JPH0670556B2 - Heat transfer tube and manufacturing method thereof - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to the structure and manufacturing method of a heat transfer tube used in a heat exchanger such as an air conditioner and a refrigerator, and particularly to a surface suitable for a single-phase flow heat transfer tube. The invention relates to the structure and the manufacturing method thereof.

[Background of the Invention]

As is well known, heat exchangers such as air conditioners and refrigerators are provided with heat transfer tubes, and the inner surface of these tubes has a smooth tube which is not processed, as well as those of U.S. Pat.No. 3,768,291. With two-dimensional ribs, or U.S. Pat.
As in the example of No. 830,087, a processing plug for rolling is inserted inside the pipe wall, and a groove on the primary side is provided by performing groove processing, and then a secondary side groove is added by additional machining. A tube having a protruding surface structure is known.

If a heat transfer tube having this surface structure is used as a heat transfer surface for a single-phase flow, for example, the projection shape of this surface structure is an acute angle without roundness, and as will be described later in detail, a separation vortex is generated by a flow that bends a corner. Occurs, the pressure loss of the fluid between the inlet and outlet of the heat transfer tube becomes high, and a large driving force of the fluid is required. Further, with respect to the plane perpendicular to the streamline of the fluid, the stagnation of the fluid in the portion causes the kinetic energy to act as a collision pressure, so that the portion wears out after a long time. The heat transfer performance is lower than the initial performance value because the rib height and rib shape change from the optimum values due to this wear.

Further, in the method using the rolling plug, since the primary groove and the secondary groove have to be processed, the number of processing steps is inevitably increased, which causes a cost increase.

[Object of the Invention]

The object of the present invention is to obtain a high heat transfer rate performance,
(EN) It is an object to provide a heat transfer tube having a heat transfer surface structure with high durability and an inexpensive manufacturing method thereof.

[Outline of Invention]

In order to achieve the above-mentioned object, the heat transfer tube of the present invention has a row of projections intermittently on the inner surface of the heat transfer tube at regular intervals along one or more spiral curves, and between the projection rows. The inner surface of the tube has a surface parallel to the tube axis, and the outer surface of the heat transfer tube has a porous heat transfer surface.
mm to 0.6 mm, circumferential pitch is 3.5 mm to 5 mm, axial pitch is 5 mm to 15 mm, and each projection has a bottom surface and a cross-sectional shape at any height of a circle, an ellipse, or a smooth shape close to these. The curved surface is formed so that the cross-sectional area continuously decreases in the height direction of the protrusion, and is formed on the outer surface of the porous heat transfer surface on the outer surface of the heat transfer tube under the epidermis of the porous heat transfer surface. It is characterized in that an opening that connects the cavity and the outer surface is provided.

In addition, the manufacturing method, the inner surface of the heat transfer tube, by plastic working,
In a case where projection lines are intermittently provided at regular intervals along a single-line or multiple-line spiral curve with a plane parallel to the pipe axis, a gear-like tool and a circular pipe having intermittent projection lines on the outer circumference. By extruding from the outside of the pipe to the inside of the pipe using a fixing tool, the circumferential pitch on the inside surface of the pipe is 3.5 mm to 5 mm.
mm, Axial pitch is 5 mm to 15 mm, and an intermittent row of protrusions is formed, and a shallow groove is formed by knurling on the outer surface of the heat transfer tube. The fins are formed, and the adjacent fins are joined together by rolling or smashing the sawtoothed fins to form cavities under the epidermis on the heat transfer surface and holes with holes on the heat transfer surface. It is characterized by forming a quality structure.

Example of Invention

An embodiment of the present invention will be described below with reference to FIGS.
A protrusion 3 is formed on the inner wall surface 1 of the heat transfer tube along a spiral curve 4. As shown in FIG. 3 (A), the protrusion 3 has
It is a projection 32 having a circular plane, or an oval projection 34 as shown in FIG. 3 (B). Alternatively, as shown in (C), an asymmetrical elliptic curve-shaped protrusion 36 similar to the cross-sectional shape of an egg may be used. Alternatively, an oval 38 such as (D) may be used. Further, the cross-sectional shape of the projections at an arbitrary height is also similar to the bottom surface, and the cross-sectional area is smaller than the bottom surface. The vertical cross-sectional shape is shown in FIG.
It is formed by a smooth curve as shown in (B), (C) and (D). The flat surface may be a curved surface similar to that shown in FIGS.

