JP4591293B2 - Liquid-liquid heat exchanger for water heater - Google Patents

Description

  The present invention relates to a liquid-liquid heat exchanger for a water heater, and in particular, a liquid-liquid heat exchanger for a high-performance water heater that has high heat exchange efficiency and excellent flexibility and enables flexible piping construction. Related to the vessel.

  2. Description of the Related Art A hot water heater such as a hot water heater is provided with a liquid-liquid heat exchanger that heats low temperature water that is a heat exchange medium with high temperature water that is a heat exchange medium. Such a liquid-liquid heat exchanger is used, for example, for reheating and reheating low-temperature water stored in a bath tub.

  This liquid-liquid heat exchanger has a double tube structure consisting of an inner tube and an outer tube, and high temperature water serving as a heat exchange medium or low temperature water serving as a heat exchange medium is passed through the inner flow path of the inner tube. The outer flow path between the inner tube and the outer tube passes low temperature water that is a heat exchange medium or high temperature water that is a heat exchange medium.

  The example of the liquid-liquid heat exchanger with which the conventional hot water heater was equipped is demonstrated using FIG. 9 and FIG. FIG. 9 is an overall view of a conventional liquid-liquid heat exchanger. FIG. 10 is a cross-sectional view (BB line) of FIG. 9, where (a) shows a case where the inner tube is a smooth circular tube, and (b) shows a case where the inner tube is a multi-leafy tube.

  The conventional liquid-liquid heat exchanger 70 has a double tube structure including an inner tube 71 and an outer tube 72. A heat medium is passed between the inner pipe 71 and the outer pipe 72, and the water passed through the inner pipe 71 is heated by the heat medium.

  In the liquid-liquid heat exchanger 70 illustrated in FIG. 10B, the inner tube 71 is a multi-leaf (six-leaf) tube so that the inner tube 71 is the smooth circular tube of FIG. Compared to the above, the heat transfer area is expanded, and a device for increasing the heat exchange efficiency has been devised (see Non-Patent Document 1).

As another example of the conventional liquid-liquid heat exchanger, there is a double-pipe heat exchanger described in FIG. The double-pipe heat exchanger is configured such that the flow path of water flowing between the inner tube and the outer tube is partitioned by a heat transfer facilitator provided on the outer surface of the inner tube in a spiral manner, thereby allowing the flow between the inner and outer tubes to flow. While increasing the flow path length of the path, the flow velocity and turbulence of the water flowing through the flow path are increased, and heat transfer from the refrigerant flowing in the inner pipe to the water flowing between the inner and outer pipes is promoted. Further, in Patent Document 1, a spiral corrugated pipe is applied to the outer pipe in order to facilitate the bending process (pipe construction) of the double pipe heat exchanger for the purpose of downsizing the entire heat exchanger. It is described.
Summary of Kanagawa Prefectural Industry-Academia Public Exchange Presentation Meeting, October 20, 2004 Oral Presentation, “Heat Transfer Characteristics of Double-Tube Heat Exchanger Using Multileaf Heat Transfer Tubes”, Nishiyama Co., Ltd. Works, Isao Katano, http://www.kanagawa-iri.go.jp/kitri/kouhou/program/H16/1701.pdf JP 2005-9832 A

  However, since the inner tube 71 described in Non-Patent Document 1 is formed by passing a smooth tube through a multi-leaf die (pulling out), the multi-leaf fin is substantially parallel to the tube axis direction. Therefore, since the turbulent flow effect of the heat exchange / heat exchange medium (fluid) is small, the heat exchange efficiency is increased only by the heat transfer area expansion. Moreover, since it is a multi-leaf fin substantially parallel to the tube axis direction, it has a disadvantage inferior in flexibility. On the other hand, the heat exchanger described in Patent Document 1 cannot be expected to have a significant effect of improving heat transfer performance because the heat transfer area of the inner pipe is not expanded. Moreover, although the heat exchanger which provided the flexibility to the outer pipe | tube is described in patent document 1, since the inner pipe | tube is being fixed only at the both ends of an outer pipe | tube, when performing a bending process, There is no guarantee that the inner tube is always fixed at the center of the outer tube, and the flow of the heat exchange medium existing between the two tubes may be hindered and the heat exchange efficiency may be reduced.

