JPS6332294A - Finned heat transfer pipe - Google Patents

Abstract

PURPOSE:To provide a heat transfer pipe which has a good heat transfer performance and is easy to manufacture and repair by providing the pipe at its both ends with a smooth mouth piece larger in diameter than its intermediate part and providing said intermediate part with multiple fins lengthwise whose height does not exceed the circular profile of the pipe including the outer surface of the mouth pieces at the ends, and further disposing partitioning plates at a suitable pitch in the grooves which are formed between the fins. CONSTITUTION:Partitioning plates 5 which partition grooves between the fins at a suitable pitch are normally made of the same material as of the fins 4, and are bonded to the pipe wall and fins 4. The outer diameter of the partition plates 5 is so selected as to be less than that of the mouth pieces 2. Cooling water passes through the interior of the heat conducting pipe 1, and condensing gas passes outside the pipe. The condensing gas outside the pipe is cooled by the cooling water in the pipe and condenses. Condensate 6 on the outer surface of the pipe and fins 4 is drained from the partition plates 5 as shown by an arrow, and does not flow to the pipe wall and fins under the same. Because of this, the condensate becomes droplets directly under the partion plates 5, and so, even if the heat transfer pipe is positioned vertically, there is less area covered by the condensate film, improving the heat transfer rate.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a finned heat exchanger tube having a large number of fins on its outer surface, and particularly to a heat exchanger tube suitable for use in a vertical condenser.

[Conventional technology]

Generally, a horizontal shell tube heat exchanger is often used in a condenser, and has a structure in which a cooling liquid flows inside the tube and a gas to be condensed, such as a condensed refrigerant, flows outside the tube. As for the tube used here.

Usually those with smooth surfaces are used.

[Problem that the invention attempts to solve]

However, in such conventional shell-tube heat exchangers.

Depending on the condensed refrigerant, the heat transfer coefficient on the outer surface of the tube is smaller than that on the inner surface, which causes a problem in that the overall heat transfer coefficient is reduced.

Let me explain this problem in more detail.

In the case of condensation, the film heat transfer coefficient α1 (-K
cal/rrr-h·”C) is expressed by the following formula.

Here, h: Height of vertical wall (m) Diameter of pipe (m) for horizontal pipe Δθ: Difference between condensation temperature and heat transfer wall temperature (C) r: Heat of evaporation of condensed refrigerant (Kcal/kg ) γ: Specific weight of liquefied refrigerant (
kg/rrr) λ: Thermal conductivity of liquefied refrigerant (Kcal/m-h-'C) η: Viscosity coefficient of liquefied refrigerant (kg-h/ff1) C1: Constant, 0.943 for vertical walls, 0 for horizontal pipes .725 As is clear from equation (1) above, as the height h of the vertical wall increases, the film heat transfer coefficient α on the outer surface of the tube decreases. To.

Conventionally, heat transfer tubes are arranged horizontally and the tube diameter is made small. In addition, when several heat transfer tubes are overlapped horizontally, the value of α decreases as it goes downward, and the value of α decreases as the number of double-layered tubes increases. Although this decreases to around 60% of the upper α1, the overall average heat transfer coefficient becomes larger than when the heat exchanger tubes are arranged vertically.

By the way, the latent heat of fluorocarbon-based refrigerants is less than 1/10 that of water vapor, and in conjunction with other properties, the heat transfer coefficient α is extremely small1. For example, when placed horizontally, it is 1600 to 2000 Kcal/ n?
It is about -h・℃. On the other hand, when water flows inside a pipe, the heat transfer coefficient between the water and the pipe wall is around 7000 Kcal/rrr -h -'C for a flow rate of 2 m/Sec, and 10000 Kcal for a flow rate of 3 m/Sec. /r
It reaches around rr-h・℃, which is several times larger than the outer surface of the tube.
It is unbalanced. Therefore, in order to improve the heat transfer coefficient of the heat exchanger tube, it is desirable to improve the heat transfer performance on the outer surface of the tube.

Conventionally, as a solution to this problem, a method has been known in which a large number of grooves are formed on the outer surface of the heat transfer tube perpendicular to the longitudinal direction, and the portion between each groove is used as a fin to increase the heat transfer area of the tube outer surface. It is being However, the fins formed in this way are low-height loaf-ins and cannot significantly increase the heat transfer area.Moreover, since the fins are low and the spacing between the fins is narrow, condensate tends to accumulate between them. The heat transfer coefficient α of the tube wall and fins was reduced, and the overall heat transfer performance could not be significantly improved.

