the corners on both sides of the fin tip should have a radius of 0.02 mm or less. By doing this, the shape of the fins 3 can be made in advance to be similar to the shape after expanding the plug when assembling the heat exchanger.
The heat transfer coefficient can be improved with almost no increase in manufacturing costs. Figures 3 and 4 show the results of experiments conducted on copper internally grooved tubes under the following conditions.The heat transfer performance data shown below were measured under the same conditions unless otherwise specified. be.

(1) Refrigerant: R-22 (2 Boiling liquid pressure crab 4 Ko/cm2G (3) Boiling liquid flow FL
: 200Ka/m2S (4) Average dryness = 0.6 (5) Heat flux: 10 w/m” (
6] Steam pressure 14.6 o/cm2G (7) Inlet superheating degree: 50℃ (8) Outlet supercooling degree = 5℃ 1 Figure 3 shows the groove depth in the tube (fin height) and heat transfer coefficient The horizontal axis shows the minimum inner diameter (Di
The ratio of the groove depth (Hf) to ) is taken (If/Di), and the vertical axis shows the heat transfer coefficient and pressure loss as a ratio to that of a smooth pipe. According to this result, the increase in heat transfer coefficient is due to H
The value of f/D i is 0.02 to 0.03 i] and is slow from 0.02 to 0.03, but the pressure loss is 0,
It tends to increase rapidly from around 03, and 1-1f/D
It can be seen that high performance can be obtained in the range of i=02 to 0.03 in which the pressure loss is not much different from that of a smooth pipe.

Figure 4 shows the most common outer diameter of 9.52 mm and the smallest inner diameter (
Di) 8.52mm, groove depth Hf) 0, 20mm
We looked at the relationship between the helix angle (β) of the groove and the heat transfer coefficient ratio for the internally grooved steel pipe.

According to this figure, during evaporation, there is a slight peak between 7° and 20°, and during condensation, the performance gradually increases as the twist angle (β) increases. However, considering that an increase in the twist angle reduces workability during pipe manufacturing by 1?1, the twist angle (β) is 7
It is preferable to keep the culm degree within the range of 30° to 30°.

In Fig. 5, the outer diameter is 9.52 scale and Di = 8.52 m.

Hf = 0.20mm, number of grooves 60. Torsion angle (β) 18
3 shows experimental results for an internally grooved copper tube having trapezoidal fins with a fin tip width of 0.60 m and a varying fin apex angle (α).

The horizontal axis represents the fin apex angle (α), and the vertical axis represents the evaporative heat transfer coefficient as a ratio to the smooth tube. The conventional product as a comparative example has a rounded triangular fin with a radius of about 0.04 degrees and a small apex angle at the tip.

According to this figure, a performance improvement of about 10% is obtained when the fin apex angle (α) is in the range of 30° to 50′.

Since the difference in surface area between the trapezoidal fin and the triangular fin is very small, the performance improvement seen here is likely due to the following reasons.

That is, in the vicinity of the triangular fin and the trapezoidal fin, the sixth
As shown in the figure, the flow of evaporated liquid (a) that is scraped up along the inside of the groove 2 is influenced by the main flow (b) in the tube axis direction when it comes near the tip of the fin 3. try to get over it. At this time, in the case of a fin with a rounded tip (a), the fin moves over the groove smoothly (c), whereas in the case of a trapezoidal fin with a sharp corner (b), the fin flows in the direction of the groove without being able to get over the tip (c). ), and a flow that generates microscopic eddies (e) before and after overcoming the groove, and these seem to either maintain the flow velocity of the flow in the groove or have no effect on promoting heat transfer due to stirring.

Figure 7 shows the influence of the groove cross-sectional area on an internally grooved copper tube with a fin apex angle (α) of 40° and other dimensions other than the number of grooves as the previous example, but with a different fin pitch. It is. The horizontal axis of this figure shows the groove cross-sectional area (S) relative to the groove depth H[).
The ratio (S/Hf) is taken, and the vertical axis shows the heat transfer coefficient as a ratio to that of a smooth tube.

Note that the conventional product as a comparative example is the same as the previous example.

According to this figure, although the product according to the present invention has higher evaporation performance than the conventional product, it has the same trends and peaks for S/Hf as the conventional product, and the condensation performance is almost the same as the conventional product.

