JP2013088045A - Heat exchanger and heat pump type water heater using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat exchanger with high heat exchange performance while suppressing radiation loss on a high temperature side, and a heat pump type water heater using the same.SOLUTION: In the heat exchanger including a fluid passage passing a heating target fluid and a refrigerant passage passing a refrigerant providing heat to the fluid, the fluid and the refrigerant pass in opposite directions. When a maximum inner diameter in a cross section of the refrigerant passage is Dr, a circumference with respect to the maximum inner diameter Dr is πDr, an inner circumference is Lr, and a ratio of the inner circumference Lr and the circumference πDr is Lr/(πDr), an average value of the ratio Lr/(πDr) on a low temperature side is larger than an average value of the ratio Lr/(πDr) on a high temperature side.

Description

  The present invention relates to a heat exchanger and a heat pump type water heater using the heat exchanger.

  2. Description of the Related Art Conventionally, a hot water supply heat exchanger that heats water using a refrigerant has been proposed in which a grooved tube or the like is applied to the refrigerant side in order to improve the performance and compactness of the heat exchanger (Patent Document 1). reference). In addition, in a heat pump hot water supply apparatus in which a heat exchanger for hot water supply, an expansion valve, an evaporator, and a compressor are sequentially connected by a refrigerant pipe and the refrigerant operates at a critical pressure or higher, the efficiency with respect to the channel length is improved. For this purpose, there has been proposed one in which the pressure loss is reduced by making the flow path cross-sectional area on the high temperature side of the heat exchanger larger than that on the low temperature side (see Patent Document 2).

JP 2008-215766 A JP 2009-168383 A

  When the prior art of Patent Document 1 is applied to a heat pump type hot water heater in which the refrigerant operates at a critical pressure or higher, the heat transfer performance may not be sufficiently improved due to the increased pressure loss due to the grooved tube.

  Moreover, in the prior art of patent document 2, the pressure loss on the high temperature side can be suppressed by making the flow path cross-sectional area on the high temperature side larger than that on the low temperature side. However, the outer surface area increases as the flow path cross-sectional area on the high temperature side increases. For this reason, in the prior art of Patent Document 2, the heat dissipation loss is larger than the effect of improving the heat exchange efficiency by suppressing the pressure loss on the high temperature side, and the heating performance as the whole heat exchanger is reduced. Resulting in.

  Therefore, an object of the present invention is to provide a heat exchanger with high heat exchange performance and a heat pump type water heater using the heat exchanger while suppressing heat dissipation loss on the high temperature side.

  The present invention relates to a heat exchanger in which a fluid flow path through which a fluid to be heated flows and a refrigerant flow path through which a refrigerant that provides heat to the fluid flows, the fluid and the refrigerant face each other. When the maximum inner diameter in the cross section of the refrigerant flow path is Dr, the circumference with respect to the maximum inner diameter Dr is πDr, the inner circumference is Lr, and the ratio between the inner circumference Lr and the circumference πDr is Lr / (πDr) The average value of the ratio Lr / (πDr) on the low temperature side is larger than the average value of the ratio Lr / (πDr) on the high temperature side.

  The maximum inner diameter in the cross section of the fluid flow path is Dw, the circumference with respect to the maximum inner diameter Dw is πDw, the inner circumference is Lw, and the ratio of the inner circumference Lw to the circumference πDw is Lw / (πDw). In this case, the average value of the ratio Lw / (πDw) on the high temperature side may be larger than the average value of the ratio Lw / (πDw) on the low temperature side.

  Further, a groove may be provided on the inner periphery of the fluid channel or the refrigerant channel on the low temperature side.

  Further, a protrusion may be provided on the inner periphery of the fluid channel or the refrigerant channel on the low temperature side.

  Further, the fluid channel and the refrigerant channel may be in contact with each other along the channel direction.

  Further, at least one of the fluid channel and the refrigerant channel may be formed in a spiral shape.

  The fluid may be water and the refrigerant may be carbon dioxide.

