JPH09318286A - Heat transfer pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate unevenness of concentration in a vertical direction of absorbing liquid at the surface of a heat transfer pipe, increase an interface disturbance and make a substantial improvement of a heat transfer performance. SOLUTION: This heat transfer pipe performs a heat exchanging operation between fluid in the pipe and fluid outside the pipe, wherein an outer circumferential surface of the heat transfer pipe 1 has at least two kinds of helical grooves M1, M2 in which directions of a twisted angle θ in respect to a pipe axis Z are opposite to each other and the twisted angle θ is in a range of 3 deg.-80 deg. and a groove depth of at least one helical groove M1 of the two kinds of helical grooves M1, M2 is different from that of the other helical groove M2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat transfer tube used for an absorber, a regenerator or an evaporator of an absorption refrigerator or an absorption chiller / heater for producing cold water.

[0002]

2. Description of the Related Art Absorption refrigerators and absorption chiller-heaters produce cold water by removing latent heat of vaporization of a refrigerant evaporated in an evaporator from water to be cooled. The refrigerant evaporated in the evaporator is absorbed by the absorbing liquid in the absorber and returns to the liquid, and at this time, the latent heat of evaporation and the heat of dilution are released. If the temperature of the absorbing liquid is high, it becomes difficult to absorb the refrigerant. Therefore, it is necessary to cool the absorbing liquid on the surface of the heat transfer tube so that the temperature does not rise due to the latent heat of evaporation and the heat of dilution. In general, for example, an absorber has a structure in which a large number of heat transfer tubes are arranged horizontally or vertically, an absorbing liquid flows down on the heat transfer tubes, and cooling water flows in the heat transfer tubes. A smooth tube is usually used as this heat transfer tube, and a high performance heat transfer tube is used only when performance improvement is required.

In order to improve the performance of the heat transfer tube in the absorber, the heat transfer area is increased, and the surface of the flowing absorbing liquid becomes thin when the surface absorbs vapor, so that the concentration of the absorbing liquid decreases in the vertical direction. Therefore, it is necessary to take measures such as eliminating the variation in the concentration of water and promoting interfacial disturbance in the absorbing liquid flowing down the surface. As such a high performance heat transfer tube, Japanese Utility Model Laid-Open No. 57-100161 is proposed in which a large number of spiral grooves are provided on the outer surface of the heat transfer tube. Further, Japanese Utility Model Laid-Open No. 58-51671 has been proposed in which a large number of spiral grooves of the same depth are crossed in opposite directions on the outer surface of the heat transfer tube. Further, Japanese Utility Model Laid-Open No. 1-73663 has been proposed in which cross grooves are provided only on the outer surface of the end of the heat transfer tube. With the microfilm of the above publication, many spiral grooves are provided on the outer surface of the heat transfer tube, spiral grooves are crossed in the opposite direction on the outer surface of the heat transfer tube, or cross grooves are provided only at the ends of the heat transfer tube. Then, it is known that the performance of the heat transfer tube is improved.

[0004]

[Problems to be Solved by the Invention]
When the outer surface of the heat transfer tube is provided with only spiral grooves of the same depth in one direction, as disclosed in the microfilms of Japanese Utility Model Publication No. 161 and Japanese Utility Model Laid-Open No. 1-73663, or only the outer surface of the end of the heat transfer tube intersects In the case where the groove was provided, the flow of the absorbing liquid on the surface of the heat transfer tube became unidirectional, and the interface disturbance of the absorbing liquid, which is one of the factors for improving the performance of the heat transfer tube, was small. In addition, 58
Even if the spiral groove of the same depth is crossed in the opposite direction on the outer surface of the heat transfer tube, which is disclosed in the microfilm of JP-A-51671, the flow of the absorbing liquid just flows down along the bottom of the spiral groove. However, there was little spread in the tube axis direction, and it was not possible to eliminate variations in the vertical concentration of the absorbing liquid. Therefore, even when the heat transfer tube is changed to a smooth tube and the above heat transfer tube is used, the rate of increase in heat transfer performance in the absorber is insufficient.

The present invention solves the above problems and provides a heat transfer tube which eliminates the variation in the vertical concentration of the absorbing liquid on the surface of the heat transfer tube, increases the interface disturbance, and significantly improves the heat transfer performance. The purpose is.

