Condensation heat transfer characteristics of CO2 in a horizontal smooth tube

The condensation heat transfer characteristics of CO2 flowing in a horizontal smooth tube were investigated. The tube diameter was 5.15 mm. The condensation temperature ranged from −10 to 5 °C, and the mass flux was from 600 to 1000 kg m−2 s−1. When the temperature changed from 0 to −10 °C, the increase rate of the heat transfer coefficient was from 9.4 to 14.6%, and the pressure drop increased from 6.2 to 52.9%. When the mass flux increased from 600 to 1000 kg m−2 s−1, the heat transfer coefficient increased from 6 to 35%, and the pressure drop increased from 60 to 165%, which were dependent on the condensation temperature. The increases come from the change of vapor velocity and thermophysical properties with condensation temperature. Considering large variation of mass flux from 200 to 1200 kg m−2 s−1 by including the existing studies, the effect of mass flux on condensation heat transfer coefficient was minor.

► Heat transfer coefficient increased with decrease of the condensation temperature.
► Pressure drop decreased with increase of the condensation temperature.
► Existing models overpredicted effect of mass flux on heat transfer coefficient.
► Liquid film thickness and the interface shape are major parameters for new model.
► The Cavallini et al. model was suitable for predicting pressure drop.