Numerical Simulation of the Effect of Gravitational Direction on Particle Deposition in Pulmonary Acinus under the Condition of Breath Holding

Abstract

A two-dimensional CFD simulation is conducted to study the effect of the gravitational direction on particle deposition in pulmonary acinus when the breath is held for a short time. The results show that for the large particles (particle diameters of 1 μm, 2 μm, and 3 μm), gravity is the dominant force, and for the small particles (particle diameter of 0.01 μm), the Brownian force is significant. Under the action of either force, the deposition time of particles is short and an equilibrium state can be reached quickly. However, for the medium-sized particles (particle diameters of 0.1 μm and 0.5 μm), the deposition time of particles is elongated because both gravity and Brownian force become weak. Meanwhile, the directions of applied gravity relative to the pulmonary acinus affect the deposition zone of these particles. Therefore, the gravitational direction has no effect on the total deposition fraction of the pulmonary acinus, but can change the local deposition fraction. Applying gravity along the +x direction would increase the local deposition fraction in some specific generations in comparison with the situation along the –y direction. The present study can provide a reliable theoretical basis for further studies on pulmonary mass transport and inhalation therapy.