GRADE EFFICIENCY AND EDDY DIFFUSIVITY MODELS

Particle transport in electrical precipitators modeled by the convecti ve diffusion equation is governed by two dimensionless quantities: the Peclet number w(th)s/D and electrical drift parameter w(th)/v. What i s concerning practical aspects, in particular grade efficiency, it doe s not make sense to keep, e.g. the electrical drift parameter constant and to vary the Peclet number or vice versa because both quantities a re functions of particle size. Therefore, this paper shows calculated efficiency results as function of particle size for different but corr esponding parameter settings by using published analytical solutions ( case of a homogeneous electrical field) and numerical solutions (case of inhomogeneous electrical field). Using the analytical solutions the grade efficiency especially for particle sizes < 0.5 mum is almost in dependent of the value of the Eddy diffusivity. Considering the local character of the electrical field by using a numerical solution the gr ade efficiency for particles < 0.5 mum is always worse than that befor e and the curves are indeed dependent of the Eddy diffusivity value. T he influence of a homogeneous ionic space charge on the grade efficien cy can also be demonstrated.