Abstract
By studying avalanches in two-dimensional, rotating drums one finds an inevitable segregation process where the heavier particles of a binary mixture of light and heavy equal-size particles are located near the centre of mass of the particles in the drum. To look at the details of this process, numerical simulations using molecular-dynamics techniques are performed. The segregation speed and the size of the final cluster are studied as a function of mass ratio M/m and gravity. The initial segregation velocity seems to scale as log (M/m).