(547i) A 1D Model for Gas-Liquid Vertical Annular Flow In Pipes or Concentric Annuli

The gas-liquid annular flow regime is observed in numerous applications, including steam generators, heat exchangers, nuclear reactors, oil wellbores, and phase separators. The annular flow regime occurs when the gas velocity exceeds the Dukler velocity, and is characterized by liquid film flowing along channel walls while gas flows in the central core.  The flow of gas through the channel’s central core applies an interfacial force on the wavy liquid film.  This causes the liquid film to shed droplets that become entrained in the gas core.  The buoyancy and inertial-driven nature of annular flows, as well as accounting for the effects of instabilities and surface tension on droplet size, make the annular flow regime very challenging to model.  Thus, mathematical models can serve as valuable tools for studying annular flow physics for different configurations or operating conditions. 

The goal of this work is to develop a 1D analytical model for predicting annular flow characteristics and average droplet size in the core.  This stand-alone model requires input parameters including pipe or annulus geometry and gas and liquid properties.  The model first calculates the average liquid film thickness m, the pressure gradient, the gas and liquid velocities and volume fractions, and the liquid film flow rate, the latter of which is difficult to estimate in annular flow. These calculated values are then used in semi-empirical formulations to predict the mean liquid droplet size in the channel.  The stand-alone model can be used for either pipe or concentric annulus geometry.  To validate the approach, the model predictions are compared against open literature data for pressure gradient, liquid film thickness, liquid volume fraction, and droplet size.  Model performance is deemed acceptable if the predicted values compare to within 30% against the available open-literature experimental data for both circular pipes and concentric annuli.  Sensitivity studies illustrate the range of operating conditions for which the model is best applicable.

References:

Ambrosini, W., Andreussi, P. & Azzopardi, B. J., A physically based correlation for drop size in annular flow, Int. J. Multiphase Flow, Vol. 17 (4), Pg. 497-507 (1991).

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).

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).

Sarimeseli, A., and Azzopardi, B. J., Correlating drop sizes in annular gas/liquid flows in vertical and horizontal pipes, Proceedings of ILASS (Europe), Pg. 248-253 (2004).