Flow pattern transition during gas liquid upflow through vertical concentric annuli - Part II: Mechanistic models

In this paper the transition boundaries between different flow regimes duri ng cocurrent upflow of gas liquid two-phase mixture through concentric annu li has been predicted theoretically. On the basis of the experimental obser vations (Das et al., 1999), mechanistic models have been proposed to formul ate mathematical equations of the regime boundaries as functions of the ann ulus dimensions, the physical properties, and velocities of the two phases. The analysis has yielded the bubbly-slug transition to occur at a limiting void fraction of 0.2, and the slug-churn transition to occur due to floodi ng of the liquid films by the Taylor bubbles. A comparison of the model pre dictions with experimental data corroborate the suitability of the proposed mechanisms.