JPS642878B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a nucleate boiling type heat exchanger tube that has improved performance when heated and boiled when immersed in a liquid.

Conventionally, various surface structures have been proposed as means for improving this type of heating and boiling performance, but each has advantages and disadvantages due to problems in heat transfer performance, manufacturing difficulty, manufacturing cost, etc.

For example, tubes with a porous layer of metal powder on their surface are susceptible to performance deterioration due to clogging, and tubes with surface structures that have many fine cavities and gaps or openings that communicate with the outside. In many cases, the cavities are provided in only one direction, such as in the circumferential direction of the pipe, and therefore, if the pitch between each cavity is made small to improve performance, it would be difficult and costly to manufacture. Becomes high. In addition, in terms of manufacturing, there are almost no products that can be manufactured in one step and that can be handled in the same way as smooth tubes or ordinary loaf inch tubes when incorporated into a heat exchanger.

As a result of various studies in view of these circumstances, the present invention aims to improve the nucleate boiling performance outside the tube by providing a surface mechanism that promotes boiling not only in the circumferential direction of the tube but also in the axial direction of the tube. This made it possible to provide heat exchanger tubes.

That is, the first aspect of the present invention is that the tube has a spiral shape with a desired pitch in the tube axis direction under the outer surface of the tube, and the cross-sectional shape and size of the tube continuously change irregularly in the longitudinal direction. A hollow portion 1 is provided in the circumferential direction of the pipe, and the hollow portion 1 has a narrow irregular shape with a width of 0.13 mm or less that communicates with the outside along the longitudinal direction, and is continuous or discontinuous in the longitudinal direction. It has a gap or opening 2 (hereinafter referred to as a gap) which may be a gap, and furthermore, a small tube is formed under the outer surface at a desired pitch in the circumferential direction so as to connect these adjacent gaps. A heat exchanger tube is provided with an axial cavity or groove 3 (hereinafter referred to as a cavity), and this cavity 3 also has a gap or opening 4 (hereinafter referred to as a gap) that communicates with the outside like the cavity 1. In this case, small irregularities may be formed on both sides and the bottom of the latter cavity 4.

In addition, the second aspect of the present invention is that the hollow portion 1 or the gap portion 2 in the circumferential direction of the former spiral tube which is located adjacent to each other is located at the center position, and the hollow portion in the axial direction of the latter which is adjacent to each other. The present invention relates to a heat exchanger tube in which chevron-shaped fins are provided between gaps 3 and 4, the longitudinal direction of which protrudes toward the circumferential direction of the tube.

A third aspect of the present invention is a heat exchanger tube in which the entire outer surface of the heat exchanger tube according to the first aspect is knurled to form a knurled surface.

Furthermore, the fourth aspect of the present invention is a heat exchanger tube according to the second aspect of the present invention, in which the entire outer surface of the tube except for the protruding portions of the chevron-shaped fins is knurled.

Hereinafter, the heat exchanger tube according to the present invention and its operation will be described in detail with reference to the drawings.

Fig. 1 relates to the fourth invention of the present application, and Fig. 2 is an enlarged view of a part of the heat transfer surface of the heat transfer tube according to the second invention of the present application. The section 1 is arranged below the outer surface of the tube with a desired pitch in the tube axis direction. Also, there is a small cavity 3 in the tube axis direction.
They are also disposed between the cavities 1, 1 at desired pitches in the circumferential direction of the tube under the outer surface of the tube.

The former circumferential cavity 1 has different shapes and sizes at the part where it intersects with the small cavity 3 in the axial direction and the intermediate part, and becomes more diverse due to changes in the relative positions of the adjacent cavities 3. It deforms and continues in its longitudinal direction (tube circumferential direction).

The fact that the cavity 1 is varied in this way is more advantageous in promoting nucleate boiling than a cavity that is continuous in a constant shape and does not change in the longitudinal direction. 2 is a gap part provided almost continuously communicating with the former cavity part 1 and the outside, or in some cases a small cavity part 3 of the latter part.
It shows a gap discontinuously provided at a pitch of It is.

