JP2011252662A - Heat transfer tube for refrigerant, and heat exchanger - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat transfer tube for refrigerant, which is a hydrothermal exchanging of a heat pump type water heater using a carbon dioxide as refrigerant, capable of suppressing an increase of a pressure loss and effectively improving a heat transfer performance, and to provide a heat exchanger with the same.SOLUTION: The heat transfer tube 20 is used for the heat exchanger of the heat pump water heater 10 using the carbon dioxide as the refrigerant, and includes: a main tube with an inner circumferential surface 20a; a plurality of fins 200 provided at the inner circumferential surface 20a; and a plurality of grooves between the plurality of fins 200. The plurality of grooves has a first groove 210 with a first width WA and a second groove 212 with a second width WB different from the first width WA.

Description

  The present invention relates to a refrigerant heat transfer tube and a heat exchanger. In particular, the present invention relates to a refrigerant heat transfer tube for a heat exchanger provided in a heat pump water heater using carbon dioxide as a refrigerant, and a heat exchanger having the refrigerant heat transfer tube.

  A heat pump refers to a system that moves heat from a heat source, which is an inexpensive and abundant resource, such as external air, groundwater, seawater, and the like, using a compressor (that is, a compressor). For example, in an electric heat pump, electric energy is not directly converted into heat energy, but by using electric energy as a power source for moving heat, heat energy nearly three times as much as power consumption (energy consumption) can be used. . This is a system that is more efficient and less burdensome on the environment than a system that uses fossil fuels such as oil to burn it into thermal energy. For this reason, heat pump heat exchange devices have been widely used in recent years.

  On the other hand, chlorofluorocarbon refrigerants have been conventionally used for general heat exchange devices (such as air conditioners, refrigerators, refrigerators, and water heaters) that use a refrigeration cycle. However, chlorofluorocarbon-based refrigerants are used instead of natural refrigerants, particularly carbon dioxide, which have a low environmental impact because of concerns about the impact on global warming. For economic and environmental reasons, for example, expectations for a natural refrigerant (particularly carbon dioxide) heat pump heat exchange device combined with the above-described heat pump are increasing rapidly, for example, for eco-cutes and car air conditioners.

  In heat pump heat exchange equipment using carbon dioxide refrigerant, a gas cooler (heat radiator) and an evaporator (heat absorber) are generally used as heat exchangers, and these heat exchangers are used. As the refrigerant heat transfer pipe, a gas cooler refrigerant pipe and an evaporator refrigerant pipe are used. In particular, in a heat pump type water heater using a carbon dioxide refrigerant, in addition to the two types of heat transfer tubes, another heat transfer tube (gas cooler water tube) that exchanges heat between the refrigerant and the heat medium is also used. The technical specifications required for these heat transfer tubes (water tube for gas cooler, refrigerant tube for gas cooler, and refrigerant tube for evaporator) are different from each other. Hereinafter, the gas cooler of the heat pump type water heater using the carbon dioxide refrigerant is referred to as a water heat exchanger. As such a refrigerant pipe for a water heat exchanger, an internally grooved pipe shown in Patent Document 1 and Patent Document 2 is known.

  The inner surface grooved tube described in Patent Literature 1 can improve the performance of the water heat exchanger by using the inner surface grooved tube, which has been proven in air conditioners, as the water heat exchanger refrigerant tube.

JP 2006-105525 A JP 2007-178115 A

  However, in the internally grooved tube described in Patent Document 1, heat exchange of the heat transfer tube is caused by mixing compressor lubricating oil, which is a lubricant for the compressor of the refrigeration cycle, into the carbon dioxide refrigerant flowing in the refrigerant tube. There is a serious problem that hinders. This is considered because the compatibility between the carbon dioxide refrigerant and the compressor lubricating oil is not good. Moreover, such a problem is a problem that was not found in conventional fluorocarbon refrigerants.

