JPH0351997B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a heat exchanger tube in which outer surface fins in the tube circumferential direction are integrally formed on the outer surface of the tube at a predetermined pitch,
In particular, the present invention relates to a heat exchanger tube that can improve heat transfer characteristics on the outer surface of the tube. Conventionally, two types of heat transfer tubes used in heat exchangers and the like have been manufactured or devised: one for promoting condensation and one for promoting evaporation. Generally, heat transfer tubes for promoting condensation are equipped with a large number of outer surface fins in the circumferential direction of the tube, and heat transfer tubes for promoting evaporation are generally provided with a large number of cavities on the outer circumferential surface of the tube that communicate with the outside of the tube. Therefore, a structure that enhances the boiling function is common. It is common for condensers and the like to use heat transfer tubes to promote condensation, and for evaporators and the like to use heat transfer tubes to promote evaporation. In a heat transfer device in which condensation and evaporation occur simultaneously in one heat transfer tube, it is not desirable to apply the above-mentioned heat transfer tubes according to function. This is because, no matter which type of heat transfer tube is used, either the condensing function or the evaporation function will not be sufficiently performed. The present invention has been made based on such circumstances, and its purpose is to provide a system that has both a condensing function and an evaporation function, and also has either one of the functions. The object of the present invention is to provide a heat exchanger tube that has improved both functions compared to conventional heat exchanger tubes. In order to achieve such an object, in the present invention, outer surface fins in the tube circumferential direction are integrally formed on the outer surface of the tube at a predetermined pitch, and protrusions are formed on the inner surface of the tube that approximately correspond to the recesses. On the other hand, in a heat exchanger tube having a groove extending in the tube circumferential direction between the outer surface fins, a plurality of recesses are formed at a predetermined interval in the length direction at the bottom of the groove; The outer fin is provided with troughs at predetermined intervals in the fin length direction at a depth that does not reach the bottom of the groove, and the bottom portion of the trough is made to protrude toward the groove. A narrowed portion is formed in the groove portion. In this way, the outer surface fins and the valleys formed in the fins improve the condensing performance, and the presence of the narrowed portions makes it possible to improve the effective boiling action and thus the evaporation performance. Moreover, the recess formed at the bottom of the groove mainly contributes to further promoting the evaporation function. This organic combination of structures provides both condensation and evaporation performance, and compared to conventional heat exchanger tubes that only have one of them, the performance of both has been dramatically improved. It became possible to provide heat exchanger tubes. Hereinafter, some embodiments of the present invention will be described in detail based on the drawings. FIG. 1 is a partially cutaway perspective view showing an example of a heat exchanger tube according to the present invention, in which 2 is a heat exchanger tube made of a metal with good thermal conductivity such as copper, copper alloy, aluminum, or aluminum alloy. be. On the outer peripheral surface of the heat transfer tube 2, spiral outer surface fins 4 made of a tube material are integrally provided at a predetermined pitch. As a result, a groove 6 is formed between the outer surface fins 4 and extends spirally in the tube circumferential direction. As is clear from FIG. 3, the outer fins 4 are formed in the form of protrusions whose thickness becomes gradually thinner toward the distal end in the height direction. Further, the outer fins 4 are provided with troughs 8 at predetermined intervals in the fin length direction, and the formation of the troughs 8 allows the outer fins 4 to reach the bottom of the groove 6. It is cut out in an almost V-shape with a depth that cannot be reached. The remaining portions of the outer surface fins 4 where the troughs 8 are not formed are ridges 10, and the ridges 10 and troughs 8 are formed alternately in the fin length direction, and are adjacent to each other. The peak portions 10 and the valley portions 8 of the matching outer fins 4 have a corresponding positional relationship in a direction substantially perpendicular to the outer fins 4. Further, the mountain portion 10 has a substantially truncated quadrangular pyramid shape, and both side surfaces facing the groove portion 6 are curved and concave toward the groove portion 6 side. Such a configuration in which the peak portions 10 and the valley portions 8 are continuous increases the contact area for a predetermined fluid brought into contact with the outer surface of the tube, and is effective in improving condensation performance. Further, it is possible to prevent the condensed fluid adhering to the outer fins 4 from forming a thick liquid film on the surface of the outer fins 4, thereby promoting the separation of the condensed liquid from the outer fins 4. In addition, the valley part 8 is the heat exchanger tube groove part 6 as mentioned above.
