JP7254307B2 - heat transfer tube - Google Patents

Description

The present invention uses the potential heat of a fluid outside the pipe (natural refrigerant, Freon refrigerant, water, etc.), the potential heat of an object outside the pipe (solid substances such as soil heat, etc.), or the radiant heat of a solar panel, etc., and the fluid flowing inside the pipe. (water, brine, etc.). The present invention particularly relates to an in-tube single-phase flow heat transfer tube suitable for use in a low-velocity region where the fluid in the tube is a single-phase flow.

Specific uses of in-pipe single-phase flow heat transfer tubes include (a) heat transfer tubes used in water-refrigerant heat exchangers used in heat pump water heaters (e.g., EcoCute (registered trademark)), (b) gas Heat transfer tubes used in water-water double-tube heat exchangers used in water heaters, (c) hot water pipes installed in solar panels of solar water heaters, (d) underground There is a heat transfer tube for soil heat-water heat exchanger piping that is embedded and used.

Efforts are being made to save energy in equipment that exchanges heat between fluids inside and outside pipes, and efforts are being made to improve the performance of the heat exchanger itself and to save energy by reducing the power required to transport the heat medium. A pump is commonly used to drive the heat transfer fluid through the heat exchanger. As a measure for reducing the power for conveying the heat medium, a method of reducing the pump operating power by reducing the flow rate of the carrier fluid is adopted.

In addition, there is a device that heats a fluid to a high temperature over a long period of time in a heat exchanger, and a representative example is a heat pump water heater. This heat pump water heater feeds water, which is a fluid, directly into the heat exchanger from a tap water supply port, and raises the temperature of the fluid in the heat exchanger over a long period of time. Therefore, in the heat pump water heater, the speed of the water in the pipe is set low, and the pressure of the water is also set low compared to the conveying power of the pump or the like. As a result, heat pump water heaters are often used with a Reynolds number of 2000 or less in the pipe because the speed of water passing through the pipe is low. In this low Reynolds number region, the water in the tube becomes a laminar flow area and the heat transfer coefficient in the laminar flow area is reduced compared to the turbulent flow condition. Therefore, it has to be dealt with by improving the performance of the heat transfer tubes themselves.

Typical heat transfer tubes currently in use include corrugated tubes described in Patent Documents 1 and 2. A corrugated pipe has spiral corrugated grooves that form deep unevenness on the inner and outer surfaces of the pipe. In addition, in Patent Document 2, in addition to the corrugated grooves, projections are formed between the corrugated grooves so as to protrude from the inner surface of the pipe. In the corrugated pipe, the irregularities and projections formed as corrugated grooves promote the formation of turbulence even when the fluid in the pipe flows in a laminar flow region, thereby improving the heat transfer coefficient.

Japanese Patent Application Laid-Open No. 2007-218486 WO2008/029639

However, in the corrugated pipes of Patent Literatures 1 and 2, when a fluid is caused to flow inside the pipe, a side flow that convects between the corrugated grooves is formed near the inner wall surface of the pipe. Since the pitch of the corrugated grooves is small, this secondary flow tends to remain near the inner wall surface of the pipe without joining with the main flow flowing through the center of the pipe, forming a velocity boundary layer and a temperature boundary layer. This boundary layer has the problem of impeding heat exchange between fluids. Further, in Patent Document 2, projections are formed between the corrugated grooves, but these projections are also smaller than the pitch width of the corrugated grooves, so that the side flow is likely to convect without colliding with the projections. Therefore, in Patent Document 2, it is difficult to form a flow that merges the main stream and the side stream with the projections, and the formation of the boundary layer cannot be suppressed. In particular, when the flow velocity of the fluid inside the corrugated pipe is in a low flow velocity region, the formation of the boundary layer becomes remarkable.

The present invention has been made in view of such problems, and provides a heat transfer tube that can suppress the formation of a boundary layer and improve the heat transfer coefficient even when the flow velocity of the fluid in the tube is low. The task is to provide

A heat transfer tube according to the present invention comprises a corrugated tube in which grooves are formed spirally at a predetermined spiral period, and a plurality of recesses are formed along the tube axial direction between the grooves extending over the entire length of the corrugated tube. In addition, the recess is formed so as to be recessed from the outer surface of the pipe toward the inner surface of the pipe, and the length of the recess in the pipe axial direction is 50 to 90% of the groove pitch width of the groove. The Reynolds number of the fluid flowing inside is 2000 or less .

According to the heat transfer tube of the present invention, since the recesses of a predetermined length are formed between the grooves, the secondary flow flowing along the grooves collides with the recesses protruding from the inner wall surface of the tube. A countercurrent is formed as a tertiary flow. Since this tertiary flow acts to join the secondary flow to the primary flow, formation of a boundary layer on the inner wall surface of the pipe is suppressed. As a result, the heat exchange between the fluids is not hindered, so the heat transfer coefficient of the heat transfer tubes is improved.