  Therefore, the object of the present invention is to increase the heat transfer area of the fluid flowing through the inner pipe and the fluid flowing between the inner pipe and the outer pipe, and to improve the heat exchange efficiency by the turbulent effect acting on both fluids. It is another object of the present invention to provide a high-performance liquid-liquid heat exchanger for a hot water heater that can be made to have excellent flexibility and enables flexible piping construction.

In order to achieve the above object, the present invention provides an inner tube having a first flow path through which one of water serving as a heat exchange medium and water serving as a heat exchange medium having a higher temperature than water serving as the heat exchange medium passes. And an outer tube having a second flow path that is disposed outside the inner tube and passes the other of the water to be the heat exchange medium and the water to be the heat exchange medium between the inner tube and the inner tube. , the inner tube, the twisting force by have a spiral pleat-shaped hollow fins formed by buckled wall seat,
The outer tube is a circular tube with a smooth inner surface, the cross-sectional area perpendicular to the flow direction in the first flow path is S, and the average inner diameter of the inner pipe is ID _i-ave = (4S / π) ^0.5 , The wall thickness of the inner pipe is TW _i , the average outer diameter of the inner pipe is OD _i-ave = ID _i-ave + 2TW _i , the volume flow rate of the fluid flowing through the first flow path is V _i , and the second When the volume flow rate of the fluid flowing through the flow path is V _o , the inner diameter ID _{o of the} outer tube is ((V _o / 2V _i ) × ID _i-ave ² + OD _i-ave ² ) ^0.5 <ID _o <(( _{2V o / V i) × ID} i-ave 2 + OD i-ave 2) liquid for water heater and satisfies the ^0.5 - providing a liquid heat exchanger.

  ADVANTAGE OF THE INVENTION According to this invention, it is excellent in flexibility, flexible piping construction is possible, and the liquid-liquid heat exchanger for hot water heaters with high heat exchange efficiency and high performance can be provided.

[First embodiment of the present invention]
(Configuration of liquid-liquid heat exchanger)
FIG. 1 is a partial cross-sectional schematic view showing the entire liquid-liquid heat exchanger according to the first embodiment of the present invention. FIG. 2 is a partial cross-sectional schematic view showing the inner tube of the liquid-liquid heat exchanger according to the first embodiment of the present invention. 3 is a cross-sectional view (AA line) of FIG. 2, where (a) shows the number of pleated hollow fins N = 3, and (b) shows the number of pleated hollow fins N = 2. Is the case.

  The liquid-liquid heat exchanger 10 includes an inner pipe 1 having a flow path A (first flow path) through which one of low-temperature water (heat exchange medium) and high-temperature water (heat exchange medium) passes, and an inner pipe 1 and an outer pipe having a flow path B (second flow path) through which the other of low-temperature water (heat exchange medium) and high-temperature water (heat exchange medium) passes between the inner pipe 1 and the inner pipe 1. 2 and configured. The outer tube 2 is a circular tube having a smooth inner surface, and an inlet 2A and an outlet 2B of water are provided at the ends of the outer tube 2, respectively. Here, low-temperature water (heat exchange medium) is water at a lower temperature than high-temperature water (heat exchange medium), and high-temperature water (heat exchange medium) is low-temperature water (heat exchange medium). It is water at a higher temperature than the medium.

  The inner tube 1 has a spiral pleated hollow fin 3 formed by buckling a wall surface by a torsional force. “To be formed by wall-buckling by torsional force” means, for example, fixing one end portion 1A of the inner tube 1, twisting the opposite end portion 1B, and wall-buckling the intermediate portion to spiral the portion 1C. Can be formed. In order to set the number of the pleated hollow fins 3 to a desired number, twisting is applied to the smooth circular pipe as a material while applying force to the same number of places as the desired number.

  The formed hollow of the pleated hollow fin 3 is integrated with the hollow inside the inner tube 1 and constitutes a part of the flow path A.

If the maximum outer diameter of the crest of the inner pipe 1 is OD _i-max , the minimum inner diameter of the valley of the inner pipe 1 is ID _i-min , and the number of spiral pleated hollow fins 3 is N, the pleated hollow The number N of the fins 3 is preferably N = 2 to 6, more preferably 3 to 4.

