TiB_2颗粒在楔形铜模铸锭中的分布以及吞噬行为(英文)

通过楔形铜模铸造实验研究工业纯铝基体中TiB2颗粒的推移吞噬行为和颗粒或团聚体与液/固界面前沿之间的作用。实验结果表明:在整个楔形试样中,颗粒或团聚体的尺寸分别服从2个独立的分布,团簇被推移到楔形试样的中间区域,而单独的颗粒或小的团簇被楔形试样的边缘吞噬。在楔形试样的不同区域颗粒的团聚程度不同,在试样的边缘和中间区域,颗粒的团聚因子分别为0.2和0.6。颗粒的直径并不服从一般的正态分布,而是基本服从对数正态分布。更重要的是,在整个试样中,颗粒或团簇尺寸服从2个对数正态分布。     

The Adhesion of Particles to Polymer Coated Substrates

A rigid polyester substrate was overcoated with 10 μm, 25 μm, and 50 μm thick coatings of polystyrene containing varying concentrations of plasticizer between 0% and 20%. Micrometer-size glass spheres were deposited onto these substrates and the deformations of the substrates resulting from the forces of adhesion were then examined using scanning electron microscopy (SEM). For substrates which were in the glassy phase, the power law dependence of the contact radius on particle radius was 0.48. In contrast, for the case of rubbery substrates, the contact radius was found to vary as the particle radius to the 0.65 power. These results are consistent with the predictions of the adhesion models of Maugis and Pollock [D. Maugis and H. M. Pollock, Acta Metall. 32, 1323 (1984) and Johnson et al., [K. L. Johnson, K. Kendall, and A. D. Roberts, Proc. Roy. Soc. London Ser. A 324, 301 (1971)], respectively. This implies that, depending on the glass transition temperature of the substrate, either plastic or elastic deformations can occur. Also presented and discussed is the observation of critical engulfment, whereby the surface forces draw the particle substantially or totally into the substrate.     

Interaction between micro- and macro-mixing during reactions in agitated tanks

The present investigation focusses on the interactions between micro-and macro-mixing in a stirred tank reactor, operated in the semi-batch mode. With long feed times only micromixing controls reaction, but below a critical feed time macroscopic gradients also become important. Experiments generated a coherent data set which can be used as a design guide and also for model validation. A competitive, consecutive azocoupling reaction was carried out, whereby imperfect mixing produces finite values of X_S (yield of secondary product) which can be conveniently used as a mixing index. The influences of feed location, feed rate, stirrer speed, concentrations and vessel size on selectivity were studied. The micromixing model of Baldyga and Bourne (1989) was extended to include interactions between macro-and micro-mixing and should be valid for feed times below the critical value, although not so short as the macromixing time in the vessel. Model predictions were compared with the experimental results.     

T型反应器内非稳态吞噬流机理

运用激光诱导荧光（PLIF）技术和大涡模拟方法对T型反应器内的流动特性进行了研究。发现随着Reynolds数（Re）的增大,T型反应器中依次出现分离流（Re<120）、稳定吞噬流（120≤Re<190）、非稳态吞噬流（190≤Re≤300）、非稳态对称流（Re>300）四种流动模式。通过大涡模拟重点考察了非稳态吞噬流的振荡特性。结果表明,在非稳态吞噬流型下,T型反应器内撞击面上会周期性地出现旋涡合并现象,合并的涡向下传递,产生自持振荡。此时撞击区的压力、速度和涡量也发生周期性变化,且变化周期与旋涡合并周期相同,这种振荡是由速度和压力的周期性转换引起的。     

Capillary Driven Motion: The „Crawling“ Drop and a Possible Link with Phagocytosis

A sessile drop at equilibrium on an ideal solid surface satisfies both Laplace's equation for the meniscus shape and Young's equation along the triple line. If, however, a single, small, energetic heterogeneity exists near the triple line, although meniscus equilibrium is assured, Young's equation is unsatisfied and a net force acts on the drop, causing it to „crawl“ in order to engulf the inhomogeneity (of higher surface free energy). A dynamic energy balance between excess capillary energy and viscous dissipation governs the crawling motion. Similarities with phagocytosis are apparent, although the latter process generally occurs in a liquid medium without the presence of a solid substrate. The behaviour of a drop is, therefore, extended to that of a model cell suspended in a liquid medium. Although very much simplified, the system is modelled as an essentially spherical cell possessing a pseudopodium in contact with a small, spherical contaminant. By analogy with the crawling drop, a dynamic balance between excess interfacial free energy and viscous dissipation is established to estimate the time of engulfment, or phagocytosis, of the contaminant.     

Modeling flame temperature profile on a fire‐engulfed cylindrical tube

In this article, experimental measurements of flame temperature profile on a cylindrical tube circumference engulfed in a small‐scale pool fire were carried out. Three models were presented for flame temperature distribution with analytical and numerical based methods. The first model that is based on correlation showed the best agreements with experimental data, and other two models had almost acceptable predictions. The results revealed that the analytical and mathematical based model is more general than correlation methods and may be used to predict flame temperature and have wider‐range application usage. Copyright © 2011 John Wiley & Sons, Ltd.     

Manikin test for flame engulfment evaluation of protective clothing: Historical review and development of a new ISO standard

The overall performance of a firefighter turnout suit can only be evaluated using both bench‐scale tests and an assessment based on an instrumented manikin under defined, close to real‐life conditions in a laboratory. Using manikins in rating protective clothing has already a long history which will be reflected in this paper. Efforts all over the world to reproduce a flame engulfment situation in a laboratory are currently being combined in a new draft international standard (ISO/DIS 13506.3). A round robin test showed an acceptable reproducibility for this method based on a manikin test and a gas burner system. An overview of existing measurement systems and the results of this round robin are discussed and possible improvements for the standard flame engulfment test method are proposed. Copyright © 2006 John Wiley & Sons, Ltd.     

INVESTIGATION OF RAPID DIRECTIONAL SOLIDIFICATION OF AL-BASED IMMISCIBLE ALLOYS Ⅲ. EFFECT OF SOLID/LIQUID INTERFACE

分析了难混溶合金凝固过程中作用在凝固界面前沿液滴上的力,建立了液滴与凝固界面相互作用行为的动力学判据.结合实验,探讨了固/液界面与液滴间相互作用对Al-Bi基难混溶合金凝固组织演变的影响.结果表明,在界面排斥和Marangoni力共同作用下,较小尺寸的富Bi液滴被凝固界面排斥并富积在凝固界面前沿.当凝固界面为枝晶/胞状晶时,临界尺寸的富Bi液滴与界面发生部分捕获,凝固后形成"蝌蚪"型的富Bi粒子;尺寸较小的富Bi液滴被捕获在枝晶/胞状晶间,凝固后富Bi粒子分布于晶界和三叉交角处.     

多层桨搅拌槽内的微观混合特性

在直径0.476 m的多层桨搅拌槽内,采用平行竞争反应工作体系,就不同的多层桨型组合、进料时间、搅拌转速及进料位置对产物分布的影响规律进行了系统的实验研究,并采用涡旋卷吸模型就加料位置等操作条件对产物分布的影响进行了模拟计算,模拟值与实验值吻合. 结果表明,对于多层桨搅拌体系,在液面处加料时产物分布主要由上层桨的桨型决定,底层桨的排出流区加料时主要由底层桨的桨型及功率决定. 卷吸模型能够较好地描述搅拌槽内的微观混合过程.