Next, the manufacturing method of the present invention will be described with reference to the drawings.

FIG. 5 shows an example of the manufacturing method of the present invention. A rotor 50 having a circular pipe fixing tool 52 and a gear-shaped tool 54 is rotated by an external power source (not shown) along the outer periphery of the circular pipe 1 whose inner and outer peripheral surfaces are smooth, and the teeth of the gear-shaped tool 54 are rotated. At 40, the tube is plastically deformed to form the protrusion 3 in the tube. In this case, the pitch in the pipe axis OO 'direction is determined by the mounting angle of the gear-shaped tool. The shape of the protrusion 3 corresponds to the tooth 40 of the tool, and the portions corresponding to the corners of the tooth 40 have roundness.

The circumferential pitch of the recess outside the tube corresponding to the protrusion 3 is equal to the circumferential pitch of the tooth 40 provided on the gear-shaped tool 54,
The height of the protrusion 3 can be determined by adjusting the pressing amount of the tool 54. When rotating the tool 54 in a direction perpendicular to the tube axis, independent rows of annular projections 3 are provided on the inner wall of the tube. When the pipe 1 is fed in the direction of the arrow while rotating the gear-shaped tool 54 as shown in the figure, a spiral projection row is formed. Even when the tube 1 is fixed and the gear-shaped tool 54 is advanced in a spiral shape, a projection row that advances in a spiral shape is formed. Incidentally, in general, the pipe is fed in the axial direction and the tool 54 is fixed and manufactured. A flat surface remains between the protrusion rows.

The concave portion formed when the projection 3 is provided outside the pipe cannot be subjected to fine processing for promoting boiling and condensation outside the pipe, and the smooth portion outside the pipe except this portion promotes the heat transfer outside the pipe. It becomes the effective area of. For this reason, a surface parallel to the tube axis is required outside the tube between each row of protrusions in order to accurately perform the machining outside the tube. At this time, if the outer surface of the tube is parallel to the tube axis, the inner surface of the tube is also parallel to the tube axis in this portion.

FIG. 5A shows a schematic diagram of the gear tool 54 used. The pitch Z in the circumferential direction of the protrusion can be changed by changing the tip tip circumferential angle β of the tool, and the tip tip height h used is larger than the depth of pushing from the outside of the tube into the tube. To give an example of the gear-like tool 54, the outer diameter D is 33 to 35 mm, the tooth height h is 0.45 to 0.8 mm, the tooth tip circumferential angle β is 10 to 20 °, and the tooth tip width w is about 1 mm. By using a gear-shaped tool of this size, a heat transfer tube having a rib height e = 0.45 to 6 mm and a circumferential pitch Z = 2.5 to 5 mm can be manufactured.

In this case, if the outer diameter D changes, the tip tip circumferential angle β forming the optimum circumferential pitch changes accordingly.

The tube axis direction rib pitch can be changed in the range of 5 to 14 mm by inclining the gear-shaped tool 54 at an angle of 5 ° to 20 ° when the angle of the gear-shaped tool 54 is 0 °.

Although the drawing shows a single row of protrusions provided by using one tool 54, a plurality of rows of protrusions may be formed by arranging a plurality of tools 54. These selections can reduce the number of steps based on the formation of the projection row, but are determined by the correlation between the circumferential pitch of the projection and the tube axial pitch of the projection row. By such a method, the lateral cross-sectional shape of the projection 3 has an arc shape, and the vertical cross-sectional shape of the projection 3 cut in the projection row direction has an arcuate undulation in the longitudinal direction of the projection row. A protrusion row having a protrusion shape can be formed on the inner wall of the tube.

As an example of the size of the protrusion, it is preferable that the major axis of the ellipse is about 2 to 5 mm and the minor axis is about 1.5 to 3 mm. As shown in the figure, the protrusion rows may have independent cone-shaped protrusions with rounded tips arranged on the inner wall surface.In the same protrusion row, the distance between adjacent protrusions may be greater than the smooth portion of the pipe inner wall. May also be undulating.

FIG. 6 shows a schematic diagram of streamlines when a single-phase fluid without phase change flows in the pipe. The fluid 60 in the central portion of the pipe flows in the winding axis direction, but the fluid 61 near the wall surface is bent in the flow direction by the protrusions, and a part of the fluid 61 flows in the pipe axial direction when flowing out of the gap between the protrusions. A vertical vortex with its axis of rotation is created.

