Investigation of spray characteristics in a MRI based human throat simulations

Knowledge of the flow patterns in the upper respiratory tract is a key factor to the understanding of airway resistance and predicting the deposition of particles. Flow in this region is, however, complex and can be patient dependent, defying the ability of simple numerical models to predict particle deposition. Computational fluid dynamics (CFD) can be used, and is perhaps best suited for predicting flow in this region for a given respiratory pattern. In this study, first air, then 70/30 helium/oxygen (Heliox) flow and particle deposition in the human throat were numerically analyzed with CFD software, Fluent (Fluent 6.2.16, Fluent Inc.). Particle ranging between SMD=0.5 um and SMD=20 um were used both Heliox and air simulations. The throat model was constructed from MRI of a 25 year old female taken at 3 mm slices. The vertex data of throat obtained from MRI by means of the OSIRIS software. After that, a 3D human airway model was created with GAMBIT software (Fluent Inc.). Consequently, the computational model was imported into Fluent solver and the steady state conservation equations of mass, momentum and energy were solved using the finite volume method. The chosen inlet velocity was based on an approximate adult breathing condition with a steady flow rate of 18 liters per minute. Both heliox and air flows reached maximum velocities at larynx region because of the laryngeal jet flow. It has been observed that flow patterns of the gas flow are similar both Heliox and air. However, Heliox presented values that are higher than the air system. It has also been found that when smaller particles (SMD=0.5 um and SMD=2 um) were injected into the flow, the whole particles deposited around the larynx and could not reach to the throat exit. Keywords: Human throat, Computational Fluid Dynamics (CFD), Fluent CFD Software, Spray characteristics, SST k–ε model