JP2006064311A - Inner helically-grooved heat transfer pipe for evaporator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inner helically-grooved heat transfer pipe for an evaporator not increasing pressure loss even when a carbon dioxide refrigerant including refrigerating machine oil is used, and having superior evaporating heat-transferring performance. <P>SOLUTION: In this inner helically-grooved heat transfer pipe 21 for the evaporator, provided with a spiral groove 22 on its inner face, an outer diameter is 3-7 mm, a height h of a fin is 0.14-0.27 mm, further a helix angle θ is 2-25 degrees, when carbon dioxide including refrigerating machine oil of 0.1-1.5 mass% is used as the refrigerant, or a cross-sectional area S of the groove part is 0.020-0.053 mm<SP>2</SP>when carbon dioxide including refrigerating machine oil of 1.5-5.0 mass%, non-inclusive of 1.5, is used as the refrigerant. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an inner grooved heat transfer tube for an evaporator of a heat exchanger, and more particularly to an inner grooved heat transfer tube for an evaporator using a carbon dioxide refrigerant containing refrigeration oil.

  Conventionally, chlorofluorocarbon solvents have been used for heat exchangers installed in air conditioners, car air conditioners, refrigerators, refrigerators, water heaters, vending machines, etc. Recently, natural refrigerants that are safe, inexpensive, and have little addition to the environment are attracting attention because they are not toxic and flammable.

Carbon dioxide (CO ₂ ), which is one of such natural refrigerants, has higher liquid constant pressure specific heat and liquid thermal conductivity that greatly affect the thermal characteristics, and heat transfer is higher than that of fluorocarbon refrigerants (R22, R134a, R410A). Excellent performance. Also, since carbon dioxide has a low surface tension, bubbles are more likely to be generated than chlorofluorocarbon refrigerants, and nucleate boiling is promoted. Therefore, when carbon dioxide is used as the refrigerant, it is transmitted compared to the case where chlorofluorocarbon refrigerant is used. Thermal performance is improved. Furthermore, since carbon dioxide has a smaller liquid viscosity and density than a chlorofluorocarbon refrigerant, the pressure loss is small. Furthermore, carbon dioxide has a feature that the vapor density and latent heat are large, and the refrigeration effect per unit excluded volume is larger than that of the fluorocarbon refrigerant.

On the other hand, carbon dioxide has a problem of low theoretical performance in a simple cycle of cooling and heating. For this reason, when carbon dioxide is used as a refrigerant, high heat transfer performance is required for the heat transfer tube through which the refrigerant flows. Conventionally, in a heat exchanger using a CO ₂ refrigerant, Since a smooth tube having a low heat transfer coefficient was used (see Non-Patent Document 1), the evaporator had to be enlarged in order to obtain a large evaporation performance. Therefore, an evaporator using an internally grooved heat transfer tube in which a plurality of grooves are formed on the tube inner surface has been proposed (see Patent Document 1). In the evaporator described in Patent Document 1, by providing a plurality of protrusions extending in the longitudinal direction of the tube on the inner wall of the heat transfer tube, the heat transfer area is expanded and the heat transfer rate of the heat transfer tube is improved. .

JP 2003-343492 A Masafumi KATSUYA, 3 others, “A STUDY EVAPORATOR OF CO2 REFRIGERANT CYCLE -Characteristics of heat transfer coefficient and pressure drop on mixing CO2 and oil (PAG)-”, Proceeding of the Asian Conference on Refrigeration and Air Conditioning 2002, November 2011 April 4, A2-3, p. 67-74

However, the conventional techniques described above have the following problems. That is, normally, the CO ₂ refrigerant flowing through the heat transfer tube contains refrigeration oil, which is a lubricant for the compressor, and evaporating performance can be achieved simply by forming a groove on the inner surface of the heat transfer tube. There is a problem that it does not improve. For this reason, sufficient heat transfer performance cannot be obtained even if the internally grooved heat transfer tube used in the conventional chlorofluorocarbon refrigerant is used for CO ₂ refrigerant. Further, in Patent Document 1, since only the relationship between the passage length of the heat transfer tube and the average inner diameter is defined, and the specific groove shape is not defined, the inner surface groove described in Patent Document 1 Similarly, when a CO ₂ refrigerant containing refrigeration oil is used for the attached heat transfer tube, the pressure loss increases and sufficient evaporation performance cannot be obtained. Such an increase in pressure loss is more significant as the refrigeration oil content in the CO ₂ refrigerant is higher.

Furthermore, when using a CO ₂ refrigerant, the pressure in the heat transfer tube increases, so the thickness of the heat transfer tube must be made thicker than when using a fluorocarbon refrigerant. For this reason, when forming a groove | channel in the inner surface of a heat exchanger tube, there also exists a problem that the groove depth is restrict | limited.