In the heat transfer tube according to the present invention, it is preferable that a plurality of recesses are formed in two cycles of the spiral cycle.
According to the heat transfer tube of the present invention, since a plurality of recesses are formed in two helical cycles, the number of recesses formed on the inner surface of the tube increases. Thereby, formation of the tertiary flow formed by the recess is promoted. As a result, the tertiary flow makes it easier for the secondary flow to join the primary flow, further improving the heat transfer coefficient of the heat transfer tube.

In the heat transfer tube according to the present invention, it is preferable that each of the plurality of concave portions formed in two cycles is formed on the same straight line.
Further, in the heat transfer tube according to the present invention, it is preferable that each of the plurality of recesses formed in two cycles is formed at positions separated from each other by 360 degrees in the tube circumferential direction.
According to the heat transfer tube of the present invention, the plurality of recesses are formed on the same straight line, that is, formed at positions separated by 360 degrees, so that the recesses are formed at the same position in the pipe circumferential direction for each cycle. . As a result, it becomes easier to form the recesses in the manufacture of the heat transfer tube, and the manufacturing cost is reduced.

In the heat transfer tube according to the present invention, it is preferable that each of the plurality of concave portions formed in two cycles is formed on different straight lines.
Further, in the heat transfer tube according to the present invention, it is preferable that each of the plurality of concave portions formed in two cycles is formed at positions separated from each other by 180 degrees in the tube circumferential direction.
Further, in the heat transfer tube according to the present invention, it is preferable that each of the plurality of recesses formed in two cycles is formed at positions separated from each other by 240 degrees or 120 degrees in the tube circumferential direction.
Further, in the heat transfer tube according to the present invention, it is preferable that each of the plurality of concave portions formed in two cycles is formed at positions separated from each other by 270 degrees or 90 degrees in the tube circumferential direction.

According to the heat transfer tube of the present invention, the plurality of concave portions formed in two cycles are formed on different straight lines. Further, the recesses are formed at positions separated from each other by a predetermined angle in the circumferential direction of the tube. Thereby, the recesses formed over the entire length of the pipe are formed at positions separated from each other by a predetermined angle when viewed from the side of the pipe orthogonal to the pipe axis. Then, the arrangement of the concave portions formed on the inner surface of the pipe becomes uniform in the circumferential direction of the pipe. As a result, the tertiary flow formed by the recess makes it easier for the secondary flow to join the primary flow, further improving the heat transfer coefficient of the heat transfer tube.

In the heat transfer tube according to the present invention, it is preferable that the concave portion is formed for each spiral period.
According to the heat transfer tube of the present invention, since the recesses are formed for each spiral period, the number of recesses formed on the inner surface of the tube increases. Thereby, formation of the tertiary flow formed by the recess is promoted. As a result, the tertiary flow makes it easier for the secondary flow to join the primary flow, further improving the heat transfer coefficient of the heat transfer tube.

In the heat transfer tube according to the present invention, it is preferable that the concave portions are formed at intervals of the predetermined spiral period.
According to the heat transfer tube of the present invention, since the recesses are formed at predetermined intervals of the spiral period, the arrangement of the recesses formed on the inner surface of the tube becomes uniform in the circumferential direction of the tube. As a result, the tertiary flow formed by the recess makes it easier for the secondary flow to join the primary flow, further improving the heat transfer coefficient of the heat transfer tube.
The heat transfer tube according to the present invention can reduce the pressure of the pump that supplies the fluid when the Reynolds number of the fluid flowing inside the tube is 2000 or less, thereby reducing the pump driving power.

ADVANTAGE OF THE INVENTION The heat exchanger tube which concerns on this invention can suppress formation of a boundary layer, and a heat transfer coefficient improves. Moreover, since the heat transfer tube according to the present invention is suitable for a low flow velocity region, it is possible to reduce the driving power of the pump that supplies the fluid, thereby saving energy.

