1. Higher CO2 critical pressure (7.38 MPa), thus the CO2 across critical refrigeration cycle working pressure, compared with the traditional subcritical two phase refrigeration cycle working pressure is much higher, about traditional refrigerating CFC or as 6 ~ 8 times the system pressure
Therefore, the piping system in the refrigerating system must be analyzed by safety.
However because the unit volume of CO2 refrigerating capacity is about 5 ~ 8 times of conventional refrigerant, CO2 volume required by the system is small, the explosion energy of the gas inside the devices as a function of the product of pressure and volume, so although system working medium pressure is high, but the volume is small, the pressure and volume differ with normal working medium is not big, the product of explosion energy increase of gas inside the devices is not much
Based on reliability theory, according to the reliability of the CO2 refrigeration system across the critical pipeline different influence factors and change law of the different pipe of the reliability of the case for in-depth research and analysis, the conclusion is: when the tube outer diameter of the pipeline system to timing, as long as reasonable choice of tubing and pipe wall thickness, can guarantee the reliability of the system under a given pressure operation and security, CO2 critical cycle across higher operation pressure can be properly solved; Basic existing steel tube can be directly applied, and the existing copper pipe is selected according to pipe diameter and wall thickness after safety analysis.
Therefore the working pressure of CO2 caused by the high security problems, will not affect the CO2 as the popularization and application of the environmental protection refrigerants.
2. The performance coefficient of CO2 single-stage compression cross critical cycle is lower than that of conventional refrigerants such as R12, R22, R134a and other conventional refrigerants under the same temperature. Aimed at the shortcoming of low CO2 refrigeration cycle performance coefficient, the scholars research discovery, can through the perfect system circulation mode, optimizing the system equipment, such as adopt two-stage compression and expansion machine recycling part of the expansion work measures to improve, to improve the efficiency of refrigeration cycle. The theoretical analysis shows that the efficiency of CO2 cross critical cycle is higher than that of conventional refrigeration.