JPH0519079B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a method of manufacturing a boiling heat transfer tube, and particularly to an economically advantageous method for promoting boiling heat transfer with good boiling heat transfer characteristics.

(Background Art) Generally, in a heat transfer tube, heat is exchanged between a heat transfer fluid flowing inside the tube and a heat transfer fluid brought into contact with the outer surface of the tube. As one type of heat tube, there is a loaf-in tube in which spiral fins are formed on the outer circumferential surface of the tube, and an inner surface in which spiral ribs are provided on the inner circumferential surface of the loaf-in tube in order to promote heat transfer of such a loaf-in tube. A ribbed loaf-in tube has been revealed.

By the way, in a loaf-in tube with a smooth interior, a heat transfer fluid film with poor heat transfer efficiency is likely to be formed on the inner peripheral surface of the tube, but in a loaf-in tube with internal ribs, the inner ribs cause the fluid flow to swirl. Due to the swirling flow that is formed, it is relatively difficult to form a film, and it is said to be effective in improving the heat transfer coefficient on the inner surface of the tube. However, even with such a swirling flow, a liquid flow that approximates a laminar flow still remains, and therefore the problem of the film cannot be solved, and there are limits to promoting internal heat transfer. It was hot.

For this reason, the inventors of the present invention first applied for patent application No.
As No. 137292 (see JP-A No. 60-29594 public relations),
In a condenser heat transfer promoting tube in which spiral outer surface fins made of a tube material are integrally formed on the outer peripheral surface of the tube, the outer surface fins are divided by cuts at predetermined intervals in the flow direction. On the other hand, we have proposed a condensing heat exchanger tube having a structure in which a plurality of inner surface protrusions are formed on the inner peripheral surface of the tube, and the inner surface protrusions are arranged in a spiral shape. With such a structure, when the heat transfer fluid flowing through the tube overcomes the plurality of inner surface protrusions or the flow direction is changed by such inner surface protrusions, a slight turbulence is generated, and Due to this change in the flow near the inner surface of the tube, the membrane that tends to form near the inner surface of the tube is effectively destroyed, effectively increasing the inner surface conductivity, and the heat transfer fluid that is brought into contact with the outer circumferential surface of the tube is effectively destroyed. The fluid can flow across the adjacent outer surface fins through the above-mentioned notches, so the fluid is brought into effective contact with the outer surface fins, and the contact area is also increased.
The external heat transfer coefficient was also increased compared to conventional methods.

On the other hand, a boiling heat transfer tube boils and evaporates a heat transfer fluid (liquid) that is brought into contact with the outer peripheral surface of the tube through a heat exchange action between the heat transfer fluid and the heat transfer fluid flowing through the tube. The structure of the condensing heat transfer tube as described above cannot be applied as is, and in order to increase its heat transfer efficiency, it is necessary to improve the boiling heat transfer characteristics, especially at low temperature differences.

For this reason, Japanese Patent Application Publication No. 59-176593 and Japanese Patent Application Publication No. 176593,
59-199137, etc., the outer fins formed integrally on the outer surface of the tube are folded down to form circumferential cavities or tunnels in the surface portion, and the cavities or tunnels are formed with a large number of fine particles. Boiling heat transfer tubes with a structure that communicates with the outside through openings or gaps have been disclosed, but their heat transfer efficiency is still insufficient, and due to the formation of such cavities or tunnels, There were problems such as the need to use complicated machining processes and complicated machining tools.

(Structure of the invention) Here, the present inventors have previously applied for
As we continued to study various types of condensing heat transfer tubes with external fins, which have a plurality of internal protrusions arranged in a spiral shape on the inner peripheral surface of the tube, we found that by folding down the external fins, a cavity was formed between the adjacent external fins.
They discovered that by forming a boiling heat transfer tube, a boiling heat transfer promoting tube having excellent boiling heat transfer characteristics could be obtained, and the present invention was completed.

That is, in the present invention, spiral outer fins made of a tube material are integrally formed on the outer peripheral surface of the tube, and the outer fins are divided by cuts spaced at predetermined intervals in the flow direction. At the same time, the tube shaft is curved or bent in one direction from the middle part thereof, and the upper part of the groove between the adjacent outer surface fins is closed, thereby forming a spiral cavity that communicates with the outside through the notch. An object of the present invention is to industrially advantageously manufacture a boiling heat exchanger tube characterized in that a plurality of inner surface protrusions are formed on the inner peripheral surface of the tube, and the inner surface protrusions are arranged in a spiral shape. .

