No (456)
Yes (118)
Used filters
(2)
Number of found documents:
574
Published from
to
Some results of theoretical and experimental studies on slurry flows of coarse solid materials in vertical pipelines
Berman, V.; Kril, S.; Vlasák, Pavel
2014 - English
The paper presents the results of theoretical and experimental investigations of the pressure gradient for flow of a mixture of large solids particles and water in straight vertical pipelines. The mathematical model of vertical two-phase flow was developed. Based on the developed model and experimental data of the solid particles liquid and liquid relative velocity, the functional dependence of the pressure gradient on the corresponding parameters was derived. This method was generalized for hydraulic transport of a broad category of solid particles conveyed in water as a function of the average size and concentration. Comparisons of our computations with experimental data for the corresponding pressure gradients are also presented.
Keywords:
two-phase flow; vertical pipeline; hydraulic gradient; slip velocity
Available on request at various institutes of the ASCR
Some results of theoretical and experimental studies on slurry flows of coarse solid materials in vertical pipelines
The paper presents the results of theoretical and experimental investigations of the pressure gradient for flow of a mixture of large solids particles and water in straight vertical pipelines. The ...
Flow of coarse-grained particles-water mixture in pipes
Vlasák, Pavel; Chára, Zdeněk; Konfršt, Jiří; Krupička, Jan
2014 - English
The advanced knowledge of coarse-grained slurry flow behavior is important for safe, reliable, and economical design and operation of the pipeline transport. The effect of the mixture velocity, solid concentration, and pipe inclination on the coarse-grained particle – water mixtures flow behavior and pressure drop in the turbulent flow regime was experimentally studied in horizontal, vertical, and inclined pipe of inner diameter D = 100 mm. The respective experimental methods, including radiometric methods for particle concentration distribution in pipe cross-section, were used. Graded basalt gravel was used as a model of solid particles. Concentration distribution in the pipe cross-section and motion of particles along the horizontal pipe invert were also studied. The study revealed that the coarse-grained particle-water mixtures in the horizontal and inclined pipes were significantly stratified. The particles moved principally in a layer close to the pipe invert. However, for higher and moderate flow velocities particle saltation becomes dominant mode of particle conveying and particles moved also in the central and upper part of the pipe cross-section.
Keywords:
heterogeneous slurry; hydraulic conveying; concentration distribution; pressure drop; pipe inclination
Available on request at various institutes of the ASCR
Flow of coarse-grained particles-water mixture in pipes
The advanced knowledge of coarse-grained slurry flow behavior is important for safe, reliable, and economical design and operation of the pipeline transport. The effect of the mixture velocity, solid ...
Simulation of particle motion in a closed conduit validated against experimental data
Dolanský, Jindřich
2014 - English
Motion of a number of spherical particles in a closed conduit is examined by means of both simulation and experiment. The bed of the conduit is covered by stationary spherical particles of the size of the moving particles. The flow is driven by experimentally measured velocity profiles which are inputs of the simulation. Altering input velocity profiles generates various trajectory patterns. The lattice Boltzmann method (LBM) based simulation is developed to study mutual interactions of the flow and the particles. The simulation enables to model both the particle motion and the fluid flow. The entropic LBM is employed to deal with the flow characterized by the high Reynolds number. The entropic modification of the LBM along with the enhanced refinement of the lattice grid yield an increase in demands on computational resources. Due to the inherently parallel nature of the LBM it can be handled by employing the Parallel Computing Toolbox (MATLAB) and other transformations enabling usage of the CUDA GPU computing technology. The trajectories of the particles determined within the LBM simulation are validated against data gained from the experiments. The compatibility of the simulation results with the outputs of experimental measurements is evaluated. The accuracy of the applied approach is assessed and stability and efficiency of the simulation is also considered.
Keywords:
particle motion; lattice Boltzmann method (LBM); simulations
Available on request at various institutes of the ASCR
Simulation of particle motion in a closed conduit validated against experimental data
Motion of a number of spherical particles in a closed conduit is examined by means of both simulation and experiment. The bed of the conduit is covered by stationary spherical particles of the size ...
Kernel density estimates used in stochastic precipitation generator
Hnilica, Jan; Puš, V.
