Drop breakage and coalescence influence the particle formation in liquid-liquid dispersions. In order to reduce the influencing factors of the whole dispersion process, single drops where coalescence processes can be ...Drop breakage and coalescence influence the particle formation in liquid-liquid dispersions. In order to reduce the influencing factors of the whole dispersion process, single drops where coalescence processes can be neglected were analyzed in this work. Drops passing the turbulent vicinity of a single stirrer blade were investi- gated by high-speed imaging. In order to gain a statistically relevant amount of drops passing the area of interest and corresponding breakage events, at least 1600 droplets were considered for each parameter set of this work. A specially developed fully automatic image analysis based on Matlab was used for the evaluation of the resulting high amount of image data. This allowed the elimination of the time-consuming manual analysis and further- more, allowed the objective evaluation of the drops＇ behavior. Different deformation parameters were consid- ered in order to describe the drop deformation dynamics properly. Regarding the ratio of both main particle axes （0axes）, which was therefore approximated through an ellipse, allowed the determination of very small de- viations from the spherical shape. The perimeter of the particle （0peri） was used for the description of highly de- formed shapes. In this work the results of a higher viscosity paraffin oil （ηd =127 mPa. s） and a low viscosity solvent （petroleum, ηd = 1.7 mPa-s） are presented with and without the addition of SDS to the continuous water phase. All results show that the experimentally determined oscillation but also deformation times underlie a wide spreading. Drop deformations significantly increased not only with increasing droplet viscosity, but also with decreasing interfacial tension. Highly deformed particles of one droplet species were more likely to break than more or less spherical particles. As droplet fragmentation results from a variety of different macro-scale de- formed particles, it is not assumed that a critical deformation value must be reached for the fragmentation pro- cess to occur. Especially for highly deformed particles thin particle filaments are assumed to induce the breakage process and, therefore, be responsible for the separation of drops.展开更多
Particle size distribution significantly influences the mechanical response of the ballast under low confining pressure.However,particle breakage usually occurs and unfavorably degrades the particle size distribution ...Particle size distribution significantly influences the mechanical response of the ballast under low confining pressure.However,particle breakage usually occurs and unfavorably degrades the particle size distribution of the ballast when sufficient load is applied.To model the triaxial stress-strain behavior and its associated evolution of particle size distribution of the ballast,a specific bounding surface model is proposed.The proposed model is based on the traditional bounding surface plasticity and a modified particle breakage index,which correlates the initial gradation and the ultimate gradation together with the current gradation.Simulation of the experimental results from the triaxial compression tests shows that the proposed model can predict the strain softening and volumetric expansion of the ballast under relatively lower confining pressure.It is also able to simulate the strain hardening and volumetric compression of the ballast under relatively higher confining pressure.Most importantly,the proposed approach was observed to have a great potential in predicting the evolution of the particle size distribution of the ballast.展开更多
基金supported by the German Research Foundation (DFG) within the project "Modelling,Simulation,and Control of Drop Size Distributions in Stirred Liquid/liquid Systems - KR1639/15-1"the "Max-Buchner-Forschungsstiftung"
文摘Drop breakage and coalescence influence the particle formation in liquid-liquid dispersions. In order to reduce the influencing factors of the whole dispersion process, single drops where coalescence processes can be neglected were analyzed in this work. Drops passing the turbulent vicinity of a single stirrer blade were investi- gated by high-speed imaging. In order to gain a statistically relevant amount of drops passing the area of interest and corresponding breakage events, at least 1600 droplets were considered for each parameter set of this work. A specially developed fully automatic image analysis based on Matlab was used for the evaluation of the resulting high amount of image data. This allowed the elimination of the time-consuming manual analysis and further- more, allowed the objective evaluation of the drops＇ behavior. Different deformation parameters were consid- ered in order to describe the drop deformation dynamics properly. Regarding the ratio of both main particle axes （0axes）, which was therefore approximated through an ellipse, allowed the determination of very small de- viations from the spherical shape. The perimeter of the particle （0peri） was used for the description of highly de- formed shapes. In this work the results of a higher viscosity paraffin oil （ηd =127 mPa. s） and a low viscosity solvent （petroleum, ηd = 1.7 mPa-s） are presented with and without the addition of SDS to the continuous water phase. All results show that the experimentally determined oscillation but also deformation times underlie a wide spreading. Drop deformations significantly increased not only with increasing droplet viscosity, but also with decreasing interfacial tension. Highly deformed particles of one droplet species were more likely to break than more or less spherical particles. As droplet fragmentation results from a variety of different macro-scale de- formed particles, it is not assumed that a critical deformation value must be reached for the fragmentation pro- cess to occur. Especially for highly deformed particles thin particle filaments are assumed to induce the breakage process and, therefore, be responsible for the separation of drops.
基金supported by the China Scholarship Council in the University of Wollongong(Grant No.201306710022)
文摘Particle size distribution significantly influences the mechanical response of the ballast under low confining pressure.However,particle breakage usually occurs and unfavorably degrades the particle size distribution of the ballast when sufficient load is applied.To model the triaxial stress-strain behavior and its associated evolution of particle size distribution of the ballast,a specific bounding surface model is proposed.The proposed model is based on the traditional bounding surface plasticity and a modified particle breakage index,which correlates the initial gradation and the ultimate gradation together with the current gradation.Simulation of the experimental results from the triaxial compression tests shows that the proposed model can predict the strain softening and volumetric expansion of the ballast under relatively lower confining pressure.It is also able to simulate the strain hardening and volumetric compression of the ballast under relatively higher confining pressure.Most importantly,the proposed approach was observed to have a great potential in predicting the evolution of the particle size distribution of the ballast.
