A Critical Review of Advanced Experimental Techniques to Measure Two- Phase Gas/Liquid Flow

Gas assisted atomization is becoming increasingly important in many industrial applications such as physical, chemical and petroleum processes. In order to achieve proper atomization it is crucial to have proper mixing of gas (air) and liquid (water) in the feeding conduit before it enters into the nozzle. The flow regime, as well as the flow pattern and structure of the flow, are some of the important parameters that describe two-phase gas/liquid flows, and identify twophase gas/liquid flow regimes. It is also desirable to know under what conditions there is a transition among the different flow regimes (dispersed, stratified, annular, annular-dispersed, slug, wavy-slug, mist-annular). Due to the existence of relative movement in the interfaces and variable interactions between two phases, two-phase gas/liquid flow is a complex transport phenomenon compared to single-phase flow. Still, there is no effective technique to identify the two-phase gas/liquid flow regimes and it is even difficult to capture the accurate flow structures in smaller conduits in turbulent flow cases. Lack of solid and comprehensive theories for predicting and calculating the pressure and void fraction variations in two-phase air/water flow situations has left engineers without essential information for proper design of two-phase flow systems. This review is an effort to explore the state of the present advanced measurement techniques in this field of research. Subsequently, some of the advanced void fraction, photonics and pressure measurement techniques and correlations for identification of two-phase gas/liquid flow regimes and bubble sizes are investigated.