It is possible to increase the heat transfer area by joining a large number of tall fins to a bare tube, but if the fins are made taller, it becomes difficult to connect the entire tube from the tube mounting hole on one tube sheet when manufacturing or repairing the heat exchanger. It is not possible to insert or remove it, which causes problems such as making manufacturing and repair work difficult.

The present invention has been made in view of such problems, and an object of the present invention is to provide a heat transfer tube that has good heat transfer performance when used in a fin-tube heat exchanger used as a condenser, and is easy to manufacture and repair. With the goal.

[Means for solving problems]

The present invention, which was made to solve the above-mentioned problems, has smooth cap portions at both ends of the tube with a diameter larger than the diameter of the intermediate portion, and the intermediate portion has a cylindrical surface including the outer surface of the cap portions at both ends. It has many fins in the longitudinal direction with a height that prevents them from protruding.
Furthermore, the heat exchanger tube with fins is characterized in that partition plates are provided at appropriate pitches in the grooves formed between each fin.

[Effect]

The above-mentioned finned heat exchanger tube has a smooth cap part at both ends with a diameter equal to or larger than the outer diameter of the intermediate fin, so when manufacturing or repairing a finned tube heat exchanger, 1 Similar to a normal smooth tube without fins,
The entire heat exchanger tube can be inserted and removed from the tube attachment hole temporarily formed in the tube, making manufacturing and repair work easier.

Furthermore, when the finned heat exchanger tube is arranged vertically and configured to condense on the outer surface of the tube, the partition plate provided between the fins will discharge the condensed liquid that adheres to the tube wall, fins, etc. above, and This prevents the condensate from flowing through the pipe walls and fins below the partition plate. This means that the value of h in the above equation (1) is not the total length of the heat exchanger tubes but the interval between the partition plates. Therefore, by appropriately selecting the distance between the partition plates, the heat transfer coefficient α can be increased compared to when the heat transfer tubes are arranged horizontally.

Since the heat transfer area on the outer surface of the tube can be increased by the fins and the partition plate, the heat transfer performance on the outer surface of the tube can be significantly improved. Therefore, when the heat transfer coefficient on the outer surface side is smaller than that on the inner surface of the tube (for example, when condensing a fluorocarbon-based refrigerant), it is possible to significantly improve the heat transfer coefficient based on the inner surface of the heat exchanger tube.

〔Example〕

The present invention will be described in detail below with reference to one drawing.

FIG. 1 is a longitudinal sectional view of a heat exchanger tube according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of the central portion of the heat exchanger tube. In the same figure, the finned heat exchanger tube is designated as a whole by reference numeral 1.

It consists of smooth cap portions 2 at both ends and a finned tube 3 in the middle, and the outer diameter of the cap portion 2 is large enough to fit the tube mounting hole in the tube plate. The outer diameter of the intermediate finned tube 3 is considerably smaller than the outer diameter of the two cap portions 2, and is typically reduced so that the outer diameter is between 60% and 70%. In the embodiment, 16 fins 4 are provided in the longitudinal direction and radially. The height of the fin 4 is selected so as not to be higher than the cylindrical surface including the outer surface of the base portion 2 at both ends. In addition.

The outer diameter of the intermediate finned tube 3, the height of the fins 4, etc. are appropriately selected depending on the heat transfer coefficient of the target refrigerant, the cost of cooling water, etc. The cap portion 2 and the intermediate finned tube 3 shown in FIG. 1 can be integrally manufactured by rolling the intermediate portion of a tube material having the same diameter and thickness as the two cap portions 2. Note that the fins 4 do not necessarily have to be formed integrally with the tube body, and may be welded, filtered, or fitted into machined grooves and tightened.

In this case, the fins are made of a material with high thermal conductivity.

Further, the cap portions 2 at both ends and the intermediate finned tube 3 are not limited to being integrally formed as described above, but may be joined by welding, the filter portion, etc. FIG. 3 shows Example IA in that case, in which a cap portion 2A formed by drawing and bending one end at right angles is attached or welded to the end of an extruded or roll-formed finned tube 3A. It is an integrated system.

