JP2020197311A - Heat exchanger and refrigeration cycle device provided with the same - Google Patents

Abstract

To provide a heat exchanger suppressing deposition of a local scale with a simple means and also having high heat exchange efficiency.SOLUTION: A heat exchanger includes an inner pipe 1, an insertion body 2 inserted into the inner pipe 1, and at least one outer pipe 3 which is fitted on the outer periphery of the inner pipe 1 and through which a second fluid is flown. The insertion body 2 is composed of an axis part 21 and a projection part 22 formed on the outer surface of the axis part 21. A first fluid flows through a spiral flow passage 23 composed of at least the inner surface of the inner pipe 1 and the projection part 22. The spiral flow passage 23 is provided with a thick projection part 22b reducing the area of the flow passage at every prescribed interval in the flow direction of the first fluid.SELECTED DRAWING: Figure 3

Description

The present invention relates to a heat exchanger in which a low temperature fluid and a high temperature fluid exchange heat.

Conventionally, in this type of heat exchanger, water is often heated by a refrigerant to generate high-temperature water. It is known that when water becomes hot, the solubility of gas (oxygen, nitrogen, etc.) dissolved in water decreases, and it precipitates in water as bubbles.

When the precipitated bubbles adhere to the heat transfer surface, the heat exchange between the water and the refrigerant is hindered, so that the heat exchange efficiency of the heat exchanger is lowered.

Further, when bubbles adhere to the heat transfer surface, a microlayer in which ion concentration occurs is formed at the interface between the bubbles and the heat transfer surface, which serves as a starting point of scale as compared with the surface to which no bubbles adhere. Many scale nuclei are locally precipitated.

The scale thus precipitated can be removed by applying shear stress.

Therefore, in order to suppress the growth of the scale, a liquid to be heated on the secondary side to which a preset pressure is applied is made to flow into the heat exchanger at a preset timing, so that the secondary side cover in the heat exchanger is covered. Shear stress that can remove the scale deposited on the contact surface with the heating liquid is applied (see, for example, Patent Document 1).

International Publication No. 2017/158938

However, the conventional configuration requires parts such as a pressure sensor and a solenoid valve, which has a problem that the flow path configuration becomes complicated and the cost increases.

The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide a heat exchanger having high heat exchange efficiency while suppressing local scale precipitation by simple means.

In order to solve the above-mentioned conventional problems, the heat exchanger of the present invention is provided on an inner pipe, an insert body inserted into the inner pipe, and at least one provided on the outer periphery of the inner pipe through which a second fluid flows. With the above outer tube, the insert is formed of a shaft portion and a protrusion formed on the outer surface of the shaft portion, and the first fluid is at least the inner surface of the inner pipe and the protrusion. In addition to flowing through the spiral flow path formed by the above, the spiral flow path is characterized in that a thick protrusion portion for reducing the flow path area is provided at predetermined intervals in the flow direction of the first fluid. Is to be.

As a result, the flow velocity of the first fluid and the shear stress of the first fluid can be increased at predetermined intervals in the spiral flow path, so that the bubbles deposited and adhering to the wall surface of the spiral flow path can be easily washed away.

In addition, since centrifugal force acts on the first fluid flowing through the spiral flow path, bubbles having a density lower than that of the first fluid are swept relatively toward the shaft portion, so that the inner surface of the inner pipe ( Reattachment to the heat transfer surface) can be suppressed.

Therefore, local scale precipitation due to bubble adhesion to the inner surface (heat transfer surface) of the inner tube can be suppressed, heat exchange can be prevented from being hindered by the scale, and in the spiral flow path, the first step is made at predetermined intervals. Since the flow velocity of one fluid can be increased and the stirring effect due to centrifugal force can be improved, the flow of the first fluid can be turbulent and the heat exchange efficiency of the heat exchanger can be improved.

According to the present invention, it is possible to provide a heat exchanger having high heat exchange efficiency while suppressing local scale precipitation by simple means.

