EXPERIMENTAL-STUDY OF FILM THICKNESS AND FREE-SURFACE VELOCITY AROUNDA ROTATING ROLL FOR NON-NEWTONIAN FLUIDS

Measurements are performed on film thickness and free surface velocity around a rotating roll for Newtonian, non-Newtonian inelastic, and vi scoelastic fluids by using noncontact methods of a capacitance probe a nd a laser Doppler velocimeter probe. The film thickness decreases wit h increasing inspection angle for Newtonian fluids. For non-Newtonian fluids, it retains an approximately constant value, owing to shear-thi nning of viscosity, except for a meniscus region development, which is dependent on fluid elasticity. Comparison of current results with the film thickness from a previous work is also made. With the increment of inspection angle, the free surface velocity increases rapidly in th e meniscus region and maintains a constant value almost equal to a rol l speed in the other region for viscoelastic fluids, while it increase s linearly for Newtonian fluids. The shear rate at a roll surface is p resented assuming that the velocity distribution in the liquid film is a polynomial equation. It is found that viscoelastic fluids exhibit d ifferent behavior from that of Newtonian and non-Newtonian inelastic f luids. Evaluation of the force acting on the liquid film for Newtonian fluids implies that the velocity gradient at a roll surface in an asc ending region may be steeper than the parabolic form assumed in this s tudy.