4. Conclusions
A study on the effects of the gas outlet duct length and shape on
the flow field inside a small cyclone and its impacts on the cut off
diameter and pressure drop was performed. This study included
thirty-seven simulations with different outlet duct configurations.
All the simulations performed in this work are based on the LES
methodology, with the dynamic sub-grid turbulence model. The
dispersed phase, treated in a Lagrangian reference frame, was simulated
in a concomitant manner. Although expensive from the
computational point of view, the methodology adopted allowed
the gas–solid simulations to be independent of turbulence dispersion
models. The mesh in the separator body was kept constant
throughout the work, ensuring minimal influence from one simulation
to another. The results show that the outlet duct length
and shape do influence the cyclone flow field, as previous stated
by [19] but contrary to their conclusions, this influence was found
to be small. Regarding the gas outlet duct shape the main conclusions
may be summarized as:
Bend Radius:
It was found that as the bend radius is increased the pressure
drop also increases and the cut-off diameter tends to decrease.
Bend Beginning position:
As the bend is moved away from cyclone top, the pressure drop
tends to decrease and the cut-off diameter tends to increase,
except for the case where the curve radius is equal to the gas
outlet duct diameter – a case where a minimum pressure drop
is theoretically expected.
Considering the gas outlet duct length, the pressure drop behavior,
when combined with the swirl motion intensity, matched the
behavior described by [1], but the cut off diameter showed a more
complicated relation, emphasizing the necessity of continuity of
the present study. It is expected that, at least as a first approach,
a greater understanding on the complex relationship between
the cut off diameter and the gas outlet duct length and shape
was achieved in this work.