CFD simulation of settling sand in water
valuable metals and minerals and it is therefore becoming more economically viable to mine these deposits. To allow large scale mining of SMS deposits, some major technological challenges have to be overcome. IHCâ€™s business units MTI Holland and Deep Sea Dredging and Mining are currently performing research on deep sea mining. One of the main objectives is to better understand the principles of hydraulic transportation in a long vertical riser. A one-dimensional model already showed that high solid concentrations might arise inside the riser. It is possible that these high solid concentrations clog the riser, which might lead to hazardous situations due to failure of the riser system. Therefore more insight on the increase of the solid concentration involved in vertical hydraulic transport is desired. The driving mechanism of the fluctuations in the solid concentration is the difference in the (hindered) settling velocity of the particles within the riser. The settling velocity is based on the equilibrium of buoyancy and drag forces. Therefore larger particles tend to settle at a higher velocity compared to smaller particles. Due to this mechanism, smaller particles tend to overtake larger particles, which may lead to an increase of the solid concentration.
My research objective is to obtain more insight on the hydraulic transport of solid particles. Several students before me have already derived a onedimensional model for the hydraulic transport, which I am now extending into a two dimensional axi-symmetric model. The model is basically a multiphase flow, in which the solid particles are considered as a continuum. In order to do this, the flow consists of one carrier phase (water) and multiple particle phases, each particle phase having its own characteristic particle size. The goal of this extension is to find out whether a correction is needed on the one dimensional model and what the effect of the radial distribution of the particles might be on the local solid concentration. Therefore I am developing a code to implement the model, along with the relevant physics, in CFD (Computational Fluid Dynamics). The numerical model will be verified with experiments in a settling column. Finally several test cases that might lead to clogging will be tested with the code. I am working for four months now on my masterâ€™s thesis. Currently I am busy with the development of the CFD code, which I hope to finish within one to two months. After that I will verify the results by experiments that a colleague is working on for his doctorate. Eventually I hope to complete my masterâ€™s thesis during the summer holiday. Rudy Helmons
References  http://www.multiform.bci.tu-dortmund.de  N.C.W.M. Braspenning J.M. van de Mortel - Fronczak, J.E. Rooda. Modeling, analysis, and implementation of infrastructure for model-based integration and testing, Systems Research Forum, 2007(2), 3-10, (2008).