Professor Kenneth Williams

Pneumatic conveying is a frequently used method of material transport particularly for in-plant transport over relatively short distances. This is primarily to exploit the degree of flexibility it offers in terms of pipeline routing as well as dust minimization. Approximately 80 % of industrial systems are traditionally dilute phase system which uses relatively large amount of air to achieve high particle velocities to stay away from trouble, such as blocking the pipeline. However, for many applications higher velocities lead to excessive levels wear of pipelines, bends, and fittings. To combat these problems, many innovative bends have been designed. These designs have solved the problem of wear in the bends, but often introduce the wear problem in the area immediately after the bend due to the changed flow conditions. Wear in pneumatic conveying is a very complex problem and at present there is limited understanding of the wear mechanisms responsible for the severe wear in certain areas of a pneumatic conveying pipeline. The ability to determine the wear mechanisms in these areas holds the key for determining the service life of pneumatic conveying pipelines in industry. Even though the fly can be conveyed at low velocity dense phase mode, wear of pipeline conveying fly ash remained a critical issue for many power plant operators. In this paper the wear mechanisms in a fly ash conveying pipeline has been analyzed. Wear samples from fly ash conveying pipeline have been collected and analyzed for dominant wear mechanisms in the critical wear areas. Analysis of the worn pipeline showed continuous wear channels along the bottom of the pipeline consistent with the abrasive wear by larger particles. The other severe wear areas are the sections after the special bends used to reduce bend wear. Scanning electron microscope (SEM) analysis of the surfaces revealed that both erosive wear and abrasive wear mechanisms are present in these areas. Formation of a surface layer similar to transfer film in alumina conveying pipelines have been recognized in this analysis. These layers seem to be removed through brittle manners such as cracking and spalling. The wear mechanisms and the wear debris seen on the surface are consistent with wear by larger particles.

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.

This study used a 3D coupled CFD¿DEM model to assess how slugs tend towards steady state in single slug horizontal pneumatic conveying. Initial slug length, inlet velocity and initial stationary layer fractions were systematically varied for a total of 72 simulations. Previously made observation that slugs tend towards a steady state was confirmed via a theoretical derivation. The derivation shows that slugs move towards their steady state lengths exponentially. This allowed for a calculation of a characteristic time scale which is a measure of how quickly a slug tends towards the steady state. The theoretical estimate which is a function of slug porosity, steady length, velocity and stationary layer fraction has good agreement with simulated results. A link between steady slug length and solids loading ratio was also shown.

This paper presents the results of using an inertial measurement unit (IMU) to study various dynamic relationships in horizontal slug flow pneumatic conveying. The accuracy of the IMU was assessed and compared to particle image velocimetry (PIV) and once good agreement was confirmed it was used to investigate various aspects of slug flow. Relative movement between core particles and slugs tails and heads was assessed using relative pressures and quantified times spent in a slug. It was found that the propagation of particles backwards through a slug is relatively constant. Pressure-velocity relationship was observed that was theorised to be related to variations in stationary layer ahead of the slugs. Observations of further nuanced features of slug motion are also included to demonstrate the capabilities of IMUs in capturing the many dynamic aspects of the flow.

This paper presents a review of numerical models for simulation of gas-solid flow in bypass pneumatic conveying. The kinetic theory, conventional frictional-kinetic model and a new modified frictional-kinetic model are described in some detail. The experimental results for pressure drops based on a number of test cases are presented and compared with numerical results obtained with different numerical models. The convergences of the modified frictional-kinetic model with different values of constants are also illustrated. Moreover, the fluidisation charts of different materials with flow mode boundaries are presented to provide guidance on what frictional approach to use for Computational Fluid Dynamics (CFD) analysis of gas-solid flow in a bypass pneumatic conveying system. Furthermore, a flow chart for the CFD simulation methodology of bypass pneumatic conveying is demonstrated. These outcomes and the associated design guidelines could assist in choosing the most appropriate models for simulation of pneumatic conveying.

