The paper presents the results of nodule and water velocity measurements at upward flow in a pipeline of D=150 mm. The investigations were conducted on an experimental stand specifically constructed for this purpose in the hydraulic laboratory in the Department of Water Engineering and Hydrotransport of the Agricultural University of Wroclaw. The mixture phase velocity measurements were carried out with the application of radioisotopes. The presented results refer to velocities of 10-, 30and 50-mm-diameter nodules and water at the volume concentration equal 10%.
One of the main elements of the technology of nodule recovery from the ocean bed is a pipeline connecting the system of nodule collection from the bed (miner) with the superficial platform. The How of the mixture of water and nodule in this pipeline is quite complex. One of the reasons is the difference in velocity between the two mixture phases. Nodules flowing upwards are moved in a direction opposite to the gravity force, i.e. in the direction of transported nodules settling. Therefore, in the vertical flow of the two-phase mixture of water and nodules, its phases move at different velocities. In Govier and Aziz's (1972) opinion, the minimal velocity for the vertical How should be tvice as high as the free fall velocity of the largest grains contained in the mixture (vm > 2Wo). However, Sellgren (1982), on the basis of pilot study with the use of granite particles, states that the minimal velocity should exceed the free fall velocity of the largest particles in still water by 4 to 5 times (vm > 4–5Wo). From the practical point of view, the knowledge of the water and nodules velocities is of primary importance in determining the actual efficiency of vertical hydraulic transport of solid material, e.g. in deep ocean mining of nodules.
