CN1526061A - Refrigeration cycle device - Google Patents

Abstract

A refrigerating cycle apparatus including a compressor of compressing carbon dioxide (CO2) refrigerant, a radiator of cooling the refrigerant pressurized by the compressor, a pressure reducing valve that is arranged more downstream of the radiator along the refrigerant flow and depressurizes and expands the cooled refrigerant, and an evaporator that heats the refrigerant depressurized by the pressure reducing valve, wherein the refrigerant flow path of the radiator and/or said evaporator is has a diameter of 1 mm or less; and a refrigeration lubricant of which main component is a polar oil miscible with the CO2 refrigerant is utilized.

Description

Refrigeration cycle device

technical field

The present invention relates to refrigeration cycle devices such as refrigerators and air conditioners using carbon dioxide (hereinafter referred to as CO ₂ ) as a main refrigerant.

Background technique

At present, fluorocarbons containing chlorine but not hydrogen are used as refrigerants in refrigeration cycle equipment such as air conditioners, refrigerators, freezers, vending machines, heat pump water heaters, etc., from the viewpoint of stable physical properties and easy handling. (hereinafter referred to as CFC) and fluorocarbons containing chlorine and hydrogen (hereinafter referred to as HCFC).

However, since CFC refrigerants and HCFC refrigerants have the property of promoting the destruction of the ozone layer, it has been proposed to use fluorinated hydrocarbons (hereinafter referred to as HFCs) containing hydrogen in molecular structure without chlorine as alternative refrigerants. In addition, since CFC refrigerants, HCFC refrigerants, and HFC refrigerants have the property of promoting global warming, it has been proposed to use natural refrigerants that have little influence on global warming as alternative refrigerants.

However, even with natural refrigerants, hydrocarbons (hereinafter referred to as HC) are highly flammable, so there is a risk of ignition and explosion, and because ammonium refrigerants are toxic, there is a problem of danger in the event of leakage. , and thus, the use of nonflammable, nontoxic, and low-cost _CO2 refrigerants is under investigation.

The refrigeration cycle device using this CO ₂ refrigerant has a structure that uses a high-pressure side line in the supercritical region because the critical temperature of CO ₂ refrigerant is 31°C, and a general refrigeration cycle device compresses the refrigerant to increase the pressure. Compressor, if necessary, four-way valve, heat radiator for cooling refrigerant, pressure reducer such as capillary tube for decompressing refrigerant, expansion valve, etc., evaporator for evaporating and vaporizing refrigerant, etc. The refrigerant circulates inside it for cooling or heating.

As the heat exchanger used in the radiator and evaporator of the refrigeration cycle device using _CO2 refrigerant, a heat exchanger called a micro tube heat exchanger is adopted. The micro tube heat exchanger is composed of flat tubes with a plurality of through holes (refrigerant flow paths) formed inside, and fins for increasing the heat transfer area between the flat tubes and the external fluid (such as air) . The cross-sectional shape of the through hole is circular, and the diameter of the hole is about 1mm.

As refrigerating machine oil for CO ₂ refrigerant, mineral oil is mostly used from the viewpoint of excellent lubricity (reference document: "Development and Experiment with a Hermetic CO ₂ Compressor" by BEFagerli, Proceeding of the 1996 International Engineering Conference at Purdue, 229-234 ).

However, since mineral oil is a non-polar oil, it is immiscible with CO ₂ refrigerant, and the refrigerating machine oil discharged from the compressor into the cycle together with the refrigerant becomes oil in the refrigerant flow path of the radiator and evaporator. Flow in the shape of drops or as an oil film covering the inner wall of the pipe in a ring shape. As a result, heat transfer is hindered and pressure loss is increased, which causes an increase in the size of the heat exchanger and a decrease in efficiency. Especially in evaporators in the non-supercritical region, the heat transfer due to refrigeration oil is significantly reduced.

In addition, when using a microtube heat exchanger, since the refrigerant flow path is a very thin heat transfer tube with a diameter of about 1 mm, it is different from the refrigerant with a cross-sectional area of about 5 mm in diameter that is conventionally used for HFC refrigerants. Compared with the flow path, the present inventors have found that the oil film and oil droplets formed on the inner wall of the tube have a large effect on heat transfer obstruction and increase in pressure loss. Its content is detailed below.

