Effect of wall conductivity on axial gas dispersion in oscillatory flow

High-frequency oscillation (HFO) is an artificial respiratory system based on small tidal volume and high frequency. Axial gas dispersion in an oscillatory flow occurs due to the interaction between radial mixing and radially nonuniform axial velocity profile. Furthermore, the dispersion can be improved by intermittent oscillatory flow. Most previous studies employ the insulating trachea wall model. However, an actual airway wall has conductivity and absorptivity of flowing gas. In the present study, numerical simulation of CO₂ gas transport in an oscillatory flow through an infinitely long straight airway was carried out to reveal the effect of wall conductivity on axial CO₂ gas transport in oscillatory flow. The ratio of resultant effective diffusivity to the effective diffusivity of the insulating wall was markedly enhanced if β<1, due to the gas exchange on the wall. The maximum ratio was more than 200 in this computation. Furthermore, by employing intermittent oscillatory flow, CO₂ gas transport resistance was improved in all airway regions, because of radial diffusion during stationary period in thick airways and wall gas exchange in thin airways.