In order to promote nucleate boiling, it is necessary to create a surface structure on the heat transfer surface that allows residual bubbles to form, but in this case, the average width of the narrow gap 2 has a large effect on heat transfer performance. affect This is because if the average width of the gap 2 is too large, the generated air bubbles cannot be secured within the cavity 1, and the number of remaining air bubbles decreases, preventing nucleate boiling from being promoted.

Furthermore, the smaller the surface tension of the boiling liquid and the specific volume of the vapor, and the larger the latent heat of evaporation, the smaller the bubbles generated.
Different boiling liquids have different limit values for ensuring the average width of residual bubbles in the gap 2. FIG. 8 shows the experimental results of the relationship between the average width of the gap 2 and the extratube boiling heat transfer coefficient (heat transfer performance) for Freon R-11 and R-22. The size of the bubbles generated is R-11>R-22. In Figure 8, R-22 has an average width of gap 2 of 0.13 to 0.15.
The average width of the gap 2 must be 0.13 mm or less in order to obtain high heat transfer performance for both boiling liquids R-11 and R-22. be.

On the other hand, the small cavity 3 in the tube axis direction also has a narrow gap 4 that communicates with the outside, and the maximum average width of this gap must also be 0.13 mm or less as described above based on the predictions from the experimental results shown in FIG.

Also, since the total length of the small cavity 3 is approximately equal to the length of the spiral cavity 1,
This greatly improves the performance in terms of boiling nucleus density compared to a surface structure consisting only of the cavity 1. This is extremely effective in promoting boiling since the cavity 3 and the gap 4 therein can become the nucleus of many bubbles.

A chevron-shaped fin 5 protrudes with its longitudinal direction facing in the circumferential direction at the center position of the adjacent spiral cavities 1 and 1 and between the small cavities 3 and 3 in the tube axis direction. In particular, in cases such as in a liquid under turbulent flow containing a large amount of bubbles, it will work effectively to further improve performance by taking advantage of its characteristics as a fin (heating of liquid and bubbles).

Moreover, the heat exchanger tube (third invention) and the first invention shown in FIG.
The knurled surface 6 provided on the outer surface of the heat exchanger tube (fourth invention) shown in the figure has an uneven part that promotes the generation of air bubbles. Compared to the smooth outer surface of the heat transfer tube (second invention), the heat transfer surface has a larger number of bubble nuclei, which is effective in improving its performance.

The heat exchanger tube of the present invention described above can be easily manufactured by first forming fins on a smooth tube and then subjecting it to deformation processing. Regardless of whether it is a single thread or multiple threads, fin forming and deformation may be performed at the same time or in separate processes.

Hereinafter, a method for manufacturing a heat exchanger tube of the present invention will be explained with reference to the drawings.

FIG. 3 is an enlarged cross-sectional view of the heat exchanger tube in the axial direction, showing an example of the processing method for the heat exchanger tube of the present invention, in which initial fin forming and subsequent deformation are performed simultaneously. The part inside the chain line circle X shows the cross section of the part where the processing has been completed.
Three tool axes A are arranged at equal intervals around the tube, and a disk tool for fin forming and a tool for deformation are attached to the tool axis A so that they can rotate together. By rotating the tool axis A, the tube is subjected to fin forming and deformation while rotating in the opposite direction to the tool axis A. Further, since the tool axis A is in a twisted position with respect to the axis of the tube, the tube is fed in the axial direction of the tube while being processed.

In FIG. 3, reference numeral 7 indicates a final-stage disc tool for forming fins, by which fins 7' are formed on the surface of the tube. 8 shows a first-stage deforming disk tool having chevron-shaped teeth all around the circumference as shown in Fig. 3-1.

The outer diameter of this disk tool 8 is made slightly smaller than the outer diameter of the above-mentioned disk tool 7 for forming fins, and the shape and pitch of the tips of the teeth on the circumferential surface may be determined as appropriate. It is better that the tip has an appropriate width as shown in the enlarged view S in Figure 3-2.

