No (235)
Yes (77)
Number of found documents:
312
Published from
to
Improvement of an unbaffled stirred tank mixing characteristics using variable speed impeller
Gebouský, Ondřej; Haidl, Jan; Bodnár, J.; Pivokonský, Martin
2024 - English
Unbaffled mixing tanks with magnetically driven impellers are increasingly used in biotechnological and pharmaceutical industries, combining the benefits of a closed, sterile environment with easy equipment cleanability. On the other hand, missing internals, such as baffles or cooling coils, have an adverse effect on the equipment mixing characteristics, namely the batch\nhomogenization time. In our previous research, we uncovered that the eccentricity and inclination of the impeller – both employed routinely to enhance the mixing characteristics of unbaffled vessels – are not fully effective in the suppression of central vortex formation resulting in the increase in the homogenization time. In this work, we propose a simple solution to counteract the central vortex formation – a periodical variation of impeller rotational speed. This approach destabilizes the central vortex, significantly reducing homogenization time while maintaining the benefits of the original unbaffled setup. This innovation can seamlessly integrate into existing industrial setups, promising efficiency gains for biotech and pharmaceutical production.
Keywords:
unbaffled mixing tanks; variable rotational speed; vortex destabilization; mixing time improvement
Available in digital repository of the ASCR
Improvement of an unbaffled stirred tank mixing characteristics using variable speed impeller
Unbaffled mixing tanks with magnetically driven impellers are increasingly used in biotechnological and pharmaceutical industries, combining the benefits of a closed, sterile environment with easy ...
Flow simulations approach for flocculation tanks
Idžakovičová, Kristýna; Bílek, Vojtěch; Haidl, Jan; Isoz, M.; Pivokonský, Martin
2024 - English
Flocculation in water treatment facilities plays a key role in the separation of colloidal inorganic and organic substances. Its optimization leads to a significant increase in its efficiency and savings of operational costs. However, it is currently based on trial-and-error experimental approaches. In this contribution, we focus on flow modeling in stirred flocculation tanks that would, after coupling with a calibrated model of particle aggregation, enable simulationbased flocculation optimization. Despite the abundance of literature on stirred tank modeling, there is no universal agreement on the methodology used to describe turbulence nor on the approach to the computational mesh creation. Consequently, there is no unified methodology for simulations and their validation. To address this, we present a best-practice methodology for economical, yet reliable flow simulations in the said device. This methodology includes the choice of the turbulence model, the approach to the design of a high quality mesh suitable for arbitrary geometries, and results evaluation. It is developed based on an extensive literature review, a multitude of flow simulations using several meshes of progressively higher quality and resolution, and various strategies to converge to steady-state flow conditions. The simulation quality indicators used here involve comparison with the experimental data on fluid velocity, stirrer power output, and flow rate through the impeller zone. Additionally, the resulting flow simulation models are compared using tracer transport simulations, hinting at their potential for coupling with particle aggregation models.
Keywords:
flocculation tank; stirring; MRF; CFD; OpenFOAM
Available in digital repository of the ASCR
Flow simulations approach for flocculation tanks
Flocculation in water treatment facilities plays a key role in the separation of colloidal inorganic and organic substances. Its optimization leads to a significant increase in its efficiency and ...
Dynamics of surface water quality changes in model headwater areas of the Czech Republic
Fraindová, K.; Matoušková, M.; Kliment, Z.; Vlček, Lukáš; Vlach, V.; Šajnarová, L.
2023 - English
River headwaters have a high environmental value. Unfortunately, the biogeochemical processes in headwaters in context of different rainfall-runoff conditions and specific land cover have not been fully examined. This study focuses on changes in correlations of 16 biogeochemical parameters related to different types of rainfall-runoff events and land cover condition for eight headwater catchments in Central Europe. Multiple methods as linear regression, Spearman rank correlation, Principal Components Analysis and C/Q hysteresis loops revealed main relationships. Presence of peatlands and waterlogged spruce forests had decisive influence on the biogeochemistry (mainly for CODMn, humins, Fe, P-PO43− TP, and N-NO3−). The strongest positive correlation of organic matter (CODMn) and Fe is represented in a catchment with the largest area of damaged forest (70%), but with a smaller proportion of wetlands (8%). High flow rates influence the release of greater amounts of organic matter and N-NO3−.
