CN101161757A - An environmentally friendly azeotropic refrigerant suitable for single-stage compression refrigeration systems - Google Patents

Abstract

The azeotropic mixed refrigerant suitable for the single-stage compression refrigeration system involved in the present invention includes 1,1,1,2-tetrafluoroethane and isobutane after physical mixing, wherein 1,1,1,2-tetrafluoroethane The molar concentration of fluoroethane is 50% to 63%, and the rest is isobutane. The mixed refrigerant has high efficiency and high evaporation pressure, and has a large refrigeration capacity under the same compressor displacement; its ODP is zero, and its GWP is greatly reduced compared with R12 and R134a; it has good miscibility with lubricating oil, and is preferred Taking into account the concentration change of the mixture in lubricating oil, it can ensure that the mixture still maintains the azeotropic property in actual operation; it can be used in cryogenic preservation technology, and it is easy to obtain a lower effective refrigeration temperature.

Description

An environmentally friendly azeotropic refrigerant suitable for single-stage compression refrigeration systems

technical field

The invention relates to a mixed refrigerant, in particular to an environment-friendly azeotropic mixed refrigerant containing alkanes and suitable for single-stage compression refrigeration systems.

Background technique

The single-stage compression refrigeration system is widely used in refrigerators, air conditioners and automobile air conditioners as an efficient and reliable refrigeration method in the general cold temperature zone. With the improvement of people's living standards, higher requirements are put forward for such refrigeration systems in terms of environmental protection and energy saving. In addition, in the design of the latest household refrigerator system, the fresh-keeping technology in the cryogenic temperature zone has become a hot spot of development, which requires this type of single-stage compression refrigeration system to still have high efficiency at -30°C or even -40°C.

The working fluids commonly used in refrigerator refrigeration systems mainly include R12 (difluorodichloromethane, CF ₂ Cl ₂ ), R134a (1,1,1,2-tetrafluoroethane, CH ₂ FCF ₃ ) and R600a (isobutane , iC ₄ H ₁₀ ) etc. Among them, R12 used to be the most widely used medium-temperature refrigerant. It has low toxicity, non-flammability, and non-explosiveness. It has good solubility characteristics with ordinary mineral oil and good thermal performance. Therefore, it was discovered in the 1930s. be widely used in the future. However, with the discovery of the mechanism of ozone layer destruction and the greenhouse effect, R12 was listed as the first working fluid to be eliminated due to its high ODP and GWP coefficients.

R134a and R600a are the two most common medium temperature alternatives. Compared with R12, R134a has better migration properties and higher gas and liquid thermal conductivity. In the same temperature range, the pressure ratio of R134a is slightly higher than that of R12, and the exhaust temperature is slightly lower. The refrigerant has low toxicity, is non-flammable, and is a very safe refrigerant. However, R134a is incompatible with conventional mineral oil and can only be dissolved in expensive POE oil or PAG oil, so it cannot be directly applied to the original R12 refrigeration system when used. Compared with the first two working fluids, R600a has a higher 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 addition, the pressure ratio of R600a is generally slightly higher than that of R12, and the cooling capacity per unit volume is much smaller than that of R12. Therefore, to achieve the same cooling capacity, a refrigeration compressor with a larger displacement should be selected. R600a has low toxicity, but is flammable, so fire and explosion protection must be paid attention to, and it is generally used in systems with small charge such as household refrigerators. In addition, R600a has good miscibility with mineral oil, so there is no need to use expensive POE or PAG oil.

In addition, based on the requirements of cryogenic preservation technology, due to the high boiling point of the above two alternative working fluids, it is difficult for the refrigeration system using ordinary compressors to achieve an effective refrigeration temperature lower than -30°C due to the low back pressure. To sum up, it has become an urgent need for the development of advanced refrigeration systems to choose a green working fluid that not only has good thermal performance, but also takes into account the needs of cryogenic preservation technology and has good lubricating oil solubility.

The choice of new alternative working fluids in pure substances has been very limited, and the selection of new working fluids has gradually shifted to mixed working fluids. Since the azeotropic working fluid has similar properties to pure working fluid near the azeotropic point, it can be divided into positive azeotrope (positive azeotrope) and negative azeotrope according to whether it has the highest azeotropic pressure (under isothermal conditions) or the lowest azeotropic pressure. Azeotrope (negative azeotrope) two. In most cases, the azeotrope is a positive azeotrope. The use of azeotropic mixture as a refrigerant has the following advantages: 1. Under equal pressure conditions, when the azeotropic refrigerant evaporates near the azeotropic point, the evaporation temperature remains basically unchanged, and it is easy to obtain a stable evaporation condition; 2. , For the positive azeotropic mixture, at the same evaporation temperature, the back pressure of the azeotropic refrigerant is higher than that of its single-component pure refrigerant, so it has a higher cooling capacity per unit volume; 3. Avoid non-azeotropic The concentration change caused by the "phase accumulation" of the boiling working substance in the whole cycle, so the stability and reliability of the refrigeration cycle can be maintained; It has a higher phase change heat transfer coefficient; 5. It can take into account the similar lubricating oil solubility properties of certain components. Therefore, the azeotropic mixture has become an important direction for the development of alternative working fluids due to its excellent comprehensive performance.

