KR20060009189A - Alternative refrigerant mixture - Google Patents

Abstract

The present invention replaces R-502, a freon-based mixed refrigerant for low temperature freezers, whose production is regulated due to environmental problems, and relates to a low temperature mixed refrigerant composition having excellent freezing capacity and performance while solving environmental problems. .

To this end, the present invention, in the mixed refrigerant composition used in the refrigeration system, propane and difluoromethane are mixed, the mixing ratio is 88 ~ 98% by weight of propane, 2 to 12% by weight of difluoromethane total 100 An alternative mixed refrigerant composition is provided that is mixed with respect to weight percent.

Refrigerant, Propane, Difluoromethane, R-290, R-32, Refrigeration, Air Conditioning, R-502

Description

Alternative refrigerant mixture

The present invention replaces R-502, a freon-based mixed refrigerant for low temperature freezers, whose production is regulated due to environmental problems, and relates to a low temperature mixed refrigerant composition having excellent freezing capacity and performance while solving environmental problems. .

In general, when pure propane is used as a refrigerant in a refrigerator system using an R-502 refrigerant, the size of the compressor has to be increased in order to have the same refrigerating capacity because the volume of the refrigerant is small.

R-502 refrigerant, which has been mainly used in low temperature freezers because of its stable chemical properties and excellent thermodynamic properties, is a freon based azeotropic mixed refrigerant in which R-22 and R-115 are mixed at a weight ratio of 48.8% and 51.2%.

However, when the CFC series refrigerant R-115 and HCFC series refrigerant R-22 contained in the refrigerant R-502 are released into the atmosphere, it is found that the chlorine (Cl) component contained in these substances destroys the ozone layer. As it turns out to be a cause of global warming, its production and use are already banned or planned to be banned.

Therefore, the development of a new material that can replace the existing refrigerant is an important research task in the refrigeration and air conditioning industry, and R-502a (R-125 / R) has been recently developed and commercialized R-502 replacement refrigerant -143a / R-134a, 44% / 52% / 4%), R-407a (R-32 / R-125 / R-134a, 20% / 40% / 40%), R-407b (R-32 / R-125 / R-134a, 10% / 70% / 20%), and R-507 (R-125 / R-143a, 50% / 50%).

Here, the alternative refrigerant described above should not include a component that destroys the global environment, and it is preferable that the thermodynamic properties are similar to those of the conventional refrigerant.

Considering the thermodynamic properties, it is very difficult to find alternative refrigerants that have properties similar to those of conventional refrigerants as pure refrigerants of one component, and in this case, two-component or multicomponent mixtures are replaced. Should be used as

Therefore, HFC-based refrigerants and mixtures of them are currently suggested as substitutes, and the above mixed refrigerants are composed of HFC-based refrigerants that do not destroy the ozone layer, but have a high global warming index and are made of synthetic materials. It is expensive and incompatible with the compressors of the compressors used in general, which has the disadvantage of exposing new problems when applied to the refrigeration system.

In particular, considering that recent weather abnormalities are caused by global warming, it is not preferable to use HFC-based refrigerants with a large global warming index, and they exist in nature as a solution to fundamentally solve these problems. There is a demand to use an alternative mixed refrigerant having excellent cooling performance by using a material that is used as a refrigerant as a refrigerant.

It is an object of the present invention to provide an alternative mixed refrigerant that can improve the freezing capacity and performance of a low temperature freezer without causing environmental problems such as ozone layer destruction and global warming. .

In order to achieve the above object, the present invention, in order to compensate for the shortcomings of propane having a low saturation pressure of the refrigerant and a small volume freezing capacity, the global warming of the HFC series refrigerant in propane (CH ₃ CH ₃ CH ₃ , R-290) Alternative refrigerants are achieved by mixing difluoromethane (CH ₂ F ₂ , R-32) with a low index.

Specifically, the present invention, in the mixed refrigerant composition used in the refrigeration system, propane and difluoromethane are mixed, the mixing ratio is 88 ~ 98% by weight of propane and 2 to 12% by weight of difluoromethane in total 100 Characterized by mixing relative to weight%.

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Basically, the alternative refrigerant of R-502 should not cause environmental problems such as global warming and ozone depletion, and it should be excellent in thermodynamic properties as refrigerant. In addition, compared to the system for the low temperature freezer using R-502, the freezing performance and the freezing capacity should be the same or larger, and an efficient alternative refrigerant should be developed to be used as a substitute material.