If the number N is 3 = 6, OD _i−max / ID _i−min is about 1 / cos (π / N) (specifically, [1 / cos (π / N)] × ( For example, the cross section is a polygonal shape as shown in FIG. 3A (triangular shape). If the number N of stripes is N = 2, OD _i-max / ID _i-min is about 2 (specifically, about 1.8 to 2.2), as shown in FIG. The cross section is elliptical. In order to increase the heat transfer area and improve the heat exchange efficiency, it is effective to increase the heat transfer area per channel area, that is, the wet edge length. In principle, the number of strips N can be 7 or more. However, in the case of polygons rather than heptagons, the rate of increase in heat transfer area per channel area compared to a circular pipe is less than 5%, and there is a significant difference. Less.

The cross-sectional area perpendicular to the flow path direction in the flow path A (first flow path) inside the inner pipe 1 is S, and the average inner diameter of the inner pipe 1 (the same cross-sectional area S as the flow path A of the inner pipe 1 is cut). ID _i-ave = (4S / π) ^0.5 , the inner tube 1 has a wall thickness TW _i , and the inner tube 1 has an average outer diameter (flow path of the inner tube 1). The outer diameter of the circular tube having the same cross-sectional area as the cross-sectional area S of A is equal to OD _i-ave = ID _i-ave +2 TWi, and the pitch of the pleated hollow fins 3 is p. The diameter ratio p / OD _i-ave is about 4 or less in terms of manufacturability, but it is desirable that 0.2 <p / OD _i-ave <1.5.

The fluid flowing inside the flow path A of the inner tube 1 flow path B between the (first flow path) volume flow V _i and the inner tube 1 of the fluid flowing through the outer tube 2 (second flow path) volume if the flow rate V _o is known in advance, an average inner diameter (equivalent inner diameter cross-sectional area (the flow path perpendicular) S, the inner tube 1 of the inner flow passage a of the inner tube 1 (the first flow path) of ) _Is ID _i-ave = (4S / π) ^0.5 , the thickness of the inner tube 1 is TW _i , and the average outer diameter (equivalent outer diameter) of the inner tube 1 is OD _i-ave = ID _i-ave + 2TW _i Then, the inner diameter ID _o of the outer tube 2 is ((V _o / 2V _i ) × ID _i−ave ² + OD _i−ave ² ) ^0.5 <ID _o <((2 V _o / V _i ) × ID _i it is desirable to satisfy the ^{_{-ave 2 + OD i-ave 2}} ) 0.5. Thereby, the flow velocity of both fluids can be made substantially the same. When the fluid is a single-phase flow such as a liquid, the heat transfer performance substantially depends on the flow velocity. Moreover, the performance of the heat exchanger can minimize the overall thermal resistance when the difference between the thermal resistances of both fluids (the inverse of the product of the heat transfer coefficient and the heat transfer area) is small. In this embodiment, since the heat transfer areas of both fluids are almost the same, the heat exchange efficiency is optimized by making the flow rates of both fluids substantially the same.

  On the other hand, since the inner tube has a predetermined spiral pleated hollow fin, the inner tube itself is extremely flexible. Furthermore, when bending the heat exchanger (double pipe), the spiral pleated hollow fin of the inner pipe plays the role of the core and can prevent plastic bending (bending) of the outer pipe, Flexible piping construction is possible.

[Second Embodiment of the Present Invention]
FIG. 4 is a schematic cross-sectional view showing a part of the liquid-liquid heat exchanger according to the second embodiment of the present invention. The liquid-liquid heat exchanger 20 according to the second embodiment is different from the liquid-liquid heat exchanger 10 according to the first embodiment in the shape of the outer tube. The outer tube 12 in the present embodiment has a corrugated shape, thereby further improving flexibility.

  For the outer tube 12 having a corrugated shape, for example, an outer tube having a spiral corrugated shape described in Patent Document 1 can be used as the corrugated shape.

