This study examines the effective thermal diffusivity of sheared particle-fluid suspensions with non-Brownian neutrally buoyant particles in a thin gap Taylor-Couette cell. A steady canonical shear flow is generated with Taylor instabilities suppressed by outer cylinder rotation. Spherical acrylic particles of 1.93 mm diameter were used with a density-matched propylene glycol-glycerol solution. Thermal diffusivity of the medium is deduced by applying a thermal pulse to the stationary inner cylinder and monitoring temporal temperature decay on the inner cylinder surface. The study documents the effects of the particle Peclet number $(<1400)$ for four different particle volume fractions of 0.14, 0.22, 0.30, and 0.36. Here the Peclet number is defined as the ratio of timescales of thermal diffusion in the liquid over the particle scale to the timescale of the imposed shear. The applied shear corresponded to particle Reynolds numbers ranging from Stokes flow $({\mathrm{Re}}_p\ll 1)$ to a maximum of 0.85, where weak inertial effects are likely present. At low Peclet number $\mathrm{Pe}<100$, the enhancement due to shear is roughly linear with the Peclet number. At higher $\mathrm{Pe}$ $(100<\mathrm{Pe}<700)$, the enhancement displays power-law behavior with an exponent of 1/2, which has been predicted by some models for concentrated suspensions, but is also consistent with the emergence of a particle-free fluid layer near one wall. At still higher $\mathrm{Pe}$, the 1/2 power-law behavior is retained for all but the highest volume fractions, with $\varphi =0.35$ exhibiting a 1/11 power-law behavior, which has been previously predicted, albeit for dilute suspensions, for the high-$\mathrm{Pe}$ limit. The thermal diffusivity measurements are complemented by limited measurements of particle velocity through particle tracking, which suggest that particle motion does not contribute significantly to the observed enhancement at high Peclet numbers.

Close

PrevNext

View figure in article

• Fluid-particle interactions
• Fluidized beds
• Particle-laden flows