New prediction methods for CO 2 evaporation inside tubes: Part I – A two-phase flow pattern map and a flow pattern based phenomenological model for two-phase flow frictional pressure drops

Abstract

An updated flow pattern map was developed for CO 2 on the basis of the previous Cheng–Ribatski–Wojtan–Thome CO 2 flow pattern map [1,2] to extend the flow pattern map to a wider range of conditions. A new annular flow to dryout transition (A–D) and a new dryout to mist flow transition (D–M) were proposed here. In addition, a bubbly flow region which generally occurs at high mass velocities and low vapor qualities was added to the updated flow pattern map. The updated flow pattern map is applicable to a much wider range of conditions: tube diameters from 0.6 to 10 mm, mass velocities from 50 to 1500 kg/m 2 s, heat fluxes from 1.8 to 46 kW/m 2 and saturation temperatures from −28 to +25 °C (reduced pressures from 0.21 to 0.87). The updated flow pattern map was compared to independent experimental data of flow patterns for CO 2 in the literature and it predicts the flow patterns well. Then, a database of CO 2 two-phase flow pressure drop results from the literature was set up and the database was compared to the leading empirical pressure drop models: the correlations by Chisholm [3], Friedel [4], Grönnerud [5] and Müller-Steinhagen and Heck [6], a modified Chisholm correlation by Yoon et al. [7] and the flow pattern based model of Moreno Quibén and Thome [8–10]. None of these models was able to predict the CO 2 pressure drop data well. Therefore, a new flow pattern based phenomenological model of two-phase flow frictional pressure drop for CO 2 was developed by modifying the model of Moreno Quibén and Thome using the updated flow pattern map in this study and it predicts the CO 2 pressure drop database quite well overall.