When manufacturing such boiling heat exchanger tubes, the following method is adopted, which eliminates the need for complicated processing tools and complicated processes.
Boiling heat transfer promoting tubes in which heat transfer is promoted on both the inner and outer surfaces can now be produced industrially and advantageously.

In such a manufacturing process, first, a plurality of fin-forming disks, which are rotated by a predetermined rotary drive shaft, are placed at a plurality of positions around the raw tube that provides the desired boiling heat exchanger tube, and are rotated by a predetermined rotational drive shaft. By pressing against the outer circumferential surface of the tube, outer surface fins of a predetermined height are successively rolled in the tube axis direction on the outer circumferential surface of the raw tube.

Next, a serrated inner surface is attached to one of the rotary drive shafts for rotationally driving the plurality of fin-forming disks so as to be located on the downstream side of the outer surface of the fin-forming disk in the fin-forming direction, and is rotationally driven at the same time. Using a protrusion processing disk, a knurling disk having a plurality of cutting edges on its outer periphery, and a fin defeating roll that gradually expands with an outer peripheral surface curved toward the upstream side, first, the inner surface protrusion processing disk is prepared. By pressing the sawtooth against the bottom of the groove between the formed outer fins, the pressed portion of the sawtooth protrudes into the inner surface of the tube, and then the knurling disk is used to press the cutting edge against the bottom of the groove between the outer fins. By pressing the top part, cuts are made at predetermined intervals in the length direction of the outer fin, and then, by pressing the outer fin with the fin-folding roll, the curvature of the fin-folding roll is The top part of the outer fin is guided by the outer peripheral surface of the outer fin, and the outer fin is curved or bent from the middle part toward the adjacent outer fin, so that the upper part of the groove between the outer fin and the adjacent outer fin is curved or bent. It is made to block it.

By using such a fin-folding roll, the outer fins are gradually and effectively curved or bent in one direction of the tube axis, so that the tops of the outer fins come into contact with the adjacent outer fins. This results in the formation of a cavity (or tunnel) beneath the surface, which is communicated with the outside at a notch in the outer fin.

(Specific description of the configuration) Hereinafter, based on the embodiments of the present invention shown in the drawings,
The configuration of the present invention will be explained in detail.

First, FIGS. 1 and 2 are a partially cutaway view and an enlarged explanatory view of an example of a boiling heat exchanger tube manufactured according to the present invention, in which 2 indicates the heat transfer coefficient of copper or the like. This is a heat transfer tube made of high quality metal.
The heat exchanger tube 2 has spiral outer fins 4 made of tube material moved from the tube wall on the outer circumferential surface of the heat transfer tube 2.
are integrally provided at a predetermined pitch, and
The outer fins 4 are curved or bent in one direction of the tube axis from the middle part, and the upper part of the groove 6 between the adjacent outer fins 4 is closed, thereby forming a spiral cavity 8. It is formed beneath the surface. Further, the cavity 8 is communicated with the outside through notches 10 provided at predetermined intervals in the length direction of the outer fin 4.

On the other hand, a plurality of inner surface protrusions 12 are formed on the inner peripheral surface of the heat exchanger tube 2. These inner surface protrusions 12 are formed on the inner circumferential surface of the tube corresponding to the grooves 6 between the outer surface fins 4, and the bottom portions of the grooves 6 in which the inner surface protrusions 12 are located are made into recesses (dimples) 14. That is, in this case, by forming the rectangular recess 14 in the bottom portion of the groove 6, the inner surface of the tube corresponding to the recess 14 is made to protrude in the shape of an elliptical hill, and the inner surface protrusion 12 is formed. be. As a result of the formation of the inner surface protrusions 12 along the spiral groove 6, the inner surface protrusions 12 are arranged in a spiral shape on the inner peripheral surface of the tube, and the pitch of the recesses 14 In addition to cases where the inner surface protrusions 12 adjacent to each other exhibit a clear spiral pattern, there are also cases where the inner surface protrusions 12 form a staggered pattern.
As long as they are arranged in a spiral,
Any of them can be adopted.

