The effect of inlet shape and slurry temperature on the classification performance of a hydro-cyclone was examined experimentally and via a simulation study.The 50% cut size of the spiral inlet is smaller than that of the tangential inlet. The slope of the partial separation efficiency for the spiral inlet is greater than that of the tangential inlet. The use of a movable slide vane with the guide wall is effective for decreasing the 50% cut size.Because the viscosity of a slurry decreases with increasing fluid temperature, the 50% cut size decreases with increasing slurry temperature. Experimental data under the increased slurry temperature region is in good agreement with numerical simulation results and a theoretical equation based on inertia theory. (C) 2004 Elsevier B.V. All rights reserved.