REFLECTIONS ON SIMILARITY LAWS CONCERNING PARTICLE-TRANSPORT IN ELECTRICAL PRECIPITATORS

Measurements in three geometrically similar wire-plate precipitators s how that in the cases of constant current density at the collecting pl ates or constant electrical field strength, larger geometries give bet ter grade efficiencies. If a dimensionless voltage (found by dimension al analysis) is held constant, the grade efficiencies are no longer de pendent on the absolute precipitator size. Introducing an 'electrical drift parameter', a generalized representation of measured and (accord ing to Deutsch) calculated grade efficiencies can be found which turns out to be a scale-up invariant in the case of constant dimensionless voltage. Overall, the results show that with decreasing particle size the measured efficiencies become increasing better than the calculated ones. For particles smaller than 1 mu m, there is little difference b etween the Deutschian and Laminar models. When common models are appli ed with space averaged values for the electrical field strength (with consideration of the ionic space charge) instead of the simple field s trength value, then a qualitatively correct scale-up behaviour emerges with respect to the grade efficiency trends. Two parameters are decis ive: the electrical drift parameter, which includes the operational st ate of the precipitator, and the relative length of the collecting zon e.