The patent application whose application number is 200310118961.4 discloses a class of near-azeotropic refrigerants (publication number is CN1546594A), which includes a binary mixture and a ternary mixture, wherein the binary mixture (R134a+R600a) and the patent The components are the same, but the concentration range is completely different. Based on the applicant's research on phase equilibrium behavior, R134a+R600a is not a near-azeotropic mixture as described in 200310118961.4, but an azeotropic mixture, so this mixture enjoys many advantages of azeotropic working fluid. In addition, based on the applicant's research on the solubility properties of R134a+R600a lubricating oil, since the solubility of the two simple substances of R134a and R600a in mineral oil is very different, a certain concentration of R134a+R600a mixture in the lubricating oil Operation in refrigeration systems will necessarily result in large deviations from the actual concentration. Therefore, the concentration range given in 200310118961.4 cannot guarantee that the R134a+R600a mixture will still maintain azeotropic characteristics during actual operation.

Contents of the invention

The object of the present invention is to provide a high-efficiency mixed refrigerant suitable for a single-stage compression refrigeration system, which has no ozone layer destruction, low greenhouse effect, good miscibility with lubricating oil and can maintain azeotropic properties.

Technical scheme of the present invention is as follows:

The azeotropic refrigerant suitable for single-stage refrigeration systems provided by the present invention comprises physically mixed 1,1,1,2-tetrafluoroethane (CH ₂ FCF ₃ is R134a) and isobutane (iC ₄ H ₁₀ is R600a);

The sum of the molar concentrations of the components in the mixed refrigerant is 100%, wherein the molar concentration of the 1,1,1,2-tetrafluoroethane is 50% to 63% (the mass concentration ranges from 63.7% to 74.9%), the rest is isobutane.

The above-mentioned mixed refrigerant including 1,1,1,2-tetrafluoroethane and isobutane has an optimized concentration ratio: the sum of the molar concentrations of each component in the mixed refrigerant is 100%, wherein 1, 1, 1, The molar concentration of 2-tetrafluoroethane is 58% to 63% (mass concentration range is 70.8% to 74.9%), and the rest is isobutane; the basis for this optimized concentration is mainly the thermal performance of the cycle, that is, the COP value, and comprehensive consideration The phase equilibrium behavior of the mixture and the concentration change after miscible with lubricating oil, etc.

The above-mentioned mixed refrigerant including 1,1,1,2-tetrafluoroethane 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, 1 , the molar concentration of 2-tetrafluoroethane is 60%-63% (mass concentration range is 72.5%-74.9%), and the rest is isobutane.

The mixed refrigerant has the characteristics of azeotropic phase equilibrium, wherein the azeotropic concentration at 101kPa is 65.4% for 1,1,1,2-tetrafluoroethane, 34.6% for isobutane, and the corresponding azeotropic temperature is 241.09 K (-32.06°C), its standard boiling point is lower than the existing working fluids such as R12, R134a and R600a, so it is easy to obtain a lower effective refrigeration temperature in cryogenic preservation technology; the azeotropic concentration at 1500kPa is 1, The molar concentration of 1,1,2-tetrafluoroethane is 73.5%, the molar concentration of isobutane is 26.5%, and the corresponding azeotropic temperature is 324.06K (50.91°C), see Figure 1. Due to the high solubility of isobutane in mineral oil, part of the isobutane component in the mixed refrigerant dissolves in the lubricating oil and the concentration shift occurs. Therefore, the isobutane concentration in the above-mentioned optimal concentration range is slightly higher than the azeotropic concentration, which can make the mixture still maintain azeotropic characteristics in actual operation after the concentration deviation occurs, and the temperature glide is small (see accompanying drawing 2) , its thermodynamic behavior is equivalent to a pure working fluid, and its thermodynamic cycle efficiency is in a very high range. The azeotropic working medium belongs to a positive azeotropic mixture, which has a lower boiling point than its single component 1,1,1,2-tetrafluoroethane (R134a) and isobutane (R600a), so it can be evaporated in the same Higher back pressure at higher temperatures and therefore greater cooling capacity per unit volume.

The mixed refrigerant also has a very high phase change heat transfer coefficient near the azeotropic point, as shown in Figure 3. Under different heat flux densities, the boiling heat transfer coefficient near the azeotropic point all achieves a maximum value, and the The heat transfer coefficient is much higher than its HFC component 1, 1, 1, 2-tetrafluoroethane, and is comparable to the traditional high heat transfer coefficient HC material isobutane.