Note that if the amount of protrusion of the inner surface protrusions 12 from the inner circumferential surface of the tube becomes too large, the pressure loss (head loss) of the heat transfer fluid flowing through the tube will increase, so the height of the inner surface protrusions 12 and the number per unit area will increase. should be appropriately determined so as not to cause too large a pressure loss. Therefore, the size of the inner protrusion 12 is generally 0.2 to 0.1 mm in height (protrusion amount).
The length in the front and rear directions and in the longitudinal direction of the protrusion is determined to be approximately 1 to 5 mm.

In the case of a heat transfer tube having such an inner surface protrusion 12, turbulence occurs in the flow of heat transfer fluid flowing through the tube when it passes over the inner surface protrusion 12. The flow of heat transfer fluid flowing in the tube axial direction along the inner surface of the tube is divided to the left and right, and in addition to this,
Combined with the spiral flow effect of the heat transfer fluid near the inner surface of the tube due to the spiral arrangement of the inner surface protrusions 12, the flow on the inner surface of the tube takes on a complex and subtle turbulent form, which causes the flow on the inner circumferential surface of the tube to The membrane that tends to form in the vicinity is effectively destroyed, and the internal transmissivity is effectively increased. Further, the fluid contact area on the inner surface of the tube is increased by the inner surface protrusion 12, and the contact area on the outer peripheral surface of the tube is also increased due to the presence of the recess 14.

Under such circumstances, a cavity 8, which is a tunnel-like cavity, is formed in a spiral shape in the circumferential direction on the outer surface side of the heat exchanger tube 2 by tilting the outer surface fins 4, and the cavity 8 is formed in a spiral shape in the circumferential direction.
Since it is connected to the outside through the heat transfer surface, it becomes a heat transfer surface with a reentrant surface structure, which is effective in promoting heat transfer during nucleate boiling. The recess 14 formed contributes to this.

Incidentally, FIG. 3 shows the boiling heat transfer characteristics of the tubes A and B of the present invention having structures as shown in FIGS. 1 and 2, and the reference tube.
As is clear from the comparison, tubes A and B of the present invention have high heat transfer efficiency at low temperature differences.

The experiment was conducted under atmospheric pressure and saturated conditions using Freon-11 as a refrigerant. Further, as a reference tube, a loaf-in tube with external fins of 26 fins/inch is used, and the tubes A and B of the present invention are shown in FIGS. 1 and 2 based on such a loaf-in tube, respectively. They are processed into a structure, and each of them has a cut of 10
The width of the opening is approximately 0.3 mm, the height of the fins (with the fins folded down) is approximately 1 mm, and in the tube A of the present invention, the pitch of the notches 10 is approximately 1 mm.
mm, and in the tube B of the present invention, the pitch of the cuts 10 is approximately 0.7 mm. The temperature difference on the horizontal axis in FIG. 3 is the difference between the saturation temperature of the freon 11 that is boiled and evaporated and the bottom temperature of the cavity 8.

By the way, the boiling heat exchanger tube 2 as shown in FIGS. 1 to 2 above can be easily manufactured by the method shown in FIGS. 4 to 7.

That is, the loaf-in rolling tool 22 is composed of a plurality of fin-forming disks 20 whose diameters gradually increase.
As shown in FIG. 4, they are arranged with a phase difference of approximately 120° around the base tube 24 that provides the target boiling heat transfer tube, and as in the conventional case, the outer peripheral surface of the base tube 24 is External fins 26 of a predetermined height are successively rolled in the tube axis direction. More specifically, a plurality of fin-forming disks 20 in each loaf-in rolling tool 22
are concentrically and integrally connected by a rotary drive shaft 28 at intervals giving the pitch of the outer fins 26, and such rotary drive shaft 28
are positioned at an angle corresponding to the lead angle of the outer surface fins 26 to be formed with respect to the center line (tube axis) of the blank tube 24, and each fin forming disk 20 is provided inside the blank tube 24. The plug 30 is inserted with only the two sides facing each other. In this state, the fin forming disk 20 is rotated by the rotary drive shaft 28 and pressed against the outer circumferential surface of the raw pipe 24, so that the desired outer surface fins 26 are gradually formed by rolling. It is.

In addition, two of the three loaf-in rolling tools 22 arranged around the raw pipe 24 are
As shown in the figure, the structure is such that a plurality of fin-forming disks 20 are simply attached to the rotary drive shaft 28, but the other one is as shown in FIG. is extended downstream in the outer surface fin forming direction, and with respect to the extended portion, at a position in the blank pipe 24 where the plug 30 is not present, a serrated disk 32 as a disk for machining the inner surface protrusion and a Also, a knurling disk 34 and a fin tilting roller 36 are installed concentrically and integrally on the downstream side.