As shown in FIG. 7, the projection of the heat transfer tube of the present invention has a rib in a vertical cross section because the projection has a curvature even if the flow collides with the projection, so that the streamline does not bend sharply. The effect of shear stress due to the viscous force of the fluid flowing along the wall and the wall surface is smaller, and the effect of erosion due to the shear stress of the fluid is smaller. Further, as shown in FIG. 8, even in the cross-section, the flow passing through the side surface of the protrusion also has a curvature, so that the direction of the streamline is changed abruptly and the amount of separation vortices is small, which is caused by the action of fluid force. The effect of erosion is negligible.

In order to confirm the corrosion resistance, an accelerated corrosion test was conducted under the conditions shown in Table 1.

As shown in Table 2, the experimental results show that the corrosion rate of the round protrusions is slower than that of the three-dimensional protrusions of rectangular shape. This is almost the same as the corrosion rate of a heat transfer tube that has a two-dimensional shape projection that has been used in the past and whose corrosion resistance has been confirmed.The three-dimensional shape with a round projection shown here may be practically acceptable. There is no degree of corrosion.

The performance of the heat transfer tube having the three-dimensional protrusion having a curvature according to the present invention will be described below. Among the parameters that affect the performance of the heat transfer tube of the present invention, the protrusion height. Focusing on the projections in the circumferential direction and the projections in the tube axis direction, experiments were conducted to clarify the effect. The inner diameter d of the heat transfer tube is 14.7 mm
Experiments were performed in the range of ~ 15.8 mm.

In Fig. 9, the pitch p in the tube axis direction is fixed to 7 mm, and the pitch z in the circumferential direction is fixed to 4 mm, and the projection height e is 0.45 mm.
The following shows the measurement results of heat transfer coefficient and pressure loss when changing to (mark), 0.5 mm (△ mark) and 0.6 mm (□ mark). The horizontal axis shows the Reynolds number (= u · d / υ, u: average flow velocity in pipe (m / s), d:
Inner diameter of pipe (mm), υ: kinematic viscosity of fluid (m ² / s)),
The vertical axis represents the dimensionless heat transfer coefficient Nu / Pr ⁰⁴ (= αd / λ /
Pr ⁰⁴ , α: heat transfer coefficient (W / m ² · K), λ: thermal conductivity of fluid (W / m · K), Pr: Prandtl number of fluid), and resistance coefficient of pipeline .

Although not shown in FIG. 9 in order to avoid complication, as a result of conducting an experiment on a smooth tube in which the inner surface of the tube is not subjected to any processing, the heat transfer coefficient is generally known to be generally known. Dittus-Boelter formula, Nu = 0.023Re ⁰⁸
It is in good agreement with Pr ⁰⁴ (Graph A), and regarding the resistance coefficient of the pipeline, Prandtl's The results are in good agreement with. The inner diameter of the tube is 15.8 mm in this case. Regarding the heat transfer coefficient, the protrusion height is 0.
Those with 5 mm and 0.6 mm have more than twice as high performance as the smooth tube (A).

As shown in FIG. 10, as the protrusion height e is increased, the increase rate of the resistance coefficient is higher than the increase rate of the heat transfer coefficient.

As shown in FIG. 9, when the height of the protrusion is increased, the pressure loss becomes high, and when the pressure loss becomes higher than a certain limit, the reduced amount of the pressure loss due to the increase of the heat transfer coefficient cannot be completely absorbed. That is, in this case, when the height of the protrusions is higher than 0.5 mm, the heat transfer promotion effect is reduced and the height of the protrusions is reduced because the resistance coefficient is increased although the increase in the heat transfer coefficient is small. It is considered that 0.5 mm is the optimum height.

In order to confirm this, the results obtained in FIG. 9 are used in the literature which is generally known about the heat transfer coefficient and the resistance coefficient (for example, RLWebb and ERGEckert “App
lication of Rough Surfaces to Heat Exchanger Desig
h ", International Journal of Heat and Mass Transfe
r, Vol.15, pl647 to pl658, 1972). For the heat transfer coefficient and resistance coefficient given by (subscript 0; smooth tube), the heat transfer tube with the above-mentioned three-dimensional projection and the smooth tube not subjected to any such processing and their ratio are Evaluation was performed based on the ratio of the collected items. These values are 1 for smooth tubes
The value increases as the heat transfer performance improves, and the experimental value shown in FIG.
10 and the physical properties corresponding to the water temperature of the refrigerator to which this heat transfer tube is applied and the case of Re = 3 × 10 ⁴ are summarized and the results are shown in FIG.

