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Flow of coarse-grained particles-water mixture in pipes
Vlasák, Pavel ; Chára, Zdeněk ; Konfršt, Jiří ; Krupička, Jan
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.
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Stationary- and sliding beds in pipe flows of settling slurry
Matoušek, Václav ; Krupička, Jan ; Chára, Zdeněk
Investigations are discussed on the effect of stationary- and sliding beds on a behavior of settling slurry flows. Results are presented of our recent experiments with two fractions of ballotini in a 100-mm-pipe loop. Experimental work contained measurements of concentration profiles and velocity profiles. The experimental results for flows with stationary deposits are compared with predictions using our formulae for solids transport and bed friction in layered flows. CFD simulations are included to validate the velocityprofile measurements and to verify the bed roughness predictions in the flows with stationary beds. Furthermore, the measured velocity profiles are compared to profiles predicted using the log law of the wall with boundary shear velocities determined from the linear distribution of shear stress across the pipe flow. The approach is successful in the flow below the upper wall of the pipe but fails above the top of the deposit where the stress distribution is different as verified by the CFD simulation. The concept of the linear-distribution of shear stress is well applicable in flows with sliding beds. An example is given of a solution for a partially-stratified flow with sliding bed using the 1-D Stress- Distribution based Model.
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Concentration distribution of coarse-grained particle-water mixture in horizontal pipe
Vlasák, Pavel ; Chára, Zdeněk ; Konfršt, Jiří ; Krupička, Jan
The paper describes the results of coarse-grained particle-water mixture measurements in an experimental pipeline loop of inner diameter 100 mm. Graded basalt pebbles of mean diameter 11 mm, conveyed by water, were investigated. The concentration distribution measurements were carried out with application of gamma-ray based device. Presented results refer to the effect of mixture velocity and overall concentration on chord-averaged concentration and local concentration distribution in the horizontal pipe. The study revealed that the coarse-grained particle-water mixtures were significantly stratified, solid particles moved principally close to the pipe invert, for higher and moderate flow velocities saltation becomes dominant mode of the sediment transport.
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