JP6223298B2 - Heat transfer tube for single-phase flow in tube - Google Patents

Description

  The present invention relates to the heat retained by the fluid outside the tube (natural refrigerant, chlorofluorocarbon refrigerant, water, etc.), the heat retained by an object outside the tube (solid material such as soil heat), or the radiant heat from the solar panel, and the single flow that flows inside the tube. In-pipe single-phase flow heat transfer tubes that exchange heat with phase flow fluids (water, brine, etc.), especially turbulent flow increases in the low flow velocity region, that is, the low Reynolds number Re region (Re is 3000 or less). In addition, the present invention relates to a single-phase flow heat transfer tube suitable for use in a low flow rate region, with a significantly improved heat transfer rate without substantially increasing the pressure loss of the fluid in the tube.

  The in-tube single-phase flow heat transfer tube is a corrugated tube in which one groove is spirally formed on the outer surface of the tube, and is made of a copper or copper alloy tube. Specific uses of this single-phase flow heat transfer pipe in the pipe include (a) a heat transfer pipe used in a water-refrigerant heat exchanger used in a heat pump water heater (for example, Ecocute), and (b) in a gas water heater. Heat-transfer tubes used in water-water double-tube heat exchangers used in (c) Hot water piping installed in solar panels of solar water heaters, (d) Used embedded in the ground There is a heat transfer pipe for soil heat-water heat exchanger piping. Some heat transfer tubes made of these corrugated tubes are partially bent or bent so as to be coiled.

  The equipment that exchanges heat between the fluid inside and outside the pipe is making efforts to save energy, and in order to improve the performance of the heat exchanger alone and reduce the heat transfer power of the heat medium, efforts are being made to save energy. ing. In order to reduce the conveyance power of the heat medium, a pump is usually used to send the fluid of the heat medium into the heat exchanger. However, as a measure for reducing the conveyance power, the flow rate of the conveyance fluid is reduced. A method of reducing pump driving power is employed.

  In addition, there is a device that heats a fluid to a high temperature in a heat exchanger, and a typical example is a heat pump water heater. In this heat pump water heater, water, which is a fluid, is directly fed into the heat exchanger from the tap water supply port, and the temperature of the fluid in the pipe is set low so that the fluid becomes high temperature in the heat exchanger over a long period of time. In addition, the pressure of this tap water is lower than the conveying force of the pump etc., and as a result, the speed of the fluid passing through the pipe becomes slow, and the Reynolds number Re in the pipe should be 3000 or less. There are many. In this low Reynolds number region, the fluid in the tube becomes a laminar flow region, and the heat transfer coefficient in the laminar flow region is lower than that in the turbulent state, so this can be improved by improving the performance of the heat transfer tube used. I have to.

  These heat transfer tubes are processed into a double-pipe heat exchanger, etc., and further assembled, and are usually incorporated into equipment such as a hot water supply device, etc., but often occupy a small space for the heat exchanger, At that time, if necessary, the heat transfer tube and the heat exchanger are often bent and incorporated into a device such as a hot water supply device. When this bending process is performed, problems such as an increase in pressure loss due to the generation of vortices and the like, and an increase in pump power occur at the bent portion.

  As typical heat transfer tubes used at present, there are a smooth tube, an internally grooved tube (Patent Document 1), a corrugated tube (Patent Document 2), and a corrugated tube (Patent Document 3) subjected to protrusion processing. The heat exchanger (patent document 4) using this is also disclosed.

  The internally grooved tube is provided with a number of spiral protrusions in the tube and promotes the turbulent flow of the medium flowing through the tube to suppress the formation of the velocity boundary layer and the temperature boundary layer on the tube wall surface. The corrugated tube is formed by forming deep irregularities in a spiral shape at a small pitch on the inner and outer surfaces of the tube. Due to the unevenness formed in this way, even when the fluid inside the pipe (including outside the pipe) flows in the laminar flow region, the turbulent flow is promoted and the heat transfer coefficient is improved. Further, for example, the corrugated pitch of the corrugated pipe of Patent Document 2 is 3 to 10 mm, and the corrugated pitch of the corrugated pipe of Patent Document 3 is 10 mm. In Patent Document 3, protrusions are formed in addition to the corrugated grooves, and the protrusions are formed at a pitch of 15 mm in the corrugated grooves, so that the protrusion on the inner surface of the tube is smaller than 10 mm. . And in this corrugated pipe, even when the fluid in the pipe flows in the laminar flow region, the turbulent flow is promoted and the heat transfer coefficient is improved by the irregularities formed as the corrugated groove. The same applies to the fluid outside the tube. Further, in the case of a corrugated tube in which small protrusions are formed in the inner surface groove portion, by providing the formed small protrusions, heat transfer performance is improved and pressure loss is reduced. The corrugated tube described in Patent Document 4 is a tube in which deep irregularities are formed spirally and at a small pitch on the inner and outer surfaces of the tube. This unevenness promotes turbulent flow and improves the heat transfer coefficient.

