In the first part of this research effort, the transport of heat, mass and momentum in two phase, macroscopically homogeneous systems is studied, both experimentally and theoretically. Familiar examples include the flow of suspensions through pipes and the heat and mass conduction through composite materials. In general, the systems that we study consist typically of two phases, in which one is finely divided; thus, on the macroscale, the composite can be viewed as an effective continuum, having a set of well-defined effective properties, such as an effective diffusivity for the transport of solutes through porous media, or an effective viscosity, for the flow of suspensions. Since, in principle, the theoretical determination of a given effective parameter requires the solution of a corresponding problem on a microscale, which from a practical standpoint is very difficult to implement, our approach is instead to determine these effective parameters using some sort of statistical averaging. In this way, we have determined the effective viscosity of neutrally buoyant suspensions, the effective reactivity, velocity and diffusivity of solutes in porous media, the mean thermocapillary velocity of polydisperse suspensions of bubbles, and the shear-induced diffusivity of suspensions of rigid spheres.
The current research aims to:
study the resuspension mechanism in detail experimentally and to develop a reliable explanatory theory;
measure the shear-induced diffusion coefficient by a novel technique over a wide range of particle sizes, particle concentrations, and degrees of polydispersity, and to construct a theory for determining this coefficient;
examine in depth the shear-induced anisotropy, as inferred from our normal stress measurements , and determine to what extent it can lead to a drift of particles in concentrated suspensions; and
identify the mechanism responsible for the, as yet, unexplained experimentally observed shear thinning behavior in concentrated suspensions.