Packed bed reactors of non-spherical particles are widely used in chemical industry with the aim to obtain a high active surface area and achieve a homogeneous flow.Despite this,little is known about the arrangement o...Packed bed reactors of non-spherical particles are widely used in chemical industry with the aim to obtain a high active surface area and achieve a homogeneous flow.Despite this,little is known about the arrangement of particles within the bed and the influence of this arrangement on the fluid flow distribution.Magnetic Resonance Imaging (MRI) is a non-invasive tomographic imaging technique that allows 3D visualisation of the packing and flow structure.However,the individual particle information is not obtained using MRI.In this work we investigate different particle detection methods to retrieve the particle position and orientation from MRI images.Results show the successful reconstruction of random packing structures of various non-spherical particle shapes: ellipsoid,spherocylinder,cylinder and cube.The applicability of each method in relation to the particle shape,as well as strengths and drawbacks of each particle detection method are discussed.This paper shows the ability to reconstruct real packed beds of non-spherical particle shapes from MRI images,which opens several research opportunities in the field of chemical engineering.展开更多
The imaging of particulate media – encompassing both the imaging of the particles themselves,as well as the study of their dynamics and bulk properties and behaviours – is crucial to improving our understanding of a...The imaging of particulate media – encompassing both the imaging of the particles themselves,as well as the study of their dynamics and bulk properties and behaviours – is crucial to improving our understanding of a diverse range of phenomena and processes spanning numerous scientific disciplines and industrial sectors.Despite interdisciplinary interest in the field and the availability,and continuous development,of a wide range of different imaging techniques,there exist nonetheless a number of limitations of these techniques,and open challenges – both technical and non-technical – facing the field as a whole.In this perspective,we discuss in detail five such challenges,identified by a team of interdisciplinary experts spanning both academia and industry: how can we work toward the imaging of systems which are more ‘real-world-relevant’,both in terms of composition and scale? How can we extract detailed,quantitative information regarding stresses from such systems? How can we image processes which are both rapid and transient,when most current technologies can manage (at best) only one of these states? How can we ensure closer and more fruitful collaboration between the academics developing particle imaging technologies and the potential industrial end-users who stand to benefit from them? How can we improve the visibility of the field and the educational opportunities available to the potential next generation of particle technologists? As one may expect for such a broad range of questions,the answers to the above are diverse and numerous.However,there are certain key themes running through them.Above all,our work highlights a need for improved collaboration,be that in terms of experts in multiple different imaging technologies working together to perform multi-modal studies so as to address the technical limitations highlighted above,researchers and industry professionals finding new ways to engage,or academics co-creating open-source educational tools to support the next generation of particle imaging experts.展开更多
In this work, the borescopic particle image velocimetry (BPIV) technique was applied to a bubbling gas-solid fluidized bed, and the results were compared with published positron emission particle tracking (PEPT) measu...In this work, the borescopic particle image velocimetry (BPIV) technique was applied to a bubbling gas-solid fluidized bed, and the results were compared with published positron emission particle tracking (PEPT) measurement data. Before performing the experiments, the sensitivity of the BPIV results to the illumination power, light reflectivity of the particles, and location of the borescope was also investigated. The BPIV and PEPT results were in fair agreement;however, some discrepancies were observed.The difference between the two sets of results were mainly caused by the intrusiveness of BPIV, the fact that the local solids volume fraction was not accounted for in the BPIV analysis, and the intrinsic differences of these two methods. Therefore, measurement of the local solids volume fraction with the borescope is highly recommended for further development of the BPIV method, which will also enable measureme nt of the local solids mass fluxes in side dense gas-solid fluidized beds.展开更多
The coefficient of restitution is widely used to characterize the energy dissipation rate in numerical simulations involving particle collisions. The challenge in measuring the coefficient of restitution is the strong...The coefficient of restitution is widely used to characterize the energy dissipation rate in numerical simulations involving particle collisions. The challenge in measuring the coefficient of restitution is the strong scatter seen in experimental data that results from varying particle properties, i.e. shape and surface roughness, and from imperfections in the experimental technique. To minimize this scattering, a novel experimental setup was developed based on two synchronized high-speed cameras capturing the collision behaviour of a particle in three dimensions. To measure the wet restitution coefficient, which describes particle impact in the presence of a liquid layer in the contact region, additional accuracy can be achieved by measuring the liquid layer thickness by a high-precision optical confocal sensor. The coefficient of restitution was measured for glass particles with two different diameters, at different relative velocities and liquid layer thicknesses, with a focus on small collision velocities and thin liquid layers, using both the improved （three dimensional） and the conventional （two dimensional） approaches to quantify the improvement of the new method＇s accuracy.展开更多
In this work, a new methodology is introduced to calculate the solids mixing rate in dense gas-fluidized beds using the two-fluid model. The implementation of this methodology into an existing two-fluid model code was...In this work, a new methodology is introduced to calculate the solids mixing rate in dense gas-fluidized beds using the two-fluid model. The implementation of this methodology into an existing two-fluid model code was carefully verified. The solids phase continuity equation was satisfied using our method, and the sensitivity of the computational results to the time step, computational cell size, and discretization scheme was investigated to determine the optimal simulation settings. Using these simulation settings, the degree of solids mixing was observed to rapidly （exponentially） increase with increasing operating pressure and linearly decrease with increasing bed diameter. Our novel methodology can be applied to analyze mixing processes in large lab-scale beds as an alternative to existing time-consuming simulation techniques such as computational fluid dynamics combined with the discrete element model.展开更多
文摘Packed bed reactors of non-spherical particles are widely used in chemical industry with the aim to obtain a high active surface area and achieve a homogeneous flow.Despite this,little is known about the arrangement of particles within the bed and the influence of this arrangement on the fluid flow distribution.Magnetic Resonance Imaging (MRI) is a non-invasive tomographic imaging technique that allows 3D visualisation of the packing and flow structure.However,the individual particle information is not obtained using MRI.In this work we investigate different particle detection methods to retrieve the particle position and orientation from MRI images.Results show the successful reconstruction of random packing structures of various non-spherical particle shapes: ellipsoid,spherocylinder,cylinder and cube.The applicability of each method in relation to the particle shape,as well as strengths and drawbacks of each particle detection method are discussed.This paper shows the ability to reconstruct real packed beds of non-spherical particle shapes from MRI images,which opens several research opportunities in the field of chemical engineering.
