Measurement of shear rate on the surface of a cylinder submerged in laminar flow of power-law fluids

Micro-electrodes made of platinum have been used to measure the local shear rate on the surface of a cylinder (length-to-diameter ratio of 11–12) exposed to the fully developed laminar flow of power-law fluids in a vertical pipe. Two Newtonian and two shear-thinning solutions are used as model test fluids to ascertain the influence of shear-thinning viscosity on the distribution of shear rate on the surface of the cylinder. The results reported herein encompass a wide range of Reynolds numbers 0.16 ⩽ Re ⩽ 75 based on the cylinder diameter and centreline velocity. Over the range of conditions, it is observed that the shear rate is a maximum at about θ = 130° and it tends to be higher in shear-thinning fluids than that in Newtonian fluids otherwise under identical conditions.

► The electrochemical polarographic technique is used to measure the local shear rate. ► The local shear rate on the cylinder surface with Newtonian and non-Newtonian fluids. ► The influence of shear-thinning viscosity on the distribution of shear rate. ► The maximum shear rate shows a positive dependence on the Reynolds number. ► The results are borne out by both experiments and idealised 2-D simulations.