JP2010185610A - Heat exchanger and heat transfer tube - Google Patents

Abstract

【選択図】図１A heat exchanger and a heat transfer tube having high heat conversion efficiency are provided.
A heat exchanger 1 according to the present invention includes a plurality of grooves 12 spirally provided on an inner peripheral surface and a plurality of fins 14 positioned between the plurality of grooves 12, and is wound by spiral winding. A first heat transfer tube formed in a cylinder; and a second heat transfer tube provided adjacent to the first heat transfer tube. The first heat transfer tube has a radius of curvature of the cylinder and a maximum inner diameter of the first heat transfer tube. When the height of the ID and fin 14 is HF, the following formula (1) is satisfied.
[Expression 1]

[Selection] Figure 1

Description

  The present invention relates to a heat exchanger and a heat transfer tube. In particular, the present invention relates to a heat exchanger and a heat transfer tube used in a hot water storage type heat pump water heater.

  A hot water storage type heat pump water heater is a device that boils hot water mainly at night, and the flow rate of water flowing through a heat exchanger tube of a heat exchanger provided in the water heater is small. Therefore, since the flow of water flowing in the heat transfer tube becomes a laminar flow, when aiming to improve the heat transfer performance as a heat exchanger, improve the heat transfer performance of the heat transfer tube through which water flows. Is essential.

  Conventionally, as a heat pump type hot water heater, a water heat transfer tube of a water refrigerant heat exchanger and one or more refrigerant heat transfer tubes are provided for one water heat transfer tube, and the water heat transfer tube is spirally wound. The refrigerant heat transfer tube is spirally wound around the outer periphery of the substantially cylindrical water heat transfer tube at a predetermined pitch. Further, at least one of the refrigerant heat transfer tubes in the cross section is a water heat transfer tube. There is known a heat pump type hot water heater that is joined over substantially the entire length of the pipe and that the direction of the water flowing through the water heat transfer tube and the direction of the refrigerant flowing inside the refrigerant heat transfer tube are opposite to each other ( For example, see Patent Document 1).

  Since the heat pump type hot water heater described in Patent Document 1 has the above-described configuration, the entire hot water heater can be reduced in size and cost, and the heat conversion efficiency can be improved.

JP 2005-133999 A

  However, although the heat pump type hot water heater described in Patent Document 1 can reduce the size and cost of the entire hot water machine and improve the heat conversion efficiency, it is possible to convert the heat from the viewpoint of countermeasures against global warming in recent years. Efficiency is not sufficient and there is room for improvement in improving heat conversion efficiency.

  Therefore, the objective of this invention is providing the heat exchanger and heat exchanger tube with high heat conversion efficiency.

In order to achieve the above object, the present invention has a plurality of grooves spirally provided on the inner peripheral surface and a plurality of fins positioned between the plurality of grooves, and is formed into a cylinder by spiral winding. 1 heat transfer tube and a second heat transfer tube provided adjacent to the first heat transfer tube. The first heat transfer tube has a radius of curvature of the cylinder R, the maximum inner diameter of the first heat transfer tube ID, and the height of the fin When HF is HF, a heat exchanger satisfying the following formula (1) is provided.

  Moreover, the said heat exchanger WHEREIN: A 2nd heat exchanger tube may be in contact with the outer surface of a 1st heat exchanger tube by being wound along the outer periphery of a cylinder.

  In the heat exchanger, the second heat transfer tube may be wound around the surface of the first heat transfer tube, and the surface of the first heat transfer tube and the surface of the second heat transfer tube may be joined.

In order to achieve the above object, the present invention includes a plurality of grooves spirally provided on the inner peripheral surface and a plurality of fins positioned between the plurality of grooves, and is formed into a cylinder by spiral winding. A heat transfer tube satisfying the following formula (1) is provided, where R is the curvature radius of the cylinder, ID is the maximum inner diameter of the heat transfer tube, and HF is the height of the fin.

  The heat exchanger and the heat transfer tube according to the present invention can provide a heat exchanger and a heat transfer tube with high heat conversion efficiency.