JP 2006-242553 A JP 2007-218486 A WO2008 / 029639 JP 2012-122714 A

  However, the smooth tube literally has no grooves on the inner surface and the outer surface, and the tube surface is a smooth surface. As described above, when the surface in contact with the fluid is smooth, when the fluid flows in the tube, a velocity boundary layer and a temperature boundary layer are formed on the tube wall surface, and the boundary layer inhibits heat exchange between the fluids. .

  In addition, the inner grooved tube has a problem that the weight of the heat transfer tube increases due to the provision of a large number of grooves on the inner surface of the tube, thereby increasing the material used and increasing the cost (Patent Document 1). ). In addition, when used in a laminar flow area, the fluidity of the fluid in the groove deteriorates due to the provision of a large number of grooves, and when the pipe is bent, more vortices are likely to occur in the bent part, resulting in pressure loss. Will increase.

  Furthermore, in the corrugated pipe, the pressure loss of the fluid in the pipe increases by forming spiral deep irregularities in a small pitch to promote turbulent flow (Patent Documents 2 and 3). In addition, there is a problem that the conveyance power increases due to an increase in pressure loss, and deposits such as scales stay in the pipe, and in an extreme case, the inside of the pipe is blocked. Furthermore, when used in a laminar flow area, the fluidity of the fluid between the projections becomes poor due to the small projection pitch, and when bending is performed, vortices are more likely to occur in the bent portion. As a result, the pressure loss increases.

  Furthermore, in the heat transfer tube in which the corrugated tube is subjected to protrusion processing, the small protrusion formed in the groove between the corrugated protrusion and the corrugated protrusion is high, and a vortex is generated due to the turbulence in the fluid downstream of the small protrusion, Pressure loss increases (Patent Document 3). When bending is performed with this heat transfer tube, vortices at the bent portion are more easily generated, and the pressure loss increases.

  Furthermore, the corrugated tube described in Patent Document 4 is also bent when a bending process is performed because the fluidity of the fluid between the protrusions deteriorates due to the formation of spiral deep irregularities at a small pitch. Vortices are more likely to occur at the part, and the pressure loss increases.

  The present invention has been made in view of such a problem, and the flow velocity of the fluid in the pipe is a low flow velocity range, without promoting turbulence, and while suppressing the increase in pressure loss of the fluid in the pipe, It is an object of the present invention to provide a heat transfer tube for a single-phase flow in a tube that can significantly improve the transfer rate.

In the heat transfer tube for single-phase flow in a tube according to the present invention, a groove is formed in a spiral shape on the outer surface of the tube, and a protrusion is formed on the inner surface of the tube corresponding to the groove. A corrugated tube in which a concave portion deeper than Dc is formed by bending a circular coil with a radius Rcoil ,
In a heat transfer tube for a single-phase flow in a pipe that flows a single-phase flow fluid in a pipe with a lay nozzle number of 3000 or less and performs heat exchange between the single-phase flow fluid and a fluid, substance, or radiant heat outside the pipe.
The tube outer diameter OD is 6 to 20 mm, the tube inner diameter ID is 5 to 19 mm,
The pitch Pc in the tube axis direction of the groove is 15 to 25 mm,
The bending radius Rcoil is 48 to 82 mm.
The single-phase flow heat transfer tube is preferably made of copper or a copper alloy.

In this in-tube single-phase flow heat transfer tube, it is preferable that the depth Dc of the recess on the inner surface of the tube satisfies Dc / ID of 0.051 to 0.097.

  In the present invention, the pitch of the grooves constituting the corrugated pipe (corrugated pitch) is 15 to 25 mm, which is longer than before. Then, a projection is formed on the inner surface of the tube by the groove on the outer surface of the tube, but the length of the recess formed between the projections becomes longer. Then, in the low Reynolds number region, the flow velocity is slow and the flow is laminar. However, when the groove pitch is increased at this low flow velocity, the main flow of the single-phase flow fluid flowing in the pipe (the fluid passing through the center of the pipe) ) And the substream of the single-phase fluid that is convection in the concave portion are easily merged, and the heat transfer performance is improved. For this reason, high heat transfer performance can be achieved even in a low Reynolds number region. Moreover, since it is a low Reynolds number region, the pressure loss of the fluid in the pipe is sufficiently small.

