Correlation between current density and layer structure for fine particle deposition in a laboratory electrostatic precipitator

On the basis of the occurrence of a geometrical pattern for the dust layer deposited in an electrostatic precipitator, the physical phenomena leading to such a deposit are characterized. The measurement of the current-density distribution on the collecting plate shows that the dust layer pattern is strongly correlated with this distribution, leading to two kinds of deposition: zones of dense packing and zones of dendritic packing. Some explanations about the observed pattern are proposed. The size distribution of the collected powder is determined for the two zones of collection and as a function of the distance downstream from the precipitator entrance. This analysis reveals the existence of a clear difference in the size distributions of deposited powder in the two collection zones. A Deutsch-like model fairly well accounts for the observed decrease of mean diameter of the collected particles as a function of the distance downstream from the precipitator entrance. In the light of some considerations on re-entrainment and electrohydrodynamic secondary flows, possible mechanisms leading to such phenomena are briefly discussed.