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In this article, the observations from two different experimental studies on CO2 two-phase flow regimes in a near horizontal pipe are analysed. These experiments show significant bubble entrainment in a stratified flow, and the bubble entrainment in liquid is found to be a dominant mechanism for the flow regime transition between the stratified and bubbly flow. The hydrodynamic slug flow is not observed in these experimental studies. The X-ray measurement of the experimental study in a near horizontal pipe of 44 mm internal diameter is processed to obtain the bubble volume fraction in the liquid layer, which is found to be a function of two-phase Froude number. This Froude number definition takes into account gas density and pipe inclination effects. A parametric study shows that the bubble entrainment into the liquid layer decreases significantly with an increase of pipe internal diameter.

Highlights • Heat transfer and multi-phase pressure drop of CO 2 near the critical point. • Homogeneous equilibrium model approach is used to evaluate the 2-phase flow. • Heat transfer and pressure drop test was conducted with a PCHE. • A new set of correlations is suggested for CO 2 2-phase flow near the critical point. Abstract In this study, condensation heat transfer and multi-phase pressure drop of CO 2 near the critical point are investigated occurring in a Printed Circuit Heat Exchanger (PCHE) for a supercritical CO 2 power cycle application in mind. Homogeneous Equilibrium Model (HEM) approach is used to evaluate and develop appropriate heat transfer and pressure drop correlations. The experiment was performed with the CO 2 test facility called SCO2PE (Supercritical CO 2 Pressurizing Experiment) in KAIST. The heat transfer and pressure drop test was conducted with the PCHE in the facility. Existing correlations were compared to the test data and a new set of correlations was necessary to be developed. A new set of correlations is newly suggested in this paper which captures physical characteristics reasonably well. [ABSTRACT FROM AUTHOR]