非相容聚合物体系熔融共混过程中分散相粒径变化的预测

以PS PP共混体系为研究对象 ,研究了非相容聚合物体系混炼过程中分散相含量、剪切速率及聚合物弹性等对分散相粒径变化的影响 ,对平衡态分散相粒径的变化进行了预测 ,并对其计算公式进行了新的改进 .研究表明 ,分散相浓度较低时 ,分散相粒径与分散相体积分数呈线性增长关系 ;在较高浓度时 ,分散相粒子的聚结作用明显 ,公式应加以修正 .实验中还观察到 ,对于PS(连续相 ) PP(分散相 )共混体系 ,随着剪切速率的增大 ,分散相粒径先不断减小 ,达到一极小值后 ,却又有所增大     

Examination of n=2 reaction mechanisms that reproduce pH-dependent reduction potentials

This work describes a new sampling method termed directly suspended droplet microextraction (DSDME) was developed. In this technique a free microdroplet of solvent is delivered to the surface of an immiscible aqueous sample while being agitated by a stirring bar placed on the bottom of the sample cell. After some time, the microdroplet of solvent is withdrawn by a syringe and analyzed. Under the proper stirring conditions, the suspended droplet can remain in a top-center position of the aqueous sample. The droplet can become partly engulfed within the sample while maintaining a stable shape with mechanical equilibrium and the mass transfer could be effectively intensified. Using 1,8-dioxyanthraquinone as a model compound and 1-octanol as the solvent, the extraction performance was investigated using HPLC. Since DSDME is based on a self-stable single microdroplet system, there are no requirements for special equipment or other supporting material like hollow fibers. Other advantages include ease of operation, free from cross contamination, quick to reach extraction equilibrium, and the ability to be combined with various analysis instruments. In our experiments, good linearity (r² = 0.9992) and precision (R.S.D. < 1%, n = 5) were achieved. DSDME is a promising pre-treatment method for the fast analysis of trace components in complicated matrices.     

Removal of SO2 from Gas Streams by Oxidation using Plasma-Generated Hydroxyl Radicals

The key problem for the removal of SO₂ by electrical discharge methods is how to obtain the hydroxyl radicals at high concentration and large production rates. With the micro-gap discharge method, O₂ and H₂O in simulated gas streams (N₂/O₂/H₂O/SO₂) are ionized into a large number of OH^. radicals to oxidize SO₂ into SO₃ which reacts with H₂O forming H₂SO₄ droplets at 120 °C in the absence of any catalyst or absorbent. The droplets are captured with an electrostatic precipitator. As a result, conversion of SO₂ to primarily H₂SO₄ is limited by the generation of OH^. radicals. By increasing the reduced field and concentrations of O₂ and H₂O, the amount of OH^. radicals increase resulting in more removal of SO₂ from gas streams. The removal efficiency of SO₂ reaches 100% when the residence time is only 0.74 s. Therefore, a new gas-phase oxidation method for removal of SO₂ without NH₃ additive is found.     

微量甲醛污染物的液滴采样装置及应用

依据气体分子扩散理论,采用自制模拟风洞液滴采样装置,并结合乙酰丙酮荧光分光光度法,探讨了液滴采样的最优化条件.实验结果表明:自制模拟风洞液滴采样装置在泵选样速度为0.1 mL/min,进样管内径为5 mm,风扇电压为9V的强制气体流动的条件下,采样效果理想,有较高的灵敏度和重现性.     

LARGE-SCALE VORTICAL STRUCTURES PRODUCED BY AN IMPINGING DENSITY JET IN SHALLOW CROSSFLOW

The large-scale vortical structures produced by an impinging density jet in shallow crossflow were numerically investigated in detail using RNG turbulence model. The scales, formation mechanism and evolution feature of the upstream wall vortex in relation to stagnation point and the Scarf vortex in near field were analyzed. The computed characteristic scales of the upstream vortex show distinguished three-dimensionality and vary with the velocity ratio and the water depth. The Scarf vortex in the near field plays an important role in the lateral concentration distributions of the impinging jet in crossflow. When the velocity ratio is relatively small, there exists a distinct lateral high concentration aggregation zone at the lateral edge between the bottom layer wall jet and the ambient crossflow, which is dominated by the Scarf vortex in the near field.     

