JP2010112565A - Heat exchanger - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light-weight and compact heat exchanger, improving a heat transferring performance of the heat exchanger even under use configuration where a flow rate of the water is small such as a storage type heat pump water heater. <P>SOLUTION: This heat exchanger includes: an inner pipe 2 in which a refrigerant passes; and an outer pipe 3 disposed outside of the inner pipe 2 to pass the water between the inner pipe 2 and the outer pipe 3. The outer pipe 3 has a spiral corrugated groove 4 formed by a corrugating processing, and the heat exchanger satisfies Pc/De≤560×(Hc/De)<SP>2</SP>-70×(Hc/De)+2.5, and Hc/De≥0.09 when a depth of the corrugated groove 4 is Hc, a clearance between the corrugated grooves 4 adjacent to each other in the pipe shaft direction is Pc, and the difference between the maximum inner diameter of the outer pipe 3 and an outer diameter of the inner pipe 2 is De. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a double-tube heat exchanger having an outer tube and an inner tube, and more particularly to a heat exchanger suitable for water-refrigerant heat exchange such as a hot water storage heat pump water heater.

  As heat exchangers used in hot water storage type heat pump water heaters (hereinafter sometimes simply referred to as “heat pump water heaters”), an outer pipe through which water flows and an inner pipe through which refrigerant (such as carbon dioxide) flows are used. A double-pipe heat exchanger composed of a heavy pipe is known.

  In such a double-pipe heat exchanger, if a hole due to corrosion is opened in the inner pipe through which the refrigerant flows, water and the refrigerant will be mixed together, so the leakage of water or refrigerant is detected and the apparatus is stopped. Therefore, a leak detection tube having a leak detection groove on the inner peripheral surface is often provided on the outer periphery of the inner tube (in this case, it can also be said to be a triple tube structure of the inner tube, the leak detection tube, and the outer tube). .

  The hot water storage type heat pump water heater boils hot water at night, and the flow rate of water flowing in the outer pipe is small and laminar. Therefore, to improve the performance as a heat exchanger, Improvement of thermal performance is essential.

  As a double tube heat exchanger for the purpose of improving heat transfer performance, the second heat transfer tube (inner tube) is constructed by spirally twisting a plurality of heat transfer tubes in the first heat transfer tube (outer tube). ) Are arranged (see Patent Document 1). According to the heat exchanger of Patent Document 1, it is described that water pressure loss and elution of scale components are small, and heat transfer can be promoted without using another component as a heat transfer accelerator.

  Further, as shown in FIG. 4, a double pipe comprising an outer pipe 41 and an inner pipe 42 inserted into the outer pipe 41 is provided, and the inner pipe 42 has a first fluid channel 43 formed therein. It consists of a plurality of refrigerant tubes 44 and a single leakage detection tube 45 that covers the plurality of refrigerant tubes 44 and has a plurality of leakage detection grooves 46 in the axial direction of the inner surface. There is one in which a second fluid channel 47 is formed between the inner wall and the inner wall (see Patent Document 2). According to the heat exchanger of Patent Document 2, since the amount of copper used can be reduced while maintaining the heat exchange performance, it is described that the weight of the heat exchanger can be reduced and the cost can be reduced. ing.

  In addition, there is a double-tube heat exchanger that includes an inner tube and an outer tube disposed outside the inner tube, and the outer tube is flexible as a corrugated tube having a spiral corrugated shape (patent) Reference 3). According to the heat exchanger of Patent Document 3, since bending workability is improved by using a corrugated tube, a small bend that is difficult to bend with a smooth tube is required, such as when the heat exchanger is coiled. That it can be used for piping.

