Slurry Transport: Fundamentals, a historical overview and the Delft Head Loss a Limit Deposit Velocity Framework
In dredging, trenching, (deep sea) mining, drilling, tunnel boring and many other applications, sand, clay or rock has to be excavated. After the soil has been excavated it is usually transported hydraulically as a slurry over a short (TSHD's) or a long distance (CSD's) Estimating the pressure losses and determining whether or not a bed will occur in the pipeline is of great importance. Fundamental processes of sedimentation, initiation of motion and erosion of the soil particles determine the transport process and the flow regimes. In all cases we have to deal with soil and high density soil water mixtures and its fundamental behavior. Although some basic knowledge about the subject is required and expected, dimensionless numbers, the terminal settling velocity (including hindered settling) the initiation of motion of particles, erosion and the flow of a liquid through a pipe are summarized. An overview is given of experiments and theories found in literature. The results of experiments are considered to be the physical reality. Semi empirical theories based on these experiments are considered to be an attempt to describe the physical reality in a mathematical way. These semi empirical theories in general match the experiments on which they are based, but are also limited to the range of the different parameters as used for these experiments. Some theories have a more fundamental character and may be more generic as long as the starting points on which they are based apply. Observing the results of many experiments gives the reader the possibility to form his/her own impression of the processes involved in slurry transport. Flow regimes are identified and theoretical models are developed for each main flow regime based on constant volumetric spatial concentration. The 5 main flow regimes are the fixed or stationary bed regime, the sliding bed regime, the heterogeneous regime, the homogeneous regime and the sliding flow regime. A new model for the Limit Deposit Velocity is derived, consisting of 5 particle size regions and a lower limit. Based on the Limit Deposit Velocity a (semi) fundamental relation is derived for the slip velocity. This relation also enables us to determine the bed height as a function of the line speed. The concentration distribution in the pipe is based on the advection diffusion equation with a diffusivity related to the LDV. Finally a method is given to determine relations for non uniform sands and gravels based on the superposition principle.