Characterization of unipolar electrical aerosol charges - Part II: Application of comparison criteria to various types of nanoaerosol charging devices
A. Marquard, J. Meyer, G. Kasper
Journal of Aerosol Science 37/9, 1069-1080
The framework presented in Part I for comparing the performance of electrical aerosol chargers is applied to published data as well as to new measurements with unipolar corona chargers of very different designs in the size range between 10 and 60 nm. Variables include the internal flow conditions, the ion production arrangement, and the type of electrical field in the mixing zone between ions and particles. Comparisons are made in terms of losses of charged particles vs. charging efficiency and/or vs. average charge per particle.
It was found that each charger has a characteristic curve of losses vs. charging effectiveness, comprising data points for a broad range of electrical and ion generation conditions.
The results further suggest that the high charge levels and low losses can be achieved by a charger design combining short residence times (associated with turbulence) and high ion concentrations. A carefully adjusted sheath flow is somewhat helpful (at the cost of diluting the aerosol), whereas an AC electric field in the mixing zone of ions and particles does not contribute to improving the charge–loss relationship, even under laminar flow conditions.
The uniformity of charging conditions for a weakly charged nanoaerosol in a given charger can be characterized without the need to determine n _t -products, from a plot of measured intrinsic average charge vs. intrinsic charging efficiency and comparing with predictions from charging theory.