Year

1994

Degree Name

Doctor of Philosophy

Department

Department of Mechanical Engineering - Faculty of Engineering

Abstract

Low-velocity pneumatic conveying is being used increasingly in industry to transport a wide range of bulk solids due to reasons of low power consumption and low product damage, etc. However, investigations into this type of conveying still are at an elementary stage. For example, the existing procedures to estimate pipeline pressure drop during low-velocity pneumatic conveying still are inaccurate and inefficient. For this reason, this thesis aims at developing a pressure prediction model that is a function of the physical properties of the material, pipeline configuration and conveying condition.

During low-velocity pneumatic conveying, particles are conveyed usually in the form of slugs. This thesis studies initially the pressure drop across a single particle slug and the stress state and distribution in the slug through theoretical analysis.

To obtain detailed information on low-velocity pneumatic conveying, a test rig is set up and four types of coarse granular material are conveyed in the rig. Major parameters such as mass flow-rate of air and solids, pipeline pressure, slug velocity and wall pressure, etc. are measured over a wide range of low-velocity conveying conditions.

Based on the experimental results and a dimensional analysis, the relationship between the slug velocity and superficial air velocity is established in terms of the physical properties of the material and pipe size. Also by using particulate mechanics, a semi-empirical correlation is developed to determine the stress transmission coefficient for the slugs flowing in the pipe with rigid and parallel walls. A model then is developed to predict the overall horizontal pipeline pressure drop of low-velocity pneumatic conveying.

This model is used to predict the pneumatic conveying characteristics and static air pressure distribution for different test rig pipelines and materials. Good agreement is obtained between the predicted and experimental results. Based on the developed model, a method for determining the economical operating point in low-velocity pneumatic conveying is presented.

Additional experimental results from the conveying of semolina show that the performance of fine powders is quite different in low velocity. Based on these experimental results, an appropriate modification to the model is made so that it can be applied to the prediction of pressure drop in low-velocity pneumatic conveying of fine powders.

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