In Figures 1 to 3, reference numeral 5 denotes a partition plate for partitioning the grooves between the fins at an appropriate pitch.
It is usually made of the same material as the fins 4 and is welded, brazed, or adhered to the tube wall and the fins 4 with a thermally conductive adhesive. Note that the outer diameter of the cutting plate 5 is also selected to be equal to or smaller than the outer diameter of the mouthpiece portion 2. FIG. 2 shows a state in which fins 4 are attached radially around the finned tube 3, and the partition plate 5 is fully fitted into the groove between the fins 4. This partition plate 5
Since it also forms part of the heat transfer area.

Providing them densely has the effect of decreasing h and increasing α1 in the above-mentioned (1) 2, and increasing the heat transfer area, which is preferable from the viewpoint of heat transfer characteristics. However, on the other hand, the cost is high, so the value should be set at an appropriate value by taking both factors into account.

FIG. 4 is a sectional view showing a vertical condenser incorporating the finned heat exchanger tube 1 described above. 11 is an upper tube sheet, 12 is a lower tube sheet, 13 is a body, and 14 is an end plate. The heat exchanger tube 1 has a tube plate 11.
It is inserted and fixed into the 12 tube mounting holes and arranged vertically. A cooling water inlet 15 is attached to the end plate 14, and a cooling water discharge passage 16 is formed below the tube plate 12. On the other hand, the shell 13 is provided with a condensed gas inlet 17 and a condensed liquid outlet 18 .

In the vertical condenser configured as described above, cooling water passes through the inside of the heat transfer tube 1, and condensed gas passes outside the tube. The condensed gas outside the tube is cooled by cooling water inside the tube and condensed. The condensed state at this time is shown in an enlarged scale in FIG. FIG. 5 is an enlarged view of part A in FIG.
is discharged from the partition plate 5 as shown by the arrow, and does not much flow into the tube wall or fins below. For this reason,
'Droplet condensation will occur directly below the partition plate 5,
Even if heat transfer tubes are used vertically, there is less film condensation and the heat transfer coefficient can be increased.

FIG. 6 shows a modification of the partition plate. This partition plate 5A is installed with a slight inclination to the pipe wall to make it easier to drain the condensate, further reducing the accumulation of condensate in the groove between the fins and improving the heat transfer coefficient. can.

FIG. 7 shows a partition plate that is easy to install.

The partition plate 5B of this embodiment consists of a partition plate part 7 located in the groove between the fins 4 and a ring part 8 connecting the partition plate part 7, and the manufacturing process thereof is shown in FIGS. 8, 9, and 10. Shown below. Figure 8 shows the (J cutting plate 5B) before installation, and shows the partition plate part 7.
and a ring portion 8.

This partition? li 5 B is formed by punching a plate material of an appropriate thickness using a press. As shown in FIG. 9, this partition plate 5B is wrapped around the finned tube 3 and the 9 positions are well aligned, and both ends 9 are butt welded, or the ends 9 are butted and welded in advance to form a ring shape. 9 Fit it into the finned tube 3 as shown in Figure 9. Next, the partition plate portion 7 is positioned between the fins 4, folded into the groove between the fins as shown in FIG. 10, and welded or brazed as required. As a result, the structure shown in FIG. 7 is formed. In this case, the ring portion 8 also acts as a heat transfer area, although the fin efficiency is slightly reduced, so it may be added to the heat transfer area in consideration of this. Note that the ring portions 8 may be slightly overlapped and spot welded.

Below, nine detailed explanations of the present invention will be given.

Example I A heat exchanger tube having the shape shown in FIGS. 1 and 2 and having the following dimensions was manufactured.

Outer diameter of mouthpiece: 20 m Fin height: 4.1 Thickness: 0.5 N Center tube outer diameter: 12 mm Tube inner diameter: 10 mm Partition plate pitch: 201 m Effective length: 1 m The heat transfer area inside and outside of this finned heat transfer tube is as follows: That's right.

+11 Tube outer surface fin surface area -0,136rr+/m Pipe surface area -0,030〃 Partition plate surface =0.022〃 Total -0,188rd/m (2) Tube inner surface inner area -0,0314rtr/m Therefore, the area outside the tube/the area inside the tube is -5,99#6.

This finned heat exchanger tube was arranged vertically, and the flow rate of the cooling water in the tube was set to 'l m/Sec, and was used for condensing R-12.

When the heat transfer coefficient was measured, the heat transfer coefficient of the entire heat exchanger tube (based on the inner surface of the tube) was 4210 Kcal/rrr-h-°C.

