No (503)
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Simulace pohybu částic v nakloněném potrubí pomocí kombinace CFD a DEM
Mildner, Michael; Konfršt, Jiří; Kysela, Bohuš; Chára, Zdeněk; Vlasák, Pavel
2017 - Czech
Numerická simulace proudění rozplavených hrubozrnných suspenzí (hydrotransport, odlučovače atp.) vyžaduje použití výpočtů pro vícefázové proudění. Za předpokladu toku suspenze (např. vody a pevných částic) v uzavřených profilech bez přístupu vzduchu můžeme úlohu zjednodušit na dvoufázové proudění (voda-pevné částice). Vhodným nástrojem pro výpočet takovéhoto dvoufázového proudění je kombinace metody konečných objemů FVM s metodou diskrétních elementů DEM. Metoda diskrétních elementů je použita na řešení kolizí mezi jednotlivými částicemi, což je nezbytnou podmínkou pro reálné řešení proudění více- koncentrovaných suspenzí. Numerická simulace byla provedena na jednoduché geometrii nakloněného potrubí, kde jsou získané výsledky porovnávány s výsledky získanými na experimentální trase pro transport suspenzí opatřené sklopnou částí. Numerical flow simulation of scattered coarse-grained suspensions (hydrotransport, separators, etc.) requires the use of calculations for multiphase flow. Assuming the suspension flow (eg. water and solid particles) in closed profiles without air access, the task can be simplified to a two-phase flow (water-solid particles). A suitable tool for calculating such two-phase flow is the combination of the finite volume method FVM, with the discrete element method DEM. The discrete element method is used to solve collisions between individual particles, which is a prerequisite for a real solution of more concentrated suspension flow. Numerical simulation was performed on a simple geometry of inclined pipeline, where the obtained results were compared with the results obtained on the experimental slurry transport route equipped with a foldable part.
Keywords:
CFD; FVM; DEM; transport of suspension
Available on request at various institutes of the ASCR
Simulace pohybu částic v nakloněném potrubí pomocí kombinace CFD a DEM
Numerická simulace proudění rozplavených hrubozrnných suspenzí (hydrotransport, odlučovače atp.) vyžaduje použití výpočtů pro vícefázové proudění. Za předpokladu toku suspenze (např. vody a pevných ...
Influence of land cover and altitude on soilmoisturespatio-temporal variability
Šípek, Václav; Hnilica, Jan; Tesař, Miroslav
2017 - English
An understanding of spatial and temporal variation of soil moisture is essential for studying other hydrological, biological or chemical soil processes, such as water movement, microbial activity and biogeochemical cycling (Bruckner et al., 1999, Ridolfi et al., 2003). Although the world-wide total amount of water stored in the soil profile is negligible compared to ocean and glacier storages, it represents a crucial variable concerning the water resources and agricultural management. This is valid especially in the context of ongoing shift in climate. Soil water exhibits a tremendous heterogeneity in space and time (Gomez-Plaza et al., 2000). Therefore, spatial and temporal variations of soil moisture have always been the critical issue. The spatial variability is influenced by variety of factors encompassing the topographical effect on lateral water redistribution (Williams et al., 2003), radiation (Grayson et al., 1997, Geroy et al., 2011), soil texture and structure (Famiglietti et al., 1998, Pan and Peters-Lidard, 2008), vegetation (Teuling and Troch, 2005), climate (Lawrence and Hornberger, 2007), precipitation pattern (Keim et al., 2005) and antecedent soil moisture (Rosenbaum et al., 2012). The land use influence on the soil moisture content variation is of complex a character covering several above mentioned factors. However, it is determined namely by the different vegetation cover, which results in different rates of interception and transpiration. It also strongly influences the soil hydraulic properties, i.e. hydraulic conductivity and water retention characteristics (Zhou et al, 2008). Hence, the reaction of an area to a rainfall and also the temporal variability of the soil moisture content might be influenced by the present land cover. Nevertheless, the studies comparing the influence of several land covers in the longer periods are missing. This knowledge would be valuable especially in the context of extreme climatic events that are present nowadays. In central Europe, the period of major floods (1997, 2002, 2013) was followed by serious dry spells (2003, 2011–2012, 2015) (Trnka et al., 2015). This observed hydrological extremity raised the questions of sustainable water management. One of the possible management practices in consideration is represented by the land cover changes intended to hold more water in the landscape and simultaneously to attenuate the rainfall-runoff response. Moreover, previous studies have investigated that spatial and temporal variation of soil water under a certain land use type, and drawing significant research attention is lacking on the differences of dynamics of soil water conditions under different land use types. Thus, it is necessary to understand the comparisons of the dynamics of soil water conditions under different land use types (Niu et al., 2015) The main aim of the presented study is therefore to understand the soil moisture variability in the vegetation season under four different land covers (coniferous/deciduous forest, meadow, grassland). This analysis is conducted in five consecutive years, encompassing both dry and wet periods. The influence of altitude is also studied in the coniferous forest.