Circuit diagram of a refrigeration cycle apparatus using a heat exchanger according to the first embodiment of the present invention. Perspective view of the heat exchanger according to the first embodiment of the present invention. (A) A-plane sectional view of the heat exchanger according to the first embodiment of the present invention (b) B-plane sectional view of the heat exchanger (A) Conceptual diagram of the flow velocity distribution of the first fluid in the A-plane sectional view of the heat exchanger according to the first embodiment of the present invention (b) The flow velocity distribution of the first fluid in the B-plane sectional view of the heat exchanger. Conceptual diagram of (A) Conceptual diagram of bubbles attached to the inner surface of the inner tube of the first embodiment of the present invention, which is a grooved tube (b) Conceptual diagram of bubbles attached to the inner surface of the inner tube of a smooth tube.

The first invention includes an inner tube, an insert body inserted into the inner tube, and at least one outer tube provided on the outer periphery of the inner tube and through which a second fluid flows, and the insert body. Is formed from a shaft portion and a protrusion formed on the outer surface of the shaft portion, and the first fluid flows through at least a spiral flow path formed by the inner surface of the inner pipe and the protrusion. The spiral flow path is a heat exchanger characterized in that a thick protrusion for reducing the flow path area is provided at predetermined intervals in the flow direction of the first fluid.

As a result, in the spiral flow path, the flow velocity of the first fluid and the shear stress of the first fluid can be increased at predetermined intervals, so that the bubbles deposited and adhering to the wall surface of the spiral flow path can be easily washed away. ..

In addition, since centrifugal force acts on the first fluid flowing through the spiral flow path, bubbles having a density lower than that of the first fluid are swept relatively toward the shaft portion, so that the inner surface of the inner pipe ( Reattachment to the heat transfer surface) can be suppressed.

Therefore, local scale precipitation due to bubble adhesion to the inner surface (heat transfer surface) of the inner tube can be suppressed, heat exchange can be prevented from being hindered by the scale, and in the spiral flow path, the first step is made at predetermined intervals. Since the flow velocity of one fluid can be increased and the stirring effect due to centrifugal force can be improved, the flow of the first fluid can be turbulent and the heat exchange efficiency of the heat exchanger can be improved.

The second invention, in particular, in the first invention, is formed by making the thickness of the protrusion in the axial direction thicker than that of other portions at predetermined intervals in the circumferential direction. It is characterized by being.

As a result, the flow velocity of the first fluid and the shear stress of the first fluid can be increased at predetermined intervals in the spiral flow path by a simple means, so that they are deposited and adhered to the wall surface of the spiral flow path. It is possible to easily flush out air bubbles.

A third invention, particularly in the first or second invention, is that the line connecting the central portions of the plurality of thick protrusions in the circumferential direction is parallel to the axial center line of the insert. It is characterized by being.

As a result, the thick protrusions provided in the spiral flow path face each other in the axial direction, so that the flow path area can be particularly reduced in the spiral flow path.

As a result, in the spiral flow path, the flow velocity of the first fluid and the shear stress of the first fluid can be increased at predetermined intervals, so that the bubbles deposited and adhering to the wall surface of the spiral flow path can be easily washed away. ..

The fourth invention, in particular, in any one of the first to third inventions, is characterized in that the thick protrusion portion is thicker in the axial direction at the root portion than at the tip portion in the height direction. Is to be.

As a result, the flow velocity of the first fluid can be increased at predetermined intervals without reducing the heat transfer area on the first fluid side, that is, the heat transfer area between the inner pipe and the first fluid, and thus the performance of the heat exchanger. Can suppress local scale growth while maintaining.

The fifth invention is characterized in that, in particular, in any one of the first to fourth inventions, the thick protrusion has the thickest axial thickness at the center of the circumferential length of the root portion. Is to be.

As a result, in the spiral flow path, the flow velocity of the first fluid and the shear stress of the first fluid can be increased at predetermined intervals, so that the bubbles deposited and adhering to the wall surface of the spiral flow path can be easily washed away. ..

At the same time, by suppressing a sudden change in the flow velocity of the first fluid as much as possible, it is possible to suppress an increase in the flow noise as much as possible.

The sixth invention is characterized in that, in any one of the first to fifth inventions, the inner pipe is an inner grooved pipe.

As a result, since the inner tube is a tube with an inner surface groove, the contact area between the inner tube wall and the bubbles that precipitate and adhere is reduced as compared with the case of the smooth tube, and the bubbles attached to the inner surface of the inner tube. Is easier to separate from the tube wall, so that air bubbles adhering to the tube wall of the inner tube can be more easily washed away, and local scale growth can be suppressed.

