Separation of particles from liquids by the solid core cyclone
A computational and physical modelling study is made of the removal of inclusions from liquid steel by use of a novel form of hydrocyclone in which a solid conical core that replaces the conventional vortex finder acts as a guide to the spiralling liquid flow and acts also as a capture surface for disentrained inclusions. In preliminary investigations, an inviscid computational model is derived that is found to be effective in outlining the general behaviour of specific hydrocyclone flows when tested against published experimental results. The more generally applicable commercial CFD code Fluent is likewise tested, from which it is shown that, among the turbulence models available, the anisotropic turbulence typical of spiralling hydrocyclone flows requires a form of Reynolds stress model for effective computation. The conventional k-c model is found to be misleading. On this basis, mathematical modelling and optimal computational design of hydrocyclones containing an axial conical solid core show that the separation efficiency of the cyclone is profoundly enhanced by the presence of a core, and that by use of a particle tracking model effective centripetal migration of inclusion particles in steel will occur towards the core. Experiments with a water model of computed optimal cyclone designs provided effective validation of the numerical study. Photographically active particles of neutral density were tracked by a novel stroboscopic technique which permitted bi-directional observation revealing instantaneous velocity, spatial position and spiral angle. Using populations of low density particles having the same spectrum of Stokes velocity as inclusions in the size range 35 to 150 microns found typically in liquid steel, sampling by Coulter counter showed that effective separation to the core surface of particles down to an equivalent size of 30 microns was achieved. In a final step, a pilot cyclone design for use with steel was established and water model tests at full scale showed that stable cyclone flow and discharge are achievable with gravity feed to the cyclone.