Economic drives dictate the exploitation of formerly less attractive ore bodies located close to or even beneath the water table. These ores can cause handling problems and expensive downtime of processing equipment due to their increased adhesive characteristics and are colloquially termed as "wet and sticky" ores.In order to gain a better understanding of the causes of poor performance in the handling process, experimental test methods for adhesion and cohesion within bulk solids samples were developed and validated. The results confirmed that adhesion of bulk solid to equipment surfaces is mainly governed by capillary pressure. It can therefore be described using the Young-Laplace equation, which implies that adhesion is primarily dependent on the interfacial water between bulk material and the adhesion partner. Accordingly, the governing material parameters of adhesion are its capillarity and permeability, as these two characterize water transport to or from the interface of the adhesion partners. Furthermore a threshold for the classification of a material as wet and sticky based on the measurements of adhesion and cohesion has been proposed.

Bypass pneumatic conveying is an alternative way to convey material which does not have dense phase transport capability. The computational fluid dynamics based commercial software Fluent 6.3 is used to investigate the pressure drop as well as the gas¿solid flow behaviour in a bypass pneumatic conveying system. The conveyed material was sand with a mean particle size of 378 µm and the solid loading ratio was in the range of 10¿123. The conventional frictional-kinetic model combining frictional and kinetic stresses simultaneously was applied for pressure drop prediction. The simulation results were then compared with experimental results from bypass pneumatic conveying tests. Selected image results from the computational fluid dynamics simulations were utilised and compared with images captured from high speed camera. In addition, a test case with low air mass flow rate and high solid loading ratio 82.49 was chosen as an example to show detailed gas¿solid flow behaviour in the simulation of highly dense flows. It was found that conventional frictional-kinetic model with modified packing limit and friction packing limit has greatly improved the pressure drop prediction result compared with kinetic theory without friction. The detailed analysis for the selected test case showed how the full bore dune formation and deformation of sand and bypass flutes interact. High amplitude fluctuations and variation in pressure and gas velocity were observed. The gas velocity vectors indicate a high degree of air penetration from the flute into the bypass pipe. This behaviour provides an aeration mechanism which is what makes the bypass system work and allows non-dense phase material to be conveyed in a dense mode of flow.

A new frictional-kinetic model is proposed and modified for pressure drop prediction of alumina in a bypass pneumatic conveying system. This new model is based on the conventional Johnson-Jackson frictional-kinetic model. The critical value of solids volume fraction and maximum packing limit are modified based on the fluidized bulk density and tapped bulk density, respectively. In addition, an offset solid volume fraction is introduced into the frictional pressure model as well as into the radial distribution functions which represents the correction factors to modify the probability of collisions between particles when solid phase becomes excessively dense. For the application of the model, computational fluid dynamics (CFD) simulations were conducted by using kinetic theory, conventional frictional-kinetic model and modified frictional-kinetic model. The simulation results were then compared with the experimental results. It was found that the modified frictional-kinetic model showed the largest improvement on pressure drop prediction results compared with results obtained from applying the kinetic theory and the conventional frictional-kinetic model, especially for denser flows with low air mass flow rates and high solid loading ratios (SLR). In addition, the solids volume investigation of CFD simulations shows a strong comparison to the actual flow conditions in the pipe, as transient slug type flow of alumina is observed.

In order to reveal the unsteady features of gas¿solid flow, the pressure fluctuations were measured at different locations along the length of the pipeline while conveying powders through the pipeline. Power spectral density (PSD) functions were obtained for the analysis of the pressure fluctuation. Two types of powders (fly ash and alumina) were used in this analysis. The PSD analysis was conducted by taking into account different aspects such as flow conditions (dilute or dense), location of transmitter (top and bottom transmitters), location of transmitter along the length of the pipeline (three different locations), material property (fly ash or alumina), etc. Analysis of signals from top and bottom transmitters shows that it is not possible to identify the flow mode at upper and lower portions of pipeline. The magnitude of power is found to be higher for alumina as compared to fly ash. PSD parametric analysis reveals that frequency bandwidth and average power decreases exponentially with increase in solid loading ratio.

