Effect of charge on the concentration decay and size growth of unipolar and bipolar charged aerosols: Model and validation

Studies on charging effects on suspended radioactive aerosol behaviour in confined environments during nuclear accident scenarios are essential for improving safety assessments. Radioactive aerosols are primarily charged with the same polarity due to the self-charging despite the presence of bipolar charging. This work presents the development and validation of a polydisperse, non-radioactive, charged (bipolar and unipolar) aerosol dynamics model based on the nodal method. The coagulation correction factor is differentiated for bipolar and unipolar charged aerosols. Electrostatic dispersion and the image force with the deposition surface are incorporated. The concentration decays and size growths of bipolar and unipolar charged aerosols with known net charge-size distributions suspended inside a steel chamber are simulated and compared with baseline conditions without charge. The simulated results are compared with the measured patterns of PAO (Polyalphaolefin) aerosol under different charged conditions reported in the literature, and show good agreement. The coagulation enhancement is feeble for bipolar charged aerosol, whereas it essentially diminishes for unipolar charged aerosol. The electrostatic dispersion due to the same net charge polarity of particles is critical, inhibiting particle size growth but enhancing concentration decay, in both charged conditions. Deposition enhancement on the conducting surface due to the image force is marginal.