It is sectional drawing of the heat exchanger which concerns on the 1st Embodiment of this invention. (A) is sectional drawing of the water heat exchanger tube which concerns on 1st Embodiment, (b) is an expanded sectional view of the part enclosed with the circle of the dashed-dotted line of (a). (A) is a perspective view in case the water heat exchanger tube which concerns on 1st Embodiment is a straight shape, (b) is a figure at the time of opening along X1-X2 in (a). . It is sectional drawing of the heat exchanger which concerns on the 2nd Embodiment of this invention. It is a figure of the heat exchanger which concerns on the modification of embodiment of this invention. It is a figure which shows the measurement result of the heat transfer performance in the case of making the water heat exchanger tube which concerns on an Example and a comparative example into a straight shape. It is a figure which shows the result of having measured the heat-transfer performance of the spiral water-heat-transfer tube which concerns on an Example and a comparative example.

[First Embodiment]
(Outline of the configuration of the heat exchanger 1)
FIG. 1 shows an outline of a cross section of a heat exchanger according to a first embodiment of the present invention.

  The heat exchanger 1 according to the first embodiment is, for example, a heat exchanger used for heat exchange between water and refrigerant in a hot water storage type heat pump water heater (hereinafter sometimes referred to as “heat pump water heater”). is there. Specifically, the heat exchanger 1 includes a water heat transfer tube 10 as a first heat transfer tube spirally wound in a cylindrical shape or a substantially cylindrical shape, and a refrigerant as a second heat transfer tube provided adjacent to the water heat transfer tube 10. A heat transfer tube 20. Water is passed through the water heat transfer tube 10, and refrigerant is passed through the refrigerant heat transfer tube 20. That is, the water heat transfer tube 10 is used as a water tube, and heat is exchanged between water flowing through the water heat transfer tube 10 and refrigerant flowing through the refrigerant heat transfer tube 20.

(Water heat transfer tube 10)
The water heat transfer tube 10 as a heat transfer tube is located between the plurality of grooves 12 provided on the inner peripheral surface thereof and the plurality of fins having a convex shape protruding inside the water heat transfer tube 10. 14. The plurality of grooves 12 are formed in a spiral shape on the inner peripheral surface of the water heat transfer tube 10, for example. The water heat transfer tube 10 according to the first embodiment is formed by spirally winding the water heat transfer tube 10 having a substantially linear shape (hereinafter sometimes referred to as “straight”), and thus has a substantially cylindrical outer shape. Presents. The plurality of fins 14 promote stirring of the water flowing through the water heat transfer tube 10.

  The water heat transfer tube 10 according to the first embodiment is formed to have a plurality of stages by being spirally wound, and the surface 10b of the water heat transfer tube 10 corresponding to one stage The surface 10b of the water heat transfer tube 10 corresponding to the next stage following the first stage is in direct contact with the contact portion 10a. The water heat transfer tube 10 according to the first embodiment can be formed, for example, by continuously bending the straight water heat transfer tube 10 and spirally winding it in a plurality of stages.

  Also, when the radius of curvature of the water heat transfer tube 10 spirally wound and formed into a substantially cylindrical shape is “R”, the maximum inner diameter of the water heat transfer tube 10 is “ID”, and the height of the fin 14 is “HF”. The water heat transfer tube 10 is formed to satisfy the following formula (1).

(Refrigerant heat transfer tube 20)
The refrigerant heat transfer tube 20 is provided in contact with the outer periphery of the water heat transfer tube 10 in the first embodiment. Specifically, the refrigerant heat transfer tube 20 is spirally wound along the outer periphery of the water heat transfer tube 10 having a substantially cylindrical shape. That is, the refrigerant heat transfer tube 20 according to the first embodiment is wound around the outer periphery of the water heat transfer tube 10 along the spiral winding direction of the water heat transfer tube 10. In other words, the refrigerant heat transfer tube 20 is arranged on the outer periphery of the water heat transfer tube 10 such that the flow direction of water to flow into the water heat transfer tube 10 and the flow direction of refrigerant to flow into the refrigerant heat transfer tube 20 are substantially parallel to each other. Wrapped around And the refrigerant | coolant heat exchanger tube 20 has the junction part 20a joined to the surface 10b of the water heat exchanger tube 10, and is formed. The refrigerant heat transfer tube 20 is integrated with the water heat transfer tube 10 through the joint portion 20a.