  The present invention has been made in view of such problems, and even when a carbon dioxide refrigerant containing refrigeration oil is used, the pressure loss does not increase and the inner surface grooved heat transfer tube for an evaporator has excellent evaporation heat transfer performance. The purpose is to provide.

  An internally grooved heat transfer tube for an evaporator according to the first invention of the present application is an internally grooved heat transfer tube for an evaporator of a heat exchanger that uses carbon dioxide having a refrigerator oil content of 0.1 to 1.5 mass% as a refrigerant. A spiral groove having an outer diameter of 3 to 7 mm and a depth of 0.14 to 0.27 mm is formed on the inner surface of the tube. The angle formed by the direction in which the groove extends is 2 to 25 °.

  In the present invention, the outer diameter is 3 to 7 mm, the groove depth is 0.14 to 0.27 mm, and the angle formed by the straight line parallel to the tube axis direction on the tube inner surface and the direction in which the groove extends is 2 to 25 °. Therefore, when carbon dioxide having a refrigerator oil content of 0.1 to 1.5% by mass is used as a refrigerant, the heat transfer rate can be improved without increasing the pressure loss, and the evaporation heat transfer performance However, an excellent heat transfer tube can be obtained.

The evaporator inner grooved heat transfer tube may have a cross-sectional area of 0.01 to 0.06 mm ² in the cross section perpendicular to the tube axis direction. Thereby, evaporation heat transfer performance can be improved more.

The inner grooved heat transfer tube for an evaporator according to the second invention of the present application is an inner groove for an evaporator of a heat exchanger that uses carbon dioxide having a refrigerator oil content of more than 1.5% by mass and not more than 5.0% by mass as a refrigerant. A heat transfer tube having an outer diameter of 3 to 7 mm, and a spiral groove having a depth of 0.14 to 0.27 mm is formed on the inner surface of the tube, and is perpendicular to the tube axis direction. The area of the groove in the cross section is 0.020 to 0.053 mm ² .

In the present invention, the outer diameter is 3 to 7 mm, the groove depth is 0.14 to 0.27 mm, and the area of the groove in the cross section perpendicular to the direction in which the groove extends is 0.020 to 0.053 mm ^2. When carbon dioxide with a refrigeration oil content of more than 1.5% by mass and less than 5.0% by mass is used as a refrigerant, the heat transfer rate can be improved without increasing the pressure loss, and evaporation A heat transfer tube with excellent heat transfer performance can be obtained.

  In this inner surface grooved heat transfer tube for an evaporator, the angle formed by the straight line parallel to the tube axis direction on the inner surface of the tube and the direction in which the groove extends may be 5 to 20 °. Thereby, evaporation heat transfer performance can be improved more.

According to the present invention, the fin height, torsion angle, and groove cross-sectional area are optimized according to the refrigeration oil content of the CO ₂ refrigerant, so that the pressure loss is increased compared to the conventionally used smooth tube. Without evaporating, it is possible to improve the evaporation heat transfer performance.

  Hereinafter, an internal grooved heat transfer tube for an evaporator according to an embodiment of the present invention will be specifically described with reference to the accompanying drawings. First, an internal grooved heat transfer tube according to the first embodiment of the present invention will be described. Fig.1 (a) is sectional drawing which shows a cross section perpendicular | vertical to a pipe-axis direction in the heat transfer tube with an inner surface groove | channel of this embodiment, FIG.1 (b) is sectional drawing which shows a cross section parallel to a pipe-axis direction. As shown in FIGS. 1A and 1B, the inner surface grooved heat transfer tube 21 of the present embodiment is made of a metal material such as copper or a copper alloy, and a plurality of spiral shapes parallel to each other are formed on the inner surface of the tube. Grooves 22 are formed at regular intervals, and between adjacent grooves 22 are mountain-shaped fins 23. The inner diameter grooved heat transfer tube 1 has an outer diameter of 3 to 7 mm, the depth of the groove 22, that is, the height h of the fin 23 is 0.14 to 0.27 mm, and is parallel to the tube axis direction on the inner surface of the tube. The angle between the straight line and the direction in which the groove 22 extends, that is, the twist angle θ is 2 to 25 °.

This inner surface grooved heat transfer tube 21 is incorporated in an evaporator of a heat exchanger using a CO ₂ refrigerant containing 0.1 to 1.5% by mass of refrigeration oil. FIG. 2 is a view showing a configuration of a heat exchanger including an evaporator in which the inner surface grooved heat transfer tube 21 of the present embodiment is incorporated. As shown in FIG. 2, the heat exchanger 30 evaporates the CO ₂ refrigerant and cools the air, water, and the like by the heat of vaporization at that time, and the CO ₂ refrigerant discharged from the evaporator 31. compressed, the compressor 32 supplies the condenser 33 with a high temperature, a condenser 33 for heating air and water or the like by the heat of the CO ₂ refrigerant, expanding the CO ₂ refrigerant discharged from the condenser 33, low temperature And an expansion valve 34 for supplying to the evaporator 31. Then, the inner surface grooved heat transfer tube 21 of the present embodiment is incorporated in the evaporator 31, CO ₂ refrigerant containing refrigerating machine oil 0.1 to 1.5 wt% is made to flow therein.