This seems to be because although the product of the present invention is inferior to conventional products in terms of liquid drainage at the fin tips, the area of the fin tips that is most effective for condensation is large, so these factors are offset. .

Figure 8 shows the overall cost benefit as S/l on the horizontal axis.
−1r is shown as a parameter. Here, assuming a fin-coil type heat exchanger for a room air conditioner, which is a typical application example, we will introduce the tube outer heat resistance including louver-slit aluminum fins, and the inner grooved copper tube with triangular fins with a large apex angle. It was assumed that the ratio of the tube inner thermal resistance was 75:25. Under these conditions, B is the total improvement in passage rate when switching only the tube from the conventional product with triangular fins with a small apex angle to the inventive product with trapezoidal fins with a small apex angle, and B is the unit weight reduction rate. Shown in A. The tube materials supplied for comparison were all made of copper and had the dimensions shown in Table 1.

Table 1 Here, if the length of the pipe material is shortened by the amount of heat transfer rate improving valve B, this will directly result in a cost advantage.

Furthermore, the reduction in the number of motorcycles in A will result in a near-zero cost benefit, if we do not take into account the decrease in workability. Therefore, A + B may be a rough guide to the merits for the pipe material purchaser.

Since the present invention focuses on improving performance while minimizing cost increase, S
In the region where the /Hf value is low, the reduction in unit weight compensates for the disadvantage, resulting in a 3-4% advantage compared to conventional products in the range of S/H[0.25-0.4. .

Naturally, the internally grooved tube according to the present invention has improved mechanical expansion using a tube expansion plug from a line contact of triangular fins to a surface contact of trapezoidal fins, and the surface pressure and deformation of the fin tips are reduced. Decrease.

When expanding the normal pipe outside diameter by about 6%, the amount of Hf reduction in the conventional product is 0.02m, while in the case of the invented product 7, it is 0.01j! lI+ and deformation m have been reduced by half,
Not only can the deterioration in heat transfer performance be minimized, but the amount of copper powder generated is also significantly reduced, and the impact on the refrigeration cycle can be minimized.

[Effects of the Invention] According to the present invention, it is possible to provide a high-performance heat exchanger tube that has excellent evaporation performance with almost no increase in tube processing costs, and is less affected by plug expansion work, and is suitable for heat exchanger tubes for air conditioners. Considering the high demand, it can be said that it is a highly effective heat exchanger tube.

Of course, if the high performance is used not only to make the heat exchanger compact, but also to improve thermal efficiency, the heat exchanger can have another advantage of low power consumption.

[Brief explanation of drawings]

Fig. 1 is an enlarged sectional view of an example of an internally grooved tube according to the present invention, Fig. 2 is a longitudinal sectional view, Fig. 3 is a diagram showing the relationship between groove depth and performance, and Fig. 4 is a graph showing the relationship between the helix angle and Diagram showing the relationship between performance. Figure 5 is a diagram showing the relationship between fin apex angle and performance. Figure 6 is a schematic diagram showing the flow in the pipe. Figure 7 is the relationship between vortex area, performance, and unit weight. FIG. 8 is a diagram showing the overall effect. 1... tube. 2... Groove. 3...Fin. Agent Patent Attorney Fujio Sato 1st year 9th! Sugaza 9 Suiseki, 1st time addition 9H 4th figure clear U angle β (@) 5th day fin ring 1! lKji) 6th (α) (b) 1 piece 1

Claims (1)

[Claims] (1) In a heat exchanger tube with internal spiral grooves suitable for use in which the internal fluid transferred by a pump undergoes a phase change, the ratio of the groove depth (Hf) to the minimum inner diameter (Di) of the tube (Hf
/Di) is 0.02 to 0.03, the helix angle of the groove with respect to the tube axis is 7° to 30°, and the ratio of the axis-perpendicular cross-sectional area (S) of each groove to the groove depth (Hf) (S/Hf ) is 0.25~
The fins located in these grooves have an apex angle of 30° to 50° in a cross section perpendicular to the grooves, and a flat end length of 0.02 to 50°. 0.
A heat exchanger tube with internal spiral grooves, characterized in that the corner portions on both sides of the tip have a trapezoidal cross section with a radius of 0.02 mm or less.