  Here, in the heat exchanger 1 according to the first embodiment, one refrigerant heat transfer tube 20 is wound around the outer periphery of the water heat transfer tube 10. Specifically, the refrigerant heat transfer tube 20 is formed on the outer periphery of the substantially cylindrical water heat transfer tube 10, the surface of the refrigerant heat transfer tube 20 corresponding to the first stage, and the refrigerant heat transfer tube corresponding to the next stage following the first stage. It winds so that the surface of 20 may space apart. For example, the refrigerant heat transfer tube 20 is placed along a hollow portion formed in a portion where the first stage water heat transfer tube 10 and the next stage water heat transfer tube 10 are in contact with each other. Can be joined to the outer periphery of the water heat transfer tube 10.

  In addition, joining methods, such as brazing joining, can be used for joining the water heat exchanger tube 10 and the refrigerant | coolant heat exchanger tube 20, for example. Further, both the water heat transfer tube 10 and the refrigerant heat transfer tube 20 are formed of a metal material having a predetermined thermal conductivity. As the metal material, for example, copper, copper alloy, aluminum, aluminum alloy or the like can be used. The inner diameter of the water heat transfer tube 10 is formed larger than the inner diameter of the refrigerant heat transfer tube 20, and the outer diameter of the water heat transfer tube 10 is formed larger than the outer diameter of the refrigerant heat transfer tube 20.

  (A) of FIG. 2A shows the outline of the cross section of the water heat transfer tube according to the first embodiment, and (b) of FIG. 2A shows the portion surrounded by the one-dot chain line circle of (a) of FIG. 2A. The outline of an enlarged section is shown.

  Referring to (a) of FIG. 2A, the water heat transfer tube 10 according to the first embodiment is provided with a plurality of grooves 12 formed on the inner peripheral surface thereof and fins provided between the plurality of grooves 12, respectively. 14. 2A, the fins 14 included in the water heat transfer tube 10 are formed on the inner peripheral surface of the water heat transfer tube 10 with a predetermined interval.

  Here, in the first embodiment, the maximum outer diameter of the water heat transfer tube 10 is “OD”, and the maximum inner diameter is “ID”. Further, the height of the fin 14, that is, the fin height from the bottom of the groove 12 to the tip of the fin 14 is “HF”, the thickness of the water heat transfer tube 10, that is, the outer peripheral surface to the inner peripheral surface of the water heat transfer tube 10. The bottom wall thickness up to (that is, the bottom of the groove 12) is “TW”.

  FIG. 2B (a) shows a perspective view when the water heat transfer tube according to the first embodiment is straight, and FIG. 2B (b) shows X1-X2 in FIG. 2B (a). The outline when cut along is shown.

  FIG. 2B (a) shows the straight water heat transfer tube 10 before bending. Then, referring to (a) and (b) of FIG. 2B, the water heat transfer tube 10 has a plurality of grooves 12 formed in a spiral shape on the inner peripheral surface thereof. Further, the water heat transfer tube 10 has a plurality of fins 14 between the plurality of grooves 12. Here, in 1st Embodiment, the space | interval of the some fin 14 is "b", and the angle (henceforth "twist angle") which the groove | channel 12 and the fin 14 make with respect to the longitudinal direction of the linear water heat exchanger tube 10 is mentioned. Is “β”.

  In the water heat transfer tube 10 according to the first embodiment, the interval between the fins 14 can be determined according to the number of grooves 12 provided on the inner surface of the water heat transfer tube 10. Further, the twist angle β can be in the range of more than 0 ° and less than 90 ° with respect to the longitudinal direction of the water heat transfer tube 10 (the axial direction of the straight water heat transfer tube 10).