  Next, the reason for the numerical limitation in the inner surface grooved heat transfer tube 21 of the present embodiment will be described.

Outer diameter: 3-7mm
When the outer diameter is less than 3 mm, the amount of increase in pressure loss is larger than the amount of increase in heat transfer coefficient, and as a result, the evaporation performance required by evaporation heat transfer performance and pressure loss is reduced. On the other hand, if the outer diameter exceeds 7 mm, the pressure in the heat transfer tube increases, and the thickness of the heat transfer tube must be increased. Therefore, in the inner surface grooved heat transfer tube 21 of the present embodiment, the outer diameter is 3 to 7 mm.

Fin height: 0.14 to 0.27 mm
In the inner surface grooved heat transfer tube 21 of the present embodiment, the heat transfer coefficient increases as the fin height h increases. However, if the fin height h exceeds 0.27 mm, the amount of increase in pressure loss is greater than the amount of increase in heat transfer coefficient, resulting in a decrease in evaporation performance. On the other hand, when the fin height h is less than 0.14 mm, the heat transfer coefficient is not improved. Therefore, in the inner surface grooved heat transfer tube 21 of the present embodiment, the fin height h is set to 0.14 to 0.27 mm.

Twist angle: 2 to 25 °
When a CO ₂ refrigerant having a refrigerator oil content of 0.1 to 1.5 mass% is used, the evaporation performance of the internally grooved heat transfer tube is greatly influenced by the twist angle θ shown in FIG. The twist angle θ is an angle formed by a straight line parallel to the tube axis direction on the inner surface of the tube and a direction in which the groove 22 extends. However, when the twist angle θ is less than 2 °, only the evaporation performance equivalent to that of the conventionally used smooth tube can be obtained. On the other hand, when the twist angle θ exceeds 25 °, the amount of refrigerating machine oil moving to the top of the fin 3 increases, and the top of the fin is covered with the refrigerating machine oil, resulting in a reduction in evaporation performance. Furthermore, when the twist angle θ exceeds 25 °, the pressure loss increases, and thus the effect of improving the evaporation performance cannot be obtained. Therefore, the twist angle in the internally grooved heat transfer tube 21 of the present embodiment is 2 to 25 °.

Refrigerating machine oil content in CO ₂ refrigerant: 0.1 to 1.5% by mass
Usually, the CO ₂ refrigerant flowing through the heat transfer tube contains refrigerating machine oil such as polyalkylene glycol oil. This refrigerating machine oil is a lubricant for compressors, improves the lubricity of moving parts such as bearings and cylinders, and cools moving parts by absorbing heat generated by friction, making the compressor better It is intended to operate. However, when the refrigeration oil content in the CO ₂ refrigerant is less than 0.1% by mass, the evaporation performance of the internally grooved heat transfer tube is determined by the area of the groove portion 22 in the cross section perpendicular to the torsion angle θ and the tube axis direction (hereinafter referred to as “below”). (Referred to as a cross-sectional area of the groove portion) is more influenced by the heat transfer area, and sufficient evaporation performance cannot be obtained even if the twist angle θ is in the above range. When the refrigeration oil content in the CO ₂ refrigerant exceeds 1.5% by mass, the evaporation performance of the internally grooved heat transfer tube is affected by the groove cross-sectional area S rather than the twist angle θ, and the twist angle Even if θ is in the above range, sufficient evaporation performance cannot be obtained. Therefore, the refrigerating machine oil content of the CO ₂ refrigerant to be passed through the inner surface grooved heat transfer tube 21 of the present embodiment is 0.1 to 1.5 mass%.

Moreover, in the inner surface grooved heat transfer tube 21 of the present embodiment, the groove cross-sectional area S is preferably 0.01 to 0.06 mm ² . Thereby, a heat transfer area increases and evaporation heat transfer performance improves more. Note that fins or protrusions may be formed on the outer surface of the internally grooved heat transfer tube 21.

