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.     

Further exploration on causes of temperature anomalies associated with the abnormal northern annular mode

This article concerns the temperature anomalies during the high index phase of the northern annual mode for the wintertime from January to March, The response of the zonal and meridional winds and the temperature advection caused by the anomalous horizontal wind are investigated. The results show that both the zonal and meridional winds experience strong anomalies and the temperature advection induced by both the anomalous zonal and meridional winds is responsible for the temperature anomalies associated with the high index northern annual mode. The temperature advection induced by the anomalous zonal wind contributes dominantly to the cooling in the Atlantic and the Bering Sea while the temperature advection induced by the anomalous merional wind contributes dominantly the warming in the United States of America and the cooling in southern Europe and Canada. The superposed influences caused the obvious warming in north Eurasia.     

一种Nb-V复合微合金化非调质钢的组织和性能

利用光学显微镜、透射电镜及力学性能测试等手段,研究了一种低碳Nb-V复合微合金化非调质钢的组织与性能.结果表明,成分为0.24%C-1.99%Mn-0.30%Si-0.51%Cr-0.08%V-0.07%Nb的非调质钢,在加热制度为1 200℃×1 h时锻造后空冷或风冷,可以获得较好的综合性能,其原因是Nb-V复合微合金化可以有效地细化非调质钢的组织,因而其冲击韧性得到提高.进一步分析表明,这种钢能够满足汽车前轴的使用要求,可以用于重卡前轴的设计和制造.     

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.     

Superconducting properties of ZnO-doped (Bi, Pb)-2223 thick film on Ni and NiO substrates prepared by spray deposition technique

The superconductivity of ZnO-doped (Bi, Pb)-2223 thick film on the Ni and NiO substrates, which was prepared by the spray deposition technique with cold forging, was investigated by characterizing the critical current density (J_c), the critical temperature (T_c), the orientation factor (f), and the microstructure of the film. The thickness of the thick film prepared by the spray deposition method was approximately 10 μm. The maximum J_c value of (Bi, Pb)-2223 film on NiO substrate was approximately 2200 A/cm² (I_c = 110 mA) when the film was sintered at 865 °C for 1 h with a cooling rate of 0.5 °C/min from 865 °C to 650 °C; in the case of Ni substrate, a maximum J_c value of approximately 2000 A/cm² (I_c = 100 mA) was obtained for the (Bi, Pb)-2223 thick film when a cooling rate was 3 °C/min. Such a difference in the J_c values of (Bi, Pb)-2223 thick film on Ni and NiO substrates is attributed to the presence of reaction layer at the (Bi, Pb)-2223 and substrate interface. In addition, the variations in the orientation factor of (Bi, Pb)-2223 thick film on NiO substrate related to those of J_c values. The J_c values of (Bi, Pb)-2223 film on NiO substrate with ZnO doping extremely depended on the amount of ZnO doping and the 0.5 wt% ZnO-doped (Bi, Pb)-2223 thick film deposited on NiO substrate, which was sintered at 835 °C for 1 h in air with a cooling rate of 1 °C/min, showed a J_c value of approximately 1200 A/cm² (I_c = 60 mA). Thus, it is considered that a small amount of ZnO doping was effective in lowering the sintering temperature of (Bi, Pb)-2223 thick film, resulting the improvement in the intragranular weak bonding or Josephson junction.     

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.