The collection efficiency is traditionally expressed by the classical Deutsch formula:
where A (m2) is the projected area of the collecting plates, and Q (m3/s) is the flow rate. The particle migration velocity designated, may be considered as an expression of the velocity at which the dust particles move towards the collecting plates under the influence of electrical forces in a fully developed turbulent flow environment.
The migration velocity depends on the particle size, the gas velocity in the filter, the DC voltage, etc. Therefore it is difficult to determine the migration velocity theoretically. Most electrostatic precipitator manufacturers have performed thorough investigations on industrial electrostatic precipitators and through experiments, determined the migration velocity to use when calculating their filters.