| Chlorofluorocarbons(CFCs)and hydrochlorofluorocarbons(HCFCs)refrigerants have been phased out by the Montreal Protocol and further amendments.The substitute refrigerants hydrocarbons(HFCs)are also subject to the Kyoto Protocol and the EU's Fluoride Gas Regulations due to their high global warming potential(GWP).Now,the refrigerant difluorochloromethane(HCFC-22,R22),which is mainly used in domestic air conditioners,and the refrigerant 1,1,1,2-tetrafluoroethane(HFC-134a,R134a),which is mainly used in automotive air conditioners,are subject to environmental regulations.Thus,it is necessary and urgent to find new alternative refrigerants.Among the many nominated alternative refrigerants,2,3,3,3-tetrafluoropropene(HFO-1234yf)and trans-1,3,3,3-Tetrafluoropropene(HFO-1234ze(E))jointly proposed by Honeywell and DuPont are considered to be the most promising and potential alternatives as new generation refrigerants to replace HCFC-22 and HFC-134a in the field of domestic air conditioning and automotive air conditioning,respectively.This type of refrigerant is an unsaturated olefin containing carbon-carbon double bonds and therefore has a low GWP value and a short atmospheric lifetime.However,it has low latent heat and mildly flammability,which limit its commercial applications.An effective and feasible solution to overcome this shortcoming is to mix it with other refrigerants that are mature and complementary in performance.Difluoromethane(HFC-32,R32)is a commonly used refrigerant with many advantages such as non-toxic,no ozone layer destruction,high latent heat,good thermal conductivity,less flammable than HFO-1234yf,etc.,but its GWP value is high.Carbon dioxide,which has a long history as a refrigerant,is an environmentally friendly,non-poisonous,non-flammable,economically applicable natural working fluid,and has been arising in the refrigeration industry in recent years.Therefore,HFO-1234yf,HFO-1234ze(E),HFC-32 and CO2 were selected as the research objects,and the related thermodynamic properties of HFO-1234yf+HFC-32 and HFO-1234ze(E)+CO2 binary systems were studied.For thermophysical properties of fluids,the relationship between temperature(7),pressure(p)and density(p)or specific volume(v)is fundamental and important.The research methods include experimental measurement and theoretical calculation,of which experimental measurement is more direct and accurate.A high-precision fluid pvT property measurement system based on a single-sinker magnetic suspension densimeter is developed in this thesis,including a magnetic suspension densimeter,temperature and pressure measurement and acquisition system,thermostatic bath and temperature control system and vacuum and sample filling system.The working principle of the device and the specific components and methods of use of the device are described in detail in the paper.By improving the level of heating and the temperature control,the temperature of the measuring cell can be quickly stabilized and the fluctuation is very mall.Considering the instrument itself and the experimental process,the measurement uncertainty of the temperature,pressure,density and composition are 6mK,0.7kPa,less than 0.06%of the measured value and less than 0.002.In order to ensure how long the temperature of the inside of the measurement cell would achieve stability,avoiding inaccuracy temperature measurement,the heat transfer and the temperature distribution inside the magnetic suspension densimeter including the measurement cell,magnetic suspension coupling and the sinker,were numerically simulated by Fluent.At the same time,the effects of different charge amounts and different fluids on the heating process of the densitometer and the internal temperature distribution were also obtained.High purity nitrogen was then selected as standard sample,and the comparison of measured pvT data with the results of NIST REFPROP verified the high accuracy of the device.Then,the gaseous pvT data of the pure HFO-1234yf in 252K-345 K and 0.07-1.91 MPa were measured using the densitometer.The experimental data were coMPared with NIST REFPROP 9.0,and the average absolute relative deviation(AARD)is 0.157%.The experimental pvT data combined with the data from other literatures were fitted using a high-precision truncated Virial equation of state.The AARD of the calculated results is 0.024%coMPared with the experimental data.HFO-1234yf+HFC-32 binary mixed system(HFO-1234yf molar fractions of 0.127,0.357,0.559 and 0.774)were measured at temperatures of 279-357K and pressures of 0.13-2.66 MPa,and a total of 153 sets of data were obtained along 8 isothermals,and the AARD of the measured density values and the calculated values of NIST REFPROP was 0.01%.The experimental data were correlated by using the Virial equation of state,and the van der Waals mixing rule was also applied.The AARD of the calculated values and the experimental data in terms of pressure and density are 0.10%and 0.1 1%,respectively.Vapor-liquid equilibrium(VLE)data is necessary for mixtures,and it is critical to evaluate the performance of refrigeration system.The methods to study VLE properties also include experimental and theoretical methods,of which experimental measurement is more direct and accurate.In this thesis,VLE properties measuring apparatus in our laboratory was improved.The temperature acquisition and control program was developed by Lab View,which can control the system stable with a temperature fluctuation withiną5mK.The apparatus is based on a circulation method.In addition to the temperature control system,it also includes a VLE equilibrium cell and an inner circulation line,a liquid bath and an air bath,a vacuum unit,an outer circulation line and a gas chromatograph.The measurement uncertainty of temperature,pressure and composition of the apparatus is 5mK,3.5kPa and less than 0.002,respectively.The saturated vapor pressures of the pure HFO-1234ze(E)were measured in the temperature range of 283.15K to 343.15K,and the AARD of the measured value with the calculated value from NIST REFPROP was 0.25%.The experimental data agree well with the calculated data,and therefore the apparatus is verified reliably.Then,a high-precision Antoine-type saturated vapor pressure equation with six parameters was obtained by fitting the experimental data.The fitted values were in good agreement with the experimental values.After that,the component calibration of HFO-1234ze(E)+CO2 binary mixture system was carried out,and the relationship between the molar fraction and the chromatographic peak fraction was obtained.Then the VLE properties of HFO-1234ze(E)+CO2 binary mixture system at 283.15K,313.15K and 343.15K were measured,and the measured pressure values were compared with the reference pressure values calculated from NIST REFPROP and the AARD is 1.57%.Finally,the PR equation of state with the vdW type mixing rule was used to correlate the experimental data.It can be seen that the values calculated by correlation agree well with the experimental data. |
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