Identifying the Flow Conditions in Pneumatic Conveying of Wheat Grains through Horizontal Straight and Bent Pipe using Pressure Drop
Date
2017-01-17
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
ORCID
0000-0001-7268-3072
Type
Thesis
Degree Level
Masters
Abstract
Pneumatic conveying is a process of transporting solids, such as granules, powder, and other bulk materials, in a gas stream through pipelines. One among many of its applications is seen in agricultural air seeders, which are used for seed planting and applying granular fertilizers. One of the most reported problems in a pneumatic conveying operation is blockage (partial/complete) of the pipeline, which occurs due to the prolonged settling of conveyed material in the pipeline. When the material settling or pipe blockage occurs during the conveying process, the overall efficiency drops significantly.
Various kinds of sensors are popularly used in the pipelines to detect the settling or blockage during the conveying operation. However, these available sensors are not able to detect the onset conditions beyond which settling or blockage generally occurs. Therefore, these sensors do not enable pro-active actions to be taken.
Some previous research has illustrated that the trend of the pressure drop in a pipeline during a pneumatic conveying process represented the corresponding flow conditions. Moreover, the trend showed a transition when the flow conditions became close to the settling conditions. These characteristics suggest that the pressure drop in a pipeline could be used to detect the approaching adverse flow condition (settling condition) before the actual settling occurs, and thus can help in identifying the optimal operating point. In addition, some studies have observed that the trend of pressure drop per unit length of pipe (pressure gradient) for a given set of flow conditions might differ with different kinds of solid materials, pipe configurations, and operating conditions.
Only a few studies have presented experimental data for the pneumatic conveying of wheat grains. This thesis research was aimed at extending the understanding of the applicability of the pressure drop in identifying the corresponding flow conditions and the optimum air flow rate for the pneumatic conveying of the wheat grains. This project also filled some gaps in the literature by conducting the experiments in a 57 mm ID horizontal pipeline for three different grain feed rates (20 - 100 g/s) and ~17 different air flow rates. To understand the effect on the pressure drop and the flow conditions upon bending the pipeline, the experiments were conducted with horizontal-straight as well as horizontal-bent pipe (with four different angles: 22.5°, 45.0°, 67.5°, and 90.0°).
The results showed that the trend of pressure drop over a range of air speeds could successfully identify the occurrence of the grains settling. The air speed corresponding to the minimum pressure drop consistently appeared to be slightly higher than the air speed at which the grains started to settle in the pipe. Therefore, the air speed corresponding to the minimum pressure drop can be recommended as the threshold and optimum air speed. The effect of bending the pipe on the pressure drop and the settling speed were found to be just minimal, probably because of the fan controller system (which maintained the air speed constant during the test) and the large radius of bend. Also, by measuring the pressure drop in local sections of the pipeline, the locations of major settling could also be successfully identified.
Description
Keywords
Pneumatic conveying, Settling, Pressure Drop
Citation
Degree
Master of Science (M.Sc.)
Department
Mechanical Engineering
Program
Mechanical Engineering