1, single refrigerant
2. Mixed refrigerant.
A single refrigerant contains only one chemical substance, and its thermophysical performance parameters are constant. Refrigerant such as R 134a and R 152a all have high energy efficiency.
Mixed refrigerant is a mixture of two or more refrigerants.
According to whether the composition of gas phase and liquid phase is equal in gas-liquid equilibrium, it can be divided into:
1, * * * boiling mixed refrigerant: when gas and liquid are in equilibrium, it belongs to * * * boiling mixed refrigerant (including phase equilibrium).
Near-boiling mixed refrigerant with approximately equal gas-liquid two-phase components),
2. Non-boiling mixed refrigerant. Unequal composition belongs to non-boiling mixed refrigerant.
* * * Selection and Energy Saving of Boiling Mixed Refrigerant * * * When the boiling mixed refrigerant evaporates and condenses under a certain pressure, the composition of gas phase and liquid phase remains unchanged and can maintain a constant temperature. It has similar thermophysical properties as a single refrigerant. This refrigeration system is the earliest and most mature refrigerant studied and applied. The * * * boiling mixed refrigerant studied now is listed in table 1.
For non-boiling mixed refrigerant, the evaporation process in the evaporator and the condensation process in the condenser are both non-ideal mixing processes. These two non-ideal mixing processes make the condensation pressure of mixed refrigerant in refrigeration system decrease, the evaporation pressure increase and the compressor exhaust temperature decrease. This reduces the pressure ratio of the refrigerator and increases the refrigeration coefficient, thus improving the energy efficiency of the refrigeration system.
Table 1 the improvement of the thermodynamic properties of the working medium by the composition and mass of the * * * boiling mixed refrigerant relative to the standard boiling point (℃) was studied. The refrigeration capacity of r12/r15a273.8/26.2-33.3 is larger than that of r 17 ~ 18%. 75-4 1.5 evaporation temperature is higher than R22/r11548.8/51.2-45.6 refrigeration capacity is higher than R2213% R23/r1345.6. R11548.2/51.8-57.2 single-stage compression can reach below 50℃. The refrigeration capacity of R 12/R3178/22-29.6 air conditioner is 8% larger than that of R12. RC3 1860/40- 12.3 the condensation pressure is relatively low r592/r2231.8/68.2-48.6r22/r15/r29044.9/.
Different kinds of mixed refrigerants have different thermophysical properties, which will provide more space for refrigerant optimization. For the fixed refrigeration system, it is required that the refrigerant must have specific thermophysical properties under its optimal operating conditions. Reasonable selection of different boiling mixed refrigerants to meet this specific thermal property can improve the thermal efficiency of refrigeration system and achieve the effect of energy saving.
Because boiling the mixed refrigerant can reduce the condensation pressure and increase the evaporation pressure at the same time, the pressure ratio of the compressor will be reduced under the condition that the condensation temperature and evaporation temperature are unchanged, thus reducing the power consumption of the compressor. Therefore, it takes less work to obtain the same cooling capacity. At the same time, the increase of evaporation pressure will reduce the vacuum degree of evaporator and make it work more stably, while the decrease of condensation pressure will make the condenser run further in a safer state. In the paper published by the 5th International Institute of Refrigeration, C. p. a. RORA, an Indian refrigeration expert, took R22/R12 (85/15) as an example to confirm this effect. Due to the decrease of pressure ratio, the volumetric efficiency, refrigeration capacity and performance coefficient of the compressor are improved. At the same time, the temperature of compressor motor dropped from 87.5℃ to 70.3℃, and the temperature of motor starting coil dropped from 97.3℃ to 58.3℃, which played an important role in the safe operation of air conditioning.
