|M.Sc Thesis||Department of Mechanical Engineering|
|Supervisor:||Prof. Haber Shimon|
|Full Thesis text - in Hebrew|
The present work is based on the assumption that aerosol particles in respiratory system are formed as a result of appearance, and the following disintegration of liquid meniscus. Therefore, hydrodynamics of a liquid meniscus in pulmonary airways and its evolution are the key subjects dealt in the present analysis.
The model contains the following assumptions and simplifications:
1. ASL is a homogeneous and Newtonian fluid.
2. Initial thickness of ASL is equal throughout the capillary length.
3. No influence of Marangoni flow.
4. The capillary is rigid and nondeformable.
5. The model is axisymmetric.
6. Air is considered as incompressible liquid.
Construction of the mathematical model for a meniscus motion applies the VOF (volume of fluid) method in two-phase formulation. A numerical solution is obtained by using a commercial CFD software FLUENT®.
As a result of the solution, it is revealed that evolution of meniscus formed in a capillary may develop by either of the three different scenarios:
1) Equilibrium meniscus motion - This is a limit case and represents steady-state motion type. It is observed that, while moving, the meniscus does not change thickness of the liquid layer on the capillary walls and, therefore, it’s volume remains constant. That is why capillary number value correspondent to this type of solution is called the critical capillary number: ().
2) Motion with volume increasing - This type of meniscus motion occurs under condition of (). It is found that, thickness of the liquid layer remaining on capillary walls after passage of meniscus is smaller than in its front. Therefore, while moving, the meniscus “collects” liquid from capillary walls and expands in volume.
3) Motion with volume decreasing - It is the opposite situation where liquid layer remaining on capillary walls after passage of meniscus is thicker than in its front. This type of meniscus motion occurs under condition of (). This process finally results in reduction of meniscus volume to a minimal critical value until it looses stability and collapses
It is found, that the is a relatively a weak function of the relative meniscus thickness () within a wide range ().At the same time, highly depends on relative mucus layer thickness value.
In the work, observed that, for most cases average drops diameter demonstrate has a tendency to increase with decreasing of surface tension on Air-ASL interface.