具有高粘度分散相的油-水分散体系的液滴破碎与粒径分布研究

对湍流搅拌槽中原油-水分散体系的液滴破碎进行了研究。在不同的温度下原油表现出不同的流变学特征，对分散过程中的液滴破碎产生不同的影响。实验研究对比了不同温度下原油-水分散体系的液滴分布及最大稳定粒径，分析了触变性对破碎过程及最大稳定粒径的影响。经过模型计算与实验结果比较，发现以初始粘度计算的理论值预测最大稳定粒径更为合适。     

基于实验的孔板节流后分散相粒径估值模型研究

节流后分散相液滴粒径的准确估值是研究低剪切节流阀的关键,然而现有节流后液滴粒径估值模型的计算结果差异较大,迄今缺乏估值精度和适用性评价等方面的专门研究。文章通过孔板节流室内实验,分析了现有湍流场内液滴破碎后粒径估值模型的精度和适用性;讨论了分散相液滴单次节流后最大粒径与多次节流后稳定粒径间的对应关系;提出了不设实验常数的液滴单次节流后粒径估值模型。结果表明:现有液滴粒径估值模型含有与分散相黏度相关的实验常数,缺乏普适性;在考察的分散相粒径范围内,液滴单次节流后最大粒径为多次节流后稳定粒径的2.74倍;当入口分散相粒径远小于节流孔孔径时,所提出的估值模型计算得到的粒径值与实测d95粒径间平均误差不大于17.2%。     

喷淋塔液滴粒径分布及比表面积的实验研究

以水和空气为实验介质,通过拍照法获得喷淋塔内液滴粒径分布,考察了不同喷淋量及空塔气速对塔内不同高度处液滴Sauter平均直径(SMD)的影响,并对液滴粒径分布进行了理论分析.结果表明,喷淋塔顶部液滴分布密集,底部稀疏,液滴群在下落过程中,平均粒径减小且趋于均匀化;塔顶处液滴SMD随喷淋量的增加而增大,处在塔中下部的液滴SMD则随喷淋量增大而减小,提高空塔气速,可减小平均粒径;理论分析认为,液滴粒径减小主要是由于发生了碰撞破碎的缘故,而塔内液滴大小不一是碰撞的主要原因;通过量纲1化拟合得到喷淋塔内液滴SMD经验关联式,其计算结果与实验值吻合较好;考虑液滴破碎的喷淋塔比表面积比不考虑破碎的比表面积大70%左右.     

单颗粒橡胶球撞击破碎的实验研究

对天然橡胶球进行单颗粒、低温撞击破碎实验,通过分析破碎产物的粒度分布,考察颗粒的撞击速度、破碎温度、板靶撞击角度和橡胶球初始粒径对破碎过程的影响规律。结果表明:颗粒撞击速度和破碎温度对天然橡胶球破碎产物粒度分布的影响最大;撞击角度在0~45°之间变化时,撞击角度对破碎产物的粒径分布影响不显著;颗粒的初始粒径越小,破碎产物中细颗粒所占的百分比越大。     

喷雾汽化器结构设计的分析与优化

为进行喷雾汽化器结构设计方法的优化,基于颗粒在气流场中的两相流受力特征,理论分析并获得了气液并流过程中,求解液滴从层流到湍流状态的运动时间和运动距离的函数关系式。以碳酸乙烯酯液滴在富氢环境中的运动为例,对比分析了该理论法和常规图解积分法,显示出理论法相比图解法在消除两方面的不确定性因素后,计算结果的准确性更高。研究发现:当液滴粒径一定时,初始速度对液滴径向减速运动时间的影响可忽略;在常见的粒径和速度下,液滴轴向减速过程非常短暂,减速段时间小于其径向减速时间的15%,且粒径越大,减速段时间占比越小。针对一系列单流体压力式工业喷嘴,得到了可直接读取喷雾汽化器直径和最小直段高度的算图。     

同向双螺杆挤出过程中多相体系相畴破碎的理论与实验研究∏:模拟与实验

针对前文 (见《中国塑料》2 0 0 0年第 3期 4 3页 )所建立的粘弹性共混体系分散相液滴破碎理论 ,用HDPE/PS共混体系进行了实验验证 ,并与牛顿体系液滴破碎理论进行比较。实验说明建立的理论模拟双螺杆挤出共混中相畴破碎过程是可行的 ,并具有普适性。理论分析说明螺杆转速N、轴向变量S对分散相破碎粒径d 的影响显著。对于螺槽非充满区域的相态变化 ,用群子统计理论模拟计算。     

