(297h) Assessment of Two-Phase Annular Flow Models for Industrial Application

The annular flow regime is observed in numerous industrial applications, including steam generators, heat exchangers, nuclear reactors, oil risers or wellbores, and phase separators. In industrial applications, the relatively large vessel sizes and the potentially harsh operating conditions, such as high temperatures and pressures, of these systems yield additional complexities to the buoyancy and inertial-driven nature present in the annular flow regime. Thus, mathematical models and numerical simulations can serve as valuable tools for studying annular flow physics within industrial applications. However, one must be mindful to accurately predict the two-phase flow regime and gas-liquid flow characteristics, while maintaining numerical simulation accuracy.

The goal of this work is to compare various models in the open literature for annular flow within a circular pipe (Asali et al., 1985; Fore et al., 2000) and concentric annulus (Kelessidis & Dukler, 1989; Caetano et al., 1992). A sensitivity study is performed to determine the range of operating conditions in which these annular flow models are most applicable. Input parameters include pipe or annulus geometry and gas and liquid fluid properties, and the goal is to characterize the vessel flow behavior in terms of pressure gradient, liquid film thickness, and liquid film flow rate. In order to identify possible deficiencies in the selected models, their predictions are validated to within 20% against the available open-literature experimental data for both circular pipes and concentric annuli. For example, a comparison of these modeling approaches shows that improper accounting for slip between gas and liquid phases can result in significant discrepancy between predicted and experimental values of gas-liquid flow quantities and overall pressure drop in the system. This causes significant concern since such a discrepancy could be much larger for a high-pressure industrial system, where the gas flow rate may likely be higher.

References: Asali, J. C., Hanratty, T. J., & Andreussi, P., Interfacial drag and film height for vertical annular flow, AIChE J., Vol. 31 (6), 895-902 (1985). Caetano, E. F., Shoham, O., & Brill, J. P., Upward vertical two-phase flow through an annulus?Part II: Modeling bubble, slug, and annular flow, Journal of Energy Resources Technology, Vol. 114, 14-30 (1992). Fore, L. B., Beus, S. G., & Bauer, R. C., Interfacial friction in gas-liquid annular flow: analogies to full and transition roughness, Int. J. Multiphase Flow, Vol. 26, 1755-1769 (2000). Kelessidis, V. C., & Dukler, A. E., Modeling flow pattern transitions for upward gas-liquid flow in vertical concentric and eccentric annuli, Int. J. Multiphase Flow, Vol. 15 (2), 173-191 (1989).