Experiments have been performed to study the differences of the flow characteristics between real and artificial manganese nodules-water mixture and synthetic nodules-water. The results show that the hydraulic gradients of the mixtures were almost identical in the case of both the real and synthetic nodules. However, when the solid volume fraction is high, the hydraulic gradients of the flow of the real manganese nodules were a little lower than those of the artificial ones, because the drag effect is not so apparent.
Hydraulic pumping system is two-phase lifting technology, by which manganese nodules are conveyed from the seafloor to the mining ship. Most of the system is located under the sea level, which demands its stability and durability more than anything else because of the difficulty in repairing. Also, economical recovery of the manganese nodules requires stable operating conditions and optimum power prediction of the lifting pump. Hydraulic pumping system is two phase lifting technology of solid and liquid. There are considerable studies on the hydraulic transportation of two-phase mixture. Newitt et al. (1961) carried out an experiment to predict the hydraulic gradients and flow rates of water and solid particles in the pipe of 1 inch in diameter. Noda et al. (1986) derived the settling velocity and drag coefficient of the particle group related to in-situ volume of solid using coal sample. Kitaha et al. (1985) dealt with the hydraulic behavior of simulated nodules and other kinds of solid with grain size up to 42 mm in the vertical pipe. Chung et al (1998) and Sumardi and Chung (1996) presented a two-phase vertically upward flow system with 1 inch diameter clear PVC pipe to test flow characteristics. Xia et al. (1997) studied the basic characteristics of solid-liquid two phase flow transport, the prediction and optimization of hydraulic pumping parameter for commercial mining system.
