Solids friction power law variations and their influence onpressure losses in fluidised dense phase pneumaticconveying

摘要

In dilute phase pneumatic conveying the particles are suspended in the carrier gas (usuallyrndry air) with the frictional losses dominated by particle-wall and particle-particle collisions.rnIn dense phase conveying, the particles are in contact with each other, with one of tworndistinct modes of flow occurring: plug/slug flow which is predominantly based on granularrnproducts and fluidised dense phase flow which is more suited to fine powders exhibitingrngood air retention capabilities. In dense phase-plug/slug flow, the resistance is dominatedrnby the radial stresses that the moving slug applies to the wall of the pipeline. In fluidisedrndense phase flow the frictional losses are characterised by a mixture of particle-wall andrnparticle-particle losses which are heavily influenced by the viscous behaviour of the gassolidrninteractions.rnTypically, an empirical based friction factor has been used to determine the associatedrnfrictional pressure losses in the fluidised dense phase pneumatic conveying. These frictionrnfactors are dominated by a power law relationship to the conveying air Froude number (Fr)rnand solids loading ratio (m*). For different materials, the exponents can vary significantly,rnwhich limits the application range of these power law models. This paper details thernvariation of the power law coefficient and exponents and their effect of these changes onrnpressure prediction. Also investigated is the application of utilising the flowabilityrnparameters of the Hausner Ratio and the permeability/de-aeration parameters in defining arngeneric fluidised dense phase friction model and the associated limitation due to therninherent sensitivity of the power law model.