  The heat exchanger, compression means for compressing the refrigerant flowing into the heat exchanger, expansion means for expanding the refrigerant discharged from the heat exchanger, and the discharge from the expansion means A heat pump type water heater provided with an evaporating means for exchanging heat between the refrigerant and the outside air is suitable.

  According to the present invention, the ratio (Lr / (πDr)) of the inner circumference Lr with respect to the circumference πDr with respect to the maximum inner diameter Dr of one section of the high temperature side refrigerant channel is made smaller than that of the low temperature side refrigerant channel. Can suppress pressure loss. In addition, heat transfer is promoted by increasing the ratio (Lr / (πDr)) of the inner circumference Lr with respect to the circumference πDr with respect to the maximum inner diameter Dr of one section in the low temperature side refrigerant flow path. As described above, the heat exchange performance can be improved while suppressing the heat dissipation loss on the high temperature side.

It is a perspective view of the heat exchanger concerning a 1st embodiment. It is a system diagram of the heat pump type water heater according to the first embodiment. It is sectional drawing of the low temperature side refrigerant | coolant flow path of the heat exchanger concerning 1st Embodiment. It is sectional drawing of the high temperature side refrigerant | coolant flow path of the heat exchanger concerning 1st Embodiment. It is an example of the temperature distribution in the heat exchanger concerning 1st Embodiment. It is a perspective view of the heat exchanger concerning a 2nd embodiment. It is sectional drawing of the low temperature side refrigerant | coolant flow path of the heat exchanger concerning 2nd Embodiment. It is a perspective view of the heat exchanger concerning a 3rd embodiment. It is a perspective view of the heat exchanger concerning a 4th embodiment. It is a perspective view of the heat exchanger concerning a 5th embodiment. It is a perspective view of the heat exchanger concerning a 6th embodiment. It is a conceptual diagram of the flow in the flow-path cross section of the heat exchanger concerning 6th Embodiment. It is a perspective view of the heat exchanger concerning a 7th embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following examples, water is assumed as the fluid 13 to be heated, and a refrigerant (for example, carbon dioxide) that circulates at a critical pressure or higher is assumed as the refrigerant 14 that supplies heat. However, the range of conditions described in this embodiment It can be implemented even if it is changed within. For example, the refrigerant may change from a gas to a gas-liquid mixed state in the process of heat exchange.

  A first embodiment will be described with reference to FIGS. FIG. 2 shows a configuration of a heat pump type water heater equipped with a heat exchanger 20 according to the present embodiment. The refrigerant outlet 12 of the heat exchanger 20 is directed to the inlet side of the expansion valve 23, the outlet side of the expansion valve 23 is directed to the inlet side of the evaporator 22, the outlet side of the evaporator 22 is directed to the suction side of the compressor 21, The discharge side of the compressor 21 is connected to the refrigerant inlet 11 of the heat exchanger 20.

  FIG. 1 shows a perspective view of the heat exchanger 20. The heat exchanger 20 includes a fluid flow path 2 through which a fluid 13 to be heated flows and a refrigerant flow path 1 through which a refrigerant 14 flows. The fluid flow path 2 and the refrigerant flow path 1 are in contact with each other along the flow path direction. ing. The fluid flow path 2 is constituted by a smooth tube having a smooth inner surface. Hereinafter, the upstream side of the refrigerant flow path 1 is referred to as a high temperature side, and the downstream side is referred to as a low temperature side. In this embodiment, the ratio of the lengths of the high temperature side refrigerant flow path 3 and the low temperature side refrigerant flow path 4 is 4: 6, a smooth tube is provided in the high temperature side refrigerant flow path 3, and an inner surface is provided in the low temperature side refrigerant flow path 4. A grooved tube having a groove 7 is used. The groove 7 of the grooved tube is formed in parallel to the flow path direction.