[0006]

The present invention has the following means to solve the above problems.

The heat transfer tube according to claim 1 of the present invention is a heat transfer tube for exchanging heat between a fluid inside the tube and a fluid outside the tube,
On the outer peripheral surface of the heat transfer tube, the direction of the helix angle with respect to the tube axis is opposite, and there are at least two types of spiral grooves within a helix angle range of 3 ° to 80 °. The groove depth of at least one of the spiral grooves is different from that of the other spiral grooves.

According to a second aspect of the present invention, the heat transfer tube is characterized in that the absolute values of the helix angle with respect to the tube axis of at least two kinds of spiral grooves having opposite directions to the tube axis are different from each other. To do.

In the heat transfer tube according to claim 1 or 2 of the present invention, the spiral groove has a groove depth of 0.1 to 1.5 mm and a circumferential pitch of 0.3 to 4.0 mm. It is desirable that the difference between the groove depths of at least two kinds of spiral grooves is 1.15 times or more.

In the heat transfer tube according to claim 3 of the present invention, at least two kinds of spiral grooves have a twist angle of 15 ° to the tube axis.
Within the range of 45 °, the absolute value of the helix angle with respect to the tube axis of the deepest spiral groove is smaller than that of the other spiral grooves, and the groove depth of the spiral groove is in the range of 0.1 mm to 1.5 mm. It is characterized by being inside. The heat transfer tube according to claim 4 of the present invention is characterized in that the heat transfer tube according to claim 4 has, on the inner peripheral surface of the tube, a spiral strip having an uneven shape corresponding to the uneven shape of the spiral groove formed on the outer peripheral surface of the tube having the largest groove depth. To do.

According to the heat transfer tube of the first aspect of the present invention, at least two kinds of heat transfer tubes are provided on the outer peripheral surface of the heat transfer tube with the directions of the helix angles with respect to the tube axis being opposite, and in the helix angle range of 3 ° to 80 °. Since the groove depth of at least one spiral groove of at least two kinds of spiral grooves is different from that of the other spiral grooves, it operates as follows. For example, when this heat transfer tube is used in a horizontally arranged absorber, a large number of projections surrounded by at least two types of spiral grooves are formed on the outer peripheral surface of the tube. Promoted. At the same time, since at least two kinds of spiral grooves are twisted in the opposite direction to the tube axis direction, the absorbing liquid film that has been disturbed by hitting some protrusions crosses the intersection of the spiral grooves, and at the outer surface of the heat transfer tube. Of the absorption liquid, and at the same time, the disturbing action of the absorption liquid film is sufficiently promoted in the downward direction (direction perpendicular to the tube axis direction) in which the absorption liquid flows down.

Further, since the twist angle of the spiral groove is in the range of 3 ° to 80 °, the disturbing action of the absorbing liquid film is further promoted. For example, when the twist angle of the spiral groove is smaller than 3 °, the flow of the absorbing liquid film occurs left and right along the groove, and the absorbing liquid films may collide with each other and spread stably in a certain direction. However, it is difficult to promote the disturbing action of the absorbing liquid film in the tube axis direction. Further, for example, when the twist angle of the spiral groove with respect to the tube axis direction is larger than 80 °, the protrusion between the spiral groove and the spiral groove interferes with the movement of the absorbent liquid film in the tube axis direction, and the absorption liquid film It becomes difficult for the disturbing action to be promoted in the tube axis direction.

The twist angle with respect to the tube axis direction is 3 ° to above.
The absorption liquid flowing down along at least two kinds of spiral grooves within the range of 80 ° has the opposite directions of flow in the layer flowing in the deep part of the groove and the layer flowing in the shallow part of the surface. The layer of the absorbent having a low concentration flowing down collides with the layer of the absorbent having a high concentration flowing deep in the groove,
Variations in the vertical concentration will disappear, and more interface disturbance will occur. Therefore, the heat transfer performance of the heat transfer tube is significantly improved, and the performance of the heat exchanger equipped with this heat transfer tube is significantly improved.

