An asymptotic description of electrostatic precipitation of charged particles in turbulent flow

Abstract

The collection efficiency of electrostatic precipitators is calculated from the transport equations for constant eddy diffusivity and mean velocity. For the non-collecting wall, a zero-flux boundary condition is used, whereas for the collecting wall, a radiation-type boundary condition is used, which is derived from the constant-flux solution of the turbulent diffusion equation. Two approximate solutions are derived, one for small values of the ratio between precipitation and friction velocity and one for large values of the velocity ratio. The two approximate solutions derived are shown to be in good agreement with the numerical solution of the transport equation. An increase in the turbulent friction velocity is shown to enhance collection efficiency for small velocity ratios, but reduce it for large ones. An indication of the effect of dust layer roughness on the performance of an electrostatic precipitator is also considered and it is shown that for small values of the velocity ratio collection efficiency increases with roughness height, but remains unaffected by it for higher values of that ratio.