JP 2004-360974 A JP 2008-57860 A JP 2005-9832 A

However, in the heat exchanger of the above-mentioned patent document 1, in addition to the complicated and costly process of twisting a plurality of heat transfer tubes in a spiral shape, the first heat transfer tube (outer tube) and the plurality of second heat transfer tubes There exists a problem that the process and structure of the heat exchanger terminal part which isolate | separates (inner pipe | tube) become complicated. Further, since a plurality of second heat transfer tubes (inner tubes) are used, there is a problem that the weight of the heat exchanger increases.
Moreover, in the heat exchanger of the said patent document 2, although the process which twists a several heat exchanger tube (inner tube) helically is abbreviate | omitted, like the patent document 1, an outer tube and a plurality of heat exchanger tubes (inner tube) There is a problem that the processing and structure of the end portion of the heat exchanger that separates the tubes are complicated. In addition, although it is possible to reduce the weight as compared with Patent Document 1, since a plurality of heat transfer tubes (inner tubes) are used, there is a problem that the heat exchanger cannot be sufficiently reduced in weight.
On the other hand, the heat exchanger of Patent Document 3 is improved in bending workability by using a corrugated tube (outer tube), and also has a single inner tube that is lightweight, compact, and has a high heat exchange rate. Can do. However, the corrugate shape and dimensions of the corrugated pipe are not particularly studied. However, the heat transfer / heat exchange performance varies greatly depending on the corrugated shape and dimensions, and the heat exchanger disclosed in Patent Document 3 may not obtain the desired performance.

  An object of the present invention is to provide a lightweight and compact heat exchanger that can improve the heat transfer performance of a heat exchanger even in a use form where the flow rate of water is small, such as a hot water storage type heat pump water heater.

  In order to solve the above problems, the present invention is configured as follows.

According to a first aspect of the present invention, in the heat exchanger including an inner pipe through which a refrigerant passes and an outer pipe disposed outside the inner pipe and through which water passes, the outer pipe includes A corrugated groove is formed by corrugation, and the depth of the corrugated groove is Hc, the distance between the corrugated grooves adjacent to each other in the tube axis direction is Pc, the maximum inner diameter of the outer tube and the outer diameter of the inner tube When the difference from the diameter is De, Pc / De ≦ 560 × (Hc / De) ² −70 × (Hc / De) +2.5
And satisfying Hc / De ≧ 0.09.

  According to a second aspect of the present invention, in the heat exchanger according to the first aspect, an angle formed by a tube axis of the outer tube and the corrugated groove is 40 ° or more.

  According to a third aspect of the present invention, in the heat exchanger according to the first or second aspect, the spiral corrugated groove is formed in 1 to 3 in the outer tube. .

  According to the present invention, it is possible to improve the heat transfer performance of a heat exchanger even in a use form where the flow rate of water is small, such as a hot water storage type heat pump water heater, and a heat exchanger that is lightweight, compact, and inexpensive. can get.

  Embodiments of a heat exchanger according to the present invention will be described below with reference to the drawings.

(First embodiment)
FIG. 1 shows the structure of a heat exchanger according to the first embodiment of the present invention. FIG. 1 (a) is a side view in which a part of the cross section including the tube axis is broken, and FIG. It is AA sectional drawing of Fig.1 (a). 2 shows the outer tube of FIG. 1, FIG. 2 (a) is a side view with a part broken away, and FIG. 2 (b) is an enlarged cross-sectional view of part B of FIG. 2 (a). .
As shown in FIG. 1, the heat exchanger 1 according to the first embodiment includes an inner pipe 2 through which a refrigerant passes and an outer pipe 3 that is disposed outside the inner pipe 2 and passes water between the inner pipe 2. Is a double tube heat exchanger.

The inner pipe 2 includes a refrigerant pipe 21 in which a refrigerant such as CO ₂ (carbon dioxide) flows, and a refrigerant pipe 21.
And a leak detection tube 22 covering the outer periphery of the tube. A leak detection groove 23 is formed along the axial direction on the inner peripheral surface of the leak detection tube 22, and the outer peripheral surface of the leak detection tube 22 serving as the outer surface of the inner tube 2 is a smooth surface.
Since the outer periphery of the refrigerant pipe 21 is covered by the leak detection pipe 22, it is possible to prevent the refrigerant and water from mixing even if a part of the refrigerant pipe 21 through which a high-temperature / high-pressure refrigerant or the like passes is broken. . Even if the refrigerant pipe 21 or the leakage detection pipe 22 is broken and the refrigerant or water leaks, the leakage can be detected by extracting the refrigerant or water to the outside through the leakage detection groove 23.

