CHE Seminars  

Speaker Dr. Ganesh Subramanian, Department of Chemical Engineering, Cornell University, USA.
Topic Particle motion in fluids: 'Moving beyond Stokes'.
Date Monday, 14 March 2005
Place L-12 Lecture Hall Complex
4.00 to 5.00 p.m.

The first part of the talk will focus on inertial effects in suspensions of spherical particles. To begin with, we will consider the interaction of a pair of particles in a simple shearing flow of a Newtonian fluid for the case where particle inertia is important. Particle inertia is shown to radically alter the topology of pair-trajectories; this has non-trivial consequences with regard to rheology, and leads to unexpectedly large shear-induced diffusive coefficients. In a similar manner, fluid inertia qualitatively alters the mechanism of heat transfer from a single particle in simple shear, leading to a convective enhancement. It is argued that the above change in streamline/pathline topology with inclusion of inertia is a generic feature expected to occur in most linear flows, and may play a role in the coagulation of particle-pairs in turbulence, as well as in the transfer of heat to/from particles in turbulent flows.
Rheological properties of suspensions of anisotropic particles are often sensitive to the orientation distribution of the particulate phase, and it is desirable to predict the particle orientation as a function of size, aspect ratio, concentration, flow parameters, etc. The second part of the talk deals with the orientation dynamics of axisymmetric particles in shearing flows. Orientation behavior in presence of micro-scale inertia is examined, a situation relevant to high speed flows of suspensions, for instance, in the processing of cellulose fibre suspensions in the paper and pulp industry. Two canonical limiting cases are considered herein - a fibre (infinite aspect ratio) and a near-sphere (aspect ratio close to unity). The Stokes limit in both cases is indeterminate. It is then shown that both particle and fluid inertia lead to a net drift of the particle either toward the flow-gradient plane or the vorticity axis of the shear flow, eliminating the indeterminacy.

Dr. Ganesh Subramanian completed his Bachelors in Chemical Engineering (B.Chem) from UDCT, Bombay, in June 1996, and thereafter, went to Caltech (California Institute of Technology, Pasadena) to do his Ph.D with Prof. John Brady. He defended his thesis on "Inertial effects in suspension dynamics" in April 2002, and went to Cornell as a post-doctoral fellow to work with Prof. Don Koch. During this time, the areas he has been working on include orientation behavior of axisymmetric particles in shear flows, inertial effects in clusters of particles, lattice-Boltzmann simulations, multi-phase flow stability etc.