6 and 7 are characteristic diagrams of evaporating capacity and pressure loss in an evaporator using a flat tube having a microtube having an equivalent diameter of 1.2 mm as a refrigerant flow path, respectively. For _CO2 refrigerants, non-polar oils that are immiscible, that is, mineral oils, are used as refrigeration oil. The horizontal axis represents the oil circulation rate obtained by dividing the refrigerant circulation amount by the oil (refrigeration machine oil) circulation amount. When immiscible oil is used, it can be seen that by increasing the oil circulation rate, the heat transfer rate decreases significantly and the pressure loss increases significantly.

Calculated values obtained from various experimental data including the data shown in Fig. 6 and Fig. 7 according to the following correlation formula, the evaporative heat transfer rate and pressure of the flat tube when circulating with oil and CO ₂ refrigerant are good. The value of the loss remains the same.

That is, the evaporation heat transfer rate is a correlation formula of the evaporation heat transfer rate in the tube. The commonly known Lyu-Winterton correlation formula is corrected by taking into account the parameter Kfh that affects the nucleate boiling heat transfer rate. The convective heat transfer rate is corrected by changing the physical property value of the liquid to the value of the mixture of the refrigerant and the oil.

(Formula 1)

h＝a·{(E·h1) ² +(S·h pool) ² } ^0.5 (Formula 1)

(Formula 2)

h pool＝55·Pr ^0.12 ·{-logPr ^-0.55 ·M ^-0.5 ·q ^0.67 ·Kfh (Formula 2)

Among them, h is the evaporation heat transfer rate, a is a constant, h1 is the forced convection heat transfer rate when only liquid layer flow is considered, h pool is the boiling heat transfer rate, E and S are the parameters of forced convection and nucleate boiling respectively .

Also, for the pressure loss, as a correlation expression of the two-phase flow pressure loss, correction is generally performed by changing the physical property value of the liquid to the value of the mixture of the refrigerant and the oil in the known Lockhart-Martnelli correlation expression.

(Formula 3)

ΔP＝φ ² ·ΔPf·KfP (Formula 3)

Among them, φ is the parameter of Martnelli, ΔPf is the pressure loss when only considering the liquid phase flow, and Kfp is the correction parameter.

Fig. 8 is a characteristic diagram (representative example) of the evaporation heat transfer rate and pressure loss of the CO ₂ refrigerant obtained from the above correlation formula. The horizontal axis represents the oil circulation rate obtained by dividing the refrigerant circulation amount by the oil circulation amount. Also, the vertical axis is the percentage of the value obtained by dividing the ratio of the pressure loss when the oil circulation rate is 0% as 100 by the ratio of the heat transfer rate when the oil circulation rate is 0% as 100 . That is, when the oil circulation rate is 0%, it is 100, and as the oil circulation rate increases, the lower the heat transfer rate and/or the larger the pressure loss increase, the smaller the value becomes.

FIG. 8 also shows the characteristics of thin tubes with different hydraulic equivalent diameters De. The smaller the hydraulic equivalent diameter De is, the greater the decrease in heat transfer rate and/or the greater the increase in pressure loss.

It will be further discussed in detail below. Figure 9 shows the relationship between the (heat transfer rate/pressure loss) reduction rate and the hydraulic equivalent diameter De when the oil circulation rate increases from 0 to 4%. When the hydraulic equivalent diameter De is further reduced from about 1 mm, it can be seen that the (heat transfer rate/pressure loss) reduction rate increases sharply. That is, if the hydraulically equivalent diameter De is further reduced from about 1 mm, due to the influence of immiscible oil, an oil film is formed on the inner wall of the tube or oil droplets are scattered in the tube, which greatly reduces the heat transfer rate and/or increases the pressure loss. get bigger.

Contents of the invention

The present invention solves the above-mentioned problems of the conventional refrigeration cycle, and an object of the present invention is to provide a small-sized, high-efficiency refrigeration cycle apparatus using CO ₂ refrigerant.

