scholarly journals Comparative analysis of mixing efficiency and distribution induced by radial impellers in bioreactors with stirred bed of immobilized cells

2010 ◽  
Vol 16 (1) ◽  
pp. 47-64
Author(s):  
Anca-Irina Galaction ◽  
Anca-Marcela Lupăşteanu ◽  
Marius Turnea ◽  
Dan Caşcaval
Keyword(s):  
Experimental Data ◽  
Comparative Analysis ◽  
Immobilized Cells ◽  
Mixing Time ◽  
Mixing Efficiency ◽  
Rushton Turbine ◽  
Mobile Bed ◽  
Main Factors ◽  
Good Concordance

The influences of the main factors on the mixing efficiency and distribution for a bioreactor with stirred/mobile bed of immobilized S. cerevisiae cells in alginate (biocatalyst particles with 4, 4.6 and 5.2 mm diameters) have been comparatively analyzed for six radial impellers: a disperser sawtooth, Smith turbine, a pumper mixer, a curved bladed turbine, a paddle with six blades, a pitched bladed turbine vs. Rushton turbine. The most efficient impellers, from the viewpoint of intensity and uniformity of the suspension circulation were found to be the Smith turbine, the paddle with six blades and the pitched bladed turbine. The mathematical correlations describing the influence of the main factors on mixing time were established for each studied impeller offering a good concordance with the experimental data (the average deviations vary from ?7.9% for pitched bladed turbine to ?12.1% for disperser sawtooth).

scholarly journals CFD simulation of the hydrodynamics and mixing time in a stirred tank

2010 ◽  
Vol 16 (4) ◽  
pp. 379-386 ◽  
Author(s):  
Aoyi Ochieng ◽  
Maurice Onyango
Keyword(s):  
Cfd Simulation ◽  
Draft Tube ◽  
Mixing Time ◽  
Operating Cost ◽  
Flow Fields ◽  
Stirred Tank ◽  
Mixing Efficiency ◽  
Phase System ◽  
Rushton Turbine ◽  
Power Draw

Hydrodynamics and mixing efficiency in stirred tanks influence power draw and are therefore important for the design of many industrial processes. In the present study, both experimental and simulation methods were employed to determine the flow fields in different mixing tank configurations in single phase system. The laser Doppler velocimetry (LDV) and computational fluid dynamics (CFD) techniques were used to determine the flow fields in systems with and without a draft tube. There was a reasonable agreement between the simulation and experimental results. It was shown that the use of a draft tube with the Rushton turbine and hydrofoil impeller resulted in a reduction in the homogenization energy by 19.2% and 17.7%, respectively. This indicates that a reduction in the operating cost can be achieved with the use of a draft tube in a stirred tank and there would be a greater cost reduction in a system stirred by the Rushton turbine compared to that stirred by a propeller.

scholarly journals Bioreactors with stirred bed of immobilized cells, 2. Studies on distribution of mixing efficiency

2007 ◽  
Vol 13 (3) ◽  
pp. 135-150 ◽  
Author(s):  
Anca-Irina Galaction ◽  
Anca-Marcela Lupasteanu ◽  
Dan Cascaval
Keyword(s):  
Rotation Speed ◽  
Immobilized Cells ◽  
Solid Particles ◽  
Mixing Efficiency ◽  
Volumetric Fraction ◽  
Main Factors

The influences of the main factors on mixing efficiency and distribution for a bioreactor with stirred bed of S. cerevisiae immobilized cells in alginate have been analyzed. Indifferent of the region inside the suspension or of the biocatalyst volumetric fraction, the most efficient mixing has been obtained for biocatalyst particles with a 4.6 mm diameter. In function of the biocatalyst diameter and concentration, the uniform mixing can be reached in a whole bulk of suspension for certain rotation speed values. Therefore, for biocatalyst particles of 4 and 5.2 mm diameter, the suspensions have been uniformly mixed for solid particles concentration of maximum 15%, the optimum rotation speed being of 100 and, respectively, 200 rpm. For intermediary size of biocatalyst particles, the uniform circulation of the suspension can be obtained for volumetric fraction up to 20%, at 150-200 rpm. Over these levels of solid particles concentration, the mixing becomes nonuniform for the entire considered domain of rotation speed.

scholarly journals Modeling of mixing in stirred bioreactors 4. mixing time for aerated bacteria, yeasts and fungus broths

2004 ◽  
Vol 58 (3) ◽  
pp. 128-137 ◽  
Author(s):  
Dan Cascaval ◽  
Anca-Irina Galaction ◽  
Corneliu Oniscu ◽  
Florina Ungureanu
Keyword(s):  
Experimental Data ◽  
Mixing Time ◽  
Biomass Concentration ◽  
Aeration Rate ◽  
Mixing Efficiency ◽  
Complex Flow ◽  
Average Deviation ◽  
Stirred Bioreactors ◽  
Turbine Impeller ◽  
Good Agreement

