分散相相互作用下液—液水力旋流分离特性

发布时间：2018-08-03 21:53

【摘要】：液-液旋流器利用混合液中不同介质因密度差而受离心力不同,将多相介质进行分离。在针对旋流器的数值模拟中,分散相液滴直径常被看作定值,从而忽略旋流器流场对分散相液滴直径的影响。本文针对分散相液滴在分离过程中产生的聚合和破裂现象,对旋流器的分离特性进行了研究。主要内容及结论如下:对旋流器内部流场、分散相液滴受力、分散相的破裂和聚合机理三个方面进行了理论分析。得出液-液旋流器内部流场主要由外旋流的自由涡和内旋流的强制涡构成。当Weber数大于12时,液滴易产生破裂;仅当两碰撞液滴的碰撞接触时间超过临界值时,才能产生液滴的聚合现象。通过数值模拟与实验数据对比的方式,对低浓度分散相系统下液-液旋流器中的聚合和破裂核函数进行了优选。同时,对液-液旋流器内部流场分布、速度场分布、分散相浓度及分散相破裂和聚合区域分布进行了分析。研究结果表明:Lerh提出的聚合和破裂核函数较其它函数更适合低浓度分散相下旋流器模拟,其与实验结果误差接近12%。各向速度和湍流强度分布呈组合涡形式与理论分析一致。对旋流器内部分散相的体积分数及源项进行了分析,且对不同入口流量下旋流器内部流场及分散相分布进行了对比。结果表明:分散相的聚合率随分散相浓度增加而增大,破裂率随湍流强度以及速度梯度的增大而增大。随着入口流量的增加,旋流器内部各向速度及湍流强度同时增大;分散相在圆柱段、大圆锥段及小圆锥段下端浓度随之增加。入口流量的增加对于破裂现象起着促进作用,且随着速度的增加,破裂现象的增强幅度随之降低。推导出一种低浓度轻质分散相下,液-液旋流器分离效率计算方法,并分别对不同入口流量和结构下的实验结果进行对比。该公式计算值与实验值平均误差为5%,当分离效率低于10%时,随着分散相直径的降低,误差逐渐增大。由于该公式未考虑分散相的相互作用,因此在分散相液滴破裂现象明显时其准确率降低。
[Abstract]:The liquid-liquid hydrocyclone separates the multiphase medium by the different centrifugal force due to the density difference in the mixed medium. In the numerical simulation of hydrocyclone, the diameter of dispersed droplet is often regarded as a constant value, so the influence of flow field on the diameter of dispersed droplet is ignored. In this paper, the separation characteristics of hydrocyclone are studied in view of the polymerization and rupture of dispersed droplets in the separation process. The main contents and conclusions are as follows: the flow field in the hydrocyclone, the droplet force in the dispersed phase, the fracture and polymerization mechanism of the dispersed phase are analyzed theoretically. It is concluded that the internal flow field of the hydrocyclone is mainly composed of the free vortex of the outer swirl and the forced vortex of the inner swirl. When the Weber number is greater than 12:00, the droplet is prone to rupture, and only when the collision contact time of the two colliding droplets exceeds the critical value, the droplet polymerization can occur. By comparing numerical simulation with experimental data, the polymerization and fracture kernel functions in liquid-liquid hydrocyclone with low concentration dispersion phase were optimized. At the same time, the distribution of flow field, velocity field, concentration of dispersed phase, fracture and polymerization region of dispersed phase in liquid-liquid cyclone are analyzed. The results show that the polymerization and rupture kernel functions proposed by the President Lerh are more suitable for the simulation of hydrocyclone with low concentration dispersion phase than other functions, and the error is close to that of the experimental results. The distributions of velocity and turbulence intensity in each direction are consistent with the theoretical analysis in the form of combined vortex. The volume fraction and source term of the dispersed phase in the hydrocyclone are analyzed, and the flow field and the dispersed phase distribution in the hydrocyclone under different inlet flow rates are compared. The results show that the polymerization rate of the dispersed phase increases with the increase of the concentration of the dispersed phase, and the fracture rate increases with the increase of the turbulence intensity and the velocity gradient. With the increase of inlet flow rate, the velocity and turbulence intensity increase simultaneously, and the concentration of dispersed phase increases at the lower end of cylinder, big cone and small cone. The increase of inlet flow rate promotes the fracture phenomenon, and with the increase of velocity, the increasing amplitude of fracture phenomenon decreases. A method for calculating the separation efficiency of liquid-liquid hydrocyclone with low concentration and light dispersion phase is derived, and the experimental results under different inlet flow rates and structures are compared respectively. The average error between the calculated value and the experimental value is 5. When the separation efficiency is lower than 10, the error increases with the decrease of the diameter of the dispersed phase. Because the interaction of dispersed phase is not taken into account in this formula, the accuracy of the formula is reduced when the droplet fracture of dispersed phase is obvious.
【学位授予单位】：武汉工程大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TQ051.8

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