KR100571359B1 - Mixed refrigerant composition for low temperature - 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. .

In the mixed refrigerant composition used in the low temperature freezer, carbon dioxide is mixed with propane, and the mixing ratio is 90 to 99.5% by weight of propane and 0.5 to 10% by weight of carbon dioxide is mixed with respect to 100% by weight in total. An alternative mixed refrigerant composition is provided.

Refrigerant, R-502, Refrigeration, Air Conditioning, Propane, Carbon Dioxide

Description

Low temperature 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 is mainly used in low temperature freezer, is a freon based azeotropic mixed refrigerant in which R-22 and R-115 are mixed in a weight ratio of 48.8% and 51.2%, and are widely used due to their stable chemical properties and excellent thermodynamic properties. come.

However, when the CFC-based refrigerants R-115 and HCFC-based refrigerant R-22 contained in the refrigerant R-502 are released into the atmosphere, it has been found that the ozone layer destruction and global warming phenomenon have already been prohibited. Or will be banned.

Therefore, the development of a new refrigerant that can replace such a conventional refrigerant is an important research task in the refrigeration and air conditioning industry, and the replacement refrigerant of the recently developed and commercialized R-502 as R-404a (R-125 / R-143a / R-134a, 44 wt% / 52 wt% / 4 wt%), R-407a (R-32 / R-125 / R-134a, 20 wt% / 40 wt% / 40 wt%), R-407b (R-32 / R-125 / R-134a, 10% by weight / 70% by weight / 20% by weight), R-507 (R-125 / R-143a, 50% by weight / 50% by weight), etc. There is this.

The above mixed refrigerants are composed of HFC refrigerants that do not cause ozone layer destruction. HFC refrigerants are increasingly being used to replace conventional CFC refrigerants, but the global warming index is high, the price is high, and they are generally used. The disadvantage is that the refrigeration oil of the compressor cannot be used.

In addition, HFC-based mixed refrigerants developed as alternatives to R-502 cause global warming problems, and therefore, they are a temporary solution as alternative refrigerants for low temperature freezers, and natural refrigerants such as hydrocarbon-based refrigerants and carbon dioxide for permanent solutions. Should be used.

Hydrocarbon-based refrigerants generally have excellent thermodynamic properties as refrigerants, except for flammability, but have a disadvantage in that a compressor must be large in order to obtain the same refrigerating capacity because of a small refrigeration capacity per unit volume. In addition, there is a disadvantage in that the pressure is lower than the R-502 refrigerant used in the low temperature freezer.

As a result, the existing alternative refrigerants still have a high global warming index and are expensive synthetic materials, which may cause new problems when applied to the refrigeration system, and thus a permanent nature-friendly alternative refrigerant is required.

The present invention was devised to meet the above demands, and it is an object of the present invention to provide a natural 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, carbon dioxide (CO ₂ ) in propane (CH ₃ CH ₂ CH ₃ , R-290) to compensate for the disadvantage of propane having a low volume freezing capacity without causing any environmental problems. Implement a low-temperature alternative mixed refrigerant prepared by mixing.

Specifically, in the mixed refrigerant composition used in the low temperature freezer,
Carbon dioxide is mixed in the propane, the mixing ratio is characterized in that 90 to 99.5% by weight of propane and 0.5 to 10% by weight of carbon dioxide is mixed with respect to 100% by weight.

<Example>

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

Comparison of thermodynamic properties of boiling point, vapor pressure, thermal conductivity, viscosity, surface tension, static pressure and static specific heat, latent heat of evaporation, global warming index, ozone depletion index, etc. between R-502, R-404a, and pure propane and pure carbon dioxide It is shown in Table 1 for the purpose of.

Thermodynamic Characteristics of Various Refrigerants R-502 R-404a Propane CO ₂ Molecular weight, kg / kmol 111.6 97.6 44.1 44.01 Boiling point, ℃ -45.4 -46.2 -42.1 -78.4 Vapor Pressure (℃ 35/40 ℃), kPa 159.8 / 1681 170.8 / 1833 137.1 / 1369 1202 / supercritical state Critical temperature, ℃ 80.73 72.14 96.70 31.06 Latent heat of evaporation (at 0 ℃), kJ / kg 147.1 165.3 374.5 231.6 Liquid static specific heat (at 0 ℃), kJ / kgK 0.6661 0.8597 1.580 0.9416 Meteorological viscosity (at 25 ° C), × 10 ^-6 kg / ms 13.0 12.53 8.737 18.9 Thermal Conductivity (Gaseous / Liquid at 0 ℃), W / mK 0.00982 / 0.07257 0.01289 / 0.07783 0.01911 / 0.09294 0.01993 / 0.1107 Surface tension (at 0 ℃), N / m 0.00854 0.00750 0.00698 0.00455 Cp / Cv (weather specific heat ratio at 0 ℃) 1.237 1.236 1.277 2.111 Ozone Depletion Index 0.23 0 0 0 Global Warming Index 4300 3750 3 One

As shown in Table 1, propane and carbon dioxide, which are natural refrigerants, have a small molecular weight, and thus, refrigerants may be saved when applied to a system having the same freezing capacity. The vapor pressure of propane is slightly smaller than that of R-502 and R-404a. .