According to the heat transfer tube of the second aspect of the present invention, since the absolute values of the twist angle with respect to the tube axis of at least two kinds of spiral grooves having the directions of the spiral groove opposite to the tube axis are different from each other, the heat transfer tube The flow of the absorption liquid on the outer surface of the heat pipe changes, for example, the absorption liquid in the spiral groove with the smaller angle promotes the flow in the axial direction of the pipe, and the absorption liquid in the spiral groove with the larger angle in the circumferential direction of the pipe. It plays the role of controlling the flow in one direction, and the synergistic effect further improves the heat transfer performance.

In the heat transfer tube according to claim 1 or 2, the spiral groove has a groove depth of 0.1 to 1.5 mm and a circumferential pitch of 0.3 to 4.0 mm. And the difference in groove depth between at least two types of spiral groove is 1.
If it is 15 times or more, it is in the optimum range for the following reasons. If the groove depth of the spiral groove and the pitch in the circumferential direction are smaller than the above range, the effect of promoting the disturbing action of the absorbing liquid film by the protrusions is small, and if it is larger than the above range, the absorbing liquid film will pass over the protrusions and form the outer peripheral surface of the pipe. Hard to spread. Moreover, since the difference in groove depth of the spiral groove is 1.15 times or more, the protrusion formed on the outer peripheral surface of the heat transfer tube can cause an optimum difference with respect to the film thickness of the absorbing liquid. As a result, the surface tension of the absorbing liquid can be made different, so-called Marangoni convection can be promoted, and the disturbing action of the absorbing liquid is promoted compared to the case where the plurality of spiral grooves have the same size, so that a more efficient heat Exchange will be carried out.

According to the heat transfer tube of claim 3 of the present invention, the twist angle of at least two kinds of spiral grooves with respect to the tube axis is 15 °.
Within the range of ˜45 °, the absolute value of the twist angle of the deep spiral groove with respect to the tube axis is smaller than that of other spiral grooves, and the groove depth of the spiral groove is in the range of 0.1 mm to 1.5 mm. Since the absorption liquid film is controlled preferentially to the deep groove to give a stable spread in the tube axis direction, the disturbing action of the absorption liquid film is also promoted in the tube axis direction, resulting in higher efficiency. Heat exchange is performed. The groove width of the spiral groove having a large groove depth and a large twist angle with respect to the tube axis is preferably larger than that of the other spiral grooves. In that case, the absorbing liquid film can be stably and easily spread in the tube axis direction. Also, it is easier to process. According to the heat transfer tube of claim 4 of the present invention, on the inner peripheral surface of the tube, the spiral groove having the uneven shape corresponding to the uneven shape of the spiral groove having the largest groove depth formed on the outer peripheral surface of the tube is provided. Therefore, a turbulent flow effect can be given to the cooling water flowing inside the heat transfer tube, and the performance inside the tube is also improved. Further, since it is possible to reduce the extra wall thickness of the inner portion of the pipe corresponding to the ridges of the ridges on the outer peripheral surface side of the pipe, the wall thickness of the pipe can be reduced in the pipe circumferential direction. Therefore, the unit weight of the entire heat transfer tube can be reduced, which is very effective for cost reduction.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to embodiments. (Embodiment 1) FIG. 1 is a perspective view showing an embodiment of the heat transfer tube of the present invention. The heat transfer tube 1 of FIG. 1 has two kinds of spiral grooves M1 and M2 on the outer peripheral surface, and the spiral grooves M1 and M2 are the tube axis Z.
And the twist angles θ1 and θ2 are opposite to each other, and the twist angle θ
The magnitudes of 1 and θ2 are different. In FIG. 1, the twist angle θ1 is smaller than the twist angle θ2. The large or small twist angle θ means the absolute value of the angle with respect to the tube axis Z, regardless of whether it is a right-hand thread or a left-hand thread.
The heat transfer tube of this embodiment shown in FIG. 1 has a tube cross section of a perfect circle, but the tube cross section is not limited to a perfect circle.
For example, there is no problem even if the shape is elliptical.

In the present specification, when the spiral groove is illustrated, the spiral groove is represented by a single straight line for convenience of illustration. The spiral groove having a deep groove depth is displayed thick. The drawings illustrating the spiral groove are similar except for FIG.
FIG. 2 is an enlarged sectional view of a main part of the heat transfer tube of FIG. The spiral groove M1 on the outer peripheral surface of the heat transfer tube 1 has a groove depth H1 and a circumferential pitch P1 larger than the groove depth H2 and the circumferential pitch P2 of the spiral groove M2. In FIG. 2, reference numeral D0
Is the outer diameter of the heat transfer tube 1.

