Study On Mixed-Refrigerant R134a/R23 And Its Auto-Cascade Refrigeration Cycle

In recent years, reachers have paid more attention to usage of energy and environment protection. Consequently alternative refrigerants and their mixture, including HFCs, HCs or nature refrigerants are studied. Autocascade refrigeration (ACR) is a kind of typical refrigeration cycle, which uses mixed refrigerant and makes good use of the mixture's characteristics. ACR takes advantage to apply in the area below -50℃.More products based on ACR have been put into market. They are deep freezer, cryopreservation, low-temperature treatment, cryogenic material and so on. But the ACR system is relatively complex, having many restraints and influence factors, and even the thermophysical properties data of mixed refrigerant are not sufficient and precise .So anlysis and research on ACR needs to be further developed.In this thesis, mixed-refrigerant HFC134a/R23 is choosed as ACR's working fluid. The thermophysical properties are calculated in detail and based on the mixture's properties, performance of the ideal ACR cycle is simulated.The main content of this thesis is shown as follows:1) In calculation of R134a/R23 properties, the traditional equation of state is corrected. Using this corrected equation, we analyze R134a/R23 P-V-T-x and get new expression of fugucity, enthalphy and entropy. By theoretical calculation, data of the mixture's VLE, enthalphy, entropy and transport properties are all obtained;2) Thermopropertes calculation is programmed and enthalphy-concentration diagram is plotted. Result data are compared with those obtained when R134a/R23 is assumed as ideal mixture. The difference from this comparison is the mixture's deviation properties;3) An analysis method based on enthalphy-concentration diagram is systematicly put forward to explain the ACR cycle. Then we priliminarily decide the cycle's constrait conditons and influence factors;4) Procedure of thermophysical calculation for ACR cycle is shown in this thesis. All state points's parameters and coefficient of performance is decided under design condition and other conditions when condensation temperature, middle tempera -ture, pressure and mixture's composition change;5) Optimization model for ACR cycle is set up and from this model we get the optimized compositon of R134a/R23 in different condensation temperature and evaporation temperature. The ultimate evaporation temperature exists when the pressure ratio limited to 13;6) This thesis's study shows that pressure ratio and evaporation temperature of ACR cycle can be decreased when internal heat exchangeris installed, however which has little influence to the optimized compositon. So ACR cycle with internal heat exchanger should be recommended.