Laser-based measurements of liquid-liquid mixing in horizontal pipes by transverse jets

Abstract

Low pipeline velocities lead to stratification of liquid-liquid flows, resulting in phase slip where the in situ phase fractions differ from the input fractions. This prevents samples being obtained that are representative of these flow’s phase fractions, and thus, mixing is used to overcome stratification. This work investigates pipeline jet mixers, obtaining measurements for comparison with theory. A review of jets for mixing is presented which establishes that few studies have been published on liquid-liquid jet mixing. Additionally, a review of prior refractive index matching experimental techniques is included, covering the techniques used within liquid-liquid and liquid-solid experimental systems. Importantly, only two liquid-liquid-solid experimental systems are found to be triply refractive index-matched and none are used for studying pipeline flows. A refractive index-matched facility is developed, consisting of a 10 mm2/s silicone oil, a 51 wt/wt % water/glycerol solution and an ETFE pipe. This allowed the mixing processes to be observed through using laser-based optical techniques, namely Particle Image Velocimetry to measure 2- and 3-component velocity fields and Planar Laser-Induced Fluorescence to measure phase distributions, interface heights and droplet sizes. Measurements are made of the incoming flows, the jet interactions and the resulting dispersions for a range of flow conditions, jet velocities and pipeline positions. Results demonstrate that mixing occurs in two zones: the first during initial jet interaction where Kelvin-Helmholtz instabilities dominate; the second occurs downstream due to secondary flows. Mixing is found to decreases as the jet velocity decreases and the aqueous phase fraction increases. Increasing the crossflow velocity decreases mixing while simultaneously pushing the point of optimum mixing downstream. Coalescence is found to dominate breakup by ten pipes diameter downstream of the jet. The results presented within will aid the understanding of these flows and provide sufficient detail to improve the predictive accuracy of computational models.