The refrigerating cycle device of the first technical solution of the present invention includes: a compressor for compressing carbon dioxide (CO ₂ ) refrigerant; a heat radiator for cooling the refrigerant boosted in the compressor; a refrigerant downstream side of the heater, a pressure reducer that decompresses and expands the cooled refrigerant; and an evaporator that heats the refrigerant decompressed by the pressure reducer,

The refrigerant flow path of the radiator and/or the evaporator is a thin tube of 1 mm or less,

A refrigerating machine oil composed mainly of a polar oil compatible with the CO ₂ refrigerant is used.

According to a second aspect of the present invention, in the refrigeration cycle apparatus according to the first aspect of the present invention, the refrigerant flow path is a plurality of through-holes formed in a flat tube.

According to a third aspect of the present invention, in the refrigerating cycle apparatus according to the first aspect of the present invention, polyether oil, polyester oil, polyglycol oil, polycarbonate oil, or a mixed oil of these oils is used as the refrigerating machine oil. .

According to a fourth aspect of the present invention, in the refrigeration cycle apparatus according to the first aspect of the present invention, the amount of water contained in the refrigerating machine oil is 100 ppm or less.

According to a fifth aspect of the present invention, in the refrigerating cycle apparatus according to the second aspect of the present invention, the through-holes are small holes with inner surface grooves formed with grooves on their inner surfaces.

According to a sixth technical solution of the present invention, in the refrigerating cycle device according to the fifth technical solution of the present invention, the groove shape of the small hole with inner grooves is trapezoidal.

A brief description of the drawings

Fig. 1 is a schematic configuration diagram of a refrigeration cycle apparatus in Example 1 of the present invention.

Fig. 2 is a structural diagram of a heat exchanger used in Example 1 of the present invention.

Fig. 3 is a structural view of the heat transfer tube used in the heat exchanger according to Embodiment 1 of the present invention.

Fig. 4 is an enlarged structural view of a main part of a heat transfer tube of a heat exchanger used in a refrigerating cycle apparatus according to Example 2 of the present invention.

Fig. 5 is an enlarged structural view of a main part of a heat transfer tube of a heat exchanger used in a refrigeration cycle apparatus according to Example 3 of the present invention.

6 is a characteristic diagram of evaporating capacity with respect to an oil circulation rate in an evaporator using a flat tube having a microtube having an equivalent diameter of 1.2 mm as a refrigerant flow path.

Fig. 7 is a characteristic diagram of pressure loss with respect to oil circulation rate in an evaporator using a flat tube having a microtube having an equivalent diameter of 1.2 mm as a refrigerant flow path.

Fig. 8 is a characteristic diagram of different thin tubes with respect to the hydraulic equivalent diameter De.

Fig. 9 is a graph showing the relationship between the decrease rate of (heat transfer rate/pressure loss) and the hydraulic equivalent diameter De when the oil circulation rate increases from 0 to 4%.

Fig. 10 is a graph showing the tensile strength characteristics of PET resin after the test in the case of an autoclave test.

Fig. 11 is a graph showing the elongation characteristics of the PET resin after the test in the case of the autoclave test.

(explanation of symbols)

1, 31, 41 flat tube

2 through holes

3 heat exchangers

9 heat sink

11 compressors

12 Radiator

13 pressure reducer

14 evaporator

15 oil separator

16 auxiliary heat exchanger

17 pressure reducers

32, 42 small hole with inner groove

Detailed ways

Embodiments of the present invention will be described below with reference to the drawings.

(Example 1)

Fig. 1 is a schematic configuration diagram of a refrigeration cycle apparatus in Example 1 of the present invention. Figure 2 is a block diagram of the heat exchanger used in the radiator and evaporator. Moreover, FIG. 3 is a block diagram of a heat transfer tube used in the above-mentioned heat exchanger.

1 to 3, 11 is a compressor, 12 is a heat radiator formed in a flat tube 1 and has a plurality of through holes 2 as a refrigerant flow path, 13 is a pressure reducer, and 14 is formed in the An evaporator with a plurality of small through-holes 2 in the flat tube 1 as a refrigerant flow path forms a closed circuit by connecting these components through piping, and constitutes a refrigeration system in which CO ₂ refrigerant circulates in the direction of the arrow in the figure. cycle.

