Concentration characteristics of large size particles in vertical pipes for hydraulic lifting were studied. A formula for the radial distribution of particle concentration was developed. Experiments were conducted to validate this formula and good agreements were observed. It was shown that the transportation concentration was not always smaller than the local concentration. Both the two concentrations were closely related to the lifting velocity.
Four definitions should be introduced beforehand. Transportation concentration (CV) is defined as the concentration transported into the receiver through the vertical pipe. Local concentration (CVl) is that which is obtained when a control body of the pipe is selected and considered. Lifting velocity is a critical velocity at which particles can be just lifted upward in the pipe. And slip velocity is the velocity difference between fluid and particles. Hydraulic lifting of solid particles through vertical pipes is encountered in deep-sea mining, coal mining, and river dredging. During the lifting process, particles moving upward tend to accumulate in the center region due to both axial and radial forces. Moreover, solid particles generally move slower than water in vertical pipes, resulting in the difference between the value of the transportation concentration and that of local concentration. In this paper, concentration of large size particles was explored in vertical pipes for hydraulic lifting. Liu and Lu (2000) once measured concentration distribution in vertical lifting and demonstrated high concentration in the pipe center and low near the wall. However, they did not make further study on the distribution but only analyzed two-phase flow velocity. Ding et al (1994) studied concentration distribution of solid phase in vertical pipe lifting. They concluded that solid phase distribution was related to solid slip velocity, gas velocity gradient, particle rotation velocity, particle diffusion coefficient and particle diameter, and developed a most complicated formula.