(Modification of the first embodiment)
In the heat exchanger 1 according to the first embodiment, one refrigerant heat transfer tube 20 is provided on the outer periphery of the water heat transfer tube 10, but in a modification of the first embodiment, a plurality of refrigerant heat transfer tubes 20 are provided. The heat tube 20 can also be provided on the outer periphery of the water heat transfer tube 10. In this case, the inner diameter of one refrigerant heat transfer tube may be different from the inner diameter of another refrigerant heat transfer tube.

(Effects of the first embodiment)
Since the heat exchanger 1 according to the first embodiment is provided with the plurality of grooves 12 and the plurality of fins 14 that satisfy the above formula (1) on the inner peripheral surface of the water heat transfer tube 10, the plurality of fins At 14, stirring of the water flowing through the water heat transfer tube 10 is promoted. Thereby, in 1st Embodiment, even when the flow rate of the water which flows through the water heat exchanger pipe 10 is slow like a hot water storage type heat pump water heater, for example, improving the heat transfer performance of the heat exchanger 1. It is possible to provide a heat exchanger 1 with high heat conversion efficiency that can contribute to measures against global warming.

  Further, the heat exchanger 1 according to the first embodiment can have a counter flow in which the direction of water flowing in the water heat transfer tube 10 and the direction of the refrigerant flowing in the refrigerant heat transfer tube 20 are reversed. . Thereby, in 1st Embodiment, the heat exchanger 1 which improved the heat exchange performance can be provided.

  Furthermore, since the heat exchanger 1 according to the first embodiment does not require twisting a plurality of hollow water heat transfer tubes in a spiral shape, for example, it occurs when the water heat transfer tube is twisted in a spiral shape. Deformation such as breakage, cracking and crushing of the obtained water heat transfer tube does not occur. Therefore, according to 1st Embodiment, the heat exchanger 1 can be manufactured with a simple manufacturing process, and the heat exchanger 1 with high reliability can be provided.

[Second Embodiment]
FIG. 3: shows the outline | summary of the cross section of the heat exchanger which concerns on the 2nd Embodiment of this invention.

  The heat exchanger 2 according to the second embodiment is the same as that of the first embodiment except that the spiral winding form of the water heat transfer tube 10 and the winding method of the refrigerant heat transfer tube 20 around the water heat transfer tube 10 are different. The heat exchanger 1 has substantially the same configuration. Therefore, a detailed description is omitted except for differences.

  The heat exchanger 2 according to the second embodiment includes a water heat transfer tube 10 that exhibits a substantially cylindrical outer diameter by spirally winding a straight water heat transfer tube 10. The water heat transfer tube 10 according to the second embodiment is formed to have a plurality of steps by being spirally wound, and the surface 10b of the water heat transfer tube 10 corresponding to one step is The surface 10b of the water heat transfer tube 10 corresponding to the next stage following this stage is separated by an interval corresponding to at least the outer diameter of the refrigerant heat transfer pipe 20. That is, the water heat transfer tube 10 according to the second embodiment includes a surface 10b of the water heat transfer tube 10 corresponding to one stage, and a surface 10b of the water heat transfer tube 10 corresponding to the next stage following the first stage. Are not touching.

  The refrigerant heat transfer tube 20 according to the second embodiment is spirally wound along the outer surface of the water heat transfer tube 10, and the contact portion between the refrigerant heat transfer tube 20 and the water heat transfer tube 10 is brazed or the like. Be joined. Specifically, the refrigerant heat transfer tube 20 includes an outer periphery and an inner periphery of the water heat transfer tube 10 having a substantially cylindrical shape, and a gap between the first stage and the next stage following the first stage. It is wound around the water heat transfer tube 10 in a spiral manner in contact with each of the surface portions. That is, the refrigerant heat transfer tube 20 according to the second embodiment is wound around the outer periphery of the water heat transfer tube 10 along a direction inclined with respect to the spiral winding direction of the water heat transfer tube 10. In other words, the refrigerant heat transfer tube 20 is wound around the outer periphery of the water heat transfer tube 10 so that the flow direction of the refrigerant to flow into the refrigerant heat transfer tube 20 is inclined with respect to the flow direction of the water to flow into the water heat transfer tube 10. It is turned on.