BRIEF DESCRIPTION OF THE DRAWINGS It is a perspective view which shows the structure of the heat exchanger tube which concerns on 1st Embodiment of this invention. FIG. 2 is a cross-sectional view taken along the line II-II of FIG. 1 and viewed from the side of the pipe; FIG. 2 is a cross-sectional view taken along line III-III of FIG. 1, schematically showing the flow of fluid inside the pipe. FIG. 5 is a front view showing the configuration of a heat transfer tube according to a second embodiment of the present invention; FIG. 5 is a cross-sectional view taken along line VA-VA of FIG. 4, showing the arrangement of recesses in a pipe side view, omitting the illustration of grooves and the like. FIG. 5 is a cross-sectional view taken along the line VB-VB in FIG. 4, showing the arrangement of recesses in a pipe side view, omitting the illustration of grooves and the like. FIG. 8 is a front view showing the configuration of a heat transfer tube according to a third embodiment of the present invention, in which recesses formed on the back side of the heat transfer tube are shown in a simplified manner. The VIIA-VIIA line in FIG. 6 shows the arrangement of the recesses in a side view of the tube, omitting the description of the grooves and the like. The line VIIB-VIIB in FIG. 6 shows the arrangement of the recesses in a side view of the pipe, omitting the illustration of the grooves and the like. FIG. 7 is a cross-sectional view taken along the line VIIC-VIIC in FIG. 6, showing the arrangement of recesses in a tube side view, omitting the illustration of grooves and the like. FIG. 11 is a front view showing another configuration of the heat transfer tube according to the third embodiment of the present invention, in which the concave portion formed on the back side of the heat transfer tube is simply shown. The line IXA-IXA in FIG. 8 shows the arrangement of the recesses in a side view of the tube, omitting the description of the grooves and the like. The IXB-IXB line in FIG. 8 shows the arrangement of the concave portions as viewed from the side of the tube, omitting the illustration of grooves and the like. FIG. 9 is a cross-sectional view taken along the line IXC-IXC of FIG. 8, showing the arrangement of recesses in a side view of the tube, omitting the illustration of grooves and the like. FIG. 11 is a front view showing the configuration of a heat transfer tube according to a fourth embodiment of the present invention, in which recesses formed on the back side of the heat transfer tube are shown in a simplified manner. The line XIA-XIA in FIG. 10 shows the arrangement of the recesses in the side view of the pipe, omitting the description of the grooves and the like. The XIB-XIB line in FIG. 10 shows the arrangement of the recesses in the side view of the tube, omitting the description of the grooves and the like. FIG. 11 is a cross-sectional view taken along line XIC-XIC in FIG. 10, showing the arrangement of recesses in a tube side view, omitting the illustration of grooves and the like. FIG. 11 is a cross-sectional view taken along the XID-XID line in FIG. 10, showing the arrangement of recesses in a pipe side view, omitting the illustration of grooves and the like. FIG. 11 is a front view showing another configuration of the heat transfer tube according to the fourth embodiment of the present invention; The XIIIA-XIIIA line in FIG. 12 shows the arrangement of the recesses in the side view of the pipe, omitting the description of the grooves and the like. The line XIIIB-XIIIB in FIG. 12 shows the arrangement of the recesses in a side view of the tube, omitting the description of the grooves and the like. FIG. 13 is a cross-sectional view taken along the line XIIIC-XIIIC of FIG. 12, showing the arrangement of the recesses in a side view of the pipe, omitting the illustration of grooves and the like. FIG. 13 is a cross-sectional view taken along the line XIIID-XIIID in FIG. 12, showing the arrangement of recesses in a side view of the tube, omitting the illustration of grooves and the like. FIG. 2 is a schematic diagram schematically showing a testing device for measuring heat transfer coefficients of heat transfer tubes. 4 is a graph showing the relationship between Reynolds number Re and heat transfer coefficient Nu. FIG.

A heat transfer tube according to an embodiment of the present invention will be specifically described.
A heat transfer tube exchanges heat between a fluid inside the tube, preferably a single-phase fluid, and a heat medium outside the tube. Single-phase fluids such as water and brine flow through the tubes of the heat transfer tubes. On the other hand, the heat medium outside the tube differs depending on the field in which the heat transfer tube of the present invention is used. When the heat transfer tube of the present invention is used in a water-refrigerant heat exchanger such as a heat pump water heater, a natural refrigerant or Freon refrigerant flows on the outer surface of the tube. In the case where the field of use is a double-pipe heat exchanger used as a water-water heat exchanger such as a gas water heater, a single-phase flow fluid such as water also flows outside the pipes. Also in other technical fields, for example, when the heat transfer tube of the present invention is used for hot water piping of a solar panel of a solar water heater, radiant heat generated by absorption of electromagnetic waves such as radiation emitted by the sun on the outer surface of the tube is Act on heat transfer tubes. Further, when the heat transfer tube of the present invention is buried in the ground and used in the field of a water-soil heat exchanger in which the soil and the outer surface of the tube are in contact, the heat accumulated in the soil and the outer surface of the tube A heat exchange occurs between them. The Reynolds number, which indicates the flow velocity of the single-phase fluid flowing through the pipe, is preferably 2000 or less. When the Reynolds number is 2000 or less, the flow rate of the fluid supplied into the pipe is reduced, and the driving power of the pump for supplying the fluid can be reduced, so that the power consumption of the equipment can be reduced.