As shown in Fig. 10, the best heat transfer performance is the heat transfer tube with a protrusion height of 0.5 mm, and when the protrusion height is higher than 0.5 mm or lower than 0.5 mm, the heat transfer performance is Indicates a low value. This optimum projection height is related to the boundary layer in the vicinity of the wall surface of the fluid, and although there is a slight difference in value depending on the pipe diameter and the like, it is considered that this optimum value is a constant value. Experimental data (e = 0.3) of conventional two-dimensional rib attachment (corresponding to US Pat. No. 3,768,291) indicated by D in FIG.
mm, p = 4 mm), the formula (1) showing the heat transfer performance is calculated to be 1.43. If the range higher than this value is the range having the characteristic of the three-dimensional ribbed tube, the range of the protrusion height is 0.45 ~ 0.
It will be 6 mm.

Next, the results of investigation of the effect of the circumferential pitch of the protrusions on the heat transfer performance by a model experiment will be described. Z in this case
Is a circumferential pitch of a protrusion on the inner surface of the tube. Fig. 11 shows that the pitch p in the tube axis direction is fixed at 7 mm, and the projection height is 0.45 mm.
The measurement results of the heat transfer coefficient and the resistance coefficient when z is changed are shown below. In the figure, z is The results for 4 mm (circle) and 5 mm (square) are shown. z =
Comparing the results of 2.5 mm and 4 mm, the heat transfer coefficient shows a high value at z = 4 mm, and the resistance coefficient is larger at z = 2.5 mm, so z = 4 mm has a higher heat transfer performance. Is clearly high.

When z = 2.5 mm, as shown in FIG. 12, the protrusion 5 and the protrusion 5 are continuous with each other and there is no gap c between the protrusion and the protrusion 5,
The vertical vortices 6 generated between the protrusions as shown in FIG. 13 are small in size, and minute vertical vortices 7 are emitted. That is, the limit where the protrusions are densely packed is the two-dimensional protrusion,
Since the mechanism for promoting heat transfer approaches from the three-dimensional protrusion to the secondary protrusion, the heat transfer performance becomes similar to that of the two-dimensional protrusion. Fig. 11 shows the measurement results for the two-dimensional protrusions (⋄, p = 7 mm, e = 0.5 mm) together with the results for the three-dimensional protrusions. As can be seen from this result, as the pitch z becomes denser, the pressure loss becomes higher as in the result of the resistance coefficient of the two-dimensional protrusion.

When z = 4 mm, as shown in Fig. 13 (b), a vertical vortex 6 having a rotation axis in the flow direction is formed from the protrusion and the gap c between the protrusions.
Occurs, which enhances the heat transfer promotion effect. The flow passing through the two-dimensional projection is accelerated in heat transfer by the flow separating at the position of the object and the reattachment of the flow at the wake of the object. In this case, the flow stagnates immediately after the object, increasing the pressure loss, but in the case of the three-dimensional protrusion, the heat transfer is promoted by the vertical vortex, so the flow energy is effectively transferred. It can be used for promotion. In this case, the gap c of the test heat transfer tube was 1 mm, and the distance b in the longitudinal direction of the protrusion was 3 mm. If the gap c becomes wider than a certain extent, a vertical vortex effective for promoting heat transfer will not be generated, and the effect of promoting heat transfer will not be so high. As shown in Fig. 11, when the circumferential pitch z is 5 mm (marked by □), the increase in heat transfer coefficient is lower than when z = 4 mm, and when the air gap c is wide, the heat transfer coefficient decreases. It supports what you do.

Also in this case, as described above, the experimental values are summarized by the formula st / st ₀ / (/ ₀ ) ^1/3 that generally displays the heat transfer performance,
It is shown in FIG. As shown in the figure, z = 4 mm takes the maximum value. The value of D is the two-dimensional rib (e =
It was obtained from the experimental value of 0.3 mm, p = 4 mm), and shows that the three-dimensional projection has a high effect of promoting heat transfer. As described above, when the range higher than the value calculated from the experimental data of the two-dimensional ribbed heat transfer tube is limited, the pitch in the circumferential direction is 3.5 mm to 5 mm.