FIG. 4 shows an example of the shape of the fin 7' when it is compressed and deformed from its top surface by the first-stage deforming disc tool 8.

That is, the first stage deforming disc tool 8 having tapered chevron-shaped teeth shown in the chain line circle Y in FIG. 3-1 and shown in FIG. 3-2 is placed on the top surface of each fin 7'. When rolling along the fins 7', each fin 7' becomes a disk tool
It is compressed and deformed into a gear shape according to the chevron teeth on the circumference of the
At this time, the meat of the valley 7'' is perpendicular to the fin 7',
It extends in the direction of the fin part (referring to the gap between the fins 7' and 7') 7 on both the left and right sides, and the valley part 7''
The amount is maximum at the bottom of . The trough 7'' formed by this deformation becomes a small cavity 3 in the tube axis direction after the final machining is completed.Here, by modifying the shape of the chevron teeth on the circumferential surface of the tool 8, the cavity can be closed. It is easy to form the cavity 3 having unevenness on the inner surface.In addition, in this deformation process, the valley part 7''
The compressive stress acting on the portion directly below the tool 8 is alleviated by the shape of the tool 8 and force distribution, and therefore the amount of deformation due to buckling is small.

Note that if the fin 7' to be deformed is a single thread, the deformation process can be performed on one fin using the deformation tool 8, but if the fin is multi-thread, the deformation process is performed on one fin. The tool 8 may be used to process multiple fins at the same time, or the multiple tools 8 may be used to deform each fin. The mutual positional relationship of the parts is arbitrary and is not limited in any way.

Next, the top surface of the fin 7', which has been deformed into a gear shape, is deformed by the second deformation tools 9 and 9-1 shown in FIG. Tool 9
The outer diameter of the tool 9-1 is normally slightly smaller than the outer diameter of the tool 8, and its thickness is slightly smaller than the pitch W of the fin 7'. At this time, both sides of the outer peripheral surfaces of the tools 9 and 9-1 are made sharp so as to serve as a shear as shown in Fig. 3-4, and the angle α is
It is preferable not to exceed 90°.

An example of processing completed using the second deformation processing tools 9 and 9-1 is shown in Fig. 2 (heat exchanger tube of the second invention), and the surface structure of the present invention is basically formed by such a process. be completed. That is, the deforming tools 9, 9
In step 1, when the shoulders of the peaks of the gear-shaped fins 7' and 7' on both sides of the fins are compressed and deformed from the top surface, the thin-walled fins 5 on the left and right sides are left. These peaks are compressed and deformed in the front, rear, right and left directions to form a cavity 1 centered around the interfin portion 7 and a small cavity 3 centered around the trough 7''.

In addition, in FIG. 4-1, in this compression deformation process, the end 11 of the top surface of the fin 7' is
Since the compressive stress is stronger than that of the fin 7', the top surface of the fin 7', which was as shown in Fig. 4-1, is compressively deformed as shown in Fig. 4-2, and the deformed end 11' is The shape projects slightly larger from the intermediate portion 12' to the inter-fin portion 7 or the valley portion 7''. Therefore, for example, by changing the outer diameters of the tools 9 and 9-1 to change the degree of compression change. , a continuous or discontinuous narrow gap 2 or 4 communicating with the outside can be formed along the longitudinal direction of the cavity 1 or 3.

That is, when the degree of compressive deformation is large, the gap becomes discontinuous, and when the degree of compressive deformation is small, the gap becomes continuous and narrow.

Although Fig. 3 shows an example of machining using two tools, tools 9 and 9-1, it is possible to use a plurality of tools with different outer diameters and widths, or for example, as shown by 9' in Fig. 3-3. However, processing may be performed using only one tool.

In addition, when thin-walled chevron-shaped fins 5 are not formed, the width of the tool 9 etc. may be made larger than the fin pitch W. In this case, the entire crest of the fin 7'7' is compressed and deformed, as shown in Fig. 6 (first invention). A surface structure without chevron-shaped fins 5 such as those of heat exchanger tubes) is obtained.