<First embodiment>
A heat transfer tube according to a first embodiment of the present invention will be described with reference to the drawings.
As shown in FIGS. 1 to 3, the heat transfer tube 1 is composed of a corrugated tube 2 in which grooves 3 are spirally formed with a predetermined spiral period so as to be recessed from the outer surface of the tube toward the inner surface of the tube. A plurality of recesses 4 are formed along the tube axial direction between the spiral grooves 3 extending over the entire length, and the recesses 4 are formed so as to be recessed from the tube outer surface toward the tube inner surface. In the heat transfer tube 1 , the length Ld of the concave portion 4 in the tube axis direction is specified as a ratio to the groove pitch width Pc of the groove portion 3 . Further, in the heat transfer tube 1, the concave portion 4 is formed for each spiral cycle of the groove portion 3, and a plurality of concave portions 4 are formed in two cycles. Further, in the heat transfer tube 1, the length directions of the plurality of concave portions 4 formed in two cycles are formed on the same straight line when viewed from the front of the tube. Moreover, the heat transfer tube 1 is formed so that the concave portions 4 are spaced apart by a predetermined spiral period.

For example, in the heat transfer tube 1, two recesses 4 are formed in two spiral cycles, and one recess 4 is formed in each cycle. Further, in the heat transfer tube 1, the length directions of the two concave portions 4 formed in two cycles are formed on one straight line parallel to the tube axis when viewed from the front of the tube. In the heat transfer tube 1, the concave portions 4 are formed at positions separated from each other by 360 degrees in the tube circumferential direction. In the heat transfer tube 1, the concave portions 4 are formed in the tube circumferential direction at intervals of one spiral period.

Each configuration of the heat transfer tube 1 will be specifically described (corrugated tube)
The corrugated pipe 2 has a helical groove 3 formed on the outer surface of the pipe main body. The material of the pipe main body is made of a metal material that conducts heat, such as copper, copper alloy, aluminum, aluminum alloy, iron, stainless steel, and titanium. Anything is more preferable. The dimensions of the tube main body of the corrugated tube 2 are appropriately set according to the field of use of the heat transfer tube.

(groove)
The groove portion 3 is formed by pressing a tool with a sharp tip against the outer surface of the smooth tube, which is the tube main body, and in this state, for example, rotating the tube and moving the tool in the axial direction of the tube. It is a groove formed in a single shape. As shown in FIGS. 2 and 3, by forming the grooves 3, protrusions are formed on the inner wall surface of the corrugated tube 2, and along the protrusions, a side flow F2 of the fluid flowing spirally near the inner wall surface of the tube is generated. be done.

A groove pitch width Pc of the groove portion 3 is preferably 15 to 25 mm. When the groove pitch width Pc is 15 mm or more, the recesses 4 having a predetermined length or longer can be formed between the grooves 3 so that the side flow F2 collides with them to generate the counterflow F31 of the fluid. Further, when the groove pitch width Pc is 25 mm or less, the turbulence of the main flow F1 of the fluid flowing through the central portion of the pipe is not promoted by the recesses 4, and the pressure loss can be suppressed.

A groove depth Dc of the groove portion 3 is preferably 0.6 to 1.2 mm. When the groove depth Dc is 0.6 mm or more, the generation of the side flow F2 is promoted. Further, when the groove depth Dc is 1.2 mm or less, the grooves 3 do not promote the turbulence of the main flow F1 at the center of the pipe, and the pressure loss can be suppressed.

In addition, the groove portion 3 is formed by a single spiral line. In this case, the groove helix angle .theta. is uniquely determined when the pipe outer diameter, groove pitch width Pc, and the number of grooves are determined. For example, this groove twist angle θ is 48 to 65 degrees. A groove width Wc of the groove portion 3 is, for example, 1.7 to 5.5 mm.

(recess)
The recess 4 is formed by pressing a tool with a sharp tip against a predetermined position on the outer surface of the corrugated pipe 2 . As shown in FIGS. 2 and 3, the formation of the recesses 4 forms protrusions on the inner wall surface of the corrugated tube 2 .

As shown in FIG. 1, the axial length Ld of the concave portion 4 is 50 to 90% of the groove pitch width Pc. When the length Ld of the recesses 4 is 50% or more of the groove pitch width Pc, the side flow F2 collides with the recesses 4 to generate a counterflow F31. The side flow F2 joins F1 and no boundary layer is generated. Further, when the length Ld of the recesses 4 is 90% or less of the groove pitch width Pc, the turbulence of the main flow F1 is not promoted by the recesses 4, and the pressure loss can be suppressed.

As shown in FIG. 2, the depth Dd of the concave portion 4 in the tube radial direction is preferably 6 to 20% of the tube outer diameter. When the depth Dd of the recess 4 is 6% or more of the tube outer diameter, the side flow F2 is likely to collide with the recess 4, and counterflows F31 to F34 are likely to be generated. Further, when the depth Dd of the recess 4 is 20% or less of the outer diameter of the pipe, the recess 4 does not promote turbulence of the main flow F1, and pressure loss can be easily suppressed.