The heat transfer coefficient on the inner surface of the tube is approximately 7000 Kcal/rrr-h ・"C for a flow rate of 2 m/Sec, so the heat transfer coefficient on the outer surface of the tube is calculated from the Kono value and the heat transfer coefficient. And, the heat transfer coefficient on the outside surface of the tube is based on the unit area of the inside surface of the tube.

α-10970Kcal/nf-h・'C.

Comparative Example ■ For comparison, the heat transfer characteristics were determined when a loaf-in type heat transfer tube with the dimensions shown below was placed horizontally.

Fin outer diameter 18.75 in l Inner diameter 15.85 dragon Pipe inner diameter 13.55 ms Number of fins: 750 fins/m The heat transfer area inside and outside the tube of this heat transfer tube is as follows.

(11 Pipe outer surface side fin surface area - 0,1182 rtr/m Pipe outer surface -
0,0498" Total = O, 1680 rrr/m (2) Inner area on the inner surface of the tube = 0.04257 n?/m Therefore, the outer area of the tube/the inner area of the tube - 3,95 = 4.

This loaf-in type heat transfer tube was placed horizontally, and the same amount of cooling water as in Example 2 was passed through the heat transfer tube to condense R-12 and measure the heat transfer coefficient. The heat transmission coefficient of the heat exchanger tube as a whole (based on the inner surface of the tube) was 2640 Kcal/r+f·h·°C. However, this value is based on the case where only IN tubes are arranged, and in an actual condenser, the heat transfer tubes are stacked in multiple layers, so the average heat transfer coefficient is smaller than the above value, and is usually about 20% lower. Considering, the average heat transfer coefficient when arranged in multiple layers is.

K,=2200Kcal/nf-h·℃.

By the way, in the case of Comparative Example I, the pipe inner diameter is larger than that in Example I, so the flow velocity when the same flow rate of cooling water as in Example I is flowed is 1.1 m /Sec. The heat transfer coefficient on the inner surface of the tube is a flow rate of 1.1 m/Sec.
4,600 Kcal/n (-h ・'C), so from this value and the average heat transfer coefficient, the heat transfer coefficient on the outside surface of the tube is calculated. What is the heat transfer coefficient on the outer surface?

α-4850Kcal/n (-h・”c.

As can be clearly seen by comparing Example I with Comparative Example ■,
The heat transfer coefficient of Example (2) is approximately 1.9 times higher than that of Comparative Example (2), and the heat transfer coefficient on the outer surface of the tube is approximately 2.2 times higher than that of Comparative Example (2).

〔Effect of the invention〕

As is clear from the above description, the finned heat exchanger tube of the present invention has a cap portion at both ends with an outer diameter equal to or larger than the fin outer diameter. Easy to install or pull out from the tube sheet for repair. Furthermore, this finned tube increases the heat transfer area with the fins on the outer surface, and by providing a partition plate, the heat transfer characteristics on the condensing side when used vertically and for condensation are improved, and the overall heat transfer is improved. This has the effect of improving the rate.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view of a heat exchanger tube according to an embodiment of the present invention. Figure 2 is a cross-sectional view of the intermediate part thereof, Figure 3 is a longitudinal cross-sectional view of a part of a heat exchanger tube according to another embodiment, and Figure 4 is a longitudinal cross-section of a vertical condenser using the heat exchanger tube of Figure 1. The top view and Figure 5 show the condensation state in the condenser, and the enlarged sectional view of part A in Figure 1, Figures 6 and 7 are the same as Figure 5 showing a modified example of the partition plate. The partial sectional views, FIGS. 8, 9, and 10 are explanatory diagrams showing the process of manufacturing the partition plate 5B of FIG. 7. 1 - Heat exchanger tube with fins 2 - Base part 3 - Tube with fins 4 - Fins 5 - Partition plate 6 = - Condensate 11.12 - Tube plate 13 - Body 15 - Cooling water population 17 - Condensed gas inlet 18 - Condensate outlet Fig. 1 Fang 3 Fig. Fang 6 Fig. Fang 7

Claims (1)

[Claims] The tube has a smooth cap part with a diameter larger than the diameter of the middle part at both ends, and a fin in the middle part has a height such that it does not protrude from the cylindrical surface including the outer surface of the cap parts at both ends in the longitudinal direction. A finned heat exchanger tube having a large number of fins, and further comprising partition plates provided at appropriate pitches in grooves formed between each fin.