Next, as shown in Fig. 3, when processing with a knurling roll 10 having a slightly larger outer diameter and the same or slightly smaller width than the tool 9-1, the shape as shown in Fig. 1 (heat exchanger tube of the fourth invention) is obtained. However, this causes the second
A stable surface structure with better performance than the shape shown in the figure (heat exchanger tube of the second invention) can be obtained.

The shape and size of the knurling may be determined as appropriate, but if the width of the tool 9 is larger than the fin pitch W, it is preferable that the width of the knurling roll 10 is also larger than the fin pitch W. Chevron fins 5 in Figure 5 (heat exchanger tube of the third invention)
A surface structure with no surface texture is obtained.

In the above explanation, a method was shown in which the fin forming disc tool 7, the deformation tools 8, 9, 9-1, and the knurling roll 10 are mounted on the same axis and processed simultaneously. may be performed in a separate process. Furthermore, as a method for forming the fins, cutting may be used instead of rolling as described above.

Next, examples of the present invention will be shown.

Example 1 According to the processing method shown in Fig. 3, the outer diameter was 18.88 mm,
Two fins 7' with a fin pitch of 35 threads/inch were formed on a copper tube with a wall thickness of 1.35 mm, and then the first stage of deformation was performed by forming 216 chevron teeth on the outer periphery with an outer diameter of 51.6 mm. This was done using a serrated tool 8. The second stage deformation process was performed in two stages using tool 9 with an outer diameter of 51.2 mm and a width of 1.4 mm and tool 9-1 with an outer diameter of 51.7 mm and a width of 1.4 mm. These second-stage deformation tools 9, 9
-1 width of 1.4mm is fin pitch 1/35 inches (=0.726
mm), and naturally the chevron-shaped fins 5 seen in FIGS. 1 and 2 were not formed, and a surface structure as shown in FIG. 6 (heat exchanger tube of the first invention) was obtained.

In addition, the fourth stage formed by the first stage deformation process
The bottom of the valley 7'' shown in the figure caved in by approximately 0.2 mm after the second stage deformation process was completed.

Finally, using tool 10, the outer diameter is 51.8 mm and the width is 0.85 mm.
Knurling was performed with a pitch of 0.5mm.

As a result of the above, the gap 2 with an average width of 0.06 mm continues in a spiral shape and the corresponding cavity 1, and the spiral gap 2 with an average width of 0.08 mm are connected in the axial direction of the pipe. As shown in Fig. 5, the pipe has a surface structure consisting of a gap 4 provided at a pitch of about 0.75 in the circumferential direction of the pipe, a corresponding small cavity 3, and a knurled surface 6 applied over the entire surface of the pipe. A heat exchanger tube (heat exchanger tube of the third invention) with an outer diameter of 18.38 mm was obtained.

Example 2 Based on the processing method shown in Figure 3, the outer diameter was 18.88 mm,
Two fins 7' with a fin pitch of 35 threads/inch are formed on a copper tube with a wall thickness of 1.35 mm, and then the first stage of deformation is performed to form fins 7' with an outer diameter of 51.6 mm and 216 chevron teeth on the outer periphery. This was carried out using a serrated tool 8 with . The second stage deformation process was performed in two stages using tool 9 with an outer diameter of 51.3 mm and width of 0.62 mm and tool 9-1 with an outer diameter of 51.75 mm and width of 0.62 mm. At this time, the bottom of the valley 7'' shown in FIG. 4 formed by the first stage deformation process is the second
After the stage deformation process was completed, it caved in by approximately 0.2 mm.

Finally, we knurled a 51.8mm outer diameter and 0.6mm width knurling.

