DE2951194A1 - HEAT TRANSFER TUBES - Google Patents

Description

DESCRIPTION

The invention relates to a heat transfer tube for condensers or water recuperators. It also refers to a heat transfer tube for various types of heat exchangers, such as steam condensers or water recuperators.

Generally in a power plant where energy goes into circulation of the working fluid such as steam is generated, or in a substance-refining chemical power station or in a factory in which substances are extracted, capacitors for conversion used by steam in liquid.

So far most used in such power plants WMrmetransfer- or transmission tubes in their horizontal Tube groups those that have a smooth surface, or ribbed tubes that have vertical or spiral ribs are formed in the longitudinal direction of the tube on the outer surface of the round tubes.

However, the coefficient of heat transfer of condensation on the surface of these tubes is not so great, so that a considerable amount Heating surface is required to achieve a desired amount of condensation.

The reason for this is based on the following fact. A factor that affects the "condensation heat flow coefficient" of the heat transfer tube is the well-known heat transfer inhibiting effect of the low heat transfer property of the liquid film that condenses on the heat transfer tube, even before the size of the intrinsic thermal conduction of a Metal material for the heat transfer tube or the condition for thermal transfer of the cooling medium. Hence became a Numerous proposals for improving transmission performance by reducing the condensation film, which is a major factor in the

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Is to inhibit heat transfer, or to reduce facility costs or installation area by downsizing the required heat transfer coefficient.

For example, a corrugated tube was developed in which a large number of vertical stripes are formed in parallel along the lengthwise direction of the heat transfer tube. In such a heat transfer tube, if the amount of condensation is small, the Performance compared to the conventional heat transfer tube with a smooth surface or one provided with fins, excellent. However, if the amount of condensation increases, since the condensate forms a film, especially since this film is on The lower part of the heat transfer tube becomes thick, the result of the provision of vertical stripes on the surface of the heat transfer tube being weakened, and this considerably reduces the performance of the condensation. Because of this, when using the corrugated tube on a condenser with a large amount of condensation requires various types of devices, as in the conventional smooth or ribbed tubes. As a result, a large number of operations or man-hours are required for manufacture.

Recently, a corrugated tube has been called a heat transfer tube proposed that has inclined grooves on the surface in the direction of a right-hand screw. Although this tube that usually has an inclination angle of 6 to 9 °, i.e. a pitch that is in the range of 8 to 12 mm for a tube with an outer diameter of 25.4 mm, has a slightly higher performance when the tube is placed horizontally is, when the corrugated tube is arranged vertically, there is no noticeable difference in performance compared to conventional smooth tubes, and the performance is quite low.

The object of the invention is to create a heat transfer tube that eliminates the disadvantages described and a remarkable

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worth high performance with vertical arrangement of the tube having.

This object is achieved by a heat transfer tube of the type described in the opening paragraph which, according to the invention, is characterized in that inclined inclined grooves in the direction of a left-hand screw are formed on the outer surface of the heat transfer tube installed in the northern hemisphere.

The heat transfer or exchange tube according to the invention has an inclined groove that runs in the direction of a left-handed Screw on the outer surface of the heat transfer tube is inclined. The inclined grooves close over the continuously a large number of aisles formed one. Since the oblique groove in the direction of a left-hand screw with a predetermined When the heat transfer tube is arranged vertically, it is inclined right downward when viewed from every direction covering 360 °.

Next, the function of the heat transfer tube of the present invention will be described. In general, as it condenses, it grows Steam on the outer peripheral surface of a vertically arranged smooth circular tube gradually increases the thickness of the condensate from the top to the bottom. The heat transfer coefficient of condensation increases as it approaches the lower Area of the heat transfer tube smaller. It has been observed that the condensate formed on the outer peripheral surface of the heat transfer tube in the northern hemisphere has the property of Has flowing down while rotating around the tube in the direction of a left-hand screw as the amount of condensation increases. It is believed that this is due to the force of a vector due to the effect of the Koriolis force generated by the rotation of the earth, when the flowing atmosphere of the condensing gas or the condensed liquid on the surface of the heat transfer tube is naturally along the wall of the Heat transfer tube after condensation and cohesion under the

