Vliv nejistoty určení reologických vlastností zahuštěných čistírenských kalů na výpočet ztráty třením při jejich proudění potrubím
Svitavská, K.; Havlík, V.; Hodaň, H.; Matoušek, Václav
2019 - Czech Příspěvek se zabývá reologickými vlastnostmi čistírenských kalů a jejich vlivem na určování energetické náročnosti potrubní dopravy kalů. V příspěvku je využita databáze reologických parametrů složená z výsledků 67 měření různých čistírenských kalů. Na naměřených hodnotách je zjištěná nejistota v určení hodnot reologických parametrů pro kal určité koncentrace převedena na vyjádření nejistoty při výpočtu ztrát třením v laminárním, resp. turbulentním režimu proudění. Při výpočtu ztrát třením jsou použity a porovnány různé přístupy a modely, přičemž součástí analýzy nejistot je i nejistota plynoucí z použití různých předpovědních přístupů, resp. výpočtových modelů. The paper deals with the rheological properties of wastewater sludge and their influence on the determination of energy requirements of pipeline sludge transport. The paper uses a database of rheological parameters consisting of the results of 67 measurements of various wastewater sludge. At the measured values, the uncertainty in the determination of the rheological parameter values for the sludge of a certain concentration is converted to the uncertainty in the calculation of friction losses in the laminar as well as turbulent flow regime. Different approaches and models are used and compared the in the calculation of friction losses. The uncertainty analysis also includes the uncertainty arising from the use of different predictive approaches and/or computational models.\n Keywords: fluid flow; friction losses; non-Newtonian suspensions; rheological properties; wastewater sludge Fulltext is available at external website. Vliv nejistoty určení reologických vlastností zahuštěných čistírenských kalů na výpočet ztráty třením při jejich proudění potrubím

Příspěvek se zabývá reologickými vlastnostmi čistírenských kalů a jejich vlivem na určování energetické náročnosti potrubní dopravy kalů. V příspěvku je využita databáze reologických parametrů složená ...

Svitavská, K.; Havlík, V.; Hodaň, H.; Matoušek, Václav
Ústav pro hydrodynamiku, 2019

The importance of the radiation balance for water retention of the landscape
Kofroňová, Jitka
2018 - English As part of the radiation balance, longwave radiation is one of the factors needed to estimate potential evapotranspiration (PET). Since the longwave radiation balance is rarely measured, many computational methods have been designed. In this study, we report on the difference between the observed longwave radiation balance and modelling results obtained using the two main procedures outlined in Manuals 24 and 56 of the FAO. The performance of these equations was evaluated in the warmer months (April to October) over eight years at the Liz experimental catchment in the Bohemian Forest (Czech Republic). The coefficients of both methods were also calibrated based on local conditions. Four commonly used methods were used to calculate the PET (Penman-Monteith, Pristley and Taylor, Kimberley-Penman, Thom and Oliver). The use of default coefficient values gave errors of 40 100 mm and 0 20 mm for the seasonal PET estimates for FAO56 and FAO24, respectively (the PET was usually overestimated). Parameter calibration decreased the FAO56 error to less than 20 mm per season (FAO24 remained unaffected by the calibration). The FAO56 approach with calibrated coefficients proved to be more suitable for estimation of the longwave radiation balance. Keywords: water retention; radiation balance; potential evapotranspiration (PET) Available in digital repository of the ASCR The importance of the radiation balance for water retention of the landscape

As part of the radiation balance, longwave radiation is one of the factors needed to estimate potential evapotranspiration (PET). Since the longwave radiation balance is rarely measured, many ...

Kofroňová, Jitka
Ústav pro hydrodynamiku, 2018

Sucho v oblastech přirozené akumulace vod
Tesař, Miroslav
2018 - Czech Fulltext is available at external website. Sucho v oblastech přirozené akumulace vod

