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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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Numerical simulations of flow over stationary deposit
Chára, Zdeněk ; Vlasák, Pavel ; Kysela, Bohuš ; Konfršt, Jiří
The paper deals with a water flow in a horizontal, circular pipe of inner diameter 40 mm with a stationary deposit. The deposit was formed by spheres of diameter d=6 mm. The thickness of the deposit was about two sphere diameters. The flow was experimentally studied by the PIV method and COMSOL Multiphysics 4.4 was used as tool for numerical simulations as well. Two approaches were used to create the stationary deposit. In the first one was the deposit was replaced by a rough wall with different values of the roughness parameter ks. In the second case the deposit was created from the identical spherical particles. The results of the simulations and the experimental data are compared.
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Some results of theoretical and experimental studies on slurry flows of coarse solid materials in vertical pipelines
Berman, V. ; Kril, S. ; Vlasák, Pavel
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.
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