The segregation phenomena of a 1:1 mixture of grain particles with different frictional properties in a rotating drum are studied by simulations. The surface flow is modeled by extending the rules from sandpile models while the rotation is modeled by a solid rotation. Radial segregation will occur only if the rotational transport rate omega is less than some critical value omega(c). Our results show that such a segregation can be described by a non-equilibrium critical phase transition in the steady state with the particle transport rate playing the role of the temperature. Employing finite-size scaling analysis similar to standard critical phenomena, critical exponents for the order parameter and its fluctuation are also obtained numerically.
