Abstract
The formation of dispersions of two immiscible liquids in a confined impinging-jets cell was studied experimentally. The jets of the liquids formed at two opposing channels and collided in a main channel, which was perpendicular to the previous two. Jet channels with diameters either 0.25 or 0.5mm and main channels with diameters either 2 or 3mm were used. The jet velocities varied from 0.17 to 6.2m/s and the dispersed to continuous phase ratios varied from 0.05 to 0.28. Deionised water and kerosene (Exxsol D80: ρ=795kg/m3 and μ=1.73mPas) were used as test fluids. Drop sizes were measured with high-speed imaging. It was found that the total velocity of the two jets was the main parameter that affected both the average drop size and the interfacial area, whilst the dispersed to continuous phase flow rate ratio was less significant. Both phases could become continuous depending on the phase flowrate ratio; drops were, however, larger in the organic continuous dispersions. The interfacial area produced with the impinging-jets cell was almost 3 times larger than in capillary contactors at similar conditions (umix=0.024–0.19m/s). The size of the main channel affected the drop size and smaller drops formed in the large channel compared to the small one. With increasing energy dissipation rate, ε, in the impingement zone, the Sauter mean diameter decreased following a relation of the form ∼ε−b. Apart from the lower velocities, the drop sizes did not change significantly at distances equal to 15 channel diameters downstream the impingement area.
Highlights
Dispersed liquid-liquid flows find many applications in process, food and pharmaceutical industries, and wastewater treatment
The effect of total jet velocity, uj,t, defined as the sum of the jet velocities of the two phases, on the Sauter mean drop diameter is shown in Fig. 5 for two different dispersed to continuous phase flowrate ratios for the 2 mm main channel and for nozzle diameters of 0.25 mm
Both aqueous and organic continuous dispersions were formed depending of the flowrate ratio of the two phases
Summary
Dispersed liquid-liquid flows find many applications in process, food and pharmaceutical industries, and wastewater treatment. Dispersions are usually generated in stirred tanks, in-line mixers, or high-pressure homogenisers (Chen and Middleman, 1967; Das et al, 2013; Daub et al, 2013; Lee and Norton, 2013; Lemenand et al, 2003), where non-uniform flow fields often result in wide drop size distributions. Microfluidic devices have been used for the generation of dispersions with narrow size distribution (Parhizkar et al, 2013). Narrow drop size distributions and high throughputs can be achieved in impinging-jets cell configurations, where two fluid streams collide with each other at high flow rates (Mahajan and Kirwan, 1996). The formation of dispersions is influenced by the energy released during the collision of the opposing jets, while the uniformity of the dispersions depends on the geometric design, the phase ratio, and the intensity of mixing in the impingement zone (Siddiqui, 2014)
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