In addition, since the vapor pressure of carbon dioxide is several times larger than other refrigerants, a small amount of carbon dioxide may be mixed with propane to form a vapor pressure similar to that of the R-502 refrigerant.

If the latent latent evaporation is large, the required cooling capacity can be obtained with a small amount of liquid refrigerant. In the case of propane, the latent latent evaporation is more than twice as high as that of R-502, and the latent latent evaporation of carbon dioxide is larger than that of R-502. Has characteristics.

That is, when the liquid specific heat is larger 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 propane and carbon dioxide, the ratio of liquid specific heat to latent heat of evaporation is smaller than that of R-502 and R-404a, thereby reducing the reduction of the freezing capacity due to the phase change in the expansion process. .

If the viscosity of the refrigerant is large, the flow resistance in the compressor increases, so the volumetric efficiency of the compressor is lowered. The gas phase viscosity of propane is smaller than that of R-502 and R-404a, and carbon dioxide has a large characteristic.

In addition, in the case of carbon dioxide, the gas phase viscosity is larger than that of other refrigerants, but the pressure drop is small because the viscosity of the abnormal state carbon dioxide in the evaporator and condenser in which heat exchange proceeds is rather small.

If the heat conductivity is low, the heat transfer area of the heat exchanger must be increased or the temperature difference with the secondary fluid must be increased. For this purpose, if the heat transfer area of the heat exchanger is increased, the unit cost of the refrigerator is increased, and if the temperature difference with the secondary fluid is increased, There is a problem of poor performance.

Therefore, the thermal conductivity of propane and carbon dioxide is very excellent compared to R-502 and R-404a is advantageous when applied to the freezer.

When 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 and carbon dioxide has a smaller surface tension than the other two refrigerants.

When the ratio of the static specific heat to the static specific heat is small, the compression ratio can be large 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 carbon dioxide has a large value.

As shown in Table 1, 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. .

On the other hand, propane and carbon dioxide, which are natural refrigerants in nature, have an ozone depletion index of zero and have a minimal effect on global warming.

Based on the thermodynamic properties described above, the mixed refrigerant according to the present invention is appropriately mixed with two refrigerants having excellent thermodynamic and environmentally friendly properties to form an excellent property as a refrigerant.

Theoretical cycle characteristics were analyzed for mixed refrigerants 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 the 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 / Carbon Dioxide Refrigerant Composition Propane, wt% CO ₂ , wt% One 99 One 2 98 2 3 95 5 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 2055 2152 2393 2735 Condensation Temperature Gradient, ℃ 0 0.27 0 6.91 9.81 15.4 20.5 Evaporation pressure, kPa 255.1 270.6 216.6 318 336 377 422.6 Evaporation Temperature Gradient, ℃ 0 0.65 0 21.02 23.8 28.8 32.5 Compression Ratio 9.14 9.41 8.69 6.46 6.40 6.35 6.47 Compressor discharge temperature, ℃ 120.4 113.7 115.8 106.8 107.2 108.8 112.2 Evaporator entrance level 0.383 0.424 0.351 0.381 0.386 0.397 0.410 Frozen load, kJ / kg 137.98 154.9 354.5 347.3 343.9 335 323 Volumetric freezing capacity, kJ / m ³ 1606.1 1680.7 1378.7 2014.0 2111.5 2316.9 2510 Coefficient of performance 2.63 2.61 2.72 3.2 3.2 3.14 3.0

Due to the above Table 3, pure propane has a small volume freezing capacity because of the large gas phase specific volume, which is obtained by mixing a small amount of carbon dioxide to obtain a mixed refrigerant having high volume freezing capacity.

In addition, the refrigeration load of the propane and carbon dioxide mixture is more than twice as large as the R-502 and R-404a, and the coefficient of performance is also large, the compressor discharge temperature of the mixed refrigerant is low and the compression ratio is small .

Therefore, the mixed refrigerant composition according to the present invention is characterized in 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.

In other words, the present invention is a refrigeration system that is similar to the existing refrigerant R-502 vapor pressure and more excellent refrigerant capacity and performance by mixing carbon dioxide and propane, a natural refrigerant having excellent thermal properties as a refrigerant without causing environmental problems It can be applied to reduce the manufacturing cost and operating cost of the refrigerator.

Claims (2)

In the mixed refrigerant composition used in the low temperature freezer, Carbon dioxide is mixed in the propane, the mixing ratio is 90 to 99.5% by weight of propane, 0.5 to 10% by weight of carbon dioxide mixed refrigerant composition for low temperature, characterized in that the mixture for 100% by weight. delete