Behavior and pressure drop of an upwardly two-phase flow through multi-hole orifices

Experimental results on hydrodynamic behavior and pressure drop of two-phase mixture flowing upwardly in a pipe containing single- and/or multi-hole orifice plate are presented. It was found from the measurement of the void fraction upstream and downstream the orifices that the flow behavior is significantly affected by the layout of the orifice plate used and the flow starts to recover after approximately 7D downstream the orifice. Furthermore, increasing orifice holes number results in decreasing the slip ratio. The standard deviation of the void fraction was used to identify the flow pattern before and after the orifices and found that the critical threshold transition occurred at a standard deviation of 0.2. The flow homogenization necessitates a minimum value of the liquid superficial velocity to occur, and the position where it takes place depends on this velocity and on the orifice holes number. It was also inferred from the two-phase pressure drop data across the orifices that three different flow regimes, where the transition between bubbly-to-slug and slug-to-churn flow, can be identified. An assessment of the predicted two-phase flow multiplier using some previous models dedicated to single-hole orifice was achieved; and found that the model proposed by Simpson et al. is the most reliable one. Single-phase pressure drop was also measured and compared with correlations from literature.