A numerical simulation is conducted to investigate the effect of the ionic wind and the effect of the electro-hydro-dynamic (EHD) flow field on the collection efficiency of a duct type electrostatic precipitator for the case of submicron size dust particles. The calculations for the ionic flow field and the EHD flow field are carried out by the Finite Element Method. Re- sults show that the flow pattern of gas in the EHD flow field depends on the EHD number. The collection efficiencies are at minimum values when the particle diameter is about 0.3 μm, both without and with the ionic wind. The collection efficiency is reduced considerably in the EHD flow field. An increase in the EHD number does not always mean that the collection efficiency will increase uniformly. The collection efficiency curves have maximum values at the EHD numbers which range within the limits in the case that the particle size is from 0.05 to 0.30 μm approximately.
Twomey's nonlinear iteration method was applied to retrieve the size distribution of atmospheric aerosols from data obtained by an Andersen low-pressure impactor. Effects of some factors on the inversion results were investigated using numerically generated data for unimodal and bimodal lognormal functions. The factors were weighting functions, first-guess distributions and treating the ends of the distribution. The pth power of response function was adopted as a weighting function and a value of 0.7 was selected for the inversion of data in most cases. Smoothed initial distribution with the treatment of the ends of the distribution gave good results in case of the distribution showing a peak near the first stage of the impactor, while uniform initial guess resulted in an oscillatory distribution. We proposed a new stopping criterion based on experimental errors which represent random errors in mass measurement and sample fluctu- ation. and the criterion is useful for inverting the data involving random errors. The procedure was also applied to estimate the size distribution for ambient aerosol samples.