Macroscopic Pipe Flow of Micellar Solutions Investigated by Ultrasound Doppler Velocimetry

Macroscopic flow properties of viscoelastic surfactant solution are investigated in pressure driven pipe flow condition. We focus on an equimolar aqueous solution of cetylpyridinium chloride sodium salicylate, which in simple shear flow exhibits a shear thinning, and at higher shear rates, a pronounced shear-thickening behavior associated with the formation of shear bands [1-6]. An ultrasound Doppler velocimetry method is used to detect these shear bands in pipe flow. The emitted ultrasonic beam is scattered by the moving sample and the time delay between emitted pulse and received echoes as well as the frequency shift is determined. This Doppler shift is related to the speed and the direction of the moving scatters and with this information, the velocity profile across the pipe is calculated [7]. The shape of the obtained velocity profile is used to determine the flow properties of the sample and the formation of shear bands at the tube's wall or within the bulk phase. For the investigated solution we do not observe shear band phenomena. This is contrary to previous investigations [5, 6, 8] where shear bands in the order of few tenth of a millimeter were found. Our results suggesting that the banded region is not detectable by the utilized UVP technique.