Theoretical And Experimental Study On Phase Equilibrium Of Novel Absorption Refrigerants

As a result of the regulation of hydrochlorofluorocarbons (HCFCs) andchlorofluorocarbons (CFCs), hydrofluorocarbons (HFCs) mixtures are considered to bepromising candidates for replacement of HCFCs and CFCs compounds because theirozone depletion potentials are zero. The studies on the thermodynamic properties ofHFCs got a great achievement, but there are few studies for the applying of HFCs inabsorption refrigeration. The researches on vapor-liquid equilibrium (VLE) of binarysystem of difluoromethane (HFC-32, CH₂F₂)+1,1,1,2-tetrafluoroethane (HFC-134a,CH₂FCF₃), trifluoromethane (HFC-23, CHF₃)+1,1,1,2-tetrafluoroethane (HFC-134a),and VLE of HFC-134a, HFC-32, HFC-23, HFC-23+HFC-134a with N,N-dimethylformamide (DMF), are carried out in this thesis.A new measurement system for VLE properties of refrigerant-absorbent with highaccuracy was developed by vapor circulation method. It consists of a temperaturemeasurement system, a pressure measurement system, a thermostat bath, a vacuumsystem and a mixture make-up system, etc. The experiments can be performed in a widetemperature range of 258.15～369.15 K and wide pressure range of 0～3.5 MPa. Theexperimental results indicated that the temperature uncertainty was estimated to be lessthan±14 mK, the pressure uncertainty of the measurement system was estimated to beless than±1.465 kPa, the liquid mole fraction of the measurement system wasestimated to be less than±0.001.New results of vapor pressure data for DMF have been measured in the temperaturerange of 307.15～369.15 K. Based on experimental data, a new Wagner-type vaporpressure equation for DMF was presented.Isothermal VLE data for the binary system of HFC-32+HFC-134a and HFC-23+ HFC-134a were measured in the temperature range of 258.15～343.15 K and 258.15～293.15 K, respectively. The experimental data were correlated with thePeng-Robinson-Stryjek-Vera (PRSV) equation of state using the Wong-Sandler (WS)mixing rule. The values calculated with the PRSV equation of state and the WS mixingrules give comparatively good agreement with experimental data.Isothermal VLE data for the binary system of HFC-134a+DMF, HFC-32+DMFand HFC-23+DMF, and ternary system of HFC-23+HFC-134a+DMF weremeasured in the temperature range of 283.15～363.15 K. The experimental data of thebinary systems were correlated by PRSV equation of state using the WS mixing ruleand LCVM mixing rule with NRTL model. The values calculated with the PR equationof state and the WS mixing rule and LCVM mixing rule give comparatively goodagreement with experimental data.Based on the calculation of activity coefficients of the binary system of HFC-134a+DMF, HFC-32+DMF and HFC-23+DMF, the deviation from ideal behavior of thesebinary systems were analysed. The binary systems of HFC-134a+DMF and HFC-32+DMF exhibit negative deviations from ideal behavior in the temperature range of 283.15～363.15 K. The binary system of HFC-23+DMF exhibits negative deviations fromideal behavior at lower temperatures while it exhibits positive deviations from idealbehavior at higher temperatures.Based on the theory of corresponding state and derivation of seudocritical constants,a new correlation for binary interaction parameters was proposed.Based on the Mie potential function theory and London disersion forces theory, andwith the introduction of pseudocritical rules and Leach's molecular shape factors, a newcorrelation for binary interaction parameters of the co-volume parameter for asymmetriccomplex mixtures was deduced. Better results were achieved when the correlation wasused to calculate the VLE of HFCs+DMF.