Levich Institute Seminar Announcement, 04/11/2006

Tuesday, 04/11/2006
2:00 PM
Steinman Hall, Room #312
(Chemical Engineering Conference Room)

Professor Carlos Rinaldi
University of Puerto Rico
Chemical Engineering Department


"Body-Couple Induced Flows and Torques in Ferrofluids"

ABSTRACT


Suspensions of magnetic nanoparticles, commonly referred to as ferrofluids, are a commercially relevant example of structured fluids where a magnetic body couple, resulting from non-colinear local magnetic field and magnetization vectors, produces a state of asymmetric stress. Such stresses result in forces and torques on surfaces in contact with these suspensions, even in the absence of bulk flow. Alternatively, the internal angular momentum that enters the system due to the action of the magnetic body couple may be transformed into vorticity and result in bulk flow. As another example, the rotational flow induced on a ferrofluid free surface by a uniform planar rotating magnetic field has long captivated the imagination of scientists and engineers. This effect was long believed to be due to body couples and asymmetric stresses on the bulk of the fluid, arising from the polarizable nature of these structured continua and described by the ferrohydrodynamic equations. However, experiments have shown that the direction of rotation can be made to reverse upon change from a concave to a convex interface, making it evident that a surface phenomenon is responsible for the observed behavior.

In the first part of the talk, we will discuss measurements of the torque required to either rotate or restrain a polycarbonate spindle surrounded by ferrofluid in a cylindrical container and subjected to the rotating field. Simultaneously, ultrasonic Doppler velocimetry was used to measure the azimuthal and axial velocity profiles in the ferrofluid contained in the annular gap of our apparatus. These torque and velocity measurements are compared to an asymptotic solution of the ferrohydrodynamic flow problem in zero spin viscosity and linear magnetization limits. In the second part of the talk, we will discuss recent experiments that have demonstrated that bulk flow occurs in agreement with the ferrohydrodynamic equations.

BRIEF ACADEMIC/EMPLOYMENT BACKGROUND:

Carlos Rinaldi obtained his undergraduate degree in Chemical Engineering from the University of Puerto Rico, Mayagüez, in 1998. Later he attended the Massachusetts Institute of Technology where he participated in the David H. Koch School of Chemical Engineering Practice (MSCEP 2001), and completed an MS (2001) and PhD (2002). He was awarded the J. Edward Vivian Award for Exemplary Performance and Commitment to the David H. Koch School of Chemical Engineering Practice. In the summer of 2002 he served as Assistant Station Director for the MIT Practice School in Mitsubishi Chemical Corporation, Mizushima, Japan. In the fall of 2002 he joined the Department of Chemical Engineering at the University of Puerto Rico, Mayagüez, as Assistant Professor. At UPRM, Carlos Rinaldi has been recognized as Distinguished Professor of Chemical Engineering (2003-2004).

CURRENT RESEARCH:

Dr. Rinaldi’s research interests are in nanostructured materials, particularly systems with dispersed magnetic nanoparticles. Students in his laboratory work on magnetic nanoparticle suspension hydrodynamics and rheology, magnetic nanoparticle based sensors, magnetic fluid hyperthermia (a novel form of cancer treatment), and developing magnetic nanofibers for anticounterfeiting applications.