(Effect of the second embodiment)
The heat exchanger 2 according to the second embodiment corresponds to the outer periphery and inner periphery of the cylinder formed from the water heat transfer tube 10 and the gap between the first stage and the next stage following the first stage. The refrigerant heat transfer tube 20 is in contact with each of the surface portions of the water heat transfer tube 10. Thereby, in 2nd Embodiment, since the contact area of the surface of the water heat exchanger tube 10 and the surface of the refrigerant | coolant heat exchanger tube 20 increases, as a result, a heat exchanger area can be increased. Therefore, according to the heat exchanger 2 which concerns on 2nd Embodiment, heat conversion efficiency can be improved significantly.

[Modification of Embodiment]
FIG. 4 shows an example of a heat exchanger according to a modification of the embodiment of the present invention.

  In FIG. 4, the refrigerant heat transfer tube 20 is not shown. And the heat exchanger which concerns on this modification is substantially the same as the heat exchanger 1 which concerns on 1st Embodiment, except that the square heat exchanger tube 15 as a 1st heat exchanger tube has a substantially square-shaped cross section. The configuration is provided. Therefore, a detailed description is omitted except for differences.

  In this modification, the rectangular heat transfer tube 15 as the first heat transfer tube is spirally wound so that the outer shape becomes a substantially cylindrical shape after the cross section is formed in a substantially square shape. And although illustration is abbreviate | omitted in FIG. 4, the refrigerant | coolant heat exchanger tube 20 is wound around the outer periphery of the rectangular heat exchanger tube 15 wound helically. And the surface of the square heat exchanger tube 15 and the surface of the refrigerant | coolant heat exchanger tube 20 are joined. In this modification, in the cross section of the rectangular heat transfer tube 15, the diagonal line on the inner surface is the maximum inner diameter “ID”, and the diagonal line on the outer surface is the maximum outer diameter “OD”.

  Here, in FIG. 4, the surface of the rectangular heat transfer tube 15 corresponding to one step and the surface of the rectangular heat transfer tube 15 corresponding to the next step following the first step are in contact with each other at the contact portion 15a. Note that, in the heat exchanger according to still another modified example of the embodiment, the surface of the rectangular heat transfer tube 15 corresponding to one stage and the one like the heat exchanger 2 according to the second embodiment, The surface of the rectangular heat transfer tube 15 corresponding to the next step following this step can be separated from the outer diameter of the refrigerant heat transfer tube 20. In this case, the refrigerant heat transfer tube 20 has a rectangular shape corresponding to a gap between an outer periphery and an inner periphery of a spirally wound rectangular heat transfer tube 15 having a substantially cylindrical shape, and a next stage following the first stage. The heat transfer tube 15 is spirally wound around the rectangular heat transfer tube 15 in contact with each of the surface portions of the heat transfer tube 15.

  According to the heat exchanger according to this modification, since the heat transfer tube through which water should flow has a square shape, the effect of the secondary flow is greater than when the cross section is circular. In addition, when the rectangular heat transfer tube 15 is spirally wound into a cylindrical shape, the rectangular heat transfer tube 15 can be prevented from being deformed flat, and thus a compact heat exchanger can be provided.

  Hereinafter, a heat exchanger according to an embodiment of the present invention will be described.

  FIG. 5 shows the measurement results of the heat transfer performance when the water heat transfer tubes according to the example and the comparative example are made straight.