The outer tube 3 is a corrugated tube in which one spiral corrugated groove 4 is formed by corrugating. Here, the corrugated tube refers to a tube having a corrugated spiral structure on the inner and outer surfaces of the tube.
Since the outer tube 3 is a corrugated tube in which the corrugated grooves 4 are formed, the outer tube 3 is more flexible than a smooth outer tube and can be bent with a small radius of curvature. Compacting can be promoted.

The heat pump water heater includes a compressor, a heat exchanger for hot water supply, an expansion valve, and a refrigeration cycle including an outdoor heat exchanger that uses outside air as a heat source, a heat exchanger for hot water supply, a water pump, and a hot water tank. It consists of a hot water supply cycle.
The double-pipe heat exchanger 1 is used, for example, as a heat exchanger for hot water supply of a heat pump type hot water heater. That is, a high-temperature and high-pressure CO ₂ refrigerant from the compressor side of the refrigeration cycle flows in the refrigerant pipe 21 of the inner pipe 2, and the annular portion between the inner pipe 2 and the outer pipe 3 flows into the water supply cycle water supply cycle. Water is flowed from the pump side, the CO ₂ refrigerant and water are heat-exchanged by a hot water supply heat exchanger, and water (hot water) that has reached a high temperature is sent to a hot water supply tank. In the heat exchanger 1, the refrigerant and water are caused to flow in opposite directions.

The shape and dimensions of the inner tube 2 and the corrugated outer tube 3 are as follows: the depth of the corrugated groove 4 is Hc, the distance between the corrugated grooves 4 adjacent in the tube axis direction (corrugated pitch) is Pc, and the maximum of the outer tube 3 Assuming that the difference between the inner diameter (original pipe inner diameter before corrugation) ID and the outer diameter of the inner pipe 2 (in this embodiment, the outer diameter of the leak detection pipe 22) do is De, Pc / De ≦ 560 × (Hc / De) ² −70 × (Hc / De) +2.5 and is set to satisfy Hc / De ≧ 0.09.

Thus, by regulating the values of Hc, Pc, and De within the above ranges, the water stirring effect when water gets over the corrugated uneven surface (corrugated surface) on the inner surface of the outer tube 3 is promoted and transmitted reliably. The thermal performance can be improved. For this reason, the problem in the water-refrigerant heat exchanger of the heat pump type hot water heater, that is, the problem that the heat transfer performance is very low because the flow rate of water becomes very small and becomes a laminar flow can be solved.
Further, since the stirring effect is promoted by defining the values of Hc, Pc, and De in the above range, compared with a heat exchanger that uses a plurality of refrigerant tubes (heat transfer tubes) 44 as shown in FIG. However, a heat exchanger having the same or better heat transfer performance can be obtained. In addition, since sufficient heat transfer performance can be obtained simply by inserting one inner tube (heat transfer tube) 2, the amount of pipe material (copper, etc.) can be reduced, the heat exchanger can be further reduced in weight, and the cost can be reduced. Can be realized. Furthermore, the pipe structure is simple, and it is excellent in manufacturability and handling.

  Further, as shown in FIG. 2, it is desirable that the twist angle βc, which is an angle formed between the corrugated groove 4 of the outer tube 3 and the tube axis Ta, be a high twist shape of 40 ° or more. Thereby, the turbulent flow of water that flows over the corrugated irregular surface formed on the inner peripheral surface by the corrugated groove 4 of the outer tube 3 can be promoted. From the definition of the corrugated tube described above, the twist angle βc is in the range of 0 ° <βc <90 °.

The corrugated pitch Pc of the outer tube 3 is not particularly limited as long as it satisfies the above relational expression of Hc, Pc, and De. For example, a corrugated pitch Pc of 3 mm ≦ Pc ≦ 30 mm can be used.
Further, the thickness Tw of the terminal smooth portion of the outer tube 3 is not particularly limited, but for example, a thickness of 0.4 mm ≦ Tw ≦ 1.7 mm can be used.
Further, the material of the inner tube 2 and the outer tube 3 is not particularly limited, but copper, copper alloy, aluminum, aluminum alloy, or the like is preferable in consideration of thermal conductivity and mechanical strength.

