(Vapour + liquid) equilibria of the {1,1,1-trifluoroethane (HFC-143a) + isobutene} system

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Abstract

Isothermal (vapour + liquid) equilibrium data were measured for the {1,1,1-trifluoroethane (HFC-143a) + isobutene} as an alternative refrigerant in the temperature range from (273.15 to 348.15) K at 15 K intervals. A circulating-type apparatus with on-line gas chromatography was used in these experiments. The experimental data were correlated well by Peng–Robinson equation of state using the Wong–Sandler mixing rules.

Introduction

Ozone depletion is one of the major environmental issues and it has the potential to seriously damage the natural environment. The production and use of substances with high ozone depletion potentials (ODPs), such as chlorofluorocarbons (CFCs), were banned under the 1987 Montreal Protocol. Since CFCs have been widely used as working fluids in the refrigeration, air-conditioning, and heat pump system, suitable alternatives for the replacement of CFCs are needed. Hydrofluorocarbons (HFCs) have been considered as possible alternative refrigerants because of their zero ODPs. Kyoto Protocol having the objective of reducing greenhouse gases, however, regulated some HFCs due to high global warming potentials (GWPs). Hydrocarbons (HCs), such as propane, n-butane, isobutene, and propylene, have also been used as possible alternatives because of their zero ODPs and near zero GWPs. However, these refrigerants have low flammability level and this property can be considered as a safety limit. Since mixing causes good effects by enhancing advantages of each refrigerant and offsetting disadvantages, a large number of (vapour + liquid) equilibrium experiments for various mixtures of HFCs and HCs were conducted [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11].

Much better information is still needed on the thermodynamic properties of the mixtures. In particular, (vapour + liquid) equilibrium data are necessary to decide the optimal composition of refrigerant mixtures and to evaluate the performance of the refrigeration system. In this study, isothermal (vapour + liquid) equilibrium data were measured for the {HFC-143a + isobutene} as an alternative refrigerant in the temperature range from (273.15 to 348.15) K at 15 K intervals. The experimental data were correlated by the Peng–Robinson equation of state (PR EoS) [12] with the Wong–Sandler mixing rules [13].

Section snippets

Materials

HFC-143a with 0.995 purity was supplied from DuPont. Isobutene with 0.995 purity was supplied from Korean Industrial Gas Co. Both of them were used without further purification in these experiments.

Experimental apparatus

The measurement of the (vapour + liquid) equilibrium data was conducted in a circulation type apparatus with a few modifications to previous apparatus [14]. The new convection oven with a refrigerator can maintain a uniform temperature within the temperature range from (253.15 to 423.15) K. The

Correlations

In this work, the experimental (vapour + liquid) equilibrium data were correlated with Peng–Robinson equation of state (PR EoS) [12] using the Wong–Sandler mixing rules [13]. The PR EoS and the Wong–Sandler mixing rules are expressed as follows:p=RTV-b-a(T)V(V+b)+b(V-b),a(T)=0.457235R2Tc2Pcα(T),b(Tc)=0.077796RTcPc,α(T)=[1+κ(1-Tr0.5)]2,κ=0.37464+1.54226ω-0.26992ω2,where Tc is the critical temperature, pc is the critical pressure, Tr is the reduced temperature, and ω is the acentric factor. For

Results and discussion

Isothermal (vapour + liquid) equilibrium data for the (HFC-143a + isobutene) system were measured at temperatures from (273.15 to 348.15) K. Experimental and calculated data are provided in table 2.

Estimation of experimental data was obtained by minimizing the following objective function through the Marquardt algorithm:F=iNpexp-pcalpexp,where N is the number of data points, pexp is the measured pressures, and pcal is the calculated pressures. As shown in figure 1, the calculated results represent

Acknowledgements

This work was supported by the Brain Korea 21 Program supported by the Ministry of Education and by the National Research Laboratory (NRL) Program supported by Korea Institute of S&T Evaluation and Planning.

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