Although it is formed at a depth that does not reach the bottom of the fourth
The depth of the valley portion 8 shown in the figure: h _t is the outer surface fin 4
If the height is h _f , it is desirable that h _t /h _f = about 1/4 to 3/4, and about 1/2 is preferable. In addition, the pitch P _t (see Fig. 2) of the valley portion 8 in the fin length direction is determined when the outer diameter of the heat exchanger tube 2 is, for example,
Around 20mm, and the height of the outer fin 4 is, for example, 1 to 3.
In the case of around mm, it can be said that P _t =0.5 mm to about 2 mm is a desirable range. Although it is not limited to such a range, if the pitch of the valley part _Pt is too small, it will be difficult to form the valley part 8, and if it is too large, it will not be possible to sufficiently increase the contact area with the outer surface of the pipe. This is because the effect of increasing condensation performance becomes smaller. Further, the bottom portions of the valley portions 8 are made to respectively protrude toward the groove portions 6 located on both sides.
That is, the outer surface fins 4 forming the bottom of the valley portion 8
The both side walls of are made to protrude laterally, respectively.
A protrusion 12 is formed. and,
The protrusions 12 of adjacent valleys 8 across the groove 6 are brought close to each other at their protruding ends, thereby narrowing the amplification in the length direction of the groove 6, as shown in FIG. narrowed part 14
will be formed. In addition, such a narrowing part 1
4, the groove portion 6 is divided into a plurality of hollow portions 16 in the longitudinal direction of the groove. Incidentally, such a narrow portion 14 is formed by pressing a knurling roller against the outer periphery (tip) of the outer fin 4 to form the trough 8, since the trough 8 is usually formed by knurling. When the outer fins 4 are crushed and plastically deformed, the tubular material constituting the outer fins 4 is moved so as to be pushed out toward the grooves 6, so that the protrusions 12 and the protrusions 12 are normally formed at the same time as the valleys 8 are formed. Thus, a narrowed portion 14 is formed. and,
A type of cavity 16 formed between the narrowed portions 14 adjacent to each other in the longitudinal direction of the groove 6 effectively functions as a boiling core and contributes to promoting the evaporation function on the outer surface of the heat exchanger tube 2. be. Note that the gap x in the narrowed portion 14 is the outer fin 4
Let P _f be the pitch of P f and t be the thickness of the outer fin 4 before forming the valley, the following range is approximately satisfied, that is, 0≦x≦(P _f −t)/2. It can be said that it is desirable to define it as follows. In other words, the protruding parts 12 forming the narrowed part 14 may be butted against each other with substantially no gap, and may be in contact with each other, and
When the abutting portions 12 are to be separated from each other to some extent, it is preferable to set the gap between the narrowed portions 14 to about 1/2 or less of the groove width of the groove portion 6 before the valley portion is formed. This is because if the gap between the narrowed portions 14 is too large, it becomes difficult to form the hollow portions 16 that serve as the core of the boiling action. On the other hand, as shown in FIG. 1, a plurality of dimples 18 are formed at the bottom of the groove 6 at predetermined intervals in the longitudinal direction of the groove. This recess 18 itself can mainly serve as the core of the boiling action and can contribute to promoting the evaporation function on the outer surface of the tube. If the recess 18 is formed in such a manner that both ends in the longitudinal direction of the groove are located at portions corresponding to the narrowed portions 14, and the recessed portion 18 is formed so as to span an appropriate number of narrowed portions 14, Since the cavity 16 formed between the narrowed portions 14 has further depth in the depth direction, the nucleate boiling effect is further promoted. However, since the recess 18 itself can become the core of the boiling action as described above, the constriction 1
Even if the grooves 6 are formed at a predetermined pitch in the longitudinal direction of the grooves 6 without having a special positional relationship with the grooves 4, this contributes to improving the evaporation function. The size of the recess 18 is such that the outer diameter of the heat transfer tube 2 is around 20 mm, and the outer fin thickness is 0.2 to 0.4 mm.