As is clear from FIGS. 6 and 7, the serrated disk 32 is provided with serrations 38 of a predetermined pitch on its outer periphery.
The radius of the circumference drawn by the tips of the teeth is set a certain amount larger than the radius of the largest diameter of the fin-forming disks 20. In addition, the knurling process disk 34
is an incisor portion 40 having an incisor line that slopes toward the upstream side.
It is shaped like a bevel gear and is provided at a predetermined pitch on its outer periphery. Furthermore, the fin-folding roll 36 has a structure that gradually expands with an outer peripheral surface 42 curved toward the upstream side. The serrated disk 32 is arranged so that its serrations 38 are pressed against the bottom of the groove 44 formed between the adjacent fins 26, and the knurling disk 34 is
The incisor portion 40 is arranged so as to be pressed against and bit into the top of the outer fin 26, and the fin tilting roll 36 is arranged so as to be able to press the top of the outer fin 26 toward the raw pipe 24. .

Therefore, with the tool equipment as shown in FIGS. 6 and 7, the outer fins 26 are integrally formed in a spiral shape on the outer peripheral surface of the raw pipe 24 by the loaf-in rolling tool 22. rear,
By pressing the saw teeth 38 of the serrated disk 32 against the bottom of the groove 44 between the outer surface fins 26, 26, the pressed portion by the saw teeth 38 is made to protrude to the inner surface of the tube, and as a result, the outer surface on the outer peripheral surface of the tube A recess 46 is formed at the bottom of the groove 44 between the fins 26, and an inner surface protrusion 46 is formed on the inner peripheral surface of the tube at a position corresponding to the recess 46.

Next, after the inner surface protrusion 46 is formed, the cutter portion 40 of the knurling disk 34 disposed downstream of the serrated disk 32 is pressed against the top of the outer circumferential fin 26 and cut into it. Accordingly, cuts 50 are formed in the outer surface fin 26 at predetermined intervals in the length direction thereof, at a predetermined depth and with a predetermined opening width.

Further thereafter, such cuts 50 are made at predetermined intervals,
In other words, the outer surface fins 26 formed with a predetermined pitch have their top portions guided downstream by the curved outer circumferential surface 42 due to the pressing action of the fin-folding rolls 36, so that It is curved or bent toward the adjacent outer circumferential fin 26 downstream from the outer circumferential fin 26, and closes the upper part of the groove 44 between the adjacent outer circumferential fin 26, as shown in FIGS. 1 and 2. A spirally extending cavity (tunnel-like cavity) 52 is formed below the outer surface. Note that this cavity 52 communicates with the outside through the notch 50 provided in the outer circumferential fin 26 .

In this way, if such a manufacturing method is followed, the inner surface,
In the boiling heat transfer promoting tube in which heat transfer is promoted on both the outer surface, after the outer surface fins are formed, the inner surface protrusion processing, the fin cutting processing, and the fin collapse processing can be performed at the same time. As a result, the heat exchanger tubes can be manufactured all at once through one continuous processing process, thereby significantly increasing the industrial productivity of such heat exchanger tubes.

Moreover, if the manufacturing method described above is followed, the fin-folding operation in the fin-folding process in particular will be significantly simplified and facilitated, so the complexity of the processing process and complicated processing tools will be completely eliminated. It was no longer necessary.

In the process of machining internal protrusions using the serrated disk 32 described above, the height (depth) of the formed internal protrusion 48 is determined by the diameter of the serrated disc 32, and also depends on the axial pitch of the spiral of the internal protrusion 48. is determined by the outer diameter and number of serrated disks 32 and the diameter of the plug 30 when the outer fins 26 are in operation.

Further, the depth of cut in sawtooth processing (forming the cut 50) using the knurling disk 34 is determined by the diameter of the disk, and the cut 50 formed thereby forms an opening at the time of nucleate boiling. Therefore, in order to further facilitate the subsequent fin folding process, such a cut 50 can be made by using a tool having a bevel gear-like structure such as the one illustrated in which the tooth tips are inclined at an angle with respect to the axial direction. It is desirable that the

Furthermore, in the fin folding process which is the final process, the outer circumferential fin 26 is
A cavity 52 is formed in the fin bottom (groove) 44 by tilting the fin to one side, but the degree to which the outer fin 26 is tilted by the fin tilting roll 36 depends on the fin tilting roll 36. In this case, the fin folding roll 36 is provided with a curved outer circumferential surface 42 so that the outer fins 26 are folded in the downstream direction during processing, as described above.

