Research On The Vapor-liquid Equilibrium Properties Of HFO And Its Binary Mixtures

In order to curb global warming,China aims to have CO₂ emissions peak before2030 and achieve carbon neutrality before 2060.To achieve this ambitious goal,it is necessary to reduce the usage of high global warming potential(GWP)working fluids and develop low GWP working fluids.So,hydrofluoroolefin(HFO)and its mixtures have a broad prospect in engineering applications.The thermophysical properties of working fluids are the necessary basis for the application of new working fluids.The vapor-liquid equilibrium(VLE)is the most fundamental thermophysical property of pure and mixed working fluids.In this paper,experimental and theoretical studies are carried out for the vapor pressure of new HFO working fluids and the vapor-liquid phase equilibrium of binary mixtures containing HFO.A high-precision steady-state vapor pressure experimental system was built.The vapor pressure of two kinds of new HFO working fluids,R-1233zd(E)and R-1336mzz(Z)were measured,and the experimental samples were carefully analyzed and purified.Based on the ideal solution model,a model to quantitatively correct the influence of impurities is developed.The high accuracy vapor pressure equations for R-1233zd(E)and R-1336mzz(Z)are correlated based on the reliable data obtained.A vapor-liquid recirculation type VLE experimental system was built.The pivotal parts such as phase equilibrium cell,circulation loop,and magnetic pump were designed;the calibration gas mixtures were prepared using the gravimetric method.The gas chromatograph was calibrated;the composition measurement uncertainties were carefully evaluated.The validation experiments of the R-125+R-290 system were carried out,and the experimental data are in good agreement with the literature data,which proves the reliability of the new VLE experimental system and the experimental method.The VLE of three kinds of binary mixtures containing HFO,i.e.,R-32+R-1234yf,CO₂+R-1234yf,and CO₂+R-1243zf,were measured.The experiment temperature exceeded the critical temperature of the low critical temperature components,and a group of experimental data with good thermodynamic consistency was obtained.The experimental data are correlated using the PRSV+WS+NRTL model,which describes the experimental data with high accuracy.The experimental data of this work show good consistency with those in the literature.A VLE predictive model for the mixtures containing HFO was developed using UNIQUAC Functional-group Activity Coefficients(UNIFAC).The group partitioning principles were examined;the volume and area parameters of new groups introduced by HFO were determined;the interaction coefficients between groups are correlated.The model is correlated by 26 HFO+HC/HFC/CO₂ binary systems and is applied to predict 7HFO+HC/HFC/CO₂ binary systems.It is concluded that the predictive model has high computational accuracy.