Laminar‐nonlaminar transition for non‐Newtonian flow in annuli

Experimental results on the laminar‐nonlaminar transition of aqueous solutions of hydroxyethyl cellulose in axial, isothermal flow in annuli are presented. For each polymer solution the end of the laminar regime is observed to occur at different flow rates at different axial distances from the entrance of the test section. For some polymer solutions in nonlaminar motion, the pressure gradient is not constant over the length of the test section. These data on transition in annuli are compared with predictions made using Hanks' transition criterion where only viscous contributions are considered and where viscous effects are considered and elastic effects accounted for approximately. Predictions where both viscous and elastic properties of the fluids are considered are in fair agreement with experiments. Predictions using purely viscous theory are less accurate than the viscoelastic predictions.