Helical parallel flow holds excess interfacial stresses

Abstract

Microchannels in poly-dimethyl siloxane (PDMS) material offer microscopic observation of multi-phase flow patterns. Embedded template-assisted fabrication of microchannels in this material fetches complexity in internal flow geometry and visualization of fluid flow inside them. In fact as an advancement, two-phase helical parallel flow with stable interface at microscale exists nowhere except in multi-helical channels. Recently in triple-helical microchannel, two different liquid-liquid parallel flows, namely, "arc parallel flow" and "clip parallel flow" having opposite orientation of interface are observed. In the same parallel flows, here we preliminarily assess interfacial stresses along possible flow directions of helical flow, circumferential flow, and radial flow along normal to interface. Unlike in two-dimensional parallel flows, excess interfacial stresses exist here; yet the interface is stable. We infer that these excess stresses are accommodated by relative motion of fluids in their respective transverse flow direction. The trends of excess shear stresses with two-dimensional interfacial contact time are in coherence with transition between the parallel flows.