Equations are derived giving the force required to cause squeeze-film motion of flat plates separated by a liquid. Two geometries are considered, discs and flat strips, and the forces calculated are those arising from fluid viscosity (Newtonian and power-law fluids), fluid inertia and from normal stresses which may be present in the liquid.
The assumptions made are carefully described. These include the additive nature of the various contributions to load bearing capacity, the existence of a "power law" relationship between normal stress and shear rate and the existence of relationships between the components of normal stress. It is shown that the force developed due to the presence of normal stresses is not strongly dependent on the relationship chosen between the components of normal stress. The influence of different variables on the contributions to load bearing is examined in a realistic squeeze film situation by using experimental data for hot, polymer-thickened oils in conjunction with the derived equations. It is shown that both fluid inertia and normal stress effects assist the load bearing process if the approach velocity of the surfaces is sufficiently high. This important conclusion has not been reached in most theoretical approaches to the problem, though it has been demonstrated experimentally.
Nomenclature
B
Constant in equation ( 26), relating normal stress to shear rate by means of a power law. F 1 to F12 Forces on plates producing squeeze film flow, derived for different flow mechanisms as in equations 1,6,7,12,13,14,18,19, 32, 37, 44 and 47 respectively. h Separation of discs or fiat strips. K Consistency index in equation relating shear stress to shear rate by means of a power law. L Strip length in direction of flow (figure l(b)). m Index in equation (26), relating normal stress to shear rate by means of a power law. Mass flowrate of liquid. Flow behaviour index in equation relating shear stress to shear rate by means of a power law. p Isotropic pressure. (Capital P refers to mean value). 217 dM dt n Applied Scientific Research 3g (1979) 217-235. All rights reserved.