Next, the inner surface grooved heat transfer tube of the second embodiment of the present invention will be described. The internally grooved heat transfer tube of this embodiment is made of a metal material such as copper or a copper alloy, and is a heat exchanger that uses a CO ₂ refrigerant containing refrigeration oil exceeding 1.5 mass% and not exceeding 5.0 mass%. This is a heat transfer tube for an evaporator. Further, the inner surface grooved heat transfer tube of the present embodiment has an outer diameter of 3 to 7 mm as in the inner surface grooved heat transfer tube 21 shown in FIG. 1, and the inner surfaces thereof are parallel to each other. A plurality of spiral grooves are formed at regular intervals, and the adjacent grooves are mountain-shaped fins. The depth of the groove, that is, the fin height h is 0.14 to 0.27 mm, and the groove cross-sectional area S is 0.020 to 0.053 mm ² . As described above, the inner grooved heat transfer tube 21 of the present embodiment and the inner grooved heat transfer tube 21 of the first embodiment described above differ in the refrigeration oil content of the CO ₂ refrigerant used. Note that the internally grooved heat transfer tube of the present embodiment is incorporated in the evaporator of the heat exchanger, and inside thereof is a CO ₂ refrigerant containing refrigeration oil exceeding 1.5 mass% and not more than 5.0 mass%. Washed away.

  Next, the reason for the numerical limitation in the inner surface grooved heat transfer tube of this embodiment will be described.

Diameter: 3-7mm
If the outer diameter is less than 3 mm, the amount of increase in pressure loss is greater than the amount of increase in heat transfer coefficient, resulting in a decrease in evaporation performance. On the other hand, if the outer diameter exceeds 7 mm, the pressure in the heat transfer tube increases, and the thickness of the heat transfer tube must be increased. Therefore, in the inner surface grooved heat transfer tube of the present embodiment, the outer diameter is set to 3 to 7 mm similarly to the inner surface grooved tube 21 of the first embodiment described above.

Fin height: 0.14 to 0.27 mm
Similarly to the inner surface grooved heat transfer tube 21 of the first embodiment described above, the heat transfer coefficient increases as the fin height h increases in the inner surface grooved heat transfer tube of the present embodiment. However, if the fin height h exceeds 0.27 mm, the amount of increase in pressure loss is greater than the amount of increase in heat transfer coefficient, and the evaporation performance is degraded. On the other hand, when the fin height h is less than 0.14 mm, the effect of improving the heat transfer coefficient cannot be obtained. Therefore, in the inner surface grooved heat transfer tube of the present embodiment, the fin height h is set to 0.15 to 0.27 mm.

Groove cross-sectional area: 0.020 to 0.053 mm ²
When a CO ₂ refrigerant having a refrigerating machine oil content of more than 1.5% by mass and 5.0% by mass or less is used, the groove section cross-sectional area S has a great influence on the evaporation performance of the internally grooved heat transfer tube. When the groove cross-sectional area S is less than 0.020 mm ² , the groove width becomes narrow and the refrigerating machine oil overflows from the groove and is covered with the refrigerating machine oil up to the fin top, so that the evaporation performance decreases. On the other hand, if the groove cross-sectional area S exceeds 0.053 mm ² , the number of grooves is reduced, so that the heat transfer area is reduced and the evaporation performance is reduced. Therefore, the groove cross-sectional area S in the internally grooved heat transfer tube of the present embodiment is 0.020 to 0.053 mm ² .

Refrigerating machine oil content in the CO ₂ refrigerant: more than 1.5% by mass and 5.0% by mass or less When the refrigerating machine oil content in the CO ₂ refrigerant is 1.5% by mass or less, the evaporation performance of the heat transfer tube is the groove It becomes more influenced by the twist θ than the cross-sectional area S, and even if the groove cross-sectional area S is in the above range, sufficient evaporation performance cannot be obtained. In addition, when the refrigeration oil content in the CO ₂ refrigerant exceeds 5.0 mass%, the amount of increase in pressure loss is larger than the amount of increase in heat transfer coefficient, and the evaporation performance decreases. Therefore, the refrigerating machine oil content of the CO ₂ refrigerant to be flown into the inner surface grooved heat transfer tube of the present embodiment is more than 1.5 mass% and 5.0 mass% or less.

Moreover, it is preferable that the twist angle θ in the internally grooved heat transfer tube of the present embodiment is 5 to 20 °. When using a CO ₂ refrigerant having a refrigerating machine oil content of 1.5 mass% or less, the effect of the twist angle θ on the evaporation performance is small, but by moving the twist angle θ to 5 to 20 °, it moves to the top of the fin. The amount of refrigerating machine oil is reduced, and the evaporation heat transfer performance can be further improved. Note that fins or protrusions may be formed on the outer surface of the internally grooved heat transfer tube of the present embodiment.