(A) is a left view which shows the state which bent the heat exchanger tube for single phase flow which consists of a corrugated tube which concerns on embodiment of this invention, (b) is the front view similarly. It is a longitudinal section showing a corrugated pipe of an embodiment of the present invention. (A), (b) is a schematic diagram which shows the flow of the fluid when a flow velocity is slow. (A), (b) is a schematic diagram which shows the flow of the fluid in case a flow velocity is quick. FIG. 6 is a plan view showing a flow in which the main flow of the fluid flowing in the pipe flows from the base point (collision point, side surface of the corrugated projection 3) when the corrugated pipe according to the embodiment of the present invention is bent leftward on the plane. is there. It is the schematic diagram of the coil which made the bending form the ellipse. It is a schematic diagram of the coil which connected the form of the bending process in the semicircular part by the linear part. It is a figure which shows the test apparatus which measures a heat transfer coefficient, a friction coefficient, etc. It is a schematic diagram which shows the structure in the pipe | tube end part at the time of incorporating the corrugated pipe | tube which concerns on embodiment of this invention in a double pipe type heat exchanger.

  Hereinafter, embodiments of the present invention will be specifically described with reference to the accompanying drawings. Fig.1 (a) is a left view which shows the heat-transfer pipe | tube for single phase flow which consists of a corrugated pipe | tube which concerns on embodiment of this invention, FIG.1 (b) is the front view similarly. FIG. 2 is a longitudinal sectional view of the corrugated tube of the present embodiment. In the corrugated tube 1, a tool with a sharp tip is pressed against the outer surface of the smooth tube, and in this state, for example, the tube is moved in the direction of the tube axis while rotating the tube. Is formed on the outer surface of the tube to form the corrugated groove 2. Protrusions 3 are formed on the inner surface of the tube by forming grooves 2 on the outer surface of the tube. Further, recesses 4 are formed between the protrusions 3 on the inner surface of the tube. In FIG. 2, OD is the tube outer diameter, ID is the tube inner diameter, tube thickness is δ, corrugated groove pitch is Pc, and corrugated groove depth is Dc. Further, since the corrugated groove 2 is formed by one spiral strip, the twist angle of the corrugated groove 2 is unambiguous if the outer diameter OD of the tube, the pitch Pc of the corrugated groove 2 and the number of strips are determined. Is determined. The material of the corrugated tube is made of a metal material that conducts heat, such as copper, copper alloy, aluminum, aluminum alloy, iron, stainless steel, titanium, etc., and particularly has good thermal conductivity such as copper or copper alloy. If so, it is still preferable.

  In the embodiment of the present invention, for example, as shown in FIG. 1, the corrugated tube 1 is bent into a coil shape and incorporated as a coil 10 in a heat exchanger. Immediately after the corrugated tube 1 is manufactured as described above, the corrugated tube 1 has a straight tube shape, and thereafter the corrugated tube 1 is bent into a coil shape except for both ends of the corrugated tube 1. The coil 10 of the corrugated tube 1 is obtained. The corrugating process and the bending process may be performed continuously, or after the corrugating process, the corrugated process may be shipped in a straight tube and bent at another factory. The bending radius of the coil 10 along the center line of the corrugated tube 1 is Rcoil. The pitch of the coil 10 is Pcoil.

  The form of bending of the corrugated tube 1 is not limited to the coil shape shown in FIG. For example, as shown in FIG. 6, the bending process may be an ellipse coil 11 having an elliptical shape, and as shown in FIG. 7, the bending process may be performed on a semicircular portion with a straight line portion. It is good also as the coil 12 of the shape which connected. Various shapes of the coil are conceivable. In the case of the elliptical coil 11 shown in FIG. 6, the small diameter is set as a bending radius Rcoil. In the case of the coil 12 shown in FIG. 7, the radius of the semicircular portion is Rcoil.

  3 and 4 are schematic views showing the relationship between the groove pitch Pc and the flow of the single-phase fluid inside the pipe. FIG. 3 shows a case where the flow velocity is slow (Reynolds number Re is small), and FIG. 4 shows a case where the flow velocity is fast (Reynolds number Re is large). 3 and 4 schematically show the shape of the corrugated tube shown in FIG. 2, and in reality, a square groove as shown in these drawings is not formed. As shown in FIG. 4, when the flow velocity is high, the shear force between the fluids is large, and as shown in FIG. 4A, the fluid in the recesses 4 is sufficient in the recesses 4 even when the groove pitch Pc is small. The heat transfer efficiency is high because convection is formed, diffused, and merges with the mainstream. On the other hand, when the pitch Pc of the corrugated groove is large, as shown in FIG. 4B, the fluid from the main flow enters the concave portion 4 and flows through the concave portion 4, so that convection diffusion occurs only at both corners of the concave portion 4. As a result, the convection diffusion of the fluid does not occur in the entire concave portion 4, so that the heat transfer efficiency is lowered.

