Geldart's classification is practical for estimation of
flow modes for pneumatic conveying systems.
However, it is unsuitable alone for prediction of
flow mode in dense phase. Moreover, Dixon's
approach is also convenient during design stage, but
provisional for an accurate prediction of flow
modes. Mainwaring and Reed's approach is more
reliable predictive method than the Geldart's and
Dixon's approaches due to based on permeability
and de:aeration factors instead of only physical
properties of particles. Fargette et al. considered the
air/particle interaction introducing a non:
dimensional parameter in terms of de:aeration time,
permeability and loose:poured bulk density.
Chambers also introduced a dimensionless
parameter similar to that proposed by Fargette et al.
using particle density instead of loose poured bulk
density. According to Sanchez, some materials do
not obey Geldart's classification due to the
secondary parameter properties of materials.
Molerus modified the Geldart's classification and
also described the criterion between Geldart's Group
A:C considering cohesion forces. Pan classified the
flow mode as a function of loose poured bulk
density and median particle diameter showing
agreement with those of Geldart, Dixon and
Mainwaring and Reed. Jones and Williams
reviewed all available studies in their study and also
proposed criteria for Geldart's Group A:B and B:D
taking into account loose poured bulk density and
permeability.
Hence there are many flow mode diagrams and
proposed criteria for determination of flow modes
for pneumatic conveying of powders/granular
particles from Geldart's approach [1] to the study of
Jones and Williams [11]. As is seen, some of the
scientists considered only physical properties of
particles/powders while others took into account
both physical properties of particles and air/particle
interaction. There are some agreements and
conflicting results among the proposed approaches.
In this paper, all proposed criteria are reviewed and
sorted out for further studies.