Regarding the effect of axial pitch, as shown in Fig. 15, when rib height e = 0.5 mm, circumferential pitch z = 4 mm, and axial pitch is 5 mm, 7 mm, 10 mm I conducted an experiment. In Fig. 15, the pitch in the pipe axis direction is 5 mm (marked with ▽),
The results for 7 mm (marked with △) and 10 mm (marked with □) are shown. The denser the axial pitch, the higher the heat transfer coefficient and the higher the pressure loss. FIG. 16 shows the results of rearranging these experimental values by the ratio (st / st ₀ ) / (/ ₀ ) ^1/3 of the heat transfer coefficient and the resistance coefficient. Pitch is 5mm as shown
And 7mm show almost the same value, but the experimental value when the pitch is 10mm is much lower than that of 5mm and 7mm. As shown in FIG. 17, when a vortex is generated in the three-dimensional protrusion portion 3, the vortex is effectively used to promote heat transfer, and the next downstream protrusion exists within the diffusion distance. The performance is kept high. In this case as shown in FIG. 17 (a), the vortex diffusion distance is about 10 times the protrusion height when the protrusion has a two-dimensional shape, and the rib height is 0.5 mm. l = 0.5 mm × 10 = 5 mm, and the portion indicated by l in FIG. 17 is estimated to be about 5 mm, that is, the axial pitch is 5 mm.
The performance at 7 mm remains high, but when the axial pitch is 10 mm, p> l as shown in Fig. 17 (b).
In this case, since the axial pitch is longer than the diffusion distance of the vortex, there are many smooth portions where no vortex is generated, and the heat transfer promotion effect is reduced. As described above, when the practical range is higher than the value (Fig. 16D) shown by the ratio of heat transfer coefficient and pressure loss calculated from the experimental data of the two-dimensional ribbed heat transfer tube and the practical range is The axial pitch range is 5 mm to 9 mm.

As a result of experimentally studying each dimension of the protrusion, the range of the height of the protrusion on the inner surface of the pipe is 0.45 mm to 0.6 mm, the pitch in the circumferential direction is 3.5 mm to 5 mm, and the pitch in the axial direction is 5 mm.
The optimum size was the projection row in the range of ~ 9 mm.

The flow passing through the rounded row of protrusions formed inside the tube differs depending on the arrangement. The flow shown in FIG. 18 shows the flow pattern when the projections 3 are arranged in a staggered pattern. The wake 90 of the projection collides with the projection of the wake part again, so that the heat transfer Although the accelerating effect is maintained, as shown in FIG. 19, when the board-shaped projections 3 are arranged, they collide with the projections again before the vortex of the projection wake 100 diffuses.
Does not show sufficient heat transfer promoting effect. Further, in the flow on the outside of the protrusions, the fluid flows linearly in the tube axis direction and heat transfer is not promoted. Therefore, the zigzag arrangement has a higher heat transfer performance than the zigzag arrangement.

On the other hand, a so-called two-dimensional ribbed tube in which corrugated projections are continuously used, which has been conventionally used, has a high heat transfer performance as shown in FIG. 11, but has a significantly high pressure loss. If the pressure loss is too high, a large amount of pump power required to circulate the same fluid is consumed, so the pressure loss is preferably low. In the case of the heat transfer tube of the present invention, due to the increase in the heat transfer coefficient, the required heat transfer area can be reduced if the heat load is the same, and the pressure loss is reduced accordingly, so the increase in the resistance coefficient is sufficiently absorbed. can do.

Also, the generation of turbulent vortices near the tube wall is not significantly affected by the tube inner diameter, so the applicable range of the heat transfer tube having this three-dimensional protrusion is 10 to 25.4 mm.

The heat transfer surface structure may be provided on the outer surface of the heat transfer tube of the present invention described above. The method will be described below. First, a protrusion is formed on the inner surface of the heat transfer tube.

If ribs are formed inside the heat transfer tube by rolling from outside the tube, it is not possible to form a microfabricated heat transfer surface structure in that part,
Since the ineffective area is increased, it is necessary to realize a heat transfer promotion surface structure on the surface of the heat transfer tube, which has no recess formed by roll processing outside the tube and is highly parallel to the tube axis. Therefore, in the next step, as shown in FIG. 20, a heat transfer surface structure 208 effective for porous boiling heat transfer is provided on the smooth portion 207 outside the tube, that is, the portion where the recess is not formed when the projection is formed. Set up. Reference numeral 230 is a recess formed when the protrusion 3 is provided.

