The flow behavior in hydrocyclones is extremely complex, leading the designers to rely on empirical equations for predicting cyclone performance. A number of classifying cyclone models have been developed and used in mineral comminution circuit simulators in the past. The problem with these empirical cyclone models is that they cannot be used outside the range of conditions under which they were developed. A semi-mechanistic hydrocyclone model is developed using the dimensionless approach based on both the fluid mechanics concepts from Computational Fluid Dynamics (CFD) simulations and the wide range of industrial cyclone performance data. The improved model consist a set of equations for the water split to underflow (R-f), reduced cut-size (d(50c)), throughput (Q) and sharpness of the separation (alpha). The model for R-f, d(50c), Qgives a very good fit to the data. The alpha model shows reasonable correlation for the cyclone design and operating conditions. Additional data sets were used to validate the new hydrocyclone model by comparing the predictions of the model equations with the experimental results. (C) 2014 Elsevier B.V. All rights reserved.