Studies On Vapor-Liquid Equilibrium Properties And Critical Properties Of Mixtures Containing Hydrofluoroolefins

With the gradual improvement of safety,economy,and environmental protection requirements,refrigerants are gradually being replaced.The early refrigerants,hydrochlorofluorocarbons(HCFCs),and chlorofluorocarbons(CFCs),have been restricted and phased out in accordance with the Montreal Protocol and related amendments.Hydrofluorocarbons(HFCs)working fluids proposed after the HCFCs and CFCs have been limited in their use due to their high Global Warming Potential(GWP)according to the Kyoto Protocol,the Fluorine Gas Regulations,and The Kigali Amendment to the Montreal protocol.Hydrocarbons(HCs)working fluids,due to their flammable and explosive characteristics,are also difficult to promote.Therefore,it is necessary and urgent to find safe,efficient,and environmentally friendly alternative refrigerants.In recent years,two kinds of hydrofluoroolefins(HFOs)working fluids,named 2,3,3,3tetrafluoropropene(HFO-1234yf)and trans-1,3,3,3-tetrafluoropropene(HFO-1234ze(E)),which have attracted wide attention and are considered to be the most promising alternative refrigerants.Their ozone depletion potential(ODP)values are both zero and GWP values are extremely low,but the lower latent heat of vaporization limits their use as pure refrigerants.Refrigerant mixtures can overcome shortcomings such as high flammability and high GWP values by adjusting the components and mole fractions,and have excellent thermodynamic and environmental performances.Both ethyl fluoride(HFC-161)and n-butane(HC-600)have low GWP values and high latent heat of vaporization but strong flammability.1,1,1-trifluoroethane(HFC-143a)has higher vapor pressures than HFO-1234ze(E)and was mainly used as a component of R404A(0.44 HFC-125+0.04 HFC-134a+0.52 HFC-143a by mass)and R507A(0.5 HFC-125+0.5 HFC-143a by mass),but it was hardly used as pure refrigeration individually because of its low critical temperature.Thus,in this thesis,the thermodynamic properties of binary mixtures containing HFO1234yf,HFO-1234ze(E),HFC-161,HC-600,and HFC-143a were studied.The vapor-liquid equilibrium(VLE)properties of working fluid mixtures are very important for evaluating their performance in a refrigeration or heat pump cycle.Experimental measurement is always the most direct and effective way to obtain these properties.Therefore,based on the vaporliquid equilibrium experimental device of our research group,the vapor-liquid equilibrium properties of the HFO-1234yf+HC-600 mixture were measured.The experimental results were correlated by the Peng-Robinson(PR)equation of state combining with van der Waals(vdW)mixing rule and Wong-Sandler(WS)mixing rule.The critical point is the endpoint of the VLE properties and also the starting point of supercritical properties of working fluids.It plays a very important role in many ways,such as the analysis of trans-critical cycles and the study of supercritical extraction.In this thesis,a set of highaccuracy experimental measurement apparatus for critical properties was established.A set of temperature control and data acquisition programs developed by our research group were used for temperature control.A gas chromatograph was used to analyze the mole fractions,and a variablevolume visible equilibrium cell was developed,which is convenient for adjusting the density and observation of the critical phenomenon.The vapor pressures and critical properties for pure HFO1234ze(E)and HFC-143a were measured by this apparatus and the experimental results were in good agreement with the data reported in literature,which means that the high accuracy of this apparatus was verified.Moreover,based on this device,the critical properties of the binary mixture HFC-143a+HFO-1234ze(E)were experimentally measured,and the high-precision correlation model was established.Experimental measurements are expensive and time-consuming and can only obtain limited data points,thus,it is also very important to use theoretical methods to simulate and predict the thermodynamic properties of working fluids.In this thesis,artificial neural network and molecular simulation were used to simulate the vapor-liquid equilibrium properties and critical properties of binary mixtures.Molecular simulation has its unique advantages in the simulation of micro-conformation and the interpretation of micro-mechanisms of macroscopic properties.With the rapid development of computer technology and chemical theory,molecular simulation methods have already been widely used.In this work,an all-atom force field for HFC-161 was developed using the configuration perturbation method which is based on first principles.And the force field was applied to carry out the Gibbs ensemble Monte Carlo(GEMC)simulations to calculate the thermophysical properties of HFC-161.Thermodynamic properties such as the saturated density at vapor and liquid phase,saturated vapor pressure,and critical properties,obtained through GEMC simulations showed good agreement with experimental data or correlated data.Moreover,based on the existing molecular force fields,GEMC simulations were carried out to simulate the vapor-liquid equilibrium properties of the binary mixture of HFC-161+HFO-1234yf.The results obtained by GEMC simulations showed good agreement with experimental data and correlated values.Artificial neural networks have been widely used in the calculation of thermodynamic properties such as viscosity,density,and saturated vapor pressure due to their fast calculation speed and high accuracy.In this thesis,high-precision artificial neural network models were established for binary mixtures containing HFO-1234yf.HFO-1234ze(E),HC-600,HFC-161and HFC-32 an the neural network models were applied to the calculations of VLE properties of the mixtures.High-precision artificial neural network models were established for binary mixtures containing HFO-1234yf,HFO-1234ze(E),CO2,HC-600,and HFC-32 and the neural network models were applied to the calculations of critical properties of the mixtures.All the calculation results showed good agreement with the experimental data.