Specifically, straight water heat transfer tubes having the specifications shown in Table 1 were produced. The specifications of the plurality of grooves formed on the inner peripheral surface of the water heat transfer tube are described in the column of spiral inner groove specifications. All of the water heat transfer tubes according to Example 1 and Example 2 and Comparative Example 1 and Comparative Example 2 were made from phosphorous deoxidized copper. The maximum outer diameter “OD” of each water heat transfer tube was 8 mm. Here, “heat transfer performance” is defined as a value obtained by dividing the Nusselt number Nu by the 0.4th power of the Prandtl number Pr in order to offset the influence of the physical properties of the fluid (ie, heat transfer performance = Nu / Pr ^{0 .4} , and the same applies to the examples and comparative examples).

  In addition, the pressure loss of the water heat transfer tube is expressed as a Darcy tube friction coefficient f which is a dimensionless number in the following description. Hereinafter, the grounds for the above formula (1) described in the first embodiment will be described based on examples.

  First, in any of the straight water heat transfer tubes used when producing the water heat transfer tubes according to Examples 1 and 2, when the Reynolds number “Re” is 2000 or less, the water according to Comparative Example 2 is a smooth tube. The heat conversion efficiency was almost the same as the heat transfer tube (the value of the heat conversion efficiency was omitted). This is because even if fins are provided on the inner surface of the water heat transfer tube, the fins are covered with the turbulent boundary layer.

  Here, the Reynolds number Re is defined by the following equation (2).

In the above formula (2), ρ is the density (kg / m ³ ) of the fluid flowing in the pipe, and μ is the viscosity (Pas) of the fluid flowing in the pipe. Further, ν is the fluid velocity (m / s), and ID is the inner diameter of the water heat transfer tube.

Here, the turbulent boundary layer is composed of a viscous bottom layer (or laminar bottom layer) that flows in a laminar flow in the vicinity of the tube wall of the water heat transfer tube, and an intermediate layer between the laminar flow and turbulent flow. Here, in order to compare the fin height and the thickness of the viscous bottom layer, the dimensionless number y ⁺ of the distance y (that is, the thickness of the viscous bottom layer) from the tube wall of the water heat transfer tube toward the tube center of the water heat transfer tube is It is defined by the following formula (3).

In the formula (3), u ^* is a friction speed and is defined by the following formula (4).

In equation (4), τ _w is the frictional stress (Pa) in the tube wall.

Usually, since the viscous bottom layer is in the range of 0 ≦ y ⁺ ≦ 5, the thickness of the viscous bottom layer can be approximated to y when y ⁺ = 5. From the above equation (3), it can be seen that the thickness y of the viscous bottom layer is inversely proportional to the friction speed u ^* . It can be seen from the above formula (4) that the friction speed u ^* is proportional to the friction stress τ _w in the tube wall. Here, the friction stress tau _w, the relationship between the pressure loss △ P in the longitudinal direction of the predetermined section L of water heat exchanger tube is indicated by the expression derived from the following equation (5) (6). Note that the pressure at one end of the section L is P1, and the pressure at the other end of the section L is P2 (where P1 ≧ P2). Further, the length of the section L is assumed to be L.

  Here, the Darcy-Weisbacha equation is as shown in the following equation (7).

  In equation (7), ν is the average flow velocity (m / s) of the fluid, and f is the pipe friction coefficient. Then, by substituting equation (7) into equation (6), the following equation (8) is obtained.

As can be seen from the equation (8), if the fluid temperature and flow velocity of the fluid flowing through the water heat transfer tube are the same, the friction stress τ _w is proportional to the tube friction coefficient f. Therefore, when the pipe friction coefficient f is increased, the thickness of the viscous bottom layer represented by the above formula (3), that is, the value of y in the case of y ⁺ = 5 is decreased. Further, the value obtained by dividing the thickness of the viscous bottom layer (that is, the value of y when y ⁺ = 5) by the maximum inner diameter ID of the water heat transfer tube is expressed by the above formula when the tube friction coefficient f is a function of the Reynolds number Re. From (2) to the above equation (8), it can be expressed as a function of the Reynolds number Re and the pipe friction coefficient f as in the following equation (9).

