A study of the modes of gas-solids flow in pipelines
A variety of gas-solids flows can be observed in the pipeline of a pneumatic conveying system. These flows may be classified as one of three modes: i. suspension flow; ii. non-suspension moving-bed type flow; iii. non-suspension plug type flow. The modes of flow that a bulk material can achieve are dependent upon its particle and bulk properties as well as the pipeline conditions. This work describes the development of mathematical models for these modes of flow as well as experimental investigations to determine the validity of the models proposed. The modelling technique was based upon the solution of the conservation equations for inter-dispersed continua. Mathematical models for phenomena, such as the aerodynamic drag force between the conveying gas and particles, were added to the general mathematical model so that the flow of the gas-solids mixture could be simulated. This resulted in successful development of models for the prediction of suspension flow and non-suspension moving-bed type flow. In addition to providing data for validation of the mathematical models, the experimental programme produced a number of other observations. For example, it was found that the solids velocity in non-suspension moving-bed type flow could be determined non-intrusively by pressure measurements due to the variation in height of the moving-bed with time at a fixed location. More importantly, observation of plug type flow has led to the proposal of a mechanism to describe the development of the flow along a pipeline.