The width Wd of the concave portion 4 in the pipe circumferential direction is appropriately set in consideration of the ease of forming the concave portion 4 and the size that can suppress the promotion of turbulent flow in the main flow F1. For example, the width Wd of the recess 4 is preferably 11 to 26% of the pipe circumference.

As shown in FIG. 3, when a fluid is supplied to the inner surface of the heat transfer tube 1, a secondary flow F2 of the fluid spiraling near the inner wall surface of the tube collides with the projections formed by the recesses 4, A counter-flow F31 of fluid flowing in the opposite direction to the main flow F1 of fluid flowing through the section is generated. The counterflow F31 flows along the bottom surface of the recess 4, collides with the groove 3, and becomes a counterflow F32 that flows along the groove 3 in the direction opposite to the side flow F2. The counterflow F32 collides with the inner wall surface of the pipe and becomes a countercurrent F33 that flows along the inner wall surface of the pipe in the direction opposite to the counterflow F31. The countercurrent F33 collides with the groove 3 and becomes a countercurrent F34 that flows along the groove 3 in the opposite direction to the countercurrent F32. The counterflow F34 again collides with the protrusion formed by the recess 4 and becomes a counterflow F31. The projections formed by the concave portions 4 in this way repeatedly generate the counterflows F31 to F34, thereby stirring the fluid near the inner wall surface of the pipe and joining the main flow F1 with the side flow F2. As a result, no boundary layer is generated near the inner wall surface of the tube, and heat exchange between fluids is improved, so that the heat transfer coefficient of the heat transfer tube 1 is increased.

<Second embodiment>
A heat transfer tube according to a second embodiment of the present invention will be described with reference to the drawings.
As shown in FIGS. 4 to 5B, in the heat transfer tube 1A according to the second embodiment of the present invention, the length direction of each of the plurality of concave portions 4 formed in two spiral cycles of the groove portion 3 is aligned with the tube front surface. It has the same configuration as the heat transfer tube 1 (see FIG. 1) of the first embodiment 1 except that it is formed on two straight lines parallel to the visible tube axis.

For example, in the heat transfer tube 1A, four concave portions 4 are formed in two spiral cycles, and two concave portions 4 are formed in each cycle. Further, in the heat transfer tube 1A, the length directions of the four concave portions 4 formed in two cycles are formed on two straight lines parallel to the tube axis when viewed from the front of the tube. Further, in the heat transfer tube 1A, the concave portions 4 formed in two cycles are formed at positions separated from each other by 180 degrees in the tube circumferential direction. Further, in the heat transfer tube 1A, the concave portions 4 are formed in the tube circumferential direction at intervals of 1/2 of the spiral period. In the heat transfer tube 1A, a plurality of recesses 4 formed over the entire length of the corrugated tube 2 are formed at positions separated from each other by 180 degrees in the tube circumferential direction when viewed from the side of the tube.

In the heat transfer tube 1A, a plurality of recesses 4 formed over the entire length of the corrugated tube 2 are formed at positions that equally divide the tube circumference into two when viewed from the side of the tube. In the heat transfer tube 1A, although not shown, a plurality of recesses 4 may be formed at two locations that unequally divide the circumference of the tube when viewed from the side of the tube. For example, in the heat transfer tube 1A, the second concave portion 4 may be formed at a position separated from the first concave portion 4 by 90 degrees in the pipe circumferential direction.

<Third Embodiment>
A heat transfer tube according to a third embodiment of the present invention will be described with reference to the drawings.
As shown in FIGS. 6 to 7C, in the heat transfer tube 1B according to the third embodiment of the present invention, the length direction of each of the plurality of recesses 4 formed in two cycles of the spiral cycle of the groove portion 3 is aligned with the tube front surface. It has the same configuration as the heat transfer tube 1A of the second embodiment (see FIGS. 4 to 5B) except that it is formed on three straight lines parallel to the visual tube axis.

For example, in the heat transfer tube 1B, three concave portions 4 are formed in two spiral cycles, and one or two concave portions 4 are formed in each cycle. Also, in the heat transfer tube 1B, the length directions of the three concave portions 4 formed in two cycles are formed on three straight lines parallel to the tube axis when viewed from the front of the tube. Further, in the heat transfer tube 1B, the concave portions 4 formed in two cycles are formed at positions separated from each other by 240 degrees in the circumferential direction of the tube in the spiral advancing direction (clockwise direction in the drawing). Further, in the heat transfer tube 1B, the concave portions 4 are formed in the tube circumferential direction at intervals of ⅔ of the spiral period. In the heat transfer tube 1B, the plurality of recesses 4 formed over the entire length of the corrugated tube 2 are formed at positions separated from each other by 120 degrees in the tube circumferential direction when viewed from the side of the tube.

