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A cyclone is a commonly-used apparatus that makes use of gravity and centrifugal force to separate solid particles from a gas stream. A typical cyclone is a cylindrical vessel with a tangential inlet and top and bottom outlets. Cyclones are widely used in various industries because they are easy to build, inspect and maintain.
Hydrocyclones are similar devices to cyclones where the operating fluid is a liquid rather then a gas. Hydrocyclones operate under pressure. The feed, a mixture of possibly gases, liquids and solids enters the hydrocyclone tangentially through the inlet which forces the mixture to spin inside the cyclone. This spinning motion generates centrifugal forces which cause the gas to disengage quickly and exit through the vortex finder. The liquid passes down into the conical section where the reduction in diameter accelerates the fluid thus generating centrifugal forces strong enough to cause the solids to separate from the liquid. The solids are forced towards the wall, because of density difference, and then travel down the length of the conical section of the hydrocyclone in a spiral pattern towards the solids outlet, termed the underflow. The gas and liquids migrate towards the center of the hydrocyclone where the flow reverses and moves upwards towards the over-flow, through the vortex finder. Separated solids fall down under gravity into the accumulator vessel situated beneath the hydrocyclone.
Because of the highly complex flows induced by the swirl, and the details of the cyclone geometry, even the fluid flow is difficult to simulate accurately. For this application, the Second Moment Closure turbulence models available in the ANSYS CFX software are very valuable for the correct prediction of the fluid flow. The behavior of the particulates can then be simulated using either the Eulerian multiphase model or the particle transport model.
ANSYS CFX simulation of a hydrocyclone.
Picture courtesy of ESSS and Petrobras.
