Material properties and flow modes in pneumatic conveying

Abstract

When bulk solid materials are transported in conventional pneumatic conveying systems, three flow modes have been observed. These are: (i) smooth transition from dilute- to fluidised dense-phase, (ii) dilute-phase, unstable-zone and slug-flow and (iii) dilute-phase only. The flow mode for a bulk solid material is totally dependant on material properties, in particular, those properties which involve particle/air interaction (e.g., permeability, air retention and de-aeration). Usually, the particle/air interaction characteristics are a function of basic particle properties, such as particle size, size distribution, density and shape. Loose-poured bulk density also is a function of these basic particle properties. Therefore, there should be a relationship between the loose-poured bulk density and the particle/air interaction characteristics. Based on experimental results and theoretical analysis, a new flow mode diagram is developed for the purpose of selecting suitable flow mode for a particular material. Based on the developed flow mode diagram, the bulk solid materials can be classified into three groups (PC1, PC2 and PC3), characterised simply by loose-poured bulk density and median particle diameter. Materials in group PC1 can be transported smoothly and gently from dilute- to fluidised dense-phase. Materials in group PC2 can be transported in dilute-phase, unstable zone or slug-flow and materials in group PC3 are conveyed in dilute-phase only. A good accuracy is achieved when many test results with the observed flow modes are superimposed on the developed flow mode diagram.