In addition, since the inner surface area of the inner tube is larger than that of the smooth tube, the heat transfer area on the first fluid side, that is, the heat transfer area between the inner surface of the inner tube and the first fluid is increased and spirally formed. Since the flow of water, which is the first fluid to flow, can be further turbulent by the inner groove, the performance of the heat exchanger can be further improved.

A seventh invention is a refrigeration cycle device formed by connecting a compressor, a heat exchanger of any one of the first to sixth aspects, a decompression device, and an evaporator in a ring shape.

This makes it possible to provide a refrigeration cycle apparatus equipped with a heat exchanger that can suppress local scale precipitation by simple means and realize high heat exchange efficiency.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The present invention is not limited to this embodiment.

(Embodiment 1)
FIG. 1 is a circuit diagram of a refrigeration cycle device using a heat exchanger according to the first embodiment of the present invention.

A compressor 31 that compresses the refrigerant that is the second fluid, a heat exchanger 32 that heats the water that is the low-temperature first fluid by radiating heat from the refrigerant that is the high-temperature second fluid compressed by the compressor 31, and the compressor. The refrigeration cycle device 36 is formed by cyclically connecting a decompression device 33 that decompresses the refrigerant, which is a high-pressure second fluid compressed in 31, to a low pressure, and an evaporator 34 that absorbs heat from the air flow generated by the blower 35. There is.

Then, in the heat exchanger 32, water as the first fluid and the refrigerant as the second fluid flow in opposite directions to exchange heat. In the heat exchanger 32, low-temperature water, which is the first fluid, is conveyed to the heat exchanger 32 by the transport device 37, heated by the refrigerant, which is the second fluid, to become hot water, and is supplied, heated, or stored. The hot water circuit 38 is connected.

FIG. 2 is a perspective view of the heat exchanger according to the first embodiment of the present invention.

In FIG. 2, the heat exchanger has an inner pipe 1 through which water, which is the first fluid, flows, an inserter 2 inserted inside the inner pipe 1, and a refrigerant (carbon dioxide refrigerant) which is the second fluid inside. ) Flows through and is composed of at least one outer tube 3 that is in close contact with the outer periphery of the inner tube 1.

The outer tube 3 is spirally wound around the outer circumference of the inner tube 1 at a predetermined pitch.

The insert body 2 includes a cylindrical shaft portion 21 and a protrusion 22 spirally provided on the outer circumference of the shaft portion 21. Water, which is the first fluid, flows through a spiral flow path 23 having a substantially rectangular cross section formed by an inner surface of the inner pipe 1, an outer surface of the shaft portion 21, and an adjacent protrusion 22.

FIG. 3A is a cross-sectional view taken along the A side of the heat exchanger according to the first embodiment. The protrusion 22 of the insert body in the A-plane cross section is a standard protrusion 22a formed with a standard wall thickness.

FIG. 3B is a cross-sectional view of the B-plane of the heat exchanger according to the first embodiment. The protrusion 22 of the insert body 2 in the B-plane cross section is a thick protrusion 22b that is thicker in the axial direction than the standard protrusion 22a.

The wall-thick protrusions 22b are formed to be thicker in the axial direction than the standard protrusions 22a at predetermined intervals in the circumferential direction, and are the centers of the lengths of the plurality of thick-walled protrusions 22b in the circumferential direction. The line connecting the portions is parallel to the axial center line of the cylindrical shaft portion 21 of the insert body 2.

For this reason, the thick protrusions 22b provided in the spiral flow path 23 face each other in the axial direction, so that the spiral flow path 23 has a predetermined interval in the flow direction of water, which is the first fluid. Each time, the flow path area is reduced.

The thickness of the wall thickness protrusion 22b gradually increases in the axial direction from the tip to the root in the height direction, and the central portion of the circumferential length of the root is in the axial direction. It is the thickest shape.

In the first embodiment of the present invention, the predetermined interval in which the thick protrusions 22b are formed in the circumferential direction is 180 ° about the axial center of the cylindrical shaft portion 21 of the insert body 2. ..