In addition, an auxiliary heat exchanger 16 is provided for the refrigerant flow path from the outlet of the heat radiator 12 to the inlet of the pressure reducer 13 , that is, the heat release side refrigerant flow path and the refrigerant flow path from the evaporator 14 . Heat exchange is performed in the evaporating side refrigerant flow path that is the refrigerant flow path from the outlet of the compressor 11 to the suction part of the compressor 11 .

Moreover, an oil separator 15 is provided between the compressor 11 and the radiator 12 . The refrigerating machine oil separated by the oil separator 15 returns to the compressor 11 through the auxiliary path 18 connected to the compressor 11 through the sub pressure reducer 17 . The refrigerating machine oil not separated by the oil separator 15 flows to the radiator 12 and the evaporator 14 of the refrigerating cycle together with the refrigerant.

As shown in FIGS. 2 and 3 , heat exchangers 3 for radiators and evaporators are laminated with a plurality of plate-shaped through-holes 2 penetrating in the longitudinal direction at approximately predetermined intervals in the plate-shaped thickness direction. The flat tube 1 (heat transfer tube). Both ends in the longitudinal direction of the plate are inserted into a pair of header pipes 4 and 5 . In order to cope with the high pressure in the supercritical state and improve the heat transfer rate in the tube, the diameter of the through hole 2 is reduced to about 1 mm, and its cross-sectional shape is circular.

Also, a partition plate 6 for dividing the interior into a plurality of header pipes 4 and 5 is provided in the longitudinal direction of the header pipes. A refrigerant inlet 7 for introducing refrigerant to the heat exchanger 3 is provided on any one of the pair of header pipes 4 and 5, and a refrigerant outlet 8 for flowing refrigerant out of the heat exchanger 3 is provided on the pair of header pipes 4 and 5. One of the. A plurality of plate-shaped flat tubes 1 are arranged at substantially equal intervals in the thickness direction, and fins (corrugated fins) 9 for increasing the heat transfer area with external fluid (such as air) are provided between the flat tubes 1 .

The refrigerant is CO ₂ refrigerant, and the refrigerating machine oil is polyglycol oil (PAG oil), which is polar oil, and the water content in the oil is adjusted to be below 100PPM.

Next, the operation of the refrigeration cycle apparatus having the above configuration will be described.

The CO ₂ refrigerant compressed by the compressor 11 is in a state of high temperature and high pressure and is introduced into the heat radiator 12 . In the heat radiator 12, when the CO ₂ refrigerant is in a supercritical state, no matter it is in the gas-liquid two-phase state, it will release heat to the medium such as air and water, and at the outlet of the heat radiator 12 from the auxiliary heat exchanger 16 Further cooling in the heat release side refrigerant passage between the inlets of the decompressor 13 . The pressure is reduced in the pressure reducer 13 , and it is introduced into the evaporator 14 in a low-pressure gas-liquid two-phase state. In the evaporator 14, heat is absorbed from the air, etc., and becomes gaseous in the evaporating-side refrigerant flow path between the outlet of the evaporator 14 of the auxiliary heat exchanger 16 and the suction part of the compressor 11, and then sucked into the refrigerant for compression. Machine 11.

By repeating this cycle, a heating action by heat release from the radiator 12 and a cooling action by heat absorption by the evaporator 14 are performed. Thus, in the auxiliary heat exchanger 16, the higher temperature CO ₂ refrigerant flowing from the radiator 12 to the pressure reducer 13 and the lower temperature CO ₂ refrigerant flowing from the evaporator 14 to the compressor 11 are separated. heat exchange. In this way, since the _CO refrigerant flowing out of the radiator 12 is further cooled and decompressed in the pressure reducer 13, the enthalpy at the inlet of the evaporator 14 is reduced, and the enthalpy difference between the inlet and outlet of the evaporator 14 Increase, increase heat absorption capacity (cooling capacity).