Although the structure of the present invention has been explained in detail in accordance with specific examples of the present invention, the present invention should not be interpreted as being limited by such specific examples, and based on the knowledge of those skilled in the art. It goes without saying that the present invention can be implemented with various changes, improvements, etc.

(Effects of the Invention) As is clear from the above description, the present invention has a spiral cavity or cavity formed under the outer surface of the tube, which is communicated with the outside through minute openings, and nucleate boiling occurs. The boiling heat transfer promoting tube has a plurality of inner surface protrusions arranged in a spiral shape on the inner circumferential surface of the tube, thereby effectively promoting heat transfer on both the inner and outer surfaces of the tube. A boiling heat exchanger tube with improved heat transfer characteristics is manufactured. In the present invention, the boiling heat transfer tube can be processed in one continuous process by simultaneously rotating an inner protrusion processing disk, a knurling processing disk, and a fin folding roll attached to the rotational drive shaft of the fin forming disk. The present invention is based on the fact that it can be manufactured all at once, and can be manufactured industrially and with high productivity without using any complicated manufacturing process or complicated processing tools. This invention has great industrial significance.

[Brief explanation of the drawing]

FIG. 1 is a partially cutaway front view showing a specific example of a boiling heat exchanger tube obtained according to the present invention, and FIG. 2 is a partially enlarged view for explaining the tube wall of such a heat exchanger tube. FIG. 3 is a graph showing one heat transfer characteristic of the boiling heat exchanger tube obtained according to the present invention, and FIGS. 4 to 7 are graphs showing the manufacturing process of the boiling heat exchanger tube of the present invention. It is an explanatory diagram showing each state,
Fig. 4 is an explanatory diagram of its cross-sectional form, Fig. 5 is an explanatory diagram of a vertical cross-sectional state showing the external fin formation form by two loaf-in rolling tools, and Fig. 6 is one of the loaf-in rolling tools. FIG. 7 is a schematic diagram for explaining the machining state in a cross-sectional form in the direction of the rotational drive shaft in FIG. 6. FIG. 2: Heat exchanger tube, 4, 26: External fin, 6, 4
4: Groove, 8, 52: Cavity, 10, 50:
Notch, 12, 48: inner protrusion, 14, 46: recess, 20: fin forming disk, 22: loaf-in rolling tool, 24: blank pipe, 28: rotational drive shaft,
30: Plug, 32: Serrated disk, 34: Knurling disk, 36: Roll for fin folding, 38: Sawtooth, 40: Incisor, 42: Curved outer peripheral surface.

Claims (1)

[Claims] 1. Pressing a plurality of fin-forming disks, each of which is placed at a plurality of positions around the raw tube that provides the desired boiling heat transfer tube, and which is rotationally driven by a predetermined rotary drive shaft, against the outer circumferential surface of the raw tube. By rolling the outer surface fins of a predetermined height on the outer circumferential surface of the blank pipe in the axial direction of the pipe, one of the rotary drive shafts that rotationally drives the plurality of fin forming disks is used to form the fins. A disk for machining serrated inner protrusions, which is mounted so as to be located on the downstream side in the direction of forming the outer fins of the disk, and is driven to rotate at the same time, and a disk for knurl machining, which has a plurality of cutting edges on its outer periphery. and a fin-folding roll having an outer peripheral surface curved toward the upstream side and gradually expanding, and first pressing the sawtooth of the inner surface protrusion processing disk against the bottom of the groove between the formed outer surface fins. By causing the pressing portion of the sawtooth to protrude to the inner surface of the tube, and then pressing the cutting edge portion of the knurling disk against the top of the outer fin, a predetermined interval is created in the length direction of the outer fin. After that, the outer fins are pressed by the fin-folding roll to guide the top portions of the outer fins on the curved outer peripheral surface of the fin-folding roll. Curving or bending the outer surface fin from its intermediate portion toward the adjacent outer surface fin,
A method for manufacturing a boiling heat exchanger tube, characterized in that the upper part of the groove between the adjacent outer surface fins is closed.