Ústav pro hydrodynamiku

Nejnovější přírůstky:
2019-08-26
09:05
Dependence of morphology of electrospun PVB nanofibres containing fumed silica on elasticity of the processed solutions
Peer, Petra ; Polášková, M. ; Filip, Petr
Application of various types of fumed silica gives a possibility to tailor a degree of hydrophilicity or hydrophobicity of the resulting electrospun nanofibrous mats where as a basic polymeric material is taken poly(vinyl butyral) (PVB) solved in methanol. Presence of fumed silica substantially changes viscoelastic attributes in comparison with the neat PVB solution.\nThe aim of this contribution is to compare morphological structures of the resulting electrospun mats generated from the solutions with presence and absence of various types of fumed silica differing in surface morphology, size and the specific surface area. This comparison is based on the rheological characteristics with the emphasis to elasticity of the pre-processed solutions. The differences in elasticity among fumed silica based solutions are indeed remarkable. The obtained results show that elasticity does not play a crucial role in creation and morphological aspects of the corresponding nanofibrous mats including fibres diameter.

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2019-08-26
09:04
Využití meteorologických dat v hydrologickém modelování na příkladu malého povodí horní Vydry
Vlček, Lukáš ; Šípek, Václav
Příspěvek se zabývá hodnocením malého výzkumného povodí tvořeným dvěma dominantními půdními typy (kryptopodzol, organozem) pramenné oblasti Vydry. Hydrometeorologická a hydropedologická měření jsou doplněná hydrologickým modelem HBV ve snaze odhadnout míru zapojení různých složek povrchového a podpovrchového proudění vody a jejich vliv na odtokový proces. Data byla získána přímým měřením v terénu v průběhu 5-ti hydrologických let (2013-2017). Jde o data půdní vlhkosti odvozené z ret. křivek a z měření potenciálu půdní vody ve dvou hloubkách (20 a 60 cm) na dvou lokalitách, hladiny podzemní vody na 5 místech ve vrchovišti. Vodní stav byl měřen automaticky v závěrovém profilu a také manuálně u dvou pramenů.\nPomocí hydrologického modelu došlo k uspokojivé reprezentaci srážko-odtokového procesu v povodí, režimu půdní vody i kolísání podzemní vody ve svrchní části vrchoviště (organozemi). Celkově je větší množství odtoku z povodí generováno z organozemi a to zejména díky nižší evapotranspiraci rašeliniště oproti ploše kryté kryptopodzolem. V suchých periodách naopak většina odtoku pochází z organominerální půdy (v této studii kryptopodzol) a organozem se na odtoku podílí jen pomalým výtokem ze spodní, dlouhodobě nasycené zóny (část katotelmu).\n

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2019-08-26
09:04

Úplný záznam
2019-05-16
18:17
Detekce mikroplatsů ve zdrojích vody a v pitné vodě na ÚV Káraný, Želivka a Podolí
Pivokonský, Martin ; Pivokonská, Lenka ; Čermáková, Lenka ; Novotná, Kateřina
Na vyžádání společnosti Pražské vodovody a kanalizace, a. s. byly analyzovány vzorky surové a upravené vody ze tří zdrojů sloužících pro zásobování pražské aglomerace pitnou vodou. Předmětem analýzy bylo stanovení množství a složení mikroplastových částic.

Úplný záznam
2019-03-14
15:59
Analýza vzniku kritické situace ohrožení kulturního dědictví přírodní pohromou
Hnilicová, Soňa ; Šípek, Václav
Analýza vzniku různých typů povodňových situací a hodnocení faktorů ovlivňující tvar povodňové vlny. Mechanismus komplexní protipovodňové ochrany včetně konkrétních opatření na území hl. m. Prahy.

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2019-03-14
15:59
Effect of pipe inclination on flow behaviour of fine-grained settling slurry
Vlasák, Pavel ; Chára, Zdeněk ; Matoušek, Václav ; Konfršt, Jiří ; Kesely, Mikoláš
The effect of flow parameters of fine-grained settling slurry on the pressure drop-velocity relationship, deposition limit velocity and local concentration distribution was studied in an experimental pipe loop of inner diameter D = 100 mm with inclinable pipe sections for pipe inclination ranging from – 45° to +45°. The slurry consisted from water and narrow particle size distribution glass beads of mean diameter d50 = 0.18 mm. The concentration distribution was studied with application of a gamma-ray densitometry. The deposition velocity was defined as the flow velocity at which stationary deposit started to be formed at the pipe invert. The study revealed the stratified flow pattern of the studied slurry in inclined pipe sections, for slurry velocities below to the deposition limit sliding or stationary bed were created in ascending pipe sections. For low pipe inclination (􀄮 < ± 25°) the effect of inclination on local concentration distribution was not significant. Mean transport concentration for descending flow was lower than that for the ascending flow Deposition limit in inclined pipe was slightly lower than that in horizontal pipe. Frictional pressure drops in ascending pipe were higher than that in descending pipe, the difference decreased with increasing velocity and inclination.