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Effects of surface tension or the van der Waals ¹ force, which the material of the heat transfer tube possesses, flows down. Due to this property of the downflow of the condensate formed on the surface of the heat transfer tube, in the conventional heat transfer tube, in which vertical stripes or inclined grooves formed in the direction of a right-hand screw on the surface of the tube, the downflow of the condensate is not smoothly caused, and consequently, in many cases, the condensate on the heat transfer surface flows off in lumps, which worsens the heat transfer coefficient of the condensation.

In view of this fact, the invention proposes a method taking into account the fact that the condensate film or the drops have a tendency to flow down in the direction of a left-handed screw as described above, before, in the heat transfer capacity by causing a rapid condensate drainage downwards or by spraying it by a centrifugal force caused by increasing the speed of the flow rotating around the heat transfer tube is being improved.

Further features and expediencies of the invention result from the description of exemplary embodiments with reference to the figures. From the figures show:

Fig. 1 is a front view showing an example of the heat transfer tube of the present invention;

FIG. 2 is a sectional view of the heat transfer tube shown in FIG. 1 along a line XX;

Fig. 3 is a front view of a further embodiment of the heat transfer tube according to the invention;

FIG. 4 is a front view of a further embodiment of FIG heat transfer tube according to the invention;

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Pig. 5a is a front view of a further embodiment of FIG heat transfer tube according to the invention;

Fig. 5b is a front view showing a position in which the in

5a shown heat transfer tube is rotated by 90 ° with the tube axis as the center;

Fig. 6 is a longitudinal section of the heat transfer tube of the present invention used in the experiments of the curves in Fig. 7;

Fig. 7 is graphs showing an example of the heat transfer performance of the heat transfer tube of the present invention; and

8 shows a front view of a further heat transfer tube according to the invention.

There are now preferred embodiments of the invention below Described with reference to the figures.

First, one according to the present invention shown in FIGS. 1 and 2 will be described Heat transfer tube or heat exchange tube described. A long inclined groove 2 inclined in the direction of a left-hand screw is on the outer surface of the heat transfer tube 1 educated. In this example, the inclined groove 2 is continuously formed over a large number of turns. The intervals between the inclined grooves 2 can be varied according to the location of the heat transfer tube 1 as needed. When the heat transfer tube For example, if it is arranged vertically, the intervals in the lower area can be lengthened.

According to the experiments, an excellent result is obtained with a freon gas R- ₃ when the inclination angle A with respect to the horizontal surface of the inclined grooves 2 is, for example, about 32 °, and the pitch P was set to about 50 mm when the outer diameter D is Heat transfer tube 1 was approximately 25.4 mm. In the case of water vapor, it was found that the angle of inclination, which is favorable for the heat transfer capacity,

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chen with the freon gas R ₁ ^ is to be reduced. The depth of the inclined groove varies considerably according to the purpose of use, but a fairly favorable result is obtained when it is set to 1 to 3 mm. As for the shape of the inclined groove 2, it is advantageous to select a shape without any edge portion formed at the junction of the heat transfer surface and the inclined groove 2 so that the condensate is easily drawn into the inclined grooves 2 down from the surface 1a of the heat transfer surface, and the shape of the cross section is preferably selected so that the condensate that has flown into the inclined groove 2 is difficult to flow out of the groove toward the lower surface 1a.