mm, and if the fin height is 1 to 3 mm and the pitch of the groove 6 is about 0.5 to 1.3 mm, it is preferable that the depth of the recess 18 is about 0.2 to 1.0 mm, and the length is about 0.5 to 5 mm. This is the range. By forming the recess 18, the inner surface of the tube corresponding to the position is formed to protrude inward within a range that substantially corresponds to the recess 18. The protrusions formed on the inner surface of the tube promote both condensation and evaporation functions. Such a function-enhancing effect occurs because, for example, when hot water is flowing through a pipe, the presence of protrusions formed on the inner surface of the pipe improves the contact between the hot water and the inner surface of the pipe, increasing the heat transfer efficiency. This is because it is possible to improve the The recess 18 can be formed relatively easily by using, for example, a serrated disk and pressing the serrations of the serrated disk against the groove 6 of the heat transfer tube 2. If the die to be inserted is offset from the serrations of the serrated disk in the tube axis direction, the portion of the groove 6 pressed by the serrations becomes the recess 18, while the tube wall there is pushed toward the inside of the tube. The above-mentioned protrusions are also formed. however,
The recesses 18 are formed after the outer fins 4 are formed.
It is desirable to carry out this step prior to forming the valley portion 8 and the narrowing portion 14. For example, by pressing a predetermined fin-forming disk against the outer circumferential surface of a raw tube that provides the intended heat transfer tube, the outer surface fins 4 are rolled and formed, while the downstream side of the fin-forming disk in the direction in which the outer surface fins are formed. A serrated disk as described above is arranged, and the serrations of the serrated disk are pressed against the bottom of the groove 6 between the outer fins, so that the portion pressed by the serrations is depressed. Furthermore, a predetermined knurling roller is arranged downstream of such a serrated disk, and the roller presses the outer circumferential portion of the outer surface fin 4 at a predetermined interval to form the trough portion 8 and the narrow portion 14.
It is preferable to form Note that when forming the troughs 8 and the narrowed portions 14, instead of using a knurling roller that presses the outer periphery of the outer fins 4 at the same time over a plurality of pitches, a trough having a width approximately equal to the width of the outer fins 4 is formed. The troughs 8 and the like may be formed by using a disk (a gear-shaped disk) and pressing the disk against the outer periphery of the outer fin 4 one pitch at a time along the fin spiral direction. In the heat transfer tube 2 as described above, the outer surface fins 4 having the peaks 10 and the valleys 8 mainly promote the condensation function on the outer surface of the tube, and also reduce the space (cavity) between the narrowed portions 14 in the grooves 6. part 16) and groove part 6
The recesses 18 formed in the tube mainly promote the nucleate boiling function and, in turn, the evaporation function on the outer surface of the tube,
Although it is a single heat exchanger tube, it has both condensing performance and evaporation performance, and compared to heat exchanger tubes that only have one function, it has dramatically improved functionality in both functions. It is something that is planned. Therefore, it can be particularly effectively used in applications where the two behaviors of condensation and evaporation occur simultaneously or with a time lag on the outer surface of the tube, such as heat exchanger tubes in heat pump heat exchangers. It can be done. Incidentally, in the above embodiment, the troughs 8 and the peaks 10 are arranged at substantially opposite positions in the tube axis direction, but as shown in FIG. There is no problem even if the troughs 8 of the fins are slightly shifted in position in the longitudinal direction of the fin, and the narrowed part 14 is formed by the vicinity of the protrusions 12 of the troughs 8 whose positions are slightly shifted. There isn't. In addition, as shown in FIG. 5, when the peaks 10 and valleys 8 of the outer surface fins 4 that