  On the other hand, when the flow velocity of the single-phase fluid inside the tube is low, the shear force between the main flow in the tube and the side flow (convection) in the recess 4 is small as shown in FIG. For this reason, as shown in FIG. 3A, when the corrugated groove pitch Pc is small, the side flow forms a weak convection in the recess 4, but this convection (side flow) does not merge with the main flow, It tends to stay in the recess 4. For this reason, when the flow velocity is slow and the corrugated groove pitch Pc is small, the heat transfer efficiency is low.

  On the other hand, as shown in FIG. 3B, even when the flow velocity of the single-phase flow fluid in the pipe is small, if the corrugated groove pitch Pc is large, the area of the portion where the fluid in the recess 4 is in contact with the main flow is sufficient. Therefore, even if the shearing force due to the main flow is small, the convection fluid in the recess 4 merges with the main flow, so the heat transfer efficiency is high.

  Thus, the present inventors have found that the heat transfer efficiency is higher when the corrugated groove pitch Pc is larger when the flow rate of the low Reynolds number is slow, and the present invention has been completed. And this invention can improve heat-transfer efficiency, without promoting a turbulent flow by making corrugated groove pitch Pc 15 mm or more also on the conditions where a single phase flow fluid is a low Reynolds number and slow flow velocity. This has been demonstrated as described later. Further, in the present invention, since turbulent flow is not promoted, pressure loss of the fluid in the pipe does not increase and the conveyance power does not increase, and deposits such as scales stay in the pipe and block the inside of the pipe. There is nothing to do.

  In the present embodiment, the heat transfer tube made of the corrugated tube 1 is bent into a coil shape having a radius Rcoil. FIG. 5 shows a state in which the corrugated tube 1 is bent leftward in a plan view. When the corrugated tube 1 is bent in this manner, as shown in FIG. 5, the fluid flowing through the corrugated tube 1 flows through the center of the corrugated tube 1 when flowing into the bent portion of the corrugated tube 1 (hereinafter, referred to as “corrugated tube”). The mainstream) travels straight and flows in as it is, and the mainstream collides with the side surface of the corrugated projection 3 formed in the bent portion. Since the corrugated projection 3 is formed in a spiral shape, the main stream that has collided flows separately on the upstream side and the downstream side along the vicinity of the downstream side wall of the recess 4 between the projections 3. That is, the main flow shown by the one-dot chain line in FIG. 5 flows downstream while heat exchange is performed on the upstream side in the fluid flow direction. And when this main stream collides with the corrugated pipe projection 3 in the bending portion, it is diverted at the base point (collision point) that is the collision point. Thereafter, the diverted fluid swirls and flows upstream and downstream.

  This diverted fluid flows in a laminar flow state (without disturbing the flow) along the downstream side of the concave portion 4 between the protrusions 3 formed on the inner surface of the pipe, and a part of the fluid flows while returning to the upstream side. Turns and flows downstream. Thereafter, the flow swirling on the downstream side of the recess 4 merges with the convection (substream) formed in the recess 4 to improve the heat transfer performance with the substream. Thereafter, as shown in FIG. 3 (b), the fluid located in the recess 4 comes into contact with the main flow at the center of the tube, and convection is generated in the recess 4, and the convection fluid and the main flow merge. The heat transfer performance is further improved.

  On the other hand, as shown in FIG. 5, unlike the region where the straight pipe portion transitions to the bent portion, the mainstream moves to the outer peripheral side by centrifugal force in the continuously bent portion such as the cylindrical coil shown in FIG. 1. The main flow moves, and the main flow collides with the protrusion 3 on the inner surface of the bending outer peripheral side and is divided into the upper part and the lower part of the pipe. Thereafter, the flow swirling on the downstream side of the concave portion 4 merges with the convection (secondary flow) formed in the concave portion 4, and the heat transfer performance with the secondary flow is improved. Thereafter, the fluid located in the recess 4 further comes into contact with the main flow at the center of the tube, and convection occurs at the portion of the recess 4, and the convection fluid and the main flow merge to further improve the heat transfer performance.

