Investigation On Fluid Flow Characteristics And Gas-liquid Mass Transfer Performance Along Scale-up In Stirred Tanks With A Long-Short Blades Agitator

This study,carried out by experimental research and computer fluid dynamic?CFD?,focuses on the fluid flow and gas-liquid mass transfer performance along the scale-up of the long-short blades?LSB?agitator in stirred tanks.Firstly,the large eddy simulation?LES?method and dynamic kinetic energy transport?DKE?model was used to investigate the fluid flow condition by the LSB agitator in 200mm-diameter stirred tank,and the simulation results were validated by the particle image velocimetry?PIV?experiments.On above foundation,the simulations were used to compare the fluid flow characteristics of LSB agitators to?Rushton turbine?RT agitators',Then,flow pattern,flow rates,turbulence,power and other characteristics of two agitators were investigated.Results show that the flow pattern of the LSB agitator is formed by a single loop and presents continuous counter-current flows along the axial direction;the pumping capacity by the short blades is vastly enhanced by the long blades and the relevant dimensionless criterion?NQp?is 1.02;the turbulent kinetic energy is more homogenous and more than twice as the RT agitators' in whole bulk.Additionally,as the liquid height increases,it presents the extremely similar flow characteristics while power consumption per unit volume?P/V?slightly declines.Secondly,the sodium sulfite oxidation method was used to investigate the gas-liquid mass transfer performance in scale-up process of the LSB agitator.The relevant measuring methods were validated by reproducing the experimental results of the reference,then power,gas-liquid dispersion,and mass transfer characteristics in 200,400&600mm-diameter stirred tanks with LSB agitators were measured and discussed.Results show that gas dispersed location was controlled by the tip velocity?Utip?in the low range of value,fragmentation and size of bubbles was influenced by the tip velocity?Utip?in high range of value;when the diameter of stirred tank is greater than 400mm,the relation between gas holdup???and power consumption per unit volume?P/V?was hardly affected by the scale-up process;the effect of the agitator speed on the power number?Po?gradually weaken along with the scale-up process and Po becomes steady;power consumption per unit volume?P/V?can be regarded as the ideal parameter that controls volumetric mass-transfer coefficient?kLa?in scale-up process and the empirical correlation is given as follow:k_La = 0.0328?P/V?^1.157...