  The cross-sectional shapes of the low temperature side refrigerant flow path 4 and the high temperature side refrigerant flow path 3 are shown in FIGS. 3 and 4, respectively. The cross-sectional shapes of the low temperature side refrigerant flow path 4 and the high temperature side refrigerant flow path 3 are the same with respect to the flow path direction. The channel cross-sectional area and the outer diameter of the grooved pipe constituting the low temperature side refrigerant flow path 4 are the same values as the smooth pipe constituting the high temperature side refrigerant flow path 3. Since the low temperature side refrigerant flow path 4 has the groove 7, the ratio (Lr / (πDr)) of the inner circumference Lr with respect to the circumference πDr with respect to the maximum inner diameter Dr is larger than 1. On the other hand, since the circumference πDr and the inner circumference Lr with respect to the maximum inner diameter Dr are the same in the high temperature side refrigerant flow path 3, (Lr / (πDr)) is 1.

  The operation of the heat pump type water heater of this embodiment will be described. The refrigerant 14 is compressed by the compressor 21 to be in a high temperature / high pressure state, and flows into the heat exchanger 20 from the refrigerant inlet 11. The refrigerant 14 flowing into the heat exchanger 20 transfers heat to the fluid 13, and the refrigerant 14 loses heat and flows out from the refrigerant outlet 12 of the heat exchanger 20. The refrigerant 14 flowing out from the heat exchanger 20 is reduced in pressure by passing through the expansion valve 23, and heat is applied from outside air in the evaporator 22, and then flows into the compressor 21 again.

  In the present embodiment, it is assumed that water at about 10 ° C. flowing from the fluid inlet 9 of the heat exchanger 20 is boiled up to about 65 ° C. or higher and flows out from the fluid outlet 10. In this case, the pressure of the refrigerant 14 becomes higher than the critical pressure from the discharge side of the compressor 21 to the heat exchanger 20 and the inlet side of the expansion valve 23. When the pressure is equal to or higher than the critical pressure, the physical properties such as density and specific heat continuously change from gas to liquid as the temperature of the refrigerant 14 decreases. FIG. 5 shows an example of temperature changes of the refrigerant 14 and the fluid 13 in the heat exchanger 20 assumed in this embodiment. Line J and line K represent the temperature change of the fluid 13 and the temperature change of the refrigerant 14, respectively. The temperature of the refrigerant 14 decreases from the inlet toward the downstream, and the difference in heat exchange temperature with the fluid 13 at the point L is minimized. And the heat exchange temperature difference expands again downstream of point L. In the operating conditions of the present embodiment, the flow path length from the refrigerant inlet 11 to the point L is about 40% of the total length of the refrigerant flow path 1.

  The region on the higher temperature side than the point L includes a region where the specific heat increases as the pressure of the refrigerant 14 increases. This means that if the pressure loss on the higher temperature side than the L point is reduced, the temperature change of the refrigerant 14 slows down. As a result, the temperature of the refrigerant 14 changes from the line K to the line M. The heat exchange temperature difference increases. When the heat exchange temperature difference increases, the amount of heat exchanged at the point L increases, so that the flow path required for the temperature of the fluid 13 to be a value equal to or higher than the point L can be shortened.

  From the above, it can be seen that by reducing the pressure loss of the high temperature side refrigerant flow path 3 more than that of the low temperature side refrigerant flow path 4, it is possible to obtain the heat exchanger 20 having high efficiency with respect to the flow path length. Therefore, in this embodiment, the structure of the refrigerant flow path 1 is changed before and after the L point. In this embodiment, the ratio of the high-temperature side refrigerant flow path 3 to the total length of the refrigerant flow path 1 is 40%, but the position of the L point changes depending on the operating conditions of the heat exchanger 20, so that the high temperature according to the purpose is high. The ratio of the side refrigerant flow path 3 can be set arbitrarily.

  Next, the difference in pressure loss between the smooth tube and the grooved tube will be described.

  In general, it is known that the pressure loss of a fluid flowing in a pipe increases as the representative diameter decreases. Here, the representative diameter is defined by the following equation.

