The Experts below are selected from a list of 82224 Experts worldwide ranked by ideXlab platform
Eva Prokopova - One of the best experts on this subject based on the ideXlab platform.
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gas hold up mixing time and gas liquid volumetric mass transfer coefficient of various multiple Impeller configurations rushton turbine pitched blade and techmix Impeller and their combinations
Chemical Engineering Science, 2003Co-Authors: Tomas Moucha, V Linek, Eva ProkopovaAbstract:Abstract Gas hold-up, mixing intensity of dispersion characterised by exchange flows between adjacent Impellers and a volumetric mass transfer coefficient are presented for 18 Impeller configurations in triple-Impeller vessel of inner diameter 0.29 m . Rushton Turbines, six Pitched Blade Impellers pumping down and hydrofoil Impellers Techmix 335 (Techmix co., Czech republic) pumping up or down and their combinations were used. 0.5 M Na 2 SO 4 aqueous solution was used as a liquid phase, which represents non-coalescent batches. Gas hold-ups and volumetric mass transfer coefficients are presented for individual configurations as functions of specific power dissipated and superficial gas velocity. The regression of the mass transfer coefficients shows large standard deviation (30%). The power number included to the regression to express the Impeller configuration effect did not improve the standard deviation significantly (23%). The Impeller configurations with low power number (less than unity) provide higher dispersion mixing intensities, while the Impeller configurations with high power number provide better mass transfer performance.
Henk Noorman - One of the best experts on this subject based on the ideXlab platform.
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power consumption local and average volumetric mass transfer coefficient in multiple Impeller stirred bioreactors for xanthan gum solutions
Chemical Engineering Science, 2014Co-Authors: Zhen Zhou, Guozhong Zhou, Yingping Zhuang, Siliang Zhang, Henk NoormanAbstract:Abstract Mass transfer and mixing performances are very critical for xanthan gum fermentation process. Power consumption, local and average volumetric mass transfer coefficient ( k L a ) were compared for six Impeller combinations in a 50 L perspex tank with xanthan gum solutions. Impellers used in various combinations can be distinguished as two categories: “small-diameter” Impeller, which include Rushton turbine, hollow blade turbine and wide-blade hydrofoil Impeller and “large-diameter” including ellipse gate Impeller, Intermig and double helical ribbon. The results show that in order to gain the same power input, the rotating speed of “small-diameter” Impeller combinations increases as the concentration of xanthan gum increases, while it decreases for “large-diameter” Impeller combinations. The two categories also show distinguished mass transfer rates. For the “small-diameter” Impeller combinations, the k L a values near the wall region drop faster than that in other areas as the concentration of xanthan gum increases. While for the “large-diameter” Impeller combinations, the distribution of k L a is homogenous except in the bottom area but with poor gas dispersion capabilities as concentration of xanthan gum increases. The averaged k L a for each impller combination was correlated well with the specific gassed power input, superficial gas velocity and effective viscosity. The obtained correlation shows that the k L a strongly depends on specific power input and viscosity, but is less influenced by the gas flow rate.
Farhad Ein-mozaffari - One of the best experts on this subject based on the ideXlab platform.
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Effect of Impeller Spacing on the Flow Field of Yield-Pseudoplastic Fluids Generated by a Coaxial Mixing System Composed of Two Central Impellers and an Anchor
Chemical Engineering Communications, 2017Co-Authors: Argang Kazemzadeh, Ali Lohi, Farhad Ein-mozaffari, Leila PakzadAbstract:The three-dimensional flow field generated by a coaxial mixer composed of double Scaba Impellers and an anchor in the mixing of the xanthan gum solution, a non-Newtonian yield-pseudoplastic fluid was investigated using the computational fluid dynamics (CFD) technique. The mixing time measurements were performed by a non-intrusive flow visualization technique called electrical resistance tomography (ERT). To evaluate the influence of the Impeller spacing on the hydrodynamics of the double Scaba-anchor coaxial mixer, the upper Impeller submergence was set to 0.140 m while the lower Impeller clearance and the spacing between two central Impellers were changed within a wide range. The experiments and simulations were conducted for both co-rotating and counter-rotating regimes at different Impeller spacing. The analysis of the collected data with respect to the power number, flow number, mixing time, and pumping effectiveness proved that the co-rotating mode had superiority over the counter-rotating regime. Fu...