  In the present embodiment, the heat transfer tube made of the corrugated tube 1 is bent into a coil shape having a radius Rcoil. When the corrugated pipe 1 is bent in this manner, as shown in FIG. 5, the coolant flowing through the corrugated pipe 1 collides with the corrugated protrusion 3 at the bent portion of the corrugated pipe 1, and a part of the refrigerant flows upstream. Come back to the side. That is, the fluid flowing in the center of the corrugated pipe 1 (hereinafter referred to as main flow) flows downstream while heat exchange is performed on the upstream side in the fluid flow direction. And when this main stream collides with the corrugated pipe wall in the bending part, it is divided into the upper part of the pipe and the lower part of the pipe with the point of collision as the base point (collision point). (Without turbulent flow), along the recess 3 between the projections 3 formed on the inner surface of the pipe, a part of the swirl flows while returning to the upstream side, and the remaining part swirls and flows downstream. Thereafter, the fluid located in the recess 3 comes into contact with the main flow at the center of the tube, and convection occurs at the portion of the recess 4, and the convection fluid and the main flow merge to further improve the heat transfer performance.

  Next, the structure of the single-phase flow heat transfer tube composed of the corrugated tube of the present invention will be described.

“Tube outer diameter OD of heat transfer tube: 6 to 20 mm, tube inner diameter ID: 5 to 19 mm”
First, for example, the outer diameter OD of the heat transfer tube is 6 to 20 mm, and the inner diameter ID is 5 to 19 mm. A single-phase fluid such as water and brine flows in the pipe. On the other hand, the heat medium outside the tube varies depending on the field in which the heat transfer tube of the present invention is used. When the field of use of the heat transfer tube of the present invention is a water-refrigerant heat exchanger such as a heat pump water heater, natural refrigerant or CFC refrigerant flows on the outer surface of the pipe, and the field of use is water- In the case of a double tube heat exchanger used for a water heat exchanger, a single-phase fluid such as water also flows outside the tube. Also, in other technical fields, for example, when the heat transfer pipe of the present invention is used for the hot water pipe of a solar panel of a solar water heater, radiant heat generated by absorption of electromagnetic waves such as radiation rays on the outer surface of the pipe is generated in the heat transfer pipe. Works. In addition, when the heat transfer tube of the present invention is embedded in the ground and the heat transfer tube is used in the field of a water-soil heat exchanger where 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 Heat exchange occurs between them.

  In this way, heat exchange is performed between the fluid in these tubes and the fluid or material outside the tubes. As a single-phase flow heat transfer tube used for such applications, the outer diameter and inner diameter are, for example, in the above range. In the present invention, the Reynolds number Re of the single-phase flow fluid flowing in the pipe is preferably 3000 or less. Preferably, the Reynolds number Re of the single-phase flow fluid flowing in the pipe is 2000 or less. The heat transfer tube of the present invention is suitable for such a low Reynolds number fluid.

“Corrugated groove pitch Pc: 15 to 25 mm”
The corrugated groove pitch Pc is 15 to 25 mm. By setting the corrugated groove pitch Pc to the above range, when the fluid is diverted into the recess 4 at the collision point and swirled, the inflow of the fluid into the recess 4 is promoted, and the fluid is not promoted and the fluid flow is not promoted. It becomes easy to swivel upstream and downstream in the flow direction. Furthermore, the area in which the fluid in the recess 4 and the main flow at the center of the tube come into contact with each other is increased, and the convection fluid in the recess 4 can easily merge with the main flow, thereby improving the heat transfer performance.

  When the corrugated groove pitch Pc is smaller than 15 mm, when the fluid diverts into the recess 4 at the collision point and turns, the inflow of the fluid into the recess 4 is inhibited, the turbulent flow is promoted, and the pressure loss increases. At the same time, the convection in the recess 4 is hindered and the heat transfer performance is reduced. Further, when the corrugated pitch Pc is larger than 25 mm, when the fluid diverts into the recess 4 at the collision point and turns, the fluid can easily flow into the recess 4, but the swirl flow becomes weak and the recess 4 The convection is hindered, the merging of the fluid in the recess 4 and the main flow at the center of the tube is not promoted, and the heat transfer performance is reduced. Accordingly, the corrugated groove pitch Pc is set to 15 to 25 mm.