Hereinafter, the effect of the Example of this invention is demonstrated compared with the comparative example which remove | deviates from the scope of the present invention. First, as a first embodiment of the present invention, the inner surface grooved heat transfer tube of Embodiments 1 to 3 having an outer diameter of 6 mm, a fin height h of 0.15 mm, and a twist angle θ of 5 °, 15 ° and 25 °. Was made. Further, as comparative examples of the present invention, the internally grooved heat transfer tubes of Comparative Examples 1 and 2 having an outer diameter of 6 mm, a fin height h of 0.15 mm, and a twist angle θ of 0 ° and 30 ° were prepared. In addition, as for groove part cross-sectional area S in each inner surface grooved heat exchanger tube, Example 1 is 0.034 mm < ² >, Example 2 is 0.034 mm < ² >, Example 3 is 0.033 mm < ² >, Comparative Example 1 is 0.034 mm < ² >. Comparative Example 2 was 0.032 mm ² .

Next, the heat transfer coefficient and pressure loss of the inner surface grooved heat transfer tubes of Examples 1 to 3 and Comparative Examples 1 and 2 were measured. FIG. 3 is a diagram showing a configuration of an apparatus used for measurement of heat transfer coefficient and pressure loss, and FIG. 4 is a diagram showing a configuration of the evaporator. As shown in FIG. 3, the measuring apparatus used in this embodiment includes a compressor 2 to a high temperature by compressing a CO ₂ refrigerant, the gas cooler 4 is a condenser, expands the CO ₂ refrigerant An expansion valve 7 for lowering the temperature and an evaporator 1 as a test part are provided. A preheater 8 and a superheater 9 for heating the CO ₂ refrigerant are respectively provided at the entrance and exit of the evaporator 1. An oil separator 3a that separates refrigeration oil in the refrigerant is provided at the outlet of the compressor 2, and further, pulsation of the refrigerant is eliminated at the inlet of the compressor 2 and the outlet of the gas cooler 4, respectively. Accumulator 5a and 5b are provided.

In this example, polyalkylene glycol oil was used as the refrigerating machine oil for the compressor 2. Then, the refrigeration oil in the CO ₂ refrigerant is separated by the oil separator 3 b provided at the outlet of the evaporator 1, and the separated refrigeration oil is cooled by the oil cooler 10, and then passes through the oil pump 11 and the flow meter 12. Then, the refrigerating machine oil content in the portion immediately before the evaporator 1 was adjusted by adding it again into the CO ₂ refrigerant. Incidentally, the refrigerating machine oil content of CO ₂ in the refrigerant, the CO ₂ refrigerant is collected in the sampling port 14 immediately before the preheater 8, was determined by measuring its mass by a precision analytical balance. Further, while supplying heat source water to the evaporator 1, cooling water was supplied to the gas cooler 4 and the oil cooler 10. Further, a direct current was supplied to the preheater 8 and the superheater 9.

  In this example, a micro motion type mass flow meter 6 with an accuracy of ± 0.4% was provided between the gas cooler 4 and the expansion valve 7, and the flow rate of the refrigerant was measured by this flow meter 6. Further, between the evaporator 1 and the superheater 9, between the oil separator 3b and the compressor 2, between the compressor 2 and the gas cooler 4, between the gas cooler 4 and the accumulator 5b, and the flow meter 6 and expansion. Refrigerant mixing chambers 18a to 18e are provided between the valves 7 respectively. The temperature and pressure of the refrigerant are respectively determined by the 0.5 mm chromel-alumel-coated thermocouples 19a to 19e and the pressure transducers 20a to 20e having an accuracy of 0.02 MPa provided in the refrigerant mixing chambers 18a to 18e. It was measured. At that time, the thermocouples 19a to 19e were calibrated in advance so that the error was within ± 0.05K.

As shown in FIG. 4, the evaporator 1 has three duplex tubes in which the inner-grooved heat transfer tube of the example or the comparative example is arranged inside the outer tube having a diameter of 18 mm and an inner diameter of 12 mm. Tubes 15a to 15c are connected in series. These double tubes 15a to 15c have a length of 0.688 m and an effective heat transfer length of 0.5 m. Then, CO ₂ refrigerant was passed through the heat transfer tubes of Example 1 or Comparative Example 1, and cooling water was passed between these heat transfer tubes and the outer tube. At that time, the flow direction of the CO ₂ refrigerant and the flow direction of the cooling water were made opposite to each other.

  The evaporator 1 is provided with a heat source 13, and the flow rate of the cooling water was measured with a gear type flow meter with an accuracy of ± 0.5% provided in the heat source 13. Further, heat source water mixing chambers 16a to 16f are provided at both ends of the double pipes 15a to 15c, respectively, and the temperature of the cooling water is 2 outside diameters installed in the heat source water mixing chambers 16a to 16f. Measured with a resistance thermometer of 0 mm. At that time, each resistance thermometer was calibrated so that the error was within ± 0.02K. Furthermore, the pressure difference between the double tubes 15a to 15c was measured by differential pressure transducers 17a to 17d with an accuracy of ± 0.25%. Furthermore, the temperature of the outer wall of each heat transfer tube was measured by placing copper-constantan thermocouples formed of a copper wire and a constantan wire having an outer diameter of 0.1 mm on the top, bottom, left and right of the outer surface of the heat transfer tube. At that time, these thermocouples were calibrated so that the error was within ± 0.05K. Furthermore, a refrigerant mixing chamber 18a is provided in the vicinity of the refrigerant outlet of the evaporator 1, and the temperature and pressure of the refrigerant were measured by a thermocouple 19a and a pressure converter 20a provided in the refrigerant mixing chamber 18a.