D _h = 4 × A _csa / L
(D _h [m]: representative diameter, A _csa [m ² ]: channel cross-sectional area, L [m]: inner circumference of channel)

  This representative diameter means a diameter for various flow channel shapes. For example, when the flow channel is a circle, the representative diameter matches the inner diameter of the flow channel. In other words, the relationship between the pressure loss and the representative diameter described above means that the pressure loss increases as the inner circumference increases with respect to the same flow path cross-sectional area. Comparing the representative diameters of the grooved tube and the smooth tube, the channel cross-sectional area is the same, but the inner periphery is longer in the grooved tube. For this reason, even if the cross-sectional area of the flow path is the same, the pressure loss of the grooved tube is higher than that of the smooth tube.

  Next, the difference in heat transfer performance between the grooved tube and the smooth tube will be described. The formula for the exchange heat quantity in the heat exchanger is shown below.

Q = K × A × ΔT
(Q [W]: Exchange heat quantity, K [W / m ² K]: Heat passage rate, A [m ² ]: Heat transfer area, ΔT [K]: Heat exchange temperature difference)

  Since the amount of exchange heat is proportional to the product of the heat transfer rate and the heat transfer area, this value is defined as the heat transfer performance and used as an index representing the performance of the heat exchanger 20. When comparing a grooved tube and a smooth tube having the same channel cross-sectional area, the heat transfer performance of the grooved tube having a large heat transfer area is increased. Therefore, if attention is paid only to the heat transfer performance, the performance of the heat exchanger 20 becomes higher if the refrigerant flow path 1 is formed as a grooved tube from the refrigerant inlet 11 to the refrigerant outlet 12 of the heat exchanger 20. However, as described above, since the pressure loss of the refrigerant 14 affects the performance of the heat exchanger 20 on the high temperature side from the L point where the heat exchange temperature difference is minimized, in this embodiment, the high temperature side refrigerant is separated from the L point. A smooth tube was used for the channel 3 and a grooved tube was used for the low-temperature side refrigerant channel 4.

  As described above, according to the present embodiment, since the pressure loss on the high temperature side can be suppressed regardless of the size of the refrigerant flow path on the high temperature side and the low temperature side, the heat exchange performance is improved while suppressing the heat dissipation loss of the high temperature side refrigerant pipe. be able to. Specifically, since the outer surface areas of the high temperature side refrigerant flow path 3 and the low temperature side refrigerant flow path 4 are the same, the increase in heat dissipation loss on the high temperature side is suppressed and the pressure loss on the high temperature side is reduced compared to the low temperature side. In addition, by improving the heat transfer performance on the low temperature side, it is possible to provide a heat exchanger 20 and a heat pump type water heater that are highly efficient with respect to the channel length.

  In the present embodiment, it is assumed that the refrigerant 14 operates at a critical pressure or higher, but the case where the refrigerant 14 changes from a gas to a gas-liquid mixed state in the process of heat exchange is also shown at the point L in FIG. Since the corresponding minimum point of the heat exchange temperature difference is generated, the performance of the heat exchanger 20 can be improved by using this embodiment. In this embodiment, the groove 7 of the grooved tube is parallel to the flow path direction. However, since the intended effect is obtained even when the groove 7 is formed in a spiral shape with respect to the flow path direction, the groove 7 Any shape can be selected.

  A second embodiment will be described with reference to FIGS. FIG. 6 is a perspective view of the heat exchanger 20 according to the second embodiment. In the present embodiment, a dimple tube having a protrusion 8 is used in the low-temperature side refrigerant flow path 4 in the first embodiment. The protrusions 8 are spirally arranged on the inner wall of the low temperature side refrigerant flow path 4. The average channel cross-sectional area obtained by dividing the channel volume of the dimple tube constituting the low-temperature side refrigerant channel 4 by the channel length is the same as the channel cross-sectional area of the high-temperature side smooth tube. The outer diameters of the dimple tube and the smooth tube are also the same.

  FIG. 7 shows a cross-sectional view of a dimple tube constituting the low temperature side refrigerant flow path 4. The ratio (Lr / (πDr)) of the inner circumference Lr based on the circumference πDr with respect to the maximum inner diameter Dr is greater than 1 at the location where the projection 8 of the dimple tube is disposed. Therefore, the average value of (Lr / (πDr)) from the inlet to the outlet of the low temperature side refrigerant flow path 4 is also larger than the value on the high temperature side.

