Experimental and theoretical studies on emulsified drag reducers in microtubes

In this work, we propose a promising emulsified drag reducer with multiple components and investigate its flow characteristic within a microtube flow system experimentally and theoretically. The drag reducer in this investigation is an emulsified drag-reducing agent, including dispersant, thickener, octanol, glycol, and polymer. The experimental results indicate flow patterns in microtube flow are quite different from those in regular-size pipe flow, which is manifested by the transition Reynolds numbers for laminar flow, transient flow, and turbulent flow. Furthermore, drag reduction of up to 20% can be achieved with a very low additional concentration of this emulsion at 1 ppm, and drag reduction can be higher at higher concentrations. In the transitional and turbulent regime of drag-reducing flow, once the concentration is known, the viscosity under this concentration can be calculated by the shear rate and shear stress at the wall, and the Reynolds number based on this viscosity can be used to predict the friction factor via a single equation. Finally, we use fast Fourier transform to interpret the chaos of fluctuation of pressure drop in turbulent flow. We propose a newly defined parameter, the dimensionless fluctuation of the pressure drop, to interpret the pressure-drop data in a chaotic state and find that owing to the decreased strength of turbulent kinetic energy in the presence of the drag reducer, the characteristic peak and area enveloped by the curve of magnitude and frequency axis in drag-reducing flow are lower than those in non-drag-reducing flow.