The temperature T _wi of the inner wall of each heat transfer tube was determined from the following formula 1.

In the above formula 1, T _wo is the temperature of the outer wall of the heat transfer tube, λ _w is the heat conductivity of the heat transfer tube, d _wi and d _wo are the inner diameter and outer diameter of the heat transfer tube, respectively, and Q is 2 The thermal conductivity of the heavy pipes 15a to 15c, and Δz is the effective heat transfer length of the double pipes 15a to 15c.

  Further, the total heat balance, that is, the ratio of the increase in the amount of heat due to the cooling water to the loss of the amount of heat due to the refrigerant is less than 5%, and the thermodynamic properties and transfer performance of carbon dioxide are REFPROP Ver. 7.0 (M. O. McLinden, 2 others, 2002, Peskin AP, NIST thermodynamic properties of reactants and refrigerant mixtures database (REFPROP), Ver. 7.0) was used for calculation.

  Further, the local heat transfer coefficient α of the heat transfer tube was obtained from the following formula 2.

Here, _{T b} in the above equation 2 is the temperature of the CO ₂ refrigerant during normal pressure in double tube 15a to 15c. Further, q is a heat flux in the double tubes 15a to 15c, and is obtained by the following mathematical formula 3.

  Note that the uncertainty of the local heat transfer coefficient α obtained by Equation 2 is less than 10%, and the uncertainty of the heat flux q obtained by Equation 3 is less than 6%.

From the heat transfer coefficient and pressure loss of each internally grooved tube measured by the above-described method with the refrigerating machine oil content of 1.0 mass%, the refrigerant pressure of 4 MPa, and the refrigerant flow rate of 360 kg / m ² s, The performance ratio defined by 4 was determined. This performance ratio is obtained by evaluating the evaporation performance of the internally grooved tube with respect to the evaporation performance of the smooth tube. The heat transfer coefficient of the internally grooved tube and the heat transfer coefficient of the smooth tube are the same value, and the internal groove When the pressure loss of the attached tube and the pressure loss of the smooth tube are the same value, that is, when the evaporation performance of the inner grooved tube and the evaporation performance of the smooth tube are the same, the value of the performance ratio is 1. At that time, the heat transfer coefficient and the pressure loss of the smooth tube are the same as those of the above-described embodiment and comparative example inner surface grooved heat transfer tube using a smooth tube having an outer diameter of 6 mm with no grooves formed on the inner surface. The value measured according to the conditions was used. The above results are summarized in Table 1 below. Table 1 below also shows the performance ratio of a smooth tube having an outer diameter of 6 mm as a conventional example.

  As shown in Table 1, the inner surface grooved heat transfer tubes of Examples 1 to 3 manufactured within the scope of the present invention have a performance ratio exceeding 1, and the evaporation performance is improved as compared with the conventional smooth tube. It was. On the other hand, the inner grooved heat transfer tube of Comparative Example 1 whose twist angle θ is smaller than the range of the present invention has a performance ratio of 0.92, and the inner groove of Comparative Example 2 whose twist angle θ is larger than the range of the present invention. The attached heat transfer tube had a performance ratio of 0.94, both of which were less superior than the smooth tube.

Next, a second embodiment of the present invention, an outer diameter of 6 mm, fin height h is 0.18 mm, the twist angle θ is 25 °, the groove cross-sectional area S is respectively 0.026 mm ² and 0.039 mm ² The inner surface grooved heat transfer tubes of Examples 4 and 5 were prepared. As a comparative example of the present invention, a comparative example 3 having an outer diameter of 6 mm, a fin height h of 0.18 mm, a twist angle θ of 25 °, and a groove section area S of 0.019 mm ² and 0.064 mm ² , respectively. And 4 internally grooved heat transfer tubes. Then, for these Examples 4 and 5 and Comparative Examples 3 and an inner surface grooved heat transfer tube 4, the refrigerating machine oil content using CO ₂ refrigerant is 3.0 mass%, the above-described first embodiment except that The performance ratio was obtained in the same manner as in Example 1. The results are summarized in Table 2 below. In Table 2, the performance ratio of a smooth tube having an outer diameter of 6 mm is also shown as a conventional example.