"Bending radius Rcoil: 48 to 82mm"
When the bending radius Rcoil of the coil 10 is smaller than 48 mm, the centrifugal force acting on the fluid becomes too strong when the fluid flowing through the heat transfer tube is swung from the collision point on the inner surface of the heat transfer tube, and the protrusion The fluid in the recess 4 between the three is separated from the tube wall, the main flow is disturbed, the merge of the tube wall and the main flow is inhibited, the heat transfer performance is inhibited, and the pressure loss increases. Further, when the bending radius of the coil 10 exceeds 82 mm, the centrifugal force acting on the fluid is weakened when turning and turning from the collision point. As a result, although the pressure loss is reduced, the fluidity when the fluid diverted at the collision point flows to the upstream side and the downstream side is lowered, so that the heat transfer performance is lowered. Therefore, the bending radius Rcoil for bending is set to 48 to 82 mm.

“Dc / ID: 0.051 to 0.097”
When the depth of the corrugated groove 2 (the depth of the concave portion 4 on the inner surface of the pipe) is Dc, the fluid is diverted to the concave portion 4 and swirls by setting Dc / ID to 0.051 to 0.097. At this time, the fluid in the recess 4 is not easily promoted for turbulent flow, but is easily swirled upstream and downstream. This makes it difficult for the convection in the recess 4 to be hindered, promotes contact and merging of the main flow in the tube center and the fluid convected in the recess 4, and promotes heat transfer performance.

  When Dc / ID is smaller than 0.051, the fluid in the recess 4 easily flows from the inside of the recess 4 to the mainstream side when the fluid diverts to the recess 4 at the collision point and turns. And the convection between the fluid in the recess 4 are hindered and the heat transfer performance is reduced. Further, when Dc / ID is larger than 0.097, when the fluid diverts into the recess 4 at the collision point and turns, the fluid in the recess 4 does not promote turbulent flow and easily flows upstream and downstream. However, as the groove depth Dc becomes deeper, the main flow fluid at the center of the tube at the bent portion is promoted for turbulence, and the pressure loss increases. Therefore, Dc / ID is set to 0.051 to 0.097.

“Groove twist angle βc: 40 ° or more”
The corrugated groove 2 is formed by a single spiral strip. In this case, the groove twist angle βc is uniquely determined if the outer diameter OD of the tube, the pitch Pc of the corrugated groove, and the number of strips are determined. Therefore, the groove twist angle βc is determined by the tube outer diameter OD and the corrugated groove pitch Pc. . For example, the groove twist angle βc can take various values such as 54 ° as described in the embodiment. Further, the thickness δ of the heat transfer tube 1 can take various values such as 0.613 mm as described in the examples.

  In the present invention, a flat portion parallel to the tube axis can be formed in the recess 4 in the tube axis direction. As a result, the turbulent flow of the single-phase fluid flowing in the pipe can be suppressed, and the fluid diverted into the concave portion 4 in the upper part of the pipe and the lower part of the pipe can be swirled and flow easily from the collision point. In the surface where the fluid in the recess 4 and the main flow at the center of the tube come into contact, the substream and the main flow that are convective in the recess 4 are more easily merged, and the heat transfer performance is improved. The length Lf of the flat portion in the tube axis direction is preferably 0.40 to 0.80 times the pitch Pc of the corrugated groove. That is, Lf is preferably 0.40 Pc to 0.80 Pc.

  In addition, when the heat transfer tube of the embodiment of the present invention is used after being processed into, for example, a double tube heat exchanger, the heat transfer tube of the present embodiment is inserted into a smooth tube. , Make a double tube structure. In the case of a double tube heat exchanger, when the heat transfer tube of this embodiment is inserted into a smooth tube and used in the form of a coil as shown in FIG. 6 or FIG. 7, the tube is bent in this inserted state. By doing so, it is bent into a coil shape and processed into a desired coil shape. At that time, the degree of bending is appropriately adjusted so that the bending radius of the heat transfer tube of the present embodiment is Rcoil. FIG. 9 shows a state of the tube end portion in which the heat transfer tube 31 of the present embodiment is inserted into the tube of the smooth tube 30 used as the outer tube of the double tube heat exchanger. After this double pipe is bent, for example, a T joint 32 (shown by a broken line in FIG. 9) or the like is inserted into the pipe end portion, and the insertion portion between the smooth pipe 30 and the T joint 32 and The T joint is attached by joining the heat transfer tube 31 and the T joint 32 by brazing or the like. In addition, the portion branched and extending above the T joint 32 is assembled by appropriately determining the direction in accordance with the time of incorporation into the heat exchanger, and connected to the fluid inlet / outlet piping. In addition, when using the heat exchanger tube of this embodiment with the water heater using a carbon dioxide refrigerant, the thin tube for making a carbon dioxide refrigerant flow around the outer peripheral surface of the corrugated pipe 1 of this embodiment is helically wound. To do.

