JP2005164126A - Boiling heat transfer tube and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a boiling heat transfer tube having improved heat transfer performance by improving the wettability of refrigerant liquid to accelerate nuclear boiling, and to provide its manufacturing method. <P>SOLUTION: On the outer peripheral face of a tube 2, fins 3 are formed by continuing spading and bending in such a manner that a spiral or annular cavity portion 31 is formed in the circumferential direction thereof. At the front ends of the fins 3, grooves 35 are formed with protruded portions 33 and recessed portions 34 by using a grooved roll for applying suppressing pressure. The grooves 35 have holes 32 at preset spaces in communication with the outside (refrigerant liquid). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a heat transfer tube for boiling and a manufacturing method thereof, and in particular, can improve the heat transfer performance of a heat transfer tube for heating and boiling the liquid refrigerant in a state of being immersed in the liquid refrigerant of a large refrigerator. The present invention relates to a heat transfer tube for boiling and a manufacturing method thereof.

  Large refrigerators such as turbo refrigerators and screw refrigerators are provided with an evaporator, and a heat transfer tube for boiling is used for this evaporator. The heat transfer tube for boiling is used to heat and boil the refrigerant liquid, and is immersed in the refrigerant liquid in the evaporator. What is important in the heat transfer tube for boiling is that heat exchange is performed effectively. For this reason, a tube in which a helical fin is formed on the outer peripheral surface of the tube has been proposed. For example, a fin is formed on the outer surface of a tube, a notch that is a hole is provided at the tip of the fin, and a cavity effective for boiling heat transfer is provided by tilting the tip of the fin (for example, Patent Document 1). , 2, 3).

  FIG. 4 shows a conventional heat transfer tube for boiling. This boiling heat transfer tube 100 is based on the technical idea disclosed in Patent Document 1, and a hollow having a predetermined cross-sectional shape is formed in the vicinity of the surface of the metal tube 101 having a uniform thickness and excellent thermal conductivity. Cavities 102 are formed at a predetermined interval. Furthermore, holes 103 communicating with the outside (refrigerant liquid) are formed in the cavity 102 at a predetermined interval in a direction perpendicular to the cavity 102.

  The ratio between the total area of the holes 103 and the total area of the outer surface is set to 2 to 50%. In addition, the cavity 102 has a function of promoting boiling, and by setting the opening area of the hole 103 as appropriate, residual vapor bubbles in the cavity 102 can be secured.

  FIG. 5 shows another conventional heat transfer tube for boiling. The boiling heat transfer tube 200 has a substantially triangular cross-sectional shape, and a hollow cavity 202 is formed in the vicinity of the surface of the metal tube 201 in a groove shape in parallel with a predetermined interval. Further, gaps 203 and 204 (which communicate with the inside of the cavity 202) having a predetermined depth are formed in the cavity 202 so as to connect the respective tops to each other, and each communicates with the cavity 202. (For example, refer to Patent Document 4).

  The cavity 202 is formed by forming a spiral U-shaped groove on the outer surface of the metal tube 201 and then compressively deforming the upper end of the U-shaped groove. By setting the widths of the gaps 203 and 204 to 0.13 mm or less, residual vapor bubbles can be secured in the cavity 202.

In addition, as a method of manufacturing a heat transfer tube for boiling, a notch groove forming disk having an inclined incising tooth is used, the incising tooth is pressed against an outer fin, and a trough portion of the fin is pressed by a pressing portion of the incising tooth. And the ridges are alternately formed in the circumferential direction, and at the same time, the outer fins are formed in a spiral shape, and a plurality of fin forming disks further suppress the reduction of the cross-sectional area at the front end portions of the outer fins ( For example, see Patent Documents 3 and 5.) Thereby, the reduction | decrease of the cross-sectional area of a fin front-end | tip part is suppressed, and a heat-transfer characteristic can be improved effectively.
Japanese Patent Publication No.53-25379 Japanese Patent Laid-Open No. 11-316096 Japanese Patent Laid-Open No. 1-60332 Japanese Patent Publication No. 64-2878 JP-A-7-151485

  However, according to the conventional heat transfer tubes for boiling, the current heat transfer performance is insufficient to meet the recent demand for higher performance and smaller heat exchangers, and further performance improvement is required. For example, in the case of the heat transfer tube of Patent Document 1, nucleate boiling by the hollow portion (referring to boiling in which bubbles are generated with the foaming point as a nucleus) is good, but the vapor bubbles separated from the holes and the surrounding refrigerant Since the liquid is hardly heated, it is difficult to improve the heat transfer performance.