[System of a water heater provided with the liquid-liquid heat exchanger of the present invention]
FIG. 5 is a system diagram of a heat pump type water heater provided with the liquid-liquid heat exchanger of the present invention. The high-temperature and high-pressure refrigerant gas compressed by the compressor 51 dissipates heat in the water-refrigerant heat exchanger 52 to produce high-temperature water. In particular, in the case of a heat pump type water heater using carbon dioxide as a refrigerant, high-temperature water at 90 ° C. can be obtained. Thereafter, the refrigerant becomes a low-pressure and low-temperature gas-liquid two-phase fluid at the expansion valve 53, absorbs heat (55 is a fan) by the refrigerant-air heat exchanger 54, completely evaporates into gas, and is sucked into the compressor 51. Repeat this cycle. On the other hand, the high temperature water stored in the hot water storage tank 56 is used for hot water supply 57, bathing (liquid-liquid heat exchanger 50), etc., as needed. That is, the liquid-liquid heat exchanger of the present invention is installed for exchanging heat by exchanging heat between hot water boiled by a heat pump type hot water heater and low-temperature water such as a bath. The high temperature water stored in the hot water storage tank 56 is sent to the water-refrigerant heat exchanger 52 by the pump 58 in order to maintain a high temperature, heated there, and returned to the hot water storage tank 56.

  A heat pump type hot water heater is energy saving compared to a hot water heater such as a gas fired heater. However, in the case of a hot water storage type, since a hot water storage tank becomes large, it is often impossible to install. Since the reheating heat exchanger is installed in the hot water storage tank unit, the high performance of the reheating heat exchanger leads to a compact hot water storage tank unit. The liquid-liquid heat exchanger of the present invention can contribute to high efficiency and compactness of the entire system by being mounted in such a system.

[Effect of the embodiment]
According to the above embodiment of the present invention, the following effects can be obtained.
(1) Since the inner tube has a predetermined spiral pleated hollow fin, the heat transfer area of both fluids flowing through the inner channel of the inner tube and the channel between the inner tube and the outer tube is increased. At the same time, the heat exchange efficiency can be increased by the turbulent effect of both fluids.
(2) Since the heat exchange efficiency can be increased and the performance can be improved, the liquid-liquid heat exchanger can be made compact.
(3) Since the inner tube has a predetermined spiral pleated hollow fin, it is possible to prevent plastic bending (bending) of the outer tube when bending the heat exchanger, and flexible piping construction Is possible. (The degree of freedom of arrangement in the water heater increases.)
(4) By using an outer tube having a corrugated shape, both the inner tube and the outer tube are excellent in flexibility, so that more flexible piping construction is possible.

  EXAMPLES Hereinafter, although this invention is demonstrated in more detail based on an Example, this invention is not limited to these.

  FIG. 6 is a diagram showing the relationship between the number of polygonal corners of the inner tube (the number of hollow fins) and the ratio of the heat transfer area to the flow path cross-sectional area. For the ratio of the heat transfer area, the ratio of the heat transfer area to the polygonal channel cross-sectional area is shown as a ratio to the case where the inner pipe is a circular pipe. That is, the rate of increase in the ratio of the heat transfer area to the same cross-sectional area of the inner pipe channel was confirmed as compared with the case where the inner pipe was a smooth circular pipe (1.00). In addition, when the number N of the pleated hollow fins was N = 2, the cross section of the inner tube was determined to be an elliptical tube (see FIG. 3B).

  From FIG. 6, the inner pipe of the liquid-liquid heat exchanger of the present invention has the largest heat transfer area when the number of pleated hollow fins is three. It can be seen that in the case of N = 2 to 6, the ratio to the case of a circular pipe is 1.05 or more. Furthermore, it can be seen that when N = 3 to 4, the ratio of the circular pipe is 1.10 or more.

  In addition, the smaller the number of pleated hollow fins, the larger the lead angle by the spiral of the pleated hollow fins, and the greater the turbulence effect.

  Moreover, since 3 or more becomes easy on manufacture (it forms by buckling a wall surface with a torsion force), the case of 3 is practically optimal.