The twist angles .theta.1 and .theta.2 of the spiral grooves M1 and M2 with respect to the tube axis Z are in the range of 3 to 80.degree. Further, the pitches P1 and P2 in the circumferential direction of the spiral grooves M1 and M2 are optimal in the range of 0.3 to 4.0 mm as a result of the test described later. Further, the groove depths H1 and H2 of the spiral grooves M1 and M2 are optimal in the range of 0.1 to 1.5 mm as a result of the test described later. Furthermore, the groove depths H1 and H2 of the spiral grooves M1 and M2 are optimal as a result of a test described later that the difference in groove depth is 1.15 times or more.

For example, as a specific dimension, the outer diameter D0
Is 19.05 mmφ, thickness is 0.8 mm, the twist angle θ1 of the spiral groove M1 with respect to the tube axis Z is 15 ° in the right-hand thread direction, the groove depth H1 is 0.6 mm, and the pitch P1 in the circumferential direction is 1.5 m.
m, the helix angle θ2 of the spiral groove M2 with respect to the tube axis Z is the left-hand thread direction (hereinafter, the left-hand thread direction is shown as a negative value) -30
The groove depth H2 is 0.4 mm and the circumferential pitch P2 is 1.15 mm. Of the above dimensions, regarding the groove depth, the peak of the deeper spiral groove may be crushed by the shallower spiral groove, but the original deeper spiral groove depth is used as a numerical value. Therefore, the depth of the spiral groove actually formed may be different.

(Embodiment 2) FIG. 3 is a perspective view showing another embodiment of the heat transfer tube of the present invention. The heat transfer tube 1A shown in FIG. 3 has two kinds of spiral grooves M3 on the outer peripheral surface, similar to the heat transfer tube of the first embodiment.
Since the spiral grooves M3 and M4 have M4, the helix angles .theta.3 and .theta.4 with respect to the tube axis Z are opposite to each other, and the helix angle .theta.3 of the spiral groove M3 is smaller than that of the spiral groove M4. The groove depth of the spiral groove M3 is larger than that of the spiral groove M4. The feature of this embodiment lies in the inner peripheral surface of the heat transfer tube.
That is, on the inner peripheral surface, a spiral strip N having a shape corresponding to the spiral groove M3 is formed at a position corresponding to the spiral groove M3 formed on the outer peripheral surface. In each of the above embodiments, the case where the number of spiral grooves formed on the outer peripheral surface is two has been illustrated, but the number of spiral grooves is not limited to two, and it is sufficient that two or more spiral grooves intersect to form a protrusion. .

FIG. 4 shows a tester for measuring the heat transfer performance of the heat transfer tube of the present invention, which will be briefly described below. Reference numeral 44 denotes an evaporator, in which heat transfer tubes 42 are arranged in two rows and five stages, and the upper and lower heat transfer tubes 42 communicate with each other to pass water therethrough. A refrigerant (pure water) is supplied to these heat transfer tubes 42 from a spray pipe 46.
Was sprayed. Reference numeral 43 is an absorber in which sample tubes 41 to be tested are arranged in five rows in one row. The upper and lower sample tubes 41 were communicated with each other and cooling water was passed through them, and an absorption liquid (lithium bromide aqueous solution) was sprayed to these sample tubes 41 from a spray pipe 45. 47 is a dilute solution tank, which is an absorber 4
It absorbs the refrigerant vapor in 3 and stores the diluted absorption liquid. The absorbing solution in the dilute solution tank 47 is added to the concentrated solution tank 48.
Lithium bromide was added to the concentrated solution tank 48 to adjust the concentration, and the concentration-adjusted absorption liquid was sprayed by the pump 50 to the sample pipe 41 through the pipe 49 and the spray pipe 45.

