Blade Rushton Turbine Research Articles

CFD Analysis of Modified Rushton Turbine Impeller

Mixing units is one of the prime components in various chemical processing industries. The mixing equipment produces a product by combing different liquids at various properties. Generally, the mixing units are axial and radial flow types. The rushton turbine is one of the radial flow types and had higher power number due to fluid resistance as disadvantage. This works aims to investigate the four bladed rushton turbine impellers at eight angles for finding optimum power without compromising radial flow patterns. The shaft eccentricity hydrodynamics effect is also analysed on the unbaffled stirred vessels. The variance of eccentric and coaxial agitation is clearly evaluated on the several power number and impeller blade angle by experimental and numerical analysis. The CFD analysis is made on the mixing chamber to find the optimum inputs of the mixing chamber numerically by varying the blade angles.

Periodic Behaviour of Mean Velocity Fields in Rushton Turbine (RT) Driven Stirred Tank

The present study predicts the periodic behavior of mean velocity fields from the properly verified and validated CFD model to determine the extent of vortex and turbulent activity in a baffled tank stirred by standard six bladed Rushton Turbine. This region includes most of the vortex and turbulent action that controls the mixing and mass transfer processes in the stirred tank. The complexity of periodicity of mean radial and tangential velocities in the radial direction and mean axial velocity in the axial direction is used to fix the proper radial as well as axial extents of the vortex generated by RT. The extent of flow periodicity in the present stirred tank configuration is confined within a cylindrical region around the impeller of radius 0.753 times the impeller diameter and a height of 0.323 times the impeller diameter above and below the impeller center plane.

Effect of baffles shape on the flow patterns and power consumption in stirred vessels

Effects of the baffles shape on the fluid velocities, flow patterns and power consumption in vessels agitated by a six blade Rushton turbine are explored in this paper. The curvature of baffles, their length, position and width are the main parameters under investigation. The study is carried out by using the Computational Fluid Dynamics tool, for a range of Reynolds number in the turbulent flow regime from 104 to 105. The comparison between the straight and curved baffles revealed that the curved shape allows wider well stirred region and more powerful radial jet of fluid than the straight baffle. In addition, the increase in baffle curvature allows a reduction in power consumption. When partial baffles are inserted in the vessel, the lowest value of power number is obtained with baffles located at the upper part of vessel, followed by those located at the center and then at the lower part. Concerning the effect of baffle length, the baffles with partial length which are located at the center position in vessel require the lowest power consumption.

The Influence of Internal Intermittency, Large Scale Inhomogeneity, and Impeller Type on Drop Size Distribution in Turbulent Liquid-Liquid Dispersions.

The influence of the impeller type on drop size distribution (DSD) in turbulent liquid-liquid dispersion is considered in this paper. The effects of the application of two impellers, high power number, high shear impeller (six blade Rushton turbine, RT) and three blade low power number, and a high efficiency impeller (HE3) are compared. Large-scale and fine-scale inhomogeneity are taken into account. The flow field and the properties of the turbulence (energy dissipation rate and integral scale of turbulence) in the agitated vessel are determined using the k-ε model. The intermittency of turbulence is taken into account in droplet breakage and coalescence models by using multifractal formalism. The solution of the population balance equation for lean dispersions (when the only breakage takes place) with a dispersed phase of low viscosity (pure system or system containing surfactant), as well as high viscosity, show that at the same power input per unit mass HE3 impeller produces much smaller droplets. In the case of fast coalescence (low dispersed phase viscosity, no surfactant), the model predicts similar droplets generated by both impellers. In the case of a dispersed phase of high viscosity, when the mobility of the drop surface is reduced, HE3 produces slightly smaller droplets.

