Experiment Study On Lifting Velocity And Concentration Of Coarse Particles For Vertical Hydraulic Lifting

The issues of hydraulic lifting in vertical pipes are frequently encountered indeep-sea mining, hydraulic coal-mining, closed mining and river sludge removing.Most previous studies on solid-liquid two-phase flow for pipeline transportation wereconcentrated on hydraulic parameters of hypothetical-homogenous flow in ahorizontal pipeline. Few efforts were paid to vertical hydraulic lifting. Slip velocitybetween particles and fluid is significant so that the two-phase flow in a verticalhydraulic-lifting pipe is quite different from the hypothetical-homogenous flow in ahorizontal pipe.Lifting velocity is the primary issue that should be determined firstly for thedesign of a vertical hydraulic lifting system. Firstly, this paper experimented onsettling velocity of coarse particles in still water, by fitting and comparing dataobtained with Strokes' Formula, the paper indicated the considerable influence ofshape coefficient on particle settling velocity. Secondly, experiments on particlefloating velocity were carried out. Due to the fact that cross-section velocity of waterdoes not distribute evenly, it was verified that floating velocity is universally less thansettling velocity on condition that we treat cross-section average as the floatingvelocity. Thirdly, according to the experiments above, critical lifting state of particleswas investigated and formula for critical lifting velocity was developed bycomprehensively taking into account of such main factors as density, diameter, shapecoefficient, concentration, and gradation of particles. At last, experiments were doneto validate the formula, and the formula was primarily proved reasonable by datafrom other resources.During the lifting process, particles moving upward tend to accumulate in thecenter region due to both axial and radial forces. In this paper, concentration of coarseparticles was explored in vertical pipes for hydraulic lifting. Forces exerted onparticles were analyzed and concentration of coarse particles was studied. A formulafor the radial distribution of particle concentration was developed. Experiments wereconducted to validate this formula and good agreements were observed. Therelationship between lifting velocity and slip velocity of particles was studied. It wascorrected that transportation concentration was not always smaller than localconcentration. Both of the two concentrations were closely related to the liftingvelocity.The formula proposed in this paper took main determinants of lifting velocityinto consideration and had definite implications. Compared with other fieldexperiment measurement data, the results indicated that the developed formula couldwell calculate critical velocity with high accuracy. It would be useful for helpingdesign and operate vertical hydraulic lifting system. Due to difficulties met in theexperiments and equipment inaccuracy, more data and experiments are needed.Concentration distribution of particles should be further studied.