Keywords:
wet years; dry years; forest; meadow; grassland; soil moisture; vegetation season
Available at various institutes of the ASCR
Influence of land cover and altitude on soilmoisturespatio-temporal variability
An understanding of spatial and temporal variation of soil moisture is essential for studying other hydrological, biological or chemical soil processes, such as water movement, microbial activity and ...
18th International Conference on Transport & Sedimentation of Solid Particles
Sobota, J.; Vlasák, Pavel; Matoušek, Václav
2017 - English
The Proceedings comprise text of 50 oral contributions dealing with two-phase and multiphase flows, Newtonian and non-Newtonian flows, designing, optimization and operation of hydrotransport and pneumotransport systems, wear and corrosions, pumps and valves, sediment transport in rivers and water reservoirs, hydraulic storage of tailings, sedimentation and thickening, methods and techniques of measurement, instrumentation for laboratory, field and industrial systems.
Keywords:
two-phase flow; multiphase flow; sediment transport; sedimentation of solid particles
Available at various institutes of the ASCR
18th International Conference on Transport & Sedimentation of Solid Particles
The Proceedings comprise text of 50 oral contributions dealing with two-phase and multiphase flows, Newtonian and non-Newtonian flows, designing, optimization and operation of hydrotransport and ...
Deposition limit velocity: effect of particle size distribution
Matoušek, Václav; Visintainer, R.; Furlan, J.; McCall, G.; Sellgren, A.
2017 - English
Industrial settling slurries often consist of particles of very different sizes - the particle size distribution may cover sizes which differ with two orders of magnitude. A broad particle size distribution affects parameters of slurry flow including deposition limit velocity. We present experimental results of the deposition limit velocity collected during a comprehensive experimental campaign testing slurry flows composed of solids of different fractions in the GIW Hydraulic Laboratory in 2016. Four narrow graded fractions (carrier fluid, pseudo-homogeneous, heterogeneous, and stratified) were tested in permutations from the individual components to the complete mixture at various concentrations. The primary experiments were carried out in a 203-mm pipe, and selected corresponding experiments were repeated in a 103-mm pipe. The experimental results show that interactions among components affect the resulting deposition limit velocity in flows of broadly graded settling slurries. The effect of particle size distribution on the deposition limit velocity is not benign. The deposit velocity is not necessarily lower in a flow of slurry composed of four components than in slurry flow of one component with the highest deposit velocity from the four components. We discuss possible modifications of a deposit velocity predictive model in order to take effects of a broad particle size distribution into account.
Keywords:
settling slurry flow; deposit in pipe; four component model; mixture flow experiment
Available at various institutes of the ASCR
Deposition limit velocity: effect of particle size distribution
Industrial settling slurries often consist of particles of very different sizes - the particle size distribution may cover sizes which differ with two orders of magnitude. A broad particle size ...
Concentration distribution and slip velocity of coarse-particle-water mixture in horizontal and inclined pipe sections
Vlasák, Pavel; Chára, Zdeněk; Konfršt, Jiří
2017 - English
Narrow particle size distribution basalt pebbles of mean particle size 11.5 mm conveyed by water in the pipe sections of different inclination were investigated on an experimental pipe loop of inner diameter D = 100 mm. Mixture flow-behaviour and the concentration distribution were studied in a pipe viewing section and with the application of a gamma-ray densitometer. The study refers to the effect of mixture velocity, overall concentration, and angle of pipe inclination on chord-averaged concentration profiles and local concentration maps. The study revealed that the coarse particle-water mixtures in the inclined pipe sections were significantly stratified, the solid particles moved principally close to the pipe invert, and for higher and moderate flow velocities particle saltation becomes the dominant mode of particle conveying.