The oblique grooves that point towards a left-hand screw are formed on the surface 1a of the heat transfer tube 1 according to the invention, agree with the type of flow of the condensed liquid on the surface 1a of the heat transfer tube 1 and the condensate flows down evenly. That is, the condensed liquid on the surface 1a of the heat transfer tube 1 first flows into the inclined groove 2 and then flows evenly along the inclined groove 2. This condensate flow increases its speed as it flows down and eventually sprays out of the inclined groove 2. As a result, the thickness of the condensed film is kept below a constant value along the entire length of the heat transfer tube 1, Moreover, the condensate is drawn in from the surface 1a of the heat transfer tube 1 to the inclined groove 2 because of the surface tension of the condensate, whereby the condensation on the surface 1a is promoted. Consequently, a similar phenomenon occurs a drop-shaped condensation on the surface 1a of the heat transfer tube 1. For this reason, the heat transfer coefficient of condensation of the heat transfer tube 1, which is in the 1 and 2 is considerably higher compared to the conventional smooth circular heat transfer tube.

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Although not shown in the figures, a vertical Groove is formed along the lengthwise direction of the heat transfer tube 1 will. Through this vertical groove, the condensate flowing around the inclined grooves is collected in the vertical groove and flows down quickly.

Fig. 4 shows a further embodiment of the invention Heat transfer tube. In this example, a smooth external surface area 3 is provided in which no inclined groove 2 fiber a predetermined length L is present. This example has essentially the same shape as that in FIG. 1 and Fig. 2 except that the region 3 is provided with a smooth external surface over a length L, and therefore the description of its shape can be omitted. The area 3 with a smooth external or outer surface can in one vertical capacitor can be used, for example, when separating plates by providing the area 3 in the smooth external Surface are to be arranged halfway through a number of parallel in the vertical direction arranged heat transfer tubes.

Fig. 5 shows a further embodiment of the invention Heat transfer tube. In Fig. 5b a position is shown in which the heat transfer tube from Fig. 5a by 90 ° around the central axis of the tube is rotated. In this example, inclined grooves 4 and 5 in the direction of a left-hand screw are independently and intermittently formed on each half of a flight, and these intermittently arranged inclined grooves 4 and 5 are formed by means of two long vertical grooves 6 and 7 provided along the lengthwise direction of the heat transfer tube 1. If such vertical grooves 6 and 7 are provided, the condensate flowing down around the inclined grooves 4 and 5 in the vertical Grooves 6 and 7 collected and flows down. As a result, the condensate can flow down to the lower portion of the heat transfer tube with extremely high efficiency. By combining these inclined grooves 4 and 5 and two vertical grooves 6 and 7

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the condensation performance on the surface 1a of the heat transfer tube 1 further improved. In the example shown in Fig. 5 it is also possible to provide a smooth surface area, in which neither inclined grooves 4 and 5 nor vertical grooves 6 and 7 are provided at a predetermined position as shown in FIG are. Although not shown in the figures, if a large number of fine vertical stripes are formed along the Longitudinal direction of the heat transfer tube 1 on the outer surface (excluding the area 3 with a length L) of the heat transfer tube 1 at a portion of the surface 1a, i.e., between the inclined grooves 2, 4 and 5, the heat transfer effect is further improved.

Each of the heat transfer tubes 1 shown in Figs. 1, 2, 4 and 5 as an example has a relatively thick tube wall, and each of the grooves of the inclined grooves 2, 4, 5 and the vertical grooves 6, 7 are usually machined shaped. However, when the wall thickness of the heat transfer tube 1 is small as shown in Fig. 3, the inclined groove 2 'is formed by extrusion using ^{rollers outside the inclined grooves 2 1} or by pressing. In the heat transfer tube 1 shown in Fig. 3, the region of the inclined grooves 2 * on the outside of the tube is formed by a strip protruding inside the tube as a result of a machining process, whereby an effect of heat transfer due to a swirling fluid flow in the tube through the protruding Strip is superimposed.

Furthermore, formation of the inclined grooves in the heat transfer tubes used in the aforementioned examples is also possible inclined double groove 2 "possible, the two parallel, closely arranged Grooves as shown in Fig. 8 is formed. As a result, if the overflows into the upper groove of the inclined double grooves condensate that has flown from the upper groove, the overflowing condensate into the lower groove or sprayed from the boundary

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the upper and lower grooves rich outwards. As a result, the condensate flowing into the inclined grooves is prevented from overflowing from the inclined grooves and flowing out to the lower heat transfer surface.

