ON THE PREDICTION OF TERMINAL SETTLING VELOCITY OF SOLIDS IN LIQUID SOLID SYSTEMS

The settling velocity of solids has been determined experimentally in a fluidizing column. The bed expansion characteristics of monodispersed (single component) systems have been noted using water as the fluid. The experimentally determined bed voidages have been plotted against particle Reynolds number, Rep on a log-log graph paper. The settling velocity, ut, has been obtained by extrapolating the resulting straight line to ε{lunate}=1.0. Close-cut size fractions of coal, graphite, sand, limestone, chalcopyrite and magnetite have been used as different solids. Water has been used as the fluidizing fluid throughout the experiment. The experimental values of Ret have been empirically correlated with the relevant system properties, e.g., particle diameter, its shape, density of liquid and solid, liquid viscosity-all of these being represented by Archimedes number and shape factor, φs. The correlation proposed is: Ret=0.103(Ar0.804(φs)0.745 The standard deviation of the proposed correlation has been calculated to be ±15.2%. The ranges of Ar and φs are: 53≤Ar≤3761; 0.5000≤φs≤0.9740. The present correlation has been compared with existing equations for monodispersed systems whereby a fair agreement is obtained. This is also found to be reasonably accurate for polydispersed systems when the calculated ut values, based on average bed properties, are compared with those calculated theoretically after being multiplied with the Pettyjohn-Christiansen sphericity correction factor. © 1990.