Validating a triboelectric charging and electrostatics model for gas-particle flows
Sippola, Petteri (2017)
Sippola, Petteri
2017
Ympäristö- ja energiatekniikka
Teknis-luonnontieteellinen tiedekunta - Faculty of Natural Sciences
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Hyväksymispäivämäärä
2017-06-07
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tty-201705261540
https://urn.fi/URN:NBN:fi:tty-201705261540
Tiivistelmä
In fluidized beds and pneumatic conveyors triboelectric charging is generally an undesirable phenomenon, as it causes agglomeration of charged particles on the walls. At worst, agglomeration of the particles and other side-effects of triboelectric charging can reduce the performance of a fluidized bed or a conveyor significantly.
In the thesis, a triboelectric charging model built onto a CFD-DEM (Computational Fluid Dynamics-Discrete Element Method) model is utilized for simulating a small fluidized bed of monodisperse particles. In the model, charge transfer is governed by the effective work function difference between the particles and the wall.
The simulation results are compared to experimental results measured in relative humidities ranging from 0 % to 60 %. It is found that the simulations capture qualitatively the most appreciable side-effect of triboelectric charging, as a layer of strongly charged particles is adhered to the wall. However, this phenomenon is not as pronounced as in the experiments, where multiple layers of particles agglomerate on the wall.
This discrepancy between the simulations and the experiments reflects to other aspects as well: for example the pressure drop over a simulated bed shows almost no change during the fluidization, while in the experiments a significant decrease in pressure drop is observed due to particle agglomeration. For more realistic results, the agglomeration of the particles should be better captured by the computational model.
In the thesis, a triboelectric charging model built onto a CFD-DEM (Computational Fluid Dynamics-Discrete Element Method) model is utilized for simulating a small fluidized bed of monodisperse particles. In the model, charge transfer is governed by the effective work function difference between the particles and the wall.
The simulation results are compared to experimental results measured in relative humidities ranging from 0 % to 60 %. It is found that the simulations capture qualitatively the most appreciable side-effect of triboelectric charging, as a layer of strongly charged particles is adhered to the wall. However, this phenomenon is not as pronounced as in the experiments, where multiple layers of particles agglomerate on the wall.
This discrepancy between the simulations and the experiments reflects to other aspects as well: for example the pressure drop over a simulated bed shows almost no change during the fluidization, while in the experiments a significant decrease in pressure drop is observed due to particle agglomeration. For more realistic results, the agglomeration of the particles should be better captured by the computational model.