  Further, in the case of the heat transfer tubes of Patent Documents 2, 3, and 4, since the hollow portion is also formed in the tube axis direction, the flow of the refrigerant liquid from the hollow portion to the hollow portion in the pipe circumferential direction (circumferential direction) Increases pressure loss. In addition, the intersection of the hollow portion in the pipe axis direction and the hollow portion in the pipe circumferential direction is in an open state, and a part of the refrigerant liquid passes from the hollow portion in the pipe axial direction to the hollow portion in the pipe circumferential direction where nucleate boiling is performed. Flows in and nucleate boiling is likely to be hindered in this area.

  Further, the above-described heat transfer tube for boiling is used by arranging a large number of heat transfer tubes in a shell filled with a refrigerant liquid. For this reason, the heat transfer tube disposed in the upper portion is covered with the vapor bubbles formed by boiling by the heat transfer tube disposed in the lower portion, so that the wettability of the refrigerant liquid is poor and the original performance cannot be exhibited.

  Accordingly, an object of the present invention is to provide a heat transfer tube for boiling which can improve the wettability of the refrigerant liquid and improve the heat transfer performance by promoting nucleate boiling, and a method for manufacturing the same.

  In order to achieve the above object, the present invention provides, as a first feature, a tube main body and a spiral or annular cavity formed in the circumferential direction of the outer peripheral surface of the tube main body. A fin formed by continuously raising the outer peripheral surface, a groove formed by suppressing the tip of the fin, and a plurality of holes formed in the groove and communicating the cavity with the outside at a predetermined interval A heat transfer tube for boiling is provided.

  According to this configuration, the fin is formed in the cavity formed in the circumferential direction of the outer peripheral surface of the tube body, the groove is formed at the tip of the fin, and the hole is further formed in the groove. The refrigerant liquid immersed in the heat transfer tube for boiling is efficiently heated, the boiling of the refrigerant liquid is promoted, the vapor bubbles are evacuated and the refrigerant liquid is smoothly flowed in, so the wettability of the refrigerant liquid is improved. As a result, good heat transfer performance can be obtained, and the performance and size of the heat exchanger can be improved.

  In order to achieve the above-mentioned object, the present invention has a second feature in that a hollow portion is formed in a spiral shape or an annular shape in the circumferential direction of the outer peripheral surface of the tube main body, and a tip portion of the hollow portion is formed by a bite. The fins are continuously raised in the circumferential direction to form fins, and the tips of the fins are suppressed by grooved rolls to form grooves, and holes for communicating the cavity to the outside are formed at predetermined intervals in the grooves. A method for producing a heat transfer tube for boiling is provided.

  According to this method, the fin is formed in the hollow portion formed in the circumferential direction of the outer peripheral surface of the pipe body by the bite, and the groove is formed by the grooved roll at the tip of the fin, and the hole is formed in the groove. As a result, the refrigerant liquid immersed in the heat transfer tube for boiling is efficiently heated, the boiling of the refrigerant liquid is promoted, the vapor bubbles are detached, and the refrigerant liquid is smoothly introduced. As a result of improving the performance and obtaining good heat transfer performance, it is possible to improve the performance and size of the heat exchanger.

  According to the heat transfer tube for boiling and the manufacturing method thereof of the present invention, the groove is formed in the circumferential direction on the outer peripheral surface, and the refrigerant liquid is efficiently heated by this groove, and the boiling of the refrigerant liquid is promoted and nucleate boiling is promoted. The accompanying refrigerant bubbles are smoothly separated and the refrigerant liquid is smoothly flowed in, so that good heat transfer performance is obtained, and the heat exchanger using the boiling heat transfer tube can be improved in performance and size.

  1 and 2 show a heat transfer tube for boiling according to an embodiment of the present invention. The heat transfer tube 1 for boiling includes a tube 2 using a metal tube such as copper, copper alloy, and aluminum having excellent heat transfer properties, and a fin 3 raised by a processing tool such as a tool near the surface of the tube 2. It is prepared for.

  The fin 3 includes a hollow portion 31 that is formed in a spiral shape or an annular shape in the circumferential direction of the tube 2 and a hole 32 that allows the hollow portion 31 to communicate with the outside (refrigerant liquid) at a predetermined interval. The surface of the fin 3 is an uneven surface in which a convex portion 33 and a concave portion 34 are formed in order between the hole 32 and the hole 32, and an inclined surface is provided on one surface of the convex portion 33.

  The cavity 31 is formed so as to be continuous in the pipe circumferential direction, and is further provided so as to be orthogonal to or inclined with respect to the pipe axis. The groove 35 formed by the convex portion 33 and the concave portion 34 has a predetermined angle (for example, 10 to 60 °) and a predetermined depth (for example, 0.1 to 0.5 mm) with respect to the tube axis. The hole 32 is formed on the extended line of the groove 35.

