Turbulence parameters in a stirred tank

Mean and fluctuating radial velocities have been measured in the inipeller stream of a baffled, turbine-agitated cylindrical tank. Auto-correlation functions, energy spectra and amplitude probabilitv density functions of the radial velocity fluctuations were also obtained. In the vicinity of the impeller, the motion is distinctly periodic, with a time scale corresponding to n_bN/60, where n_b is the number of turbine blades and N is the rpm. The amplitude of the periodic component was found to decrease with radial distance from the inipeller tip and was used to correct the measured turbulence intensities.     

Break-up of a drop in a stirred tank

The drop break-up mechanism was studied in a stirred tank containing two immiscible liquids. The daughter drops formed by break-up of a single drop of known size were recorded photographically. From the experiments at constant agitator speed the following results were obtained. There is a critical drop size under which drops do not break up under given conditions. The break-up frequency increases approximately linearly with increase in drop volume. The number of daughter drops, v, is a random variable with a mean v > 2 which increases with the volume of the mother drop. The relative volume of a daughter drop has a β-distribution.     

Viscoplastic fluid mixing in a rotating tank

The laminar 2D mixing of viscoplastic fluids with an anchor impeller in a stirring tank is studied numerically. The flow structures, and particularly the static and moving rigid zones induced by the plasticity such as the presence of vortices, are examined in detail. Calculations are made for a wide range of yield and inertia values. It is shown that the application of a small yield stress can eliminate vortices. On the other hand, the increase in rotation velocity, i.e. the inertia, is not generally sufficient to reduce the size of the rigid zones. Power consumption is calculated and the mixing quality is determined by particle tracking. The calculations are made for different types of impeller configurations and an optimum configuration is proposed.     

Intensified biogas purification in a stirred tank

The present study aims at intensifying the absorption of carbon dioxide in aqueous phases. For this purpose, a second immiscible liquid phase is used to improve the mass transfer of carbon dioxide in water. Absorption measurements are carried out in a stirred cell by online infrared monitoring of the output carbon dioxide concentration. As dispersed phase, 1-octanol shows an improvement in mass transfer whereas colza oil retards it. Toluene has no significant effect in the range of concentrations investigated. Mass transfer coefficients are determined using a chemical method. Nevertheless, the variety of behaviors could not be explained simply by solubility or variation of mass transfer coefficients. In order to understand the complex gas–liquid–liquid interactions and deduce the mass transfer mechanism between these three phases, surface and interface tension measurements and direct observation of bubbles and droplets are also carried out.     

一种新型平流式沉砂池的设计

通过在沉砂池的进水处加调流墙、在溢流堰上沿水流方向设溢流槽、对排砂装置进行改进以及设置辅助冲砂设施三个方面对传统平流式沉砂池进行了改进,设计提出了一种新型平流式沉砂池,可以大大提高沉砂池的沉淀效率,特别是对细颗粒泥砂的沉淀具有很好的效果。