FIG. 7 is a result of comparative evaluation of the heat transfer performance of the heat exchanger of the present invention with respect to the heat transfer performance of a heat exchanger composed of a smooth tube of the prior art. In the heat exchanger of the present invention, the number of spiral pleated hollow fins in the inner tube is 3, and the ratio of the pitch p of the spiral fins to the average outer diameter OD _i-ave of the inner tube (p / OD _i-ave ). As a parameter, the heat transfer performance was measured. The double tube heat exchanger used as a comparison was a smooth circular tube having an inner tube outer diameter equal to the average outer diameter OD _i-ave . All the outer tubes were smooth circular tubes with the same specifications. In the heat exchanger of the present invention, when the maximum outer diameter of the crest of the inner tube is OD _i-max , the minimum inner diameter of the trough is ID _i-min , and the number of spiral pleated hollow fins is three , OD _i-max / ID _i-min is about 2. Further, the average outer diameter of the inner tube is OD _i-ave , the average inner diameter of the inner tube is ID _i-ave , the volume flow rate of the fluid flowing in the flow path inside the inner tube is V _i , and between the inner tube and the outer tube If the volume flow rate of the fluid flowing through the flow path is V _o , the inner diameter ID _o of the outer tube is ((V _o / 2V _i ) × ID _i-ave ² + OD _i-ave ² ) ^0.5 <ID _o < ((2V _o / V _i ) × ID _i-ave ² + OD _i-ave ² ) ^0.5 was satisfied.

The inner tube of the heat exchanger of the present invention has a p / OD _i-ave of about 4 or less due to its manufacturability, but the performance ratio with the smooth double tube is 2.1 or more, When the ratio is 2 to 1.5, the performance ratio is 2.2 or more, which is desirable.

  On the other hand, according to Non-Patent Document 1, the heat transfer performance of the conventional multi-leaf fin-shaped heat exchanger is about twice that of the smooth tube. Therefore, from FIG. It can be seen that higher performance can be achieved than the multi-leaf fin heat exchanger.

FIG. 8 shows the result of comparative evaluation of the heat transfer performance of the heat exchanger of the present invention and the heat exchanger to be compared. The heat exchanger according to the present invention (Example 3) has spiral pleat-shaped hollow fins formed by wall-buckling by a torsional force, and the number N of the pleat-shaped hollow fins is 3, and the inner tube The ratio OD _i-max / ID _i-min of the maximum outer diameter OD _i-max of the peak portion and the minimum inner diameter ID _i-min of the valley portion of the inner pipe is 2, and the pitch p of the spiral fin of the inner pipe is An inner tube having an average outer diameter OD _i-ave ratio (p / OD _i-ave ) of 0.5, and an inner diameter ID _o of ID _o = (ID _i-ave ² + OD _i-ave ² ) ^0.5 A heat exchanger composed of an outer tube was used. On the other hand, the compared heat exchangers are the outer tube having the same inner diameter ID _o as the heat exchanger of the present invention (Example 3), and the inner tube is a multi-leaf (six-row) tube described in Non-Patent Document 1. A heat exchanger (Comparative Example 1), a heat exchanger (Comparative Example 2) in which the inner tube has the same shape (spiral corrugated tube) as the outer tube described in FIG. It is a heat exchanger (comparative example 3) comprised with the pipe | tube. The amount of heat exchange was measured when the flow rate flowing through the flow path between the inner tube and the outer tube and the inlet temperature difference between the inner tube and the outer tube were fixed and the flow rate of the liquid flowing through the inner tube was changed.

  When the flow rate of the liquid flowing through the inner pipe is 8 l / min (liter / min), the heat exchanger of the present invention (Example 3) is compared with the heat exchanger of Comparative Example 1 that has been conventionally evaluated to be relatively high performance. It can be seen that the difference in the heat exchange amount of) is higher by 20% or more. In addition, it can be seen from the comparison with Comparative Example 2 that a clear difference appears depending on the wavy shape. It can also be seen that the performance is significantly higher than that of Comparative Example 3.

