Two or more different types of granular material are mixed using mixers,
in large amounts to produce a uniform mixture
in the paint, fertilizer, and pharmaceutical industries. A common problem
with these mixers
is that particulates or granules of dissimilar size, shape and density tend
to segregate and
separate out as clumps.
Prof. D. V. Khakhar and his student of Department of Chemical Engineering
specially designed impellers to the central shaft of the rotating drums
used for such mixing.
Impellers are similar to blades of a fan which protrude out from the shaft
of the rotor.
They actively churn the flow of the material near the drum axis and also
heavy material that tends to accumulate near the central axis.
The researchers have demonstrated the efficacy of this improvisation by
a novel experiment,
where glass beads of two different size and colors (red and colorless)
into a horizontal drums, one with impeller and one without, and rotated.
The drum with
impeller showed superior mixing along both the axial (along the length
of the drum) and
radial (across the circular cross section of the drum) directions. The
impeller was designed
to have 'inverse S' shape. Best results were obtained when the impeller
was rotated at a considerably higher speed compared
to that of the drum and in the same direction as that of the drum.
Although uniform dispersion of the beads of different colours could
be clearly visualized in snapshots of the rotating drum,
quantitative measurements confirmed that the mixing index was high
and segregation index was low. In particular they
found that for certain size of the impeller blades, the distribution
of smaller particles varies rather uniformly across the
cross-section and thus core formation was prevented. This invention
will result in more efficient industrial mixers.
Indian patent application no. 809/MUM/2003 Patent grant no. 213856
Inventors: D V Khakhar and S Hajra