Convective Diffusion From a Non-Uniformly Distributed Source in Non-Newtonian Fluids: A Theoretical Investigation and Experimental Confirmation

Abstract

This work presents a complete theoretical study of the process of convective diffusion from a non-uniformly distributed source in a non-Newtonian fluid flowing through a straight tube. The influence of the governing parameters on the dispersion process is studied and the results areexamined in terms of the interaction of rheology, fluid mechanics anddiffusion. Experimental studies have been conducted to obtain the diffusivity values of NaOH in aqueous polymer solutions and provide the first test of the potential of this technique for diffusivity measurement in difficult systems.Measurement of molecular diffusion coefficients of solutes in non-Newtonian media is crucially important from the point of view of being able to understand the pragmatically important convective diffusion processes, which occur in these media. The state-ofthe-art in this area was recently reviewed by Astarita and Mashelkar (1977). This review clearly emphasizes the need for more experimental data on molecular diffusivities in non-Newtonian media but more importantly, it showed that reliable flow techniques are essential for the diffusivity determination in highly viscous non-Newtonian media since in the conventional static techniques a very long time is required to attain an appreciable concentration gradient. In the present work, we analyse theoretically the possibility of using the technique of convective diffusion from a non-uniformly distributed source and set up experiments to simulate the model conditions. We then provide experimental results to show how such a technique can be used for diffusivity measurements.BACKGROUND