A compressible two‐fluid multiphase model for CO2 leakage through a wellbore

This paper introduces an effectively mesh‐independent and computationally efficient model for CO₂ leakage through wellbores. A one‐dimensional compressible two‐fluid domain, representing a homogeneous air gas and a multiphase CO₂ with a jump at the interface between them, is modeled. The physical domain is modeled using the drift‐flux model, and the governing equations are solved using a mixed finite‐element discretization scheme. The standard Galerkin FEM, the partition of unity method, and the level‐set method are integrated to solve the problem. All important physical phenomena and processes occurring along the wellbore path, including fluid dynamics, buoyancy, phase change, compressibility, thermal interaction, wall friction, and slip between phases, together with the jump in density and enthalpy between air and CO₂, are considered. Two numerical examples illustrating the computational capability and efficiency of the model are presented. Copyright © 2015 John Wiley & Sons, Ltd.     

高温超导块材磁通汇聚效应的数值模拟研究

高温超导块材在零场冷条件下感应产生的涡流可以有效地屏蔽外加磁场, 从而改变空间磁场分布. 通过合理的设计, 该效应可以被用来约束、 聚集磁通, 从而增大局域磁通密度, 对于需要高磁通密度和磁场梯度的应用具有重要意义. 本论文利用基于 H 方程的二维有限元数值模拟, 结合 GdBa2Cu3 O7 -δ 材料实测的Jc (B ,T ) 关系,研究了 GdBa2Cu3 O7 -δ 超导块材的磁通汇聚效果, 分析了超导块材的空间位置、 工作温度及不同外加磁场对其磁通密度放大效果的影响. 结果显示在30 K 的温度下, 外加11 T 的外加磁场时, 可以在间距为2 mm 的两块超导块体间隙获得17.2 T 的磁场, 磁场放大效率达到56 % .     

Recent advances in sodium alginate-based membranes for dehydration of aqueous ethanol through pervaporation

Sodium alginate (SA) is a progressive material for membrane fabrication. The technological development of SA-based membranes has made a significant contribution to the separation techniques, especially in aqueous organic solutions. The outstanding performance of SA is attributed to its outstanding structural flexibility and hydrophilicity. In view of structural characteristics, SA membranes have immense utilization in the pervaporation separation of organics. Among various organics, dehydration of aqueous ethanol is employed as a standard to check the success of pervaporation (PV) membrane. Because ethanol and water have comparable molecular sizes, thus difficult to extract water from aqueous ethanol mixtures than it is for other organics. A literature survey shows that wide-ranging data are available on the PV performance of SA and its modified membranes. In this context, the present review addresses the recent advances made in SA membranes for enhanced ethanol dehydration performance during the last decade. Available data since 2010 has been compiled for grafted, crosslinked, blend, mixed matrix, and composite hybrid sodium alginate membranes in terms of separation factor, permeation flux, and pervaporation separation index PSI. The data are assessed with reference to the effect of feed composition, membrane selectivity, flux, and swelling behavior.     

Computational fluid dynamics applied to the aerodynamic design of a land‐based supersonic vehicle

The BLOODHOUND SSC project was publicly announced in October 2008, with a primary engineering objective of designing, constructing and running a vehicle capable of achieving a speed of 1000 mph on land. The aerodynamic design of this vehicle is to be accomplished using computational simulation only and this paper describes the development and application of the approach adopted. The computational model employs a cell vertex finite volume algorithm for the solution of compressible viscous flow problems on unstructured hybrid meshes. A one equation turbulence model is adopted and the solution of the steady flow equations is obtained by explicit relaxation. For the combination of high Mach number, complex geometry and complex boundary conditions, involving rotating surfaces and a rolling ground, a consistent HLLC numerical flux function is adopted to ensure a stable procedure. To illustrate the impact of the approach upon the final configuration, a number of simulations undertaken to aid the aerodynamic design are described. © 2010 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2010     

