Efficiency of PBT Impellers with Different Blade Cross-Sections

In this study, the mixing power and the axial and radial velocity distributions were determined for the standard PBT45-6 impeller with inclined blades and for three NACA impellers with airfoil blades. On the basis of the velocity distributions obtained by means of PIV techniques, the pumping efficiency and the size of the secondary circulation for the tested impellers were determined. The next stage was to calculate the efficiency of the impeller operation, in which the comparative criteria were the values of the mixing energy in the form of a dimensional and dimensionless criterion. The lowest mixing energy was obtained for impellers with symmetrical profiled NACA0021 blades, which was 20% lower than the similar mixing energy obtained for the standard PBT45-6 impeller.

Influence of Interfacial Force Models and Population Balance Models on the kLa Value in Stirred Bioreactors

Optimal oxygen supply is vitally important for the cultivation of aerobically growing cells, as it has a direct influence on cell growth and product formation. A process engineering parameter directly related to oxygen supply is the volumetric oxygen mass transfer coefficient kLa. It is the influences on kLa and computing time of different interfacial force and population balance models in stirred bioreactors that have been evaluated in this study. For this investigation, the OpenFOAM 7 open-source toolbox was utilized. Firstly, the Euler–Euler model with a constant bubble diameter was applied to a 2L scale bioreactor to statistically examine the influence of different interfacial models on the kLa value. It was shown that the kL model and the constant bubble diameter have the greatest influence on the calculated kLa value. To eliminate the problem of a constant bubble diameter and to take effects such as bubble breakup and coalescence into account, the Euler–Euler model was coupled with population balance models (PBM). For this purpose, four coalescence and five bubble breakup models were examined. Ultimately, it was established that, for all of the models tested, coupling computational fluid dynamics (CFD) with PBM resulted in better agreement with the experimental data than using the Euler–Euler model. However, it should be noted that the higher accuracy of the PBM coupled models requires twice the computation time.

The Influence of Hydrodynamic Changes in a System with a Pitched Blade Turbine on Mixing Power

This paper presents an analysis of hydrodynamics in a tank with a 45° and 60° pitched blade turbine impeller operating while emptying the mixer and with an axial agitator working during axial pumping-down of water at different water levels above the impeller. Measurements made with the PIV method confirmed the change in direction of pumping liquid after the level dropped below the critical value, with an almost unchanged liquid stream flowing through the mixer. It was found that an increase in the value of the tangential velocity in the area of the impeller took place and the quantity of this increase depended on the angle of the blade pitch and the rotational frequency of the impeller. Change in this velocity component increased the mixing power.

A General Review of the Current Development of Mechanically Agitated Vessels

The mixing process in a mechanically agitated vessel is a widespread phenomenon which plays an important role among industrial processes. In that process, one of the crucial parameters, the mixing efficiency, depends on a large number of geometrical factors, as well as process parameters and complex interactions between the phases which are still not well understood. In the last decade, large progress has been made in optimisation, construction and numerical and experimental analysis of mechanically agitated vessels. In this review, the current state in this field has been presented. It shows that advanced computational fluid dynamic techniques for multiphase flow analysis with reactions and modern experimental techniques can be used with success to analyse in detail mixing features in liquid-liquid, gas-liquid, solid-liquid and in more than two-phase flows. The objective is to show the most important research recently carried out.

Numerical investigation of the turbulent flow generated with a radial Turbine using a converging hollow blade

The aim of this study is to investigate the effect of the blade shape on the characteristic of the flow patterns in a stirred tank. A new impeller blade design has been proposed. It is characterized by a converging hollow. The investigations of the flow structure generated in the vessel are made by using the computer code ANSYS CFX (version 16.0). The analysis has shown that the converging hollow blade yields highly radial flows which gave an increase in the radial velocity by 35% with less power consumption than the flat blade. Also, the effectiveness of the energy dissipation and the quality of mixing has been obviously noted. A validation test of our predicted results with other literature data was done, and a satisfactory agreement has been found.

Flow field investigation of high solid anaerobic digestion by Particle Image Velocimetry (PIV)

High solid anaerobic digestion (HSAD) is a promising anaerobic digestion technology. Homogenization and mixing mechanism are essential for HSAD's performance, but relative knowledge still remains poor. In order to investigate HSAD's mixing behavior, a novel flow field measuring approach was proposed as following. Firstly, laponite suspension was selected as the model fluid of HSAD digestate, because the rheological properties and material structure they displayed were highly similar. Then, water and polyacrylamide (PAAm) solution were chosen as basic reference fluid and another non-Newtonian fluid respectively. Flow fields of the three fluids under different rotation speeds were measured via Particle Image Velocimetry (PIV). The evolution of working fluids did induce consecutively the significant flow and mixing behavior of HSAD, because their rheological properties and complexity were getting progressively closer to the real HSAD digestate. Results indicated that the flow field of simulated HSAD fluid was quite different from those of water and PAAm solution, i.e. only the fluid around the impeller could be mixed in HSAD. Besides, increasing rotation speed could not significantly enhance the mixing area of HSAD. Thus, multilayer impellers arranged abreast were recommended for HSAD's mixing. Considering that HSAD's flow field had never been measured before, this study proposed a novel flow field measuring method for such opaque non-Newtonian fluid for the first time. The visualization of HSAD's complex hydrodynamic conditions was also firstly achieved in this study, and thus could further help improve the homogenization of HSAD.