This work focuses on the characterisation and quantification of the stirring action that takes place inside a continuous mixer of particulate solids, under several operating conditions. Pure products, as well as 50% mass mixtures, are investigated to provide a basis for a better prediction of the behaviour of bulk mixture flow. The hold up in the mixer has been experimentally related to the flow rate and the rotational speed for the cases studied here. A single correlation has been derived to link the mean residence time to the rotational speed through a simple power law dependence. This seems to be a good basis for scale-up of such continuous mixers. The existence of different flow regimes inside a general dense phase forced transport has also been demonstrated and qualitatively explained. It may be of importance when considering mixtures of low concentration in the finest product. (c) 2005 Elsevier B.V All rights reserved.