The Prediction And Measurement Of Vapor-Liquid Equilibrium For The Ternary Mixed Refrigerants Containing R1234yf

The mixed refrigerant is a multi-component mixture of two or more single-component refrigerants.The mixed refrigerant refrigeration cycle is generally different from the single-component refrigerant refrigeration cycle.Utilizing the unique properties of the mixed refrigerant,the refrigeration system can be subjected to a Lorenz Cycle or an auto-cascade refrigeration cycle of a single compressor.Here,the vapor-liquid equilibrium characteristics of the mixed refrigerant play an important role.At present,limited to international conventions,refrigerant substitution has become a hot and difficult issue in the refrigeration and air conditioning industry.Since R1234yf has a short atmospheric lifetime（0.029）,GWP<1,and ODP of 0,it is an ideal replacement for R134a in pure refrigerants.Considering that R1234yf has the disadvantages of microflammability and low latent heat of vaporization,the combination of R1234yf and other refrigerants to complement the advantages of each other and make a new mixture as an alternative refrigerant has become the current research focus.In this paper,we mainly look for efficient and environment-friendly alternative mixed refrigerants with potential for single-stage vapor compression refrigeration equipment,and predict and provide accurate and reliable vapor-liquid equilibrium（VLE）data,and conduct a preliminary study of the phenomenon that vapor-liquid-liquid three-phase co-existence of mixtures may occur at low temperatures.Aimed at the phase equilibrium characteristics of mixed refrigerants,theoretical and experimental studies have been carried out.The basic properties and research methods of the related refrigerants also have important applications in the chemical field.The main contents and conclusions include the following aspects:（1）The new refrigerant R1234yf was mixed with R134a and R290 to get a new alternative refrigerant R1234yf+R134a+R290,and R1234yf was mixed with R23,R170and R14 to obtain the new two kinds of strong-zeotropic refrigerants,R1234yf+R23+R14and R1234yf+R170+R14,which are suitable for auto-cascade refrigeration cycle（ARC）.Based on the database of Dortmund Data Bank（DDB）and comparing and analyzing the advantages and disadvantages of various equations,a new G^E-EoS model―PR-WS-MUNIFAC model with predictive function was proposed based on the equation of state method and group contribution method.The VLE data of R152a+R1234yf,R161+R1234yf,R14+R1234yf,R1234yf+R600a+R134a and R32+R125+R134a mixtures were calculated by using the model,and the calculation results are compared with the literature experimental data to verify the reliability of the model.The results show that the model has a higher calculation precision.In a comprehensive comparison,the average absolute relative deviation（AARD）of the pressure is about 2%,and the average absolute deviation（AAD）of the mass fraction of the vapor component is about0.006,which meets the requirements of the practical engineering application.（2）Using the experimental data given in the literature,the binary interaction coefficient of the WS mixing rule in PR-WS-MUNIFAC model is regressed,and the group parameters in MUNIFAC were obtained based on the DDB database and the related literature correlation results.The isothermal VLE behavior of R1234yf+R134a+R290 at253.15K³13.15K temperature range,the isobaric VLE properties of R1234yf+R23+R14under 0.2MPa,0.4MPa,1.5MPa and 2.2MPa,R1234yf+R170+R14 under 0.1MPa,0.2MPa,0.5MPa were predicted by using PR-WS-MUNIFAC model and the related three-dimensional phase equilibrium diagrams were plotted.It is predicted that R1234yf+R134a+R290 may exist the phenomenon of vapor-liquid-liquid equilibrium（VLLE）,and the upper critical end point（UCEP）pressure is 1.627MPa.The maximum slip temperature of the latter two systems is about 73K.The predicted results have certain guidance and reference for the related experimental research and practical engineering application.（3）A set of visualized VLE experiment table with high precision was designed and built independently.Through the window of liquid-visual mirror,we can observe the equilibrium situation in the equilibrium cell constantly and control the vapor-liquid interface at the proper position to ensure the accuracy of the experimental data.The device is equipped with a PID detector gas chromatograph and a TCD detector gas chromatograph,which can simultaneously analyze the composition content of organic matter and inorganic matter.Within the full range,the expanded uncertainty of the measurement of system temperature,pressure and mass fraction is 78mK,4.01kPa and0.0022,respectively.The experimental table can test the vapor-liquid equilibrium properties of common refrigerants in the temperature range of 150K³50K.