The Process of the Intensification of Coal Fly Ash Flotation Using a Stirred Tank

Pulp preconditioning using a stirred tank as a pretreatment process is vital to the flotation system, which can be used to improve the flotation efficiency of mineral particles. The kinetic energy that is dissipated in the stirred tank could strengthen the interaction process between mineral particles and flotation reagents to improve the flotation efficiency in the presence of the preconditioning. In this paper, the effect of the conditioning speed on the coal fly ash flotation was investigated using numerical simulations and conditioning-flotation tests. The large eddy simulation coupled with the Smagorinsky-Lilly subgrid model was employed to simulate the turbulence flow field in the stirred tank, which was equipped with a six blade Rushton turbine. The impeller rotation was modelled using the sliding mesh. The simulation results showed that the large eddy simulation (LES) well matched the previous experimental data. The turbulence characteristics, such as the mean velocity, turbulent kinetic energy, power consumption and instantaneous structures of trailing vortices were analysed in detail. The turbulent length scale (η) decreased as the rotation speed increased, and the minimum value of η was almost unchanged when the rotation speed was more than 1200 rpm. The conditioning-flotation tests of coal fly ash were conducted using different conditioning speeds. The results showed that the removal of unburned carbon was greatly improved due to the strengthened turbulence in the stirred tank, and the optimal results were obtained with an LOI of 3.32%, a yield of 78.69% and an RUC of 80.89% when the conditioning speed was 1200 rpm.

Assessment of Interaction between Baffles and Impeller Blades in Stirred Tanks

In this work, the sensitivity of hydrodynamics on stirrer position is considered when the Multiple Reference Frame technique is applied to simulate mixing tanks of single and multiphase systems. A typical stirred reactor equipped with four baffles and a six blade Rushton turbine was chosen for the studies. Operational conditions of constant speed (5 rps) and 2.653·10 −4 m/s gas superficial velocity with single bubble size (1 mm) were set. The reactor was simulated in Fluent 15 with four different impeller blade positions. The results were averaged and validated against experimental data produced by Particle Image Velocimetry. The comparison was made using profiles of velocity components along the sampled lines representing various zones of the vessel. The impeller angle of rotation with respect to baffle position was found to contribute to the overall reactor hydrodynamics especially for multiphase systems. Averaging of the simulation results was found to improve the accuracy of the simulated mixing hydrodynamics.

A novel stirrer design and its application in submerged fermentation of the edible fungus Pleurotus ostreatus.

In this study, a straight diagonal-pitched blade stirrer was designed, built and characterized in a 5-L fermenter. Compared with the six straight blade Rushton turbine, the power consumption of the new stirrer is lower at a given speed under conditions of no ventilation. The oxygen transference is poorer at the same agitation speed in the cultivation conditions and scales investigated, which confirms that the shear stress of the new stirrer is lower and the gas dispersion is weaker. The new stirrer was installed in a 5-L bioreactor and evaluated in submerged fermentation of the edible fungus Pleurotus ostreatus. The results showed that the maximum dry weight of mycelium is increased by 47% and reached 7.47g/L, and the maximum laccase activity is increased by 15% up to 2,277U/L. Glucose consumption was also found to be relatively faster. The power consumption is 2.8% lower than that of the Rushton turbine.

스테레오 PIV 기법에 의한 임펠러 와류유동의 3차원 구조측정

The three-dimensional spatial structures of impeller flow created by a six bladed Rushton turbine have identified based on the volumetric velocity information from multi-plane stereoscopic PIV measurements. A total of 10 planes with 2 mm space and a 50 mm by 64 mm size of the field of view were targeted. To reduce the depth of focus, we adopted an angle offset configuration which satisfied the Scheimpflug condition. The distortion compensation procedure was utilized during the in situ calibration. Phase-locked instantaneous data were ensemble averaged and interpolated in order to obtain mean 3-D. volumetric velocity fields on a 60 degree sector of a cylindrical ring volume enclosing the turbine blade. Using the equi-vorticity surface rendering, the spatial structure of the trailing vortices was clearly demonstrated. Detail flow characteristics of the radial jet reported in previous studies of mixer flows were easily identified.