1 is a partial cross-sectional schematic view showing the entire liquid-liquid heat exchanger according to a first embodiment of the present invention. It is a partial cross section schematic diagram which shows the inner tube | pipe of the liquid-liquid heat exchanger which concerns on the 1st Embodiment of this invention. It is sectional drawing (AA line) of FIG. 2, (a) is the case where the number N of pleated hollow fins is N = 3, (b) is the case where the number N of pleated hollow fins is N = 2. is there. It is a cross-sectional schematic diagram which shows a part of liquid-liquid heat exchanger which concerns on the 2nd Embodiment of this invention. It is a system diagram of a heat pump type hot water heater provided with the liquid-liquid heat exchanger of the present invention. It is a figure which shows the relationship between the polygonal angle | corner number (the number of hollow fins) of an inner tube, and the ratio of the heat-transfer area with respect to flow-path cross-sectional area. It is the result of comparing and evaluating the heat transfer performance of the heat exchanger of this invention with respect to the heat transfer performance of the heat exchanger comprised with the smooth tube of a prior art. It is the result of comparing and evaluating the heat transfer performance of the heat exchanger of the present invention and the heat exchanger to be compared. It is a general-view figure of the whole conventional liquid-liquid heat exchanger. It is sectional drawing (BB line) of FIG. 9, (a) is a case where an inner tube is a smooth circular tube, (b) is a case where an inner tube is a multileaf tube.

Explanation of symbols

10, 20: Liquid-liquid heat exchanger 1: Inner pipe 1A, 1B: Terminal part 1C: Spiral part 2, 12: Outer pipe 2A: Inlet 2B: Outlet 3: Hollow fin 50: Reheating heat exchanger 51 : Compressor 52: water-refrigerant heat exchanger 53: expansion valve 54: refrigerant-air heat exchanger 55: fan for refrigerant-air heat exchanger 56: hot water storage tank 57: hot water supply 58: pump 59: water supply 70: liquid-liquid Heat exchanger 71: Inner pipe 72: Outer pipe

Claims (4)

An inner pipe having a first flow path for passing one of water to be a heat exchange medium and water to be a heat exchange medium having a temperature higher than that of the water to be the heat exchange medium, and disposed outside the inner pipe, An outer pipe having a second flow path through which the water to be the heat exchange medium and the other water to be the heat exchange medium pass, between the inner pipe and the inner pipe;
The inner tube, the twisting force by have a spiral pleat-shaped hollow fins formed by buckled wall seat,
The outer tube is a circular tube with a smooth inner surface, the cross-sectional area perpendicular to the flow direction in the first flow path is S, the average inner diameter of the inner pipe is ID _i-ave = (4S / π) ^0.5 , The wall thickness of the inner pipe is TW _i , the average outer diameter of the inner pipe is OD _i-ave = ID _i-ave + 2TW _i , the volume flow rate of the fluid flowing through the first flow path is V _i , and the second When the volume flow rate of the fluid flowing through the flow path is V _o , the inner diameter ID _{o of the} outer tube is ((V _o / 2V _i ) × ID _i-ave ² + OD _i-ave ² ) ^0.5 <ID _o <(( 2V _o / V _i ) × ID _i-ave ² + OD _i-ave ² ) A liquid-liquid heat exchanger for hot water heaters satisfying ^0.5 . When the maximum outer diameter of the crest of the inner pipe is OD _i-max , the minimum inner diameter of the valley of the inner pipe is ID _i-min , and the number of strips of the pleated hollow fin is N, the pleated hollow fin The number N of stripes is N = 2 to 6, OD _i-max / ID _i-min when N = 2 is 1.8 to 2.2, and OD _i-max / N when N = 3 to 6 ID _i-min is [1 / cos (π / N)] × (0.9 to 1.1), The liquid-liquid heat exchanger for a hot water heater according to claim 1. The cross-sectional area perpendicular to the flow path direction in the first flow path is S, the average inner diameter of the inner pipe is ID _i-ave = (4S / π) ^0.5 , the wall thickness of the inner pipe is TW _i , and the inner pipe OD _i-ave = ID _i-ave + 2TW _i , and p is the pitch of the pleated hollow fins, the ratio p / OD _i-ave between the pitch and the average outer diameter is 0.2 < The liquid-liquid heat exchanger for a hot water heater according to claim 1, wherein p / OD _i-ave <1.5 is satisfied.   The liquid-liquid heat exchanger for a hot water heater according to claim 1, wherein the outer tube has a corrugated shape on a wall surface.