Keywords:
hydraulic conveying; concentration distribution; pipe inclination; Gamma-Ray radiometry; mixture flow behaviour
Available on request at various institutes of the ASCR
Concentration distribution and slip velocity of coarse-particle-water mixture in horizontal and inclined pipe sections
Narrow particle size distribution basalt pebbles of mean particle size 11.5 mm conveyed by water in the pipe sections of different inclination were investigated on an experimental pipe loop of inner ...
Měření velikosti kapek ve dvoufázovém systému
Kysela, Bohuš; Konfršt, Jiří; Chára, Zdeněk; Kotek, M.; Šulc, R.
2017 - Czech
The in-situ measurement method of droplet size in an agitated vessel based on droplet visualisation and image analysis were developed. The image analysis was enhanced by the finding edges algorithm and circularity analysis. The proposed method was validated by the measurements of precise solid particles and used for liquid-liquid mesurements in an agitated vessel. The in-situ measurement method of droplet size in an agitated vessel based on droplet visualisation and image analysis were developed. The image analysis was enhanced by the finding edges algorithm and circularity analysis. The proposed method was validated by the measurements of precise solid particles and used for liquid-liquid mesurements in an agitated vessel.
Keywords:
droplet size; agitated vessel; liquid-liquid; image analysis
Available at various institutes of the ASCR
Měření velikosti kapek ve dvoufázovém systému
The in-situ measurement method of droplet size in an agitated vessel based on droplet visualisation and image analysis were developed. The image analysis was enhanced by the finding edges algorithm ...
Flow of heterogeneous slurry in horizontal and inclined pipes
Vlasák, Pavel; Chára, Zdeněk; Konfršt, Jiří; Kysela, Bohuš
2017 - English
Narrow particle size distribution heterogeneous slurries were investigated on an experimental pipe loop with the horizontal and inclined pipe sections of inner diameter 100 mm. The investigation was focused on the effect of the pipe inclination, average slurry velocity and overall concentration and on the local concentration distribution, pressure drop, deposition limit and carrier liquid-particle slip velocity. The local concentration distribution was studied with the application of a gamma-ray densitometer. Mixture flow-behaviour and particles motion were investigated in a pipe viewing section. The study revealed that the heterogeneous slurries in the horizontal and inclined pipe sections were significantly stratified, the solid particles moved principally close to the pipe invert, and particle saltation becomes the dominant mode of particle conveying for higher and moderate flow velocities. Carrier liquid-particle slip velocity depends not only on the mixture velocity, but also on particle position in the pipe cross-section. The effect of pipe inclination on the frictional pressure drop in inclined pipe sections depends on mixture velocity, in ascending pipe section decreases with increasing mixture velocity and in descending pipe section the frictional pressure drop gradually decreased with increasing pipe inclination.
Keywords:
solid-liquid mixture; pipe inclination; slip velocity; mixture flow behaviour; concentration distribution
Available at various institutes of the ASCR
Flow of heterogeneous slurry in horizontal and inclined pipes
Narrow particle size distribution heterogeneous slurries were investigated on an experimental pipe loop with the horizontal and inclined pipe sections of inner diameter 100 mm. The investigation was ...
The role of sonication of polyethyleneoxide solutions containing magnetic nanoparticles on morphology of nanofibrous mats
Peer, Petra; Stěnička, M.; Filip, Petr; Pizúrová, Naděžda; Babayan, V.
2017 - English
Properties of the resulting polymer nanofibers are often tailored by sonication technique applied prior or past an electrospinning process. The aim of this contribution is to evaluate morphology of nanofibrous mats formed by poly(ethylene oxide) with distributed magnetic nanoparticles (MNP) (about 20 nm in diameter) in dependence on time of sonication of the used polymer solutions. The solutions were exposed to sonication (intensity 200W, frequency 24 kHz) for 10, 30, and 60 minutes. It was shown that rheological characteristics (viscosity, storage and loss moduli) strongly depend on time of sonication (particularly phase angle) in contrast to electric conductivity and surface tension. For analysis of homogeneous distribution of MNP in polymer solution, the rheological measurements were carried out also in presence of external magnetic field. Magnetorheological efficiency (a relation of corresponding viscosities) was determined for 80, 170, and 255 mT. Consequently, changed rheological characteristics participate significantly in the process of electrospinning and resulting quality of the obtained nanofibrous mats. Qualitative changes were described by\nmeans of scanning electron microscopy (variance of mean diameter of nanofibers), transmission electron microscopy (distribution of MNP within nanofibrous mats). Static magnetic properties were determined by a vibration sample magnetometer. It was shown that even distribution of MNP in the mats can be achieved by mere sonication process without application of external magnetic field during an electrospinning process. However, time of sonication generates a degree of embedding of MNP into individual nanofibers.
