A model for crack formation during active solid pyrolysis of a char-forming solid: crack patterns; surface area generation; volatile mass efflux

A model is developed for the formation and propagation of cracks in a material sample that is heated at its top surface, pyrolyses, and then thermally degrades to form char. In this work the sample is heated uniformly over its entire top surface by a hypothetical flame (a heat source). The pyrolysis mechanism is described by a one-step overall reaction that is dependent nonlinearly on the temperature (Arrhenius form). Stresses develop in response to the thermal degradation of the material by means of a shrinkage strain caused by local mass loss during pyrolysis. When the principal stress exceeds a prescribed threshold value, the material forms a local crack. Cracks are found to generally originate at the surface in response to heating, but occasionally they form in the bulk, away from ever-changing material boundaries. The resulting cracks evolve and form patterns whose characteristics are described. Quantities examined in detail are: the crack spacing in the pyrolysis zone; the crack length evolution; the formation and nature of crack loops which are defined as individual cracks that have joined to form loops that are disconnected from the remaining material; the formation of enhanced pyrolysis area; and the impact of all of the former quantities on mass flux. It is determined that the mass flux from the sample can be greatly enhanced over its nominal (non-cracking) counterpart. The mass efflux profile qualitatively resembles those observed in Cone Calorimeter tests.     

单层n型MoS2/p型c-Si异质结太阳电池数值模拟

单层二硫化钼(MoS₂)是一种具有优异光电性能的半导体材料,在太阳能能量转换中表现出很大的应用潜力。本文基于AMPS模拟软件,对单层n型MoS₂/p型c-Si异质结太阳电池进行了数值模拟与分析。通过模拟优化,n型MoS₂的电子亲和能为3.75 eV、掺杂浓度为10¹⁸ cm^-3,p型c-Si的掺杂浓度为10¹⁷ cm^-3时,太阳电池能够取得最高22.1%的转换效率。最后模拟了n型MoS₂/p型c-Si异质结界面处的界面态对太阳电池性能的影响,发现界面态密度超过10¹¹ cm^-2·eV^-1时会严重影响太阳电池的光伏性能。     

离心力场作用下多孔介质中强制对流换热的研究

对离心流化床中空气通过多孔物料层的强制对流换热进行了理论和实验研究。获得了气流和物料间强制对流换热的准则关联式。研究结果表明,在气流速度和温度梯度方向一致的条件下,强制对流换热比通常的边界层强制对流换热有所强化,其换热的准则关联式具有 Nu=CRePr的线性形式。从而验证了改变气流方向和热流密度矢量之间夹角可以强化换热的这一强化传热新原理。     

左手介质椭圆光波导基模传播特性

在椭圆柱坐标系中，采用分离变量方法，得出了左手介质椭圆光波导本征方程的近似解，通过数值计算，分析了椭圆波导偏心率、左手介质的电容率、磁导率对椭圆光波导基模传播特性的影响，并将左介质光波导与右手介质光波导基模特性进行对比，得出左手介质光波导的基模特性与右手介质光波导基模特性差别不大的结论.     

Studying the process of ionization of hydrogen in conditions of its forced delivery to a porous nickel oxide electrode

The hydrogen ionization process is studied experimentally on an industrial sintered nickel oxide electrode in models of sealed nickel-metal hydride batteries. It is shown that the hydrogen ionization rates that are reached during overcharge by high current densities in conditions of forced gas delivery into the electrode pores (up to 40 mA cm^?2) exceed the self-discharge rate of a nickel-hydrogen battery by two orders of magnitude. Up to 70% of hydrogen delivered into the compact assembly block undergoes ionization during forced charge of models of sealed nickel-metal hydride batteries with a closed hydrogen cycle. Two independent methods (potentiostatic and manometric) are used to determine the relationship between rates of hydrogen ionization with the degree of the electrode filling with gas and perform estimation of the process intensity at a unit reaction surface. It is established that, in conditions of forced gas delivery, practically all the hydrogen oxidation current is generated at the surface of the nickel oxide electrode beneath thin films of an electrolyte solution at the rate of 4–5 mA cm^?2. It is shown that the hydrogen oxidation rate on a nickel oxide electrode filled in part by gas is independent of the electrode potential, probably because of a tangible contribution made by diffusion limitations to the overall hampering of the process.     

Mathematical modeling of flows through inelastic porous solids

We propose a framework, based on classical mixture theory, to describe the isothermal flow of an incompressible fluid through a deformable inelastic porous solid. The modeling of the behavior of the inelastic solid takes into account changes in the elastic response due to evolution in the microstructure of the material. We apply the model to a compression layer problem. The mathematical problem generated by the model is a free boundary problem.     

硬X射线磁圆二色实验方法的建立

在北京同步辐射装置(BSRF)1W1B光束线和XAFS实验站上国内首次建立了硬X射线波段的磁圆二色实验(XMCD)方法. 以单晶金刚石作为相位延迟片, 在透射劳埃(Laue)模式下, 利用衍射双折射效应, 将入射的单色线偏振光转变为相应的左旋和右旋圆偏振光, 测量磁化样品对左旋和右旋圆偏振光吸收的差异, 获得了XMCD信号. 本实验使用透射方法测量了Pt-Fe合金Pt L_2,3边的XMCD, 获得了XMCD信号. XMCD实验方法的建立, 为研究磁性材料尤其是磁性薄膜材料的电子结构和磁结构提供了实验基础.     

转移矩阵法在负折射率介质材料平板波导中的应用研究

利用严格电磁理论，推导出了适用于负折射率介质材料光波导的转移矩阵，分析讨论了转移矩阵的性质和应用.利用转移矩阵方法，推导出导波层为负折射率介质材料、覆盖层和衬底为右手材料的三层对称介质光波导的本征色散方程.用图解法研究了负折射率介质波导中TE波的异常色散特性.在负折射材料介质波导中没有零阶模，最低阶为1阶模，并且有截止频率,只有波导参量满足一定条件的时候才会存在，导模的横向波数可以为实数和纯虚数，而正折射率介质波导导模的横向波数只能为实数.     

半球蓝宝石整流罩制造技术研究

整流罩在高速飞行中既要对空气进行整流,同时又起光学窗口的作用。蓝宝石材料硬度高,加工非常困难。分别从精磨模、精磨磨料、抛光膜层、抛光辅料、机床速度和压力等方面介绍了一种加工蓝宝石整流罩的工艺方法。     

声诱饵仿真试验系统

文章介绍了声诱饵仿真试验系统中的有关问题，包括：系统的组成、工作原理、对接装置结构等。建立了对接装置声耦合状态下的数学模型，对近场声压分布进行了仿真计算，得出了匹配材料厚度、发射和接收换能器的选取原则。