M.Sc Thesis

M.Sc StudentShahar Mark
SubjectAerodynamic Removal of Viscous Liquid Drops Attached to a
Tube or Channel Wall
DepartmentDepartment of Aerospace Engineering
Supervisors PROF. Jacob Cohen
Full Thesis textFull thesis text - English Version


The critical flow conditions causing the movement and removal of viscous droplets adhering to a surface in a channel were investigated. The research may promote the understanding of typical phenomena in the field of respiratory physiology, e.g. situations in which secretion clearance in ventilated patients is necessary. The rheological parameters of the liquid droplets and surface material were chosen so they will mimic the characteristics of the physiologic fluids and tissue (viscosity values between 15 to 700 Poise, and surface tension values between 61 to 82 mN/m).

A specially designed experimental systems was built, comprising of : A surface angular positioning device, enabling accurate measurement of the droplet's contact angles, up to the point of movement, a computerized air flow system for controlling the volumetric flow in the channel, and an optical system acquiring and processing real time images of the droplet while shear flow is passed in the channel. The flow regime and velocity profiles were mapped by using a hot wire anemometer velocity measurement system, so the velocity near the drop and flow could be acquired. The droplet's advancing and receding contact angles were used to verify the surface tension values of the liquid, and the critical aerodynamic forces applied on the droplet during its movement.

The critical Weber numbers for which the droplet started to slide on the surface were in the range of 0.38-0.48, depending on the surface tension and viscosity values. In addition, a numerical analysis of the flow conditions and aerodynamic forces acting on the droplet was performed. Convergence of the numerical results leads to the conclusion that there is a good agreement between numerical and empirical data.  The results of this research are particularly important to the implementation of new ventilation techniques, and the analysis of critical conditions leading to removal of viscous droplets by using aerodynamic forces.