(Second Embodiment)
FIG. 3 is a partially broken side view showing the structure of the outer tube used in the heat exchanger according to the second embodiment of the present invention.
The outer tube 3 of the first embodiment is a corrugated tube in which a single spiral corrugated groove 4 is formed by corrugation, whereas the outer tube 5 of the present embodiment has a three-spiral shape. It is a corrugated pipe in which a corrugated groove 6 is formed. The outer pipe 5 is also used as a water pipe constituting a double-pipe heat exchanger, and an inner pipe through which a refrigerant flows is arranged in the outer pipe 5 as in the first embodiment.
When the number of corrugated grooves is increased, the processing speed is increased, resulting in a large manufacturing cost advantage.
The twist angle βc of the corrugated groove tends to be smaller in the case of the three-row processing than in the case of the single-row processing, but by increasing the interval between the adjacent corrugated grooves, that is, the corrugated pitch Pc, the twist angle is high by 40 ° or more. A twist angle can be realized. If this is not an outer tube with a corrugated structure but an inner grooved tube is used as the outer tube, its manufacture is difficult.

  In the above-described embodiment, the outer tube provided with the first and third corrugated grooves has been described, but two or four or more corrugated grooves may be formed in the outer tube. The number of corrugated grooves is preferably 1 to 3. This is because the outer tube having the corrugated structure having 1 to 3 corrugated structures easily realizes a high twist angle that is difficult with an internally grooved tube.

  Next, examples of the present invention will be described.

In this example, the performance of the heat exchanger according to the first embodiment shown in FIG. 1 was examined by variously changing the shape and dimensions of the corrugated structure of the outer tube. Table 1 shows the heat transfer tube specifications of the inner and outer tubes studied. In addition, No. 1 to No. 15 in Table 1 are examples of heat exchangers having the same structure as FIG. 1, but No. 16 is an example of simulating the heat exchanger having the conventional structure shown in FIG. . In Table 1, OD is the maximum outer diameter of the outer pipe (original pipe outer diameter before corrugating), Tw is the thickness of the outer pipe, ID is the maximum inner diameter of the outer pipe (original pipe inner diameter before corrugating), and Hc is The depth of the corrugated groove, Pc is the corrugated pitch, do is the outer diameter of the inner tube, and De is the difference between the maximum inner diameter ID of the outer tube and the outer diameter do of the inner tube.
In addition, De in No. 16 which simulated the heat exchanger of the conventional structure shown in FIG. 4 is De = 4.
It calculated | required from S / L. Here, S is a flow path area, and S = (π / 4) × (ID ² −2 · do ² ). L is the length of the wet wrinkle and L = π (ID + 2do).

The method which calculated | required the water side heat transfer coefficient of the heat exchanger of Table 1 is shown below.
Warm water at 30 ° C. was allowed to flow through the inner pipe of the double-pipe heat exchanger shown in Table 1, and cold water at 20 ° C. was allowed to flow through the annular part of the outer pipe and the inner pipe for heat exchange. The flow rate in the inner pipe, the flow rate of the annular portion, and the inlet / outlet temperature thereof were measured, and the heat exchange amount Q and the heat passage rate K were determined. The heat transfer coefficient in the inner pipe is represented by the average value of the inlet / outlet temperature, the Prandtl number Pr = μCp / λ (where μ: viscosity coefficient, Cp: specific heat, λ: thermal conductivity), and Reynolds number Re = ρvdi / μ (where ρ: density, v: flow velocity, di: inner diameter of the inner tube) is obtained, and the Dittus-Boelter equation (Nussell number Nu = 0.023 · Re ^0.8 Pr ^0.4 ) and representative From the thermal conductivity λ at temperature, the in-tube heat transfer coefficient αi = Nuλ / di was obtained. From this, the external heat transfer coefficient αo = 1 / (1 / K−1 / αi) is obtained.

Next, the method for obtaining the heat exchange amount of the heat exchanger is shown below.
The external heat transfer coefficient obtained by the above-described method was formulated, and the heat exchange amount was calculated by simulation considering the physical properties of CO ₂ . Table 2 shows the calculation conditions at this time.

