Diffusion in flowing films of dilute polymeric solutions

Abstract

This work deals with the measurement of diffusivity of gases (D) in polymeric solutions under flow conditions. The wetted sphere technique is used for this purpose. The relevant convective diffusion equation for pseudoplastic fluids is first solved. The theoretical results are then used in conjunction with experimental measurements with six different polymer systems to determine the values of D. The polymer addition results in an enhancement in D also showing the presence of an hitherto unreported maximum. Although the results appear to indicate that D values are independent of shear rate on the surface of the sphere, a critical analysis indicates that gas absorption from a stress-free interface may not be a sensitive technique of studying shear rate dependence of D. The influence of viscoelastic fluid stretching, end effects etc. is studied semi-theoretically.