As a result of the above, the gap part 2 with an average width of 0.04 mm is connected in a spiral shape, the corresponding cavity part 1, and the spiral gap part 2 with an average width of 0.07 mm are connected in the axial direction of the pipe. A gap 4 is provided at a pitch of approximately 0.75 mm in the circumferential direction of the tube so as to connect the gap 4, a small cavity 3 corresponding to the gap 4, and a central position between the adjacent spiral cavities 1 and 1. Between the small cavities 3 and 3 in the circumferential direction, a chevron-shaped fin 5 with a thickness of about 0.1 mm and a height of about 0.25 mm that protrudes with its longitudinal direction facing the circumferential direction of the tube, and the entire surface of the tube excluding the fin portion. A heat exchanger tube (heat exchanger tube of the fourth invention) having an outer diameter of 18.88 mm as shown in FIG. 1 and having a surface structure consisting of a knurled surface 6 was obtained.

Freon R-1 using the heat exchanger tubes of Examples 1 and 2
A graph showing the boiling heat transfer coefficient per unit length in No. 1 is shown in FIG. In the figure, A is the heat exchanger tube of Example 1, B is the heat exchanger tube of Example 2, and for comparison, the boiling point per unit length of the finch tube having almost the same outer diameter (18.8 mm) and 26 pitches/inch. The heat transfer coefficient is also written as C.

Incidentally, the above graph shows the performance actually measured using a single tube, and the boiling pressure was 1.5 Kg/cm ² abs.

The features and effects of the heat exchanger tube according to the present invention are summarized as follows.

(1) Various types of heat exchanger tubes with surface features to improve boiling performance have been proposed, but conventional ones have cavities only in one direction, such as in the circumferential direction. There are many things,
If it is desired to further improve the performance, it is necessary to make the pitch between the cavities finer, which results in manufacturing difficulties and high costs.

According to the present invention, the boiling promoting mechanism is provided not only in the tube circumferential direction but also in the tube axial direction, and also has the advantage of being easy to manufacture and having high performance.

(2) Furthermore, in the surface structure of the present invention, the spirally provided cavity has a continuous cross-sectional shape that changes irregularly in the longitudinal direction, and this helps to promote the boiling effect. ing.

(3) Generally, the refrigerant vapor generated in the evaporator of a refrigerator needs to be in a superheated state. When thin-walled chevron-shaped fins are provided on the entire surface of the tube, the characteristics of the fins can be used to remove liquid and bubbles, especially in cases of intense boiling, that is, in a liquid under turbulent flow containing a large amount of bubbles. It is effective for heating and improving performance.

(4) To install a tube in a shell-and-tube heat exchanger, insert the tube into the tube hole from the tube sheet on one side of the assembled shell, and fix the tube end to the tube sheet by expanding or welding. , the outside diameter of the tube must be smaller than the tubesheet bore diameter over its entire length. Further, a tube support is often used, and in this case, the outer diameter of the tube at the position of the tube support is required to be equal to the outer diameter of the tube end in order to ensure support of the tube.

The outer diameter of the heat transfer tube to which the surface mechanism of the present invention is applied will not be larger than that of the original tube, and like the loaf inch tube, a skip portion of the same size as the smooth portion of the unprocessed tube end can be freely formed. This shows the advantage that it can be installed and processed in one step. Therefore, when incorporated into a heat exchanger, it can be handled in the same way as a smooth tube or a loaf-in tube, and can be obtained at a relatively low cost.

[Brief explanation of drawings]

FIG. 1 is a partially enlarged view of the heat transfer surface having the surface structure of the fourth invention, FIG. 2 is a partially enlarged view of the heat transfer surface having the surface structure of the second invention, and FIG. 3 is the heat transfer tube of the present invention. FIG. 3-1 is a plan view of the first deforming tool 8, and FIG. 3-2 is a diagram showing the chevron-shaped tooth portion of the tool 8. FIG. 3-3 is an illustrative view showing another processing method and arrangement of tools for the surface structure of the heat exchanger tube of the present invention, FIG. 3-4 is a side view of tools 9 and 9-1,
FIG. 4 is an enlarged view of a portion of the shape after processing with the tool 8 in FIG. 3, FIG. 2 is an explanatory diagram of the shape of the top surface of the fin 7' after being compressed and deformed, FIG. 5 is an enlarged view of a portion of the heat transfer surface of the third invention, and FIG. FIG. 7 is a partial enlarged view of the thermal surface; FIG. 7 is a graph showing the outside boiling heat transfer characteristics of the heat transfer tubes of Example 1 and Example 2 of the present invention and a comparative product; FIG. 8 is a graph showing the tube circumference. It is a graph showing the extra-tube boiling heat transfer characteristics in which heat transfer experiments were conducted by changing the average width of the gap portion 2 of the cavity portion in the direction. 1...Cavity part in the circumferential direction of the tube, 2...Gap part on the same left, 3...Small cavity part in the direction of the tube axis, 4...Gap part on the left, 5...Chevral fin, 6...Knurled surface, 7 ...Disc tool for fin forming, 7'...Thick wall fin, 7''...Trough on the same left, 7...Between the fins, 8...Disc tool for first stage deformation, 9,9 ―
1,9'...Second stage deformation disc tool, 10...
...Roretsu Troll.

