Experimental study on velocity field between two adjacent blades and gas-solid separation of a turbo air classifier

The velocity field between two adjacent blades in a turbo air classifier was measured using the particle image velocimetry (PIV) technique equipped with a self-developed synchronizer. It was found that vortex swirling flow existed between the two blades or in the annular region between the impeller and the side wall. Under a given condition, the swirling intensity was higher while the swirling zone was smaller in the horizontal plane of the upper stream. As the impeller rotational speeds increased, the swirling became more intensive and the vortex center moved toward the side wall; when total air flow rate Q increased, the swirling intensity increased but the swirling center barely changed. The performance experiments showed that the overall classification efficiency eta increased with S firstly and then decreased with the further increase of S. Correspondingly, non-monotonic variation trend was found for the cut size of the passing through particles d(50). At a higher inlet solid concentration C-s, the dependence of d(50) on S was more profound. d(50) decreased significantly with the increasing Cs when Cs was smaller than a critical value and then barely changed when Cs kept increasing. For the tested turbo air classifier, when Q = 750 m(3).h(-1), the minimum d(50) was similar to 32 mu m, occurring at the condition of C-s approximate to 0.08 kg.m(-3) and s approximate to 120 rpm. The classification performance could be well explained by the velocity field near the entrance of the impeller and particle aggregation in the classifier. (C) 2015 Elsevier B.V. All rights reserved.