润湿性梯度驱动液滴运动的格子Boltzmann模拟

运用考虑了固体与液体间分子作用力的格子Boltzmann方法,数值研究了由于固液界面上表面张力梯度引起的Marangoni效应驱动的液滴运动.当表面张力梯度较小时,计算结果和前人的理论预测符合较好.而表面张力梯度较大时,由于液滴不变形和准平衡态等假设不再满足,理论预测的液滴运动速度高于数值模拟的结果.计算结果显示,在向亲水端运动过程中液滴内部出现旋涡结构,当润湿性梯度较大时,其前进速度和接触角随时间变化出现振荡.     

Planar Droplet Sizing for the Characterization of Droplet Clusters in an Industrial Gun‐Type Burner

An important problem in spray combustion deals with the existence of dense regions of droplets, called clusters. To understand their formation mechanism, the droplet dynamics and fuel concentration profile are investigated by means of planar laser techniques in an industrial gun‐type burner. The simultaneous measurement of elastic Mie scattering and Laser Induced Fluorescence (LIF) allows the instantaneous measurement of the Sauter Mean Diameter (SMD), after proper calibration. Using two different CCDs to get the two signals requires a detailed calibration of the CCD response before getting absolute diameters. Pixels are binned 6 by 6 to obtain the final SMD map, this is a compromise between spatial accuracy and noise. Velocity field is measured on both sets of images using standard Particle Image Velocimetry (PIV) algorithms. The comparison of cross‐correlation technique with PDA results shows that the velocity measured on the LIF images are close to the velocity based on D₃₀, whereas the Mie scattering results are similar to D₂₀. On Mie scattering images, regions of high interfacial area forming clusters can be detected. A special tracking scheme is used to characterize their dynamics in terms of velocity and diameters by ensuring that the same volume of fluid is tracked. It is shown that the clusters have a velocity similar to the velocity of droplets with the same diameter as the mean SMD of the cluster. It is also shown that an increase of pressure tends to trigger the appearance of such a group of droplets, due to a smaller diameter of the droplets caused by the increase of pressure discharge. Uncertainties for the different techniques used are discussed.     

Mechanism of preparing monodisperse poly(acrylamide/methacrylic acid) microspheres in ethanol. I

The precipitation polymerization of acrylamide/methacrylic acid (AAm/MAA) in ethanol (EtOH) was thoroughly investigated from detecting the homogeneity of the initial solution prior to polymerizations to the final products of the polymerizations. Dynamic light scattering and scanning electron microscopy were employed for the investigations. The solutions of AAm and AAm/acrylic acid (AAm/AA) were homogeneous. However, the solutions of AAm/MAA, AAm/poly(MAA) (PMAA), and AAm/poly(AA) (PAA) were not homogeneous as they are usually considered to be: entities with size distributions of around 150, 40, and 17 nm, respectively, were detected at the polymerization temperature of 60 °C. Accordingly, analogous to the entities that are similar to the structure of micelles formed in the solutions of AAm/PMAA and AAm/PAA because of polymer–AAm interactions, it was suggested that the complexes of AAm/MAA stemming from the molecular interactions, particularly the (lypo‐) hydrophobic interaction, aggregated to form minimonomer droplets at 60 °C. The monodisperse microspheres were prepared only in the AAm/MAA‐EtOH systems, whereas the microspheres were not prepared in the homogeneous AAm‐EtOH systems despite the precipitation of PAAm. The results obtained from various polymerizations showed that the microspheres originated from the polymerization within the minimonomer droplets. A new mechanism was established that describes the processes for the formation of all products possibly generated in the AAm‐MAA‐EtOH polymerization system. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2823–2832, 2004     

Droplet Shapes for a Class of Models in \mathbb{Z}^2 at Zero Temperature

In this work we consider the Wulff construction at zero temperature for a class of Gibbs models and study the shape of the obtained droplets. Considering zero temperature we avoid all difficulties connected with the competition between energy and entropy. It allows us to study a quite wide class of models which provides a variety of shapes. The motivations of the study come from attempts to describe isotropic properties of some models on 2D lattice at zero temperature. The studied models are binary (the spin space is 0,1) with a ferromagnetic behavior such that the potential functions are not equal to zero only for some tiles with size 3×3. In fact, we study herein droplet shapes of a subclass of the ferromagnetic models with potential functions as mentioned above. This subclass of models is defined by a condition called regularity. We call the model classified here as having regular micro-boundaries. Several examples of non-regular models are also presented.     

电子器件制造过程中的一种均匀化加热法的数值研究

本文提出了喷嘴沿被加热物体宽度方向往复移动式射流冲击加热方法,该加热方法可提高被加热物体的等温性。通过进行数值模拟,得到了在任意时刻,被加热物体的温度分布及全体计算时间内被加热物体表面平均温度分布,进而得到了喷嘴移动周期与被加热物体的等温性的关系。