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Excellent heat rejection from CO2 near the critical point: opportunity for high efficiency.

Author(s) : KONDOU C., HRNJAK P.

Summary

This paper is focused on heat rejection from CO2 flow near the critical point which is the condition outdoor units of a/c and refrigeration systems spend most of operation hours. The experimental results are provided: heat transfer coefficients (HTC) and pressure drop at mass flux 100 to 240 kg/m2.s and pressure 5, 6, and 7.5 MPa in a horizontal smooth tube of 6.1 mm inner diameter. Data are compared to correlations proposed for other working fluids or other conditions. Heat rejection process is categorized as occurring in superheated, two-phase, and subcooled zone which bulk mean refrigerant temperature being superheated, saturated, and subcooled respectively. Results show much higher values of HTC than correlation proposed for single-phase turbulent flow in superheated zone. The occurrence of condensation in superheat zone is assumed when tube wall temperature is below saturation temperature. The results show that simplified calculations of heat rejection in superheated zone significantly oversize the condenser.

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Details

  • Original title: Excellent heat rejection from CO2 near the critical point: opportunity for high efficiency.
  • Record ID : 2011-0030
  • Languages: English
  • Source: IIR/Eurotherm sustainable refrigeration and heat pump technology conference. Proceedings of the Eurotherm Seminar No. 88, Stockholm, Sweden, June 13-16, 2010.
  • Publication date: 2010/06/13

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