טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentRahimi Shai
SubjectTheoretical and Experimental Investigation of Magneto-
Rheological Droplet Impact on a Rigid
Surface
DepartmentDepartment of Aerospace Engineering
Supervisor Research Professor E Daniel Weihs
Full Thesis textFull thesis text - English Version


Abstract

The kinematics of magneto-rheological fluid (MRF) droplet impact on a smooth surface, subjected to an external magnetic field was studied experimentally and theoretically. MRF are two-phase non-Newtonian colloidal suspensions containing micron-scale permanently magnetized particles in oil or water surroundings. These fluids can flow in response to forces applied by a magnetic field creating a strong paramagnetic directional response due to the particles alignment in the fluid.

We investigated the kinematics of the MRF impact process on a smooth and rigid surface. A time dependent one dimensional model of the spreading process, as typified by the kinematics of the droplet top center point height, during the impact process is developed. The proposed model is described by an ordinary differential equation of the second order with a variable damping coefficient. We show that the decay parameter for predicting the MRF droplet impact phenomena can be represented by either the combination of the Mason number and the Weber number, or equivalently by that of the Reynolds number and the Weber number. A series of experiments were conducted in order to validate the theoretical model. The Reynolds, Weber and Mason non dimensional groups were determined in order to analyze the effects of the fluid viscosity, inertia and the external magnetic effect on the impact kinematics. We show significant differences (of up to 2.5 times) between the final maximum central point heights obtained under magnetic fields to that obtained with no magnetic field. Furthermore, we found that the effect of an external magnetic field on the droplet maximum deceleration is significant at low Weber numbers. Maximum deceleration of more than 200g under conditions of maximum impact velocity was measured. The novel kinematical model based on a variable damping function shows very good agreement with the experimental data for a wide range of Weber, Reynolds and Mason numbers.