Another configuration of the heat transfer tube according to the third embodiment of the present invention will be described with reference to the drawings.
As shown in FIGS. 8 to 9C, in the heat transfer tube 1C having another configuration, each of the plurality of recesses 4 formed in two cycles of the spiral cycle of the groove portion 3 is arranged in the spiral advancing direction (clockwise in the figure), It has the same configuration as the heat transfer tube 1B of the third embodiment (see FIGS. 6 to 7C) except that they are formed at positions separated from each other by 120 degrees in the tube circumferential direction.

For example, in the heat transfer tube 1C, six concave portions 4 are formed in two spiral cycles, and three concave portions 4 are formed in each cycle. Further, in the heat transfer tube 1C, the concave portions 4 are formed in the tube circumferential direction at intervals of ⅓ of the spiral period. Also, in the heat transfer tube 1C, similarly to the heat transfer tube 1B, the plurality of recesses 4 formed over the entire length of the corrugated tube 2 are formed at positions separated from each other by 120 degrees in the tube circumferential direction when viewed from the side of the tube. .

In the heat transfer tubes 1A and 1B, a plurality of recesses 4 formed over the entire length of the corrugated tube 2 are formed at positions that equally divide the tube circumference into three when viewed from the side of the tube. In the heat transfer tubes 1A and 1B, although not shown, a plurality of recesses 4 may be formed at three locations that unequally divide the tube circumference when viewed from the side of the tubes. For example, in the heat transfer tubes 1A and 1B, the second concave portion 4 is formed at a position separated from the first concave portion 4 by 90 degrees in the spiral traveling direction in the tube circumferential direction, and the third concave portion 4 is formed at the second place. may be formed at a position 120 degrees away from the recessed portion 4 in the spiral advancing direction in the pipe circumferential direction.

<Fourth Embodiment>
A heat transfer tube according to a fourth embodiment of the present invention will be described with reference to the drawings.
As shown in FIGS. 10 to 11D, in the heat transfer tube 1D according to the fourth embodiment of the present invention, each of the plurality of concave portions 4 formed in two cycles of the spiral cycle of the groove portion 3 extends along the tube circumference in the spiral advancing direction. It has the same configuration as the heat transfer tube 1B of the third embodiment (see FIGS. 6 to 7C) except that they are formed at positions separated from each other by 270 degrees in direction.

For example, in the heat transfer tube 1D, three concave portions 4 are formed in two spiral cycles, and one or two concave portions 4 are formed in each cycle. Also, in the heat transfer tube 1D, the length directions of the three concave portions 4 formed in two cycles are formed on three straight lines parallel to the tube axis when viewed from the front of the tube. Further, in the heat transfer tube 1D, the concave portions 4 are formed at positions separated from each other by 270 degrees in the circumferential direction of the tube in the spiral advancing direction.

In addition, in the heat transfer tube 1D, four concave portions 4 are formed in three cycles of the spiral cycle, and the length direction of each of the four concave portions 4 formed in three cycles is It is formed on four parallel straight lines. Further, in the heat transfer tube 1D, the concave portions 4 are formed at positions separated from each other by 270 degrees in the circumferential direction of the tube in the spiral advancing direction.

Further, in the heat transfer tube 1D, the concave portions 4 are formed in the tube circumferential direction at intervals of 3/4 of the spiral period. In the heat transfer tube 1D, a plurality of recesses 4 formed over the entire length of the corrugated tube 2 are formed at positions separated from each other by 90 degrees in the tube circumferential direction when viewed from the side of the tube.

Another configuration of the heat transfer tube according to the fourth embodiment of the present invention will be described with reference to the drawings.
As shown in FIGS. 12 to 13D, in the heat transfer tube 1E having another configuration, the length direction of each of the plurality of concave portions 4 formed in two cycles of the spiral cycle of the groove portion 3 is are formed on four straight lines parallel to each other, and each of the recesses 4 is formed at positions separated from each other by 90 degrees in the circumferential direction of the pipe in the spiral advancing direction (clockwise in the figure). It has the same configuration as the heat transfer tube 1D of the embodiment (see FIGS. 10 to 11D).

For example, in the heat transfer tube 1E, eight concave portions 4 are formed in two spiral cycles, and four concave portions 4 are formed in each cycle. Further, in the heat transfer tube 1E, the eight concave portions 4 formed in two cycles of the spiral cycle are formed at positions separated from each other by 90 degrees in the circumferential direction of the tube in the spiral advancing direction (clockwise direction in the figure). there is Further, in the heat transfer tube 1E, the concave portions 4 are formed in the tube circumferential direction at intervals of 1/4 of the spiral period. Also in the heat transfer tube 1E, similarly to the heat transfer tube 1D, the plurality of recesses 4 formed over the entire length of the corrugated tube 2 are formed at positions separated from each other by 90 degrees in the tube circumferential direction when viewed from the side of the tube. .

