BIPOLAR DIFFUSION CHARGING : EXPERIMENTAL AND THEORETICAL EVALUATION OF THE PARAMETERS AFFECTING THE CHARGE DISTRIBUTION OF NANOPARTICLES IN THE SIZE RANGE 10-100 nm

Experiments involving measurements of the charged ratio of particles having sizes in the range 10-100 nm that have undergone bipolar diffusion charging, are reported in this thesis. The effect of relative humidity levels of the carrier gas to the process of bipolar diffusion charging was investigated. Measurements of the bipolar charging ratio were taken for different values of relative humidity. The experimental results were compared with calculations of the Fuchs’ limiting sphere for the case of bipolar diffusion charging. The values calculated by the model show good agreement with the widely accepted ones provided by Wiedensohler (1988). Results from the measurements show that higher relative humidity in the carrier gas causes smaller charging ratio applied to the particles. Measurements of the charging ratio were also taken in order to determine the effect of altering the charge neutralizer radioactivity. Moreover, measurements were taken for two different aerosol flow rates, in order to estimate if the particles have reached the charge distribution equilibrium. Results show that the radioactivity values investigated, do not provoke significant change on the charging ratio of the particles