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Heat transfer performance and oil behaviour for R744 with PAG oil in air-cooled heat exchanger.

Author(s) : YOSHIOKA S., KIM H. Y., KASAI K.

Summary

Carbon dioxide (R744) has become a great issue in the application to refrigerators and air conditioning systems as a natural refrigerant. In the R744 heat pump system, PAG oil is commonly used for lubrication of the compressor, while it was reported that the PAG oil is influential on the heat transfer performance due to its immiscibility against R744. This paper deals with an experimental study on the heat transfer performance of fin and tube heat exchangers working with R744 as a refrigerant taking PAG oil effect into account. From experiments on two types of air-cooled heat exchangers with smooth tubes and grooved tubes at varying the PAG oil circulation rate (OCR), it was found that the heat transfer performance decreases significantly as OCR increases in both evaporator test and gas-cooler test, however the deterioration was different between smooth and grooved tubes. For the understanding of these phenomena, the oil retention rate in each heat exchanger was measured and it was found that the heat transfer characteristics can be correlated with the oil retention rate. In addition, flow inside tube was visualized to observe the oil behaviour in refrigerant flow at gas-cooler condition. It was confirmed that a large amount of oil flows as liquid film along the tube wall and certain portion of droplets moves mixed with the main refrigerant flow.

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Pages: 2008-2

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Details

  • Original title: Heat transfer performance and oil behaviour for R744 with PAG oil in air-cooled heat exchanger.
  • Record ID : 2009-0071
  • Languages: English
  • Source: 8th IIR-Gustav Lorentzen Conference on Natural Working Fluids (GL2008)
  • Publication date: 2008/09/07

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