Prediction Of Thermophysical Properties And PVTx Measurement Of Refrigerant Mixtures

According to the Montreal Protocol and its amendments, chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs), which were commonly used as refrigerants would be phased out for ozone depletion. Thus, it is very necessary to look for environmentally acceptable alternative refrigerants. Hydrofluorocarbons (HFCs) and hydrocarbons (HCs) are considered as the promising alternative refrigerants for their zero ozone depletion potentials. However, it is difficult to find a pure refrigerant with both excellent refrigeration performance and environmentally acceptable properties. Refrigerant mixtures are more and more interesting for their optional components and adjustable fractions.. The vapor liquid equilibrium (VLE) properties of refrigerant mixtures are essential for evaluating the performance of refrigeration or heat pump cycles and determining their optimal compositions. Nowadays, measurement is still the main source to obtain basic VLE data. But it is much more difficult and burdensome than pure refrigerant for the complexity of mixtures, Thus, prediction methods with high accuracy for VLE properties of refrigerant mixtures are very important for both scientific reseach and engineering application.The corresponding state principle and equation of state (EoS) method were used to research VLE properties of refrigerant mixtures including HFC/HFCs, HFC/HCs and HC/HCs; The experimental and theoretical researches on VLE were performed for a new promising refrigerant mixture pentafluoroethane/isobutane (HFC-125/HC-600a), which could be considered as a potential alternative to HCFC-22; A program was developed to calculate thermophysical properties by using MBWR EoS and Lemmon-Jacobsen mixing rules. Thermodynamic properties diagrams of RMA (R125/R600a: 50/50mass%) were presented.The modified pressure equations of bubble and dew point were deduced. According to the principle of iso-corresponding-parameters, relationships of corresponding thermodynamic properties of saturated refrigerant mixtures were developed, the Dalton's law at iso-temperature was modified as a partial pressure law at iso-corresponding-temperature for average pressure of mixing solutions, and predictions of bubble and dew point pressure for refrigerant mixtures were extended to the near-critical region.Basing on the corresponding state principle, new definitions of corresponding temperature and corresponding thermodynamic parameters were proposed for refrigerant mixtures, where the characteristic differences of parameters were regarded as corresponding characteristic parameters. The relationships between corresponding thermodynamic parameters and corresponding temperature of refrigerant mixtures according with that of pure components were revealed. The generalized equations of saturated vapor and liquid enthalpies, densities, entropies and latent heat of refrigerant mixtures was obtained. Three methods were introduced to determine the characteristic parameters of refrigerant mixtures according to the different application conditions. The characteristic parameters of refrigerant mixtures were calculated with the characteristic values of pure refrigerants by using linear series-type expressions, parallel-type expressions and modified liner expressions in method 3, respectively. Then the saturated parameters were calculated for five kinds of refrigerant mixtures by the generalized equations and characteristic values, and the calculated values accurately accorded with the data in literatures.VLE data of HFC/HFCs, HFC/HC.s and HC/HCs mixtures were mined from available literatures. Then Peng-Robinson(PR) EoS with the van-der-Waals(vdW) mixing rule were used to correlate these VLE data and 39 interaction parameters k_ij of these binary refrigerant mixtures were obtained.During Researching EoS principle of refrigerant mixtures, a mixing factor notion was proposed for pure refrigerant and interaction parameters of mixtures can be calculated by mixing factors of their pure components. A differential model was set up for interaction parameters calculation from mixing factors of pure components. The mixing factors of ten HFC refrigerants (HFC23, HFC32, HFC125, HFC134a, HFC143a, HFC152a, HFC227ea, HFC236ea, HFC236fa and HFC245fa) and three HC refrigerants (HC290, HC600a and HC600) were obtained by the least square method. Finally, 78 binary interaction parameters of HFC/HFCs, HFC/HCs and HC/HCs were obtained.PVTx measurement system was set up for VLE measurement by improving the PVT measurement apparatus and a component correction method was presented for VLE measurement results treatment. Isothermal VLE data for R410A, R125/R60Oa and R143a/R227ea binary systems were measured at 243.15-333.15 K, where there are only data at three temperatures for R125/R600a mixture and no available data for R143a/R227ea mixture.VLE data of R125/R600a mixture were correlated with equation of state to obtain interaction parameters at different temperatures. Pressures and vapor mole fractions of R125/R600a mixture were calculated and agreed well with the experimental values in this work and literature. Interaction parameters k₁₂ were fitted as an inverse relation of temperature.Basing on the refrigerant database REFPROP 7.0, a program was developed to calculate thermophysical properties of refrigerant mixtures by using MBWR EoS and Lemmon-Jacobsen mixing rules. The thermodynamic calculation was completed for RMA (R125/R600a: 50/50 mass %), and pressure-enthalpy diagram, temperature-entropy diagram, specific isobaric heat capacity diagram and saturated properties table were presented. The saturated properties were also predicted by corresponding method and the results were accorded with that of MBWR EoS.Lastly, the analysis for the performance of refrigeration and heat pump cycles of RMA was completed. Besides zero ODP and low GWP, the COP and compression ratio of RMA are close to that of R22. Compared with R22, RMA has lower exhaust temperature and higher unit mass refrigeration capacity. The disadvantage of RMA is lower unit volume refrigeration capacity, but it is higher than that of R600a. The fiammability of RMA is lower than that of R600a.