Keywords:
headwater areas; organic matter; waterlogged areas; peatbogs; raifall-runoff events; water quality; electric conductivity
Fulltext is available at external website.
Dynamics of surface water quality changes in model headwater areas of the Czech Republic
River headwaters have a high environmental value. Unfortunately, the biogeochemical processes in headwaters in context of different rainfall-runoff conditions and specific land cover have not been ...
Dynamics of dissolved organic carbon in surface water during extreme rainfall-runoff events
Matoušková, M.; Fraindová, K.; Bejčková, M.; Kliment, Z.; Vlach, V.; Vlček, Lukáš
2023 - English
The release of a greater amount of natural organic matter (NOM) within climate change is registered in many catchments with peatbog areas. The aim of our research is to study the dynamics of releasing dissolved organic carbon (DOC) into surface water in headwater areas with peatbogs. DOC concentrations are analysed in relation to extreme rainfall-runoff (R-R) events and according to the hydrological preconditions of the basin. These preconditions are described using selected hydroclimatic variables (14 days before the R-R event). The source data comes from stations of the Faculty of Science, Charles University, and the Czech Hydrometeorological Institute. For the evaluation of relations and processes, the Principal component analysis (PCA), hysteresis loops or Pearson correlation coefficient was used. The lag time of DOCmax for Qmax, the dependence of DOCmax and groundwater levels were studied. The influence of flow rate on the decline and ascent phases of DOC\nconcentrations by hysteresis loops and the influence of the number of partial flow maximums on the amount of transported DOC during the R-R event was analysed. Our first results show that great influence on the dynamic of DOC concentration in surface water has the change in groundwater-levels in the peatbog and the outflow amount during the R-R event. The hydroclimatic preconditions of the basin have also a significant influence on the DOC release. Changes in concentrations during R-R events also occurred for other compounds that were studied additionally. Particularly significant was the increase in metals (mainly Fe, Al, Mn) and base cation (K) and decrease in nitrate nitrogen.
Keywords:
natural organic matter; dissolved organic carbon; peatbog; surface water
Fulltext is available at external website.
Dynamics of dissolved organic carbon in surface water during extreme rainfall-runoff events
The release of a greater amount of natural organic matter (NOM) within climate change is registered in many catchments with peatbog areas. The aim of our research is to study the dynamics of releasing ...
Summary of the Liquid-Gas Ejector Hydraulic Behavior - Theory and Practice
Gebouský, Ondřej; Haidl, Jan
2023 - English
Liquid-gas ejectors (LGEs) are fascinating devices that use the kinetic energy of the liquid jet to entrain and eventually compress the gas. LGEs find applications in both industry and everyday life, e.g., as sprayers. However, a complex and reliable method for LGE design was not available in the open literature until recently. This contribution follows up on our recent works about the hydraulic behavior of LGE with undisturbed and destabilized liquid jets. This paper aims to summarize the device’s complicated hydraulics and characterize its optimal design for three industrially relevant applications - (a) LGE as the vacuum pump, (b) LGE as the gas purification equipment, and (c) LGE as the gas distributor for bioreactors.
Keywords:
liquid-gas ejector; jet pump; design method
Available in digital repository of the ASCR
Summary of the Liquid-Gas Ejector Hydraulic Behavior - Theory and Practice
Liquid-gas ejectors (LGEs) are fascinating devices that use the kinetic energy of the liquid jet to entrain and eventually compress the gas. LGEs find applications in both industry and everyday life, ...