That is, water, which is the first fluid flowing through the spiral flow path 23, is supposed to collide with the thick protrusion 22b every half circumference.

This is because when the insert body 2 is formed of a resin material, the wall-thick protrusion 22b has a shape in which the central portion having a circumferential length at the root portion has the thickest axial thickness. This is because the insert body 2 can be manufactured by using the two lines connecting the central portions of the root portion of the wall-thick protrusion 22b in the circumferential direction as the dividing surface (PL) of the mold.

Here, the property that the liquid adheres to the solid surface is called "wetting property", and the length of the inner surface of the inner pipe 1 forming the flow path cross section of the spiral flow path 23 through which water, which is the first fluid flows, is defined. It is defined as the wet length of the heat transfer surface.

At this time, the wet length Lb of the heat transfer surface of the thick protrusion 22b is secured to be about the same as the wet length La of the heat transfer surface of the standard protrusion 22a, and the inner tube 1 is finely grooved on the inner surface. It is a tube with an inner groove.

The operation and operation of the heat exchanger 32 configured as described above will be described below when the heat exchanger 32 is mounted on a CO ₂ heat pump water heater.

The heat exchanger is a high-temperature carbon dioxide that flows inside the outer tube 3 as a second fluid, and a first fluid that flows through a spiral flow path 23 formed between the inner tube 1 and the insert 2. Heat is exchanged by flowing low-temperature water in opposition to generate high-temperature hot water.

Since centrifugal force acts on the first fluid flowing through the spiral flow path 23, a secondary flow is generated on the surface perpendicular to the flow direction as in the case of the curved pipe.

As a result, the flow of water, which is the first fluid, is more turbulent, and the temperature distribution of water, which is the first fluid on the surface perpendicular to the flow direction, is improved. Therefore, water is used like a CO ₂ heat pump water exchanger. Even when the flow velocity is slow, the heat exchange efficiency of the heat exchanger 32 can be improved.

As described above, the CO ₂ heat pump type water heater that uses carbon dioxide as the refrigerant as the second fluid can raise the heating temperature of water.

On the other hand, on the outlet side of the heat exchanger 32 where the temperature of water, which is the first fluid, becomes high, the solubility of the dissolved gas (oxygen, nitrogen, etc.) decreases, so that the wall surface of the spiral flow path 23 becomes bubbles. There is a concern that it will precipitate in the water and locally inhibit scale precipitation and heat exchange.

In the first embodiment of the present invention, as shown in FIGS. 3A and 3B, the protrusions 22 of the insert body 2 have thick protrusions 22b that are thick in the axial direction at predetermined intervals. Have.

Therefore, in FIG. 3A, the spiral flow path 23 through which water, which is the first fluid, flows is formed by the inner surface of the inner pipe 1, the outer surface of the shaft portion 21, and the outer surface of the standard protrusion 22a. ing.

Further, in FIG. 3B, the inner surface of the inner pipe 1 and the outer surface of the thick protrusion 22b are formed.

In this way, since the thickness of the protrusion 22 in the axial direction is thicker in the thick protrusion 22b than in the standard protrusion 22a, the cross-sectional area of the flow path through which water, which is the first fluid, also passes through the thick protrusion 22b. It is smaller when you do.

Therefore, the spiral flow path 23 is provided with thick protrusions 22b at predetermined intervals in the water flow direction, which is the first fluid, and is not on the inner surface side of the inner pipe 1 but on the outer surface side of the shaft portion 21. By narrowing the flow path width of, the flow path cross-sectional area is reduced.

That is, as shown in FIG. 3A, the spiral flow path 23 through which water, which is the first fluid, flows is formed by the inner surface of the inner pipe 1, the outer surface of the shaft portion 21, and the outer surface of the standard protrusion 22a. That is, the cross-sectional area of the flow path formed in the A cross section is S1.

On the other hand, as shown in FIG. 3B, the spiral flow path 23 through which water, which is the first fluid, flows is formed by the inner surface of the inner pipe 1 and the outer surface of the thick protrusion 22b, that is, that is, Let S2 be the cross-sectional area of the flow path formed in the B cross section.

At this time, the relationship between the flow path cross-sectional area S1 and the flow path cross-sectional area S2 is S1> S2.