  The angle is an optimal value for smoothly performing the separation of the vapor bubbles from the cavity 31 and the inflow of a refrigerant liquid such as water into the cavity 31. Since the detached vapor bubbles move in the direction opposite to the gravity, the convex portion 33 becomes a resistance in parallel to the tube axis (0 °), and the vapor bubbles cannot be smoothly separated. In addition, when the angle is 60 ° or more, the holes 32 are formed to be elongated, and the vapor bubbles cannot be removed smoothly. Therefore, an angle of 10-60 ° is suitable. On the other hand, if the depth of the recess 34 is too shallow, the surface area is reduced. Conversely, if the depth is too deep, resistance when forming the holes 32 with a grooved roll or the like increases, making it difficult to process the cavity 31. Therefore, it is appropriate that the depth of the groove 35 is 0.1 to 0.5 mm.

  Further, the cavity 31 is formed at a predetermined interval in the tube axis direction. If the interval in the tube axis direction is too short, the nucleate boiling region decreases, and conversely, if the interval is too wide, heat transfer from the heat transfer wall is deteriorated. For this reason, the interval in the tube axis direction is suitably 0.1 to 0.8 mm.

  The refrigerant liquid such as water is heated on the inner wall surface of the cavity 31. By this heating, the refrigerant liquid boils, and steam bubbles are actively generated from inside the cavity 31. When this vapor bubble grows to a certain size, it begins to detach through the plurality of holes 32. However, by reducing the size of the hole 32, not all of the vapor bubbles detach, A part of the gas becomes small vapor bubbles and remains in the cavity 31.

  On the other hand, in the convex part 33 and the recessed part 34, since a surface area increases rather than a smooth surface, a refrigerant | coolant liquid can be heated efficiently. Further, an amount of refrigerant liquid corresponding to the detached vapor bubbles flows into the cavity 31 from the recess 34. The refrigerant liquid newly flowing into the hollow portion 31 is heated on the side wall surface of the outer groove 35 in advance before flowing in, and thus reaches a boiling temperature with a small amount of heat. Therefore, the vapor bubble grows rapidly with the vapor bubble remaining in the cavity 31 as a nucleus.

  Since the vapor bubbles that leave the cavity 31 have a lower density than the refrigerant liquid, they move upward. The refrigerant liquid corresponding to the vapor bubbles flows into the hollow portion 31 from the recess 34, but since this portion is depressed, the path through which the vapor bubbles emerge from the hollow portion 31, and the heated liquid is hollow. Since the course of flowing into the portion 31 is different, the refrigerant liquid smoothly flows into the hollow portion 31.

  In general, many heat transfer tubes for water use are incorporated in the shell. However, according to the heat transfer tube 1 for boiling having the above-described configuration, since the fine groove 35 is formed in a spiral shape on the outer periphery, heat exchange is performed. Even when incorporated in the upper part of the vessel, the vapor bubbles generated in the lower part are less likely to enter the recess 34 and the refrigerant liquid is better wetted, so that the heat transfer efficiency can be improved compared to the conventional configuration. it can.

  FIG. 3 shows groove processing and hole processing of the fin in the manufacturing process of the heat transfer tube 1 for boiling. Based on FIG. 3, the manufacturing method of the heat exchanger tube 1 for boiling is demonstrated below.

  First, a tube 2 having a smooth outer peripheral surface and a groove 2a on the inner surface was prepared. The groove 2a is formed by ribs 2b formed in a spiral shape or an annular shape at a predetermined interval. The rib 2b is indispensable for promoting heat transfer of the fluid in the pipe.

  Next, as shown in FIG. 3A, a cutting tool 41 having a cutting edge angle of 60 ° is used so that the predetermined cutting angle, the cutting amount, and the interval between the fins 3 to be formed have predetermined dimensions. In addition, the cutting tool 41 was rotated in the circumferential direction of the tube 2 and the tube 2 was moved in the tube axis direction to raise the fins 3. Here, the cutting angle of the cutting tool 41 was 24 °, and the cutting amount was 0.35 mm. Further, the rotational speed of the cutting tool 41 and the feed speed of the pipe 2 were adjusted so that the interval between the hollow portions 31 in the pipe axis direction was 0.5 mm. Since the fin 3 is raised by the cutting tool 41 having the shape and usage as described above, the tip of the fin 3 is not perpendicular to the tube axis, but is formed in a shape inclined according to the cutting edge angle of the cutting tool 41. .

