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Molecular dynamics study of CO2/lubricant oil diffusion characteristics a statistical improvement approach based on small molecule/large molecule mixture.

Author(s) : DUAN Y., XU X.

Type of article: IJR article

Summary

In CO2 air conditioning/ heat pump systems, the lubricant oil in the compressor inevitably mixes with the CO2 and flows into the entire system. Studying the mutual diffusion coefficient and diffusion characteristics in CO2/ lubricant oil mixtures is crucial for accurately describing the heat and mass transfer processes within the system. Due to the significant differences in molecular structure and diffusion behavior between small molecules and large molecules, directly using the existing equilibrium molecular dynamics statistical approach to calculate the mutual diffusion coefficient is no longer applicable to mixtures containing large molecules. This paper proposes using the center of the molecular structure for large molecules as reference points to describe their spatial position in the mixture. Using this improved approach, the self-diffusion coefficient and mutual diffusion coefficient of the CO2/PEC4 mixture are calculated at different PEC4 molar fractions. The results indicate that as the PEC4 molar fraction increases, the diffusion coefficient of the mixture exhibits an exponential decay characteristic.We develop a predictive model for the Fick diffusion coefficient applicable to the CO₂/PEC4 mixture, which accounts for the effects of temperature and PEC4 mole fraction. The deviation of our model ranges from +20 % to -20 %.

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Pages: 11 p.

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Details

  • Original title: Molecular dynamics study of CO2/lubricant oil diffusion characteristics a statistical improvement approach based on small molecule/large molecule mixture.
  • Record ID : 30034365
  • Languages: English
  • Subject: Technology
  • Source: International Journal of Refrigeration - Revue Internationale du Froid - vol. 179
  • Publication date: 2025/11
  • DOI: http://dx.doi.org/https://doi.org/10.1016/j.ijrefrig.2025.07.022

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