（4）In the temperature range of 253.15K³23.15K,the saturated vapor pressure data of R134a and R290 were measured,the results were regressed by the saturated vapor pressure equation of Antoine and Wagner to obtain the constants of the equations,and the value of the NIST database were added to the comparative analysis as well.The AAD of saturated vapor pressure of R134a for the two equations of Wagner and Antoine is4.12kPa and 4.13kPa,respectively.The AARD are 0.69%and 0.70%,respectively,which are better than 5.35kPa and 0.81%of NIST,and the deviation of R290 is similar.The comparison results indicated that both of the two equations could express the saturated vapor pressure of R134a and R290 pure refrigerants.In the temperature range of（253.15K-313.15 K）at 10 K intervals,the VLE data of R134a+R290 binary system was measured.The reliability of the experimental data and the device was verified.At the same time,the NRTL-RK model was used to correlate the experimental data,and the pressure and concentration range of the possible existence of VLLE in the system was analyzed in order to guide further experimental verification.（5）The VLE data of R1234yf+R134a+R290 ternary mixture was measured over the temperature range of 283.15K³23.15K at 10K intervals.The experimental results were associated with the NRTL-RK model and the Wilson-RK model,and the corresponding binary interaction parameters were obtained by using the VLE data of the ternary system,so that the model can describe the VLE properties of the ternary mixtures more accurately.The results demonstrate that the two models have similar computational accuracy and all of them can well express the VLE properties of the mixture.The AARD of pressure and the AAD of the vapor phase mass fraction of Wilson-RK model is 0.33%,0.0054 and 0.0057 respectively,which is slightly better than the 0.40%,0.0128 and0.0121 of the NRTL-RK model.Meanwhile,the experimental data were compared to the prediction results of the PR-WS-MUNIFAC model in the preceding work.It was found that the predicted results of pressure were in good agreement with the experimental data,and more than 90%of the data deviations are within 5%.Based on the UNIFAC（Dortmund）group contribution method,two new functional groups of C2H2F and CFH2were proposed,and the surface area parameter R and volume parameter Q of the new functional groups were regressed based on the experimental data,as well as the six group binary parameters₈9)),₈9)),₈9)),₉8)),₉8))and₉8)).By applying the improved parameters into the PR-WS-MUNIFAC model,the AARD of the pressure is 0.59%,and the AAD of the vapor phase mass fraction is 0.0174 and 0.0158,respectively.（6）The VLE data of the strong-zeotropic mixture of R1234yf+R23+R14 were measured over the temperature range of 253.15K²73.15K.The experimental results were correlated by NRTL-RK model,Wilson-RK model and PR-WS-MUNIFAC model,and the relevant parameters of the model were fitted.The results show that the NRTL-RK model and the Wilson-RK model have an obvious decrease in the calculation accuracy of composition in the high temperature region,and the AARD of pressure and AAD of vapor phase mass fraction are 0.40%,0.0165,0.0198 and 0.38%,0.0230 and 0.0384 respectively.PR-WS-MUNIFAC is almost not affected by temperature,and the calculation accuracy is higher with the deviation is 0.34%,0.0062 and 0.0078,respectively.Based on the UNIFAC（Dortmund）group contribution method,CF4 was proposed as a new functional group.The surface area parameter R,the volume parameter Q of CF4 and the six group binary parameters were obtained based on the regression of experimental data.（7）The VLE data of the strong-zeotropic mixture of R1234yf+R170+R14 were measured over the temperature range of 253.15K²73.15K.The experimental results were correlated by NRTL-RK model and PR-WS-MUNIFAC model,and the relevant model parameters were obtained.The AARD of pressure and AAD of vapor phase mass fraction of PR-WS-MUNIFAC model are 0.32%,0.0098 and 0.0185,slightly better than those of 0.28%,0.0077 and 0.0277 for NRTL-RK model.At the same time,the group parameters are collected and analyzed based on the regression analysis of the VLE experimental data of three different ternary mixtures,and compared with the group parameters in the DDB database.The results show that the group parameters are accurate and reliable,and effectively supplemented the physical parameters of the chemical database,and expanded the application range of the UNIFAC（Dortmund）group contribution method in the fluorine containing refrigerants.