Computational Biomechanics-NavidAllahverdi CYCLONE THEORY -PritamPatil
Cyclone Rotational effects and gravity Fluid flows in a spiral pattern Heavier particles have high inertia Strike the wall and fall off Forced vortex removes air from top
Models 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 convention. 3] Reynolds’ Stress Model (RSM): It solves a transport equation for each component of Reynolds’ Stress.
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
Geometry Sketch circles Skin/Loft Extrude
Mesh Comparison Paper ANSYS
Pressure 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 vortex.
Tangential Velocity 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 wall.
Axial Velocity Forced vortex is a twisted cylinder and not completely axially symmetric, esp. in the conical section. 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.
Radial Velocity 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 curve. In the conical section, the radial velocity is much larger than that of the cylindrical section..
Comparison ANSYS Velocity Tangential Velocity
……. ANSYS Pressure Static Pressure
Mass Flow Rate
Results 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
References Numerical study of a Gas-Solid flow in a cyclone separator. (Wang et al) Dec 2003 http://en.wikipedia.org/wiki/Cyclonic_separation