Mass Transfer of Diffusive Species with Nonconstant In-Flight Formation and Removal in Laminar Tube Flow. Application to Unattached Short-Lived Radon Daughters

This article deals with convective-diffusive aerosol transport with in-flight formation and removal and is applied to the unattached fraction of short-lived radon decay products. Two novel contributions to previous studies are given in this numerical and experimental work: on the one hand, we solve the mass-transport equations for all the short-lived radon daughters; on the other hand, we include the ²¹⁸Po neutralization into the mass-transport equation of the first radon decay product. Concerning the mass-transfer of all short-lived radon daughters, numerical calculations lead to the development of simple correlations for the ²¹⁴Pb and ²¹⁴Bi penetration fractions. Those correlations can be used to determine the diffusion coefficient of ²¹⁴Pb and ²¹⁴Bi using the 2-filter method. In our experiments, a diffusion coefficient equal to 5 X 10^-6 m² s^-1 is found for the ²¹⁴Pb. Concerning the ²¹⁸Po neutralization, better agreement is observed between our numerical and experimental results when ²¹⁸Po neutralization is taken into account. These results confirm the neutralization rates found by Howard and Strange (1994).