  In addition, in the internally grooved tube described in Patent Document 2, an increase in pressure loss is not studied for improving heat dissipation performance, that is, heat transfer coefficient. In particular, in a water heat exchanger, if the pressure loss of the carbon dioxide refrigerant increases, the refrigerant temperature decreases even with the same heat exchange amount. Therefore, a temperature difference between water and the refrigerant cannot be ensured and heat exchange is not possible (i.e., Pinch point) occurs. This phenomenon does not occur in air conditioners using chlorofluorocarbon refrigerants, but is caused by heat exchange between the heat of carbon dioxide and water heat that is gas-cooled in the supercritical region. Occurs when is large.

  The refrigerant temperature is determined by the refrigerant pressure and enthalpy, and the heat exchange amount of the heat transfer tube is calculated by the product of the refrigerant flow rate and the enthalpy difference. Here, if the enthalpy is the same, the temperature decreases as the refrigerant pressure decreases. That is, when the pressure loss of the refrigerant increases, the temperature of the refrigerant decreases, so the heat exchange amount of the heat transfer tubes decreases.

  From the above, in the water heat exchanger, it is necessary to suppress the increase in pressure loss of the refrigerant pipe to an extent commensurate with the improvement in heat transfer performance.

  Accordingly, an object of the present invention is hydrothermal exchange of a heat pump water heater using carbon dioxide as a refrigerant, and can suppress an increase in pressure loss and effectively improve heat transfer performance. It is to provide a heat pipe and a heat exchanger.

  (1) In order to achieve the above object, the present invention is a refrigerant heat transfer tube used in a heat exchanger of a heat pump water heater using carbon dioxide as a refrigerant, the main tube having an inner peripheral surface, and the inner periphery A plurality of fins provided on the surface, and a plurality of groove portions between the plurality of fins, wherein the plurality of groove portions have a first groove portion having a first width and a width different from the first width. A refrigerant heat transfer tube having a second groove portion having the second width is provided.

  (2) In the refrigerant heat transfer tube, it is preferable that the second groove is periodically provided on the inner peripheral surface.

  (3) Moreover, in the said heat exchanger tube for refrigerant | coolants, it is preferable that each of these fins has a height of 0.15 mm or more.

  (4) In the refrigerant heat transfer tube, each of the plurality of fins preferably has a twist angle of 0 ° to 3 °.

  (5) Moreover, in order to achieve the said objective, this invention provides a heat exchanger provided with the heat exchanger tube for refrigerant | coolants as described in any one of said (1)-(4).

  According to the refrigerant heat transfer tube and the heat exchanger according to the present invention, it is a hydrothermal exchange of a heat pump type water heater using carbon dioxide as a refrigerant, and an increase in pressure loss can be suppressed and heat transfer performance can be effectively improved. A heat transfer tube for a refrigerant and a heat exchanger that can be improved can be provided.

It is a schematic diagram of the structure of the heat pump type hot water heater which concerns on the 1st Embodiment of this invention. It is sectional drawing of the heat exchanger tube for refrigerant | coolants which concerns on the 2nd Embodiment of this invention. It is sectional drawing of the heat exchanger tube for refrigerant | coolants which concerns on the 3rd Embodiment of this invention. It is a schematic diagram of the structure of the water heat exchanger which concerns on the 4th Embodiment of this invention. It is a schematic diagram of the structure of the water heat exchanger which concerns on the 5th Embodiment of this invention. It is a schematic diagram of the double-pipe heat exchanger for evaluating heat transfer performance. When the oil concentration is 5.0%, for Example 1 and Comparative Example 1 (inner grooved tube), the average refrigerant temperature, the in-tube heat transfer coefficient smooth tube ratio (ratio to Comparative Example 4), and the pressure loss smooth tube ratio It is a figure which shows the evaluation result which showed the relationship with ratio (henceforth a performance pressure loss ratio).

[Summary of embodiment]
In a heat transfer pipe for a refrigerant used in a heat exchanger of a heat pump water heater using carbon dioxide as a refrigerant, a main pipe having an inner peripheral surface, a plurality of fins provided on the inner peripheral surface, and between the plurality of fins A plurality of groove portions, wherein the plurality of groove portions have a first groove portion having a first width and a second groove portion having a second width different from the first width. A heat transfer tube is provided.

