VI-7

J. Tihon

Academy of Sciences of Czech Republic

Abstract

The liquid film flowing down an inclined plate was studied experimentally. The experiments were focused on the region of small inclination angles and low flow rates, where the non-Newtonian effects were expected to come to light. Aqueous solutions of carboxymethylcellulose, polyacrylamide and polyethyleneoxide were used ads the model non-Newtonian fluids. The instantaneous film thickness was measured by using the capacitance method. The effects of the elasticity and the shear thinning on the characteristics of periodic waves (length, amplitude, phase velocity and frequency) were systematically studied at various experimental conditions (inclination angle, distance from distributor, flow rate and consistency of the liquid). The longitudinal profiles of wave characteristics were measured to obtain a realistic picture of the wave evolution.

The Orr-Sommerfeld problem formulated for the film flow of a non-Newtonian fluid was solved analytically in long-wave approximation. The linear film stability was investigated over the range of parameters corresponding to the wave inception region. The effects of shear thinning and elastic normal stresses on the critical Reynolds number and other parameters of linear stability theory (wavelength, celerity, and exponential growth factor) were discussed and confronted with the experiments.