• Energy Research

Abstract The poorly understood mechanisms of slug flow remain an obstacle for widespread application of this dense phase flow. The parameters that characterise the flow have repeatedly been observed to have a bounded range of operating conditions; however, the ability to reliably predict these boundaries has not achieved the same level of repeatability. This paper presents a model to predict the absolute maximum transport boundaries for slug velocity and the absolute minimum transport boundaries for the layer fraction as a function of the gas mass flow rate. The predicted transport boundaries are supported by measurements, following which, the model is further developed as a prediction tool, where very good agreement with measurements is achieved. As the model provides relationships between all of the key parameters of slug flow, analysis is provided demonstrating the ability of the model to be applied as a convenient design tool for slug flow pneumatic conveying systems.

Abstract The poorly understood mechanisms of slug flow remain an obstacle for widespread application of this dense phase flow. The parameters that characterise the flow have repeatedly been observed to have a bounded range of operating conditions; however, the ability to reliably predict these boundaries has not achieved the same level of repeatability. This paper presents a model to predict the absolute maximum transport boundaries for slug velocity and the absolute minimum transport boundaries for the layer fraction as a function of the gas mass flow rate. The predicted transport boundaries are supported by measurements, following which, the model is further developed as a prediction tool, where very good agreement with measurements is achieved. As the model provides relationships between all of the key parameters of slug flow, analysis is provided demonstrating the ability of the model to be applied as a convenient design tool for slug flow pneumatic conveying systems.

A wedged plane-flow hopper and horizontal belt feeder is employed to investigate the flow patterns and stress field redistribution at the hopper and feeder interface. The flow patterns are recorded by a high speed camera in conjunction with coloured material layers. The three-dimensional stress field in the feed zone and its influence on the feeder operation are discussed. The vertical stresses acting on the feeder for initial filling and flow conditions are measured along with longitudinal shear feeder loads. The experimental results are compared with theoretical values derived using relevant feeder load theories. The influences of different filling heights and clearance between the hopper bottom and feeder surface on feeder loads are presented. Numerical simulations using the Discrete Element Method (DEM) are carried out additionally to analyse feeder loads at the hopper and feeder interface, with the results being compared with those obtained experimentally.

A wedged plane-flow hopper and horizontal belt feeder is employed to investigate the flow patterns and stress field redistribution at the hopper and feeder interface. The flow patterns are recorded by a high speed camera in conjunction with coloured material layers. The three-dimensional stress field in the feed zone and its influence on the feeder operation are discussed. The vertical stresses acting on the feeder for initial filling and flow conditions are measured along with longitudinal shear feeder loads. The experimental results are compared with theoretical values derived using relevant feeder load theories. The influences of different filling heights and clearance between the hopper bottom and feeder surface on feeder loads are presented. Numerical simulations using the Discrete Element Method (DEM) are carried out additionally to analyse feeder loads at the hopper and feeder interface, with the results being compared with those obtained experimentally.

Slug-flow pneumatic conveying is a full-bore mode of flow within the dense-phase flow regime where bulk materials are transported in the form of slugs at conveying speeds below saltation velocity. The mechanism of slug-flow pneumatic conveying consists of the particles being picked up from the stationary bed in front of a moving slug while the same amount of material is deposited behind the slug. Stress field modeling of the material slug is the first step in developing a prediction model for the pressure drop along a pneumatic conveying line. However, a reliable prediction strongly relies on an accurate assessment of several factors, including the particle properties, pipeline dimensions, and operating conditions. So far, the particle diameter has always been one of the crucial parameters, which is not desirable in regards to the limitations it imposes on the choice of bulk materials. This article focuses on one parameter, the stress transmission coefficient kw, which relates the lateral wall stress with...

Slug-flow pneumatic conveying is a full-bore mode of flow within the dense-phase flow regime where bulk materials are transported in the form of slugs at conveying speeds below saltation velocity. The mechanism of slug-flow pneumatic conveying consists of the particles being picked up from the stationary bed in front of a moving slug while the same amount of material is deposited behind the slug. Stress field modeling of the material slug is the first step in developing a prediction model for the pressure drop along a pneumatic conveying line. However, a reliable prediction strongly relies on an accurate assessment of several factors, including the particle properties, pipeline dimensions, and operating conditions. So far, the particle diameter has always been one of the crucial parameters, which is not desirable in regards to the limitations it imposes on the choice of bulk materials. This article focuses on one parameter, the stress transmission coefficient kw, which relates the lateral wall stress with...

Within the field of pneumatic conveying horizontal (Plug-1) and vertical plug flows have been investigated only in the context of cohesive fine powders. This paper considers a series of experiments using fuzzy cottonseeds, which greatly differ in particle and bulk properties from fine powders, to investigate plug formation. In this study, several possible dense phase behaviours were observed, which were consistent in vertical and horizontal orientations and mostly influenced by the batch size of feeding into the rig due to its influence on particle arrangement. Particle arrangement at the plug base or rear was found to be critical for achieving stable plugs, with a requirement of the rear or base batch having the length of more or equal to pipe diameter. This work sheds light on the general features and mechanisms governing horizontal and vertical plug formation.