[First Embodiment]
FIG. 1: shows the outline | summary of a structure of the heat pump type water heater comprised using the heat exchanger tube for refrigerant | coolants which concerns on the 1st Embodiment of this invention.

  The heat pump type hot water heater 10 according to the first embodiment is a heat pump type hot water heater 10 as a carbon dioxide refrigerant heat pump type hot water heater using carbon dioxide as a refrigerant. The heat pump type water heater 10 includes a compressor 11, a water heat exchanger 12 as a heat exchanger having a refrigerant heat transfer tube 20 described later, an expansion valve 13, and a heat absorber (evaporator) 14. The compressor 11 and the water heat exchanger 12 are connected to each other by a pipe 15, the water heat exchanger 12 and the expansion valve 13 are connected to each other by a pipe 15a, and the expansion valve 13 and the heat absorber 14 are connected to each other by a pipe 15b. The refrigeration cycle is configured by connecting the heat absorber 14 and the compressor 11 to each other via a pipe 15c. The carbon dioxide refrigerant is enclosed in the refrigeration cycle. Here, in the region from the discharge part of the compressor 11 to the inlet part of the expansion valve 13 through the water heat exchanger 12, the refrigerant is in a supercritical state (that is, a state exceeding the critical pressure). In addition, as lubricating oil of the compressor 11, polyalkylene glycol oil (PAG oil) can be used, for example.

(Operation of the heat pump type water heater 10)
Next, the operation of the heat pump type water heater 10 will be described. First, the carbon dioxide refrigerant as the refrigerant is compressed in the compressor 11. The compressed carbon dioxide refrigerant is introduced from the compressor 11 to the gas cooler (water heat exchanger) 12 in a state (supercritical state) exceeding the critical pressure (about 7.4 MPa). In the present embodiment, the refrigerant is compressed to, for example, about 10 MPa in the compressor 11.

  The supercritical carbon dioxide refrigerant is not liquefied (that is, not in a gas-liquid two-phase state) and becomes a high-temperature and high-pressure state. The supercritical carbon dioxide refrigerant exchanges heat with water or the like in the gas cooler (water heat exchanger) 12 (that is, dissipates heat from the refrigerant). Thereafter, the carbon dioxide refrigerant is decompressed by an expansion valve (decompressor) 13 to be in a low-pressure gas-liquid two-phase state and introduced into the heat absorber 14. In the present embodiment, the carbon dioxide refrigerant in the expansion valve 13 is reduced to a pressure of about 3.5 MPa, for example.

  The carbon dioxide refrigerant in the gas-liquid two-phase state absorbs heat from the air (atmosphere) in the heat absorber 14 to be in a gas state (that is, a gas phase single-phase state), and is sucked into the compressor 11 again. By repeating such a cycle, the heating action by the heat radiation from the refrigerant in the water heat exchanger 12 and the cooling action by the heat absorption of the refrigerant in the heat absorber 14 are continued.

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

  The refrigerant heat transfer tube 20 according to the second embodiment is formed of a metal material such as copper, and includes a main tube having an inner peripheral surface 20a and an outer peripheral surface 20b, and a plurality of fins 200 provided on the inner peripheral surface 20a. A plurality of grooves are provided between the plurality of fins 200. The plurality of groove portions include a first groove portion 210 having a first width “WA” and a second groove portion 212 having a second width “WB” different from the first width “WA”. Have In the present embodiment, the second width “WB” is formed wider than the first width “WA”.

  The refrigerant heat transfer tube 20 can be manufactured as follows. First, a copper tube is prepared. Then, a grooved plug is arranged on the drawing side (front side) inside the copper tube, and a floating plug is arranged on the rear side. Subsequently, the copper tube is pulled out while pressing the ball revolving on the outer surface of the copper tube where the grooved plug is located. Thereby, the groove | channel of the grooved plug is rolled on the inner surface of a copper pipe, and the heat exchanger tube for refrigerant | coolants which is an inner surface grooved pipe | tube with which the several groove | channel was formed in the inner surface is manufactured. Here, the refrigerant heat transfer tube 20 according to the present embodiment can be manufactured by using a grooved plug in which grooves are not provided at predetermined intervals in the circumferential direction. For example, a grooved plug in which every fourth groove is not provided in the circumferential direction can be used.

