ENTRAINMENT OF DROPLETS FROM WATER POOLS

The aim of this work is to study the phenomena of droplet entrainment from water pool. This phenomenon could be either a consequence of boiling or depressurization. In a bubble column, droplets are released from the surface of the pool by bubble burst (in bubbly flow regime) or by detachment from liquids sheets (in churn turbulent flow regime) depending on the hydrodynamics inside the pool. Eventually, these droplets will be entrained by the streaming gas (superficial gas velocity) or fall back due to gravity.
Many experimental studies have been conducted, and several numerical simulations were performed for a better understanding of the phenomena of entrainment. Numerical simulation are a good tool to simulate an experiment due to limitations of data. To that end, CFD showed to be a good candidate to perform such a simulation, yet these it demand high computational performance and are time consuming. However, Lumped Parameter codes (LP) are widely used due to their simplicity and fast running.
The number of correlations that quantify the entrainment previously developed based on empirical, semi-empirical and theoretical approaches are limited to a specific regime in the water pool, thermal hydraulic conditions or even to a specific geometry
For this purpose, after an extensive study, an empirical correlation is proposed to cover the flow regimes from bubbly to churn turbulent, and could be applied to a wide range of geometries.
The current correlation shows an increase until a maximum entrainment of about 2.10-4, corresponding to gas velocity of 0.05 m/s for bubbly flow regime, a slight decrease to 2.10-5, for the transition regime for superficial gas velocities up to 0.1 m/s, and a sharp increase as the superficial gas velocity goes up to 5 m/s
The experimental database used to develop the present empirical correlation covers a broader range of boundary conditions, namely pressure [1 bar – 15 bar], water pool thermal condition [subcooled – boiling], vessel diameter[0.19m- 3.2 m], pool diameter [0.1 m – 1.4 m], superficial gas velocity up to 5.0 m/s and for soluble and insoluble aerosols. Therefore, the proposed empirical correlation aims to constitute an important tool to transfer the experimental results to reactor application.