On unipolar diffusion charging of aerosols in the continuum regime

Some recently completed unipolar diffusion charging experiments in the continuum regime are described. Monodisperse acrosols generated by the vibrating orifice generator and the mobility classification method were exposed to unipolar positive ions produced by a corona discharge under conditions approximating pure ionic diffusion, and the resulting particle charge was measured as a function of the charging parameter, N₀t, where N₀ is the unipolar ion concentration and t is the charging time. The particle diameter was varied between 0.1 and 5.04 μm and the N₀t product, between 2.56 × 10⁶ and 5.1 × 10⁷ (ions/cm³) (sec). A comparison of the data with the available theories shows that the best agreement is obtained with the theory of Fuchs and Bricard, whereas the agreement with the theory of White is less satisfactory. It is concluded that for unipolar charging in the continuum regime, the theory of Fuchs and Bricard should be used.