Heat Transfer Measurements in Neutrally Buoyant Suspensions in the Inertial Regime

Recent interest in dense granular suspensions has focused on characterizing their rheology and modeling the viscosity, whereas little is known about other transport properties such as thermal diffusivity. The goal of this study is to understand the role of particle inertia and fluid turbulence on thermal transport in sheared granular suspensions. The study uses a Taylor-Couette cell with a rotating outer cylinder and fixed inner cylinder to create a uniform shear flow. Spherical polystyrene beads of 2 mm were used to make a suspension with propylene glycol -water mixture as the base fluid. Particle volume fractions in the range 5-50 % are studied. By changing the rotation speed, and therefore the shear rate, particle Reynolds numbers are varied from 0-100, going from Stokes flow to turbulence with increasing inertia. We study the thermal diffusivity of the suspension by examining the decay of the inner wall temperature after a sharp thermal pulse has been applied. The thermal diffusivity is extracted from the observed temperature decay using a model for one-dimensional diffusion into the particle suspension. A non-monotonic behavior of thermal diffusivity with volume fraction is observed.