The test conditions are shown below. Absorbent: LiBr aqueous solution Inlet concentration: 58 ± 0.5 wt. % Inlet temperature: 40 ± 1 ° C. Flow rate: 0.021 ± 0.002 kg / m · s (Mass flow rate of absorbing liquid film flowing to one side of heat transfer tube per unit length) Surfactant: Add 250 ppm of octyl alcohol Absorption Liquid spraying device Pore size: 1.5 mm, Spacing 24 mm Absorber cooling water Inlet temperature: 28 ± 0.2 ° C. Flow velocity: 2.0 m / s Absorber / evaporator pressure: 15 ± 0.5 mmHg Arrangement of heat transfer tubes : Heat transfer tubes with a length of 500 mm are vertically arranged in 5 rows and 1 row

The heat transfer tube of the present invention is made of phosphorus deoxidized copper and has an outer diameter of 1
The heat transfer tubes shown in Tables 1 to 3 below were produced using a 9.05 mm element tube, and heat transfer measurements were performed on each sample under the above conditions. Although phosphorus deoxidized copper is generally used as the material of the heat transfer tube for the absorption chiller, cupronickel or stainless steel may be used depending on the usage environment of the heat transfer tube. The heat transfer tube of the present invention is also effective for these materials. The heat transfer rates of the heat transfer tube samples (Invention 1 to Invention 15) of the present invention are shown in the rightmost columns of Tables 1 to 3. As conventional examples 1 and 2, heat transfer tubes manufactured by the methods disclosed in the microfilms of Japanese Utility Model Publication No. 57-100161 and Japanese Utility Model Publication No. 1-73663 were also measured.

[0025]

[Table 1]

[0026]

[Table 2]

[0027]

[Table 3]

From the measurement results of the present inventions 1 to 4 and Comparative Examples 1 and 2 in Table 1, the influence of the twist angle θ with respect to the tube axis direction can be judged. FIG. 5 is a graph in which the horizontal axis represents the twist angle and the vertical axis represents the specific heat transmission rate of the conventional example. It can be seen from the graph of FIG. 5 that the heat transfer rate is improved in the range of 3 to 80 ° with respect to the tube axis direction as compared with the conventional example. The desirable range of the helix angle of the deep spiral groove is 15 ° to 45 °. Also,
From a comparison between Invention 2 and Invention 3, it can be seen that the heat transfer rate is improved when the absolute value of the twist angle of the spiral groove having a large groove depth is smaller than that of the other spiral groove. If the twist angle is less than 3 °, the flow of the absorbing liquid film occurs in the tube axis direction, and it becomes impossible to stably spread the absorbing liquid film in a certain direction. As a result, the disturbing action of the absorbing liquid film is also promoted. Can not do it.

When the twist angle is set to 80 ° or more, the movement of the absorbent liquid film in the tube axis direction is hindered by the ridges of the spiral groove, and the disturbing action of the absorbent liquid film cannot be promoted in the tube axis direction. Table 2
It is possible to judge the influence of the groove depth H or the groove pitch P from the measurement results of the present inventions 5 to 12 and the conventional example 2. FIG.
The horizontal axis shows the ratio of the depth of the deep groove to the depth of the shallow groove, that is, the value of the depth of the deep spiral groove when the depth of the shallow spiral groove is 1, and the vertical axis shows the specific heat passage of the conventional example. It is the graph which took the rate. In Conventional Example 2, the value on the horizontal axis is 1.0. It can be seen from FIG. 6 that the heat transmission rate of the example of the present invention is higher than that of the conventional example 2. Furthermore, the groove depth ratio is 1.1.
It turns out that it is more desirable if it is 5 times or more.

According to Table 2, the groove depth is 0.1 to 1.5 m.
m, groove pitch 0.3 to 4.0 mm is 5 than the conventional example
It has been improved by more than%. If the groove depth and groove pitch are smaller than the above ranges, the effect of disturbing the absorbing liquid film by the protrusion cannot be expected. If the groove depth and the groove pitch are larger than the above ranges, the crests of the spiral grooves act to prevent the absorbing liquid film from disturbing, and the heat transfer performance cannot be expected to be improved. Further, if the difference in groove depth is within 1.15 times, the solution flowing down will only flow down along the spiral groove, and it will not be stirred in the vertical direction, so improvement in heat transfer performance cannot be expected.