In this case, it is possible to first perform the external micromachining to improve the external heat transfer coefficient, and then perform the roll processing to form the internal ribs. Depending on the structure of the tool, the external heat transfer promotion surface structure that was previously formed may be crushed.Therefore, when performing internal pipe processing first to form internal pipe ribs and then performing external micromachining, Let me explain.

As an example, first, a shallow groove (0.1 to 0.2 mm) is formed in a direction of about 45 ° with respect to the tube axis by loretto processing. Next, the fin 212 is formed by punching with a cutting tool substantially at right angles to the pipe axis. The fin height is about 1 mm, and the pitch is 0.4 to 0.6 mm. By doing so, a saw-toothed fin array is provided on the smooth surface before processing. Next, let the saw-tooth fins bend by roll processing etc.,
Alternatively, adjacent fins can be joined together by a method such as crushing fins to form a porous projecting structure 208 having a cavity 209 and an opening 210 under the epidermis of the heat transfer surface. Figure 21 shows the appearance of the heat transfer tube.

For example, the case where water flows in the tube of such a heat transfer tube and Freon refrigerant, which is a low boiling point organic medium, flows outside the tube is taken as an example. The shell tube type heat exchanger in which a large number of heat transfer tubes are inserted in a cavity is widely used as an evaporator of a turbo refrigerator. It is customary for the temperature of the water inside the tube to be about 5-10 ° C higher than the temperature of the Freon refrigerant outside the tube. Due to the presence of the protrusions, the flow in the pipe generates turbulence in the vicinity of the wall surface, and the heat exchange between the wall inside the pipe and the main flow of the flow in the pipe is performed more actively than in the case of a smooth surface.

On the other hand, in heat exchange between the outer wall of the tube and the Freon liquid refrigerant on the outer side of the tube, once boiling occurs, vapor bubbles are retained in the cavity, and a thin Freon liquid film is formed between the cavity inner wall and the vapor bubble. The evaporation of the thin liquid film promotes latent heat transport based on the evaporation of the liquid.

FIG. 22 shows the effect of the projection pitch P on the heat transfer efficiency of the heat transfer tube, taking the embodiment of FIG. 21 and the projection height of 0.3 mm as an example. As can be seen from the figure, there is an optimum range of the protrusion pitch P that can obtain high heat transfer efficiency. That is, when P is large, the area of the smooth portion on the outer side of the tube becomes large, and the heat transfer area for forming the porous structure can be widened by the machining effective for boiling heat transfer. Therefore, the heat transfer efficiency on the outside of the pipe is improved by the increase in area.

On the other hand, the heat transfer coefficient on the inside of the pipe suddenly increases as P increases, because the turbulence 70 of the flow caused by the projections 3 does not affect the wall side portion on the flow side as shown in FIG. 23. The heat transfer efficiency decreases. In this case, the rate of decrease in heat transfer performance due to forced convection inside the tube is higher than the rate of improvement in boiling performance outside the tube. Therefore, the overall heat transfer efficiency of the heat transfer tube sharply decreases as P increases. Next, when P is small, the heat transfer surface range affected by the turbulence does not increase even if P is smaller than a certain level, and therefore the heat transfer efficiency of the forced convection in the tube does not change so much. On the other hand, on the outer side of the tube, when P becomes smaller, the ratio of the area occupied by the outer hollows to the area of the entire outer tube sharply decreases, so that the boiling heat transfer performance outside the tube also sharply decreases. Therefore,
The overall heat transfer efficiency of the heat transfer tube drops sharply even if P becomes small. Due to the phenomenon as described above, there exists an optimum range of the protrusion pitch P for keeping the overall heat transfer efficiency of the heat transfer tube high. From Fig. 22, the optimum range of the heat transfer coefficient of the heat transfer tube is 5 mm to 15 mm.

By the way, when a shell-tube heat exchanger is constructed by the heat transfer tube of the present invention, as shown in FIG.
After expanding 215 and performing projection formation processing, tube plate 2
It is possible to insert a heat transfer tube into 16 and join the tube plate and the heat transfer tube by expanding the tube. The conventional method of providing protrusions inside the tube by plug processing or drawing processing is only possible if both ends of the heat transfer tube are straight.Therefore, after performing internal tube protrusion processing, cut the protrusions at both ends. The pipe is expanded after making it smooth. Therefore, the heat transfer tube according to the present invention can reduce the number of assembling steps when forming a shell-tube heat exchanger.

