CFD-PBM simulation of bubble coalescence and breakup in top blown-rotary agitated reactor

Gas–liquid flow and bubble coalescence and breakup behavior were studied in a top blown-rotary agitated reactor for steelmaking.Several important models of bubble coalescence and breakup mechanisms were considered and compared,and water model experiment was carried out to verify and optimize the mathematical models.The influence of different operating parameters including paddle arrangement,stirring speed and top blowing flow rate on the bubble size and distribution was revealed.The results show that the predicted bubble size and distribution present a good agreement with the experimental results using the improved Luo–Laakkonen combination model.As the position of the stirring paddle moves from the center to the side wall,the bubble distribution in the reactor becomes more uniform,and the bubble size gradually decreases.With the increase in the paddle rotation speed,the bubble size decreases.However,this effect begins to weaken when the paddle rotation speed exceeds 150 r/min.Increasing the top blowing flow rate will increase the bubble size in the reactor,but it has a weak effect on bubble dispersion.When the top blowing rate exceeds 2.0 m^(3)/h,the bubble size in the bath is basically not less than 5 mm.

Bubble Coalescence Heat Transfer During Subcooled Nucleate Pool Boiling

Bubble coalescence during subcooled nucleate pool boiling was investigated experimentally using constant wall temperature boundary conditions while the wall heat flux was measured at a various locations to understand the effects of coalescence on the heat transfer.The observations showed that the coalesced bubble moved and oscillated on the heater surface with significant heat transfer variations prior to departure.Some observations also showed coalescence with no increase in the heat transfer rate.The heat flux for boiling with coalescence fluctuated much more than for single bubble boiling due to the vaporization of the liquid layer trapped between the bubbles.

The Effects of Frothers and Particles on the Characteristics of Pulp and Froth Properties in Flotation—A Critical Review

The pulp and froth zones are the main components of froth flotation as it defines both quality of the end product and overall efficiency. The importance of the properties of the two zones, which include pulp hydrodynamics, froth bubble coalescence rate, water overflow rate, air recovery, etc., is being increasingly recognized. The properties are depending not only on the type and concentration of the frother but also on the nature and amount of the particles present in the flotation system, and as well as the frother-particle interactions and potentially of bubble-particle interactions. To date, there is no specific criterion to quantify pulp and froth properties through the interactions between frothers and particles because the various related mechanisms occurring in the pulp and froth are not fully understood. Linking the properties to the metallurgical performance is also challenged. In order to better understand the effect of these issues in flotation, in this review paper, the past and recently published articles relevant to characterizations of pulp and froth properties are widely reviewed;the findings and the gap of knowledge in this area are highlighted for further research.

Simulation of bubble column reactors using CFD coupled with a population balance model

Bubble columns are widely used in chemical and biochemical processes due to their excellent mass and heat transfer characteristics and simple construction.However,their fundamental hydrodynamic behaviors,which are essential for reactor scale-up and design,are still not fully understood.To develop design tools for engineering purposes,much research has been carried out in the area of computationalfluid dynamics(CFD)modeling and simulation of gas-liquidflows.Due to the importance of the bubble behavior,the bubble size distribution must be considered in the CFD models.The population balance model(PBM)is an effective approach to predict the bubble size distribution,and great efforts have been made in recent years to couple the PBM into CFD simulations.This article gives a selective review of the modeling and simulation of bubble column reactors using CFD coupled with PBM.Bubble breakup and coalescence models due to different mechanisms are discussed.It is shown that the CFD-PBM coupled model with proper bubble breakup and coalescence models and interphase force formulations has the ability of predicting the complex hydrodynamics in differentflow regimes and,thus,provides a unified description of both the homo-geneous and heterogeneous regimes.Further study is needed to improve the models of bubble coalescence and breakup,turbulence modification in high gas holdup,and interphase forces of bubble swarms.