Boiling point, vapor pressure, thermal conductivity, viscosity, surface tension, ratio of static pressure and static specific heat, evaporative latent heat, global warming index, ozone depletion index, etc. of pure propane, R-32 and R-502 and R-404a Thermodynamic properties are shown in Table 1 for the purpose of comparison.

Thermodynamic Characteristics of Various Refrigerants R-502 R-404a Propane R-32 Molecular weight, kg / kmol 111.6 97.6 44.1 52.02 Boiling point, ℃ -45.4 -46.2 -42.1 -51.65 Vapor Pressure (℃ 35/40 ℃), kPa 159.8 / 1681 170.8 / 1833 137.1 / 1369 221.4 / 2478 Critical temperature, ℃ 80.73 72.14 96.70 78.11 Latent heat of evaporation (at 0 ℃), kJ / kg 147.1 165.3 374.5 315.29 Liquid static specific heat (at 0 ℃), kJ / kgK 0.6661 0.8597 1.580 0.9386 Meteorological viscosity (at 25 ° C), × 10 ^-6 kg / ms 13.0 12.53 8.737 13.05 Thermal Conductivity (Gaseous / Liquid at 0 ℃), W / mK 0.00982 / 0.07257 0.01289 / 0.07783 0.01911 / 0.09294 0.01179 / 0.1541 Surface tension (at 0 ℃), N / m 0.00854 0.00750 0.00698 0.01099 Cp / Cv (weather specific heat ratio at 0 ℃) 1.237 1.236 1.277 1.470 Ozone Depletion Index 0.23 0 0 0 Global Warming Index 4300 3750 3 650

As shown in Table 1, propane and R-32, which are the constituents of the mixed refrigerant, have a small molecular weight, and thus, refrigerants may be saved when applied to a system having the same refrigeration capacity. Slightly smaller than

In addition, although the vapor pressure of R-32 is larger than that of other refrigerants, by mixing a small amount of R-32 with propane, a vapor pressure similar to that of the R-502 refrigerant can be formed.

If the latent latent heat of vaporization is large, there is an advantage in that required cooling capacity can be obtained with a small amount of liquid refrigerant, and propane and R-32 have a feature of greater than twice the latent latent vaporization compared to R-502.

That is, when the liquid specific heat of the refrigerant is greater than the latent heat of evaporation, a large amount of gaseous refrigerant is generated during the expansion process, and the refrigerant vapor generated during the expansion process has no freezing capacity, thereby reducing the freezing capacity.

Therefore, in the case of R-32, the ratio of liquid specific heat to latent heat of evaporation is about half as small as that of conventional refrigerants, and propane is slightly smaller than that of R-502 and R-404a. There is an advantage to reduce the decrease in the freezing capacity.

When the viscosity of the refrigerant is small, the flow resistance in the compressor can be reduced, so that the volumetric efficiency of the compressor can be increased. The vapor phase viscosity of propane is smaller than that of R-502 and R-404a, and R-32 is slightly larger. Because of its characteristics, mixing it properly allows the volumetric efficiency of the compressor to be operated more advantageously.

The heat exchanger is the main part of the refrigerator and occupies most of the system volume. The heat transfer characteristics of the refrigerant must be excellent for efficient heat exchange in the heat exchanger of the proposed size.

Here, if the thermal conductivity is low, the heat transfer area of the heat exchanger should be increased or the temperature difference with the secondary fluid should be increased. If the heat transfer area of the heat exchanger is enlarged, the unit price of the freezer will be increased and the temperature difference with the secondary fluid will be increased. Falling problem occurs.

Therefore, since the thermal conductivity, which is one of the factors for determining the heat transfer characteristics, is very superior to that of R-502 and R-404a in the case of propane and R-32, the cooling efficiency of the heat exchanger in the body volume is higher than that of propane and R-32. By mixing.

If the surface tension is small, the surface of the evaporator heat exchanger tube is well wetted by the liquid refrigerant, and the heat transfer effect is increased. The surface tension of propane is smaller than that of the existing two refrigerants, and R-32 has a larger characteristic, so propane R-32 Is mixed properly to form alternative refrigerant.

If the ratio of the static specific heat to the static specific heat is small, the compression gas can be set wider because the rise of the refrigerant gas temperature is not large at the time of compression in the compressor, and the refrigerator can be configured by one-stage compression even when the evaporation temperature is low. .

