Effects of zero-shear rate viscosity and interfacial tension on immiscible Newtonian-Non-Newtonian fluids morphology in radial displacement inside the Hele-Shaw cell

We report on experimental study of interfacial instability in immiscible Newtonian-Non-Newtonian radial displacement occurs in Hele-Shaw cell where liquid paraffin was injected to displace carboxymethyl cellulose (CMC) solution. For the benchmark system, tip-splitting pattern was observed. Results indicated that the maximum change in the shear rate and viscosity of CMC solution occurs in the very early stage of the displacement process. The comparison between Newtonian-Non-Newtonian and Newtonian-Newtonian interfacial development, showed higher number of fingers for Newtonian displacement, but wider and longer fingers for non-Newtonian system. Investigation of concentration effect indicated that the interfacial instability decreased in displacing of 0.5%wt CMC solution. In contrast with literature, the instability increased significantly for 1.5%wt CMC solution, and dendritic pattern emerged instead of tip-splitting. This was due to the significant reduction in interfacial tension and rise in viscose forces. Moreover, the results showed that increasing the initial injection radius led to increment in fingers number and reduction in velocity of the dominant fingertip. Additionally, increasing the injection flowrate resulted in fingering pattern change from tip-splitting to dendritic type. Finally, comparing the number of the observed fingers with literature, suggested that using average capillary number; Ca <= 10(-3), Paterson's theory may be followed by the experimental results. (C) 2021 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

Automated summary

In the experimental study of interfacial instability in immiscible Newtonian-Non-Newtonian radial displacement, different phenomena were observed in the displacement process at different concentrations. The comparison between Newtonian-Non-Newtonian and Newtonian-Newtonian interfacial development revealed differences in finger patterns. Additionally, the increase in initial injection radius and flowrate led to changes in finger patterns and dominant fingertip velocity.