On the behaviour of inhaled fibres in a replica of the first airway bifurcation under steady flow conditions

Inhaled fibres can potentially cause inflammation of the lung tissue and interstitium, which after long-term exposure may lead to lung cancer, malignant mesothelioma, or pulmonary and pleural fibrosis. To reduce the risk and set the appropriate occupational hygiene regulations, it is important to be able to precisely calculate the fate of inhaled fibres depending on their physical characteristics and inhalation conditions. In the absence of experimental data on the real behaviour - trajectories, orientation and flipping - of inhaled fibres, a new test rig was assembled for visualization and recording of flowing fibres in a replica of the human trachea and the first bronchial bifurcation. Fibres prepared from commercially produced glass fibres have been processed, dispersed, and introduced into the airway replica. Visualization was performed using a powerful LED light and a high-speed camera. The flow of fibres was evaluated upstream and downstream of the realistic asymmetrical bifurcation and dependence on flow conditions was sought. The fractions of parallelly and perpendicularly flowing fibres were statistically evaluated in three locations. The frequency of flipping was also analysed. The results show that the parallel orientation of the fibres is less dominant than expected. The fibre orientation tables for various conditions can be used to adjust and improve computational simulations of inhaled fibres in the human airways.