CN101165136A - An azeotropic refrigerant for single-stage compression refrigeration systems - Google Patents

Abstract

The invention relates to an azeotropic refrigerant for a single-stage compression refrigeration system, which comprises physically mixed 1, 1-difluoroethane and isobutane; the sum of the molar concentrations of all the components in the mixed refrigerant is 100%, wherein the molar concentration range of the 1, 1-difluoroethane is 73-85%, and the balance is isobutane; the efficiency of the mixed refrigerant is higher than that of the traditional excellent working medium R12, the mixed refrigerant has good lubricating oil solubility, and can directly replace the R12 working medium without great change in a refrigeration system; the ODP is zero, and the GWP is far smaller than that of a conventional fluoride working medium and is equivalent to that of a natural working medium.

Description

An azeotropic refrigerant for single-stage compression refrigeration systems

technical field

The invention belongs to a mixed refrigerant used in a single-stage compression refrigeration system, in particular to an efficient and environment-friendly azeotropic mixed refrigerant used in a single-stage compression refrigeration system.

Background technique

Single-stage compression refrigeration systems are widely used in refrigerators, air conditioners, and automotive air conditioners. Since the energy consumption of such systems accounts for a considerable proportion of the total energy consumption in society, it is important to promote the establishment of a "saving society". Today, how to improve the efficiency of the single-stage compression refrigeration system to save more energy has become an important topic in the development of the refrigeration industry.

In the past, the most commonly used refrigerant in the refrigerator refrigeration system was R12 (difluorodichloromethane, CF ₂ Cl ₂ ), which has comprehensive advantages such as low toxicity, non-flammable, non-explosive, high intrinsic efficiency, and good oil solubility. , so it has high efficiency when used in a single-stage compression refrigeration system. However, with the discovery of the mechanism of ozone layer destruction and the greenhouse effect, R12 was listed among the first eliminated working fluids due to its higher ODP and GWP coefficients.

The most commonly developed refrigerants used to replace R12 are R134a (1,1,1,2-tetrafluoroethane, CH ₂ FCF ₃ ) and R600a (isobutane, iC ₄ H ₁₀ ). Pure working fluid. Compared with R12, R134a has better migration properties and higher gas and liquid thermal conductivity, and the exhaust temperature is slightly lower. However, R134a is not compatible with conventional mineral oil, so it cannot be directly applied to the original R12 refrigeration system when used. In addition, the cooling capacity per unit volume and cycle efficiency of R134a are lower than that of R12, and the pressure ratio is higher than that of R12, so it is not conducive to the efficient operation of the compressor. Although the cycle efficiency of another alternative refrigerant R600a is slightly higher than that of R12, its pressure ratio is also higher, and the cooling capacity per unit volume is much smaller than that of R12. compressor. In addition, R600a has a high boiling point. In most cases, R600a in the evaporator is in a negative pressure state, and it is easy to mix air and water vapor and other substances, resulting in a decrease in system performance.

In summary, the original refrigerant R12 in the refrigerator refrigeration system and its substitutes R134a and R600a have relatively large limitations. Therefore, how to choose a refrigerant that is efficient, environmentally friendly, and can directly replace R12 has become an issue. Become the bottleneck of the further development of refrigerator refrigeration system.

Due to the limited number of existing pure substances, and most of them have been screened and partially used in the replacement research of the above-mentioned working fluids, the results are not satisfactory, so it is a general trend to switch the selection of new working fluids to mixed working fluids. Studies have shown that the azeotropic mixture in the mixed working fluid has the following advantages, and it is very likely to become the best choice to replace the original working fluid: 1. The azeotropic working fluid has similar properties to the pure working fluid near its azeotropic region , easy to obtain stable evaporation conditions; 2. For the positive azeotrope (positive azeotrope) mixed working fluid, its back pressure is higher than that of its single-component pure working fluid at the same evaporation temperature, so it has a higher Refrigeration capacity per unit volume; 3. Avoid the concentration change of the non-azeotropic working substance in the whole cycle, so the stability and reliability of the refrigeration cycle can be maintained; 4. Most azeotropic working substances are closer to the azeotropic point than their single-component Pure working fluid has a higher phase change heat transfer coefficient; 5. It can take into account the solubility properties of lubricating oil similar to a certain component; 6. The pressure ratio of most azeotropic working fluids in the same temperature range is smaller than that of its single-component pure The working fluid is beneficial to improve the efficiency of the compressor. It can be seen that azeotropic mixtures have great potential in the research of alternative working fluids.

