Showing papers by "Sreenivas Jayanti published in 2004"

Computational Study of Particle-Eddy Interaction in Sedimentation Tanks

Abstract: Sedimentation tanks are used in the process industry to separate the solid particles from the slurry to get the clarified liquid. A detailed study of the hydrodynamics of sedimentation tanks is presented here using an Eulerian-Lagrangian approach to study the motion of solids in the tank. The model, in its present form, is applicable only to nonflocculent discrete (Type I) settling. It is shown that a typical particle-eddy interaction can be characterized by a lower cut-off size below which the particles would be entrained by the eddy; and an upper cut-off size above which the particle would continuously settle through the sedimentation tank in spite of the recirculation. The effect of inlet configuration on the flow field as well as on the settling characteristics has been investigated. The simulations show that both the upper and the lower cut-off sizes for a sedimentation tank are considerably reduced by providing a tulip type of inlet with a conical deflector as compared to a straight inlet.

Pressure Losses and Flow Maldistribution in Ducts with Sharp Bends

Abstract: Pipelines and ducting systems used in process industry applications are characterized by large sizes, sharp bends and successive bends connected by short straight sections. Systematic studies of such flow situations have not been reported in the literature and the design of such ducting systems is based on rules of thumb and scaled-model testing. Taking advantage of the potential size-insensitivity of CFD-based calculations, a large number of calculations of typical flow situations has been carried out in the present study to address such issues as the optimum location of guides vanes, the influence of an upstream bend on the loss coefficient and the scaling laws for proper extrapolation of laboratory results to industrial scale applications. It is shown that the ideal radial location of a vane for a square duct is given by (RiRo)0.5 and that the influence of an upstream bend on the loss coefficient is beneficial in most cases. Thus, the calculation of bend losses treating each bend as being isolated is likely to be conservative. The velocity profile is uniformly improved by the use of vanes. The loss coefficient is not very sensitive to the fluid scaling, but the effect of wall roughness has to be considered carefully in scaled-down conditions.