  Hereinafter, in order to demonstrate the effects of the present invention, examples that fall within the scope of the present invention and comparative examples that fall outside the scope of the present invention will be described.

  First, a test method for heat transfer performance of a single-phase flow fluid will be described. FIG. 8 is a schematic diagram showing this test apparatus. In this test apparatus, water was used as a medium on both the heating side and the 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 via the pipe 22a and returned to the heated water tank 21 via the pipe 22b. A heat transfer pipe 15 is horizontally disposed in the heat exchange tank 13. Hot water is supplied from the hot water tank 11 through the pipe 12 a into the heat transfer pipe 15, and passes through the heat transfer pipe 15. After flowing, it is returned to the hot water tank 11 through the pipe 12b. The temperature of the heated water tank 21 is controlled by the constant temperature circulation device 24 so that the temperature of the heated water becomes a constant temperature (32 ° C., 37 ° C. or 42 ° C.). In the hot water tank 11, the temperature of the hot water 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 15 through the mixers 20a and 20b, and the temperature of the hot water supply to and from the heat transfer tube 15 is measured by the platinum in the mixers 20a and 20b installed at the entrance and exit of the heat transfer tube. It can be measured using a temperature resistor. The flow rate of the hot water supply is adjusted stepwise by the valve 25 so as to be a constant flow rate. Moreover, the average temperature of the heat exchanger tube 15 in the heat exchange tank 13 can be measured by a change in electric resistance value accompanying a temperature change. And the pressure of the pressure tap installed in the entrance / exit of this heat exchanger tube 15 is guide | induced to the differential pressure converter 17 by the piping 16, and the differential pressure converter 17 is switched and measured to 1 kPa, 10 kPa, 50 kPa, or 200 kPa. The heat exchange tank 13 is agitated by a stirrer 14, the hot water tank 11 is agitated by a stirrer 19, and the heated water tank 21 is heated by a stirrer 23 so that the temperature of the water is made uniform. It has been. The heat transfer tube 15 is a coil having the shape shown in FIG. 1, and the number n of coil turns is 5.5. For bending, a bending jig matched to a predetermined coil diameter was manufactured, and a straight corrugated pipe was bent into a coil using the bending jig.

  The heat exchange amount Qs of the cooling water can be obtained by the following formula 1, where the hot water flow rate is W, the constant pressure specific heat is cp, the hot water outlet temperature is Tsout, and the hot water inlet temperature is Tsin. The heat transfer coefficient αi is the heat flux qi, the tube average temperature obtained by voltage drop Twi, the tube wall surface temperature corrected in consideration of the heat conduction of the tube Twm, and the arithmetic average temperature of the hot water inlet / outlet temperature. As Tsn, it can obtain | require by following Numerical formula 2. However, qi, Twi, and Tsn can be obtained by the following mathematical formulas 3, 4, and 5, respectively. 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 thickness. The in-pipe Nusselt number Nui and the Reynolds number Re are obtained by the following formulas 6 and 7. However, ρ is the density of hot water, vi is the flow rate of hot water, and μ is the viscosity of hot water. Then, ΔP is the pressure loss, x is the length of the test section, and the friction coefficient fi is obtained by the following formula 8.

  As the first embodiment of the present invention, the influence on the pressure loss and the heat transfer coefficient due to the difference in the shape and size of the heat transfer tubes will be described. The shape dimensions of each test heat transfer tube are shown in Tables 1 to 3 below. The Nusselt number and the friction coefficient of each test heat transfer tube are shown in Tables 4 to 6 below.

  In Tables 1 to 3, the reference 1 is a smooth tube. Reference 2 is a straight tubular corrugated tube. Examples 1 to 9 are examples that fall within the scope of claim 3 of the present invention, and examples 10 to 12 are examples that satisfy only claim 1 of the present invention. Comparative Examples 1 to 7 are corrugated tube coils that are out of the scope of the present invention. Examples 1 to 12 and Comparative Examples 1 to 7 are coiled heat transfer tubes having the shape shown in FIG. 1, and are heat transfer tubes using corrugated tubes having the shape shown in FIG. 2. The number of strips is 1. In Tables 4 to 6, the Nui ratio represents the in-pipe Nusselt number Nui, and is expressed as a ratio with respect to the standard 1 smooth tube. The fi ratio is a coefficient of friction, which indicates the flow resistance of the fluid and is a characteristic indicating the magnitude of pressure loss. This fi ratio is also shown as the ratio to the standard 1 smooth tube. Furthermore, in the pipe Nusselt number Nui ratio and the friction coefficient fi ratio, (1), (2), and (3) are characteristics when the Reynolds number Re is 3000, 2000, and 1000, respectively. That is, for example, when the Reynolds number Re is 3000, the ratio of the in-tube Nusselt number to the smooth tube (reference 1) is the Nui ratio (1), and the ratio of the frictional resistance to the smooth tube (reference 1) is the fi ratio (1). ). The larger the Nusselt number Nui in the tube, the higher the heat transfer performance, and the smaller the friction coefficient fi, the smaller the pressure loss and the better the heat transfer tube.

