Prediction of gas-liquid two-phase mixture flow in a vertical pipe with a sudden expansion in diameter

The principle of gas-lift pumps is applied to vacuum-decarburization with the RH (Ruhrstahl Heraeus) process to circulate molten steel. Gas-lift pumps are also applicable to the transportation of molten iron/steel between different refining processes. This paper treats theoretical analysis of steady-state flow characteristics of gas-liquid two-phase mixtures rising in a vertical pipe with an abrupt expansion of its diameter. The system of governing equations is based upon a one-dimensional multi-fluid model. Flow pattern transitions are taken into consideration. A new numerical procedure to predict the flow characteristics at the sudden expansion has been proposed. Experiments have also been performed for several conditions to confirm the applicability as well as the validity of the present numerical model. It has been found that the predictions agree reasonably well with the experimental data. Next, the effect of the sudden expansion of pipe diameter on the pump performance was investigated numerically. As a result, it has been confirmed that the sudden expansion of pipe diameter contributes to improve the pump efficiency.