Investigation of particle-surface impacts in pneumatic conveying systems

The work reported in this thesis aims to investigate single particle impacts typical of those occurring in pneumatic conveying systems through experimental investigations, simple analytical models of the measurement system and finite element analysis modelling. The experimental section can be divided into two main areas, the experiments undertaken using a piezoelectric force transducer and the experiments using conducting particles in an electrical resistance circuit. The experimental results for two different types of material and two different particle diameters for each material type have shown that the short contact time can excite a resonant response in a piezoelectric force transducer, a result which will be useful in informing measurements of this type. The results for the electrical resistance circuit have shown good agreement with Hertz theory for elastic contact, but show a better correlation with the theory for a two particle impact than they do for a particle against a mass flat surface.

The analytical modelling section reports on outcomes based on previous work and on the development of two new models of a particle impacting a measurement system. In the first of the two new models the particle is modelled as a time varying force impacting a measurement system modelled as a mass-spring system. The second new model models the particle as a mass-spring system impacting the same measurement system model. The simple mass-spring models of the measurement system were used to demonstrate the influence of the time of application of force to the response of a resonant system, and showed good qualitative agreement with the experimental results for long and short contact time events. The models were also used to make general statements about the relative mass and stiffness of the measurement system compared to the particle. It was concluded that the mass of the measurement system should be much larger than the particle, and the measurement system should always be much stiffer also. In practice the latter is harder to achieve than the former. This information will assist in the design of measurement systems for short contact time impacts.

The finite element analysis modelling firstly compared the suitability of two different commercial solvers to the axisymmetric modelling of a particle with a surface based on the work of Wu et al (2005). The comparison of these results represented a comparison of the contact time from Wu et al (2005) and from Hertz theory for an elastic collision, and also a comparison of the size of the impact substrate relative to the particle radius. The success of the ANSYS LS-DYNA software in replicating these results led to the modelling of the response of the piezoelectric force transducer measurement system. The piezoelectric crystal material in the model was defined as isotropic and with no electromechanical properties, and a range of impact particle materials and sizes were modelled. The purpose of these models was to determine the effect on the contact time at the point of impact and on the response of the piezoelectric crystal material to the applied force resulting from the impact. These models have shown potential in predicting the contact force and the contact time, and have shown that for particles typical of those conveyed pneumatically that the actual contact time is not changed as a result of the presence of the piezoelectric force transducer. The output from the piezoelectric crystal material nodes has shown good qualitative agreement with the experiment and it is this model data that will be used in the future to predict contact times for small particles. This prediction would be achieved through a combination of the previous experimental measurements and the outputs from the model showing the response of the piezoelectric crystal nodes to the impact event.