Tesař, Miroslav
Ústav pro hydrodynamiku, 2018

Evaluation of the turbulent kinetic dissipation rate in an agitated vessel
Kysela, Bohuš; Konfršt, Jiří; Chára, Zdeněk; Sulc, R.; Jašíková, D.
2017 - English The design of agitated tanks depends on operating conditions and processes for that are used for. An important parameter for the scale-up modelling is the dissipation rate of the turbulent kinetic energy. The dissipation rate is commonly assumed to be a function of the impeller power input. But this approach gives no information about distribution of the dissipation rate inside the agitated volume. In this paper the distributions of the dissipation rate inside the agitated vessels are estimated by evaluations of the CFD (Computational Fluid Dynamics). The results obtained from RANS (Reynolds Averaged Navier-Stokes equations) k-epsilon turbulent model and LES (Large Eddy Simulations) with Smagorinsky SGS (Sub Grid Scale) model are compared. The agitated vessels with standard geometry equipped with four baffles and stirred by either a standard Rushton turbine or a high shear impeller were investigated. The results are compared with mean dissipation rate estimated from the total impeller power input. Keywords: flow; large-eddy simulation Fulltext is available at external website. Evaluation of the turbulent kinetic dissipation rate in an agitated vessel

The design of agitated tanks depends on operating conditions and processes for that are used for. An important parameter for the scale-up modelling is the dissipation rate of the turbulent kinetic ...

Kysela, Bohuš; Konfršt, Jiří; Chára, Zdeněk; Sulc, R.; Jašíková, D.
Ústav pro hydrodynamiku, 2017

Local velocity scaling in T400 vessel agitated by Rushton turbine in a fully turbulent region
Šulc, R.; Ditl, P.; Fořt, I.; Jašíková, D.; Kotek, M.; Kopecký, V.; Kysela, Bohuš
2017 - English 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 Rushton turbine 133 mm in diameter. The velocity fields were measured in the zone in upward flow to the impeller for impeller rotation speeds from 300 rpm to 850 rpm and three liquids of different viscosities (i.e. (i) distilled water, ii) a 28% vol. aqueous solution of glycol, and iii) a 43% vol. aqueous solution of glycol), corresponding to the impeller Reynolds number in the range 50 000 < Re < 189 000. This Re range secures the fully-developed turbulent flow of 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 0.388 to 0.540, which corresponds to the high level of turbulence intensity. Keywords: agitated vessel; Rushton turbine; PIV Fulltext is available at external website. Local velocity scaling in T400 vessel agitated by Rushton turbine in a fully turbulent region

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 ...

Šulc, R.; Ditl, P.; Fořt, I.; Jašíková, D.; Kotek, M.; Kopecký, V.; Kysela, Bohuš
Ústav pro hydrodynamiku, 2017

Simulation of collagen solution flow in rectangular capillary
Kysela, Bohuš; Skočilas, J.; Zitny, R.; Stancl, J.; Houska, M.; Landfeld, A.
2017 - English The viscoelastic properties of foods and polymers can be evaluated from flow of the material in capillary with specified dimension and shape. The extrusion rheometer equipped by capillary with rectangular cross-section was used for determination of the rheological behaviour of water collagen solution. The measurements of the axial profiles in longitudinal direction of the total stresses at capillary wall were performed for various shear rates. The linear viscoelastic model of Oldroyd B type: White-Metzner model was used for simulation of fluid flow in OpenFOAM software package. The simulations describe the effect of relaxation time on wall total stress in convergent-divergent capillary. Keywords: collagen; viscoelastic model; convergent-divergent capillary Fulltext is available at external website. Simulation of collagen solution flow in rectangular capillary

The viscoelastic properties of foods and polymers can be evaluated from flow of the material in capillary with specified dimension and shape. The extrusion rheometer equipped by capillary with ...

Kysela, Bohuš; Skočilas, J.; Zitny, R.; Stancl, J.; Houska, M.; Landfeld, A.
Ústav pro hydrodynamiku, 2017

The minimum record time for PIV measurement in a vessel agitated by a Rushton turbine
Šulc, R.; Ditl, P.; Fořt, I.; Jašíková, D.; Kotek, M.; Kopecký, V.; Kysela, Bohuš
2017 - English In PIV studies published in the literature focusing on the investigation of the flow field in an agitated vessel the record time is ranging from the tenths and the units of seconds. The aim of this work was to determine minimum record time for PIV measurement in a vessel agitated by a Rushton turbine that is necessary to obtain relevant results of velocity field. The velocity fields were measured in a fully baffled cylindrical flat bottom vessel 400 mm in inner diameter agitated by a Rushton turbine 133 mm in diameter using 2-D Time Resolved Particle Image Velocimetry in the impeller Reynolds number range from 50 000 to 189 000. This Re range secures the fully-developed turbulent flow of agitated liquid. Three liquids of different viscosities were used as the agitated liquid. On the basis of the analysis of the radial and axial components of the mean- and fluctuation velocities measured outside the impeller region it was found that dimensionless minimum record time is independent of impeller Reynolds number and is equalled N. t(Rmin) = 103 +/- 19. Keywords: agitated vessel; Rushton turbine; PIV; averaging limits Fulltext is available at external website. The minimum record time for PIV measurement in a vessel agitated by a Rushton turbine

In PIV studies published in the literature focusing on the investigation of the flow field in an agitated vessel the record time is ranging from the tenths and the units of seconds. The aim of this ...

