Influence of flowing fluid property through an elastic tube on various deformations along the tube length

The study of fluid flow characteristics in collapsible elastic tubes is useful to understand biofluid mechanics encountered in the human body. The research work presented here is aimed at thoroughly investigating the influence of both Newtonian and/or non-Newtonian fluids (low and high shear thinning) during steady flow through an elastic tube on various tube deformations, which enables understanding of the interaction between wall motion, fluid flow, and intestinal transmembrane mass transfer as a crucial contribution to a mechanistic understanding of bioaccessibility/bioavailability. It is observed that for a given steady volume flow rate, the tube is buckled from an elliptical shape to a line or area contacted two lobes as the critical external pressure is increased. The downstream transmural pressure is found to get more negative than that at the upstream as the outlet pressure decreased due to stronger tube collapse resulting in a reduced cross-sectional area. The experimental results depict that the tube cross-sectional area decreased by only about a factor of one for PEG (polyethylene glycol) and about a factor of six for both CMC (carboxymethyl cellulose) and PAA (polyacrylamide) from the undeformed one under an applied external pressure of 105 mbar. The corresponding maximum velocity increased by a factor of two during steady flow of shear-thinning fluids. The shear-thinning behavior of both CMC and PAA solutions is clearly observed at a constant flow rate of 17 ml/s as the tube cross-sectional area decreased due to an increase in compressive transmural pressure. In addition, the viscosity of PAA is drastically decreased due to its high shear-thinning behavior than that of the CMC under the same applied external pressure.