  Further, the twist angle of the plurality of fins 200 formed on the inner surface 20a is set to 0 ° or more and 3 ° or less, preferably approximately 0 °. The “twist angle” is an angle formed by the tube center axis direction and the groove direction in the internally grooved tube.

(Effects of the first and second embodiments)
According to the first and second embodiments, in the water heat exchanger 12 of the heat pump water heater 10 using carbon dioxide as a refrigerant, the refrigerant heat transfer tube 20 having an excellent performance pressure loss ratio can be provided. The heat exchange efficiency of the heat exchanger 12 can be improved. That is, since the plurality of second groove portions 212 wider than the first groove portion 210 are periodically provided between the plurality of fins 200 provided in the refrigerant heat transfer tube 20, the lubricating oil of the compressor 11 is supplied to the pipe 15. Even if mixed in, the mixed lubricating oil can easily flow outside the tube along the groove 212 in the refrigerant heat transfer tube 20. Thereby, the pressure loss resulting from mixing of the lubricating oil into the refrigerant heat transfer tube 20 can be reduced. Therefore, the effect of improving the heat transfer coefficient in the refrigerant heat transfer tube 20 can be increased more than the increase in pressure loss of the refrigerant heat transfer tube 20 and the influence of heat transfer inhibition due to the mixing of the lubricating oil.

[Third Embodiment]
FIG. 3: shows the outline | summary of the cross section of the heat exchanger tube for refrigerant | coolants which concerns on the 3rd Embodiment of this invention.

  The refrigerant heat transfer tube 30 according to the third embodiment has substantially the same configuration and function as the refrigerant heat transfer tube 20 according to the second embodiment except for the interval between the plurality of fins 300. Therefore, a detailed description is omitted except for differences.

  In the refrigerant heat transfer tube 30, a groove portion having a second width “WB” wider than the first width “WA” is provided in a part of the inner surface. Moreover, the refrigerant | coolant heat exchanger tube 30 is manufactured using the grooved plug in which the groove | channel is not formed partially similarly to the refrigerant | coolant heat exchanger tube 20 which concerns on 2nd Embodiment.

[Fourth Embodiment]
FIG. 4 shows an outline of the structure of the water heat exchanger according to the fourth embodiment of the present invention.

  The heat exchanger 400 according to the fourth embodiment is configured by winding the refrigerant heat transfer tube 20 according to the second embodiment around a water heat transfer tube. If necessary, the outer surface of the water heat transfer tube and the refrigerant heat transfer tube 20 can be fixed together by brazing or the like. In the heat exchanger 400, heat is exchanged between the water flowing in the water heat transfer tube 41 and the refrigerant flowing in the refrigerant heat transfer tube 20 in contact with the outer periphery of the heat transfer tube 41. In the fourth embodiment, one example of the refrigerant heat transfer tube 20 wound around the water heat transfer tube 41 is shown. However, a plurality of refrigerant heat transfer tubes 20 may be provided depending on use conditions. it can. Further, the water heat transfer tube 41 is an example of a corrugated tube. The corrugated pipe shown in the drawing forms a spiral convex groove on the inner peripheral surface by forming a spiral concave groove as a corrugated groove on the outer peripheral surface of the smooth pipe. More specifically, the corrugated groove is a smooth tube made of a corrugated disk-shaped disk made of a smooth tube, i.e. a tube whose inner peripheral surface is a perfect circle when cut perpendicular to the tube axis. It is formed by revolving around the smooth tube and moving the smooth tube at a predetermined speed while rotating while pressing continuously on the smooth tube while being inclined with respect to the direction perpendicular to the central axis. . That is, although the illustrated corrugated tube has a slightly convex shape toward the outside of the tube, many substantially smooth portions remain, and the first refrigerant heat transfer tube is wound along the corrugated groove. Thereafter, the second refrigerant heat transfer tube can be wound along the first refrigerant heat transfer tube. In addition, the width | variety of a corrugated groove | channel is substantially the same as the width | variety of the disk shaped disk used for the manufacturing method, and is 0.5 mm-1.5 mm in the measurement on the surface of a smooth tube. Moreover, although the heat-transfer pipe | tube 41 for water showed the example of the corrugated pipe | tube, it can also be set as a smooth pipe | tube, an inner surface grooved tube, or an inner surface grooved corrugated tube according to use conditions.

