Viscoplastic fluid flow in pipes: A rheological study using in-situ laser Doppler velocimetry

This experimental study focuses on exploiting laser Doppler velocimetry (LDV), a non-intrusive technique, for rheological characterization based on analyzing flows of Carbopol solutions at two distinct concentrations and two different temperatures within a pipe. The velocity profiles obtained using LDV and the pressure drops associated with each flow rate were exploited to establish the behavioral law of aqueous Carbopol solutions. Two approaches were used: the first was an analytical velocity model to fit the experimental profile, and the second used the first derivative of the experimental velocity profile and the pressure drops to reconstruct the flow curve. In addition, a third reference characterization was carried out using a rotary rheometer equipped with a vane geometry. This study’s three rheological characterization methods showed excellent agreement concerning the Herschel–Bulkley model. Finally, all the laws resulting from these three methods were validated using an empirical law relating to Darcy’s coefficient of friction.