2014 - English
The kernel density estimates were tested to be suitable to describe the probability distribution of daily precipitation sums. For this purpose, a stochastic precipitation generator using the kernel density estimates was constructed and it was compared with the LARS-WG generator. The data from meteorological stations from the Cidlina river basin were used to evaluate the performances of the generators. It was found that the kernel density estimates capture the probability density better than histograms used in LARS-WG.
Keywords:
kernel density estimate; daily precipitation sum; stochastic generator
Available on request at various institutes of the ASCR
Kernel density estimates used in stochastic precipitation generator
The kernel density estimates were tested to be suitable to describe the probability distribution of daily precipitation sums. For this purpose, a stochastic precipitation generator using the kernel ...
Testování parametrizací složek dlouhovlnného záření v podmínkách malého šumavského povodí
Muller, J.; Dohnal, M.; Tesař, Miroslav
2014 - Czech
Dlouhovlnné záření je významnou, zřídkakdy měřenou, částí radiační bilance zemského povrchu. Dopadající a vyzářené dlouhovlnné záření jsou často odhadovány z empirických vztahů s řadou kalibračních koeficientů. Při testování dostupných parametrizací složek dlouhovlnného záření v podmínkách malého horského povodí se podařilo prokázat spolehlivost a robustnost výpočtu vyzářeného dlouhovlnného záření. Naproti tomu odhad čistého dlouhovlnného záření je zatížen značnou nejistotou, kterou se nepodařilo zmenšit ani kalibrací příslušných koeficientů. The incoming and outgoing longwave radiations are often estimated from empirical relationships with a number of calibration coefficients. When testing the parameterization of available components of longwave radiation in the frame of a small mountaineous catchment we were able to demonstrate the reliability and robustness of calculating the outgoing longwave radiation. The estimate of net longwave radiation is burdened by considerable uncertainty, which could not be reduced by calibration of the coefficients.
Keywords:
emissivity of air; water vapor pressure; nonlinear optimization; pyrgeometr; radiated longwave radiation; longwave radiation
Available on request at various institutes of the ASCR
Testování parametrizací složek dlouhovlnného záření v podmínkách malého šumavského povodí
Dlouhovlnné záření je významnou, zřídkakdy měřenou, částí radiační bilance zemského povrchu. Dopadající a vyzářené dlouhovlnné záření jsou často odhadovány z empirických vztahů s řadou kalibračních ...
Seasonal snow accumulation in the mid-latitude forested catchment
Šípek, Václav; Tesař, Miroslav
2014 - English
The article deals with the snow cover characteristics (snow depth – SD and snow water equivalent - SWE) concerning the mid-latitude forested catchment. Namely, the influence of forest canopy (spruce and beech forest) and altitude (ranging from 835 m a.s.l. to 1118 m a.s.l.) was investigated. Forest cover was proved to have a significant influence on the snow cover accumulation, reducing the SWE by 48 % on average, compared to open sites. The elevation gradient concerning SWE ranged from 30 to 40 mm and from 5 to 20 mm per 100 m in open and forested sites, respectively. Its magnitude was found to be temporarily variable and positively related to total seasonal snowfall amount. The differences among interception losses, concerning various elevations and forest canopy, were not statistically significant.
Keywords:
snow depth,; snow water equivalent; forested catchment
Available on request at various institutes of the ASCR
Seasonal snow accumulation in the mid-latitude forested catchment
The article deals with the snow cover characteristics (snow depth – SD and snow water equivalent - SWE) concerning the mid-latitude forested catchment. Namely, the influence of forest canopy (spruce ...
Plant transpiration, entropy production and gross primarily productivity
Šír, M.; Tesař, Miroslav; Lichner, Ľ.
2014 - English
The Earth is a self-organized system. The source of information for self-organization is the degradation of solar radiation. The solar energy is highly organized and carried by photons. Earth absorbs this energy and then releases it back to the Universe. However, energy released to the environment is in the form of electromagnetic radiation, which is on average at longer wavelengths than the absorbed photons. The flow of the entropy associated with the energy conversion, which is at disposal for the self-organization, is approximately equal to 1.16·10.sup.38./sup. bit·.sub.s./sub..sup.-1./sup. (Roland-Mieskowski, 1994). The nature of self-organization is a theme of contemporary scientific discussion. The core of this discussion is the role of biotic processes. Lovelock and Margulis (1974) formulated a theory that the self-organization in a global scale is an emergent characteristic of the Earth’s biota (Gaia theory).