In the heat transfer tubes 1D and 1E, a plurality of recesses 4 formed over the entire length of the corrugated tube 2 are formed at positions that equally divide the tube circumference into four parts when viewed from the side of the tube. In the heat transfer tubes 1D and 1E, although not shown, a plurality of recesses 4 may be formed at four locations that unequally divide the circumference of the tube when viewed from the side of the tube. For example, in the heat transfer tubes 1D and 1E, the second recessed portion 4 is formed at a position 45 degrees apart from the first recessed portion 4 in the spiral traveling direction in the tube circumferential direction, and the second, third, and fourth recessed portions 4 may be formed at positions separated from each other by 90 degrees in the pipe circumferential direction.

<Modification>
Although not shown, the heat transfer tube according to the present invention may have the following configuration.
In the heat transfer tube according to the present invention, a plurality of recesses 4 having the same length Ld are formed. A plurality of concave portions 4 may be formed by mixing them with the concave portions 4 which are relatively short.

In the heat transfer tube according to the present invention, the length direction of each of the plurality of recesses 4 is formed on a straight line parallel to the tube axis when viewed from the front of the tube. The heat transfer tube may be recesses 4 formed such that the length direction of each of the recesses 4 is inclined in the tube circumferential direction from a straight line parallel to the tube axis in a front view of the tube.

In the heat transfer tube according to the present invention, at least one concave portion 4 is formed in each helical cycle of the groove portion 3, and is continuously formed over a plurality of cycles. The concave portions 4 may be formed discontinuously over a plurality of cycles.

In the heat transfer tube according to the present invention, the length directions of the plurality of concave portions formed in the two cycles may be formed on five or more straight lines parallel to the tube axis when viewed from the front of the tube.

In the heat transfer tube according to the present invention, the corrugated tube 2 may have a plurality of grooves. The plurality of grooves are composed of grooves 3 which are main grooves and auxiliary grooves which act to assist the formation of sub-flows F2 (see FIG. 3) by the grooves 3 . The auxiliary groove is helically formed over the entire length of the pipe so as to be recessed from the outer surface of the pipe toward the inner surface of the pipe. The auxiliary groove may be formed so as to intersect with the groove 3 or may be formed so as not to intersect with the groove 3 . The groove pitch width Pc, groove depth Dc, groove twist angle θ, and groove width Wc of the auxiliary groove may be the same as or different from those of the groove 3 . Further, the spiral winding direction of the auxiliary groove portion may be the same as or opposite to that of the groove portion 3 when viewed from the side of the tube. The auxiliary groove may be formed so as to intersect the recess 4 or may be formed so as not to intersect the recess 4 . Note that even when a plurality of grooves are formed in the corrugated pipe 2 , the length of the recesses 4 in the pipe axis direction is specified as a ratio to the groove pitch width Pc of the grooves 3 .

In order to demonstrate the effects of the present invention, examples within the scope of the present invention and comparative examples outside the scope of the present invention will be described below.

First, a test method for measuring the heat transfer coefficient of heat transfer tubes will be described. FIG. 14 is a schematic diagram showing this test apparatus. In this test apparatus, water was used as a medium on both the heating side and hot water supply side. Heated water is stored in the heat exchange tank 13, and this heated water is supplied from the heated water tank 21 through the pipe 22a and returned to the heated water tank 21 through the pipe 22b. A heat transfer tube 1 is horizontally arranged in the heat exchange tank 13, and hot water is supplied from a hot water supply tank 11 to the heat transfer tube 1 through a pipe 12a. After flowing, it is returned to the hot water tank 11 through the pipe 12b. The heating water tank 21 is controlled so that the temperature of the heating water is constant (32° C., 37° C. or 42° C.) by the constant temperature circulation device 24 . In addition, the temperature of the hot water supplied from the hot water supply tank 11 is controlled to be constant at 20° C. by the constant temperature circulation device 18 .

The hot water enters and exits the heat transfer tube 1 via the mixers 20a and 20b. It can be measured using a temperature resistor. The flow rate of the hot water supply is adjusted step by step by the valve 25 so as to keep the flow rate constant. Also, the average temperature of the heat transfer tubes 1 in the heat exchange tank 13 can be measured by the change in electrical resistance due to the temperature change. Then, the pressure of the pressure tap installed at the inlet and outlet of the heat transfer tube 1 is introduced to the differential pressure converter 17 through the pipe 16, and the differential pressure converter 17 is switched to 50 kPa, 10 kPa, or 1 kPa for measurement. The inside of the heat exchange tank 13 is stirred by the stirrer 14, the inside of the hot water supply tank 11 is stirred by the stirrer 19, and the inside of the heating water tank 21 is stirred by the stirrer 23, so that the temperature of the water is uniformed. It is

