The segregation phenomena of a mixture of two types of particles with different frictional properties in a rotating drum are studied by simulations which mimic the granular flow by a: surface flow and a bulk solid rotation, The surface flow is modeled. by rules similar to sandpile models. Radial segregation is clearly observed but will occur only if the rotational transport rate is less than some critical value. Furthermore, linear growth in segregation is also observed in the early stage of demixing, similar to observations of real experiments.
