Experiments have been performed to study the differences in flow characteristics between real and artificial manganese nodules-water mixture and synthetic nodules-water. The results show 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.
The hydraulic pumping system is a 2-phase lifting technology By which manganese nodules are conveyed from the seafloor to the mining ship. Most of the system is located under sea level, which demands the system's stability and durability more than anything else because of the difficulty of repair. Also, economical recovery of the manganese nodules requires stable operating conditions and optimum power and efficiency of the lifting pump. The system is a 2-phase lifting technology of solid and liquid. There are considerable studies on the hydraulic transportation of a 2-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 1-inch-diameter pipe. Noda et al. (1986) derived the settling velocity and drag coefficient of the particle group related to the in-situ volume of a solid using a coal sample. Kitahara et al. (1985) dealt with the hydraulic behavior of simulated nodules and other kinds of a solid with a grain size up to 42 mm in the vertical pipe. Chung et al. (1998) and Sumardi and Chung (1996) presented a 2-phase (solid-water) vertically upward flow system with a clear PVC pipe 1 inch in diameter to test flow characteristics.