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Flow and heat transfer characteristics of refrigerant and PAG oil in the evaporator of a CO2 heat pump system.

Author(s) : GAO L., HONDA T.

Summary

The boiling heat transfer characteristics in a CO2 heat pump evaporator were investigated experimentally in the cases of almost pure CO2 and CO2-oil mixtures. In the case of almost pure CO2, the flow boiling heat transfer is dominated by nucleate boiling when the saturation temperature is 10°C. In the case of CO2-oil mixtures, the oil separates with CO2 liquid and becomes an oil film and oil droplets. It is also observed that CO2 liquid becomes cloudy. It is considered that the cloudiness is due to emulsion phenomenon by mixing of PAG oil. The local heat transfer coefficient was much lower than that in the case of almost pure CO2. The reason for this decrease is considered due to the nucleate boiling being suppressed by the oil film. The flow boiling heat transfer changes from nucleate boiling dominated regime to convective evaporation dominated regime.

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Pages: 2006-2

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Details

  • Original title: Flow and heat transfer characteristics of refrigerant and PAG oil in the evaporator of a CO2 heat pump system.
  • Record ID : 2008-0378
  • Languages: English
  • Source: 7th IIR-Gustav Lorentzen Conference on Natural Working Fluids (GL2006). Proceedings
  • Publication date: 2006/05/29

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