An investigation of segregation and mixing in dense phase pneumatic conveying |
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Authors: | Jiansheng Xiang Don McGlinchey John-Paul Latham |
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Affiliation: | (1) University of Pittsburgh, Pittsburgh, PA, USA;(2) Neuhofen, Germany;(3) The Da Vinci Institute of Technology Management, Johannesburg, South Africa; |
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Abstract: | Pneumatic conveying of bulk materials has become an important technology in many industries: from pharmaceuticals to petro-chemicals
and power generation. Particulate segregation has been investigated in many solids handling processes. However, little work
has been published on the segregation and mixing in pneumatic conveying pipelines, particularly in dense phase pneumatic conveying.
Due to the character of dense phase flow, it is difficult to investigate the segregation in a flowing plug. A sampling device
was designed and built to take samples from the pneumatic conveying pipeline after “catching a plug”. Several experiments
were conducted over a range of gas–solids flow conditions with 3 mm nylon pellets and 3 mm ballotini as a segregating mixture.
Experimental data combined with video footage were analysed to describe the segregation and mixing of solids plugs in pipes.
This investigation provides initial research on establishing a segregation index in a flowing plug. A gas–solids two-dimensional
mathematical model was developed for plug flow of a nylon-glass particulate mixture in a horizontal pipeline in dense phase
pneumatic conveying. The model was developed based on the discrete element method (DEM). 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 the gas phase, the Navier Stokes equations were integrated by the semi-implicit method for
pressure-linked equations (SIMPLE) using the scheme of Patankar employing the staggered grid system. 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. For particle contact, a model with a simple non-linear
spring and dash pot model for both normal and tangential components was used. This model employed a mixture of 3 mm pellets
and ballotini as virtual materials with properties of nylon and glass. The results from the model are discussed and compared
with experimental work and show qualitative agreement. Further modelling and experimental work in key areas is proposed. |
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