[Fifth Embodiment]
FIG. 5 shows an outline of the structure of the water heat exchanger according to the fifth embodiment of the present invention.

  The heat exchanger 500 according to the fifth embodiment is configured by bringing a water heat transfer tube and the refrigerant heat transfer tube 30 of the third embodiment in parallel contact with each other. If necessary, the outer surface of the water heat transfer tube and the refrigerant heat transfer tube 30 can be fixed together by brazing or the like. In the heat exchanger 500, heat is exchanged between the water flowing in the water heat transfer tube 51 and the refrigerant flowing in the refrigerant heat transfer tube 30 in contact with the outer periphery of the heat transfer tube 51. The water heat transfer tube and the refrigerant heat transfer tube 30 can be made compact by winding them in a cylindrical shape, an elliptical shape, or a substantially square shape while keeping the water heat transfer tube 30 in parallel contact. In the fifth embodiment, an example in which the refrigerant heat transfer tube 30 is brought into contact with the water heat transfer tube 41 is shown. However, a plurality of refrigerant heat transfer tubes 30 may be used depending on the use conditions. You can also. Furthermore, although the example of the corrugated pipe | tube was shown as the heat transfer pipe | tube 51 for water, according to use conditions, a smooth pipe, an inner surface grooved pipe | tube, or an inner surface grooved corrugated pipe | tube can also be used. In the case of a tube having many substantially smooth portions as shown in the figure, the contact area can be increased, or the distance between the tubes can be shortened, and the heat exchange rate can be increased.

  FIG. 6 shows a schematic diagram of a double-pipe heat exchanger for evaluating heat transfer performance.

As shown in FIG. 6, a double pipe heat having a refrigerant heat transfer pipe 60 as an inner pipe and a water pipe 61 for flowing water for removing heat from the refrigerant in an annular shape (jacket shape) outside the inner pipe. An exchanger 62 was configured. In FIG. 6, “Gr” is the refrigerant mass flow rate (kg / h), “Pr1” is the refrigerant inlet pressure (MPa), “T _r1 ” is the refrigerant inlet temperature (° C.), and “Pr2” is the refrigerant outlet pressure ( MPa), “T _r2 ” is the refrigerant outlet temperature (° C.), “G _w ” is the water mass flow rate (m ³ / s), “T _w1 ” is the water outlet temperature (° C.), and “T _w2 ” is the water inlet temperature. (° C.).

  Table 1 shows the specifications of the evaluated refrigerant heat transfer tubes.

  In Example 1 and Example 2, the heat transfer tube according to the second embodiment was used, and in Example 3, the heat transfer tube according to the third embodiment was used.

  Specifically, the heat transfer tube used in Example 1 and Example 2 is composed of two first grooves 210 (both of which are formed by three fins 200, like the refrigerant heat transfer tube 20 according to the second embodiment). , Having a first width WA), and when the three fins are used as fin regions, a second groove 212 having a second width is formed following the fin regions. And the fin area | region and the 2nd groove part 212 are made into a pair, and the said pair is formed in the inner surface of a heat exchanger tube repeatedly. In the heat transfer tube used in Example 3, like the refrigerant heat transfer tube 30 according to the third embodiment, the plurality of fins 200 are arranged on the inner surface at equal intervals (that is, the first width WA). The second groove 212 having the second width is formed only at one position on the inner surface.