The patent application with publication number CN1125958A (application number 94192550.1) discloses a mixed working fluid for mechanical refrigeration. The disclosed working fluid has the same components as the patent of the present invention, but the concentration range is completely different. The above-mentioned patent application is based on the early research in the 1990s, and has deficiencies in the following key aspects: it has not undergone accurate phase equilibrium research, so its concentration range cannot cover the azeotropic range of the actual operating condition of the mixed working fluid, so it cannot Enjoy the many advantages of azeotropic mixtures, and the excessive temperature glide will cause the system performance to drop; in addition, the above-mentioned patent application fails to carry out accurate thermophysical property analysis, so within its recommended concentration range, the refrigeration coefficient of the working fluid may not necessarily be Highest; the known patent fails to specify the oil-dissolving properties and oil-dissolving mechanism of the mixture.

The following summary of the invention will elaborate on the advantages and significance of the suggested concentration range of the present invention.

Contents of the invention

The object of the present invention is to provide an azeotropic refrigerant used in a single-stage compression refrigeration system that is highly efficient, environmentally friendly and has good miscibility with lubricating oil.

Technical scheme of the present invention is as follows:

The azeotropic refrigerant used in the single-stage compression refrigeration system provided by the present invention comprises physically mixed 1,1-difluoroethane (CHF ₂ CH ₃ ie R152a) and isobutane (iC ₄ H ₁₀ ie R600a );

The sum of the molar concentrations of the components in the mixed refrigerant is 100%, wherein the molar concentration of the 1,1-difluoroethane is 73%-85% (mass concentration range is 75.4%-86.6%), The remainder is isobutane.

The above-mentioned mixed refrigerant including 1,1-difluoroethane and isobutane has an optimal concentration ratio: the sum of the molar concentrations of each component in the mixed refrigerant is 100%, and the molar concentration of 1,1-difluoroethane is The concentration is 73% to 80% (mass concentration range is 75.4% to 82.0%), and the rest is isobutane; the basis for this optimized concentration is mainly the cycle thermodynamic performance, that is, the COP value. In addition, the phase equilibrium behavior of the mixture, temperature slip Problems such as shift and heat transfer in the azeotropic interval.

The above-mentioned mixed refrigerant including 1,1-difluoroethane and isobutane also has an optimal concentration range: the sum of the molar concentrations of each component in the mixed refrigerant is 100%, wherein 1,1-difluoroethane molar The concentration is 73%-77% (mass concentration range is 75.4%-79.2%), and the rest is isobutane.

The mixed refrigerant has the characteristics of azeotropic phase equilibrium, wherein the azeotropic concentration at 101kPa is 1,1-difluoroethane molar concentration is 67.8%, isobutane is 32.2%, and the corresponding azeotropic temperature is 245.53K (- 27.62°C); the azeotropic concentration at 1500kPa is 1,1-difluoroethane molar concentration is 78.5%, isobutane molar concentration is 21.5%, corresponding azeotropic temperature is 331.06 (57.91°C), see accompanying drawing 1 . The above-mentioned optimal concentration range is within the range of high and low pressure azeotropic concentration, which can make the temperature slip of the mixture smaller in the actual operation process (see accompanying drawing 2), and its thermodynamic behavior is equivalent to a pure working medium, and its thermodynamic cycle Efficiency is in the high range. Since the azeotropic working medium belongs to a positive azeotropic mixture, it has a lower boiling point than its single component 1,1-difluoroethane and isobutane, so it has a higher back pressure at the same evaporation temperature, Therefore, it has a larger cooling capacity per unit volume.

