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Thermodynamic property model of a partially miscible CO2-PAG68 mixture.

Number: 0019

Author(s) : DOMIN D., MECKLENFELD A., TEGETHOFF W., KÖHLER J.

Summary

Many CO2 vapor compression systems use a polyalkylene glycol (PAG) based oil to lubricate the compressor. Some of this oil is entrained by the refrigerant flow, causing a CO2-PAG mixture to circulate in the system. The phase behavior and the thermodynamic properties of the mixture differ from those of the pure refrigerant. Though, most state of the art model libraries for the simulation of vapor compression systems neglect the presence of oil and use pure refrigerant property data. To further improve the accuracy of such simulations, a thermodynamic property model is required that describes the phase behavior and the mixture properties throughout the entire operating range. Since detailed experimental data on CO2-PAG mixtures is scarce, a physically based approach is required to provide reasonable extrapolation capability. However, only a few adjusted thermodynamic models are available to describe these mixtures.  
In this work, different approaches to model the phase behavior and the phase properties of CO2-oil mixtures are theoretically discussed. Consequently, a modified RKS cubic equation of state is applied to describe the pVT behavior of a CO2-PAG68 mixture in a temperature range from -20 °C to 114 °C and vapor pressures up to 150 bar. The adapted equation of state is compared with experimental data to describe the CO2 mass fraction in the liquid phase of the vapor liquid equilibrium and the miscibility gap as well as the liquid phase density, with statistical evaluations showing average absolute deviations of 0.76 mass%, 1.8 mass% and 7 kg/m3 respectively.

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Pages: 10

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Details

  • Original title: Thermodynamic property model of a partially miscible CO2-PAG68 mixture.
  • Record ID : 30030978
  • Languages: English
  • Subject: Technology
  • Source: 10th IIR Conference on Ammonia and CO2 Refrigeration Technologies.
  • Publication date: 2023/04/27
  • DOI: http://dx.doi.org/10.18462/iir.nh3-co2.2023.0019

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