Abstract
Some substances currently used as working fluids in mechanical vapour compression refrigeration systems, such as hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs), will have to be replaced in the near future by refrigerants with lower global warming and ozone depletion potentials. Carbon dioxide (R-744) is regarded as one of the most promising environmentally friendly refrigerants due to its non-flammability, non-toxicity and low cost. Refrigeration compressors need lubricant oil to minimise the mechanical losses, and the selection of the most appropriate oil type to operate with R-744 is influenced by the complex phase behaviour observed in mixtures of R-744 and the most commonly used oil types. In this work, the phase equilibrium and density behaviour of mixtures of R-744 and two synthetic lubricants, namely, a polyolester (POE) ISO 68 and an alkylbenzene (AB) ISO 32, were investigated experimentally at 285, 298, 308, 328 and 348 K. The 81 data points were correlated with the PC-SAFT equation of state using a single temperature-dependent interaction parameter for each mixture. The absolute average deviations associated with the refrigerant mass fraction predictions were 5.87% (R-744/POE) and 3.81% (R-744/AB). Liquid densities were predicted with absolute average deviations of 5.32% (R-744/POE) and 1.58% (R-744/AB).
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