Therefore, propane has a value similar to the specific heat ratio of R-502 and R-404a, and R-32 has a large value.

As described above, R-502, a mixed freon refrigerant, destroys the ozone layer and has a high global warming index. R-404a, a HFC mixed refrigerant, has a zero ozone depletion index but a high global warming index.

In contrast, propane, a natural refrigerant present in nature, has an ozone layer depletion index of zero (0) and little effect on global warming, and R-32 has a lower global warming index than other HFC refrigerants. In mixed refrigerants, a small amount of R-32 is mixed with propane, which has little effect on global warming.

As a result, the mixed refrigerant according to the present invention is suitably a combination of two refrigerants having excellent thermodynamic properties and environmentally friendly properties based on the thermodynamic properties described above, and is configured to have excellent properties as a refrigerant.

Table 2 shows selected combinations of specific refrigerants of the mixed refrigerants of the present invention. In addition, the theoretical cycle characteristics analysis was performed on the mixed refrigerant of the specific composition shown in Table 2, and R-502, R-404a and pure propane, and the results are shown in Table 3.

Here, ASHRAE L.B.P was used as a standard condition for theoretical cycle characteristics analysis. REFPROP 6.01, a refrigerant properties program, was used to calculate the thermal properties of the refrigerant, and the efficiency of the compressor was assumed to be 100%.

In addition, in order to compare a mixed refrigerant whose temperature is changed during the heat exchange with a refrigerant which does not change in temperature, a method of equalizing the average temperature of the refrigerant during heat exchange was used.

Propane / R-32 Mixed Refrigerant Composition Propane, wt% R-32, wt% One 96 4 2 94 6 3 92 8 4 90 10

Theoretical Cycle Characteristic Analysis (ASHRAE L.B.P) R-502 R-404a Propane One 2 3 4 Condensing pressure, kPa 2331 2545.5 1883 2070 2159 2242 2326 Condensation Temperature Gradient, ℃ 0 0.27 0 5.07 7.05 8.7 10.05 Evaporation pressure, kPa 255.1 270.6 216.6 265.5 285 301 315 Evaporation Temperature Gradient, ℃ 0 0.65 0 9.30 12.21 14.35 15.89 Compression Ratio 9.14 9.41 8.69 7.80 7.58 7.45 7.38 Compressor discharge temperature, ℃ 120.4 113.7 115.8 113.9 113.7 113.9 114.5 Evaporator entrance level 0.383 0.424 0.351 0.367 0.373 0.377 0.381 Frozen load, kJ / kg 137.98 154.9 354.5 344.5 339.9 335.4 331.1 Volumetric freezing capacity, kJ / m ³ 1606.1 1680.7 1378.7 1662.9 1770.9 1854.4 1924.7 Coefficient of performance 2.63 2.61 2.72 2.84 2.86 2.87 2.85

Due to the above Table 3, the volumetric refrigeration capacity of the pure propane has a small volume freezing capacity, and a small amount of R-32 was mixed to obtain a mixed refrigerant having a high volume freezing capacity of the refrigerant.

In addition, the refrigeration load of the mixed propane and R-32 refrigerant is more than twice as large as the R-502 and R-404a, has a large coefficient of performance, and the compression ratio of the compressor of the mixed refrigerant has a small feature.

Therefore, the mixed refrigerant composition according to the present invention has a feature that all of the refrigerating load, the volume freezing capacity, and the performance coefficient are larger than the conventional refrigerant.

As described above, the present invention can replace the low-temperature refrigeration refrigerant R-502, which is defined as a material that destroys the global environment, and can expect better effects in terms of freezing capacity and performance.                     

That is, in the present invention, the global warming phenomenon is minimized and does not cause an environmental problem, and by mixing propane and R-32 having excellent thermal properties as a refrigerant, the vapor pressure is similar to that of the existing refrigerant, and the freezing capacity and performance are more. By applying excellent refrigerants to the refrigeration system, it is possible to reduce the freezer manufacturing cost and operating costs.

Claims (2)

In the mixed refrigerant composition used in the refrigeration system, Alternative mixed refrigerant composition, characterized in that the mixture of propane and difluoromethane. Alternative mixed refrigerant composition, characterized in that 88 to 98% by weight of propane and 2 to 12% by weight of difluoromethane are mixed with respect to 100% by weight.