A fine particle outlet was designed and introduced to a centrifugal air classifier to improve its classification performance. Effects of the inserted depth and diameter of fine particle outlet were investigated experimentally and numerically. The turbulent airflow was modeled using the Reynolds Stress Model. The calculated pressure drop of the classifier agrees well with the experimental date. The experimental results, indicate that the insertion of fine particle outlet significantly enhanced the particle classification efficiency. Optimal particle classification can be achieved when the fine particle outlet inserted depth ratio is 0.5. Increasing the fine particle outlet diameter decreases both the tangential velocity and the turbulent intensity, thereby increasing the cut size. Both too large and too small fine particle outlet diameters lead to poor classification performance. Moreover, the fine particle outlet diameter has a more significant effect on pressure drop compared to the insertion of fine particle outlet. The obtained results can provide a guideline for design of the centrifugal classifier. (C) 2016 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.