Particle motion paper offers pneumatic conveying insights

News from The Centre for Industrial Bulk Solids Handling at Glasgow Caledonian University, Scotland.

Top research student Jiansheng Xiang has gained his Doctorate of Philosophy degree with a thesis entitled “Investigation of Particle Motion In Dense Phase Pneumatic Conveying.”

The aim of his project was to investigate the motion of particles in a flowing gas-solids mixture in order to study some of the processes which may occur during dense phase pneumatic transport through pipes, such as segregation, or mixing.

An experimental technique was developed to measure various characteristics of plug flow in dense phase pneumatic conveying systems. The use of standard ‘smart’ differential pressure transducers to check pressure variations in plugs was investigated in this study and in particular the influence of the finite response time of the transducers was considered. The results were obtained from an analysis of the measurements taken from the axial pressure drop along the pipe and confirmed by examining video footage of the tests. This measuring technique has been found effective in detecting solids plugs travelling through horizontal pipes and will distinguish various flow regimes. As such, it may have a direct application in industry as it provides a useful and easily applied tool for system optimizing and benchmarking pneumatic conveying systems.

This technique was employed and developed in further experiments. Experiments were conducted over a wide range of gas-solids flow conditions. The experiments focused on the influence of plug position, and mass flow rate of solids and gas on plugs velocities. In order to get the information about plugs formation and development, in-line measurement of pressure drop near the feeding point was carried out.

A special sampling device was designed and built to take samples from the pneumatic conveying pipeline after “catching a plug”. This device was used to analyze segregation and mixing of particles in binary mixtures. Experiments were conducted over several gas-solids flow. Experimental data combined with video footage were analyzed to describe the segregation and mixing of solids plugs in pipes. It is clear from the results and discussions within this study that segregation did happen in dense phase under the conditions shown in the present study.  The data were also used to validate the mathematical model.

A gas-solids two-dimensional mathematical model was developed based on a combined approach of the Discrete Element Method (DEM) and Computational Fluid Dynamics (CFD). The model was used to simulate the motion of particles both in a homogeneous flow and as binary mixtures taking into account the various interactions between gas, particles and pipe wall. For gas motion, the Navier-Stokes equations were integrated by the semi-implicit method for pressure-linked equations (SIMPLE) scheme of Patankar employing the staggered grid system. For particle contact, a model with a nonlinear spring-dashpot-slider model for both normal and tangential components was used. For the particle motion, the Newtonian equations of motion of individual particles were integrated, where repulsive and damping forces for particle collision, the gravity force, and the drag force were taken into account.  The main results (such as pressure drop, plug velocity, segregation and mixing, etc) were compared with experimental data and very good agreement was found.

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