Next, the operation of the heat exchanger 3 functioning as the radiator 12 will be described in detail. As shown by the solid line arrow in Figure 2, the refrigerant flows from the refrigerant inlet 7 into the space above the partition plate 6 in the main pipe 4 in a supercritical state, (1) through the space above the partition plate 6 inserted into the main pipe 4 The through holes 2 of a plurality of flat tubes 1 flow into the upper part of the main pipe 5, (2) turn back from the upper part of the main pipe 5 through the middle part (the upper space higher than the partition plate 6), (3) pass through the small through holes of the flat tubes 1 2 flows into the middle part of the main pipe 4, (4) turns back from the middle part of the main pipe 4 through the lower part, (5) flows into the lower part of the main pipe 5 (the lower space than the partition plate 6) through the through hole 2 in the flat tube 1, and The low temperature flows out from the refrigerant outlet 8.

In this embodiment, polyglycol oil (PAG oil), which is a polar oil, is used, so the refrigerating machine oil discharged from the compressor in the cycle together with the CO ₂ refrigerant is dissolved in the CO ₂ refrigerant. As a result, even if the refrigerant flow path is made into a thin tube of 1 mm or less, an oil film acting as a thermal resistance is formed on the inner wall surface of the tube through the small hole 2 of the flat tube 1 constituting the refrigerant flow path of the radiator without reducing the temperature. The heat transfer performance can effectively utilize the high heat transfer rate of the _CO2 refrigerant having a supercritical state. Also, since no oil film is formed on the inner wall surface of the tube passing through the small hole 2, and oil droplets do not flow, no increase in pressure loss occurs. Thereby, the heat transfer rate in the tube is very high, performance degradation due to pressure loss can be suppressed, and a small and high-performance heat radiator can be produced.

On the evaporator side, _CO2 refrigerant in a low-pressure gas-liquid two-phase state flows into the through holes 2 of the flat tubes 1 constituting the refrigerant flow path of the evaporator together with the refrigerating machine oil, and absorbs heat from the air, etc. While evaporating, it becomes a circular spray flow and flows. In this way, although the heat transfer rate on the inner wall of the heat transfer tube has a great influence on the overall performance, in this embodiment, as in the case of the radiator, because polyglycol oil (PAG oil) dissolved in _CO2 refrigerant is used ), so even if the refrigerant flow path is made into a thin tube of 1 mm or less, no oil film acting as thermal resistance is formed on the inner wall surface of the flat tube 1 through the small hole 2, so the evaporator does not cause a drop in heat transfer and The increase in pressure loss can make the evaporator smaller and more efficient.

In the above description, the use of polyglycol oil (PAG oil) as a polar oil has been described, but other polyol ester oils (POE oils), polyvinyl ether oils, polycarbonate oils or these The mixed oil of oil, as a polar oil, can obtain the same effect because of its high solubility to CO ₂ refrigerant.

Also, in this embodiment, since the water content in the refrigerating machine oil is adjusted to be 100 ppm or less, when polar oil is used, the refrigerating machine oil is not degraded by hydrolysis and reliability is not impaired.

By adjusting the amount of moisture contained in the refrigerating machine oil to 100 ppm or less, the amount of moisture immersed in the refrigerating cycle is adjusted to 100 ppm or less, so that the following effects can be achieved.

The inventors of the present invention confirmed new facts and effects obtained by the following methods through the following experiments. _CO2 refrigerant, PET (polyethylene terephthalate) resin film, and refrigerating machine oil containing 200ppm of moisture were enclosed in an autoclave container, and autoclaved at a temperature of 140°C, a pressure of 8MPa and 11MPa, and a test time of 500 hours test. The PET resin used is a resin that has a proven track record in the market as an edge film for R134a refrigerant compressors. 10 and 11 respectively show the tensile strength and elongation characteristics of the PET resin after the test. Compared with the initial properties before the test, it can be seen that the tensile strength, elongation properties of the PET resin exposed to the high-pressure CO ₂ refrigerant deteriorated significantly. In addition, when the amount of water contained in the refrigerator oil was adjusted to 100 ppm or less, the tensile strength and elongation properties of the PET resin were not substantially deteriorated compared with the initial properties. Of course, among the R134a refrigerants, it is known from the market experience that the PET resin does not deteriorate. Therefore, the degradation phenomenon of the resin due to moisture is a characteristic characteristic of CO ₂ refrigerants.