Keywords:
plant transpiration; plant temperature; plant entropy production; Gaia theory; ecological optimality theory
Available on request at various institutes of the ASCR
Plant transpiration, entropy production and gross primarily productivity
The Earth is a self-organized system. The source of information for self-organization is the degradation of solar radiation. The solar energy is highly organized and carried by photons. Earth absorbs ...
Saturation overshoot as a basis for emergent flow phenomena in unsaturated homogeneous porous media
Fürst, T.; Vodák, R.; Šír, Miloslav; Tesař, Miroslav
2014 - English
Understanding and description of fluid motion in unsaturated porous media rates among the most challenging and still not fully resolved problems. Traditionally, porous media flows were described by the continuum mechanics apparatus [1]. The continuum mechanics based models lead to partial differential equations which are mathematical formulations of the balance of mass, momentum, and energy. The most celebrated model is the so called Richards’ Equation (RE) [2]. Other continuum models (see [3], [4] and the reference and discussion therein) are various extensions built on similar principles as the RE.
Keywords:
unsaturated homogeneous porous media; emergent flow; saturation overshoot; oscillatory discharge
Available on request at various institutes of the ASCR
Saturation overshoot as a basis for emergent flow phenomena in unsaturated homogeneous porous media
Understanding and description of fluid motion in unsaturated porous media rates among the most challenging and still not fully resolved problems. Traditionally, porous media flows were described by ...
Radioisotope method of compound flow analysis
Petryka, L.; Zych, M.; Hanus, R.; Sobota, J.; Vlasák, Pavel; Malczewska, B.
2014 - English
The paper presents gamma radiation application to analysis of a multicomponent or multiphase flow. Such information as a selected component content in the mixture transported through pipe is crucial in many industrial or laboratory installations. Properly selected sealed radioactive source and collimators, deliver the photon beam, penetrating cross section of the flow. Detectors mounted at opposite to the source side of the pipe, allow recording of digital signals representing composition of the stream. In the present development of electronics, detectors and computer software, a significant progress in know-how of this field may be observed. The paper describes application of this method to optimization and control of hydrotransport of solid particles and propose monitoring facilitating prevent of a pipe clogging or dangerous oscillations.
Keywords:
compound flow analysis; Cross Correlation Analysis; hydrotransport of solid particles
Available on request at various institutes of the ASCR
Radioisotope method of compound flow analysis
The paper presents gamma radiation application to analysis of a multicomponent or multiphase flow. Such information as a selected component content in the mixture transported through pipe is crucial ...
Evaluation and accuracy of the local velocity data measurements in an agitated vessel
Kysela, Bohuš; Konfršt, Jiří; Chára, Zdeněk; Kotek, M.
2014 - English
Velocity measurements of the flow field in an agitated vessel are necessary for the improvement and better understanding of the mixing processes. The obtained results are used for the calculations of the impeller pumping capacity, comparison of the power consumption etc. We performed various measurements of the local velocities in an agitated vessel final results of which should be processed for several purposes so it was necessary to make an analysis of the obtained data suitability and their quality. Analysed velocity data were obtained from the LDA (Laser Doppler Anemometry) and PIV (Particle Image Velocimetry) measurements performed on a standard equipment where the flat bottomed vessel with four baffles was agitated by the six-blade Rushton turbine. The results from both used methods were compared. The frequency analyses were examined as well as the dependency of the data rates, time series lengths etc. The demands for the data processed in the form of the ensemble-averaged results were also established.
Keywords:
Laser Doppler Anemometry (LDA); Particle Image Velocimetry (PIV); velocity; measurements
Available on request at various institutes of the ASCR
Evaluation and accuracy of the local velocity data measurements in an agitated vessel
Velocity measurements of the flow field in an agitated vessel are necessary for the improvement and better understanding of the mixing processes. The obtained results are used for the calculations of ...
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