Squeezing flow of a highly viscous incompressible liquid pressed between slightly inclined lubricated wide plates

The theoretical force-height relationships of Newtonian and pseudo plastic liquids compressed between slightly tilted frictionless plates are compared with those produced when the plates are perfectly parallel. It is shown th at a very small inclination angle can distort the flow curve to such an ext ent that a Newtonian liquid will appear as a pseudo plastic fluid, and a ps eudo plastic liquid as having a flow index considerably smaller than its tr ue one. The shape of the biaxial elongational viscosity vs biaxial strain r ate relationship is also highly sensitive to the plates' inclination angle. Thus, if an experimental force-height relationship is used to determine a material's biaxial elongational viscosity, an unsuspected slight tilt will result in a considerable underestimate of the viscosity. A slight tilt will also produce an apparent strain rate dependency in a Newtonian liquid, whi ch obviously does not exist. The mathematical model developed to reach thes e conclusions was tested with commercial mayonnaise, a self-lubricating flu id. A reasonable agreement was found between the predicted force-height rel ationships and those experimentally determined at tilts of 1 degrees, 3 deg rees, and 5 degrees.