Slip in Couette flow with pressure gradient: Theoretical and experimental investigation of hydrodynamic characteristics considering slip effect

Abstract

A new slip velocity model based on molecular potential theory and macro-force analysis, which is applied in Couette flow with pressure gradient, is built up. The model is validated by later being introduced in hydrodynamic system to predict film distribution, which shows a good agreement with experimental data obtained from multi-beam intensity-based tests with Fe and Cu ball materials under accurate controlled temperature, load and different wall velocities. Results show that the slip length for Fe case is ignorable so it seems like no slip, but for Cu case, the slip length is large to make 20% discrepancy with no slip simulation and also behaves shear-dependently. Moreover, during the experimental cases when both Fe and Cu ball velocities rise from −133 mm/s to 1 330 mm/s, the slip velocity changes its direction with entrainment velocity and thus contributes to first enhance and then diminish the hydrodynamic film, but due to slip length on Cu case varying largely than that on Fe case, the film from Cu case and from Fe case has a clear cross-point between ub=80mm/s and ub = 220 mm/s (ub is the ball speed). The results above support strongly that Cu surface will lead to stronger slip than Fe case because of its smaller solid-liquid interaction, and obviously slip will influence hydrodynamic characteristics prominently.