According to Wark et al. (18), In order to account
for the effect of Reynolds number, Re in the relationship
between impaction number and impaction efficiency, an
approximation has been developed referred to as Langmuir
approximation. In the approximation, an estimate of the
efficiency is made by first determining the theoretical
efficiencies based on viscous flow (Re < 1) and potential
flow (Re > 2000) described by (16);