In this paper, the pressure drop of liquid−liquid slug flow was studied. The effects of flow velocity, slug length, and interfacial tension on the pressure drop were investigated individually. Furthermore, the frictional and interfacial pressure drops were investigated. Computational fluid dynamics (CFD) simulation was used to modify the Hagen−Poiseuille equation to predict the frictional pressure drop with end effects. According to the findings, the interfacial pressure drop exhibits different characteristics for developing and fully developed slug flows. For the developing and fully developed slug flows, the interfacial pressure drop is considerably affected and unaffected, respectively, by the slug length and interfacial tension. These findings have not been reported in previous studies and cannot be well explained by the most commonly used pressure drop models. A criterion parameter was proposed to predict the transition of the developing slug flow to the fully developed slug flow. A new pressure drop model was established for the two flow patterns. The experimental results presented in this paper and other study can be well predicted using the new model, demonstrating its wide applicability.

Droplet size and interfacial tension are key parameters related to two‐phase flow. However, current methods for measuring these parameters are usually based on visualization and are therefore not applicable for invisible two‐phase flow systems. Moreover, real‐time determination of interfacial tension is difficult because conventional methods cannot be employed in the flow field. This study presents a novel method for simultaneously measuring the droplet size and real‐time interfacial tension in a two‐phase flow system. A T‐shaped microdevice was designed and integrated with the two‐phase flow equipment. The pressure variation as the droplets flowed through the microdevice was used as a probe to detect the two key parameters, that is, visualization is not required. Monodispersed and multidispersed droplet flows in different equipment were used to verify the method. Both the droplet size distribution and real‐time interfacial tension can be determined using the developed approach.