Úplný záznam
2019-03-14
15:59
Local velocity scaling in upward flow to tooth impeller in a fully turbulent region
Šulc, R. ; Ditl, P. ; Fořt, I. ; Jašíková, D. ; Kotek, M. ; Kopecký, V. ; Kysela, Bohuš
The hydrodynamics and flow field were measured in an agitated vessel using 2-D Time Resolved Particle Image Velocimetry (2-D TR PIV). The experiments were carried out in a fully baffled cylindrical flat bottom vessel 400 mm in inner diameter agitated by a tooth impeller 133 mm in diameter. Distilled water was used as the agitated liquid. The velocity fields were investigated in the upward flow to the impeller for three impeller rotation speeds – 300 rpm, 500 rpm and 700 rpm, corresponding to a Reynolds number in the range 94 000 < Re < 221 000. This means that fully-developed turbulent flow was reached. This Re range secures the fully-developed turbulent flow in an agitated liquid. In accordance with the theory of mixing, the dimensionless mean and fluctuation velocities in the measured directions were found to be constant and independent of the impeller Reynolds number. On the basis of the test results the spatial distributions of dimensionless velocities were calculated. The axial turbulence intensity was found to be in the majority in the range from 0.4 to 0.7, which corresponds to the middle level of turbulence intensity.

Úplný záznam
2019-03-14
15:59
Droplets breakage in flow conditions of an agitated tank
Kysela, Bohuš ; Konfršt, Jiří ; Chára, Zdeněk ; Šulc, R. ; Kotek, M.
Production of two immiscible liquid dispersions used in chemical or metallurgical industry is usually performed by a mixing process. The droplets of secondary liquid are predominantly dispersed by the shear flow forces to the primary liquid. It is well known, that the real droplet size distribution is limited by the physical properties of both liquids, the acting forces and residence time. This phenomenon is investigated experimentally or numerically simulated by several methods. In this study, the simplified mixing test case was studied. The single droplet dispergation was simulated using finite volume method and multiphase VOF (Volume-of-Fluid) model. The capability of the local remeshing method was investigated. The increase of calculation performance and the phases mass imbalance during automatic mesh refinement is summarized.

Úplný záznam
2019-03-14
15:59
Settling slurry flow near deposition velocity in inclined pipe of negative slope
Kesely, Mikoláš ; Matoušek, Václav ; Vlasák, Pavel
Pipe flow of sand-water slurry (settling slurry) is sensitive to pipe inclination. The effect of the angle to which the partially stratified flow is inclined from the horizontal has been subject to investigation in numerous studies. However, almost all of them focus on ascending flows, i.e. flows inclined to positive angles of inclination. It is well known that settling slurry flows inclined to negative slopes (descending flows) differ from those inclined to positive slopes, particularly at velocities near the deposition limit. The deposition limit velocity is the flow velocity at which stationary deposit starts to be formed at the bottom of the pipe. We investigate the effect of the negative slope on pipe flow near deposition limit velocity in the broad range of inclination angles. Besides the deposition limit, we focus on the distribution of solids across the pipe cross section. We combine experimental approach with mathematical modelling. Our new experiments with medium-to-coarse sand (mass-medium grain size 0.87 mm) in a 100-mm pipe inclined from 0 to -45 degree provide suitable data for a validation of predictions of our layered model for partially stratified flows in inclined pipes.

Úplný záznam
2019-03-14
15:59
Measurement of drop size distribution time rate for liquid-liquid dispersion using IPI method
Jašíková, D. ; Kotek, M. ; Kysela, Bohuš ; Šulc, R. ; Kopecký, V.
The liquid-liquid dispersion properties are studied mainly by image analysis (IA) and Interferometric Particle Imaging (IPI). Drop sizes will be investigated in dilute dispersion since in this case the break up phenomena is the dominating and is not affected by phase fraction. Characteristics of the size distribution and the evolution of two liquid-liquid phase’s disintegration were studied. The IPI method was used for subsequent detailed study of the disintegrated droplets. We compared two liquids: Rhodosil Oil 47V50, and Silicone Oil AP1000 under stirrer rate of 540 rpm, and 760 rpm. The experiment run in the scaled model of agitated tank with Rushton turbine.

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