常压下液氮窄缝池沸腾实验研究

采用玻璃钢 (FRP)制成的矩形窄缝 ,对三种不同的间隙尺寸 ,分加热面与水平面呈 0°,4 5°,90°,135°,180°五种角度 ,以液氮为工质进行了 15组池沸腾实验。得出结论 :液氮在窄缝中的沸腾传热有明显的强化换热效果 ;加热面所处角度不同 ,在相同热负荷下壁面过热度亦不同 ,滑移汽泡和微液膜蒸发机理在通道中发挥的作用也相应不同。该研究对于有限空间传热强化的机理和实际应用都有一定的参考价值和指导意义。     

The development and influence of gas bubbles in phreatic aquifers under natural flow conditions

In a phreatic aquifer, bubbles may result from the entrapment of air during groundwater recharge and/or bacterial metabolism. The calculated critical depth of about 1 m at which bubbles are most likely to be found in a granular aquifer, coincides with the depth of 0.60 m of an almost stagnant water layer (specific discharge 1 × 10^-6 cm sec^-1) found at the water table region under natural flow conditions. Bubbles clog pores and therefore reduce the hydraulic conductivity without significantly reducing the volumetric water content. Stagnation at the water table region results since prevailing pressures (in the order of 10^-1 atmospheres) are not sufficiently large to move bubbles through porous media in a water environment.     

Ocean Spray Modelling for Tropical Cyclone Wind Speeds

Because of the potentially important influence of spray cooling on the thermodynamics of Tropical Cyclones, there is a need for estimates of ocean spray distribution at extreme wind speeds, at least twice those for which detailed spray observations have been made. To assist in such extrapolation, a simplified probabilistic model is developed, with the three main effects (gusts, gravity, evaporation) that influence how spray droplets are distributed taken into account, but with as much simplicity as possible in other respects.     

Non-Classical Traveling Solutions in a Nonlinear Klein Gordon Model

A model with interparticle inharmonic interaction under the Φ⁴ external potential is studied. Making use of the special relation of relevant parameters, in the continuous limit, it was possible to obtain various non-classical soliton solutions, specifically, compact and peak-like solutions. The solutions undergo a jump on their first derivatives at some points of the space-time manifold. These analytic solutions were obtained by considering strong restrictions on their velocities and on the jump conditions. The energy concentrated in these solutions shows in several cases a discrete spectrum.     

On the void distribution and size in shaped sapphire crystals

Ribbon and rod sapphire pulling has been performed in three different crystal growth equipments in order to study the effect of the installation, of the atmosphere, of the die shape, of the feed material and of the pulling rate on the distribution, number and diameter of the characteristic voids (micro‐bubbles) in the crystals. The location of the bubbles in the crystals depends on the die geometry; however, in most cases they are essentially located close to the crystal periphery and then can be efficiently removed by lapping. After statistical analysis of the results, it is demonstrated that the number of gas moles incorporated in the crystals, inside the voids, is totally independent of any growth parameter. It is also shown that the bubble diameter depends only on the pulling rate. Consequently, for a given pulling rate, the number of bubbles auto‐adjusts in order to satisfy the constant molar gas incorporation. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Quasi-one-dimensional foam drainage

