Abstract: Break-up behaviors and mechanism of oil-in-water emulsion droplets at the restricting element in the pipeline flow were investigated by experiments. The results show that that the break-up of droplets mainly occurs in the near wall region and downstream of the circular orifice, and the break-up probability is an increasing function of the ratio between the available amount of turbulent stress acting on the droplets and their surface energy, and also an increasing function of the Weber number based on the maximal pressure drop through the orifice. In the turbulent pipe (Re>4000), oil droplets fully oscillate and gain more velocity gradient, shear force and inertia force, being easy to break up. The interfacial tension of Red Sudan IV colored n-heptane system has the value of 23.6 mN/m, decreasing from 47 mN/m without its coloring, the function of viscous force on the break-up of droplets decreases, but the function of inertia force caused by flow velocity and pressure drop is dominant, leading to stronger action on the break-up of droplets. The flow velocity, governed by the flow rate and restriction ratio, controls the turbulent shear force on the dispersed phase oil droplets. Larger injected volumes of n-heptane (0.5~5 mL) weaken the function of the orifice on the break-up of droplets, and the two-phase system tends to generate bigger diameter daughter-droplets with the median diameters from 20 to 35 mm.

Key words: oil-in-water emulsion, restriction, oil droplet, median diameter, break-up, mechanism

摘要： 实验研究了水包油型乳化液油滴在管内节流元件处的破碎行为，分析了破碎机理. 结果表明，液滴破碎主要发生在节流元件内壁及下游附近，其概率是施于液滴上湍流应力与液滴表面能之比的递增函数，是流体韦伯数及节流元件两侧最大压差的递增函数；在湍流状态(Re>4000)下，液滴充分振荡且受到较大的水流惯性力和速度梯度剪切力，更易破碎；由苏丹红IV染色的正庚烷体系界面张力由非染色时的47 mN/m降到23.6 mN/m，黏性力对液滴破碎的影响程度下降，受流速、压差等影响的惯性力起决定性作用，液滴破碎程度更大；流速决定流体对分散相油滴的湍流剪切破碎力，流速增大则油滴粒径破裂程度加大，而流速取决于流量和节流比；注入染色正庚烷油相体积增大(0.5~5 mL)，削弱了节流元件的液滴破碎作用，两相流体系倾向于形成更大直径的液滴，中位径一般为20~35 mm.

关键词: 水包油型乳化液, 节流元件, 油滴, 中位径, 破碎, 机理