Generalized correlation for onset flooding velocity in vertical channels

Flooding due to gas-liquid counter-current flow might significantly impact engineering applications such as boilers, heat exchangers, and nuclear reactors. Despite the extensive body of literature, there is still a notable disagreement on the appropriate definition of the characteristic length regarding the onset flooding velocity in rectangular and annular channels. The primary motivation for this study is to examine which geometric dimension is the most suitable to predict the onset of flooding velocity. This study measured the onset of flooding velocity in one circular and two different annular channels. The channel geometries are considered such that the hydraulic diameter trend is inverse to the average circumference. The study's findings show that the hydraulic diameter cannot be used as a characteristic length for annular and rectangular channels to describe the onset flooding velocity. Instead, the average circumference for the annular channel and channel width for rectangular channels exhibit superior performances. The flooding air velocity was increased by increasing the average circumference of the annular channel or channel width for the rectangular channel. New Wallis-type generalized relationships are derived based on the wide range of channel geometries and dimensions. The novel generalized empirical correlation could be defined regardless of the channel geometry.