  The operation of the second embodiment will be described. The refrigerant 14 that has flowed into the heat exchanger 20 flows through the high-temperature smooth tube and then flows into the dimple tube. In the portion where the projection 8 in the dimple tube is disposed, the inner circumference Lr is longer than that of the smooth tube having the same flow path cross-sectional area. Therefore, for the same reason as in the first embodiment, pressure loss and transmission are compared with those of the smooth tube. Increases thermal performance. With the above mechanism, it can be seen that this embodiment can obtain the same effects as those of the first embodiment. In this embodiment, the protrusions 8 in the tube are arranged in a spiral shape, but any desired shape can be selected because the intended effect can be obtained regardless of the arrangement method.

  A third embodiment will be described with reference to FIG. The third embodiment is the same as that of the first embodiment, except that the high temperature side fluid flow path 5 uses a grooved tube having a groove 7 parallel to the flow path direction.

  The operation of this embodiment will be described. Since a grooved tube is used for the high temperature side fluid flow path 5, heat transfer performance is improved as compared with the case where a smooth tube is used. Due to the improvement of heat transfer performance on the high temperature side, the required flow path length when the exchange heat quantity is constant is reduced, so this embodiment further suppresses heat loss on the high temperature side and improves the efficiency with respect to the flow path length. Prompted.

  In this embodiment, a grooved tube having a groove 7 parallel to the flow path direction is used for both the low temperature side refrigerant flow path 4 and the high temperature side fluid flow path 5, but a spiral groove is formed in the flow path. Since the same effect can be obtained also in the case of having 7 or the case of having the protrusion 8, any one can be selected according to the purpose.

  A fourth embodiment will be described with reference to FIG. In the fourth embodiment, the contact method between the fluid flow path 2 and the refrigerant flow path 1 is changed from the first embodiment. The refrigerant flow path 1 is wound in a spiral shape with the fluid flow path 2 as a core tube. Yes. Thereby, since the heat transfer area with respect to the unit length of the fluid flow path 2 increases compared with the case where the straight pipes are brought into contact with each other, the effect similar to that of the first embodiment is obtained, and the small size of the heat exchanger 20 is obtained. Can be realized.

  A fifth embodiment will be described with reference to FIG. In the fifth embodiment, the positional relationship between the fluid flow path 2 and the refrigerant flow path 1 is changed from the first embodiment, and the refrigerant flow path 1 is arranged inside the fluid flow path 2. As a result, the entire outer surface of the refrigerant flow path 1 contributes to the heat transfer, so that the heat transfer area increases, and the heat exchanger 20 can be downsized while obtaining the same effects as in the first embodiment.

  A sixth embodiment will be described with reference to FIG. The heat exchanger 20 of the sixth embodiment is obtained by changing the curvature of the flow path with respect to the first embodiment. The fluid flow path 2 and the refrigerant flow path 1 are each formed in a spiral shape, and the refrigerant flow path 1 is disposed outside the fluid flow path 2. Here, the refrigerant flow path 1 is in contact with the fluid flow paths 2 for two adjacent pitches. This structure can be easily manufactured by first forming the fluid flow path 2 in a spiral shape and then winding the refrigerant flow path 1 around the outside.

  FIG. 12 shows a schematic diagram of the flow in the cross section of the fluid channel 2 and the refrigerant channel 1 in the present embodiment. In the spiral flow path, the flow velocity in the flow path direction of the spiral structure outer side 16 is higher than that of the spiral structure inner side 15. In a place where the flow velocity is high, the static pressure of the fluid decreases according to the law of conservation of energy, and conversely, in a place where the flow velocity is slow, the static pressure increases. Due to the static pressure difference in the flow path, a secondary flow from the inside toward the outside is generated, and a vortex is generated. As a result, the mixing of the fluid in the flow path is promoted as compared with the case of the straight pipe, so that the temperature of the wall surface is easily transmitted to the fluid.

