Volute profile plays an important role in guiding the airflow for a turbo air classifier. The traditional volute design is based on the method of analogue and there is a lack of uniform theoretical design basis and guidance. To meet the needs of guiding the airflow better, a logarithmic spiral volute design method is put forward based on the analyses of airflow motion in the volute and classification characteristics of the turbo air classifier. The numerical simulations on flow field distribution in the turbo air classifier show that the logarithmic spiral volute has a good effect on guiding the airflow and can form a well-distributed flow field in the classifier, which is conducive to improve the classification performance. The single particle trajectory verifies that the logarithmic spiral volute makes the airflow flow along the guide vanes circumferentially uniformly, forming a well-distributed flow field in the annular region of the classifier. So the classification results for the particles with the same size are in correspondence when the logarithmic spiral volute is applied. The numerical simulations of both gas phase and discrete phase indicate that the logarithmic spiral volute can provide a well-distributed flow field for the classification and this volute deign method for turbo air classifier is feasible. (C) 2019 Published by Elsevier B.V.