Conventional modeling of condensers typically assumes three zones: de-superheating, condensation, and subcooling zone, even though it is clear that condensation occurs in the de-superheating zone at some conditions and subcooling occurs during condensation. This article discusses the actual situation and provides experimental validation of the hypothesis. The experimental results show heat transfer coefficients (HTC) of CO2 and R410A at mass fluxes from 100 to 240 kg m-2 s-1, heat fluxes from 3 to 25 kW m-2, and reduced pressures from 0.68 to 1.00 in a horizontal smooth tube of 6.1 mm inner diameter. Data are compared to correlations proposed for other working fluids or other conditions. Results show much higher values of HTC than the correlation proposed for single-phase turbulent flow in the superheat zone. The occurrence of condensation in the superheat zone is evident when tube wall temperature is below saturation temperature. The results suggest that simplified calculations of heat rejection in a superheated zone could oversize condensers. The semi-empirical correlation, which is here proposed as the combination of existing correlations for single-phase turbulent and saturated condensation, satisfactorily predicts HTC of the superheat zone condensation.
ASJC Scopus subject areas
- Condensed Matter Physics
- Mechanical Engineering
- Fluid Flow and Transfer Processes