Fine powders (Formula presented.)) behave analogously to liquids when aerated by air. Hence, methods (e.g. Couette method) used to determine the flow performance of liquids can be adopted to investigate the similar flow properties (e.g. apparent shear resistance) of aerated powders. By this means, the understanding and handling techniques for aerated fine powders can be significantly enhanced. This research aims to investigate the apparent shear resistance of aerated fine powders through a specialised viscometer. Such a viscometer is combined with a fluidisation system and a common rotary viscometer. Three types of fine powders (alumina, cement and flyash) were selected as testing materials. Experimental results indicated that aerated fine powders behave similarly to Herschel¿Bulkley non-Newtonian fluids. Subsequently, the apparent shear resistance for three fine powders were modelled by modifying the original Herschel¿Bulkley rheology model. Consequently, the apparent shear resistance of a specific aerated powder can be measured and modelled using the bench scale system developed in this study, thus can be utilised to predict the flow performance of fine powders in pneumatic conveyors.

The safe ocean transport of bulk cargoes on large bulk ships is vitally dependent on the stability of the cargo under the influence of the rolling pitching and yawing motion of the ship and the transmission of vibration from the ship's engine and propulsion machinery as well as wave motion induced whipping. Safety standards for ship transport are set by such bodies as the International Maritime Organisation with recommended tests for the assessment of bulk ores deemed suitable for safe ship transport. These test procedures are somewhat empirical and take no account of the well established and proven flow property tests, analysis and design methodologies widely accepted in field of bulk solids handling. These matters are discussed in this article. The stress states in loaded bulk cargoes are examined with respect to the establishment of maximum limits for surface rill angles as a function of a ship's roll angles.

Pressure drop in fluidized dense phase pneumatic conveying involves frictional interactions among gas, particle and pipe wall. There have been numerous correlations proposed by different researchers for predicting the pressure drop in fluidized dense phase conveying. In this paper steady state flow equations have been written for different phases and these equations are solved by assuming certain factors for different conveying materials. For writing the flow equations, a single gas phase and certain number of solids phases (which are chosen based on the particle size distribution of the conveying material) have been considered. Experimental data have been used as initial conditions at the exit of the pipeline in order to solve for the value of the flow parameters at the inlet of the pipeline. Experimental data have also been used to find the maximum possible conveying distance or maximum possible conveying pipeline diameter by imposing certain limiting conditions of conveying. Scaling equations for the solids mass flow rate and the air mass flow rate have been used to predict the pressure drop for different pipeline diameters and pipeline lengths. © 2012 Elsevier B.V.

Mathematical models of pneumatic conveying in dilute mode of flow have been presented by many researchers. Continuum approach is the most commonly used approach of modeling this kind of flow. In the present work a mathematical model has been developed which is in the form of governing equations such as continuity, momentum and energy equation. Energy equation has been written including a parameter called granular temperature. In this model, the dilute mode of conveying has been described as chaotically moving particles as granular gas characterized by granular temperature. Simulations have been performed in order to predict different parameters. The predicted pressure drop values were found to be in good agreement with the experimental data. Variations of important parameters such as absolute pressure, granular temperature along the length of the pipeline have been analyzed for different values of normal and restitution coefficients. © 2013 Elsevier B.V.

Pressure drop in pneumatic conveying is due to frictional interaction among gas, particle, and pipe wall. Fictional forces due to solids can be calculated using a solids friction factor. Many correlations have been proposed for predicting solids friction factor in dilute phase pneumatic conveying. These correlations are calculated based on value of the parameters calculated for a long pipeline or value of the parameter at the inlet of the pipeline. Pneumatic conveying in long pipelines suggests that some of the flow parameters are not constant along the length of the pipeline. This article presents a modeling technique for predicting solid friction factor taking into account of the local value of flow parameter. In this method, the solids friction factor is presented in terms of coefficient and exponents. The values of coefficient and exponents are predicted for fluidized dense phase conveying using different types of conveying materials. Values of coefficient and exponents are found to be different for different types of conveying materials. Variations of different parameters are studied using the calculated optimum values of coefficient and exponents. Experimental data are also used to find the possible maximum conveying distance or pipe diameter by imposing certain limiting conditions of conveying. © 2013 Copyright Taylor and Francis Group, LLC.

