We present an experimental study of segregation of granular matter in a
quasi-two dimensional silo emptying out of an orifice. Size separation is
observed when multi-sized particles are used with the larger particles found in
the center of the silo in the region of fastest flow. We use imaging to study
the flow inside the silo and quantitatively measure the concentration profiles
of bi-disperse beads as a function of position and time. The angle of the
surface is given by the angle of repose of the particles, and the flow occurs
in a few layers only near the top of this inclined surface. The flowing region
becomes deeper near the center of the silo and is confined to a parabolic
region centered at the orifice which is approximately described by the
kinematic model. The experimental evidence suggests that the segregation occurs
on the surface and not in the flow deep inside the silo where velocity
gradients also are present. We report the time development of the
concentrations of the bi-disperse particles as a function of size ratios, flow
rate, and the ratio of initial mixture. The qualitative aspects of the observed
phenomena may be explained by a void filling model of segregation.Comment: 6 pages, 10 figures (gif format), postscript version at
http://physics.clarku.edu/~akudrolli/nls.htm
