2018 Volume 58 Issue 1 Pages 1-9
In order to compare the agglomeration and breakup behavior of fine particles in liquid by various mixing operations, model experiments were carried out and a mathematical model was developed and compared with the experimental results. Three kinds of mixing operations were examined: mechanical stirring by impeller (impeller), gas blow mixing (gas), and gas and liquid jet blow mixing by RH degasser (RH). Polymethylmethacrylate (PMMA) particles of 2.8×10−6 m in mean diameter and 3.0×103 mol·m−3 of KCl solution were used in the experiment as solid and liquid phases, respectively. Total number of PMMA particles at each mixing process decreased with the increasing time, although the agglomeration rate decreased. The PMMA agglomeration rate at the same mixing energy input in the liquid was in the following decreasing order: impeller, gas, and RH mixing. The experimental results of the impeller mixing were able to be explained by a turbulence agglomeration model. A breakup model of particles was newly developed assuming that the agglomerated PMMA particles adhered to the surface of bubbles during bubble floating in the liquid was divided into two pieces on the gas/liquid free surface at the moment of bubble bursting. By introducing this breakup model in addition to the agglomeration one, the calculation results for both of the gas and RH mixing agreed well with the experiment.