Correlate viscosity and solubility of lubricant-refrigerant mixture by using pseudo-ideal-solution model.

A comprehensive thermodynamic model – Pseudo Ideal Solution Model (PISM) – was developed to correlate the viscosity and solubility of lubricant-refrigerant mixture. PISM is based on concepts from ideal solution theory, lattice model in liquid state, and local composition theory of liquid mixture. The key points of this model are creating a ‘pseudo’ ideal solution by molecules rearrangement method, and eliminating the interaction forces between two different types of molecules, such as small size refrigerant and large size lubricant. Therefore, PISM is a practicable mixing rule for lubricant-refrigerant mixture. By combining PISM with Eyring’s reaction rate theory and Clausius–Clapeyron relation, we successfully create a set of new models to correlate the viscosity and solubility of lubricant-refrigerant mixtures. We have developed some various types of POE lubricants (viscosity ranges from 32 to 90cst) for R32 refrigerant and conducted viscosity and solubility experiments by PVT instrument. Experimental data were correlating by using PISM, empirical equations, and theoretical models to describe the viscosity and vapour pressure of binary systems. The results showed that PISM gives a high degree of accuracy with experimental data in lubricant-refrigerant mixtures, and are comparable to the results from empirical quadratic equation, NRTL model and Flory-Huggins model. In addition, PISM is not only easy for calculation, the coefficients of PISM can also account for the interaction forces between two molecules.