Phase and viscosity behaviour of refrigerant–lubricant mixtures

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The understanding of thermophysical properties and phase behaviour of refrigerant–lubricant oil mixtures is highly important for the optimal design of refrigeration and air-conditioning systems. Refrigerant–lubricant mixtures, which are likely to have strong asymmetry, can show complex phase behaviour such as closed miscibility gaps, open miscibility gaps, liquid–liquid–vapour equilibrium, and even barotropic phenomena (density inversions). In fact, the type of phase behaviour that refrigerant–lubricant mixtures may show is linked to the transition between different types of phase diagrams, mainly as a function of the molecular asymmetry. This also has a profound effect in the mixture transport properties. Thus, in this work the general aspects of phase and viscosity behaviour linked to the type of asymmetry found in refrigerant–lubricant mixtures are discussed in the context of phase behaviour phenomenology.