Since the difference in groove depth is required to be 1.15 times or more, the groove depth of the deeper spiral groove is 0.15 to 1.5.
mm, and the groove depth of other spiral grooves is preferably set within the range of 0.1 to 1.3 mm. It should be noted that the cross-sectional shape of the spiral groove may be triangular, trapezoidal, arcuate, or any shape within the above numerical values even if the shape changes in the pipe longitudinal direction. Further, comparing Table 7 with Invention 7 and Invention 13, it can be seen that the heat transfer performance is improved when the twist angles of the two types of spiral grooves are different. From these experiments,
The desirable shape for obtaining the effect of the heat transfer tube of the present invention is 2
The twist angle of the spiral groove of more than one kind with respect to the tube axis is 15 ° to 4
Within the range of 5 °, the absolute value of the twist angle with respect to the tube axis of the deep spiral groove is set smaller than that of other spiral grooves,
Moreover, the groove depth of the spiral groove is in the range of 0.1 mm to 1.5 mm. The groove width of the spiral groove having a large groove depth and a large twist angle with respect to the tube axis is preferably larger than that of the other spiral grooves. In that case, the absorbing liquid film can be stably and easily spread in the tube axis direction. Also, it is easier to process.

The above description has been made on the example in which the heat transfer tube of the present invention is used in the absorber of the absorption refrigerator.
By the way, the evaporator of the absorption refrigerator and the falling film regenerator are
As with the absorber, a heat transfer tube is installed horizontally, and liquid is dropped or sprayed from above, and the liquid drops fall downward due to gravity, and they flow over the heat transfer tube one after another. By mounting the heat transfer tube of the present invention on this evaporator or falling film regenerator, it is possible to expect the expansion of the refrigerant in the evaporator, the expansion of the solution in the regenerator, and the stirring effect. That is, the heat transfer tube of the present invention is also effective when used as a high performance heat transfer tube in an evaporator or a falling liquid film type regenerator.

[0033]

As described above, according to the heat transfer tube of claim 1 of the present invention, the direction of the helix angle with respect to the tube axis is opposite to the outer circumferential surface of the heat transfer tube, and the helix angle is 3 ° to 3 °. It has at least two kinds of spiral grooves in the range of 80 °, and the groove depth of at least one spiral groove of at least two kinds of spiral grooves is
Different from that of other spiral grooves, so at least 2
A large number of projections surrounded by spiral grooves of various kinds are formed on the outer peripheral surface of the tube, and the absorbing liquid collides with the projections to further promote the disturbing action. At the same time, since at least two kinds of spiral grooves are twisted in the opposite direction to the tube axis direction, the absorbing liquid film that has been disturbed by hitting some protrusions crosses the intersection of the spiral grooves, and at the outer surface of the heat transfer tube. The absorption liquid is sufficiently spread, and at the same time, the disturbing action of the absorption liquid film is sufficiently promoted in the downward direction (direction perpendicular to the tube axis direction) in which the absorption liquid flows down.

Further, the absorbing liquid flowing down along at least two kinds of spiral grooves having a twist angle with respect to the tube axis direction in the above range of 3 ° to 80 ° has a layer flowing in a deep part of the groove and a shallow surface. However, since the flowing direction of the flowing layer is opposite to that of the flowing flowing layer, the layer of the absorbing liquid having a low concentration flowing down the surface collides with the layer of the absorbing liquid having a high concentration flowing in the deep part of the groove, and the concentration of the vertical direction is decreased. There will be no variation and a lot of interface disturbance will occur. Therefore, the heat transfer performance of the heat transfer tube is significantly improved, and the performance of the heat exchanger equipped with this heat transfer tube is significantly improved.

According to the heat transfer tube of the second aspect of the present invention, since the absolute values of the twist angle with respect to the tube axis of at least two kinds of spiral grooves having the directions of the spiral groove opposite to the tube axis are different from each other, the heat transfer tube The flow of the absorption liquid on the outer surface of the heat pipe changes, for example, the absorption liquid in the spiral groove with the smaller angle promotes the flow in the axial direction of the pipe, and the absorption liquid in the spiral groove with the larger angle in the circumferential direction of the pipe. It plays the role of controlling the flow in one direction, and the synergistic effect further improves the heat transfer performance.