  As shown in Table 2, the inner surface grooved heat transfer tubes of Examples 4 and 5 manufactured within the scope of the present invention have a performance ratio exceeding 1.00, and the evaporation performance is improved over the conventional smooth tube. Was. On the other hand, the internally grooved heat transfer tube of Comparative Example 3 in which the value of the groove cross-sectional area S is smaller than the range of the present invention has a performance ratio of 0.95, which is lower than the conventional smooth tube. In addition, the inner surface grooved heat transfer tube of Comparative Example 4 in which the value of the groove section sectional area S was larger than the range of the present invention had a performance ratio of 0.59, and only a performance equivalent to that of a smooth tube was obtained.

Next, as a third embodiment of the present invention, an outer diameter is 6 mm, a twist angle θ is 25 °, a plurality of internally grooved heat transfer tubes are manufactured by changing the fin height h, and the refrigerator oil content is 1. The CO ₂ refrigerant of 0% by mass was used, and the performance ratio was determined by the same method as in the first example described above. In addition, the groove part sectional area S of each internally grooved heat transfer tube was 0.02 to 0.06 mm ² . FIG. 5 is a graph showing the relationship between the fin height h and the performance ratio, with the horizontal axis representing the fin height h and the vertical axis representing the performance ratio. As shown in FIG. 5, the performance ratio of the internally grooved heat transfer tube increased as the fin height h increased, but decreased when the fin height h exceeded about 2.0 mm. This is because when the fin height h exceeds about 2.0 mm, the rate of increase in pressure loss is greater than the rate of increase in heat transfer coefficient. However, the inner grooved heat transfer tube having a fin height h of 0.14 to 0.27 mm within the range of the present invention has a performance ratio exceeding 1, and the evaporation performance is improved over the conventional smooth tube.

Next, as a fourth embodiment of the present invention, the outer diameter is 6 mm, the fin height h is 0.15 mm, the groove cross-sectional area S is 0.034 mm ² , and the torsion angle θ is changed to change a plurality of internally grooved heat transfer tubes. Was made. For these internally grooved heat transfer tubes, a CO ₂ refrigerant having a refrigerating machine oil content of 1.0 mass% and 3.0 mass% is used, and the other methods are the same as in the first embodiment. The performance ratio was determined.

  FIG. 6 is a graph showing the relationship between the twist angle θ and the performance ratio with the twist angle θ on the horizontal axis and the performance ratio on the vertical axis. As shown in FIG. 6, when the refrigerating machine oil content is 1.0 mass%, the performance ratio becomes maximum when the twist angle θ is about 10 to 15 °, and the performance becomes smaller as the twist angle θ becomes smaller or larger than this. The ratio declined. Further, when the twist angle θ is out of the range of the present invention and becomes smaller than 2 °, the performance ratio becomes smaller than 1 and the superiority to the smooth tube is lost. Similarly, when the twist angle θ is out of the range of the present invention and becomes larger than 25 °, the performance ratio becomes smaller than 1 and the superiority to the smooth tube is lost. On the other hand, when the refrigerating machine oil content was 3.0 mass%, when the twist angle θ was smaller than 5 °, the performance ratio was smaller than 1, and the superiority over the smooth tube was lost. Similarly, when the twist angle θ is out of the range of the present invention and becomes larger than 20 °, the performance ratio becomes smaller than 1 and the superiority to the smooth tube is lost.

Next, as a fifth embodiment of the present invention, the outer diameter is 6 mm, the fin height h is 0.18 mm, the twist angle θ is 25 °, and the groove cross-sectional area S is changed to produce a plurality of internally grooved heat transfer tubes. did. For these internally grooved heat transfer tubes, a CO ₂ refrigerant having a refrigerating machine oil content of 1.0 mass% and 3.0 mass% is used, and the other methods are the same as in the first embodiment. The performance ratio was determined.

FIG. 7 is a graph showing the relationship between the groove section sectional area S and the performance ratio, with the groove section sectional area S on the horizontal axis and the performance ratio on the vertical axis. As shown in FIG. 7, when the refrigeration oil content is 3.0% by mass, the groove section sectional area S is about 0.03 to 0.04 mm ² , and the performance ratio becomes maximum, and the groove section sectional area S is larger than this. The performance ratio decreased as it became smaller or larger. Furthermore, when the groove cross-sectional area S is out of the scope of the present invention and becomes smaller than 0.02 mm ² , the performance ratio becomes smaller than 1 and the superiority to the smooth tube is lost. Similarly, when the groove cross-sectional area S is out of the scope of the present invention and becomes larger than 0.053 mm ² , the performance ratio becomes smaller than 1 and the superiority to the smooth tube is lost. On the other hand, when the refrigerating machine oil content is 1.0% by mass, the performance ratio does not change greatly even if the groove cross-sectional area S is changed, but the performance ratio becomes maximum when the groove cross-sectional area S is about 0.03 mm ^2. It was.