Here, for example, when the water heat transfer tube is a smooth tube, the tube friction coefficient f _s of the straight water heat transfer tube is a turbulent flow equation (Brazius equation: f _s = 0.3164 / Re ^0.25 ). As shown by the laminar basin formula (f _s = 64 / Re from Hagen-Poiseuille's law), it is inversely proportional to the Reynolds number Re to the 0.25th power or the Reynolds number Re. Therefore, in the case of a straight smooth tube, as can be seen by referring to the above equation (9), the thickness of the viscous bottom layer (that is, the value of y when y ⁺ = 5) is set to the maximum inner diameter ID of the water heat transfer tube. The value divided by decreases as the Reynolds number Re increases.

  On the other hand, the tube friction coefficient ratio k between the spirally wound water heat transfer tube and the straight water heat transfer tube is defined by the following equation (10).

  In equation (10), De is the Dean number, and is defined by the following equation (11) where R is the curvature radius of the spirally wound water heat transfer tube and Re is the Reynolds number.

  Here, the Reynolds number Re of the hot water storage type heat pump water heater increases as the water temperature rises during boiling. The Reynolds number Re also varies depending on the inner diameter of the water heat transfer tube, the number of heat exchanger paths provided in the hot water storage heat pump water heater, the capacity of the heat exchanger, outdoor conditions, and the like. Therefore, the outdoor conditions and hot water supply conditions are set to intermediate conditions (that is, outdoor air temperature: 16 ° C., incoming water temperature: 17 ° C., outgoing hot water temperature: 65 ° C.), and the intermediate water temperature is set to 41 ° C. The Reynolds number Re was calculated according to the conditions shown in Table 2 below for the inner diameter of the water heat transfer tube, the number of passes of the heat exchanger, and the capacity of the heat exchanger. The inner diameter of the water heat transfer tube, the number of heat exchanger passes, and the capacity of the heat exchanger were set to be large within a range that can be considered from constraints such as the size required for the hot water storage type heat pump water heater. Table 2 also shows the Dean number De when the radius of curvature R of the spiral winding is 20 mm, and the tube friction coefficient ratio k of each of the spirally wound water heat transfer tube and the straight water heat transfer tube.

  Referring to Table 2, the minimum Reynolds number Re is 1300. In this case, the viscous bottom layer is the thickest. Therefore, the present inventors have found that the fin height of the water heat transfer tube in which grooves and fins are formed on the inner peripheral surface is the Reynolds number Re = It was found that the thickness of the viscous bottom layer at 1300 is required to be higher.

The minimum critical Reynolds number R _ec of the spirally wound water heat transfer tube is defined by the following equation (12).

The minimum critical Reynolds number R _ec decreases as the radius of curvature R of the spiral winding increases and the inner diameter ID of the water heat transfer tube decreases. Here, considering the size required for the hot water storage type heat pump water heater, the radius of curvature R of the spiral winding is about 200 mm at the maximum, and the minimum value of the inner diameter ID is set to, for example, 6.8 mm shown in Table 2 In this case, the minimum critical Reynolds number Rec is about 5400. Therefore, the fluid flowing through the spiral water heat transfer tube having such characteristics becomes a laminar flow over almost the entire area of the water heat transfer tube, and the pipe friction coefficient f _s = 64 / Re in the straight smooth tube in the laminar flow region. By multiplying the tube friction coefficient ratio k, which is the ratio of the tube friction coefficient of the spiral-wound water heat transfer tube shown in the above formula (10), and the tube friction coefficient of the straight water heat transfer tube, the tube in the spiral wound smooth tube friction coefficient _f (= k × f _s) can be calculated.

Therefore, using the above equations (10) and (11) and the pipe friction coefficient f _s = 64 / Re in a straight smooth tube in a laminar flow region, the above equation (9) is expressed by the following equation (13): Can be organized like

  And according to the water heat transfer tube spirally wound based on the above equation (13) and satisfying the relationship of the following equation (1), the inventor determines the viscous bottom layer of the fluid flowing in the water heat transfer tube from the fin height. The knowledge that it can be made thin was obtained.

