Partial slip boundary condition in squeeze flow

International audienceSqueeze flow rheometry is used increasingly as a means for measuring the rheological properties of many fluids. A number of different exact or approximated solutions of such a flow have been established. These solutions depend on fluid rheological behaviour, outer edge conditions at the plates and particularly wall boundary conditions. Also, rough plates are commonly used to impose sticking flow. Perfect slip is obtained with lubricated plates. However, in the squeezing, friction effects can produce and play a significant role. So, several studies have shown that some slip with friction arises during flow rather than perfect slip or stick. This phenomenon depends on the solid-fluid interaction and the fluid particle size, and currently produces with concentred suspensions. To study this problem, the crucial assumption is to know the location and the shape of the part where wall slip may or may not occurs. This question is investigated from experimental results. For this, squeeze flow experiments are carried out to visualize the flow pattern at the walls. Influence of boundary conditions is particularly studied using different plate surface condition. As a result, we propose to develop a flow modelling divided in two zones. A circular central zone of the sample sticks on the plates ; beyond that zone the sample slips at the plates with friction. Finally, we discuss the impact of such a flow pattern on the rate-of-strain tensor