Correlations of Single-Stage and Cascaded Two-Stage Single-Stage Precipitation Efficiencies to Particle Resistivity

Precipitation efficiencies for redispersed welding smoke are measured as functions of humidity and hence resistivity for a single-stage precipitator and for a cascaded two-stage-single-stage combination. Weight efficiencies are obtained through measurements of dust delivered by a feeder apparatus and dust collected on a filter beyond the precipitation section. A maximum in collection efficiency occurs at an intermediate resistivity value, with decreasing efficiency at high resistivities due to back ionization and decreasing efficiency at low resistivities due to a reversal in direction of the electrical force on the precipitated layer. The cascaded combination yields increased efficiency over the single-stage acting alone over the entire range of resistivity values.