Experimental validation of granular flow kinetic theory under turbulent flow conditions
Haidl, Jan; Chára, Zdeněk; Matoušek, Václav
2022 - English
The mixed classical and extended kinetic theory of granular ows is used for modeling the characteristics of particles-water turbulent sheet ow. The open-source solver sedFoam v3.1 is used for the 1-D and 2-D ow simulations. The simulation results are compared to the experimental data measured in the open channel. After that, the simulation parameters are optimized to achieve the best possible agreement between the simulation and the experimental results. The unsatisfactory performance of the KT models and the observed simulation instabilities are discussed.
Keywords:
kinetic theory; granular flow; sedFoam
Available at various institutes of the ASCR
Experimental validation of granular flow kinetic theory under turbulent flow conditions
The mixed classical and extended kinetic theory of granular ows is used for modeling the characteristics of particles-water turbulent sheet ow. The open-source solver sedFoam v3.1 is used for the 1-D ...
Correlation between the onset of beadless character of nanofibrous webs and rheological characteristics of electrospun polymer solutions
Zelenková, Jana; Peer, Petra; Filip, Petr
2021 - English
An overwhelming majority of applications of nanofibrous webs requires sufficiently smooth character of nanofibres surface. This character is apart other parameters strongly influenced by a concentration of chosen polymeric material in the solvents. Qualitative attributes roughly depend on the prepared concentration, specifically whether it belongs to one of the four basic regions: dilute, semidilute unentangled, semidilute entangled and concentrated. A concentration separating the latter two regions is often taken as a zero-th approximation indicating an onset of beadless nanofibrous webs. The present contribution uses as a more precise indicator behaviour of so-called phase angle relating viscous and elastic moduli, in other words mutual participation of viscous and elastic components. To this aim three frequently used polymers were used: copolymer of poly(vinylidene fluoride) and hexafluoropropylene (PVDF-co-HFP), poly(ethylene oxide) (PEO) and poly(vinyl butyral) (PVB). For materials exhibiting first a constant behaviour or moderate decrease in a phase angle for lower concentrations, an approximation of the starting concentration is given by a concentration value where a phase angle curve starts to decrease, apparently reflecting a more progressive viscoelastic nature. As shown, such approximation provides relatively very good approximation enabling to eliminate a traditional trial-and-error method.
Keywords:
nanofibres; beadless morphology; PVDF-co-HFP; polymer concentration; rheology
Available in digital repository of the ASCR
Correlation between the onset of beadless character of nanofibrous webs and rheological characteristics of electrospun polymer solutions
An overwhelming majority of applications of nanofibrous webs requires sufficiently smooth character of nanofibres surface. This character is apart other parameters strongly influenced by a ...
Antibacterial electrospun membrane prepared from poly(vinylidene fluoride)-co-hexafluoropropylene with lauric acid monoacylglycerol
Zelenková, Jana; Peer, Petra; Pleva, P.; Janalíková, M.; Sedlaříková, J.; Filip, Petr
2021 - English
The aim of this study was to prepare an antibacterial nanofibrous membrane using electrospinning technique. The nanofibrous membranes were spun from polymer solution of poly(vinylidne fluoride)-co-hexafluoropropylene (PVDF-co-HFP) dissolved in N,N´-dimethylformamide. Monoacylglycerol of lauric acid (MAG C12) was used as an antimicrobial agent at the concentrations ranging from 1 to 3 wt%. The impact of MAG C12 incorporation on the rheological, structural and antibacterial properties was investigated. The rheological tests of polymer solutions, as steady shear and oscillatory shear, proved that addition of MAG C12 changed marginally rheological quantities such as viscosity, elastic (storage) and viscous (loss) moduli. Measurement of mean nanofibres diameter indicated a slight decrease with increasing MAG C12 concentration. Antimicrobial activity of PVDF-co-HFP nanofibre membranes with incorporated MAG C12 against Gram-positive bacteria Staphylococcus aureus and Gram-negative Escherichia coli was studied. An antibacterial activity was revealed for the samples containing MAG C12 at all concentrations against Gram-positive bacteria Staphylococcus aureus by the disk diffusion method.
