Abstract
In this study, the flow fields of two‐stage impellers, consisting of combinations of different impeller types on one shaft, are investigated using stereo particle image velocimetry. Based on ...the results of torque measurements, diameters for different impellers are determined in order to achieve matching power input of the individual turbines. When implemented adequately, both selected impellers are able to contribute their respective characteristics, resulting in flow fields that differ significantly from those induced by single‐stage impellers as well as two‐stage setups consisting of identical impellers.
The azo dyes Reactive Orange‐16 and Reactive Green‐19 were removed using Aliquat‐336‐incorporated Amberlite XAD7HP resin in batch and in a continuous stirrer vessel. The prepared resin was ...characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, Brunauer‐Emmett‐Teller method, and X‐ray photoelectron spectroscopy. The effect of dosage, initial dye concentration, time, pH, and temperature on the removal efficiency of both dyes was evaluated. Equilibrium, kinetic, and diffusion models were fitted to the batch data. Design calculations for single‐stage batch adsorption were done to scale up the process industrially. The resin was regenerated using ethanol. To intensify the process further, continuous studies were performed in a recirculating stirred vessel at different flow rates and stirring speeds.
The wastewater of textile industries contains large amounts of reactive dyes. Aliquat‐366‐based impregnated Amberlite XAD7HP resin was found a suitable adsorbent for the removal of different types of dyes. The azo dyes Reactive Orange‐16 and Reactive Green‐19 were successfully eliminated from their aqueous solutions in batch and in a recirculating flow vessel. The resin was regenerated with ethanol.
We consider the mixing dynamics of an air–liquid system driven by the rotation of a pitched blade turbine (PBT) inside an open, cylindrical tank. To examine the flow and interfacial dynamics, we use ...a highly parallelised implementation of a hybrid front-tracking/level-set method that employs a domain-decomposition parallelisation strategy. Our numerical technique is designed to capture faithfully complex interfacial deformation, and changes of topology, including interface rupture and dispersed phase coalescence. As shown via transient, a three-dimensional (3-D) LES (large eddy simulation) using a Smagorinsky–Lilly turbulence model, the impeller induces the formation of primary vortices that arise in many idealised rotating flows as well as several secondary vortical structures resembling Kelvin–Helmholtz, vortex breakdown, blade tip vortices and end-wall corner vortices. As the rotation rate increases, a transition to ‘aeration’ is observed when the interface reaches the rotating blades leading to the entrainment of air bubbles into the viscous fluid and the creation of a bubbly, rotating, free surface flow. The mechanisms underlying the aeration transition are probed as are the routes leading to it, which are shown to exhibit a strong dependence on flow history.
Suspending particles in liquids is an important and versatile case for industrial stirring processes. By using advanced optical, non‐invasive measurement techniques like particle image velocimetry ...(PIV), it is possible to gain deep insights into the involved fluid dynamics without affecting the flow. However, for suspensions, the application of PIV is not trivial since both, suspended and tracer particles are present and need to be discerned during experiments. The here presented method development solves this problem and thus leads to a better insight into turbulent kinetic energy distribution, which can be utilized for process optimization through improved stirred vessel design.
The power requirement for suspension generation of different agitators depending on their diameter and installation height in a flat‐bottomed vessel with internals was investigated. Coupled with velocity and turbulent kinetic energy distribution of the suspended particles, recommendations for an energy‐optimized vessel design could be provided.
In this study, laser-induced fluorescence is used to investigate the homogenization in stirred vessels equipped with single- and two-stage stirrers. The acquired local mixing times across the reactor ...cross-section are plotted as mixing time distribution (MTD) and then compared with the previously measured flow fields of the identical systems. With the help of a novel evaluation method, the mixing times are characterized with a normal distribution fit. With mean value and standard deviation as determined parameters, the mixing results of different installation heights and stirrer combinations are quantitatively evaluated and lead to clear recommendations for installations that enable efficient mixing.