Further, the wall thickness protrusion 22b is gradually thickened in the axial direction from the tip portion to the root portion in the height direction, and further, the central portion of the circumferential length of the root portion is in the axial direction. It is the thickest shape.

On the other hand, the wet length Lb of the heat transfer surface of the thick protrusion 22b is secured to the same extent as the heat transfer surface wet length La of the standard protrusion 22a.

As a result, the cross-sectional area of the flow path can be changed without changing the length of the inner surface of the inner pipe 1 forming the cross-section of the spiral flow path 23 through which water, which is the first fluid, flows.

Therefore, when the heat transfer area between the water as the first fluid and the inner surface of the inner pipe 1 is the same and the spiral flow path 23 is formed by the thick protrusion 22b, the spiral flow path 23 is formed. By making the flow path cross-sectional area smaller than when it is formed by the standard protrusion 22a, the flow velocity of water, which is the first fluid, can be increased.

FIG. 4A is a conceptual diagram of the flow velocity distribution of the first fluid in the A-plane cross-sectional view of the heat exchanger according to the first embodiment of the present invention. The protrusion 22 of the insert body in the A-plane cross section is a standard protrusion 22a formed with a standard wall thickness.

FIG. 4B is a conceptual diagram of the flow velocity distribution of the first fluid in the B-plane cross-sectional view of the heat exchanger according to the first embodiment of the present invention. The protrusion 22 of the insert body 2 in the B-plane cross section is a thick protrusion 22b that is thicker in the axial direction than the standard protrusion 22a.

As shown in FIGS. 4A and 4B, the flow velocity of water as the first fluid is higher than that of the flow velocity Ub when the spiral flow path 23 is formed by the thick protrusion 22b. Since the flow velocity Ua when the spiral flow path 23 is formed by the standard protrusion 22a is larger than the flow velocity Ua, the velocity gradient near the wall surface of the spiral flow path 23 is formed by the spiral flow path 23 formed by the thick protrusion 22b. If it is, it will be larger.

数１において、τは粘性流体のせん断応力、μは粘性係数、ｄｕ／ｄｚは流れと垂直な方向の速度勾配を示す。

In Equation 1, τ is the shear stress of the viscous fluid, μ is the viscosity coefficient, and du / dz is the velocity gradient in the direction perpendicular to the flow.

Here, as shown in Equation 1, the shear stress τ of the viscous fluid is proportional to the velocity gradient in the direction perpendicular to the flow.

Therefore, the velocity gradient near the wall surface of the spiral flow path 23 is larger when the spiral flow path 23 is formed by the thick protrusion 22b, so that the first fluid flowing through the spiral flow path 23 The shear stress of the water is also larger when the spiral flow path 23 is formed by the thick protrusion 22b than when the spiral flow path 23 is formed by the standard protrusion 22a. I understand.

Therefore, when the spiral flow path 23 is formed by the thick protrusion 22b, even if bubbles are deposited and adhered to the wall surface of the spiral flow path 23, a larger shear stress acts on the bubbles. Bubbles can be flushed from the wall.

As a result, local growth of the scale starting from the bubbles can be suppressed, and heat transfer inhibition by the bubbles can also be prevented.

Further, since centrifugal force acts on the first fluid flowing through the spiral flow path 23, bubbles having a density lower than that of water, which is the first fluid washed away from the wall surface of the spiral flow path 23, are relatively axial. Since it is swept toward the portion 21, reattachment of air bubbles to the inner surface (heat transfer surface) of the inner tube 1 can be suppressed.

That is, in the heat exchanger of the first embodiment of the present invention, as shown in FIGS. 3 (a) and 3 (b), the wall thickness is formed to be thicker in the axial direction than the standard protrusion 22a. The predetermined interval in which the protrusions 22b are formed in the circumferential direction is 180 ° about the axial center of the cylindrical shaft portion 21 of the insert body 2.

The line connecting the central portions of the plurality of thick protrusions 22b in the circumferential direction is parallel to the axial center line of the cylindrical shaft portion 21 of the insert body 2.

For this reason, the thick protrusions 22b provided in the spiral flow path 23 face each other in the axial direction, so that the spiral flow path 23 has a configuration in which the flow path area is reduced every half circumference. ing.

