Séminaire de Mécanique d'Orsay

Le Jeudi 6 mars à 14h00 - Salle de conférences du FAST

Visco-plastic lubrication: from theory to application

Sarah Hormozi
Laboratoire Navier (École des Ponts, IFSTTAR, CNRS)

A common problem in multi-layer shear flows, especially from the perspective of process engineering, is the occurrence of interfacial instabilities. For purely viscous fluids these occur at low Reynolds numbers. However, multi-layer duct flows can be stabilised by astute positioning of a visco-plastic fluid as the lubricant that remains unyielded at the interface. This technique has been termed visco-plastic lubrication. In this talk, I will start with an introduction to Visco-Plastically Lubricated (VPL) flows. Then I will present the results of a systematic study aimed at extending visco-plastic lubrication from a theoretical concept towards more industrial applications. The results come in two parts. Firstly, a computational study of VPL flows will be presented in the setting of a Newtonian core fluid surrounded by a Bingham lubricating fluid, within pipe and channel configurations. Flow development and start-up are explored. Non-linear perturbations are also studied to obtain better understanding about the stability of these flows, e.g. what role does the unyielded plug play, do perturbations remain concentric or develop asymmetries, how large an amplitude of perturbation can be withstood and at what flow rate. These are essential questions for industrial prototyping. Secondly, I will show the feasibility of VPL flows with visco-elastic core fluids from both experimental and theoretical perspectives. Visco-elastic fluids are frequently used in the polymer and food industries, which are large areas for application. I will close by connecting visco-plastic lubrication to potential novel applications in stable core-annular oil pipelining, in manufacturing and in droplet encapsulation. These and other areas reviewed represent future directions that I intend to pursue.