  In Comparative Examples 2 to 7 of the present invention, the in-tube Nusselt number Nui (1) is 1.76 to 1.81, whereas Examples 10 to 12 satisfying only Claim 1 of the present invention are in-pipe Nusselt number Nui ( In Examples 1 to 9 where 1) satisfies 1.88 to 2.02 and Claim 3 of the present application, the in-pipe Nusselt number Nui (1) is 1.99 to 2.02. Therefore, Examples 1-12 of this invention have improved heat-transfer performance rather than Comparative Examples 2-7, Furthermore, Examples 1-9 which satisfy | fill Claim 3 are Examples which satisfy only Claim 1. The lower limit of the tube Nusselt number is higher than 10 to 12, indicating that the heat transfer performance is high. On the other hand, the pressure loss (coefficient of friction (1)) is 2.87 to 3.41 in Comparative Examples 2 to 7 of the present invention, 2.98 to 3.07 in Examples 10 to 12, and in Examples 1 to 9. 2.98 to 3.02. Therefore, it can be said that Examples 1-12 of this invention are comparable with Comparative Examples 2-7 in a pressure loss. Therefore, Examples 1-12 of the present invention have the same pressure loss as Comparative Examples 2-7, while the heat transfer performance is significantly higher than Comparative Examples 2-7. On the other hand, the comparative example 1 has a high Nusselt number (1) in the pipe of 2.83 and is superior in heat transfer performance to Examples 1 to 12, but the frictional resistance (pressure loss) of Comparative Example 1 is fi ratio. (1) is 6.52, which is much higher than the example of the present invention (maximum value of fi ratio (1) 3.07), and it can be said that the heat transfer tube of Comparative Example 1 is difficult to use. The same applies to the other Nui (2) and fi (2) and Nui (3) and fi (3).

  On the other hand, the straight tubular corrugated pipe of the reference 2 is different from the coiled corrugated pipe of the first embodiment in that other reference factors are the straight pipe and the first embodiment is a coil having a bending radius Rcoil of 60 mm. Although the same, in contrast, the heat transfer performance of Example 1 is higher than that of Reference 2, and by having the bent portion, the refrigerant flowing through the pipe collides with the protrusion 3 and is transferred. Improved thermal performance has been obtained. However, the pressure loss of Example 1 is higher than that of Reference 2 due to the bent portion. However, the difference between the heat transfer performance is small from the comparison between Standard 2 and Comparative Examples 1 to 7, and Comparative Examples 1 to 7 have the same heat transfer performance as that of the straight corrugated pipe, and the improvement of the heat transfer performance is obtained. You can see that it is not.

  INDUSTRIAL APPLICABILITY The present invention is extremely useful as a heat transfer tube for applications in which a fluid with a low Reynolds number flows, because heat transfer performance can be remarkably enhanced while suppressing an increase in pressure loss in the range of the low Reynolds number.

1: Heat transfer tube, 2: Corrugated groove, 3: Protrusion, 4: Recess, 15: Heat transfer tube

Claims (3)

Grooves are formed spirally outside the tube surface, the projections on the inner surface corresponding to the groove is formed, the corrugated tube Dc only deeper recess than the projecting tip is formed between the projections of the inner surface radius It is made of Rcoil bent into a circular coil shape ,
In a heat transfer tube for a single-phase flow in a pipe that flows a single-phase flow fluid in a pipe with a lay nozzle number of 3000 or less and performs heat exchange between the single-phase flow fluid and a fluid, substance, or radiant heat outside the pipe.
The tube outer diameter OD is 6 to 20 mm, the tube inner diameter ID is 5 to 19 mm,
The pitch Pc in the tube axis direction of the groove is 15 to 25 mm,
A heat transfer tube for single-phase flow in a tube, wherein the bending radius Rcoil is 48 to 82 mm. The in-tube single-phase flow heat transfer tube according to claim 1, wherein the corrugated tube is made of copper or a copper alloy. The in-tube single-phase flow heat transfer tube according to claim 1 or 2, wherein the depth Dc of the recess on the inner surface of the tube satisfies Dc / ID of 0.051 to 0.097.

Images