  Next, as shown in FIG. 3B, the grooved roll 42 in which the oblique grooves 42 a are provided at predetermined intervals in the circumferential direction is pressed against the outer surface of the tube 2. The grooved roll 42 is rotated in the circumferential direction of the tube 2 while suppressing the tube 2, the tube 12 is pulled out in the tube axis direction, and the tip of the fin 3 is suppressed by the grooved roll 42. As a result, a groove 35 having a depth of 0.2 mm is formed at 45 ° with respect to the tube axis and a cavity 31 is formed on the outer peripheral surface of the tube 2. At this time, the convex portion 33 of the outer circumferential groove 35 is bent while being restrained by the groove 42 a of the grooved roll 42, and projects toward the adjacent convex portion 33. The amount by which the grooved roll 42 is pushed in is adjusted so that the protruding amount reaches the adjacent convex portion 33 and the hole 32 connecting the cavity portion 31 and the outside is not blocked.

  In this way, the boiling heat transfer tube 1 as shown in FIGS. 1 and 2 is obtained in which the hollow portion 31 continuous in the tube circumferential direction extends while being inclined with respect to the tube axis. The refrigerant liquid that has flowed into the cavity 31 boils by being heated in the cavity 31, and steam bubbles are actively generated. Further, due to the convex part 33 and the concave part 34 formed at an angle with respect to the tube axis, the path through which the vapor bubbles come out from the cavity 31 and the path through which the heated liquid flows in are different, so the separated vapor bubbles The amount of the refrigerant liquid corresponding to the flow of the refrigerant liquid flows smoothly into the cavity 31 and the refrigerant liquid is efficiently heated. Therefore, the vapor bubble grows rapidly with the vapor bubble remaining in the cavity 31 as a nucleus. In addition, since the heat transfer tube 1 for boiling has a fine groove 35 formed in a spiral shape by the convex portion 33 and the concave portion 34 on the outer surface portion, the vapor bubble separated from the cavity portion 31 moves upward while being stirred. As a result, the surrounding refrigerant liquid is agitated, and the temperature unevenness of the refrigerant liquid can be reduced. As described above, in the heat transfer tube 1 for boiling according to the embodiment of the present invention, the heat transfer efficiency can be improved.

It is a perspective view which shows the heat exchanger tube for a boiling which concerns on embodiment of this invention. It is a top view of the heat exchanger tube for boiling of FIG. The groove processing of a fin and the hole processing in the manufacturing process of the heat exchanger tube for boiling concerning an embodiment of the invention are shown, (a) is a perspective view showing the groove processing of a fin, (b) is the hole processing by a slotted roll. It is a perspective view shown. It is a perspective view which shows the conventional heat exchanger tube for boiling. It is a perspective view which shows the other conventional heat exchanger tube for boiling.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Heat transfer tube for boiling 2 Tube 2a Groove 2b Rib 3 Fin 31 Cavity 32 Hole 33 Protrusion 34 Recess 35 Groove 41 Byte 42 Grooved roll 42a Groove 100 Boiling heat transfer tube 101 Metal tube 102 Hollow portion 103 Hole 200 Boiling transfer Heat tube 201 Metal tube 202 Cavity 203, 204 Gap

Claims (6)

A tube body;
A fin formed by continuously raising the outer peripheral surface of the tube body so that a spiral or annular cavity is formed in the circumferential direction of the outer peripheral surface of the tube body;
A groove formed by suppressing the tip of the fin;
A heat transfer tube for boiling, comprising a plurality of holes formed in the groove and communicating with the cavity at a predetermined interval.   The heat transfer tube for boiling according to claim 1, wherein the hollow portions are provided at intervals of 0.1 to 0.8 mm in the tube axis direction.   2. The heat transfer tube for boiling according to claim 1, wherein the groove has an inclined surface of 10 to 60 [deg.] With respect to the tube axis and has a depth of 0.1 to 0.5 mm.   2. The heat transfer tube for boiling according to claim 1, wherein the tube main body is provided with a spiral rib on the inner surface thereof. Forming a cavity in a spiral or ring shape in the circumferential direction of the outer peripheral surface of the tube body,
The tip of the cavity is continuously raised in the circumferential direction by a cutting tool to form a fin,
A method of manufacturing a heat transfer tube for boiling, wherein the tip of the fin is suppressed by a grooved roll to form a groove, and holes for communicating the cavity to the outside are formed in the groove at a predetermined interval.   6. The method of manufacturing a heat transfer tube for boiling according to claim 5, wherein the groove has an inclined surface of 10 to 60 [deg.] With respect to the tube axis and has a depth of 0.1 to 0.5 mm.

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