乙醇溶液液滴降压蒸发过程传热传质特性

针对单个乙醇溶液液滴在降压环境下蒸发的传热传质过程建立了数学模型。模型基于液相的能量守恒和 传质扩散理论,利用经典拓展模型计算液滴的质量蒸发率,并引入活度系数考虑液滴表面的蒸气分压。采用液 滴悬挂法进行实验,分别记录了乙醇溶液液滴和乙酸溶液液滴在降压蒸发过程中的液滴内温度变化。将实验数 据与计算结果对比,验证了模型的有效性。通过模型计算获得了液滴内部温度分布以及浓度分布随时间的变化。 结果表明:快速降压阶段空气流动较快,加之乙醇工质易挥发,液滴表面温度下降迅速,液滴内部温差和乙醇 浓度梯度较大;压力稳定后,空气流速为零,液滴内部温差和乙醇浓度梯度逐渐减小。由于液滴内部的热扩散 速率大于传质扩散系数,内部温度随时间的变化比浓度随时间的变化更快。     

同向双螺杆挤出过程中多相体系相畴破碎的理论与实验研究：Ⅱ：模拟 …

针对前文（见《中国塑料》２０００年第３期４３页）所建立的粘弹性共混体系分散相液滴破碎理论，用ＨＤＰＥ／ＰＳ共混体系进行了实验验证，并与牛顿体系液滴破碎理论进行比较。实验瓣理论模拟双螺杆挤出共混中相畴破碎过程是可行的，并具有普适性。理论分析说明螺杆转速Ｎ、轴向变量Ｓ对分散相破碎粒径ｄ＊的影响显著。对于螺槽非充满区域的相态变化，用群子统计理论模拟计算。     

玻璃熔窑烟气脱硫系统脱硫效率的研究

建立了玻璃熔窑烟气脱硫过程中脱硫效率的数学模型,计算分析并讨论了液滴初始粒径、液滴初始速度、烟气入口温度、烟气入口速度和SO2入口浓度等因素对脱硫效率的影响.这些研究为脱硫装置的结构优化和运行提供理论指导.     

喷雾干燥法烟气脱硫过程的数学模拟

影响喷雾干燥法烟气脱硫过程的因素很多，如液滴初始粒径、液滴初始速度、烟气入口温度、烟气入口速度和SO2入口浓度等。在分析喷雾干燥塔内气液两相流动及单个粒子与气相之间传热传质过程的基础上，建立了喷雾干燥法烟气脱硫过程的数学模型，模拟分析并讨论了上述各因素对脱硫效率的影响，并通过实验对模型进行了验证。     

湍流分散体系中液滴破碎频率模型的黏性修正

在分析研究分散相黏度对液滴变形和破碎影响的基础上,提出了一个改进的液滴破碎频率模型并拓展了液滴破碎判据标准.同时通过Monte Carlo模拟的随机方法,得到了湍流搅拌槽中液-液分散体系的液滴直径分布和Sauter平均直径d₃₂.通过与文献中关于d₃₂的实验结果比较发现,该模型预测的Sauter平均直径更接近实验值,对于黏性分散相改进的液滴破碎频率模型要优于Coulaloglou和Tavlarides提出的模型.计算结果表明对于黏性分散相液滴,其黏度限制了液滴变形,使得液滴破碎频率被大大减少, 液滴直径明显增加,液滴直径分布向右偏移.     

油水两相分散流液滴粒径预测模型

油水两相分散流的液滴粒径及其分布在很大程度上影响管路压降等流动参数,研究液滴粒径预测模型对揭示油水两相流的流动特性具有重要意义。通过研究湍流脉动动能与乳状液的界面能之间的平衡、管流径向速度脉动与摩擦速度之间的关系以及泵的剪切作用,建立了油水两相管流中分散相液滴粒径预测模型;在水平管道上对油水两相分散流的液滴特性进行了实验研究,采用高速摄像和显微镜拍摄获得液滴数据,探索含油率、流量和温度等因素对粒径的影响。预测模型计算结果与不同流量、温度和含油率条件下的实验数据吻合较好。根据预测模型计算了有泵和无泵情况下分散流液滴粒径,发现泵的剪切和扰动作用使得分散液滴具有更小的粒径,泵对液滴粒径及其分布起到了显著作用。     

Drop break-up in intermittent turbulence: Maximum stable and transient sizes of drops

A multifractal method describing the fine-scale structure of turbulence, including its intermittency, is applied to derive the drop breakage functions for drops whose diameter falls within the inertial subrange of turbulence, including effects of the viscosity of the dispersed phase. The model predicts well the transient drop size distributions of dispersions undergoing breakage at long stirring times. Concepts of quasi-stable and asymptotically stable drop sizes are presented and discussed in relation to the exponent on the Weber number. The functions for drop break-up in the viscous subrange are proposed and discussed.     

