Flow pattern and pressure drop of upward two-phase flow in vertical capillaries

Gas-liquid two-phase flow patterns were investigated visually with a digital camera for upward air-water flow in capillaries with diameters of 1.47, 2.37, and 3.04 mm. Several distinctive flow patterns were observed and described. The flow pattern maps developed in this work were compared with the conventional flow-pattern transition criteria for larger-diameter tubes and the experimental data that have been published. The total pressure drop in capillaries was measured with a differential pressure transducer for Taylor flow, which existed broadly in multiphase monolith reactors and microchannel reactors. A new correlation was presented to calculate the total pressure gradient (TPG) of Taylor flow. In addition, the other three models, which were proposed previously by other researchers, were also used to predict the TPG. The four theoretical results all were in overall agreement with the experimental data. Finally, the effects of method used to calculate the void fraction on the TPG were checked. It was observed that the void fraction influenced the TPG remarkably, and the drift flux model was not suitable to evaluate the void fraction under the present experimental conditions