Keywords:
nanofibres; electrospinning; antibacterial memrane; rheology; polymer solution
Available at various institutes of the ASCR
Antibacterial electrospun membrane prepared from poly(vinylidene fluoride)-co-hexafluoropropylene with lauric acid monoacylglycerol
The aim of this study was to prepare an antibacterial nanofibrous membrane using electrospinning technique. The nanofibrous membranes were spun from polymer solution of poly(vinylidne ...
Magnetic properties of electrospun polyvinyl butyral/Fe2O3 nanofibrous membranes
Peer, Petra; Cvek, M.; Urbánek, M.; Sedlačík, M.
2020 - English
In this contribution, magnetic Fe2O3 nanoparticles (MNPs) were successfully incorporated into the polyvinyl butyral (PVB) nanofibrous membranes using the electrospinning process. The effects of the MNP concentration on the morphology of the nanofibres and their magnetic properties were investigated. Scanning electron microscopy and transmission electron microscopy confirmed their concentration-dependent, yet uniform diameter, and the presence of well-embedded MNPs inside the PVB nanofibres. The magnetic properties of the PVB/MNP membranes were studied using the vibrating-sample magnetometry. The saturation magnetization increased from 6.4 to 45.5 emu/g as the MNP concentration in the feedstock solution increased from 1 to 15 wt%. The fabricated PVB/MNP nanofibrous membranes possessed the ability to respond to the external magnetic fields, which determines their potential in the development of the advanced smart textiles.
Keywords:
electrospinning; polyvinyl butyral; nanofibres; magnetic properties
Available at various institutes of the ASCR
Magnetic properties of electrospun polyvinyl butyral/Fe2O3 nanofibrous membranes
In this contribution, magnetic Fe2O3 nanoparticles (MNPs) were successfully incorporated into the polyvinyl butyral (PVB) nanofibrous membranes using the electrospinning process. The effects of the ...
Flow behaviour of sand-water mixture in horizontal and inclined pipes
Vlasák, Pavel; Chára, Zdeněk; Matoušek, Václav; Kesely, Mikoláš; Krupička, Jan; Konfršt, Jiří; Mildner, Michael
2019 - English
Pipelines transporting slurries in different industrial applications often contain inclined sections. The effect of pipe inclination, slurry concentration and mean velocity on the flow behaviour, deposition\nlimit velocity, and internal structure of a settling slurry was studied in an experimental pipe loop of inner diameter D = 100 mm. The slurry consisted from water and a narrow particle size distribution sand of mean diameter d50 = 0.55 mm. The experiments focused on the effects of the pipe inclination on solids distribution and deposition limit velocity. The concentration distribution in pipe cross-section was studied with application of a gamma-ray densitometer. The study revealed the stratified flow pattern of the medium sand-water mixture in inclined pipe sections. Experimental results show that the degree of the slurry stratification decreased with an increasing angle of inclination in the ascending pipe sections. The slurry stratification affected the deposition limit velocity. Mean in situ concentration for the descending flow was always lower than that for the ascending flow. The deposition limit in ascending pipe, in comparison with that in a horizontal pipe, slightly increased up to inclination angle about +25°, and then remained practically constant. For negative pipe inclination over – 30° no deposition limit was observed.
Keywords:
slurry flow; inclined pipe; deposit limit velocity
Available at various institutes of the ASCR
Flow behaviour of sand-water mixture in horizontal and inclined pipes
Pipelines transporting slurries in different industrial applications often contain inclined sections. The effect of pipe inclination, slurry concentration and mean velocity on the flow behaviour, ...
NRGL provides central access to information on grey literature produced in the Czech Republic in the fields of science, research and education. You can find more information about grey literature and NRGL at service web
Send your suggestions and comments to nusl@techlib.cz
Provider
Other bases