| Hydrofluorocarbons (HFCs) and hydrocarbons (HCs) are consided as the promis-ing alternative refrigerants, since their0ozone depleting potential (ODP), which means that they do not deplete the ozone layer. However, HFCs generally have high global warming potentials (GWPs) and long atmospheric lifetime. According to the EU F-Gas regulation, the use of high GWP fluorine-containing refrigerants in new equipment was restricted. While, HCs are highly flammable and explosive. Thus, finding novel environmental friendly alternative refrigerant is extremely urgent. In recent years, Hon-eywell and DuPont have jointly developed a new refrigerant2,3,3,3-tetrafluoropropene (HFO-1234yf)(GWP<1and ODP=0), with a very short atmospheric lifetime (0.029years), is considered as a very promissing environmental friendly alternative refriger-ant. Whereas its low latent heat values and mildly flammable property become great obstacles in its using as a pure working fluid.It is difficult to find a pure refrigerant with both favorable refrigerantion perfor-mance and environmental friendly properties, while the suitable alternative refrigerants are hopeful to be obtained from refrigerant mixtures for their optional components and adjustable fractions. A major factor of whether a refrigerant mixture can be used is its thermodynamic properties, in which the vapor liquid equilibrium (VLE) property is the essential property for the cycle thermodynamic analysis. Currently, the experimental measurement is the most accurate way to obtain the vapor liquid equilibrium data. Thus, it is essential to establish an experimental apparatus with high precision for VLE data measurement for the refrigerant mixtures.The VLE apparatus was set up by improving the PVT system with a sampling sys-tem for mixed refrigerant, a mole fraction measuring system and an air thermostatic bath. The VLE properties of HFC-134a/HFC-227ea binary mixtures measured by this apparatus agree well with the values from the literature,which proves that this experi-mental apparatus is of high accuracy, with stable and reliable operation.The VLE properties of the binary and ternary mixed refrigerant containing HFO-1234yf were measured,using the developed apparatus, namely HFC-143a/HFO-1234yf, HFO-1234yf/HFC-152a, HFO-1234yf/HFC-227ea, HFO-1234yf/HFC-600a, HFC-161/HFO-1234yf and HFC-134a/HFO-1234yf/HC-600a system. The experimental data for all these binary mixtures were correlated by Peng-Robinson (PR) equation and van-der-Waals (vdW) mixing rule and the interaction parameters were obtained. The calculated results show that PR EoS with vdW mixing rules can be used to calculated the VLE properties for mixtures which contain HFO-1234yf. In our previous work, a differential-model for binary interaction parameter kij was proposed for10HFCs and3HCs. In this work, new componets of HFC-161and HFC-134were added to the former refrigerants list, and the critical point parameters and acentric factor were brought in to obtain the modified model called interaction-weighting differential-model. The accuracy of the interaction-weighting differential-model is higher than the original one. The reported experimental VLE data of HFO-1234yf/HFC and HFO-1234yf/HC were collected, and their binary interaction param-eter were correlated using the PR equation of state with the vdW mixing rules. The interaction-weighting differential-model was extended to HFO-1234yf, the results showed the calculation accuracy for HFO-1234yf/HFC systems can meet the engineering re-quirements, while the deviation of calculation is larger for HFO-1234yf/HC systems. Taking into account the impact of the carbon-carbon double bond, the binary interaction parameter of HFO-1234yf/HC systems were modified, and the calculation accuracy can be more satisfied with application.The azeotropic point of the binary mixtures which were composed of HFO, HFC and HC was calculated with the interaction-weighting differential-model.39mixtures of HFO/HC and HFC/HC were investigated, among which30groups have obvious azeotropic behavior, while the other9groups have none azeotropic. The interaction-weighting differential-model was applied to predict the VLE properties of the ternary mixtures. The predicted results were compared with the experimental data of five sys-tems reported in literatures and one system of this work, and calculated data of12sys-tems from REFPROP. For most of the ternary systems, the overall average absolute de-viations of pressures are less than2%, and vapor phase compositions are within0.0100. Only the deviation of pressure for the HC-290/HC-600a/HFC-32system is8.05%, much lager than the other systems. Thus illustrating that the interaction-weighting differential-model can be used to predict the VLE properties of different ternary mixture refriger-ants.The interaction-weighting differential-model was employed to predict the azeotropic properties for the ternary mixture. The ternary mixtures which are composed by16kind of pure components, in which each of two components consist the azeotropic or near azeotropick binary mixtures were studied.There are53ternary mixtures meeting this criterion. The prediction results show three ternary mixtures have obvious azeotropic behaviors. The azeotropic point of HFC-32/HFC-125/HFC-143a systems appear when the temperature lower than220K, which agree well with the result in literature,it proves that prediction result has agreat guiding significance. |
PDF Full Text Request