Experimental examination of the redispersion behavior of particles in electrostatic fields

在项目的最后阶段，测量了SiO_2和Al_2O_3颗粒层的比电阻，以及颗粒在叠加电晕的电场中受到气流时从最上层脱离的情况。SiO_2和Al_2O_3颗粒层的比电阻表现为非欧姆行为。这取决于尘埃层的厚度。只有SiO_2和Al_2O_3颗粒层的比电阻在16小时(或更长时间)后才获得恒定值。这一相当长的均衡期不能用H2O在颗粒层上和从颗粒层上的吸附和解吸动力学来解释。更确切地说，热均衡期和电均衡期是叠加的，电均衡期持续的时间要长得多。在测量粒子从最上层剥离时，可以观察到尘埃层内的电荷与粒子剥离之间的关系。在电晕的存在下，电荷转移到粉尘层，颗粒之间的粘附力增加。当关闭电晕时，电荷会在粒子层中保留几秒钟。在下一个周期内，应测量在SiO_2、Al_2O_3和飞灰颗粒层内诱发反向放电(反电晕)的特定电流，以量化粉尘层厚度和时间的依赖关系。在Cottbus中与Riebel教授合作，颗粒层的比阻测量应该扩大并继续进行。计划在这些衡量标准的基础上联合出版。在该项目的下一阶段，建议量化粒子在施加由电晕和气流叠加的电场时从最上层脱离的情况。测量范围应通过在电晕和电场上施加更长时间的粒子层来扩展。这样得到的数据将与Riebel教授小组测量的颗粒-颗粒粘附力的实验数据和E.Schmidt教授在Wuppertal的小组进行的颗粒-颗粒粘附力模拟的实验数据进行比较。还计划使用商业模拟框架Ansys-FLUENT来实现例程，以模拟颗粒层的脱离。在过去的一段时间里，复杂流场中颗粒受力的数值模拟已经成功地实现了。

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.