Investigations into the Local Mass Flux of Dust to Be Precipitated at the Collecting Electrode

The paper is dealing with the presentations of collecting efficiencies of electrostatic precipitators. Whereas the total separation efficiency and effective migration rates respectively bear some problems in interpretation and discussion an observation of the flux of locally precipitated dust should lead to more clarity and an improved insight of precipitation because it is only based on physical terms. The paper presents model calculations accounting for the size-dependent local particle transport. The local mass flux was calculated for varying median particle size and width of the particle size distribution. One interesting result is the influence of the classification along the duct, due to the size dependence of the particle migration velocity, on the local mass flux. It causes an increasing curvature resulting in a higher flux at the entrance of the precipitator, and a higher flux at the outlet for increasing width of the particle size distribution. Furthermore one can show that higher fluid velocities cause a shift of the classification towards the back part of the precipitator. Furthermore an integration over the precipitator length yields the total mass flux and therefore the total separation efficiency may be calculated. From this quantity effective migration rates weff according to the modelequations of Deutsch and Matts-Öhnfeldt can be recalculated. The so-called 'applied Deutsch-equation' yields a weff which is very sensitive to the classification effect whereas the empirical formula by Matts and Öhnfeldt yields a weff which is less sensitive in a certain range. Preliminary experimental investigations of the local precipitated dust show the influence of an evolving particle concentration profile at the entrance of the duct.