Experimental examination of the redispersion behavior of particles in electrostatic fields

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Within the last period of the project the specific resistance of SiO2 - and Al2O3 - particle layers has been measured as well as the detachment of particles from the uppermost layer when subjected to an air-flow within an electrical field superimposed by a corona. The specific resistance of SiO2 and Al2O3 particle layers shows a non-Ohmic behavior. It is dependent on the dust layer thickness. Constant values of specific resistance for the SiO2 - and Al2O3 - particle layers only were obtained after 16 hours (or more). This rather long equalizing period cannot be explained as a whole by adsorption and desorption kinetics of H2O onto and from the particle layers. It is rather presumed, that the thermic and electric equalizing periods are superimposed with the electric equalization periods lasting much longer. In measuring the detachment of particles from the uppermost layer a correlation between the charge within the dust layer and the detachment of particles can be observed. In presence of a corona charges are transferred into the dust layer and the adhesion forces between particles increase. When switching off the corona, the charges remain for a couple of seconds within the particle layer. Only thereafter a detachment of particles can be identified.Within the next period specific currents inducing back discharge (back corona) within SiO2, Al2O3 and fly ash particle layers should be measured to quantify the dependence on dust layer thickness and time. In cooperation with Prof. Riebel in Cottbus the measurement of specific resistance of particle layers should be extended and performed onward. A joint publication is planned on basis of these measurements. For the next period of the project it is proposed to quantify the detachment of particles from the uppermost layer when applied to an electrical field superimposed by a corona and an air-flow. The measurement range should be extended by imposing the particle layer to the corona and to the electrical field for longer periods. Data thus obtained will be compared to experimental data from particle-particle adhesion forces measurement by the group of Prof. Riebel and particle-particle adhesion forces simulations performed by the group of Prof. E. Schmidt in Wuppertal. It is also planned to implement routines with the commercial simulation framework ANSYS-Fluent to simulate the detachment of particle layers. Numerical simulation of forces on particles in complex flow fields has been successfully implemented in the past period.