The mixing time for bioreactors depends mainly on the rheoiogicai properties of the broths, the biomass concentration and morphology, mixing system characteristics and fermentation conditions. For quantifying the influence of these factors on the mixing efficiency for stirred bioreactors, aerated broths of bacteria (P. shermanii), yeasts (S. cerevisiae) and fungi (P. chrysogenum, free mycelia and mycelial aggregates) of different concentrations have been investigated using a laboratory bioreactor with a double turbine impeller. The experimental data indicated that the influence of the rotation speed, aeration rate and stirrer positions on the mixing intensity strongly differ from one system to another and must be correlated with the microorganism characteristics, namely: the biomass concentration and morphology. Moreover, compared with non-aerated broths, variations of the mixing time with the considered parameters are very different, due to the complex flow mechanism of gas-liquid dispersions. By means of the experimental data and using a multiregression analysis method some mathematical correlations for the mixing time of the general form: tm = a1*Cx2+a2*Cx+a3*IgVa+a4-N2+a5-N+a6/a7*L2+a8*L+a9 were established. The proposed equations offer good agreement with the experiments, the average deviation being ?6.7% - ?9.4 and are adequate for the flow regime Re < 25,000.

scholarly journals Optimization of the mixing in stirred bioreactors, 1. Comparative analysis of the mixing efficiency with different radial impellers for simulated broths

2007 ◽  
Vol 13 (1) ◽  
pp. 1-20 ◽  
Author(s):  
Dan Cascaval ◽  
Anca-Irina Galaction ◽  
Elena Folescu
Keyword(s):  
Mixing Time ◽  
Ph Sensor ◽  
Mixing Efficiency ◽  
Energetic Efficiency ◽  
Rushton Turbine ◽  
Stirred Bioreactor ◽  
Mixing Intensity ◽  
Bulk Volume ◽  
Shear Effects ◽  
Stirred Bioreactors

Although radial impellers, especially the Rushton turbine, are widely used in stirred bioreactors, their applicability is limited by the high apparent viscosities of the broth. Beside the intensification of broth circulation, the energetic efficiency and the shear effects on biocatalysts must be taken into account to select the optimum impeller or impellers combination. In this context, the paper presents a comparative study on the efficiency of seven different radial impellers for simulated broth mixing in a stirred bioreactor. The analysis was made by means of the mixing time values obtained by vertically changing the position of the pH-sensor in the broths, in correlation with the energy consumption needed for a certain level of mixing time or for the uniform distribution of the mixing intensity into the bulk volume of the broths.

scholarly journals Optimization of mixing in stirred bioreactors, 2: Selection of optimum impeller combinations for non-aerated simulated broths

2007 ◽  
Vol 13 (1) ◽  
pp. 21-26 ◽  
Author(s):  
Anca-Irina Galaction ◽  
Elena Folescu ◽  
Dan Cascaval
Keyword(s):  
Fermentation Broth ◽  
Mixing Time ◽  
Maximum Level ◽  
Specific Power ◽  
Mixing Efficiency ◽  
Mechanical Mixing ◽  
Rushton Turbine ◽  
Shear Effects ◽  
Stirred Bioreactors ◽  
Selection Of

Although radial impellers, especially the Rushton turbine, are widely used in stirred bioreactors, their applicability is limited by the high apparent viscosities of the broths. For optimizing mechanical mixing by selecting the appropriate impeller for a specific fermentation broth or process, the comparative analysis of the mixing efficiency, energy costs and shear effects on the biocatalysts is required. By means of this analysis, three different combinations of radial impellers for water and viscous simulated broths were selected for attaining optimum mixing in a bioreactor. The proposed impellers combinations offer the most intense and uniformly distributed mixing and the lowest specific power consumption required for reaching a maximum level of mixing time of less than one minute.

CFD Analysis and Design Optimization in a Curved Blade Impeller

2017 ◽  
Vol 15 (1) ◽  
Author(s):  
Nazila Sutudehnezhad ◽  
Ramin Zadghaffari
Keyword(s):  
Flow Field ◽  
Mixing Time ◽  
Computational Method ◽  
Stirred Tank ◽  
Mixing Efficiency ◽  
Rushton Turbine ◽  
Stirred Tank Reactors ◽  
Analysis And Design ◽  
Curved Blade ◽  
Reported Data

Abstract Mixing efficiency in stirred tank reactors is an important challenge in the design of many industrial processes. The effect of blade shape on mixing efficiency has been studied in the present work. The computational method has been used to investigate the flow field, power consumption, pumping capacity, hydraulic efficiency, and mixing time in a fully baffled tank stirred by a Rushton turbine and different curved blade impellers. Flow in a stirred tank reactor involves interactions between flow around rotating blades and stationary baffles. The flow field was developed using the sliding mesh (SM) approach in computational fluid dynamics (CFD). The realizable k-ε was used to model the turbulence. A reasonable agreement between the experimental reported data and simulation results indicated the validity of CFD model. It has been revealed that increasing the blade curvature, at approximately the same mixing time would enhance the mixing efficiency up to 61.3 % in comparison with the Rushton turbine. This mixing efficiency would favor the employment of curved blade impellers due to the cost-benefits of stirred tank operations.