From the above experimental results, it can be seen that when the amount of moisture contained in the refrigeration cycle exceeds 100 ppm, the edge film such as PET resin in the refrigeration cycle will deteriorate, but when it is less than 100 ppm, there is basically no deterioration. Thus, in this embodiment, by adjusting the amount of moisture contained in the refrigerating machine oil to 100 ppm or less, the amount of moisture immersed in the refrigerating cycle is adjusted to 100 ppm or less, so that the resin of the refrigerating cycle is not deteriorated, and reliability can be improved.

Also, the present embodiment has explained the refrigeration cycle provided with the oil separator 15. Since the present invention uses polar oil dissolved in the refrigerant, it is obvious that the effect can be exhibited particularly in the case of no oil separator 15.

(Example 2)

A refrigeration cycle apparatus in Embodiment 2 of the present invention will be described below with reference to the drawings.

FIG. 4 is an enlarged structural view of a main part of a heat transfer tube of a heat exchanger used in the refrigeration cycle apparatus of Example 2. FIG. The difference from Embodiment 1 is that the refrigerant passages of the heat radiator and evaporator, that is, the plurality of small through-holes formed in the flat tube 31 are used as small grooves with inner surfaces provided with many small triangular grooves on the inner surface. Hole 32. The outer diameter (imaginary diameter connected to the bottom of the groove) of the small hole 32 with the inner surface groove is 1mm, and the groove depth is 0.1mm. In addition, polyol ester oil (POE oil), which is a polar oil, is used as the refrigerating machine oil, and the water content in the oil is adjusted to be below 100 ppm.

In this way, since the refrigerant flow path of the heat exchanger, that is, the through hole is used as the small hole 32 with inner surface grooves with many small triangular grooves on its inner surface, the heat transfer area of the refrigerant flow path is increased, At the same time, the heat transfer rate of the refrigerant can be greatly improved by utilizing the stirring action of the refrigerant by the tiny grooves.

In addition, in this embodiment, polyol ester oil (POE oil), which is a polar oil, is used, so the refrigerating machine oil discharged from the compressor in circulation together with the CO ₂ refrigerant is dissolved in the CO ₂ refrigerant. As a result, an oil film that acts as a thermal resistance is formed on the inner wall surface of the flat tube 31 with the small hole 32 on the inner surface of the refrigerant flow path of the radiator and evaporator, which can effectively utilize the oil film without reducing the heat transfer performance. High heat transfer rate with CO ₂ refrigerant.

Also, since no oil film is formed on the inner wall surface of the tube with the inner grooved small hole 32, and the oil droplets do not flow, the pressure loss does not increase. Thereby, the heat transfer rate in the tube is very high, performance degradation due to pressure loss can be suppressed, and a small and high-performance heat exchanger can be produced.

In the above description, polyol ester oil (POE oil) was used as the polar oil, but even if other polar oil is used, the same effect can be obtained because of its high solubility to CO ₂ refrigerant.

Also, in this embodiment, since the water content in the refrigerating machine oil is adjusted to 100 ppm or less, hydrolysis does not degrade the refrigerating machine oil when polar oil is used, and reliability is not impaired.

(Example 3)

A refrigeration cycle apparatus in Embodiment 3 of the present invention will be described below with reference to the drawings.

Fig. 5 is an enlarged structural view of a main part of a heat transfer tube of a heat exchanger used in the refrigeration cycle apparatus of the third embodiment. The difference from Embodiment 2 is that the shape of the plurality of small holes with inner surface grooves formed in the flat tube 41, which is the refrigerant flow path of the heat radiator and evaporator, is trapezoidal. . The outer diameter (imaginary diameter connected to the bottom of the groove) of the small hole 42 with the inner surface groove is 1 mm, and the groove depth is 0.1 mm. And the number of grooves is the same as that of the triangular grooves (dotted line 43 in Fig. 5) of the above-mentioned embodiment 2, and the shape of the grooves is trapezoidal. In addition, polyol ester oil (PVE oil), which is a polar oil, is used as the refrigerating machine oil, and the water content in the oil is adjusted to be 100 ppm or less.

