Study On Replacing Of Nature Refrigerants Cascaded Refrigeration Cycle With CO₂ Working In Low Temperature Stage

In the dissertation study on replacing of nature refrigerants cascaded refrigeration cycle with CO₂ in lower temperature stage are done, the main work and results are as follow:(1) Thermodynamic analyzing of nature refrigerants R290/CO₂ and R22/R13 cascaded refrigeration cycle are studied based on the investigation on replacing of nature refrigerants cascaded refrigeration cycle, results are concluded: the COP of R290/CO₂ cascaded refrigeration cycle is a little higher than that of R22/R13, the cooling capacity both mass and volume of CO₂ at lower temperature stage are much higher than that of R13, Considering about the integrated effect of pressure ratio and mass flow ratio between high temperature stage and lower temperature one, from the thermodynamic view the cascade refrigeration cycle R290/CO₂ could substitute for R22/R13 one used in small size apparatus when the evaporating temperature ranged from -40 degree to -55 degree.(2) Numerical modeling of CO₂ refrigerant flow in the adiabatic capillary tubes and simulation program are built based on the previous research on CO₂ flow characteristic in adiabatic capillary, results from simulation program are compared with the experiment results, which leads to a conclusion that: the results from simulation program show an agreement with the experiment results, and relative roughness has an influence on the veracity of numerical modeling of CO₂ refrigerant flow characteristic in the capillary tubes, the linear characteristics of CO₂ flow through adiabatic capillary tubes are found in our experiment research field, and its application of linear characteristics is helpful to modify or simplify the design and rating method of capillary tubes based on empirical or half-empirical model.