Molecular Dynamics Simulation of Miscibility of Supercritical CO2 With PAG Lubricating Oil
Supercritical CO2 and polyethylene glycol synthetic oil(PAG lubricating oil)were selected as the research object,and molecular dynamics simulation method was used to investigate the change law of miscibility of CO2 and PAG lubricating oil in supercritical CO2 system,PAG lubricating oil system and their mixed system under different conditions of temperature,pressure,CO2 content and PAG lubricating oil content.The results show that for the mixed system with CO2 molar fraction of 100％and PAG lubricating oil mass fraction of 22.23％,when the pressure is 10 MPa and the temperature rises from 313.15 K to 353.15 K,the difference of solubility parameter increases by 80.5％,the intermolecular binding energy decreases by 13.8％,and the miscibility of CO2 and PAG lubricating oil is weakened;when the temperature is 393.15 K and the pressure rises from 10 MPa to 50 MPa,the difference of the solubility parameters decreases by 55.7％,the intermolecular binding energy increases by 19.1％,and the miscibility of CO2 and PAG lubricating oil is enhanced;when the molar fraction of CO2 in the mixed system increases from 25％to 100％,the system density and solubility parameters both increase,and the solubility of CO2 is improved,as a result of which the solubility parameter difference decreases by 52.9％,and the miscibility of CO2 and PAG lubricating oil is enhanced.When the mass fraction of PAG lubricating oil in the mixed system increases to more than 60％,the miscibility of CO2 and PAG lubricating oil is mainly related to the content of lubricating oil.Research results for the change law of miscibility of CO2 and lubricating oil provide theoretical support for the development and application of offshore high-pressure supercritical CO2 compressors.
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