Experimental study on drop breakup time and breakup rate with drop swarms in a stirred tank

The direct experimental data for breakup parameters of drop breakup time, multiple breakage, and breakup rate are urgently required to understand drop breakup phenomena. In this regard, drop breakup experiments were carried out in a stirred tank using a high-speed online camera. The influences of the rotating speed, interfacial tension, and drop viscosity on the above breakup parameters were then quantitatively investigated. An mechanism correlation for the breakup time is proposed and is further verified by comparing with the results of Solsvik and Jakobsen (Chem Eng Sci, 2015;131:219-234). The percentage of multiple breakage comparing to binary breakup was statistically counted. The results indicated that the dimensionless drop diameter η = d/d_max can be adopted to characterize the proportion of binary breakup. Finally, the breakup rate was experimentally measured and the breakup probability was calculated using the inverse method.     

Size distribution of drops formed from nozzles in liquid-liquid systems at velocities below jetting

The size distribution of drops formed from four different diameter nozzles (d=l.O, 1.6, 2.6 and 3.5 mm) was measured over the flow rate range of 0.17 to 3.0 cm3/s (below jetting). Kerosene was used as the dispersed phase and distilled water was used as the continuous phase. The experimental drop size distributions were described adequately by the upper limit number and volume distributions. Plots of the maximum and the minimum diameters versus the mean diameter yielded straight line with slopes of 1.11 and 0.87, respectively.     

Study of the pressure drop of dense phase gas-solid flow through nozzle

Pressure drops are measured on different nozzles of various pipe sizes in dense phase pulverized coal pneumatic conveying. From the experimental results, we conclude that the effect of the gas phase nozzle pressure drop is negligible when comparing with the solid phase pressure drop in the experimental range. The main influence factors contributing to the nozzle pressure drop are gas and solid mass flow rate, solids loading ratio, and the diameters of the nozzle inlet and outlet. A new model was developed to predict the nozzle pressure drop in dense phase pneumatic conveying of pulverized coal based on the Barth's pneumatic conveying theory. The pressure drop predictions from the model are in good agreement with the experimental values. The model quantified the important influence factors of the nozzle pressure drop.     

Development of method for estimating drop diameter in the manufacturing process of functional O/W microcapsules

A new method for preparing functional O/W microcapsules using a process involving O/W/O emulsion as particle formation was developed. Coenzyme Q10 (CoQ10) or reduced coenzyme Q10 (QH) was used as the core substance. QH oxidized fast when exposed to air. O/W microcapsules were manufactured by conventional liquid phase drying method (LPD). The purpose of this study is to develop a simple method of estimating drop diameter which is possible to evaluate immediately the mean drop diameter during the microencapsulation process without the usual photographic measurement. This developed estimation is possible to predict a Sauter mean diameter by measuring the amount of inner CoQ10 released from O/W emulsion droplet. The amount of inner oil phase released from O/W emulsion has correlation with increased total surface area of O/W emulsion droplet caused by breaking droplet. Released rate of CoQ10 from O/W emulsion droplet to outer continuous phase under different rotational speed and emulsion viscosity was measured with an absorption spectrometer. As a result of the changes of released inner CoQ10 amount, droplet breakage under low emulsion viscosity was promoted by agitation speed. It is concluded that droplet dispersion state during manufacturing of O/W microcapsules was evaluated well by applying the developed estimation method.     

Modelling of droplet breakage probabilities in an oscillatory baffled reactor

The breakage of droplets dispersed in a continuous aqueous phase determines the performance of many mixing devices and reactors that rely on effective contact between two phases, e.g. emulsion mills, liquid-liquid extraction columns, stirred tank reactors and Oscillatory Baffled Reactors. Quantitative knowledge of the mechanisms involved in the breakage provides parameters for design and prediction. In the work presented here, oil was dispersed in water in a continuous OBR, and a High Speed Camera was used to record the events of breakage of individual oil droplets and probabilities of breakage were estimated. It was confirmed that breakage was more sensitive to changes in the amplitude of oscillation than in the frequency of oscillation. A novel integral model was developed based on an analysis of the total work effected on the deforming droplet in order to interpret the results. The quantitative results from direct observation were compared to the model predictions. The model with fitted parameters was finally extrapolated to smaller diameters, in an attempt to predict the critical drop diameter for breakage.     

Prediction of maximum stable diameter of viscous drops in a turbulent dispersion

A new Paradigm has been developed fro the prediction of maximum stable diameter of viscous drops in turbulent dispersions using the Voigt model. The model assumes that a drop would break if its deformation reaches unity. The prediction from the model compares quite well with the available experimental results.