• Rotational effects
• Fluid flows in a
• Heavier particles
have high inertia
• Strike the wall and
• Forced vortex
removes air from top
• 1] k-έ model: It assumes isotropic turbulence, so
it is not suitable for the flow in a cyclone which
has anisotropic turbulence.
• 2] ASM model: It ignores the effect of stress
• 3] Reynolds’ Stress Model (RSM): It solves a
transport equation for each component of
3 Forces on particles
• r(p) Radius of Particle
• ρ(f) Density of Fluid
• ρ(p) Density of particle
• r Rotational radius of the
particle in the cyclone.
• Fd Drag force
• Fc Centrifugal force
• Fb Buoyant Force
• Pressure decreases radially
from wall to centre and a
negative pressure zone
appears in forced vortex.
• The pressure gradient is the
largest along the radial
direction, as there exists a
highly intensified forced
• The value of tangential velocity
equals zero on the wall and the
centre of the field.
• The high speed fluid enters the
inlet and is accelerated up to
1.5-2 times the inlet velocity.
• Then the velocity decreases as
the gas spins down along the
• Forced vortex is a twisted
cylinder and not completely
axially symmetric, esp. in the
• The forced vortex does not
coincide with the geometrical
centre of the cylindrical body
of the cyclone.
• The diameter of the forced
vortex is a little larger than
that of the vortex finder.
• The forced vertex in the centre
is a twisted cylinder.
• Its axis does not coincide with
the geometrical axis of the
cyclone and is not a line but a
• In the conical section, the
radial velocity is much larger
than that of the cylindrical
• 1] The geometry in Ansys is exactly similar to the one discussed in the paper.
• 2] CFX-mesh generated warnings and also the numbers of elements generated were very large.
• 3] Solver run almost took 2 hours to compile the results since the number of elements very large.
• 4] Boundary condition given at the inlet was Mass Flow Rate instead of the inlet velocity.
• 5] The results were obtained only on the surface and not over the entire volume.
• 6] Velocity results agree with the paper velocity results, i.e. Fluid are accelerated as it enters and the
velocity decreases as the fluid reaches toward the bottom of the cyclone.
• 7] Pressure results agree the paper pressure results, i.e. Pressure decreases radially from the wall toward
the centre however a negative pressure zone was not seen in the ANSYS results probably since the results
of the whole volume of the cyclone was not seen (or calculated by ANSYS)
• 8] But, Mass Flow Rate at the top surface was negative indicating that the velocity is in the opposite
direction demonstrating the formation of the forced
• Numerical study of a Gas-Solid flow in a cyclone
separator. (Wang et al) Dec 2003