Heat and Mass transfer intensification in sheared suspensions – ITS

The goal of this project is to study a source of heat and mass transfer specific to suspensions, that of « shear-induced diffusion », which occurs in suspensions undergoing shear when the motion of the particles due to shear-induced interparticle interactions is much greater than that arising from Brownian motion . We thus confine ourselves to suspensions where the Péclet number is large. This encompasses a wide range of important suspension flows such as the diffusion of red blood cells in arteries [2], but also paint and cement in civil engineering as well as a large number of applications in the food and pharmaceutical industries.

To understand more fully the phenomenon of « shear-induced self-diffusion », consider a single marked particle immersed in a viscous suspension of otherwise identical particles undergoing a simple shear flow (see figure below). In the absence of any interparticle interactions, inertial forces, and Brownian-motion effects, the particle will not experience a drift and will simply translate along the streamlines in the flow. When this particle interacts with the other particles in the suspension, it will suffer a series of displacements normal to the fluid streamlines which, when taken together, constitute a random walk.

This process is akin to the classical Brownian motion except that here the origin of the diffusive motion is not thermal energy (which is negligible) but arises from the large number of interactions between particles and from the permanent rearrangement of the suspension microstructure. In essence, the particles behave as so many "stirrers". The questions raised are what is the effect of this mixing on the transfer of heat and mass in sheared suspensions ? Can we use this phenomenon to increase the heat and mass transfer capacity of certain industrial devices ? What will be the influence of the particle size, their volume fraction and the applied shear on the heat or mass transfer ?