In this way, since the refrigerant flow path of the heat exchanger, that is, the through hole, is provided with a small trapezoidal groove on its inner surface, the small hole with inner surface groove 42, therefore, it is different from the triangular shape with the same groove depth and the same number of grooves. Compared with the heat transfer tube of the above-mentioned embodiment 2, the heat transfer area of the refrigerant flow path is increased, and at the same time, the length of the wetted edge of the refrigerant flow path is increased, and the rather large diameter is reduced. The stirring effect of the refrigerant played by the tank, etc., and because the retention capacity of the refrigerant in the tank is increased, and the thickness of the liquid film is uniform in the case of annular flow, etc., the heat transfer rate of the refrigerant can be greatly improved. In addition, in the above-mentioned embodiment 2, a high heat transfer rate can be realized, but because of the existence of the groove, there may be a problem of promoting the formation of oil droplets. In the embodiment 3, the trapezoidal shape can further reduce the formation of oil film.

In addition, in this embodiment, polyvinyl ether oil (PVE oil), which is a polar oil, is used, so the refrigerating machine oil discharged from the compressor in circulation together with the CO ₂ refrigerant is dissolved in the CO ₂ refrigerant. As a result, an oil film that acts as a thermal resistance is formed on the inner wall surface of the flat tube 41 with the small hole 42 on the inner surface of the refrigerant flow path of the radiator and the evaporator, which can effectively utilize the heat transfer performance without reducing the heat transfer performance. High heat transfer rate with CO ₂ refrigerant.

Also, since no oil film is formed on the inner wall surface of the tube with the small hole 42 having the inner surface groove, and the oil droplets do not flow, the pressure loss does not increase. Thereby, the heat transfer rate in the tube is very high, performance degradation due to pressure loss can be suppressed, and a small and high-performance heat exchanger can be produced.

In the above description, polyvinyl ether oil (PVE oil) was used as the polar oil, but even if other polar oil is used, the same effect can be obtained due to its high solubility to CO ₂ refrigerant.

Also, in this embodiment, since the water content in the refrigerating machine oil is adjusted to 100 ppm or less, the refrigerating machine oil is not degraded by hydrolysis when polar oil is used, and reliability is not impaired.

Industrial availability

As can be seen from the above description, the present invention uses a plurality of small through-holes formed on the flat tube as the refrigerant flow path of the heat exchanger for the CO ₂ refrigerant, and uses polar oil as the main composition. The refrigerating machine oil forms an oil film on the inner wall surface of the tube passing through the small hole, which acts as thermal resistance and flow resistance, thereby suppressing a decrease in the heat transfer rate and an increase in pressure loss in the heat exchanger, and realizing a compact and usable High-efficiency CO ₂ refrigerant refrigeration cycle device.

Claims (6)

1. A refrigerating cycle device, comprising: a compressor for compressing carbon dioxide (CO2) refrigerant; a heat radiator for cooling the refrigerant boosted in the compressor; On the downstream side of the refrigerant, a pressure reducer that decompresses and expands the cooled refrigerant; and an evaporator that heats the refrigerant decompressed by the pressure reducer, wherein The refrigerant flow path of the radiator and/or the evaporator is a thin tube of 1 mm or less, A refrigerating machine oil mainly composed of a polar oil compatible with the CO ₂ refrigerant is used. 2. The refrigeration cycle apparatus according to claim 1, wherein the refrigerant flow path is a plurality of through holes formed in a flat tube. 3. The refrigerating cycle apparatus according to claim 1, wherein polyether oil, polyester oil, polyglycol oil, polycarbonate oil, or a mixed oil of these oils is used as the refrigerating machine oil. 4. The refrigerating cycle apparatus according to claim 1, wherein the moisture contained in the refrigerating machine oil is 100 ppm or less. 5. The refrigerating cycle apparatus according to claim 2, wherein the small through-hole is a small hole with inner surface grooves formed on the inner surface. 6 . The refrigerating cycle device according to claim 5 , wherein the groove shape of the small hole with grooves on the inner surface is trapezoidal. 6 .

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