Keywords:
ultrasound; poly(ethylene oxide); magnetic nanoparticles; magnetorheology; electrospinning
Available on request at various institutes of the ASCR
The role of sonication of polyethyleneoxide solutions containing magnetic nanoparticles on morphology of nanofibrous mats
Properties of the resulting polymer nanofibers are often tailored by sonication technique applied prior or past an electrospinning process. The aim of this contribution is to evaluate morphology of ...
Discharged stream from radial impeller, comparison of LDA and PIV measurements
Kysela, Bohuš; Konfršt, Jiří; Chára, Zdeněk; Jašíková, D.; Němcová, L.; Kopecký, V.
2016 - Czech
Míchání je v procesní technice velice důležitá operace, která má za úkol vytvořit homogenní\nsměs, homogenní suspenzi, lépe rozdružit materiál v disperzích, atp. Míchaná nádoba je\naparát, kde má docházet k energeticky co nejpříznivějšímu míchání různých látek. V této\npráci se zaměřujeme na míchané nádoby s tzv. radiálním rychloběžným míchadlem.\nModelování velkých nádob na základě experimentů na malých nádobách je prováděno\npomocí podobnostních přepočtů. Základní parametry přepočtů lze analyzovat především na\nzákladě znalostí proudového pole v míchaném objemu, případně dalších veličin, jejichž\nvýsledky jsou stále předmětem ověřování a zpřesňování.\nV této práci jsme se zaměřili na měření rychlostního pole na výtoku z tzv. Rushtonova\nturbínového míchadla [1,2,3], kde vytékající proud z lopatek bývá popisován analogicky jako\ntok v zatopeném proudu [4]. Rychlostní profily byly měřeny pomocí dvousložkového LDA\nměření (radiální a tangenciální složka). Třetí (axiální) složka byla měřena následně po\npřestavění měřícího LDA systému. Získaná data časových záznamů byla podrobena další\nanalýze při vyhodnocování statistických veličin časově středních hodnot rychlostí a velikosti\nfluktuačních složek. Two velocity measurement methods in discharged stream from Rushton turbine are compared. The tested methods are LDA (Laser Doppler Anemometry) and stereo TR PIV (Time Resolved Particle Image Velocimetry). The discrepancy of evaluated data from stereo PIV affected by transforming recalculation in discharged stream is presented.
Keywords:
mixing vessel; Rushton turbine; LDA; PIV
Available at various institutes of the ASCR
Discharged stream from radial impeller, comparison of LDA and PIV measurements
Míchání je v procesní technice velice důležitá operace, která má za úkol vytvořit homogenní\nsměs, homogenní suspenzi, lépe rozdružit materiál v disperzích, atp. Míchaná nádoba je\naparát, kde má ...
Chlorečnan jako jeden z vedlejších produktů desinfekce vody Chlornanem sodným
Drdová, Š.; Parschová, H.; Pivokonský, Martin; Janda, V.
2016 - Czech
Příspěvek je zaměřen na problematiku chlorečnanů, které vznikají jako vedlejší produkt desinfekce vody za využití chlornanu sodného. Pozornost byla věnována zejména době a způsobu skladování roztoku chlornanu sodného s ohledem na tvorbu chlorečnanů i dalších vedlejších produktů. The study deals with the formation of chlorate as a disinfection by-product when using sodium hypochlorite. The relationship between aging and storing conditions of sodium hypochlorite and the production of chlorite and other DBPs was investigated.
Keywords:
chlorate; DBPs (Disinfection By-Products); sodium hypochlorite; sodium hypochlorite
Available on request at various institutes of the ASCR
Chlorečnan jako jeden z vedlejších produktů desinfekce vody Chlornanem sodným
Příspěvek je zaměřen na problematiku chlorečnanů, které vznikají jako vedlejší produkt desinfekce vody za využití chlornanu sodného. Pozornost byla věnována zejména době a způsobu skladování roztoku ...
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