Refrigerant classification and selection requirements
【】Refrigerants are also called refrigeration working fluids, commonly known as refrigerants in some areas in the south. It is a working substance that continuously circulates in the refrigeration system and realizes refrigeration through its own state changes. The refrigerant absorbs the heat of the cooling medium (water or air, etc.) in the evaporator to vaporize, and transfers the heat to the surrounding air or water in the condenser to condense. Today, I will take you to learn more about the classification and selection requirements of refrigerants.
1. Classification of refrigerants
Refrigerants can be divided into three categories according to the condensation pressure at room temperature and the evaporation temperature at atmospheric pressure:
1, low pressure and high temperature refrigerant
The evaporation temperature is higher than 0℃, and the condensing pressure is lower than 29.41995×104Pa.
2, medium pressure and medium temperature refrigerant
evaporation temperature -50~0℃, condensing pressure (196.113~29.41995)×104Pa.
3, high-pressure low-temperature refrigerant
The evaporation temperature is lower than -50℃, and the condensing pressure is higher than 196.133×104Pa.
Second, refrigerant selection requirements
1, the working temperature and working pressure of the refrigerant should be moderate.
At atmospheric pressure, the evaporation temperature of the refrigerant must be low enough to meet the cooling temperature requirements;
At room temperature, the refrigerant must have a relatively low condensing pressure, because When the condensing pressure is too high, the structural strength of the sealing performance agent of the refrigeration system is high. Generally, the condensing pressure of the refrigerant is required to be: 12×105~15×105Pa;
At room temperature, the refrigerant must have a relatively high evaporation pressure, because if the pressure in the evaporator is lower than the atmospheric pressure , The outside air can easily enter the refrigeration system through the gap, which increases the pressure in the system, reduces the refrigeration capacity and increases the power consumption. At the same time, moisture in the air will cause ice blockage and other adverse effects in the refrigeration system.
2. The refrigerant must have a relatively large unit volume refrigeration capacity
The refrigeration equipment of the same specification, when the selected refrigerant has a large unit volume refrigeration capacity, a larger capacity can be obtained Cooling capacity.
Under the same working conditions, when the cooling capacity is constant, the unit volume of the refrigerant has a large cooling capacity, which can reduce the refrigerant volume of the system and reduce the size of the compressor accordingly.
3. The critical temperature of the refrigerant should be high, and the freezing point should be low
The critical temperature is high, which is convenient for the refrigerant to condense and weigh at ambient temperature as a liquid; the freezing point is low, so it can be made lower Temperature, expand the use temperature range of the refrigerant, reduce throttling loss, and improve the coefficient of refrigeration.
4. The viscosity and density of the refrigerant should be as small as possible.
The viscosity and density are small, which can make the flow resistance of the refrigerant cycle in the system small and reduce the cycle power consumption. Reduce the diameter of the pipe and allow the pipe to have a smaller bending radius (and this is very important for reducing the pressure loss of the evaporator), and can also reduce the impact of the refrigerator on the valve group of the compressor and extend the compressor’s Service life.
5. The thermal conductivity and heat release coefficient of the refrigerant should be high.
The high thermal conductivity and heat release coefficient can appropriately reduce the structure of the heat exchanger in the refrigeration system, and Improve the heat exchange efficiency of the heat exchanger.
6. Requirements for other aspects of refrigerant
is non-flammable, non-explosive, non-toxic, non-corrosive, affordable, easy to buy, etc.
What are the requirements for the selection of cold storage refrigerant?
The nature of refrigerant will directly affect the type, structure, size and operating characteristics of the refrigerator. It will also affect the form, equipment structure and economic and technical performance of the refrigeration cycle. Therefore, a reasonable choice of refrigerant is a Very important question. Generally, the performance requirements of refrigerants are considered from the aspects of thermodynamics, physical chemistry, safety, environmental impact and economy.
1. Thermodynamic requirements
1. The boiling point should be low, and a lower evaporation temperature can be obtained.
At the same time, the low boiling point refrigerant has a higher The vapor pressure.
2, the critical temperature should be high, and the solidification temperature should be low.
The critical temperature should be high and the freezing temperature should be low to ensure that the refrigerant works safely in a wide temperature range.
3. The refrigerant must have an appropriate working pressure
requires the evaporation pressure of the refrigerant to be close to or slightly higher than the atmospheric pressure to avoid vacuum in the low pressure part of the refrigeration system and increase the air mixing Opportunity to enter the system. The condensing pressure must not be too high. Low condensing pressure can reduce the strength and construction requirements of refrigeration equipment and pipelines, and reduce the construction investment of refrigeration systems and the possibility of refrigerant leakage. The pressure ratio and pressure difference between the condensing pressure and the evaporating pressure are required to be small.
4. The latent heat of vaporization of the refrigerant should be large.
When the refrigeration system obtains the same cold output, the large latent heat of vaporization can reduce the circulation of the refrigerant. At the same time, it can also reduce the investment of refrigerators and equipment, reduce operating energy consumption, and improve refrigeration efficiency.
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