The calculation of the physical properties of CO ₂ uses Propath, and CO _{2 in the} supercritical state can be treated as a single-phase flow. Therefore, the heat transfer coefficient is the Dittus-Boelter equation, the pressure loss is the Blasius equation (pipe friction coefficient f = 0.3).
164 · Re− ^0.25 ). The simulation was performed by dividing the heat exchanger into 20 parts, and the heat exchange amount was calculated.
The length of the heat exchanger No. 16 in Table 1 was set to 8 m, and the amount of heat exchange was calculated. The weight of the heat exchanger No. 16 was calculated from the heat exchanger having the structure shown in FIG. Table 3 shows the configurations of No. 1 to 15 and No. 16 inner pipes (refrigerant pipe and leakage detection pipe) in Table 1.

In FIG. 5, the heat exchange of No. 1-15 when it is set as the heat exchange performance equivalent to the weight of the heat exchanger of No. 16 which is the conventional structure in Table 1, and this No. 16 heat exchanger. The weight ratio with the weight of the vessel is shown. If the weight ratio is smaller than 1, it is shown that the heat exchanger can be reduced in weight by shortening the length of the tube due to higher performance.

As shown in FIG. 5, in the case of No. 1 to 4 (Hc / De = 0.19), the weight can be reduced more than No. 16 in all corrugated pitches Pc.
In the case of No. 5 to 8 of Hc / De = 0.15 (in the case of Hc / De = 0.15), No. 6 to 8 can be lighter than No. 16.
In the case of No. 9 to 12 (in the case of Hc / De = 0.13), No. 11 and 12 are lighter than No. 16.
In the case of No. 13 to 15 (when Hc / De = 0.09), only No. 15 can be reduced in weight.

From the above results, the heat exchanger (Hc / D
e, Pc / De) values are plotted in FIG. FIG. 6 also shows Pc / De = 560 (Hc / De) ² -70 (Hc / De) +2.5, which is an approximate curve that approximates these plotted points. If the heat exchanger satisfies the (Hc / De, Pc / De) value of the area below the approximate curve and having Hc / De of 0.09 or more (the hatched area in the figure), No. 1
Higher performance and lighter weight than 6 heat exchangers.

1 shows a heat exchanger according to an embodiment of the present invention, in which FIG. 1 (a) is a side view in which a section including a tube axis is broken, and FIG. 1 (b) is an A- It is A sectional drawing. 2 shows the outer tube of FIG. 1, FIG. 2 (a) is a partially cutaway side view, and FIG. 2 (b) is an enlarged cross-sectional view of part B of FIG. 2 (a). It is the side view which fractured | ruptured a part which shows the outer tube | pipe used for the heat exchanger which concerns on other embodiment of this invention. It is a cross-sectional view showing a conventional heat exchanger. With respect to the weight of the heat exchanger of No. 16 when the heat exchangers of No. 1 to No. 15 in Table 1 examined in the examples have the same performance as the heat exchanger of No. 16 having the conventional structure in Table 1 It is the graph plotted by weight ratio and Pc / De value. It is the graph which plotted the (Hc / De, Pc / De) value of the heat exchanger used as the heat exchanger of No. 16 of Table 1, and equivalent weight.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Heat exchanger 2 Inner tube 21 Heat transfer tube 22 Leak detection tube 3 Outer tube 4 Corrugated groove 5 Outer tube 6 Corrugated groove Hc Corrugated groove depth Pc Distance between adjacent corrugated grooves in the tube axis direction De Maximum inner diameter ID of outer tube Difference between the outer diameter do and the inner pipe Ta

Claims (3)

In a heat exchanger comprising an inner pipe for passing a refrigerant and an outer pipe disposed outside the inner pipe and passing water between the inner pipe,
A spiral corrugated groove is formed in the outer tube by corrugation, the depth of the corrugated groove is Hc, the interval between the corrugated grooves adjacent in the tube axis direction is Pc, the maximum inner diameter of the outer tube and the When the difference from the outer diameter of the inner tube is De, Pc / De ≦ 560 × (Hc / De) ² −70 × (Hc / De) +2.5 and Hc / De ≧ 0.09 is satisfied. A heat exchanger characterized by   The heat exchanger according to claim 1, wherein an angle formed by the tube axis of the outer tube and the corrugated groove is 40 ° or more.   The heat exchanger according to claim 1 or 2, wherein the outer corrugated groove is formed with 1 to 3 spiral corrugated grooves.