  Accordingly, the present inventor provides, for example, a heat exchanger that can improve the heat exchange performance according to the present embodiment within the range of the Reynolds number of the heat pump water heater, and a heat transfer tube for the heat exchanger. I got the knowledge that I can do it.

  In Table 3, HF / ID, which is the ratio of the inner diameter to the fin height of the water heat transfer tube in which a plurality of grooves are spirally formed on the inner peripheral surface shown in Table 1, and the curvature of the spiral winding in the above equation (13) It shows the value (y / ID) of the ratio of the inner diameter to the thickness of the viscous bottom layer when the radius R is 20 mm.

  FIG. 6 shows the results of measuring the heat transfer performance of the spirally wound water heat transfer tubes according to the example and the comparative example.

  FIG. 6 is a result of measuring the heat transfer performance when the radius of curvature R of the spirally wound water heat transfer tube is 20 mm for each of the water heat transfer tubes according to Examples 1 and 2 and Comparative Example 1. Referring to FIG. 6, when spirally wound, the heat transfer performance was improved with respect to the smooth tube (Comparative Example 2) when the Reynolds number Re was 1300 in Examples 1 and 2. On the other hand, in Comparative Example 1, the heat transfer performance was comparable to that of a smooth tube.

(Effect of Example)
For example, the flow rate of water in a heat exchanger that exchanges heat between water and refrigerant in a heat pump water heater is very small. Here, when a smooth tube or a straight heat transfer tube is used, the fluid (for example, water) flowing through these becomes a laminar flow, so the heat transfer performance is very low. However, from the results of Examples 1 and 2, the spirally wound water heat transfer tubes according to Example 1 and Example 2 have a plurality of spiral grooves and a plurality of grooves satisfying a predetermined relationship on the inner peripheral surface. According to the water heat transfer tube having a plurality of fins positioned at the height of the fin, the height of the fin can be made higher than that of the viscous bottom layer by utilizing the characteristics of the spiral groove formed on the inner peripheral surface. Thereby, the heat conversion efficiency can be effectively improved by the agitation of the fluid by the plurality of fins and the effect of increasing the surface area where the fins and the fluid contact each other. Furthermore, heat conversion efficiency can be improved by the secondary flow by the spiral winding of the groove | channel provided in the internal peripheral surface of the water heat exchanger tube.

  While the embodiments and examples of the present invention have been described above, the embodiments and examples described above do not limit the invention according to the claims. It should be noted that not all combinations of features described in the embodiments and examples are necessarily essential to the means for solving the problems of the invention.

DESCRIPTION OF SYMBOLS 1, 2 Heat exchanger 10 Water heat exchanger tube 10a Contact part 10b Surface 12 Groove 14 Fin 15 Rectangular heat exchanger tube 15a Contact part 20 Refrigerant heat exchanger tube 20a, 20b Joint part

Claims (4)

A first heat transfer tube having a plurality of grooves spirally provided on the inner peripheral surface and a plurality of fins positioned between the plurality of grooves, and formed into a cylinder by spiral winding;
A second heat transfer tube provided adjacent to the first heat transfer tube,
The first heat transfer tube is a heat exchanger that satisfies the following formula (1) when the radius of curvature of the cylinder is R, the maximum inner diameter of the first heat transfer tube is ID, and the height of the fin is HF.

  The heat exchanger according to claim 1, wherein the second heat transfer tube is in contact with an outer surface of the first heat transfer tube by being wound along an outer periphery of the cylinder. The second heat transfer tube is wound along the surface of the first heat transfer tube,
The heat exchanger according to claim 1, wherein a surface of the first heat transfer tube and a surface of the second heat transfer tube are joined. A heat transfer tube comprising a plurality of grooves spirally provided on the inner peripheral surface and a plurality of fins positioned between the plurality of grooves, and formed into a cylinder by spiral winding,
A heat transfer tube that satisfies the following formula (1), where R is the radius of curvature of the cylinder, ID is the maximum inner diameter of the heat transfer tube, and HF is the height of the fin.

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