  On the other hand, Comparative Examples 1-3 used the internally grooved pipe | tube produced by the rolling process using the conventional grooved plug. The heat transfer tubes used in Comparative Examples 1 to 3 do not have the second groove 212, and a plurality of fins are evenly arranged on the inner surface of each heat transfer tube at intervals of the first width WA. A smooth tube was used as the heat transfer tube according to Comparative Example 4. The groove width WA indicates the narrower width of the groove between the fins, and the groove width WB indicates the wider groove width.

  The heat transfer performance of each refrigerant heat transfer tube shown in Table 1 was measured. Table 2 shows the measurement conditions in the heat transfer performance measurement. The heat transfer coefficient in the tube was evaluated as the heat transfer performance.

  Here, in order to suppress the influence of the heat flux, measurement was performed while adjusting the refrigerant temperature range (measured temperature range) (that is, the refrigerant inlet temperature to the refrigerant outlet temperature were divided into three areas, and the heat flow in each area was measured. Measured by adjusting the water flow rate so that the bundles were equal).

  In addition, the lubricating oil concentration (PAG oil concentration) in the refrigerant is obtained by collecting the refrigerant circulating in the cycle in the sampling container before the refrigerant inlet of the double-pipe heat exchanger, and the volume of the sampling container and the collected refrigerant. The mass was calculated by the so-called weight method. The accuracy (control / measurement error) under the measurement conditions is about ± 0.3 ° C., pressure is about ± 0.1%, and the refrigerant mass velocity is relative to the values in Table 2 (the values are average values). Is about ± 0.4%, and the PAG oil concentration is about ± 0.1% by mass.

  Next, the in-tube heat transfer coefficient α was calculated as follows.

First, refrigerant inlet temperature T _r2 [unit: K], refrigerant outlet temperature T _r1 [unit: K], water pipe inlet temperature T _w1 [unit: K], water pipe for each refrigerant temperature range in the double-pipe heat exchanger outlet temperature _{T w2} [unit: K], and the mass flow rate _{G w} [unit: kg / s] of water was measured. Then, the representative temperature calculated from the water inlet / outlet temperatures (average temperature T _{w [unit:} K]) to calculate the specific heat at constant pressure Cp _w of water on the measuring path from the following equation (1), the relationship (2) From the above, the heat flow rate q [unit: kW / m ² ] and the logarithm average temperature difference ΔT _L [unit: K] were calculated.

In the formula (1), “A” is a heat exchange area (that is, a surface area of a heat transfer tube for refrigerant in contact with water in a double tube heat exchanger) [unit: m ² ].

  Here, Formula (3) and Formula (4) are as follows.

Further, by dividing the heat flux q in logarithmic average temperature difference [Delta] T _L, the heat transfer coefficient of the double-pipe heat exchanger K ^{[Unit: kW / (m 2 K)} ] was calculated from the following equation (5) .

On the other hand, from the representative temperature (average temperature T _w ) calculated from the inlet / outlet temperature of the water pipe, each physical property value (density, specific heat, viscosity, thermal conductivity λ _w ) at that temperature is determined, and the Prandtl number Pr is calculated. did. Further, the Reynolds number Re was calculated from the physical property value of water and the mass flow rate, and the heat transfer coefficient α _w [unit: kW / (m ² K)] of water was calculated according to the relationship of the following equation (6).

Here, d _e is (a value obtained by dividing 4 times the flow area at the wetted perimeter) equivalent diameter of the annular flow of the water [unit: m], d _i is the inner diameter of the water pipe [unit: m], OD is It is the outer diameter [unit: m] of the heat transfer tube for refrigerant.

The heat transfer coefficient α in the tube [unit: kW / (m ² K)] is the heat transfer coefficient K, the heat transfer coefficient α _{w of} water, the outer diameter OD of the refrigerant heat transfer tube, and the inner diameter ID of the refrigerant heat transfer tube [unit: m] was used to calculate the following equation (7).

  FIG. 7 shows that when the oil concentration is 5.0%, the average refrigerant temperature, the in-tube heat transfer coefficient smooth tube ratio (compared to Comparative Example 4), and the pressure loss for Example 1 and Comparative Example 1 (inner grooved tube). The evaluation result which showed the relationship with ratio (henceforth a performance pressure loss ratio) with a smooth tube ratio is shown.