are adjacent to each other are provided with their positions shifted, the valley forming disk as mentioned above is used and the pressure is applied. By selecting the pitch of the teeth, the positional configuration of the valley portions 10 and the peak portions 8 can be appropriately selected. Furthermore, in addition to forming the outer fins 4 continuously in a spiral shape in the circumferential direction of the tube, a large number of annular outer surface fins concentric with the tube axis may be formed at predetermined intervals in the circumferential direction. It's okay. Moreover, the formation of the peak portion 10 is not limited to the quadrangular truncated pyramid shape as described above, but may be formed into any other suitable shape. Furthermore, when the troughs 8 are provided at relatively large intervals in the fin length direction, the crests and troughs do not alternate; The benefits of invention can be enjoyed. Next, in order to clarify the effects of the present invention more specifically, experimental data of experiments conducted on the heat exchanger tube according to the present invention will be shown below. However, it goes without saying that the present invention should not be construed as being limited by such data. This experiment was conducted on a heat exchanger tube 2 as shown in FIGS. 1 and 2, with spiral outer fins 4.
Heat exchanger tube C formed with 19 ridges/inch and heat exchanger tube D formed with 26 ridges/inch are targeted, and for comparison, neither troughs 8 nor recesses 18 are formed. Similar experiments were conducted on heat exchanger tubes A and B with spiral outer surface fins formed with 19 threads/inch and 26 threads/inch, respectively, and the results are shown in Table 1. Also shown. The heat exchanger tubes used in these experiments had an outer diameter of 19.05 mm and an effective length of 2000 mm.
Furthermore, for the tubes C and D of the present invention, the ratio between the depth of the valley portion 8 and the height of the outer surface fin 4; h _t /h _f ≈1/2
and the gap between the narrowed portions 14; x≒(P _f −t)/
4, and the pitch of the spiral outer fin 4 was 1 _mm . The test conditions are also listed in Table 1.

【table】

[Table] As is clear from the experimental results shown in Table 1, for the tubes C and D of the present invention, the condensation heat transfer coefficient and evaporation heat transfer coefficient, which indicate the condensation performance and evaporation performance, respectively, on the outside surface of the tube are as follows. Both are superior to conventional tubes A and B, with the condensation heat transfer coefficient improved by approximately 40% to nearly 80% compared to conventional tubes, and the evaporation heat transfer coefficient improved by approximately 80% to over 100%. It is understood that the target rate has been achieved.
It _was found that the smaller the pitch of the outer fins, the more effective the narrowing part was formed.
No significant difference was observed in the range of h _f from 1/4 to 3/4.

[Brief explanation of drawings]

FIG. 1 is a partially cutaway perspective view showing a specific example of a heat exchanger tube according to the present invention, and FIG. 2 is a plan view of FIG. 1. Figure 3 shows - in Figure 2.
FIG. 4 is a cross-sectional view of - in FIG. 2.
FIG. FIG. 5 is a partial plan view showing another embodiment of the present invention, and corresponds to FIG. 2. 2: Heat exchanger tube, 4: External fin, 6: Groove, 8:
Valley, 10: Peak, 12: Protrusion, 14: Constriction, 16: Cavity, 18: Recess.

Claims (1)

[Scope of Claims] 1. A heat exchanger tube in which outer fins extending in the tube circumferential direction are integrally formed on the outer surface of the tube at a predetermined pitch, and grooves extending in the tube circumferential direction are formed between the outer fins, the bottom of the groove. A plurality of recesses are formed at predetermined intervals in the length direction, and portions of the inner surface of the tube corresponding to the recesses are formed as protrusions. The narrowed portion is formed in the groove by providing valleys at predetermined intervals in the length direction of the fin and having a bottom portion of the valley protrude toward the groove. heat exchanger tube.