Jan Krupička

Experimental investigation of coarse particles-water mixture flow in horizontal and inclined pipes

Abstract The effect of solid concentration and mixture velocity on the flow behaviour, pressure drops, and concentration distribution of coarse particle-water mixtures in horizontal, vertical, and inclined smooth stainless steel pipes of inner diameter D = 100 mm was experimentally investigated. Graded basalt pebbles were used as solid particles. The study revealed that the coarse-grained particle-water mixtures in the horizontal and inclined pipes were significantly stratified. The solid particles moved principally in a layer close to the pipe invert; however for higher and moderate flow velocities, particle saltation became the dominant mode of particle conveyance. Frictional pressure drops in the horizontal pipe were found to be markedly higher than in the vertical pipe, while the frictional pressure drops in the ascending pipe increased with inclination angle up to about 30°.

On equivalent roughness of mobile bed at high shear stress

On equivalent roughness of mobile bed at high shear stress The friction conditions at the top of a mobile bed are discussed for flows in the upper-plane-bed regime, i.e. for the flows with values of the bed Shields parameter larger than approximately 0.6. A special attention is devoted to flows of the bed Shields parameter bigger than 2. Experimental data for flows at high bed shear are collected from literature and new data are added from own measurements of flows of a 1.36-mm sand slurry in the 100-mm pipe loop of the Institute of Hydrodynamics. The database represents flows of very different solids and covers friction conditions within a broad range of Shields parameters up to the maximum value of about 23. The paper analyses the data in order to evaluate a relationship among the equivalent roughness of the top of the bed and other relevant parameters. A semi-empirical formula is proposed that relates the equivalent roughness to the bed Shields parameter, the ratio of flow velocity and particle settling velocity, and the ratio of flow hydraulic radius and particle diameter. The formula is applicable primarily to flows of combined load (contact- and suspended loads together). Hydraulická drsnost pohyblivého dna za vysokých smykových napětí Příspěvek se zabývá mechanismem tření na povrchu erodovatelného dna za podmínek horního režimu pohybu splavenin nad plochým dnem, to jest při hodnotách Shieldsova parametru větších než přibližně 0,6. Zvláštní pozornost je věnována proudění při Shieldsově parametru větším než 2. Z literatury byla sebrána experimentální data pro proudění za vysokých smykových napětí, ke kterým byla přidána nová data z vlastních měření s pískem velikosti středního zrna 1,36 mm v potrubí průměru 100 mm trubního okruhu Ústavu pro hydrodynamiku AV ČR. Databáze obsahuje výsledky měření pro částice různých vlastností v širokém rozsahu hodnot Shieldsova parametru až do hodnoty okolo 23. Příspěvek analyzuje data za účelem stanovení závislosti hydraulické drsnosti povrchu sedliny na ostatních parametrech proudění. Je navržen semiempirický vztah, který předpokládá závislost hydraulické drsnosti na Shieldsově parametru, poměru rychlosti proudění k usazovací rychlosti částic a poměru hydraulického poloměru průtočného profilu k velikosti částic. Tento vztah se doporučuje především pro proudění nesoucí jak dnové splaveniny, tak suspendované částice.

Gamma-ray-based measurement of concentration distribution in pipe flow of settling slurry: vertical profiles and tomographic maps

Abstract Principles of gamma-ray-based measurement are summarized and their application is demonstrated on an operation of the radiometric facility installed in the test loop for slurry flows at the Institute of Hydrodynamics. The facility is able to measure vertical profiles of chord-averaged concentrations and concentration maps in the pipe cross section. A methodology of measurement is proposed including detection and quantification of random and systematic errors. Experimental results are discussed in the light of the proposed methodology. Experimentally determined vertical profiles of concentration are presented for slurry flows of four different fractions of glass beads. The tomographic application of the radiometric device is demonstrated on a measured concentration map and a suitable image reconstruction method is tested. High reliability of measured concentration distributions is proved except for regions near the pipe wall. The radiometric method is shown to be a useful tool for measurement of concentration distribution in slurry flow through a pipe.

Experimental investigation of internal structure of open-channel flow with intense transport of sediment

Abstract Gravity-driven open-channel flows carrying coarse sediment over an erodible granular deposit are studied. Results of laboratory experiments with artificial sediments in a rectangular tilting flume are described and analyzed. Besides integral quantities such as flow rate of mixture, transport concentration of sediment and hydraulic gradient, the experiments include measurements of the one-dimensional velocity distribution across the flow. A vertical profile of the longitudinal component of local velocity is measured across the vertical axis of symmetry of a flume cross section using three independent measuring methods. Due to strong flow stratification, the velocity profile covers regions of very different local concentrations of sediment from virtually zero concentration to the maximum concentration of bed packing. The layered character of the flow results in a velocity distribution which tends to be different in the transport layer above the bed and in the sediment-free region between the top of the transport layer and the water surface. Velocity profiles and integral flow quantities are analyzed with the aim of evaluating the layered structure of the flow and identifying interfaces in the flow with a developed transport layer above the upper plane bed.

Analysis of Concentration Profiles in Dense Settling-Slurry Flows

In summer 2012, an extensive measurement campaign was carried out in a new test loop composed of pipes of the internal diameter of 100 mm. Four fractions of glass ballotini were used for preparation of settling slurries of different properties. During the tests, different patterns of slurry flows were observed. The tests included measurements of concentration profiles in a cross section of the slurry pipe.The paper analyzes shapes of measured concentration profiles with an aim to recognize flow patterns and dominating particle-dispersion mechanisms in the observed slurry flows. It is shown that particles are supported both through an interaction with the flowing carrier (turbulent dispersion) and through an interaction with other particles (collisional dispersion). A measure of each particular support is quantified through relating a distribution of concentration with a distribution of solids stresses across a flow discharge area in a pipe.Copyright

Liquid-Solid Flows Above Deposit in Pipe: Prediction of Hydraulic Gradient and Deposit Thickness

A predictive model for the pressure drop in a slurry flow above a stationary bed was presented at the last Liquid-Solid Flow Symposium in 2007. Since then the model has been further refined and validated using experimental data from the tests performed at the Institute of Hydrodynamics ASCR and from the literature. The new version of the model enables to choose a set of appropriate equations in order to predict the hydraulic gradient (the frictional pressure drop) and the thickness of the stationary bed for pipe flows of various average velocities of slurry and delivered concentrations of solids. The paper describes the structure and components of the model and discusses model predictive abilities by comparing model predictions with the new experimental data gained for slurries of two different fractions of sand (respectively fine to medium and medium sands) at various velocities and solids concentrations in a 100-mm pipe.© 2009 ASME