Accompanying drawing 3 shows, the temperature-pressure curve of this azeotropic working substance is very close to R12, therefore can use the same compressor as R12 to work. The component 1,1-difluoroethane in the mixture has a small solubility in ordinary mineral oil, but the azeotropic working medium also has better solubility in mineral oil due to the presence of isobutane component , Therefore, the azeotropic working medium can be directly applied to the original R12 refrigeration system without major changes.

The azeotropic mixed refrigerant used in the single-stage compression refrigeration system proposed by the present invention has the following advantages: its ozone depletion potential ODP is zero, and long-term use will not cause damage to the atmospheric ozone layer. Since the greenhouse effect coefficients GWP of the pure working fluid components 1,1-difluoroethane (R152a) and isobutane (R600a) are very small, the mixed refrigerant GWP coefficients provided by the present invention are far smaller than the existing R12, R134a and other series of refrigerants are close to the natural refrigerant R600a. The concentration interval of the present invention is close to the azeotropic interval of the mixture under actual operating conditions, so the temperature glide is small and the heat transfer coefficient is high. Another advantage of the present invention is that the azeotropic working medium has very high intrinsic efficiency. Within the recommended concentration range, the refrigeration capacity per unit volume is equivalent to that of R12 and the coefficient of performance COP is higher than that of R12. Considering the excellent transmission efficiency of the azeotropic working medium Thermal properties and other advantages, the present invention proposes that the efficiency of the azeotropic working medium will be greatly improved compared with R12 in actual operation. In addition, since the temperature-pressure range of the azeotropic working fluid is close to that of R12 and has good lubricating oil solubility, the working fluid can directly replace R12 in the original refrigeration system.

Description of drawings

Accompanying drawing 1 is the phase diagram of the mixed refrigerant comprising 1,1-difluoroethane (R152a) and isobutane (R600a) at 101kPa and 1500kPa.

Accompanying drawing 2 is the bubble dew point temperature difference (temperature glide) under different saturation pressures of embodiment 1, embodiment 2, embodiment 4, embodiment 6 of the present invention.

Accompanying drawing 3 is the vapor pressure comparison of embodiment 1 of the present invention and existing refrigerant.

Detailed ways

Example 1: 1,1-difluoroethane with a molar concentration of 73% and isobutane with a molar concentration of 27% are physically mixed at room temperature to obtain a mixed refrigerant that can be applied to a single-stage compression refrigeration system .

Example 2: 1,1-difluoroethane with a molar concentration of 75% and isobutane with a molar concentration of 25% are physically mixed at room temperature to obtain a mixed refrigerant that can be applied to a single-stage compression refrigeration system .

Example 3: 1,1-difluoroethane with a molar concentration of 77% and isobutane with a molar concentration of 23% are physically mixed at room temperature to obtain a mixed refrigerant that can be applied to a single-stage compression refrigeration system .

Example 4: 1,1-difluoroethane with a molar concentration of 80% and isobutane with a molar concentration of 20% are physically mixed at room temperature to obtain a mixed refrigerant that can be applied to a single-stage compression refrigeration system .

Example 5: 1,1-difluoroethane with a molar concentration of 82% and isobutane with a molar concentration of 18% are physically mixed at room temperature to obtain a mixed refrigerant that can be applied to a single-stage compression refrigeration system .

Example 6: 1,1-difluoroethane with a molar concentration of 85% and isobutane with a molar concentration of 15% are physically mixed at room temperature to obtain a mixed refrigerant that can be applied to a single-stage compression refrigeration system .

According to the relevant regulations in the national standard GB9098-88 of "Full Enclosed Motors for Refrigerators-Compressors", the design conditions are determined to be evaporation temperature -23.3°C, suction temperature 32.2°C, condensation temperature 54.4°C, and supercooling temperature 32.2°C °C, the ambient temperature is 32.2 °C. According to the cycle calculation, the cycle performance parameters of the above six embodiments and the performance comparison results with existing refrigerants are listed in the following table, wherein the relative cooling capacity and relative efficiency are the comparative values based on R12.