Claims (1)

[Scope of Claims] 1. A hollow portion 1 in the circumferential direction of the tube is provided on the outer surface of the tube in a spiral shape having a predetermined pitch in the tube axis direction and whose cross section changes. , continuous or discontinuous narrow gap 2 of irregular shape with a width of 0.13 mm or less communicating with the outside along its longitudinal direction
A small cavity 3 in the tube axis direction is provided at a predetermined pitch in the tube circumferential direction so as to connect the gap portions 2 adjacent in the tube axis direction. A nucleate boiling type heat exchanger tube characterized in that a narrow gap 4 having a width of 0.13 mm or less is provided along its longitudinal direction and communicating with the outside. 2. On the outer surface of the tube, a circumferential hollow portion 1 is provided which has a spiral shape with a predetermined pitch in the tube axis direction and whose cross section changes. Continuous or discontinuous narrow irregularly shaped gap with a width of 0.13mm or less that communicates with the outside 2
A small cavity 3 in the tube axis direction is provided at a predetermined pitch in the tube circumferential direction so as to connect the gap portions 2 adjacent in the tube axis direction. A narrow gap 4 with a width of 0.13 mm or less is provided along the longitudinal direction of the tube and communicates with the outside, and further, on the surface of the tube surrounded by the gap 2 in the circumferential direction and the gap 4 in the tube axis direction, A nucleate boiling type heat exchanger tube characterized by having chevron-shaped fins 5 arranged along the circumferential direction of the tube. 3. On the outer surface of the tube, a circumferential hollow portion 1 is provided which has a spiral shape with a predetermined pitch in the tube axis direction and whose cross section has changed, and the hollow portion 1 extends along the longitudinal direction of the tube. Continuous or discontinuous narrow irregularly shaped gap with a width of 0.13 mm or less that communicates with the outside 2
A small cavity 3 in the tube axis direction is provided at a predetermined pitch in the tube circumferential direction so as to connect the gap portions 2 adjacent in the tube axis direction. A narrow gap 4 with a width of 0.13 mm or less is provided along the longitudinal direction of the tube and communicates with the outside, and further, on the surface of the tube surrounded by the gap 2 in the circumferential direction and the gap 4 in the axial direction, A nucleate boiling type heat exchanger tube characterized by having a knurled surface 6. 4. A hollow portion 1 in the circumferential direction of the tube is provided on the outer surface of the tube in a spiral shape having a predetermined pitch in the tube axis direction and whose cross-sectional shape and size are changed,
The cavity 1 has a continuous or discontinuous narrow gap 2 of an irregular shape with a width of 0.13 mm or less that communicates with the outside along its longitudinal direction, and the gap 2 adjacent to each other in the tube axis direction A small cavity 3 in the tube axis direction is provided at a predetermined pitch in the circumferential direction of the tube so as to connect between the tubes. A gap 4 of less than mm is provided, and the surface of the tube surrounded by the gap 2 in the circumferential direction and the gap 4 in the axial direction is provided with chevron-shaped fins 5 and knurled surfaces 6 arranged along the circumferential direction of the tube. A nucleate boiling type heat transfer tube characterized by being provided with.