*Article* **Bubble Motion and Interfacial Phenomena during Bubbles Crossing Liquid–Liquid Interfaces**

**Hongliang Zhao 1,2, Jingqi Wang 1, Wanlong Zhang 1, Mingzhuang Xie 1, Fengqin Liu 1,2,\* and Xiaochang Cao <sup>3</sup>**


Received: 11 September 2019; Accepted: 3 October 2019; Published: 10 October 2019

**Abstract:** In metallurgical and chemical engineering processes, the gas–liquid–liquid multiphase flow phenomenon is often encountered. The movement of bubbles in the liquid, and the influence of bubbles on the liquid–liquid interface, have been the focus of extensive research. In the present work, an air–water–oil system was used to explore the movement of bubbles and the phenomenon that occurs when bubbles pass through an interface with various oil viscosities at various gas flow rates. The results show that bubble movement is greatly influenced by the viscosity of the oil at low gas flow rates. The type of phase entrainment and the jet height was changed when increasing the gas flow rate. The stability of the water–oil interface was enhanced with increasing viscosity of the oil phase.

**Keywords:** bubble motion; interfacial phenomena; entrainment; moving path
