(Vapour + liquid) equilibria of the {trifluoromethane (HFC-23) + propane} and {trifluoromethane (HFC-23) + n-butane} systems
Introduction
Chlorofluorocarbons (CFCs) are non-toxic, non-flammable compounds that do not react with other chemical compounds. Due to these characteristics, CFCs have been used as commercial and home refrigerants, solvents, and blowing agents. However, in recent years depletion of the ozone layer has become a major environmental problem. The principal cause of this is the release of CFCs, which have high ozone depletion potentials (ODPs). CFCs are therefore being phased out as a result of the Montreal Protocol on Substances that Deplete the Ozone Layer enacted in 1987. This has lead to the urgent need in refrigeration industry to find alternative CFCs. One possible class of refrigerants is hydrofluorocarbons (HFCs) on account of their near zero ODPs. However, these substances are also regulated by the Kyoto Protocol of 1997 due to their global warming potentials (GWPs). The least environmental problematic refrigerants are hydrocarbon (HCs), which have zero ODPs and near zero GWPs in addition to being relatively cheap compared with HFCs. Unfortunately, HCs are prone to explosion because of a low flammability level. Therefore, refrigerants thus far do not satisfy environmental conditions or safety standards. A compound consisting of HFCs and HCs could be an alternative and solve those problems. [1], [2], [3], [4], [5], [6], [7], [8], [9], [10].
Isothermal (vapour + liquid) equilibrium data are important in deciding the optimal composition of mixtures and to evaluate the performance of refrigeration cycles. In this study, isothermal (vapour + liquid) equilibrium data were measured in two systems, {trifluoromethane (HFC-23) + propane} and {trifluoromethane (HFC-23) + n-butane}, tested as alternative refrigerants in a temperature range from 283.15 K to 313.15 K at 10 K intervals. The experimental data were correlated by the Peng–Robinson equation of state (PR EoS) [11] with the Wong–Sandler mixing rules [12] using the NRTL model [13].
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Materials
HFC-23 of 99.7% purity was supplied by Daikin industries, Ltd. Propane and n-butane of 99.5% purity were supplied by Korea industrial gases. All components were used without further purification in these experiments.
Experimental apparatus
Measurement of isothermal (vapour + liquid) equilibrium data was conducted in a circulation type apparatus, the details of which were given in our previous studies [8]. Inner volume of the equilibrium cell is about 200 cm3 made out of 316-stainless steel. In addition, two windows were
Correlations
In this study, the experimental (vapour + liquid) equilibrium data were correlated with the Peng–Robinson equation of state (PR EoS) [11] using the Wong–Sandler mixing rules [12]. The PR EoS and the Wong–Sandler mixing rules are expressed as follows:where Tc is the critical temperature, pc is the critical pressure, Tr is the reduced temperature, and ω is the acentric factor.
Results and discussion
Isothermal (vapour + liquid) equilibrium data for the (HFC-23 + propane) and (HFC-23 + n-butane} systems were measured at temperatures ranging from 283.15 K to 313.15 K at 10 K intervals. Experimental and calculated data are provided in tables 2 and 3.
Parameters were obtained by minimizing the following objective function through the simplex algorithm:where N is the number of data points, pexp is the measured pressures and pcal is the calculated pressures. As shown in FIGURE 1, FIGURE 2
Acknowledgements
This work was supported by the Brain Korea 21 Program supported by the Ministry of Education and by Korea institute of Energy and resources Technology Evaluation and Planning (KETEP).
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