Air-gravity conveyors, commonly referred to as air-slides, are widely used in industry to convey bulk materials with the advantages of low particle velocities, low levels of particle attrition, potentially very high conveying rates and low power consumption. Most current designs are based on empirical design charts and past experience as there have been relatively few investigations attempting to model the flow of aerated powders on air-gravity conveyor systems. In this paper, ANSYS FLUENT has been used to simulate the air-gravity flow, where a steady, three-dimensional fluidized granular flow is considered in a rectangular channel having frictional side walls for different flow conditions. The results of simulated bed heights along the air-gravity channel are discussed. Moreover, this paper reports on work which attempts to develop a fundamental conveying model for air-gravity conveyor flows in inclined channels with an emphasis on the conservation of momentum taking into account the rheology of the gas-solid mixture. The conveying model shows the relationship between mass flow rate and bed height. The developed model well predicts the steady flow bed heights for each mass flow rate. A sensitivity analysis has been carried out which demonstrates that the conveying model can be applied to powders in a fluidized state to predict the bed heights of the flow under inclination angles between 1° to 10°.

The stationary layer of material between slugs in horizontal slug flow pneumatic conveying is an important reflection on the state and dynamics of a system. The gas-liquid analogy model of Konrad has been shown to accurately predict the layer fraction for a range of cases but the model breaks down near blockage conditions and does not consider material properties. A new model based on the rate of change of the layer fraction with respect to slug velocity was developed that accounts for material properties and is applicable at blockage conditions. Results from tests on polypropylene pellets were compared to the new model and the model of Konrad with both models satisfactorily predicting the layer fraction in the range of slug velocities that were observed for the material. At the higher extremity of slug velocity the new model predicted an earlier onset of a change in flow types than the model of Konrad which was supported by experimental observations but not enough data was obtained on the test material to compare predictions near blockage conditions. A material dependent constant in the new model was found for polypropylene pellets with further investigations needed to explore this constant as a predictive or classifying tool for materials and their ability to slug.

Erosion is observed in many industrial situations such as pneumatic conveying pipelines, shot peening and sand blasting where interaction between particle and surface is expected. A number of particle impact parameters and material surface properties are involved in the erosion process. Extensive studies have been conducted to understand the effects of the process parameters on erosion; however, only limited studies can be found in the literature associated with material surface and subsurface properties. In order to get a better understanding of the material surface and subsurface behaviour due to particle impacts for different parameters, erosion tests were performed for different impact angles and different particle velocities using a micro-sandblaster. Angular silicon carbide (SiC) particles were impacted on two different ductile surfaces, mild steel and aluminium, with a constant particle flux. Wear mechanisms were studied in terms of particle kinetic energy. Subsequently, the worn surfaces and their cross-sections were observed using scanning electron microscope (SEM) to relate the subsurface damage characteristics to different impact conditions, and to wear mechanisms. Results showed that at a lower impact angle, material was removed through cutting mechanism, while at a higher angle; material removed through predominantly deformation process. Also, subsurface cracking and subsurface damage were observed up to a certain depth from the worn surface. It appears both the depth of subsurface cracking and subsurface damages increases with increasing impact velocity. The variation is consistent with increase in surface and subsurface temperature at higher velocities. With increased temperature, the depth of the heat affected zone increases, which increases the work hardening layer thickness. In addition, subsurface microstructural damage is consistent with attainment of higher temperature which can be explained through the high strain-rate deformation and thermo-physical properties of the surface.

Bypass pneumatic conveying systems provide the capacity of transporting some materials that are not naturally suited to dense phase flow in a low velocity, dense phase flow regime. Bypass pneumatic conveying systems also provide a passive capability to reduce minimum particulate transport velocities. Therefore, particle degradation and pipe line wear can be much reduced. In this paper, the operation of internal bypass system was investigated by both experiments and modelling. An entire bypass system was numerically modelled based on the mass conservation. An integrated version of the Ideal Gas Equation was applied to evaluate pressures at the central point of each node for air flow in the bypass pipe and the main pipe. The bypass pneumatic experimental system was built with a main pipe of 79mm in diameter and an internal bypass pipe with orifice plate flute arrangement. Fly ash and alumina were used in the tests. High speed video camera visualization and differential pressure transmitters were employed to investigate the operation of dense phase bypass pneumatic transport systems and the mechanism of material blockage inhibition provided by this system. The bypass system was found to consume more energy than conventional system when using the same air mass flow rate due to the increase of friction. The conveying velocity of alumina in bypass system was much lower than that of conventional pipelines, which resulted in much reduced specific energy consumption. In this system, particulate material blockages were inhibited in bypass systems due to the air penetration into the particulate volume, as was reflected in differential pressure transmitter measurement data and flow visualization.