Foam drainage is considered in a froth flotation cell. Air flow through the foam is described by a simple two-dimensional deceleration flow, modelling the foam spilling over a weir. Foam microstructure is given in terms of the number of channels (Plateau borders) per unit area, which scales as the inverse square of bubble size. The Plateau border number density decreases with height in the foam, and also decreases horizontally as the weir is approached. Foam drainage equations, applicable in the dry foam limit, are described. These can be used to determine the average cross-sectional area of a Plateau border, denoted A, as a function of position in the foam. Quasi-one-dimensional solutions are available in which A only varies vertically, in spite of the two-dimensional nature of the air flow and Plateau border number density fields. For such situations the liquid drainage relative to the air flow is purely vertical. The parametric behaviour of the system is investigated with respect to a number of dimensionless parameters: K (the strength of capillary suction relative to gravity), α (the deceleration of the air flow), and n and h (respectively, the horizontal and vertical variations of the Plateau border number density). The parameter K is small, implying the existence of boundary layer solutions: capillary suction is negligible except in thin layers near the bottom boundary. The boundary layer thickness (when converted back to dimensional variables) is independent of the height of the foam. The deceleration parameter α affects the Plateau border area on the top boundary: weaker decelerations give larger Plateau border areas at the surface. For weak decelerations, there is rapid convergence of the boundary layer solutions at the bottom onto ones with negligible capillary suction higher up. For strong decelerations, two branches of solutions for A are possible in the K = 0 limit: one is smooth, and the other has a distinct kink. The full system, with small but non-zero capillary suction, lies relatively close to the kinked solution branch, but convergence from the lower boundary layer onto this branch is distinctly slow. Variations in the Plateau border number density (non-zero n and h) increase individual Plateau border areas relative to the case of uniformly sized bubbles. For strong decelerations and negligible capillarity, solutions closely follow the kinked solution branch if bubble sizes are only slightly non-uniform. As the extent of non-uniformity increases, the Plateau border area reaches a maximum corresponding to no net upward velocity of foam liquid. In the case of vertical variation of number density, liquid content profiles and Plateau border area profiles cease to be simply proportional to one another. Plateau border areas match at the top of the foam independent of h, implying a considerable difference in liquid content for foams which exhibit different number density profiles. Received 3 July 2001     

Oxygen Microbubble Generator Enabled by Tunable Catalytic Microtubes

Rolled‐up catalytic Ti/Cr/Pt microtubes, consisting of inorganic nanomembranes integrated on‐chip, are used to generate oxygen microbubbles in solutions of hydrogen peroxide. Oxygen bubble parameters (frequency, radius and volumetric flow rate) are optimized at different concentrations of hydrogen peroxide and common dish soap. Increasing the aspect ratio of the microtube (e.g., tube length/diameter) leads to the formation of smaller bubbles, but at higher frequencies. Longer tubes produce less total oxygen volume in comparison to shorter tubes. We attribute this observation to the specific dynamic behaviours of bubbles in tubes.     

二次阳极氧化技术的理论依据及其局限性

二次阳极氧化技术在多孔阳极氧化铝和氧化钛纳米管的制备过程中得到广泛应用,但其理论依据还不清楚。本文详细综述了二次阳极氧化和预压印技术的由来及其理论依据,阐明了二次阳极氧化过程中传统“场致助溶”理论无法解释的实验事实,分析了二次阳极氧化和预压印技术在多孔阳极氧化铝制备中的局限性和前提条件,并用氧气气泡模型对文献中报道的一些特殊孔道的形成机制进行了诠释,揭示了气泡模具和氧化物的黏性流动对圆柱形、规则有序孔道的形成的重要影响,展望了电子电流和氧气气泡模具对多孔氧化铝、氧化钛纳米管的制备和结构调控的指导作用。本综述对阳极氧化钛纳米管的制备和机理的深入研究,促进其在光催化和太阳能电池领域的应用有重要的意义。     

改进热交换法生长蓝宝石晶体的气泡研究

采用改进的热交换法生长的蓝宝石晶体,气泡是其主要缺陷之一.本文采用数值模拟研究了晶体生长过程中氦气流量对坩埚内温场、固液界面形状的影响.并结合晶体生长实验结果,分析了在实际的晶体生长过程中,氦气流量的线性增加对晶体内气泡的尺寸、形态和分布的影响.     

同相气泡耦合特性实验研究

设计实验, 利用电火花打火生成气泡来研究两个气泡之间以及两个气泡与自由面的相互作用, 在实验过程中, 精确控制打火电路, 使两个电火花气泡的生成时间间隔控制在67\mus以内, 实现了气泡的同相生成. 大量实验后发现, 两气泡相互作用过程中可能会出现融合、蘑菇状气泡、对射流、射流方向逆转、反向射流等现象, 自由面附近不同安置方式的两同相气泡会出现不同的脉动形式. 通过系列实验提出了气泡之间的无量纲距离、无量纲周期差等参数来描述气泡耦合特性, 为气泡群的相互作用提供实验依据.}