Šulc, R.; Ditl, P.; Fořt, I.; Jašíková, D.; Kotek, M.; Kopecký, V.; Kysela, Bohuš
Ústav pro hydrodynamiku, 2017

Sezónní proměnlivost parametrů půdních modelů
Šípek, Václav; Tesař, Miroslav
2016 - Czech Simulace nasycení půdního profilu v malém horském povodí a testování dvou sezónních setů parametrů. Simulation of saturation of the soil profile in the small mountain river basins and testing of two seasonal sets of parameters. Keywords: soil moisture; seasonal variability; saturated hydraulic conductivity; poresize distribution; hydrological modelling; soil hydraulic parameters Available in digital repository of the ASCR Sezónní proměnlivost parametrů půdních modelů

Simulace nasycení půdního profilu v malém horském povodí a testování dvou sezónních setů parametrů....

Šípek, Václav; Tesař, Miroslav
Ústav pro hydrodynamiku, 2016

Multi-functional composites with integrated nanostructured carbon nanotubes based sensing films
Slobodian, P.; Pertegás, S.L.; Schledjewski, R.; Matyáš, J.; Olejník, R.; Říha, Pavel
2016 - English Carbon nanotubes are exceptional nano-objects with respect to their remarkable properties, holding great potential in new polymeric materials design with unique characteristics. To illustrate it, the conventional glass reinforced epoxy composite is combined with a layer of entangled network of carbon nanotubes deposited on polyurethane non-woven membrane. The prepared nano-composite is studied for their diverse mjulti-functional applications involving extension and compression strain sensing composite, remoulding by means of resistance Joule heating and radiating as a planar micro strip antenna operating at frequencies of 2MHz up to 4GHz. Keywords: epoxy composite; glass fibers; carbon nanotubes; electro-mechanical properties Fulltext is available at external website. Multi-functional composites with integrated nanostructured carbon nanotubes based sensing films

Carbon nanotubes are exceptional nano-objects with respect to their remarkable properties, holding great potential in new polymeric materials design with unique characteristics. To illustrate it, the ...

Slobodian, P.; Pertegás, S.L.; Schledjewski, R.; Matyáš, J.; Olejník, R.; Říha, Pavel
Ústav pro hydrodynamiku, 2016

Systém včasného varování před přívalovými povodněmi s uvažováním stavu vody v půdě – příklad pro horní Úpu
Tesař, Miroslav
2015 - Czech Contribution describes an early warning system for flash flood detection that has been built in the Giant Mts. This system is located in the upper part of the Úpa River basin and Lysečinský Brook basin. The closing profiles of these basins are situated in Horní Maršov (81,7 km2 and 18,3 km2). Forecasting of flood risk is based on model approach, which uses measured hydrological and hydrometeorological quantities (rain intensity and total, discharge, soil moisture, tensiometric pressure of the soil water, air and soil temperature) as input data. Contribution describes an early warning system for flash flood detection that has been built in the Giant Mts. This system is located in the upper part of the Úpa River basin and Lysečinský Brook basin. The closing profiles of these basins are situated in Horní Maršov (81,7 km2 and 18,3 km2). Forecasting of flood risk is based on model approach, which uses measured hydrological and hydrometeorological quantities (rain intensity and total, discharge, soil moisture, tensiometric pressure of the soil water, air and soil temperature) as input data. Keywords: early warning system; flash flood; surface and soil water monitoring Available in digital repository of the ASCR Systém včasného varování před přívalovými povodněmi s uvažováním stavu vody v půdě – příklad pro horní Úpu

Contribution describes an early warning system for flash flood detection that has been built in the Giant Mts. This system is located in the upper part of the Úpa River basin and Lysečinský Brook ...

Tesař, Miroslav
Ústav pro hydrodynamiku, 2015