This study provides the influence of different heat exchanger internals (helical pipe coils, heating plugs, pipe registers) and reactor bottom shapes (torispherical/dished (Kloepper‐shape), ...hemispherical, and flat) on the flow field, the turbulent kinetic energy, and the ratio of tangential flow in stirred vessels, based on extensive stereo PIV measurement series in refractive index‐matched, optically completely accessible systems. The investigations impressively show advantages and disadvantages of the various equipment, which have a massive influence on both heat transport and the flow.
This study proves the massive influence of different heat exchanger internals and reactor bottom shapes on both the flow field and the heat transport in stirred vessels. The investigations impressively show the advantages and disadvantages of the various equipment, diverse recommendations for an optimized vessel design are provided.
The turbulence energy dissipation rate (
ε) in the impeller stream of a vessel of diameter
T=100
mm
stirred by a Rushton turbine of diameter
D=
T/3 was directly measured with particle image ...velocimetry (PIV). Both 2-D and 3-D PIV techniques were employed to measure the mean velocities, Reynolds stresses and
ε in the vessel for Reynolds numbers of 15
000–40
000.
ε was determined directly from measurements of the fluctuating velocity gradients by analysing the PIV images with a resolution of
100
μm
. The values of the normalised ensemble-averaged dissipation rate (
ε/
N
3
D
2) in the impeller stream were in the range 5–10. The measured fluctuating velocity gradients compared well with similar data obtained using a four-channel laser anemometer. The results are also compared with those of earlier works employing non-direct methods to estimate
ε and show that some of these methods yield comparable values, although the spread of the some of the data previously reported is significant. The present results show the feasibility of direct measurement of the
ε distribution with PIV and provide useful information for the design of mixing processes as well as for its more accurate estimation in future work.
•Energy efficiency in gas–solid–liquid stirred vessels handling ultrahigh solids concentrations was investigated.•The power consumed by impeller was used most efficiently at Cv=0.2–0.3 (v/v) in the ...absence and presence of gas.•Effect of baffling configuration on impeller power efficiency was studied at various gas flow rates.•Increase in particle size resulted in lower energy efficiency and this phenomenon was more prominent in the absence of baffles.•Complete solids dispersion with decreased power input was obtained at just suspended condition.
In this work, suspension of high-concentration slurry in the presence of gas was investigated using different baffling configurations, particle sizes, gas flow rates, and impeller types with the goal of improving the agitation energy efficiency. A term defined as power efficiency factor εjsg−1 (kg/W) was used as an indication of the amount of solid particles that could be suspended per unit of power consumed by an impeller. By varying operational parameters like solids concentration and gas flow rate, and design parameters like impeller type and baffling condition, it was found that the εjsg−1 values can be maximised by operating the tank with an optimum range of solids concentration, which is around 0.2–0.3 (v/v) for the systems studied in this work. Increase in particle size resulted in lower εjsg−1 values and this phenomenon was more prominent in unbaffled tanks. Another term, known as baffling efficiency factor, ‘Rɛ’, was used to study how baffle removal influences the energy efficiency of impellers in three-phase systems. It was observed that the absence of baffles could lead to decreased energy efficiency for axial- and mixed-flow impellers at particular operating conditions. The investigations also included the effect of baffle removal on solids dispersion, and results of this investigation indicate that it is possible to obtain complete solids dispersion with reduced power input, whilst the solids were suspended from the tank bottom.
The most important scale‐up parameters of aerated bioreactors are investigated in 42 and 340 L vessels, with water and various xanthan gum and carboxymethyl cellulose solutions. The study focuses ...mainly on mass transfer (kLa) measurements under various operating conditions. The relevance of existing correlations is discussed. The traditional viscosity‐contribution approach appears unable to predict the changes in kLa during scale‐up and an alternative formulation is proposed. The effect of rheology on power consumption and mixing time is in fair agreement with works published on this topic.