Comparative Study of Wetting and Cooling Performance of Polymer–Salt Hybrid Quench Medium With Conventional Quench Media

Wetting kinetics, kinematics, and cooling performance of a polymer–salt hybrid quenchant were investigated. The rewetting phenomenon for brine, water, polymer, and polymer–salt hybrid solutions was characterized as rapid uniform, fast non-uniform, slow uniform, and fast uniform processes, respectively. A dimensionless rewetting time was proposed to assess the nature of the wetting front. The hybrid quenchant showed higher heat transfer during vapor and transition boiling and lower heat transfer during nucleate boiling and convective cooling. The presence of salt in the hybrid solution resulted in early destabilization of the vapor film and an increase in wetting front velocity and rewetting temperature. The polymer constituent delayed the rewetting phenomenon.     

A nonlocal convective flux limiter for upwind‐biased finite volume simulations

Finite volume methods on structured and unstructured meshes commonly use second‐order, upwind‐biased linear reconstruction schemes to approximate the convective terms. Limiters are employed to reduce the inherent variable overshoot and undershoot of these schemes in discontinuous regions; however, they also can significantly increase the numerical dissipation of a solution in smooth regions. This paper presents a novel nonlocal, nonmonotonic (NLNM) limiter developed by enforcing cell minima and maxima on dependent variable values projected to cell faces. The minimum and maximum values for a cell are determined primarily through recursive reference to the minimum and maximum values of its upwind neighbors. The new limiter has been implemented into an existing flow solver. Various test cases are presented, which highlight the ability of the NLNM limiter to eliminate nonphysical oscillations while maintaining negligible levels of limiter‐induced dissipation into the solution. Results from the new limiter are compared with those from other limited and unlimited second‐order upwind and first‐order upwind schemes. For the cases examined in the study, the NLNM limiter was found to improve accuracy without significantly decreasing overall simulation efficiency and robustness.Copyright © 2011 John Wiley & Sons, Ltd.     

碳酸钙镁石家族非线性光学晶体研究进展

自倍频晶体是将激光和非线性光学效应集于一体的一类晶体,可以实现波长变换、调幅、开关、记忆等功能,被广泛应用于光电子、光通信、激光等领域。然而现有的Nd∶LiNbO₃(Nd∶LN)、Nd∶Na₃La₉O₃(BO₃)₈(Nd∶NLBO)、Nd∶La₂CaB₁₀O₁₉(Nd∶LCB)等晶体由于固有的光折变效应、二次谐波(SHG)输出功率低、光学均匀性差等缺点限制了其进一步的应用,发展新的激光自倍频晶体具有重要的意义和价值。碳酸钙镁石家族硼酸盐晶体由于具有较大的非线性光学(NLO)系数、不易潮解、优异的光学性能和机械性能等优点,近几十年来成为人们重点研究的对象。本文从晶体结构、生长方法、性能、发展趋势等方面,着重介绍了碳酸钙镁石家族REM₃(BO₃)₄(RE为稀土元素La-Lu和Y;M为Al,Ga,Sc)和La_xRE_ySc_z(BO₃)₄(RE=Gd,Y,Nd,Lu,Sm,Tb;x+y+z=3)共取代型硼酸盐非线性光学晶体。对比了不同助熔剂、气氛、方法生长的晶体的紫外(UV)截止边、光学性能、非线性性能的差异。通过改善生长工艺,进行元素掺杂等可以得到光学性能良好、非线性性能显著、有广泛市场应用前景的自倍频(SFD)晶体。     

利用介质光子晶体提高红光发光二极管的光通量的研究

本文利用光子晶体的光栅衍射原理, 在发光二极管(light emitting diode, LED)上制作了光子晶体结构以提高出光效率. 在红光LED器件中引入了SiO₂层的介质光子晶体结构, 并进行了相应的理论分析和实验验证. 结果表明: 介质光子晶体结构对于提高红光LED器件的光提取效率有显著效果, 引入介质光子晶体后, 红光LED的光通量比普通LED增加了26%.