文摘The imaging of particulate media – encompassing both the imaging of the particles themselves,as well as the study of their dynamics and bulk properties and behaviours – is crucial to improving our understanding of a diverse range of phenomena and processes spanning numerous scientific disciplines and industrial sectors.Despite interdisciplinary interest in the field and the availability,and continuous development,of a wide range of different imaging techniques,there exist nonetheless a number of limitations of these techniques,and open challenges – both technical and non-technical – facing the field as a whole.In this perspective,we discuss in detail five such challenges,identified by a team of interdisciplinary experts spanning both academia and industry: how can we work toward the imaging of systems which are more ‘real-world-relevant’,both in terms of composition and scale? How can we extract detailed,quantitative information regarding stresses from such systems? How can we image processes which are both rapid and transient,when most current technologies can manage (at best) only one of these states? How can we ensure closer and more fruitful collaboration between the academics developing particle imaging technologies and the potential industrial end-users who stand to benefit from them? How can we improve the visibility of the field and the educational opportunities available to the potential next generation of particle technologists? As one may expect for such a broad range of questions,the answers to the above are diverse and numerous.However,there are certain key themes running through them.Above all,our work highlights a need for improved collaboration,be that in terms of experts in multiple different imaging technologies working together to perform multi-modal studies so as to address the technical limitations highlighted above,researchers and industry professionals finding new ways to engage,or academics co-creating open-source educational tools to support the next generation of particle imaging experts.
文摘In this work, the borescopic particle image velocimetry (BPIV) technique was applied to a bubbling gas-solid fluidized bed, and the results were compared with published positron emission particle tracking (PEPT) measurement data. Before performing the experiments, the sensitivity of the BPIV results to the illumination power, light reflectivity of the particles, and location of the borescope was also investigated. The BPIV and PEPT results were in fair agreement;however, some discrepancies were observed.The difference between the two sets of results were mainly caused by the intrusiveness of BPIV, the fact that the local solids volume fraction was not accounted for in the BPIV analysis, and the intrinsic differences of these two methods. Therefore, measurement of the local solids volume fraction with the borescope is highly recommended for further development of the BPIV method, which will also enable measureme nt of the local solids mass fluxes in side dense gas-solid fluidized beds.
文摘The coefficient of restitution is widely used to characterize the energy dissipation rate in numerical simulations involving particle collisions. The challenge in measuring the coefficient of restitution is the strong scatter seen in experimental data that results from varying particle properties, i.e. shape and surface roughness, and from imperfections in the experimental technique. To minimize this scattering, a novel experimental setup was developed based on two synchronized high-speed cameras capturing the collision behaviour of a particle in three dimensions. To measure the wet restitution coefficient, which describes particle impact in the presence of a liquid layer in the contact region, additional accuracy can be achieved by measuring the liquid layer thickness by a high-precision optical confocal sensor. The coefficient of restitution was measured for glass particles with two different diameters, at different relative velocities and liquid layer thicknesses, with a focus on small collision velocities and thin liquid layers, using both the improved （three dimensional） and the conventional （two dimensional） approaches to quantify the improvement of the new method＇s accuracy.
文摘In this work, a new methodology is introduced to calculate the solids mixing rate in dense gas-fluidized beds using the two-fluid model. The implementation of this methodology into an existing two-fluid model code was carefully verified. The solids phase continuity equation was satisfied using our method, and the sensitivity of the computational results to the time step, computational cell size, and discretization scheme was investigated to determine the optimal simulation settings. Using these simulation settings, the degree of solids mixing was observed to rapidly （exponentially） increase with increasing operating pressure and linearly decrease with increasing bed diameter. Our novel methodology can be applied to analyze mixing processes in large lab-scale beds as an alternative to existing time-consuming simulation techniques such as computational fluid dynamics combined with the discrete element model.