The use of boiling mixed refrigerant can reduce the discharge temperature of compressor, which is closely related to the properties of refrigerant. It is proved that the larger the heat capacity of refrigerant or the smaller the adiabatic index, the lower the exhaust temperature of compressor. Refrigerant R 1 15, R1/4 and RC3 18 all have large heat capacities, and as components of mixed refrigerants, they all have the ability to reduce the compressor discharge temperature. For example, if * * * boiling mixed refrigerant R22/r115 (48.8/51.2) has a condensation temperature of 44℃ and an evaporation temperature of-12℃, its exhaust temperature will be100. When R 12 is used, the exhaust temperature is 1 12℃.
Application and Energy Saving of Non-boiling Mixed Refrigerant During evaporation and condensation, the temperature and gas-liquid composition of Non-boiling Mixed Refrigerant are constantly changing. It is precisely because of its temperature change in evaporator and condenser that non-isothermal heat exchange is realized in evaporator and condenser, showing its unique energy-saving characteristics. Table 2 lists the non-boiling mixed refrigerants being used and studied.
The phenomenon of component mixing and separation occurs in the phase change process of non-boiling mixed refrigerant. The condensation process is the process of condensation of high-boiling components and dissolution of low-boiling components. Each component will release its own latent heat of liquefaction and mixing heat, which will eventually increase the condensation heat of unit refrigerant. The evaporation process is a process of desorption of low-boiling components and evaporation of high-boiling components. At this time, each component will absorb its latent heat of vaporization and the corresponding heat of separation, which will lead to the increase of heat absorption per unit refrigerant, that is, the increase of refrigeration capacity. This is because the refrigeration system increases the refrigeration capacity without increasing power consumption. At the same time, the refrigeration capacity per unit volume of refrigerant is also improved accordingly. The research shows that the energy consumption of refrigeration system is significantly reduced after using non-boiling mixed refrigerant. If R22/R 1 14(50/50) non-boiling mixed refrigerant is used to replace R22 in heat pump, the refrigeration coefficient will be increased by 25%. After R22/R 1 1(50/50) replaces R 12 in the refrigerator, the power consumption is reduced.
Table 2 Non-boiling mixed refrigerants studied
The use and research results of component mass ratio r12/r190/10/r12/r13b65438 for heat pump. R 1 1450/50 is more energy-efficient than R 12 for refrigeration. Compared with R 12, heat pump energy saving 16%, r12/r12 = 50 ~ 70%, heat pump and pure components energy saving 10%, r/. Mainly used to improve the cycle parameter R22/R 1 150/50 for refrigeration, energy saving12% R22/r1150 for heat pump, energy saving 25% r13b.
The difference of gas-liquid interweaving of non-boiling mixed refrigerants affects the thermal performance of non-boiling mixed refrigerants. The obvious difference between gas phase and liquid phase in the phase change process makes the components of non-boiling mixed refrigerant easier to mix and separate, thus achieving the purpose of adjusting the mixing ratio. During the operation of some civil air conditioners throughout the year, the external environmental conditions change greatly. Conventional air conditioners with single refrigerant, such as R22, have a small scope of application and good performance indicators under certain climatic conditions. However, when the climatic conditions change, the performance index will decline. Non-boiling mixed refrigerant has strong adaptability to off-design operation because its proportion changes with phase change, and the concentration of each refrigerant component can be adjusted according to the change of climatic conditions. If R22/R 13B 1 is used, high concentration R22 will be used for cooling in summer and R 13B 1 for heating in winter. After using this non-boiling mixed refrigerant, the air conditioner can run with high thermal efficiency all year round, and the energy saving effect is remarkable.
In addition, Lorentz cycle can be realized by using non-boiling mixed refrigerant, which has higher average temperature of heat absorption and lower average temperature of heat release, so it has higher Carnot efficiency. As shown in figure 1, when the refrigerant works under the variable temperature heat source given in (a), the theoretically realizable inverse Carnot cycle is abcda in (b), while the Lorentz cycle is ABCDA in (c). As can be seen from the figure, for the reverse cycle, that is, the refrigeration cycle, Lorenz cycle saves more work than the corresponding reverse Carnot cycle.