Although the inclination angle A of the grooves 2, 4 and 5 to be formed on the outer surface of the heat transfer tube 1 are corresponding the type of condensate is different, the condensate flow is made even by setting optimal angles of inclination A, taking into account the type of the tiling condensate Speed increases and the condensate is sprayed 2 a heat transfer similar to a teardrop-shaped condensation can be achieved.

Essentially, in the heat transfer tube of a condenser In practice, an excellent result was achieved with an inclination angle A of the inclined groove in the range from 14 to 35 °. Further a suitable pitch P or an interval of the inclined grooves corresponding to the inclination angle A is in the range of 14 to 35 degrees from 20 to 56 mm with an outer diameter D of the heat transfer tube of 25.4 mm.

In the heat transfer tube of the present invention constructed as described above, thick condensate films are hardly formed on the heat transfer tube, and even if they are formed, the condensate film becomes Film as a whole kept sufficiently thin. Consequently, with the heat transfer tube according to the invention, a considerably higher Heat transfer effect can be achieved compared with conventional heat transfer tubes with smooth surfaces, or with oblique grooves that have the direction of a right-hand screw.

The experimental heat transfer performance of the heat transfer tube of the present invention will now be described with reference to FIG the curves shown in FIG. 7 are described. The curves show that

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experimentally achieved value of the condensation of an inventive, In Flg. 6, which has a tube length of 1.6 m, Freon gas R _{11 is used} outside the tube and water is used inside the tube. As an excellent result, it has been found in the present invention that the dimensionless heat transfer coefficient is increased by 60% as compared with smooth tubes when the dimensionless flow rate of condensate is 1000 as compared with smooth tubes. In the curves shown in Fig. 7, (I) is a curve of values experimentally obtained with a heat transfer tube of the present invention described above, and (II) is a curve of values experimentally obtained with a smooth tube.

It should be noted that the invention does not extend to the above described embodiments is limited. A particularly remarkable effect is achieved when the invention Heat transfer tube is used for condensers, but also when used for other heat exchangers will be sufficient Effect achieved. The heat transfer tube of the present invention exhibits a remarkable effect when applied to multi-tube capacitors or heat exchangers and especially in vertical types. The heat transfer tube is not a circular tube but also includes elliptical or other tubes. In the case of an elliptical tube, it is advantageous to have a vertical groove on the outer surface along the direction of the to form the shorter axis of the ellipse.

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Claims (7)

Nikko Engineering Kabushiki Kaisha, Tokyo-to / Japan Heat transfer tube PATENT CLAIMS 1.Heat transfer tube for condensers or water recupators, "characterized in that inclined oblique grooves (2) on the outer surface in the direction of a left-hand screw the heat transfer tube (1) installed in the northern hemisphere. 2. Heat transfer tube according to claim 1 / characterized in that that the oblique grooves (2) inclined in the direction of a long-running screw continuously over a large number of turns are formed. 3. Heat transfer tube according to claim 2, characterized in that a long vertical groove (6) is formed along the longitudinal direction of the heat transfer tube. 4. A heat transfer tube according to claim 1, characterized in that the inclined grooves inclined in the direction of a lingsgangigen screw are formed independently and intermittently with an interval of half a pitch and these intermittent inclined grooves (4, 5) by two long vertical grooves (6 ) are connected along the length of the heat transfer tube. 030029/0673 5. Heat transfer tube according to one of claims 1 to 4, characterized characterized in that the inclined in the direction of a left-hand screw inclined grooves are formed as parallel double grooves (2 "). 6. Heat transfer tube according to one of claims 1 to 5, characterized characterized in that a large number of vertical stripes are formed along the lengthwise direction on the outer surface of the heat transfer tube between the oblique grooves inclined in the direction of a left-hand screw. 7. Heat transfer tube according to one of claims 1 to 6, characterized characterized in that a smooth outer surface (3) on which neither inclined grooves nor vertical stripes are formed over a predetermined length is provided. η 3 c ο 2 9 / η h