In order to compare particle separation performance of various
apex cone angles, the CFD simulation would be effective to find out
the difference of physical phenomena around the apex cone region.
The three-dimensional Navier–Stokes equations and equations of
particle motions were solved numerically. Table 1 summarizes the
basic equations used in the simulation. The direct flow method, that
solves Navier–Stokes Equations directly, was used to calculate the
flow field in the cyclone [8]. To calculate the non-linear convection
terms, the artificial viscosity coefficient of 1/3 was selected to obtain a
stable flow field [9]. The control volume method was used in the
simulation [10].
Fig. 6 shows the grid distributions for the various apex cone angles.
In order to make clear the grid near wall region, the scales in
horizontal and vertical directions are not the same. In order to
calculate the partial separation efficiency for small particles, the radial
grid spacing near the cylindrical, conical and the apex cone walls are
designed to be as small as possible. The fluid boundary conditions on
the wall, including the apex cone in the dust box, were set to zero.
Grid numbers in axial, radial and circumferential directions are 51, 44,
and 53, respectively. The boundary-fitted curvilinear coordinate
system was used in the simulation. In order to obtain reliable results
in calculating small particle diameters, the radial grid spacing near the
conical and cylindrical walls should be as small as possible. In the
calculations, the equations of mono-sized particle motions were
solved by the RKG method [11].
It was assumed that particles are collected when they touch the
wall surface and particle repulsion was not taken into consideration.