The azeotropic mixed refrigerant suitable for single-stage compression refrigeration systems proposed by the present invention has the following advantages: its ozone depletion potential value ODP is zero; The global warming potential GWP of the refrigerant is smaller than that of the existing R12, R134a and other series refrigerants. Another advantage of the present invention is that the mixed refrigerant and lubricating oil have good mutual solubility. Due to the presence of alkanes, the mixed refrigerant provided by the present invention can use conventional mineral lubricating oil. Therefore, the mixed refrigerant provided by the present invention can be used in There is no need to replace lubricating oil when replacing the R12 system; and the present invention gives priority to the important concentration change problem of the mixture during operation, so that the mixture can still maintain the azeotropic characteristic during actual operation. In addition, the mixed refrigerant provided by the present invention has a high evaporation pressure and a small increase in the condensation pressure, which brings many benefits to the actual system, especially the increase in the evaporation pressure, so that the refrigerator can avoid the system running under vacuum during operation ; In addition, in the case of the same compressor displacement, the actual cooling capacity is increased. The mixed working medium proposed by the invention can also be applied to cryogenic preservation technology, and a lower effective refrigeration temperature can be obtained.

Description of drawings

Accompanying drawing 1 is the phase diagram of the mixed refrigerant comprising 1,1,1,2-tetrafluoroethane (R134a) and isobutane (R600a) at 101kPa and 1500kPa.

Accompanying drawing 2 is the bubble dew point temperature difference (temperature glide) of embodiment 1, embodiment 2, embodiment 4, embodiment 5 of the present invention under different saturation pressures.

Accompanying drawing 3 is the boiling heat transfer curve of R134a/R600a under 0.5MPa pressure.

Accompanying drawing 4 is the vapor pressure comparison of Example 1 of the present invention and existing refrigerant.

Detailed ways

Example 1: 1,1,1,2-tetrafluoroethane with a molar concentration of 63% and isobutane with a molar concentration of 37% are physically mixed at room temperature to obtain a single-stage compression refrigeration system. of mixed refrigerants.

Example 2: 1,1,1,2-tetrafluoroethane with a molar concentration of 61% and isobutane with a molar concentration of 39% are physically mixed at room temperature to obtain a single-stage compression refrigeration system of mixed refrigerants.

Example 3: 1,1,1,2-tetrafluoroethane with a molar concentration of 60% and isobutane with a molar concentration of 40% are physically mixed at room temperature to obtain a single-stage compression refrigeration system of mixed refrigerants.

Example 4: 1,1,1,2-tetrafluoroethane with a molar concentration of 58% and isobutane with a molar concentration of 42% are physically mixed at room temperature to obtain a single-stage compression refrigeration system of mixed refrigerants.

Example 5: 1,1,1,2-tetrafluoroethane with a molar concentration of 55% and isobutane with a molar concentration of 45% are physically mixed at room temperature to obtain a single-stage compression refrigeration system of mixed refrigerants.

Example 6: 1,1,1,2-tetrafluoroethane with a molar concentration of 50% and isobutane with a molar concentration of 50% are physically mixed at room temperature to obtain a single-stage compression refrigeration system of mixed refrigerants.

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 four embodiments and the performance comparison results with existing refrigerants are listed in the table below, 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 Evaporation pressurekPa Pressure ratio Exhaust temperature ℃ Relative volume cooling capacity relative efficiency 1 1612 148 10.89 110.31 1.037 0.933 2 1606 148 10.85 109.99 1.036 0.934 3 1603 147 10.90 109.81 1.035 0.935 4 1596 147 10.86 109.47 1.034 0.937 5 1584 147 10.78 108.93 1.034 0.941 6 1560 147 10.61 107.97 1.035 0.951 R12 1345 132 10.19 125.83 1.0 1.0 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 is based on the theoretical calculation results of the standard working conditions. In the actual operation process, the improvement of the compressor efficiency brought about by the reduction of the pressure ratio of the refrigerant refrigerant provided by the present invention and the good phase change heat transfer performance are taken into account. , so the actual efficiency of the refrigerant refrigerant provided by the present invention should be higher than R134a and equivalent to the traditional excellent refrigerant R12.

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 between the embodiment and the existing refrigerants in terms of 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 environmentally friendly azeotropic refrigerant suitable for single-stage compression refrigeration systems, characterized in that the mixed refrigerant comprises physically mixed 1,1,1,2-tetrafluoroethane and isobutane; The sum of the molar concentrations of the components in the mixed refrigerant is 100%, wherein the molar concentration of the 1,1,1,2-tetrafluoroethane ranges from 50% to 63%, and the rest is isobutane. 2. The azeotropic mixed refrigerant suitable for single-stage compression refrigeration systems according to claim 1, characterized in that: the molar concentration of said 1,1,1,2-tetrafluoroethane ranges from 58% to 63% %, the rest is isobutane. 3. The azeotropic mixed refrigerant suitable for single-stage compression refrigeration systems according to claim 1, characterized in that: the molar concentration of said 1,1,1,2-tetrafluoroethane ranges from 60% to 63 %, the rest is isobutane.

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