Within the field of pneumatic conveying horizontal (Plug-1) and vertical plug flows have been investigated only in the context of cohesive fine powders. This paper considers a series of experiments using fuzzy cottonseeds, which greatly differ in particle and bulk properties from fine powders, to investigate plug formation. In this study, several possible dense phase behaviours were observed, which were consistent in vertical and horizontal orientations and mostly influenced by the batch size of feeding into the rig due to its influence on particle arrangement. Particle arrangement at the plug base or rear was found to be critical for achieving stable plugs, with a requirement of the rear or base batch having the length of more or equal to pipe diameter. This work sheds light on the general features and mechanisms governing horizontal and vertical plug formation.

Abstract The process of pneumatic conveying is widely used in industries for conveying materials such as cement, fly ash, alumina etc. Modeling of dense phase or non-suspension flow of fine particles is complex due to several interactions among the carrier gas, particles and the pipe wall. In the present study, dense phase conveying experiment was conducted using alumina as conveying material. The pressure data were recorded at the inlet and the outlet section of the pipeline under different flow conditions. A model of section of pneumatic conveying pipeline was developed in the commercial CFD software Fluent 6.3 Particle size distribution of conveying material has been included in the model in terms of number of solid phases of different mean particle diameters. Simulations were performed by means of Fluent software using the Euler–Euler approach, accounting for four-way coupling. The predicted pressure drop values were found to be in good agreement with the experimental data. Variations of important parameters such as solids volume fraction, gas/solids velocity across the pipe cross-section were analyzed.

Abstract The process of pneumatic conveying is widely used in industries for conveying materials such as cement, fly ash, alumina etc. Modeling of dense phase or non-suspension flow of fine particles is complex due to several interactions among the carrier gas, particles and the pipe wall. In the present study, dense phase conveying experiment was conducted using alumina as conveying material. The pressure data were recorded at the inlet and the outlet section of the pipeline under different flow conditions. A model of section of pneumatic conveying pipeline was developed in the commercial CFD software Fluent 6.3 Particle size distribution of conveying material has been included in the model in terms of number of solid phases of different mean particle diameters. Simulations were performed by means of Fluent software using the Euler–Euler approach, accounting for four-way coupling. The predicted pressure drop values were found to be in good agreement with the experimental data. Variations of important parameters such as solids volume fraction, gas/solids velocity across the pipe cross-section were analyzed.

Abstract Current models for pressure drop prediction of slug flow pneumatic conveying in a horizontal pipeline system assume some type of steady state conditions for prediction, which limits their capability for increased predictive accuracy relative to experimental data. This is partly because of the nature of slug flow pneumatic conveying system, which, as a dynamic system, never becomes stable. By utilising conservation of mass (airflow), a dynamic pressure analysis model is proposed on the basis of the derivative of the upstream pressure behaviour. The rate of air permeation through slug, one of the important factors in the conservation model, is expressed as a function of a slug permeability factor. Other factors such as slug velocity, slug length and the fraction of stationary layer were also considered. Several test materials were conveyed in single-slug tests to verify the proposed pressure drop model, showing good agreement between the model and experimental results.

Abstract Current models for pressure drop prediction of slug flow pneumatic conveying in a horizontal pipeline system assume some type of steady state conditions for prediction, which limits their capability for increased predictive accuracy relative to experimental data. This is partly because of the nature of slug flow pneumatic conveying system, which, as a dynamic system, never becomes stable. By utilising conservation of mass (airflow), a dynamic pressure analysis model is proposed on the basis of the derivative of the upstream pressure behaviour. The rate of air permeation through slug, one of the important factors in the conservation model, is expressed as a function of a slug permeability factor. Other factors such as slug velocity, slug length and the fraction of stationary layer were also considered. Several test materials were conveyed in single-slug tests to verify the proposed pressure drop model, showing good agreement between the model and experimental results.

Abstract This paper presents the results of a preliminary investigation utilising an inertial measurement unit (IMU) within horizontal slug flow pneumatic conveying. Challenges of using an IMU within pneumatic conveying were discussed, in particular the importance of sensor fusion. Different sensor fusion algorithms were considered and Madgwick's filter was selected as most appropriate. Two IMUs were simultaneously inserted into the pipeline allowing the particle velocity to be measured as the sensors mimicked the motion of the slug particles. Furthermore, barometers on the IMUs allowed for in-situ pressure to be measured as the particles travelled through the slug. Benefits and drawbacks of the use of IMUs, particularly in relation to slug flow pneumatic conveying, were discussed and results of a preliminary investigation conveying plastic pellets in a horizontal pipe were presented. By analysing the pressure outputs of the two IMUs it was shown that the pressure profile over the slug is not linear. Lastly, by examining the pressure and velocity trends, it could be seen that there is an inverse relationship between pressure and velocity. Moreover, it was discovered that there exists a time delay where velocity changes occur first, followed by a delayed change in pressure.