An Investigation into Flow Mode Transition and Development of Model for Pressure Drop Calculation in Dense Phase Pneumatic Conveying System

Abstract

This work presents an experimental investigation into the pneumatic conveying characteristics (PCC) for horizontal straight pipe section to address dense to dilute phase transition phenomenon and development of model for solids friction factor to predict the pressure drop throughout the pipeline for conveying of fine powders in fluidized dense phase. Pressure minimum curve (PMC) is the unique curve on the straight pipe pneumatic conveying characteristics (PCC) curve which indicates dense to dilute phase transition. An attempt has been made to address pressure minimum curve (PMC) by imposing constant Stokes number and constant solid loading ratio lines on straight pipe pneumatic conveying characteristics (PCC) curve. For reliable system design, accurate prediction of pressure drop throughout the pipeline is very important. Pressure drop occurs due to interaction between various phases of flow (e.g. gas-solid particles, particles-particles, particles-wall and gas-wall), mainly due to friction and momentum loss. In this article solids friction factor is modeled by using particle terminal velocity, Stokes number, solid loading ratio, average flow velocity, particle density and density of conveying medium by regression analysis. Fly ash (median particle diameter: 30 μm and 20 μm; particle density: 2300 kg/m3 and 2370 kg/m3; loose-poured bulk density: 700 kg/m3 and 660 kg/m3) was conveyed through 65 mm I.D. × 254 m (Fujian Longking Co.), 69 mm I.D. × 168 m and 69 mm I.D. × 554 m (University of Wollongong) pipelines and cement (median particle diameter: 19 μm; particle density: 2910 kg/m3; loose-poured bulk density: 1080 kg/m3 ) was conveyed through 65 mm I.D. v × 254 m (Fujian Longking Co.), pipeline for wide range of air and solids flow rate. During fluidized dense phase conveying, a high concentration layer of material occupies the bottom portion of the pipeline. Where as in the upper portion of the pipeline, particles are suspended in conveying medium. Two-layer model is very much suitable to address fluidized dense phase flow phenomenon. In this study, solid fiction factor is modeled by using terminal velocity and solid loading ratio for immature dune flow (initial stage of dune flow). For complete dune flow (e.g. two layer flow), solids friction factor is modeled by using existing "Weber A4" model with weightage factor τ1 and newly developed model based on solid loading ratio, Stokes number and particle density to conveying medium density with weightage factor τ2. Where, the summation of τ1 and τ2 is 1.