  Due to the above mechanism, the heat flow performance of the spirally formed flow path is higher than that of the straight pipe. Therefore, the flow path of the heat exchanger 20 can be obtained while obtaining the same effect as the first embodiment. Can be shortened.

  A seventh embodiment will be described with reference to the perspective view of FIG. In the seventh embodiment, the heat exchanger 20 is changed to a different structure on the high temperature side and the low temperature side in the first embodiment. The high temperature side has a structure in which the high temperature side refrigerant flow path 3 and the high temperature side fluid flow path 5 are contacted along the flow path direction. On the other hand, the low temperature side has a structure in which the low temperature side refrigerant flow path 4 is wound around the outer surface of the low temperature side fluid flow path 6 formed in a spiral shape. The low temperature side refrigerant flow path 4 is in contact with the adjacent two pitch low temperature side fluid flow paths 6.

  With the above method, an optimum heat exchanger can be selected for the purpose of improving the heat transfer performance on the low temperature side while reducing the pressure loss on the high temperature side as compared with the low temperature side. Besides the present embodiment, the heat exchanger 20 on the high temperature side and the low temperature side can be changed to any one according to the purpose.

  The fourth to seventh embodiments described above are derived from the first embodiment, but are described in the second and third embodiments in the high temperature side fluid flow path 5 and the low temperature side refrigerant flow path 4. The same effect can be obtained when a combination of flow paths is applied.

DESCRIPTION OF SYMBOLS 1 Refrigerant flow path 2 Fluid flow path 3 High temperature side refrigerant flow path 4 Low temperature side refrigerant flow path 5 High temperature side fluid flow path 6 Low temperature side fluid flow path 7 Groove 8 Projection 9 Fluid inlet 10 Fluid outlet 11 Refrigerant inlet 12 Refrigerant outlet 13 Fluid 14 Refrigerant 15 Helix structure inner side 16 Helix structure outer side 20 Heat exchanger 21 Compressor 22 Evaporator 23 Expansion valve

Claims (8)

A fluid flow path through which the fluid to be heated flows;
A refrigerant flow path through which a refrigerant that provides heat to the fluid flows;
In the heat exchanger in which the fluid and the refrigerant flow in opposition,
When the maximum inner diameter in the cross section of the refrigerant flow path is Dr, the circumference with respect to the maximum inner diameter Dr is πDr, the inner circumference is Lr, and the ratio of the inner circumference Lr to the circumference πDr is Lr / (πDr), An average value of the ratio Lr / (πDr) on the low temperature side is larger than an average value of the ratio Lr / (πDr) on the high temperature side.   When the maximum inner diameter in the cross section of the fluid channel is Dw, the circumference with respect to the maximum inner diameter Dw is πDw, the inner circumference is Lw, and the ratio of the inner circumference Lw to the circumference πDw is Lw / (πDw), 2. The heat exchanger according to claim 1, wherein an average value of the ratio Lw / (πDw) on the high temperature side is larger than an average value of the ratio Lw / (πDw) on the low temperature side.   The heat exchanger according to claim 1 or 2, wherein a groove is provided in an inner periphery on a low temperature side of the fluid channel or the refrigerant channel.   The heat exchanger according to claim 1, wherein a protrusion is provided on an inner periphery on a low temperature side of the fluid flow path or the refrigerant flow path.   The heat exchanger according to claim 1 or 2, wherein the fluid channel and the refrigerant channel are in contact with each other along a channel direction.   The heat exchanger according to claim 1 or 2, wherein at least one of the fluid channel or the refrigerant channel is formed in a spiral shape. The fluid is water;
The heat exchanger according to claim 1 or 2, wherein the refrigerant is carbon dioxide. The heat exchanger according to claim 1 or 2,
Compression means for compressing the refrigerant flowing into the heat exchanger;
Expansion means for expanding the refrigerant discharged from the heat exchanger;
A heat pump type hot water heater comprising: an evaporating unit configured to exchange heat between the refrigerant discharged from the expansion unit and outside air.