A Dynamical Systems Approach to Mixing in Circulating Flows

Circulating flows are found in a variety of mixing equipment such as stirred tanks and airlift loop vessels. This paper presents a different route towards modeling the mixing in circulating flows. This route is based on an innovative use of Poincare maps and suspended flows, concepts which are found in dynamical systems theory. The mixing model is developed for an arbitrary recirculating flow and uses a circulation time distribution function that is incorporated into the transport equations for an inert tracer injected into the flow system. Two cases are used to study the application of the mixing model in this work. The first case addresses the question of whether the mixing model can be used to study airlift vessels differing in scale and the second case highlights the application of the model to a standard stirred tank. In the first case, model predictions have been compared with experimental data obtained from two geometrically similar airlift systems of different volumes and good agreement is observed. A single parameter correlation for the mixing time is also proposed. In the second case, computational fluid dynamics was used to obtain the flow field of a standard stirred tank fitted with a six bladed Rushton turbine. From the flow field, the distribution of the circulation times is extracted and used to determine the tracer concentration profile in the stirred tank. Good agreement between the model predictions and published experimental data is observed thus indicating that the mixing model shows promise as a technique for studying the mixing in stirred tanks.

Characterization of Single Phase Flows in Stirred Tanks via Computer Automated Radioactive Particle Tracking (CARPT)

Single phase flows in stirred tanks have been extensively characterized using different experimental techniques like Hot Wire Anemometry1, Laser Doppler Anemometry2, and Digital Particle Imaging Velocimetry3. None of these techniques however, show much promise for the interrogation of opaque multiphase flows. Hence, little or no information of the local fluid dynamics of multiphase flows in stirred tanks is available. Non-optical techniques like Computer Automated Radioactive Particle Tracking (CARPT) and Computed Tomography (CT) have been successfully applied to probe a variety of multiphase reactors4–5 such as bubble columns6–7, risers8 etc., over a range of dispersed phase holdups. CARPT provides the local fluid dynamic information such as velocities and the turbulence parameters throughout the system that is investigated. CT provides time averaged local dispersed phase holdup profiles in various planes of the entire reactor. In this study, it is proposed to extend these techniques to characterize gas-liquid flows in stirred tank reactors. As a first step, CARPT is implemented in characterization of single phase flows in stirred tanks. CARPT experiments have been performed with water at 150 rpm in a 0.20m cylindrical tank quipped with a six bladed Rushton turbine (0.067m dia) conforming to the standard Holland and Chapman9 configuration. The CARPT technique is shown to capture some of the important flow phenomena observed in such flows, like the two recirculating loops above and below the impeller and the dead zones at the bottom of the tank. Radial pumping numbers determined by CARPT (0.67 near the impeller tip) compare reasonably well with data reported in the literature. Comparison of the complete three dimensional mean velocity profiles from CARPT with similar PIV, LDA and other data reported in the literature reveals that CARPT captures the right order of magnitude of the radial and the tangential velocities. Comparisons of the fluctuating velocity components, like the root mean squared (rms) velocity and the turbulent kinetic energy, suggest that the CARPT experiments were limited by large tracer particle size (dp = 2.3 mm) from sampling the high frequency fluctuations of the fluid. In addition, the three dimensional profiles of the components of the Reynolds stress tensor are measured. The detailed comparisons, even with the large tracer particle, indicate that CARPT measurements capture all the important qualitative features of the flow and quantitatively capture the right order of magnitude of the mean flow parameters. The quantitative comparisons suggest that the current size of the tracer particle restricts it from responding completely to the fluid phase fluctuations. Some Lagrangian measures of the fluid dynamics like the ‘Sojourn’ time distributions (STDs) in different zones of the reactor, Circulation Time Distributions (CTDs), Particle Return Maps to specific planes, Poincarre sections and Hurst exponents are evaluated from the collected CARPT data.

The trailing vortex system produced by Rushton turbine agitators

Further studies of the discharge from a six blade Rushton turbine are reported. Photographic velocity measurements have been used to examine the trailing vortex system in water and aqueous glycerol. An analysis of the vortex field in terms of a solution to the simplified Navier-Stokes equations shows reasonable agreement with the measured velocity profiles. Pressure field determinations at two different scales prove that Reynolds number alone is a sufficient scale-up parameter. The centrifugal accelerations and shear rates associated with the trailing vortices are shown to be much greater than previous literature has implied. Although restricted to single phase flow the results presented are of importance to most applications of disc turbines to dispersion operations.