As a result, the flow velocity of water, which is the first fluid flowing through the spiral flow path 23, increases at least every half circumference, and the shear stress also increases.

Therefore, the bubbles can be swept away more reliably, and the reattachment of the bubbles to the inner surface (heat transfer surface) of the inner tube 1 can be prevented, so that local scale growth and inhibition of heat exchange can be ensured. Can be suppressed.

FIG. 5A is a conceptual diagram of bubbles adhering to the inner surface of the grooved pipe in the first embodiment of the present invention.

Further, FIG. 5B is a conceptual diagram of bubbles adhering to the inner surface of which the inner tube is a smooth tube for comparison with FIG. 5A.

In the first embodiment of the present invention, the inner tube 1 is an inner grooved tube having a fine grooved inner surface.

As shown in FIGS. 5A and 5B, when the inner tube 1 is a tube with an inner groove, the contact area between the air bubbles adhering to the heat transfer surface and the heat transfer surface is smooth on the inner tube 1. In the case of a tube, it is smaller than the contact area between the air bubbles adhering to the heat transfer surface and the heat transfer surface.

As a result, since the inner pipe 1 is a pipe with an inner surface groove, the contact area between the pipe wall of the inner pipe 1 and the bubbles that precipitate and adhere is reduced as compared with the case of the smooth pipe, and the inner surface of the inner pipe 1 is covered. Since the attached bubbles are more easily separated from the tube wall, the bubbles adhering to the tube wall of the inner tube 1 can be more easily washed away, and the local scale growth can be suppressed.

In addition, since the inner surface area of the inner tube 1 is larger than that of the smooth tube, the heat transfer area on the first fluid side, that is, the heat transfer area between the inner surface of the inner tube 1 and the first fluid is increased, and the spiral Since the flow of water, which is the first fluid flowing in a shape, can be further turbulent by the inner groove, the performance of the heat exchanger can be further improved.

In the present embodiment, carbon dioxide is used as the refrigerant flowing inside the outer pipe 3 as the second fluid, but hydrocarbon-based or HFC-based (R410A, R32, etc.) refrigerants, or these. It may be an alternative refrigerant of.

Further, in the present embodiment, the wall-thick protrusions 22b are formed at a predetermined interval in the circumferential direction at 180 ° around the axial center of the cylindrical shaft portion 21 of the insert body 2. The same effect can be obtained with the numerical value of.

As described above, the heat exchanger according to the present invention can be applied to air-conditioning equipment, hot water supply equipment, and the like because it can suppress local scale precipitation by simple means and realize high heat exchange efficiency.

1 Inner pipe 2 Insert 3 Outer pipe 21 Shaft 22 Protrusion 22a Standard protrusion 22b Thick protrusion 23 Spiral flow path 31 Compressor 32 Heat exchanger (radiator)
33 Decompression device 34 Evaporator 36 Refrigeration cycle device

Claims (7)

Inner tube and
The insert inserted into the inner tube and
At least one outer pipe provided on the outer circumference of the inner pipe and through which the second fluid flows, and
With
The insert body is formed of a shaft portion and a protrusion formed on the outer surface of the shaft portion.
The first fluid flows through a spiral flow path formed by at least the inner surface of the inner pipe and the protrusion, and also flows.
A heat exchanger characterized in that the spiral flow path is provided with thick protrusions for reducing the flow path area at predetermined intervals in the flow direction of the first fluid. The heat according to claim 1, wherein the wall-thick protrusions are formed by making the thickness of the protrusions in the axial direction thicker than other parts at predetermined intervals in the circumferential direction. Exchanger. The heat exchanger according to claim 1 or 2, wherein the line connecting the central portions of the circumferential lengths of the plurality of thick protrusions is parallel to the axial center line of the insert. .. The heat exchanger according to any one of claims 1 to 3, wherein the thick protrusion portion is thicker at the root portion than at the tip portion in the height direction. The heat exchanger according to any one of claims 1 to 4, wherein the thick protrusion has the thickest axial thickness at the center of the root portion in the circumferential direction. The heat exchanger according to any one of claims 1 to 5, wherein the inner tube is an inner grooved tube. A refrigeration cycle device formed by connecting a compressor, a heat exchanger according to any one of claims 1 to 6, a decompression device, and an evaporator in a ring shape.

Images