  In FIG. 7, the average refrigerant temperature is an average temperature in each temperature region obtained by dividing the refrigerant inlet temperature to the refrigerant outlet temperature shown in Table 2 into three regions (that is, the refrigerant inlet temperature and the refrigerant outlet temperature in the temperature region). Average).

  For Examples 1 to 3 and Comparative Examples 1 to 3, the average refrigerant temperature and the performance pressure loss ratio were calculated as shown in FIG. 7, and the results of averaging the performance pressure loss ratio for each average refrigerant temperature at each oil concentration are shown in Table 3. Shown in

  In Example 1 and Comparative Example 1, not only the inner surface area increase rate is the same, but also the fin height and the number of fins are the same. At this time, regardless of whether the oil concentration is 0.3% or 5.0%, the heat transfer tube according to the second embodiment of the present invention (that is, the heat transfer tube of Example 1) has a high performance pressure loss ratio. It has been shown.

  Although Example 2 and Comparative Example 2 have the same fin height, the number of fins is different (that is, the number of heat transfer tubes according to Example 2 is smaller). Is big. When the oil concentration is 0.3%, the heat transfer tube according to the second embodiment of the present invention (that is, the heat transfer tube of Example 2) has a high performance pressure loss ratio, but when the oil concentration is 5.0%, Comparative Example 2 is used. It was equivalent.

  In Example 3 and Comparative Example 3, the inner surface area increase rate is the same, but the fin height and the number of fins are different from each other. When the oil concentration is 0.3%, the heat transfer tube of the third embodiment of the present invention (that is, the heat transfer tube of Example 3) has a high performance pressure loss ratio, but when the oil concentration is 5.0%, it is higher than that of Comparative Example 3. It became low.

  When Example 1 and Comparative Example 3 having the same fin height are compared, the inner surface area is larger in Comparative Example 3, but both the oil concentration is 0.3% and 5.0%. The performance pressure loss ratio became larger. Moreover, since Example 1 had only 3/4 the number of fins compared with Comparative Example 3, it was shown that the effect of weight reduction was also great.

  From the above, when the oil concentration is 0.3%, since all of Examples 1 to 3 are effective, the fin height is preferably 0.15 mm or more. When the fin height is less than 0.15 mm, the oil covers the surface of the fin, so that the heat exchange rate of the heat transfer tube is about a smooth tube. On the other hand, when the oil concentration is 5.0%, the fin height is preferably 0.24 mm or more based on the results in Example 2 and Example 3.

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

DESCRIPTION OF SYMBOLS 10 Heat pump type hot water heater 11 Compressor 12 Water heat exchanger 13 Expansion valve 14 Heat absorber 15, 15a, 15b, 15c Pipe 20 Heat transfer pipe for refrigerant 20a Inner surface 20b Outer surface 30 Heat transfer pipe for refrigerant 41 Water pipe 51 Water pipe 60 For refrigerant Heat transfer tube 61 Water tube 62 Double tube heat exchanger 200 Fin 210 First groove 212 Second groove 300 Fin 400 Heat exchanger 500 Heat exchanger

Claims (5)

A refrigerant heat transfer tube used in a heat exchanger of a heat pump water heater using carbon dioxide as a refrigerant,
A main pipe having an inner peripheral surface;
A plurality of fins provided on the inner peripheral surface;
A plurality of grooves between the plurality of fins,
The refrigerant heat transfer tube, wherein the plurality of groove portions include a first groove portion having a first width and a second groove portion having a second width different from the first width.   The refrigerant heat transfer tube according to claim 1, wherein the second groove portion is periodically provided on the inner peripheral surface.   The refrigerant heat transfer tube according to claim 2, wherein each of the plurality of fins has a height of 0.15 mm or more.   The refrigerant heat transfer tube according to claim 3, wherein each of the plurality of fins has a twist angle of 0 ° to 3 °.   A heat exchanger provided with the heat exchanger tube for refrigerant according to any one of claims 1 to 4.

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