〔The invention's effect〕

It is possible to maximize the effect of a vertical vortex having an axis in the flow direction that occurs in the flow past the protrusions, and it is possible to greatly improve the single-phase heat transfer coefficient. Further, on the outer side of the tube, the heat transfer efficiency can be improved because the heat transfer area can be widened due to the porous structure. As a result, a heat transfer tube having a high heat transfer coefficient and high durability can be obtained, and it can be manufactured at low cost.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a heat transfer tube according to an embodiment of the present invention, FIG. 2 is an enlarged perspective view of an essential part showing a heat transfer tube structure of the present invention, and FIGS. 3 (A), (B), ( C) and (D) are plan views showing another embodiment of the present invention, FIGS. 4 (A), (B),
(C) and (D) are respectively (A), (B), and FIG.
(C), (D) cross-sectional views, FIGS. 5 and 5A are views showing an example of the production method of the present invention, FIG. 6 is an explanatory view of the characteristics of the present invention, and FIG. 7 is an illustration of the present invention. A cross-sectional view of the heat transfer tube, FIG. 8 is a front view thereof, and FIGS. 9 to 11 and 14 to 17 are views showing an example of experimental data of the present invention, FIG. 12, FIG. 13 and FIG. 18th
Figures and 19 show the relationship between the protrusion pitch and the heat transfer efficiency.
20 and 21 are diagrams showing an example of a heat transfer tube to which the present invention is applied, FIGS. 22 to 23 are diagrams for explaining the performance of the embodiment of FIG. 20, and FIG. 24 is an implementation of FIG. It is a figure which shows the example of use of an example. 1 ... Heat transfer tube, 3 ... Protrusion, 40 ... Tooth, 52 ... Tool for fixing circular tube,
54 ... Gear-shaped tool.

Front page continuation (72) Inventor Takehiko Yanagida 502 Jinritsu Machinery Research Center, Tsuchiura City, Ibaraki Pref., Inside the Mechanical Research Laboratory, Hiritsu Manufacturing Co., Ltd. (72) Inventor Shigeo Sugimoto 603 Jinritsu-cho, Tsuchiura-shi, Ibaraki Inside the Hitachi Co., Ltd., Tsuchiura Plant (72) Inventor Kiyoshi Oizumi 3550, Kidayo-cho, Tsuchiura-shi, Ibaraki Inside the Tsuchiura Plant, Hitachi Cable Co., Ltd. (56) Reference References JP-A-60-29594 (JP, A) JP-B 63-16037 (JP, B2) JP-B 64-2878 (JP, B2)

Claims (2)

[Claims] 1. An inner surface of a heat transfer tube is provided with rows of projections intermittently at regular intervals along one or more spiral curves, and the tube inner surface between each row of projections is parallel to the tube axis. In the one having a surface and a porous heat transfer surface on the outer surface of the heat transfer tube, each of the protrusions has a height of 0.45 mm to 0.6 mm and a circumferential pitch of 3.5 m.
m ~ 5 mm, axial pitch 5 mm ~ 15 mm, and each projection has a bottom surface and a cross-sectional shape at an arbitrary height consisting of a circle, an ellipse, or a smooth curve similar to these, and the cross-sectional area is the height of the projection. Formed to decrease continuously in the direction
A heat transfer tube, wherein an outer surface of the heat transfer tube is provided with an opening that connects the outer surface of the porous heat transfer surface with a cavity formed under the epidermis of the porous heat transfer surface and the outer surface. 2. A heat transfer tube, wherein the inner surface of the heat transfer tube is provided with intermittent projection rows at regular intervals by plastic working to form a surface parallel to the tube axis along one or more spiral curves, By performing extrusion from the outside of the pipe to the inside of the pipe using a gear-shaped tool with intermittent projection rows and a tool for fixing the circular pipe, the circumferential pitch on the inner surface of the pipe is 3.5 mm to 5 mm, axial pitch Form an intermittent row of protrusions of 5 mm to 15 mm, form a shallow groove by knurling on the outer surface of the heat transfer tube, and form a saw-toothed fin by punching with a bite almost at right angles to the tube axis. By rolling or rolling the sawtoothed fins, the adjacent fins are joined together to form a hollow structure under the epidermis of the heat transfer surface and a porous structure with holes on the surface of the heat transfer surface. Of the heat transfer tube Production method.