Experimental Validation of a Computational Fluid Dynamics Model of The Upper Respiratory Airways Utilizing a Heat Transfer Approach

Abstract

Tobacco smoking is one of the leading causes of death and disease globally. E-CIGS (e-cigarettes) were introduced in 2004 and marketed as a safer alternative. However, there is growing concern that instead of displacing combustible cigarette use, E-CIGS are attracting large numbers of nicotine-naïve youth who may not have smoked otherwise. Factors such as attractive flavors, advertising targeting youth, and the introduction of nicotine salts are responsible for the rise in prevalence among youth. Unlike free-base nicotine, nicotine salts are nonvolatile and do not induce throat harshness when inhaled. One regulatory approach that has been proposed is to set a floor on the throat harshness of electronic cigarette aerosols to deter previously nicotine-naïve youth from using them. However, the relationship between throat harshness and various electronic cigarette variables, including nicotine concentration, nicotine salt fraction, electrical power, and inhalation patterns, has not been closely examined. Recently, a theoretical model was developed to quantify nicotine deposition and throat harshness from key electronic cigarette variables. This model is partly derived from a computational fluid dynamics simulation of flow through the upper respiratory airways.

This thesis aims to experimentally validate the CFD simulations used in the 1-D model derivation of the segmental heat transfer correlations. The study involved the construction of a physical model that replicates the complex geometry of the human airway used in CFD computations and measuring the temperature at various points in the model. At the same time, air was drawn through it at different flow rates (1 SLPM to 20 SLPM ). Then, temperature measurements, appropriately non-dimensionalized, were compared to the CFD-predicted temperatures at the same flow rates. An experimental setup was developed to mimic the idealized boundary conditions used in the CFD model. The setup rigorously treated measurement uncertainty and optimized temperature measurement locations in the flow path. Key measurement outcomes included temperature, relative temperature change across locations, and relative temperature change across flow rates.

Experimental results aligned with the CFD predictions after optimizing for the dominant source of uncertainty, the position of the thermocouples. This experimental set-up was deemed a working approach to validating this computational fluid dynamic simulation across the upper respiratory tract. However, to improve this setup, a more precise method is needed to locate the thermocouples inside the physical model after its construction.