Performance summary of mixed refrigerants in the examples and performance comparison table with existing refrigerants

Example Condensing pressurekPa Evaporating pressurekPa The maximum temperature glide K in the range of 101 ~ 1500kPa Pressure ratio Exhaust temperature °C Relative volume cooling capacity relative efficiency 1 1380 122 0.17 11.34 123.25 0.961 1.002 2 1381 122 0.30 11.36 124.16 0.965 1.005 3 1382 121 0.43 11.40 124.97 0.968 1.008 4 1382 121 0.63 11.45 126.23 0.972 1.012 5 1380 120 0.76 11.49 127.09 0.974 1.016 6 1376 119 0.91 11.57 128.46 0.974 1.021 R12 1345 132 / 10.19 125.83 1.000 1.000 R134a 1470 115 / 12.78 118.95 0.921 0.978 R600a 762 63 / 12.10 102.64 0.502 1.013

The above calculation results show that as the concentration of 1,1-difluoroethane increases, the cooling capacity per unit volume and cycle efficiency increase slightly, but if the concentration of 1,1-difluoroethane increases away from the azeotropic interval, the temperature slides shift will increase, and the pressure ratio will increase accordingly, and will lose the advantages of high heat transfer coefficient brought by azeotropic behavior. Therefore, based on the above considerations, in the concentration range proposed by the present invention, the concentration of 1,1-difluoroethane It should not be too high, and the recommended mass concentration is 75.4% to 86.6% (73% to 85% molar concentration).

The above calculations are based on the results of the internationally recognized standard physical property calculation software REFPROP 7.0, which has high accuracy, and its analysis results are different from the patent application number 94192550.1. Within the concentration range proposed by the above-mentioned known patents (it is considered that 1,1-difluoroethane has a higher refrigeration coefficient when the mass concentration is 60% to 75%), after recalculation, its relative volumetric refrigeration capacity and relative efficiency are respectively For: 0.928～0.960, 0.992～1.001, all are inferior to the scheme that the present invention proposes.

The above theoretical calculation results based on the standard working conditions show that the refrigeration working fluid provided by the present invention has a considerable improvement in all other indicators except the exhaust temperature compared with the existing alternative working fluids R134a and R600a. Compared with the traditional high-quality working medium R12, the cooling capacity per unit volume is basically the same and the efficiency is improved. If other advantages such as heat transfer enhancement are considered, its actual operating efficiency will be higher than that of R12 to a large extent.

The mixed refrigerant suitable for the single-stage compression refrigeration system proposed by the present invention has good environmental protection characteristics. The following table shows the comparison of three examples with the existing refrigerants in ozone depletion potential (ODP) and global warming potential (GWP). It can be seen that the new mixed refrigerant proposed by the present invention greatly reduces the GWP value.

^* Existing refrigerant and pure quality data are quoted from "Refrigerant User Manual, edited by Cao Desheng and Shi Lin, Beijing, Metallurgical Industry Press, 2003"

^** Based on ODP values of pure components weighted by mass concentration.

Claims (3)

1. An azeotropic refrigerant for a single-stage compression refrigeration system, characterized in that the mixed refrigerant comprises physically mixed 1,1-difluoroethane and isobutane; The sum of the molar concentrations of the components in the mixed refrigerant is 100%, wherein the molar concentration of the 1,1-difluoroethane ranges from 73% to 85%, and the rest is isobutane. 2. The azeotropic refrigerant for single-stage compression refrigeration system according to claim 1, characterized in that: the molar concentration of said 1,1-difluoroethane ranges from 73% to 80%, and the rest is isobutyl alkyl. 3. The azeotropic refrigerant for single-stage compression refrigeration system according to claim 1, characterized in that: the molar concentration of said 1,1-difluoroethane ranges from 73% to 77%, and the rest is isobutyl alkyl.

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