The heat exchange amount Qs of the cooling water can be obtained by the following formula (1), where W is the hot water supply flow rate, cp is the constant pressure specific heat, Tsout is the hot water supply outlet temperature, and Tsin is the hot water supply inlet temperature. The heat transfer coefficient αi is the heat flux qi, the pipe average temperature obtained from the voltage drop Twi, the pipe inner wall temperature corrected in consideration of the heat conduction of the pipe Twm, and the arithmetic mean temperature of the inlet and outlet temperatures of the hot water supply. Tsm can be obtained by the following formula (2). However, qi, Twi, and Tsm can be obtained by the following equations (3), (4), and (5), respectively. Note that L is the effective heat transfer length, di is the maximum inner diameter, do is the outer diameter, λ is the heat transfer coefficient of copper, and δ is the wall thickness. Then, the in-tube Nusselt number Nui, which is an index of the heat transfer coefficient of the heat transfer tube 1, is obtained by the following equation (6). Further, the Reynolds number Re, which is an index of the flow velocity of the fluid flowing through the inside of the heat transfer tube 1 at that time, is obtained by the following equation (7). where ρ is the density of the hot water, vi is the flow velocity of the hot water, and μ is the viscosity coefficient of the hot water.

(Example)
A heat transfer tube 1 shown in FIGS. 1 to 3 was prepared as the heat transfer tube of the example. The dimensions of each part of the heat transfer tube 1 are as follows.
Tube outer diameter of corrugated tube 2: 12.5 mm
Tube inner diameter of corrugated tube 2: 11.4 mm
Number of grooves 3: 1 Groove torsion angle θ of groove 3: 54 degrees Groove depth Dc of groove 3: 0.9 mm
Groove pitch width Pc of groove portion 3: 20 mm
Length Ld of concave portion 4: 15.5 mm
Width Wd of recess 4: 5.5 mm
Depth Dd of recess 4: 1.869 mm
For the heat transfer tube 1 of the example, the relationship between the flow velocity (Reynolds number Re) of the fluid flowing through the tube and the heat transfer coefficient (Nusselt number Nu) was measured by the test method described above. The results are shown in FIG.

(Comparative example)
As a heat transfer tube of a comparative example, a heat transfer tube similar to that of the example was prepared except that the concave portion 4 was not formed. For the heat transfer tube of the comparative example, the relationship between the Reynolds number Re and the Nusselt number Nu was measured in the same manner as in the example. The results are shown in FIG.

As shown in FIG. 15, the heat transfer tube of the example has a higher heat transfer coefficient than the heat transfer tube of the comparative example in the low Reynolds number region. In particular, in the low Reynolds number region of 2000 or less, the heat transfer tubes of the examples had higher heat transfer coefficients than the heat transfer tubes of the comparative example.

1, 1A, 1B, 1C, 1D, 1E Heat transfer tube 2 Corrugated tube 3 Groove 4 Recess Pc Groove pitch width Wc Groove width Dc Groove depth θ Groove torsion angle Ld Length Wd Width Dd Depth F1 Main flow F2 Side flow F31, F32, F33, F34 Countercurrent

Claims (10)

Consists of a corrugated pipe in which the groove is spirally formed with a predetermined spiral period,
A plurality of recesses formed along the pipe axis direction between the grooves over the entire length of the corrugated pipe,
The recess is formed so as to be recessed from the outer surface of the tube toward the inner surface of the tube,
The recess has a length in the tube axis direction of 50 to 90% of the groove pitch width of the groove,
A heat transfer tube , wherein the Reynolds number of a fluid flowing inside the tube is 2000 or less . 2. The heat transfer tube according to claim 1, wherein a plurality of said recesses are formed in two cycles of said spiral cycle. 3. The heat transfer tube according to claim 1, wherein each of the plurality of concave portions formed in two cycles is formed on the same straight line. 4. The heat transfer tube according to claim 3, wherein the plurality of recesses formed in two cycles are formed at positions separated from each other by 360 degrees in the tube circumferential direction. 3. The heat transfer tube according to claim 1, wherein the plurality of recesses formed in two cycles are formed on different straight lines. 6. The heat transfer tube according to claim 5, wherein the plurality of recesses formed in two cycles are formed at positions separated from each other by 180 degrees in the tube circumferential direction. 6. The heat transfer tube according to claim 5, wherein the plurality of recesses formed in two cycles are formed at positions separated from each other by 240 degrees or 120 degrees in the tube circumferential direction. 6. The heat transfer tube according to claim 5, wherein the plurality of recesses formed in two cycles are formed at positions separated from each other by 270 degrees or 90 degrees in the tube circumferential direction. The heat transfer tube according to any one of claims 1 to 8, wherein the recess is formed for each spiral period. 10. The heat transfer tube according to any one of claims 1 to 9, wherein the recesses are formed at intervals of the predetermined spiral period.

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