Next, as a sixth embodiment of the present invention, there is provided an internally grooved heat transfer tube having an outer diameter of 6 mm, a fin height h of 0.15 mm, a twist angle θ of 15 °, and a groove section area S of 0.034 mm ^2. Produced. And about this inner surface grooved heat transfer tube (Example) and a smooth tube (conventional example) having an outer diameter of 6 mm, a CO ₂ refrigerant having a different refrigeration oil content is used. The performance ratio was determined by the same method and conditions.

FIG. 8 is a graph showing the relationship between the refrigeration oil content and the heat transfer performance, with the horizontal axis representing the amount of refrigerating machine oil in the CO ₂ refrigerant and the vertical axis representing the heat transfer performance reduction rate. In addition, the heat-transfer performance fall rate shown in FIG. 8 is a value when the heat-transfer performance in case the refrigerator oil content in the heat transfer tube with an inner surface groove of an Example is 0% is set to 100%. As shown in FIG. 8, the heat transfer performance reduction rate when the refrigeration oil content is increased in the inner surface grooved heat transfer tube of the embodiment is larger than that of the smooth tube of the conventional example, but the heat transfer performance is in the entire range. It was higher than the conventional smooth tube.

(A) is sectional drawing which shows a cross section perpendicular | vertical to a pipe-axis direction in the heat transfer tube with an inner surface groove | channel of the 1st Embodiment of this invention, (b) is sectional drawing which shows a cross section parallel to a pipe-axis direction. . It is a figure which shows the structure of the heat exchanger provided with the evaporator with which the heat transfer tube with an inner surface groove | channel of 1st Embodiment of this invention was integrated. It is a figure which shows the structure of the apparatus used for the measurement of a heat transfer rate and a pressure loss. It is a figure which shows the structure of the evaporator shown in FIG. It is a graph which shows the relationship between fin height h and a performance ratio by taking fin height h on a horizontal axis and taking a performance ratio on a vertical axis | shaft. FIG. 5 is a graph showing the relationship between the twist angle θ and the performance ratio, with the twist angle θ on the horizontal axis and the performance ratio on the vertical axis. It is a graph which shows the relationship between groove part cross-sectional area S and a performance ratio, taking a groove part cross-sectional area S on a horizontal axis and taking a performance ratio on a vertical axis | shaft. Take the refrigeration oil of CO ₂ refrigerant in the horizontal axis, the vertical axis represents the heat transfer performance degradation rate is a graph showing the relationship between the refrigerating machine oil content and the heat transfer performance.

Explanation of symbols

1, 31; Evaporator 2, 32; Compressor 3a, 3b; Oil separator 4; Gas cooler 5a, 5b; Accumulator 6, 12; Flow meter 7, 34; Expansion valve 8; Preheater 9; Oil cooler 11; Oil pump 13; Heat source 14; Sampling port 15a-15c; Double pipe 16a-16f; Heat source water mixing chamber 17a-17d; Differential pressure converter 18a-18f; Refrigerant mixing chamber 19a-19f; 20a to 20f; pressure transducer 21; inner surface grooved heat transfer tube 22; groove 23; fin 30; heat exchanger 33; condenser h; fin height S;

Claims (4)

An internal grooved heat transfer tube for an evaporator of a heat exchanger that uses carbon dioxide having a refrigerating machine oil content of 0.1 to 1.5% by mass as a refrigerant, having an outer diameter of 3 to 7 mm, Is formed with a spiral groove having a depth of 0.14 to 0.27 mm, and an angle formed between a straight line parallel to the tube axis direction on the inner surface of the tube and a direction in which the groove extends is 2 to 25 °. An internally grooved heat transfer tube for an evaporator. ^{2. The} inner grooved heat transfer tube for an evaporator according to claim 1, wherein an area of the groove portion in a cross section perpendicular to the tube axis direction is 0.01 to 0.06 mm ² . An internal grooved heat transfer tube for an evaporator of a heat exchanger that uses carbon dioxide having a refrigerator oil content of more than 1.5 mass% and not more than 5.0 mass% as a refrigerant, and has an outer diameter of 3 to 7 mm A spiral groove having a depth of 0.14 to 0.27 mm is formed on the inner surface of the tube, and the area of the groove in a cross section perpendicular to the tube axis direction is 0.020 to 0.053 mm ^2. An internally grooved heat transfer tube for an evaporator, characterized in that 4. The inner grooved heat transfer tube for an evaporator according to claim 3, wherein an angle formed by a straight line parallel to the tube axis direction on the inner surface of the tube and a direction in which the groove extends is 5 to 20 degrees.

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