In the heat transfer tube of claim 1 or 2, the spiral groove has a groove depth of 0.1 to 1.5 mm and a circumferential pitch of 0.3 to 4.0 mm. And the difference in groove depth between at least two types of spiral groove is 1.
If it is 15 times or more, it is in the optimum range for the following reasons. If the groove depth of the spiral groove and the pitch in the circumferential direction are smaller than the above range, the effect of promoting the disturbing action of the absorbing liquid film by the protrusions is small, and if it is larger than the above range, the absorbing liquid film will pass over the protrusions and form the outer peripheral surface of the pipe. Hard to spread. Also,
Since the difference in groove depth of the spiral groove is 1.15 times or more, the protrusion formed on the outer peripheral surface of the heat transfer tube can cause an optimum difference with respect to the film thickness of the absorbing liquid. As a result, the surface tension of the absorbing liquid can be made different, so-called Marangoni convection can be promoted, and the disturbing action of the absorbing liquid is promoted compared to the case where the plurality of spiral grooves have the same size, so that a more efficient heat Exchange will be carried out.

According to the heat transfer tube of claim 3 of the present invention, the twist angle of at least two kinds of spiral grooves with respect to the tube axis is 15 °.
Within the range of ˜45 °, the absolute value of the twist angle of the deep spiral groove with respect to the tube axis is smaller than that of other spiral grooves, and the groove depth of the spiral groove is in the range of 0.1 mm to 1.5 mm. Since the absorption liquid film is controlled preferentially to the deep groove to give a stable spread in the tube axis direction, the disturbing action of the absorption liquid film is also promoted in the tube axis direction, resulting in higher efficiency. Heat exchange is performed. The groove width of the spiral groove having a large groove depth and a large twist angle with respect to the tube axis is preferably larger than that of the other spiral grooves. In that case, the absorbing liquid film can be stably and easily spread in the tube axis direction. Also, it is easier to process. According to the heat transfer tube of claim 4 of the present invention, on the inner peripheral surface of the tube, the spiral groove having the uneven shape corresponding to the uneven shape of the spiral groove having the largest groove depth formed on the outer peripheral surface of the tube is provided. Therefore, a turbulent flow effect can be given to the cooling water flowing inside the heat transfer tube, and the performance inside the tube is also improved. Further, since it is possible to reduce the excess wall thickness of the inner portion of the pipe corresponding to the convex ridges on the outer peripheral surface side of the pipe, it is possible to reduce the wall thickness of the pipe in the pipe circumferential direction. Therefore, the unit weight of the entire heat transfer tube can be reduced, which is very effective for cost reduction.

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment of a heat transfer tube of the present invention.

FIG. 2 is an enlarged cross-sectional view of the heat transfer tube of FIG.

FIG. 3 is a perspective view showing another embodiment of the heat transfer tube of the present invention.

FIG. 4 is a schematic diagram of a tester for measuring the performance of the heat transfer tube of the present invention.

FIG. 5 is a relationship diagram showing heat transfer performance of the heat transfer tube of the present invention.

FIG. 6 is a relationship diagram showing heat transfer performance of the heat transfer tube of the present invention.

[Explanation of symbols]

 1 Heat transfer tube H Groove depth M Spiral groove P Pitch Z Pipe axis θ Twist angle

(72) Inventor Takeshi Nishizawa 2-6-1, Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd. (72) Masanori Ozaki 2-6-1, Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Industry Co., Ltd.

Claims (4)

[Claims] 1. A heat transfer tube for exchanging heat between a fluid inside a tube and a fluid outside the tube, wherein the tube outer peripheral surface of the heat transfer tube has a twist angle direction opposite to a tube axis and a twist angle of 3 to 8
It has at least two kinds of spiral grooves in the range of 0 °, and at least one spiral groove of the at least two kinds of spiral grooves has a groove depth different from that of the other spiral grooves. Heat transfer tube. 2. The heat transfer tube according to claim 1, wherein the absolute values of the helix angle with respect to the tube axis of at least two kinds of spiral grooves having the directions of the spiral groove opposite to the tube axis are different from each other. 3. The twist angle of at least two kinds of spiral grooves with respect to the tube axis is in the range of 15 ° to 45 °, and the absolute value of the twist angle with respect to the tube axis of the deepest spiral groove is larger than that of other spiral grooves. And the groove depth of the spiral groove is 0.1 m
The heat transfer tube according to claim 1 or 2, wherein the heat transfer tube has a diameter in the range of m to 1.5 mm. 4. The inner peripheral surface of the pipe is provided with a spiral strip having an uneven shape corresponding to the concavo-convex shape of the spiral groove formed on the outer peripheral surface of the pipe and having the largest groove depth. The heat transfer tube as described in 3.