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A novel and energy-efficient coaxial mixer for agitation of non-Newtonian fluids possessing yield stress
Chemical Engineering Science, 2013Co-Authors: Leila Pakzad, Farhad Ein-mozaffari, Simant R. Upreti, Ali LohiAbstract:Abstract A novel Impeller called ASI (a combination of the A200 and the Scaba Impellers) has been introduced in this paper. By using electrical resistance tomography (ERT) and computational fluid dynamics (CFD), the performance of the ASI Impeller in the agitation of the yield-pseudoplastic fluids was assessed and compared to the performances of the Rushton (a radial Impeller), ARI (an axial–radial Impeller), and A200 (an axial Impeller) Impellers in terms of power consumption and cavern sizes. The new ASI Impeller exhibited superior performance in the mixing of the pseudoplastic fluid possessing yield stress. Agitation of such a non-Newtonian fluid in a vessel results in the formation of cavern around the Impeller. An enlarged cavern can be achieved by increasing the Impeller speed. However, this leads to increased power consumption as well as non-uniform mixing in the vessel, i.e. a high-shear region around the Impeller and dead zones at the wall and the bottom. These issues can be resolved by using a coaxial mixer, a combination of a central Impeller and an anchor. Our data revealed that the anchor-ASI Impeller, the combination of the novel Impeller and the anchor, was the most efficient mixer for the agitation of the yield-pseudoplastic fluids in term of mixing energy compared to the other coaxial mixers employed in this study.
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CFD Investigation of the Mixing of Yield‐Pseudoplastic Fluids with Anchor Impellers
Chemical Engineering & Technology, 2009Co-Authors: Poonam Prajapati, Farhad Ein-mozaffariAbstract:The study was carried out to simulate the 3D flow domain in the mixing of pseudoplastic fluids possessing yield stress with anchor Impellers, using a computational fluid dynamics (CFD) package. The multiple reference frames (MRF) tech- nique was employed to model the rotation of the Impellers. The rheology of the fluid was approximated using the Herschel-Bulkley model. To validate the model, the CFD results for the power consumption were compared to the experimental data. After the flow fields were calculated, the simulations for tracer homogenization were performed to simulate the mixing time. The effects of Impeller speed, fluid rheology, and Impeller geometry on power consumption, mixing time, and flow pattern were explored. The optimum values of c/D (Impeller clearance to tank diameter) and w/D (Impeller blade width to tank diameter) ratios were determined on the basis of minimum mixing time.
Tomas Moucha - One of the best experts on this subject based on the ideXlab platform.
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gas hold up mixing time and gas liquid volumetric mass transfer coefficient of various multiple Impeller configurations rushton turbine pitched blade and techmix Impeller and their combinations
Chemical Engineering Science, 2003Co-Authors: Tomas Moucha, V Linek, Eva ProkopovaAbstract:Abstract Gas hold-up, mixing intensity of dispersion characterised by exchange flows between adjacent Impellers and a volumetric mass transfer coefficient are presented for 18 Impeller configurations in triple-Impeller vessel of inner diameter 0.29 m . Rushton Turbines, six Pitched Blade Impellers pumping down and hydrofoil Impellers Techmix 335 (Techmix co., Czech republic) pumping up or down and their combinations were used. 0.5 M Na 2 SO 4 aqueous solution was used as a liquid phase, which represents non-coalescent batches. Gas hold-ups and volumetric mass transfer coefficients are presented for individual configurations as functions of specific power dissipated and superficial gas velocity. The regression of the mass transfer coefficients shows large standard deviation (30%). The power number included to the regression to express the Impeller configuration effect did not improve the standard deviation significantly (23%). The Impeller configurations with low power number (less than unity) provide higher dispersion mixing intensities, while the Impeller configurations with high power number provide better mass transfer performance.
Zhen Zhou - One of the best experts on this subject based on the ideXlab platform.
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power consumption local and average volumetric mass transfer coefficient in multiple Impeller stirred bioreactors for xanthan gum solutions
Chemical Engineering Science, 2014Co-Authors: Zhen Zhou, Guozhong Zhou, Yingping Zhuang, Siliang Zhang, Henk NoormanAbstract:Abstract Mass transfer and mixing performances are very critical for xanthan gum fermentation process. Power consumption, local and average volumetric mass transfer coefficient ( k L a ) were compared for six Impeller combinations in a 50 L perspex tank with xanthan gum solutions. Impellers used in various combinations can be distinguished as two categories: “small-diameter” Impeller, which include Rushton turbine, hollow blade turbine and wide-blade hydrofoil Impeller and “large-diameter” including ellipse gate Impeller, Intermig and double helical ribbon. The results show that in order to gain the same power input, the rotating speed of “small-diameter” Impeller combinations increases as the concentration of xanthan gum increases, while it decreases for “large-diameter” Impeller combinations. The two categories also show distinguished mass transfer rates. For the “small-diameter” Impeller combinations, the k L a values near the wall region drop faster than that in other areas as the concentration of xanthan gum increases. While for the “large-diameter” Impeller combinations, the distribution of k L a is homogenous except in the bottom area but with poor gas dispersion capabilities as concentration of xanthan gum increases. The averaged k L a for each impller combination was correlated well with the specific gassed power input, superficial gas velocity and effective viscosity. The obtained correlation shows that the k L a strongly depends on specific power input and viscosity, but is less influenced by the gas flow rate.
