环形狭缝中过冷沸腾空泡率的研究

以环形狭缝通道中流动沸腾传热的实验数据为初始条件,运用四阶龙格-库塔法对过冷沸腾空泡率的机理模型进行了数值求解,并对计算结果进行了分析。     

ANALYSIS OF VELOCITY ANNULAR EFFECT OF OSCILLATORY FLOW INSIDE PARALLEL PLATE CHANNEL

为了分析管内交变流动速度环状效应的特性,通过数值模拟对平板流道内可压缩交变流动的速度环状效应进行研究．根据速度环状效应的产生机理,分析得出在黏性流体管内交变流动中必然存在速度环状效应,并且在流道截面中心速度为零相位下最容易观察到速度环状效应．为了定量描述速度环状效应,根据流道中心速度为零相位下的速度分布曲线的斜率情况,提出定量评价指标速度环状效应系数,并针对平行平板流道内层流交变流动,利用该评价指标定量分析了无量纲参数（包括瓦伦西数Va和最大雷诺数Remax）对速度环状效应的影响．     

Green’s function solution for transient heat conduction in annular fin during solidification of phase change material

The Green’s function method is applied for the transient temperature of an annular fin when a phase change material (PCM) solidifies on it. The solidification of the PCMs takes place in a cylindrical shell storage. The thickness of the solid PCM on the fin varies with time and is obtained by the Megerlin method. The models are found with the Bessel equation to form an analytical solution. Three different kinds of boundary conditions are investigated. The comparison between analytical and numerical solutions is given. The results demonstrate that the significant accuracy is obtained for the temperature distribution for the fin in all cases.     

Direct numerical simulation of turbulent heat transfer in annuli: Effect of heat flux ratio

Fully developed turbulent flow and heat transfer in a concentric annular duct is investigated for the first time by using a direct numerical simulation (DNS) with isoflux conditions imposed at both walls. The Reynolds number based on the half-width between inner and outer walls, δ=(r₂-r₁)/2, and the laminar maximum velocity is Re_δ=3500. A Prandtl number Pr=0.71 and a radius ratio r^*=0.1 were retained. The main objective of this work is to examine the effect of the heat flux density ratio, q^*=q₁/q₂, on different thermal statistics (mean temperature profiles, root mean square (rms) of temperature fluctuations, turbulent heat fluxes, heat transfer, etc.). To validate the present DNS calculations, predictions of the flow and thermal fields with q^*=1 are compared to results recently reported in the archival literature. A good agreement with available DNS data is shown. The effect of heat flux ratio q^* on turbulent thermal statistics in annular duct with arbitrarily prescribed heat flux is discussed then. This investigation highlights that heat flux ratio has a marked influence on the thermal field. When q^* varies from 0 to 0.01, the rms of temperature fluctuations and the turbulent heat fluxes are more intense near the outer wall while changes in q^* from 1 to 100, lead to opposite trends.     

Experimental study on critical heat flux in bilaterally heated narrow annuli

Critical heat flux (CHF) experiments using deionized water as working fluid have been conducted in a range of pressure from 0.6 to 4.2 MPa, mass flow velocity from 60 to 130 kg/m² s and wall heat flux from 10 to 90 kW/m² for vertical narrow annuli with annular gap sizes of 0.95 and 1.5 mm. We found that the CHF, occurring only on the inside tube, or on the outside tube or on both tubes of the annular channel, depends on the heat flux ratio between surfaces of the outside and inside tubes. The CHF, occurring on the surface of the inside tube, reaches the maximum value under the pressure of 2.3 MPa while it occurring on the surface of the outside tube keeps increasing with the increase of the pressure. The CHF, occurring on the inside or outside tubes, increases with the increase of the mass flow velocity and the annular gap size; and decreases with the increase of critical quality and the other tube wall heat flux. Empirical correlations, which agree quite well with the experimental data, have been developed to predict the CHF occurring on surfaces of the inside or outside tubes of the narrow annular channel on the conditions of low pressure and low flow.     

The quantum spectral analysis of the two-dimensional annular billiard system

Based on the extended closed-orbit theory together with spectral analysis, this paper studies the correspondence between quantum mechanics and the classical counterpart in a two-dimensional annular billiard. The results demonstrate that the Fourier-transformed quantum spectra are in very good accordance with the lengths of the classical ballistic trajectories, whereas spectral strength is intimately associated with the shapes of possible open orbits connecting arbitrary two points in the annular cavity. This approach facilitates an intuitive understanding of basic quantum features such as quantum interference, locations of the wavefunctions, and allows quantitative calculations in the range of high energies, where full quantum calculations may become impractical in general. This treatment provides a thread to explore the properties of microjunction transport and even quantum chaos under the much more general system.     

Directionality of partially coherent annular flat-topped beams propagating through atmospheric turbulence

The closed-form expression for the angular spread of partially coherent annular flat-topped beams propagating through atmospheric turbulence is derived by using the integral transform technique. In comparison with previous work, the results obtained in this paper are more general. It is shown that, except for equivalent Gaussian Schell-model (GSM) beams as pointed out in Ref. [T. Shirai, A. Dogariu, E. Wolf, Opt. Lett. 28 (2003) 610], there also exist equivalent annular and non-annular beams which may generate the same directionality as the corresponding fully coherent Gaussian beam both in free space and in turbulence. The theoretical results are illustrated by numerical examples and interpreted physically.     

强流环形电子束在同轴永磁Halbach结构磁路中传输的初步分析

利用有限元程序SUPERFISH计算求解了同轴永磁Halbach结构磁路的磁场, 并推导出该磁场位形磁感应强度各分量的近似表达式. 利用流体模型分析了作用在电子束上的力并导出了改进马丢方程形式的径向力平衡方程, 给出了平衡条件; 利用2.5维全电磁粒子模拟程序研究了强流环形电子束在该周期系统中传输的物理过程. 计算得出强流相对论电子束的稳定传输与电子束电流, 电子束厚度, 磁场强度, 电子束入射角度等因素有关. 分析认为利用同轴永磁Halbach结构磁路导引数KA的环形电子束, 并使之稳定传输是可能的. 同时该磁场聚焦形式也为Ubitron中的束--波相互作用提供了一个作用机制.     

环形腔内双层薄液层热毛细对毛细对流的渐近解

为了解水平温度梯度作用下环形腔内双层薄液层热毛细对流的基本特性,采用渐近线方法 获得了热毛细对流的近似解. 环形腔外壁被加热,内壁被冷却,上、下壁面绝热. 结果表明, 当环形腔宽度与内半径比趋于零时,环形腔退化为矩形腔,所得到的主流区速度场和温度场 的表达式演化为Nepomnyashchy 等得到的矩形腔内的结果;与数值模拟结果的比较 发现,在主流区渐近解与数值解吻合较好.     

Suppressing the hot carrier injection degradation rate in total ionizing dose effect hardened nMOSFETs

Annular gate nMOSFETs are frequently used in spaceborne integrated circuits due to their intrinsic good capability of resisting total ionizing dose (TID) effect. However, their capability of resisting the hot carrier effect (HCE) has also been proven to be very weak. In this paper, the reason why the annular gate nMOSFETs have good TID but bad HCE resistance is discussed in detail, and an improved design to locate the source contacts only along one side of the annular gate is used to weaken the HCE degradation. The good TID and HCE hardened capability of the design are verified by the experiments for I/O and core nMOSFETs in a 0.18 μm bulk CMOS technology. In addition, the shortcoming of this design is also discussed and the TID and the HCE characteristics of the replacers (the annular source nMOSFETs) are also studied to provide a possible alternative for the designers.