Impact of the divorce experience on the marital and family mindsets

2018 ◽  
pp. 88-96
Author(s):  
Елена Лактюхина ◽  
Elena Laktyukhina ◽  
Георгий Антонов ◽  
Georgy Antonov
Keyword(s):  
Comparative Analysis ◽  
Demographic Characteristics ◽  
Representative Sampling ◽  
First Marriage ◽  
Active Population ◽  
Volgograd Region ◽  
The Social ◽  
Marriage Stability ◽  
Main Factors ◽  
The Individual

The article presents a comparative analysis of marital and family mindsets of two categories of the demographically active population of modern Russia: (1) individuals that have no experience of a divorce and (2) those who have already experienced one or more official termination of a marriage. The empirical base of the analysis is the data of the author’s questionnaire survey conducted by representative sampling in Volgograd and Volgograd Region in 2015–2016. The analysis was made on the following basic empiric indicators: optimal (from the viewpoint of the respondents) age for the first marriage, frequency of mentioning marital and family statuses as the respondents describe their own social and demographic “portrait”, legitimate causes of a divorce and a number of others. It is found that, in the case of sufficiently strong traditional marital and family mindsets, perception of marital norms is adjusted, if an “abnormal” event (such as a divorce) occurs in the individual’s life course. At the same time, perception of the marriage stability is less variable and does not depend on the social and demographic characteristics of the respondents, including the presence/absence of a marriage termination experience. The “strongest” factor that affects the change of the marital and family mindsets is age. With age (and, consequently, experience accumulation), importance of the majority of main factors capable of preventing the individual from a divorce decreases and, therefore, the risk of such event increases.

Comparative analysis and verification of engineering methods of shallow cracks effect for fracture toughness prediction for reactor pressure vessels

2020 ◽  
pp. 140-165
Author(s):  
V. I. Kostylev ◽  
B. Z. Margolin
Keyword(s):  
Experimental Data ◽  
Fracture Toughness ◽  
Comparative Analysis ◽  
Nuclear Reactor ◽  
Probabilistic Approach ◽  
Pressure Vessels ◽  
Local Methods ◽  
European Method ◽  
Shallow Crack ◽  
Reactor Pressure

The main features of shallow cracks fracture are considered, and a brief analysis of methods allowing to predict the temperature dependence of the fracture toughness KJC (T) for specimens with shallow cracks is given. These methods include DA-method, (JQ)-method, (J-T)-method, “local methods” with its multiparameter probabilistic approach, GP method uses power approach, and also two engineering methods – RMSC (Russian Method for Shallow Crack) and EMSC (European Method for Shallow Crack). On the basis of 13 sets of experimental data for national and foreign steels, a detailed verification and comparative analysis of these two engineering methods were carried out on the materials of the VVER and PWR nuclear reactor vessels considering the effect of shallow cracks.

Effects of vessel baffling on the drawdown of floating solids

2009 ◽  
Vol 63 (2) ◽  
Author(s):  
Joanna Karcz ◽  
Beata Mackiewicz
Keyword(s):  
Experimental Data ◽  
Power Consumption ◽  
Strain Gauge ◽  
High Speed ◽  
Vessel Diameter ◽  
Rushton Turbine ◽  
Agitated Vessel ◽  
Dimensionless Equation ◽  
Inner Diameter ◽  
Floating Particles

AbstractThe effects of baffling of an agitated vessel on the production of floating particles suspension are presented in this paper. Critical agitator speed, needed for particles dispersion in a liquid agitated in a vessel of the inner diameter of 0.295 m, was determined. The just drawdown agitator speeds were defined analogously to the Zwietering criterion. Specific agitation energy was calculated from the power consumption experimental data obtained by means of the strain gauge method. The experiments were carried out for twelve configurations of the baffles differing in number, length and their arrangement in the vessels. The following high-speed impellers were used: up- and downpumping six blade pitched blade turbines, Rushton turbine, and propeller. The impeller was located in the vessel in the height equal to two-thirds or one-third of the vessel diameter from the bottom of the vessel. The results were described in the form of a dimensionless equation.

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